WO2025073958A1

WO2025073958A1 - Dielectric heating aerosol-generating device having a zoned dielectric heating

Info

Publication number: WO2025073958A1
Application number: PCT/EP2024/078046
Authority: WO
Inventors: Stefan LAUENSTEIN; Oleg Mironov
Original assignee: Philip Morris Products SA
Current assignee: Philip Morris Products SA
Priority date: 2023-10-05
Filing date: 2024-10-04
Publication date: 2025-04-10
Anticipated expiration: 2026-04-05

Abstract

The present invention relates to an aerosol-generating device, and specifically to an aerosol-generating device configured to heat an aerosol-forming substrate by dielectric heating. The disclosure provides an aerosol-generating device for dielectrically heating an aerosol-forming substrate. The aerosol-generating device comprises a power source; an oscillation circuit powered by the power source; a dielectric heating element fed by the oscillation circuit, the dielectric heating element being arranged for dielectrically heating the aerosol-forming substrate by dipole rotation when subjected to an electric field caused by the dielectric heating element; and a controller for controlling heating of the aerosol-forming substrate by changing a parameter or configuration of the aerosol-generating device. The dielectric heating element is shaped such that opposing electrodes have a variable, preferably increasing, distance towards each other along a given direction between the two opposing electrodes, wherein the controller is configured to change the parameter to cause a spatially and temporally varying profile of the electric field strength in a space or volume for receiving the aerosol-forming substrate along the given direction, wherein the spatially varying profile changes over time in response to the changing of the parameter or configuration of the aerosol-generating device.

Description

Dielectric heating aerosol-generating device having a zoned dielectric heating

The present invention relates to an aerosol-generating device, and specifically to an aerosolgenerating device configured to heat an aerosol-forming substrate by dielectric heating. The present disclosure further relates to a method of dielectrically heating an aerosol-forming substrate by means of an aerosol-generating device, and to an aerosol-generating system comprising an aerosolgenerating device, and an aerosol-generating article comprising an aerosol-forming substrate.

Background

Known electrically operated aerosol-generating systems typically heat an aerosol-forming substrate by one or more of: conduction of heat from a heating element to an aerosol-forming substrate, radiation of heat from a heating element to an aerosol-forming substrate, or drawing heated air through an aerosol-forming substrate. Most commonly, heating is achieved by passing an electrical current through an electrically resistive heating element, giving rise to Joule heating of the heating element. Inductive heating systems have also been proposed, in which Joule heating occurs as a result of eddy currents induced in a susceptor heating element.

A problem with these heating mechanisms is that they may give rise to undesired non-uniform heating of the aerosol-forming substrate. The portion of the aerosol-forming substrate closest to the heating element is heated more quickly or to a higher temperature than portions of the aerosolforming substrate more remote from the heating element.

Systems that dielectrically heat an aerosol-forming substrate have been proposed, which advantageously provide uniform heating of the aerosol-forming substrate. However, known dielectric heating systems are less efficient than inductive heating systems and require complex electrical circuitry in order to achieve the necessary voltages and frequencies for dielectric heating of an aerosol-forming substrate.

Furthermore, the various components which are comprised in an aerosol-forming substrate and are heated to form an aerosol comprising a mixture of constituents may have different temperatures at which they evaporate. Thus, when providing a particularly homogenous heating of a homogenously loaded substrate, ingredients evaporating at lower temperatures may evaporate too soon and the mixture ratio of the aerosol to be consumed may change over time. A possible solution to this problem would be to provide different heating elements at different locations. However, such a set-up would be complicated to control and costly.

Consequently, there may be a need for providing a dielectric heating concept, which allows a uniform aerosolization over time even for aerosol-forming substrates with ingredients that evaporate at different temperatures.

Moreover, for ensuring an efficient aerosol generation on the one hand and avoiding hazardous over-heating on the other hand, there may be a need of controlling the temperature of the heated substrate itself within well-defined limits. It would be desirable to provide a system that dielectrically heats an aerosol-forming substrate with greater efficiency, while still being realisable in a compact or handheld system.

Summary of Invention

According to a first aspect, the disclosure provides an aerosol-generating device for dielectrically heating an aerosol-forming substrate. The aerosol-generating device comprises a power source; an oscillation circuit powered by the power source; a dielectric heating element fed by the oscillation circuit, the dielectric heating element being arranged for dielectrically heating the aerosol-forming substrate by dipole rotation when subjected to an electric field caused by the dielectric heating element; and a controller for controlling heating of the aerosol-forming substrate by changing a parameter or configuration of the aerosol-generating device. The dielectric heating element is shaped such that opposing electrodes have a variable, preferably increasing, distance towards each other along a given direction between the two opposing electrodes, wherein the controller is configured to change the parameter to cause a spatially and temporally varying profile of the electric field strength in a space or volume for receiving the aerosolforming substrate along the given direction, wherein the spatially varying profile changes over time in response to the changing of the parameter or configuration of the aerosol-generating device.

More specifically, the dielectric heating element is shaped such that opposing electrodes have a variable, preferably increasing, distance towards each other along a given direction between the two opposing electrodes, wherein the controller is configured to change the parameter to cause a spatially and temporally varying profile of the electric field strength in a space or volume for receiving the aerosol-forming substrate along the given direction, wherein the spatially varying profile changes over time in response to the changing of the parameter or configuration of the aerosolgenerating device. Thus, it is possible to increase or decrease the heating power (e.g. a supply voltage or a switching frequency) to thereby move a given electric field strength profile along the given direction (axis). This allows to move a heating zone or point along the given direction. The temperature profile is a result of the temporally and spatially varying electric field strength that causes a selective dielectric heating that varies along the given direction.

Advantageously, such a varying profile, which changes over time has the effect that components, which evaporate at lower temperatures, do not completely evaporate too early before components that evaporate at higher temperatures are aerosolized. Rather, a travelling isotherm may be generated which causes a more uniform composition of the aerosol over time. The spatial profile may vary along a longitudinal axis or across to the longitudinal axis. A combination of a variation along a longitudinal axis and across to the longitudinal axis is also possible.

The dielectric heating element may be shaped so that in operation an electric field strength has a varying intensity along at least one defined direction.

When using dielectric heating, the change of the electric field strength directly influences the heating energy and thus the generated temperature. A particularly efficient manner of providing a temperature profile can thereby be achieved. The varying intensity may be a decreasing intensity gradient along the at least one defined direction.

This allows to generate a uniformly travelling heat zone within the heated substrate. The defined direction may be straight, but may also be meandering or otherwise deviating from a straight line.

The spatially varying profile may be such that a predetermined temperature along the spatially varying profile moves in the at least one direction.

The controller may be configured to set or control a timely displacement rate of the spatially varying profile to a predetermined value or predetermined curve.

The change over time of the spatially varying profile is performed during a heating session for consumption of at least one puff.

Changing of the parameter or configuration of the aerosol-generating device may comprise increasing a supply voltage to the oscillation circuit.

Thus, the travelling heat zone can be achieved in a particularly efficient and reproducible manner.

Generally, the electric field strength is increased, which can be done by increasing the RF voltage over the load capacitor, which can be done by increasing a supply voltage to the oscillating circuit, or PWM, or any other type of temperature control.

The dielectric heating element may comprise at least two electrodes arranged to accommodate the aerosol-forming substrate in a heating cavity, the heating cavity defining a longitudinal axis, wherein the at least two electrodes may have a distance from each other which increases along the longitudinal axis.

The at least two electrodes may be arranged in a tubular arrangement forming a cylindrical heating cavity therein, the at least two electrodes having opposite polarity forming a gap between each other, wherein the gap may have a width which increases along the longitudinal axis of the tubular arrangement.

The dielectric heating element may comprise at least two substantially flat electrodes opposing each other and having an increasing distance from each other in a direction that is in the plane of a flat heating cavity.

The dielectric heating element may comprise interdigitated or strip electrodes in a flat configuration and separated by at least one gap, wherein in a given direction the width of the gap increases.

The dielectric heating element may comprise at least two electrodes, which are separated by at least one gap, and may have a cylindrical or tubular shape, wherein the gap between the electrodes increases in a direction of a cylindrical axis.

The dielectric heating element may comprise cylindrical segments or strips forming a cylindrical or tubular heater having a cylindrical axis, wherein the spatially varying profile may change over time in a direction transverse to the cylindrical axis. Advantageously, the following scenarios can be envisaged according to embodiments of the present disclosure. Firstly, two substantially flat electrodes may be arranged opposing each other and may have an increasing distance from each other in a direction that is in the plane of the flat aerosol-forming substrate. Secondly, interdigitated or strip electrodes may be provided in a flat configuration, where in a given direction the gaps between the interdigitated electrodes or strips increase. This could also include a pair of such interdigitated flat electrodes that oppose each other, to form a wedge-like space for the flat aerosol-forming substrate therebetween. Further, this can also include plate like islands or patches of electrodes with an increasing gap in a given direction.

Thirdly, a cylindrical or tubular heater may be provided, where the gaps between the electrodes increase in a direction of the cylindrical axis. The electrodes can be arranged (i) to be substantially parallel to the cylindrical axis, (ii) formed as rings around the cylindrical axis, or (iii) any other arrangement and a combination of (i) and (ii), for example plate like islands as a checkerboard or matrix on the cylindrical or tubular heater, with increasing gaps along the cylindrical axis (of course this can also include ovals).

Finally, cylindrical segments or strips can be provided for a cylindrical or tubular heater (or oval, square, pentagon, hexagon, etc. shaped heater), being arranged in parallel to each other with no increasing gaps, but the one defined direction being transverse to the cylinder or tube. By the arrangement of the electrodes seen from the transverse direction, a gap between opposing electrodes increases. By increasing the oscillation voltage, energy can reach deeper into the substrate for heating inner areas, and therefore the depth of heating is increased in a direction that is radial.

The at least two electrodes may be arranged opposite to each other, wherein a distance across the longitudinal axis increases linearly from a first end towards a second end.

The at least two electrodes may be arranged opposite to each other, wherein a distance across the longitudinal axis increases logarithmically from a first end towards a second end.

The oscillation circuit may comprise a resonant feedback circuit including the dielectric heating element, so that the oscillation circuit is self-resonating.

The oscillation circuit may comprise an oscillation unit for controlling the switching unit with a defined switching frequency.

The oscillation unit may comprise a DC-to-AC converter or a stripline oscillator.

The oscillation circuit may further comprise a delay line DL (sometimes referred to as a delay element), the delay line DL branching out from a path of the resonant oscillating feedback circuit.

A delay-line oscillator is a form of electronic oscillator that uses a delay line, or delay element as its principal timing element. A delay-line oscillator may be set to oscillate by inverting the output of the delay line or delay element and feeding that signal back to the input of the delay line or delay element with appropriate amplification.

The delay element may be realized with a physical delay line (such as an LC network or a transmission line). In some examples, capacitances and inductances may be distributed across the length of the delay element. In some examples, the delay element comprises a cascade of logic gates for creating a gate delay. The timing of an oscillation circuit using a physical delay element may be much more accurate. It is also easier to get such an oscillation circuit to oscillate in the desired mode.

The aerosol-generating device may further comprise a temperature determining unit for measuring a value indicative of one or more temperatures of the aerosol-forming substrate, wherein the controller is operable for controlling the temperature of the aerosol-forming substrate by changing the parameter or configuration of the aerosol-generating device based on a signal from the temperature determining unit.

Providing a temperature determining unit enhances the safety of the aerosol-generating device and improves the accuracy of the heating process.

The temperature determining unit may comprise at least two temperature sensors which are arranged distanced away from each other along a defined direction.

The change of the parameter or configuration of the aerosol-generating device may include enabling or disabling the switching unit by respectively making or breaking a connection between the power source and the switching unit.

The change of the parameter or configuration of the aerosol-generating device may include enabling or disabling the switching unit by using a biasing circuit to respectively enable or disable a switching of a transistor of the switching unit by moving the switching unit into an inoperable range of voltage or current.

The change of the parameter or configuration of the aerosol-generating device may include enabling or disabling the switching unit by respectively enabling or disabling a resonant feedback circuit.

The change of the parameter or configuration of the aerosol-generating device may include changing a switching frequency of the switching unit.

The change of the parameter or configuration of the aerosol-generating device may include controlling by the controller a DC supply voltage provided by the power source based on a signal from the temperature determining unit.

The aerosol-generating device may further comprise a voltage controlling unit electrically interconnected with the power source, configured to provide the DC supply voltage with a timevariable level.

The voltage control unit may include a DC-DC converter, preferably a boost, buck, halfbridge, or full bridge converter, a voltage regulator, a charge pump circuit, or a combination thereof.

The DC supply voltage may be provided as the output voltage of a voltage regulator or of a DC-DC converter.

The change of the parameter or configuration of the aerosol-generating device may be performed so that the oscillation circuit is enabled when the temperature of the aerosol-forming substrate is below a first threshold value, and the oscillation circuit is disabled when the temperature of the aerosol-forming substrate is above a second threshold value.

The change of the parameter or configuration of the aerosol-generating device may be performed by controlling the heating of the aerosol-forming substrate in a pulse width modulation, PWM, operation, wherein a ratio of a heating pulse width to a non-heating pulse width may be changed based on a signal from the temperature determining unit.

The signal from the temperature determining unit may be compared to a defined set value, wherein the change of the parameter or configuration of the aerosol-generating device is performed in response to a result of the comparison, so that a closed loop temperature control is performed.

The controller may be operable to control the temperature of the aerosol-forming substrate by first applying a preheating phase to reach a first target temperature at which at least one component of the aerosol-forming substrate vaporizes or at which a maintenance heat level is reached.

The target temperature could also be below the temperature at which at least one component of the aerosol-forming substrate vaporizes, in case some maintenance heat is provided by the dielectric heater, but in any case it is advantageous to get over the vaporization temperature of water.

The controller may be operable to control the temperature of the aerosol-forming substrate to perform, after performing the preheating phase, a puff heating phase where the temperature is maintained at least at a second target temperature.

The controller may be operable to provide a first heating power during the preheating phase, the first heating power being higher than a second heating power provided during the puff heating phase.

The controller may be operable to provide to the oscillation circuit, during the preheating phase, at least 70% of a maximum supply voltage of the power source, preferably more than 80% of the maximum supply voltage of the power source.

The controller may be operable to provide to the oscillation circuit, during the puff heating phase, between 40% and 60% of a maximum supply voltage of the power source, preferably around 50% of the maximum supply voltage of the power source.

The temperature determining unit may include a temperature sensor that is operable to capture a temperature of an element of the aerosol-generating device that has dielectric properties.

The dielectric heating element may comprise at least two electrodes that are placed on a dielectric carrier film or material, and wherein the temperature determining unit is operable to capture the temperature of the dielectric carrier film or material.

The dielectric heating element may comprise at least two electrically conductive electrodes and wherein the temperature determining unit is operable to capture a temperature of at least one of the electrodes.

The temperature determining unit may comprise a thermistor, a resistance-based temperature detector, a thermocouple, a fiber-optic temperature sensor, or a thermopile. The temperature determining unit may comprise a non-contact temperature sensor arranged for detecting a heat radiation indicative of the temperature of the aerosol-forming substrate.

The temperature determining device may comprise an infrared temperature sensor, an infrared camera, a pyrometer, a pyroelectric sensor, a time-of-flight sensor, or a combination thereof.

The aerosol-generating article comprising the aerosol-forming substrate may include a plate or surface exposed towards the temperature sensor, the plate or surface having an increased thermal radiation emissivity compared to the rest of the aerosol-forming substrate.

The temperature determining unit may comprise a temperature probe arranged for penetrating the aerosol-forming substrate, when the aerosol-forming substrate is arranged in operational connection with the dielectric heating element.

The temperature determining unit may comprise a dielectric resonator or antenna for detecting an electric field at the aerosol-forming substrate, and wherein the controller is operable to derive the temperature of the aerosol-forming substrate from the detected electric field.

The temperature determining unit may be operable to determine the temperature of the aerosol-forming substrate based on a heating cavity temperature, a DC supply voltage, and/or a DC supply current.

The controller may comprise a trained artificial intelligence network for deriving the temperature of the aerosol-forming substrate.

The temperature determining unit may comprise a current sensor for monitoring changes of a DC supply current, wherein the controller may be operable to derive the temperature of the aerosolforming substrate from the detected changes in the DC supply current.

The temperature determining unit may comprise at least one temperature marker, the temperature marker transitioning from a first physical state into a second physical state when reaching a defined marker temperature.

Because such a marker only detects the transgression of a temperature threshold, the signal processing is particularly simply and accurate.

The temperature marker may comprise a magnetic susceptor having a Curie temperature defining the marker temperature, wherein a magnetic characteristic of the temperature marker changes when reaching the marker temperature.

The temperature marker may comprise a dielectric marker, the dielectric marker changing a dielectric characteristic when reaching the marker temperature.

The dielectric marker may comprise water and the marker temperature is an evaporation temperature of water.

The aerosol-generating device may comprise a flexible low-dielectric carrier film and wherein at least a part of the oscillation circuit is formed on the flexible low-dielectric carrier film.

The aerosol-generating device may comprise a temperature determining unit formed on or within the flexible low-dielectric carrier film. According to a second aspect, the disclosure provides a method of dielectrically heating an aerosol-forming substrate by means of an aerosol-generating device, the method comprising the following steps: dielectrically heating the aerosol-forming substrate by dipole rotation when subjected to an electric field caused by a dielectric heating element, wherein the dielectric heating element is comprised in an oscillation circuit of the aerosol-generating device, the oscillation circuit being fed by a power source; controlling heating of the aerosol-forming substrate by changing a parameter or configuration of the aerosol-generating device. The dielectric heating element is shaped such that opposing electrodes have a variable, preferably increasing, distance towards each other along a given direction between the two opposing electrodes, wherein the controller is configured to change the parameter to cause a spatially and temporally varying profile of the electric field strength in a space or volume receiving the aerosolforming substrate along the given direction, wherein the profile changes over time in response to the changing of the parameter or configuration of the aerosol-generating device.

The dielectric heating element may be formed so that in operation an electric field strength has a varying intensity along at least one defined direction.

When using dielectric heating, the change of the electric field strength directly influences the heating energy and thus the generated temperature. A particularly efficient manner of providing a temperature profile can thereby be achieved.

The varying intensity may be a decreasing intensity gradient along the at least one defined direction.

The change over time of the spatially varying profile may be performed during a heating session for consumption of at least one puff.

Changing of the parameter or configuration of the aerosol-generating device may comprise increasing a supply voltage to the oscillation circuit. Thus, the travelling heat zone can be achieved in a particularly efficient and reproducible manner.

The aerosol-generating device may further comprise a temperature determining unit for measuring a value indicative of the temperature of the aerosol-forming substrate, wherein the controller is operable for controlling the temperature of the aerosol-forming substrate by changing the parameter or configuration of the aerosol-generating device based on a signal from the temperature determining unit.

The change of the parameter or configuration of the aerosol-generating device may include enabling or disabling the switching unit by respectively enabling or disabling the resonant feedback circuit.

A voltage controlling unit electrically interconnected with the power source may be configured to provide the DC supply voltage with a time-variable level.

The DC supply voltage may be provided as the output voltage of a voltage regulator or of a

DC-DC converter. The change of the parameter or configuration of the aerosol-generating device may be performed so that the oscillation circuit is enabled when the temperature of the aerosol-forming substrate is below a first threshold value, and the oscillation circuit may be disabled when the temperature of the aerosol-forming substrate is above a second threshold value.

The signal from the temperature determining unit may be compared to a defined set value, and wherein the change of the parameter or configuration of the aerosol-generating device may be performed in response to a result of the comparison, so that a closed loop temperature control is performed.

The temperature of the aerosol-forming substrate may be controlled by first applying a preheating phase to reach a first target temperature at which at least one component of the aerosolforming substrate vaporizes or at which a maintenance heat level is reached.

After performing the preheating phase, a puff heating phase may be performed where the temperature is maintained at least at a second target temperature.

A first heating power may be provided during the preheating phase, the first heating power being higher than a second heating power provided during the puff heating phase.

During the preheating phase, at least 70% of a maximum supply voltage of the power source, preferably more than 80% of the maximum supply voltage of the power source, may be provided to the oscillation circuit.

During the puff heating phase, between 40% and 60% of a maximum supply voltage of the power source, preferably around 50% of the maximum supply voltage of the power source, may be provided to the oscillation circuit.

The controller may further determine whether a user session has started and applies the preheating phase in response to the start of the user session.

The dielectric heating element may comprise at least two electrically conductive electrodes and wherein the temperature determining unit may be operable to capture a temperature of at least one of the electrodes. The temperature determining unit may comprise a thermistor, a resistance-based temperature detector, a thermocouple, a fiber-optic temperature sensor, or a thermopile.

The temperature determining unit may comprise a non-contact temperature sensor arranged for detecting a heat radiation indicative of the temperature of the aerosol-forming substrate.

The aerosol-forming substrate may include a plate or surface exposed towards the temperature sensor, the plate or surface having an increased thermal radiation emissivity compared to the rest of the aerosol-forming substrate.

The temperature determining unit may comprise a temperature probe that can penetrate the aerosol-forming substrate, when the aerosol-forming substrate is arranged in operational connection with the dielectric heating element.

The temperature determining unit may comprise a dielectric resonator or antenna for detecting an electric field at the aerosol-forming substrate, and wherein the controller derives the temperature of the aerosol-forming substrate from the detected electric field.

The temperature determining unit may comprise a current sensor for monitoring changes of a DC supply current, and wherein the controller may be operable to derive the temperature of the aerosol-forming substrate from the detected changes in the DC supply current.

According to a third aspect, the disclosure provides an aerosol-generating system comprising: an aerosol-generating article comprising an aerosol-forming substrate, and an aerosolgenerating device for dielectrically heating the aerosol-forming substrate, the aerosol-generating device comprising: a power source; an oscillation circuit powered by the power source; a dielectric heating element fed by the oscillation circuit, the dielectric heating element being arranged for heating the aerosol-forming substrate by dipole rotation when subjected to an electric field caused by the dielectric heating element; a controller for controlling heating of the aerosol-forming substrate by changing a parameter or configuration of the aerosol-generating device. The dielectric heating element is shaped such that opposing electrodes have a variable, preferably increasing, distance towards each other along a given direction between the two opposing electrodes, wherein the controller is configured to change the parameter to cause a spatially and temporally varying profile of the electric field strength in a space or volume for receiving the aerosolforming substrate along the given direction, wherein the profile changes over time in response to the changing of the parameter or configuration of the aerosol-generating device.

The changing of the parameter or configuration of the aerosol-generating device may comprise increasing a supply voltage to the oscillation circuit.

Thus, the travelling heat zone can be achieved in a particularly efficient and reproducible manner. The dielectric heating element may comprise at least two electrodes arranged to accommodate the aerosol-forming substrate in a heating cavity, the heating cavity defining a longitudinal axis, wherein the at least two electrodes may have a distance from each other which increases along the longitudinal axis.

The dielectric heating element may comprise cylindrical segments or strips forming a cylindrical or tubular heater having a cylindrical axis, wherein the spatially varying profile may change over time in a direction transverse to the cylindrical axis.

The oscillation circuit may comprise a resonant feedback circuit including the dielectric heating element, so that the oscillation circuit may be self-resonating.

The aerosol-generating system may further comprise a temperature determining unit for measuring a value indicative of one or more temperatures of the aerosol-forming substrate, wherein the controller may be operable for controlling the temperature of the aerosol-forming substrate by changing the parameter or configuration of the aerosol-generating device based on a signal from the temperature determining unit.

The temperature determining unit may comprise at least two temperature sensors which are arranged distanced away from each other along a defined direction. The change of the parameter or configuration of the aerosol-generating device may include enabling or disabling the switching unit by respectively making or breaking a connection between the power source and the switching unit.

The aerosol-generating system may further comprise a voltage controlling unit electrically interconnected with the power source, configured to provide the DC supply voltage with a time-variable level.

The change of the parameter or configuration of the aerosol-generating device may be performed so that the oscillation circuit may be enabled when the temperature of the aerosol-forming substrate is below a first threshold value, and the oscillation circuit may be disabled when the temperature of the aerosol-forming substrate is above a second threshold value.

The controller may be operable to control the temperature of the aerosol-forming substrate by first applying a preheating phase to reach a first target temperature at which at least one component of the aerosol-forming substrate vaporizes or at which a maintenance heat level is reached. The target temperature could also be below the temperature at which at least one component of the aerosol-forming substrate vaporizes, in case some maintenance heat is provided by the dielectric heater, but in any case it is advantageous to get over the vaporization temperature of water.

The aerosol-forming substrate may comprise a solid matrix containing an aerosol former.

The dielectric heating element may be formed as a separate insertable part or as an integral part of the aerosol-generating device.

The temperature determining unit may be at least partly received within the solid matrix.

The temperature determining unit may be formed to encompass at least a part of the solid matrix.

The temperature determining unit may include a temperature sensor that may be operable to capture a temperature of an element of the aerosol-generating device that has dielectric properties.

The dielectric heating element may comprise at least two electrodes that are placed on a dielectric carrier film or material, and wherein the temperature determining unit may be operable to capture the temperature of the dielectric carrier film or material.

The dielectric heating element may comprise at least two electrically conductive electrodes and wherein the temperature determining unit may be operable to capture a temperature of at least one of the electrodes.

The temperature determining unit may comprise a thermistor, a resistance-based temperature detector, a thermocouple, a fiber-optic temperature sensor, or a thermopile.

An aerosol-generating article comprising the aerosol-forming substrate may include a plate or surface exposed towards the temperature sensor, the plate or surface having an increased thermal radiation emissivity compared to the rest of the aerosol-forming substrate. The temperature determining unit may comprise a temperature probe arranged for penetrating the aerosol-forming substrate, when the aerosol-forming substrate is arranged in operational connection with the dielectric heating element.

The temperature determining unit may comprise a dielectric resonator or antenna for detecting an electric field at the aerosol-forming substrate, and wherein the controller may be operable to derive the temperature of the aerosol-forming substrate from the detected electric field.

The dielectric marker may comprise water and the marker temperature may be an evaporation temperature of water.

The aerosol-generating device may comprise a flexible low-dielectric carrier film and wherein at least a part of the oscillation circuit may be formed on the flexible low-dielectric carrier film.

A temperature determining unit may be formed on or within the low-dielectric carrier film.

A target aerosolization temperature may be in between 80°C to 365°C, preferably 180°C to 320°C, more preferably 180°C to 220°C.

The controller may cause dielectric heating of the aerosol-forming substrate that is located between the two electrodes with an average dielectric heating power density in a range between 1W/cm³ to 25W/cm³, preferably between 1.5W/cm³ and 15W/cm³ per volume of substrate material during a time period of less than 15 minutes. In particular, during a heat-up phase, the average dielectric heating power density may be controlled or set to be in a range between 7W/cm³ to 25W/cm³, and during a target heating phase (also called maintenance heating phase) during consumption, the average dielectric heating power density is in a range between 1 W/cm³ to 7W/cm³. In an example, the feedback loop may suspended between a power supply and ground of the oscillation circuit, meaning that there is no direct connection between the feedback loop and the supply voltage or ground - e.g., there may be at least one electrical component (for example, a resistor or capacitor) creating a non-negligible potential difference between the feedback loop and the power supply and ground in the oscillation circuit. This may reduce noise and ground influences for more predictable operation in the feedback loop.

As used herein, the term “aerosol-generating device” relates to a device that interacts with an article comprising an aerosol-forming substrate to generate an aerosol.

As used herein, the term “aerosol-forming substrate” relates to a substrate capable of releasing volatile compounds that can form an aerosol. Such volatile compounds can be released by heating the aerosol-forming substrate.

As used herein, the term “puff” means the action of a user drawing an aerosol into their body through their mouth or nose.

As used herein, the term “relative permittivity” (also known as dielectric constant) relates to the permittivity of a material that forms the aerosol-forming substrate expressed as a ratio with the permittivity of vacuum. Mathematically, relative permittivity is expressed as the following: er = e/eO. The parameters in this equation are defined as follows: e is the permittivity of a material that forms the substrate; eO is the permittivity of vacuum; and er is the relative permittivity of a material that forms the substrate. In particular, the term “relative permittivity” may also be referred to as the real part of the complex, frequency-dependent relative permittivity, measured at a temperature of 20°C , in an alternating electric field with at a very low frequency (VLF) of 1 Kilohertz or less, as defined in the international standard IEC 62631-2-1 :2018. It will be appreciated that the frequency value of 1 Kilohertz is included here solely as a general reference and other definitions may use different frequencies.

The invention is defined in the claims. However, below there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein.

Example Ex1. An aerosol-generating device for dielectrically heating an aerosol-forming substrate, the aerosol-generating device comprising: a power source; an oscillation circuit powered by the power source; a dielectric heating element fed by the oscillation circuit, the dielectric heating element being arranged for dielectrically heating the aerosol-forming substrate by dipole rotation when subjected to an electric field caused by the dielectric heating element; and a controller for controlling heating of the aerosol-forming substrate by changing a parameter or configuration of the aerosol-generating device, wherein the dielectric heating element is shaped to cause a spatially varying profile of the temperature in the aerosol-forming substrate, wherein the spatially varying profile changes over time in response to the changing of the parameter or configuration of the aerosol-generating device. Example Ex2. The aerosol-generating device according to Ex1 , wherein the dielectric heating element is shaped so that in operation an electric field strength has a varying intensity along at least one defined direction.

Example Ex3. The aerosol-generating device according to any of Ex1 or Ex2, wherein the spatially varying profile is such that a predetermined temperature in operation moves along at least one direction.

Example Ex4. The aerosol-generating device according to any of Ex1 to Ex3, wherein the controller is configured to set or control a timely displacement rate of the spatially varying profile to a predetermined value or predetermined curve.

Example Ex5. The aerosol-generating device according to any of Ex1 to Ex4, wherein the change over time of the spatially varying profile is performed during a heating session for consumption of at least one puff.

Example Ex6. The aerosol-generating device according to Ex2, wherein the varying intensity is a decreasing intensity gradient along the at least one defined direction.

Example Ex7. The aerosol-generating device according to one of Ex1 to Ex6, wherein changing of the parameter or configuration of the aerosol-generating device comprises increasing a supply voltage to the oscillation circuit.

Example Ex8. The aerosol-generating device according to any of the preceding examples, wherein the dielectric heating element comprises at least two electrodes arranged to accommodate the aerosol-forming substrate in a heating cavity, the heating cavity defining a longitudinal axis, wherein the at least two electrodes have a distance from each other which increases along the longitudinal axis.

Example Ex9. The aerosol-generating device according to Ex8, wherein the at least two electrodes are arranged in a tubular arrangement forming a cylindrical heating cavity therein, the at least two electrodes having opposite polarity forming a gap between each other, and wherein the gap has a width which increases along the longitudinal axis of the tubular arrangement.

Example Ex10. The aerosol-generating device according to any of the preceding examples, wherein the dielectric heating element comprises at least two substantially flat electrodes opposing each other and having an increasing distance from each other in a direction that is in the plane of a flat heating cavity.

Example Ex11. The aerosol-generating device according to any of the preceding examples, wherein the dielectric heating element comprises interdigitated or strip electrodes in a flat configuration and separated by at least one gap, wherein in a given direction the width of the gap increases.

Example Ex12. The aerosol-generating device according to any of the preceding examples, wherein the dielectric heating element comprises at least two electrodes, which are separated by at least one gap, and has a cylindrical or tubular shape, wherein the gap between the electrodes increases in a direction of a cylindrical axis. Example Ex13. The aerosol-generating device according to any of the preceding examples, wherein the dielectric heating element comprises cylindrical segments or strips forming a cylindrical or tubular heater having a cylindrical axis, and wherein the spatially varying profile changes over time in a direction transverse to the cylindrical axis.

Example Ex14. The aerosol-generating device according to any of Ex8 or Ex9, wherein the at least two electrodes are arranged opposite to each other, wherein a distance across the longitudinal axis increases linearly from a first end towards a second end.

Example Ex15. The aerosol-generating device according to any of Ex8 or Ex9, wherein the at least two electrodes are arranged opposite to each other, wherein a distance across the longitudinal axis increases logarithmically from a first end towards a second end.

Example Ex16. The aerosol-generating device according to any of the preceding examples, wherein the oscillation circuit comprises a resonant feedback circuit including the dielectric heating element, so that the oscillation circuit is self-resonating.

Example Ex17. The aerosol-generating device according to any of the preceding examples, wherein the oscillation circuit comprises an oscillation unit for controlling the switching unit with a defined switching frequency.

Example Ex18. The aerosol-generating device according to Ex17, wherein the oscillation unit comprises a DC-to-AC converter or a stripline oscillator.

Example Ex19. The aerosol-generating device according to any of the preceding examples, further comprising a temperature determining unit for measuring a value indicative of one or more temperatures of the aerosol-forming substrate; and wherein the controller is operable for controlling the temperature of the aerosol-forming substrate by changing the parameter or configuration of the aerosol-generating device based on a signal from the temperature determining unit.

Example Ex20. The aerosol-generating device according to Ex19, wherein the temperature determining unit comprises at least two temperature sensors which are arranged distanced away from each other along a defined direction.

Example Ex21. The aerosol-generating device according to Ex19 or Ex20, wherein the change of the parameter or configuration of the aerosol-generating device includes enabling or disabling the switching unit by respectively making or breaking a connection between the power source and the switching unit.

Example Ex22. The aerosol-generating device according to any of Ex19 to Ex21 , wherein the change of the parameter or configuration of the aerosol-generating device includes enabling or disabling the switching unit by using a biasing circuit to respectively enable or disable a switching of a transistor of the switching unit by moving the switching unit into an inoperable range of voltage or current.

Example Ex23. The aerosol-generating device according to any of Ex19 to Ex22, wherein the change of the parameter or configuration of the aerosol-generating device includes enabling or disabling the switching unit by respectively enabling or disabling a resonant feedback circuit.

Example Ex24. The aerosol-generating device according to any of Ex19 to Ex23, wherein the change of the parameter or configuration of the aerosol-generating device includes changing a switching frequency of the switching unit.

Example Ex25. The aerosol-generating device according to any of Ex19 to Ex24, wherein the change of the parameter or configuration of the aerosol-generating device includes controlling by the controller a DC supply voltage provided by the power source based on a signal from the temperature determining unit.

Example Ex26. The aerosol-generating device according to Ex25, further comprising a voltage controlling unit electrically interconnected with the power source, configured to provide the DC supply voltage with a time-variable level.

Example Ex27. The aerosol-generating device according to Ex26, wherein the voltage control unit includes a DC-DC converter, preferably a boost, buck, half-bridge, or full bridge converter, a voltage regulator, a charge pump circuit, or a combination thereof.

Example Ex28. The aerosol-generating device according to any of examples Ex25 to Ex27, wherein the DC supply voltage is provided as the output voltage of a voltage regulator or of a DC-DC converter.

Example Ex29. The aerosol-generating device according to any of Ex19 to Ex28, wherein the change of the parameter or configuration of the aerosol-generating device is performed so that the oscillation circuit is enabled when the temperature of the aerosol-forming substrate is below a first threshold value, and the oscillation circuit is disabled when the temperature of the aerosol-forming substrate is above a second threshold value.

Example Ex30. The aerosol-generating device according to any of Ex19 to Ex29, wherein the change of the parameter or configuration of the aerosol-generating device is performed by controlling the heating of the aerosol-forming substrate in a pulse width modulation, PWM, operation, wherein a ratio of a heating pulse width to a non-heating pulse width is changed based on a signal from the temperature determining unit.

Example Ex31. The aerosol-generating device according to any of Ex19 to Ex30, wherein the signal from the temperature determining unit is compared to a defined set value, and wherein the change of the parameter or configuration of the aerosol-generating device is performed in response to a result of the comparison, so that a closed loop temperature control is performed.

Example Ex32. The aerosol-generating device according to any of Ex19 to Ex31 , wherein the controller is operable to control the temperature of the aerosol-forming substrate by first applying a preheating phase to reach a first target temperature at which at least one component of the aerosol-forming substrate vaporizes or at which a maintenance heat level is reached.

Example Ex33. The aerosol-generating device according to Ex32, wherein the controller is operable to control the temperature of the aerosol-forming substrate to perform, after performing the preheating phase, a puff heating phase where the temperature is maintained at least at a second target temperature.

Example Ex34. The aerosol-generating device according to any of Ex32 or Ex33, wherein the controller is operable to provide a first heating power during the preheating phase, the first heating power being higher than a second heating power provided during the puff heating phase.

Example Ex35. The aerosol-generating device according to any of examples Ex32 to Ex34, wherein the controller is operable to provide to the oscillation circuit, during the preheating phase, at least 70% of a maximum supply voltage of the power source, preferably more than 80% of the maximum supply voltage of the power source.

Example Ex36. The aerosol-generating device according to any of Ex33 to Ex35, wherein the controller is operable to provide to the oscillation circuit, during the puff heating phase, between 40% and 60% of a maximum supply voltage of the power source, preferably around 50% of the maximum supply voltage of the power source.

Example Ex37. The aerosol-generating device according to any of Ex19 to Ex36, wherein the temperature determining unit includes a temperature sensor that is operable to capture a temperature of an element of the aerosol-generating device that has dielectric properties.

Example Ex38. The aerosol-generating device according to any of Ex19 to Ex37, wherein the dielectric heating element comprises at least two electrodes that are placed on a dielectric carrier film or material, and wherein the temperature determining unit is operable to capture the temperature of the dielectric carrier film or material.

Example Ex39. The aerosol-generating device according to any of Ex19 to Ex38, wherein the dielectric heating element comprises at least two electrically conductive electrodes and wherein the temperature determining unit is operable to capture a temperature of at least one of the electrodes.

Example Ex40. The aerosol-generating device according to any of Ex19 to Ex39, wherein the temperature determining unit comprises a thermistor, a resistance-based temperature detector, a thermocouple, a fiber-optic temperature sensor, or a thermopile.

Example Ex41. The aerosol-generating device according to any of Ex19 to Ex40, wherein the temperature determining unit comprises a non-contact temperature sensor arranged for detecting a heat radiation indicative of the temperature of the aerosol-forming substrate.

Example Ex42. The aerosol-generating device according to Ex41 , wherein the temperature determining device comprises an infrared temperature sensor, an infrared camera, a pyrometer, a pyroelectric sensor, a time-of-flight sensor, or a combination thereof.

Example Ex43. The aerosol-generating device according to any of Ex41 or Ex42, wherein an aerosol-generating article comprising the aerosol-forming substrate includes a plate or surface exposed towards the temperature sensor, the plate or surface having an increased thermal radiation emissivity compared to the rest of the aerosol-forming substrate. Example Ex44. The aerosol-generating device according to any of Ex19 to Ex43, wherein the temperature determining unit comprises a temperature probe arranged for penetrating the aerosol-forming substrate, when the aerosol-forming substrate is arranged in operational connection with the dielectric heating element.

Example Ex45. The aerosol-generating device according to any of Ex19 to Ex44, wherein the temperature determining unit comprises a dielectric resonator or antenna for detecting an electric field at the aerosol-forming substrate, and wherein the controller is operable to derive the temperature of the aerosol-forming substrate from the detected electric field.

Example Ex46. The aerosol-generating device according to any of Ex19 to Ex45, wherein the temperature determining unit is operable to determine the temperature of the aerosolforming substrate based on a heating cavity temperature, a DC supply voltage, and/or a DC supply current.

Example Ex47. The aerosol-generating device according to any of Ex19 to Ex46, wherein the controller comprises a trained artificial intelligence network for deriving the temperature of the aerosol-forming substrate.

Example Ex48. The aerosol-generating device according to any of Ex19 to Ex47, wherein the temperature determining unit comprises a current sensor for monitoring changes of a DC supply current, and wherein the controller is operable to derive the temperature of the aerosolforming substrate from the detected changes in the DC supply current.

Example Ex49. The aerosol-generating device according to any of Ex19 to Ex48, wherein the temperature determining unit comprises at least one temperature marker, the temperature marker transitioning from a first physical state into a second physical state when reaching a defined marker temperature.

Example Ex50. The aerosol-generating device according to Ex49, wherein the temperature marker comprises a magnetic susceptor having a Curie temperature defining the marker temperature, wherein a magnetic characteristic of the temperature marker changes when reaching the marker temperature.

Example Ex51. The aerosol-generating device according to Ex49, wherein the temperature marker comprises a dielectric marker, the dielectric marker changing a dielectric characteristic when reaching the marker temperature.

Example Ex52. The aerosol-generating device according to Ex51 , wherein the dielectric marker comprises water and the marker temperature is an evaporation temperature of water.

Example Ex53. The aerosol-generating device according to any of the preceding examples, wherein the aerosol-generating device comprises a flexible low-dielectric carrier film and wherein at least a part of the oscillation circuit is formed on the flexible low-dielectric carrier film.

Example Ex54. The aerosol-generating device according to Ex53, wherein a temperature determining unit is formed on or within the flexible low-dielectric carrier film. Example Ex55. A method of dielectrically heating an aerosol-forming substrate by means of an aerosol-generating device, the method comprising the following steps: dielectrically heating the aerosol-forming substrate by dipole rotation when subjected to an electric field caused by a dielectric heating element, wherein the dielectric heating element is comprised in an oscillation circuit of the aerosol-generating device, the oscillation circuit being fed by a power source; controlling heating of the aerosol-forming substrate by changing a parameter or configuration of the aerosolgenerating device; wherein the dielectric heating element is shaped to cause a spatially varying profile of the temperature in the aerosol-forming substrate, wherein the profile changes over time in response to the changing of the parameter or configuration of the aerosol-generating device.

Example Ex56. The method according to Ex55, wherein the dielectric heating element is shaped so that in operation an electric field strength has a varying intensity along at least one defined direction.

Example Ex57. The method according to any of Ex55 or Ex56, wherein the spatially varying profile is such that a predetermined temperature along the spatially varying profile moves in the at least one direction.

Example Ex58. The method according to any of Ex55 to Ex57, wherein the controller is configured to set or control a timely displacement rate of the spatially varying profile to a predetermined value or predetermined curve.

Example Ex59. The method according to any of Ex55 to Ex58, wherein the change over time of the spatially varying profile is performed during a heating session for consumption of at least one puff.

Example Ex60. The method according to Ex56, wherein the varying intensity is a decreasing intensity gradient along the at least one defined direction.

Example Ex61. The method according to any of Ex55 to Ex60, wherein changing of the parameter or configuration of the aerosol-generating device comprises increasing a supply voltage to the oscillation circuit.

Example Ex62. The method according to any of Ex55 to Ex61 , wherein the oscillation circuit comprises a resonant feedback circuit including the dielectric heating element, so that the oscillation circuit is self-resonating.

Example Ex63. The method according to any of Ex55 to Ex62, wherein the oscillation circuit comprises an oscillation unit for controlling the switching unit with a defined switching frequency.

Example Ex64. The method according to Ex63, wherein the oscillation unit comprises a DC-to-AC converter or a stripline oscillator.

Example Ex65. The method according to any of Ex55 to Ex64, wherein the aerosolgenerating device further comprises a temperature determining unit for measuring a value indicative of the temperature of the aerosol-forming substrate; and wherein the controller is operable for controlling the temperature of the aerosol-forming substrate by changing the parameter or configuration of the aerosol-generating device based on a signal from the temperature determining unit.

Example Ex66. The method according to Ex65, wherein the temperature determining unit comprises at least two temperature sensors which are arranged distanced away from each other along a defined direction.

Example Ex67. The method according to Ex65 or Ex66, wherein the change of the parameter or configuration of the aerosol-generating device includes enabling or disabling the switching unit by respectively making or breaking a connection between the power source and the switching unit.

Example68. The method according to any of the Ex65 to Ex67, wherein the change of the parameter or configuration of the aerosol-generating device includes enabling or disabling the switching unit by using a biasing circuit to respectively enable or disable a switching of a transistor of the switching unit by moving the switching unit into an inoperable range of voltage or current.

Example 69. The method according to any of Ex65 to Ex68, wherein the change of the parameter or configuration of the aerosol-generating device includes enabling or disabling the switching unit by respectively enabling or disabling the resonant feedback circuit.

Example Ex70. The method according to any of Ex65 to Ex69, wherein the change of the parameter or configuration of the aerosol-generating device includes changing a switching frequency of the switching unit.

Example Ex71. The method according to any of Ex65 to Ex70, wherein the change of the parameter or configuration of the aerosol-generating device includes controlling by the controller a DC supply voltage provided by the power source based on a signal from the temperature determining unit.

Example Ex72. The method according to any of Ex65 to Ex71 , wherein a voltage controlling unit electrically interconnected with the power source is configured to provide the DC supply voltage with a time-variable level.

Example Ex73. The method according to Ex72, wherein the voltage control unit includes a DC-DC converter, preferably a boost, buck, half-bridge, or full bridge converter, a voltage regulator, a charge pump circuit, or a combination thereof.

Example Ex74. The method according to any of Ex71 to Ex73, wherein the DC supply voltage is provided as the output voltage of a voltage regulator or of a DC-DC converter.

Example Ex75. The method according to any of Ex65 to Ex74, wherein the change of the parameter or configuration of the aerosol-generating device is performed so that the oscillation circuit is enabled when the temperature of the aerosol-forming substrate is below a first threshold value, and the oscillation circuit is disabled when the temperature of the aerosol-forming substrate is above a second threshold value.

Example Ex76. The method according to any of Ex65 to Ex75, wherein the change of the parameter or configuration of the aerosol-generating device is performed by controlling the heating of the aerosol-forming substrate in a pulse width modulation, PWM, operation, wherein a ratio of a heating pulse width to a non-heating pulse width is changed based on a signal from the temperature determining unit.

Example Ex77. The method according to any of the Ex65 to Ex76, wherein the signal from the temperature determining unit is compared to a defined set value, and wherein the change of the parameter or configuration of the aerosol-generating device is performed in response to a result of the comparison, so that a closed loop temperature control is performed.

Example Ex78. The method according to any of Ex65 to Ex77, wherein the temperature of the aerosol-forming substrate is controlled by first applying a preheating phase to reach a first target temperature at which at least one component of the aerosol-forming substrate vaporizes or at which a maintenance heat level is reached.

Example Ex79. The method according to Ex78, wherein, after performing the preheating phase, a puff heating phase is performed where the temperature is maintained at least at a second target temperature.

Example Ex80. The method according to any of Ex78 or Ex79, wherein a first heating power is provided during the preheating phase, the first heating power being higher than a second heating power provided during the puff heating phase.

Example Ex81. The method according to any of Ex78 to Ex80, wherein, during the preheating phase, at least 70% of a maximum supply voltage of the power source, preferably more than 80% of the maximum supply voltage of the power source, is provided to the oscillation circuit.

Example Ex82. The method according to any of Ex79 to Ex81 , wherein, during the puff heating phase, between 40% and 60% of a maximum supply voltage of the power source, preferably around 50% of the maximum supply voltage of the power source, is provided to the oscillation circuit.

Example83. The method according to any of Ex55 to Ex82, wherein the controller further determines whether a user session has started and applies the preheating phase in response to the start of the user session.

Example Ex84. The method according to any of Ex65 to Ex83, wherein the temperature determining unit includes a temperature sensor that is operable to capture a temperature of an element of the aerosol-generating device that has dielectric properties.

Example Ex85. The method according to any of Ex65 to Ex84, wherein the dielectric heating element comprises at least two electrodes that are placed on a dielectric carrier film or material, and wherein the temperature determining unit is operable to capture the temperature of the dielectric carrier film or material.

Example Ex86. The method according to any of Ex65 to Ex85, wherein the dielectric heating element comprises at least two electrically conductive electrodes and wherein the temperature determining unit is operable to capture a temperature of at least one of the electrodes. Example Ex87. The method according to any of Ex65 to Ex86, wherein the temperature determining unit comprises a thermistor, a resistance-based temperature detector, a thermocouple, a fiber-optic temperature sensor, or a thermopile.

Example Ex88. The method according to any of Ex65 to Ex87, wherein the temperature determining unit comprises a non-contact temperature sensor arranged for detecting a heat radiation indicative of the temperature of the aerosol-forming substrate.

Example Ex89. The method according to Ex88, wherein the temperature determining device comprises an infrared temperature sensor, an infrared camera, a pyrometer, a pyroelectric sensor, a time-of-f light sensor, or a combination thereof.

Example Ex90. The method according to any of Ex88 or Ex89, wherein the aerosolforming substrate includes a plate or surface exposed towards the temperature sensor, the plate or surface having an increased thermal radiation emissivity compared to the rest of the aerosol-forming substrate.

Example Ex91. The method according to any of Ex65 to Ex90, wherein the temperature determining unit comprises a temperature probe that can penetrate the aerosol-forming substrate, when the aerosol-forming substrate is arranged in operational connection with the dielectric heating element.

Example Ex92. The method according to any of Ex65 to Ex91 , wherein the temperature determining unit comprises a dielectric resonator or antenna for detecting an electric field at the aerosol-forming substrate, and wherein the controller derives the temperature of the aerosol-forming substrate from the detected electric field.

Example Ex93. The method according to any of Ex65 to Ex92, wherein the temperature determining unit is operable to determine the temperature of the aerosol-forming substrate based on a heating cavity temperature, a DC supply voltage, and/or a DC supply current.

Example Ex94. The method according to any of Ex65 to Ex93, wherein the controller comprises a trained artificial intelligence network for deriving the temperature of the aerosol-forming substrate.

Example Ex95. The method according to any of the Ex65 to Ex94, wherein the temperature determining unit comprises a current sensor for monitoring changes of a DC supply current, and wherein the controller is operable to derive the temperature of the aerosol-forming substrate from the detected changes in the DC supply current.

Example Ex96. The method according to any of the Ex65 to Ex95, wherein the temperature determining unit comprises at least one temperature marker, the temperature marker transitioning from a first physical state into a second physical state when reaching a defined marker temperature.

Example Ex97. The method according to example Ex96, wherein the temperature marker comprises a magnetic susceptor having a Curie temperature defining the marker temperature, wherein a magnetic characteristic of the temperature marker changes when reaching the marker temperature.

Example Ex98. The method according to example Ex96, wherein the temperature marker comprises a dielectric marker, the dielectric marker changing a dielectric characteristic when reaching the marker temperature.

Example Ex99. The method according to Ex98, wherein the dielectric marker comprises water and the marker temperature is an evaporation temperature of water.

Example Ex100. An aerosol-generating system comprising: an aerosol-generating article comprising an aerosol-forming substrate, and an aerosol-generating device for dielectrically heating the aerosol-forming substrate, the aerosol-generating device comprising: a power source; an oscillation circuit powered by the power source; a dielectric heating element fed by the oscillation circuit, the dielectric heating element being arranged for heating the aerosol-forming substrate by dipole rotation when subjected to an electric field caused by the dielectric heating element; a controller for controlling heating of the aerosol-forming substrate by changing a parameter or configuration of the aerosol-generating device; wherein the dielectric heating element is shaped to cause a spatially varying profile of the temperature at the aerosol-forming substrate, wherein the profile changes over time in response to the changing of the parameter or configuration of the aerosol-generating device.

Example Ex101. The aerosol-generating system according to Ex100, wherein the dielectric heating element is formed so that in operation an electric field strength has a varying intensity along at least one defined direction.

Example Ex102. The aerosol-generating system according to any of Ex100 or Ex101 , wherein the spatially varying profile is such that a predetermined temperature along the spatially varying profile moves in the at least one direction.

Example Ex103. The aerosol-generating system according to any of Ex100 to Ex102, wherein the controller is configured to set or control a timely displacement rate of the spatially varying profile to a predetermined value or predetermined curve.

Example Ex104. The aerosol-generating system according to any of Ex100 to Ex103, wherein the change over time of the spatially varying profile is performed during a heating session for consumption of at least one puff.

Example Ex105 The aerosol-generating system according to Ex101 , wherein the varying intensity is a decreasing intensity gradient along the at least one defined direction.

Example Ex106. The aerosol-generating system according to one of the Ex100 to Ex105, wherein changing of the parameter or configuration of the aerosol-generating device comprises increasing a supply voltage to the oscillation circuit.

Example Ex107. The aerosol-generating system according to any of Ex100 to Ex106, wherein the dielectric heating element comprises at least two electrodes arranged to accommodate the aerosol-forming substrate in a heating cavity, the heating cavity defining a longitudinal axis, wherein the at least two electrodes have a distance from each other which increases along the longitudinal axis.

Example Ex108. The aerosol-generating system according to Ex107, wherein the at least two electrodes are arranged in a tubular arrangement forming a cylindrical heating cavity therein, the at least two electrodes having opposite polarity forming a gap between each other, and wherein the gap has a width which increases along the longitudinal axis of the tubular arrangement.

Example Ex109. The aerosol-generating system according to any of the Ex100 to Ex108, wherein the dielectric heating element comprises at least two substantially flat electrodes opposing each other and having an increasing distance from each other in a direction that is in the plane of a flat heating cavity.

Example Ex110. The aerosol-generating system according to any of Ex100 to Ex109, wherein the dielectric heating element comprises interdigitated or strip electrodes in a flat configuration and separated by at least one gap, wherein in a given direction the width of the gap increases.

Example Ex111. The aerosol-generating system according to any of Ex100 to Ex110, wherein the dielectric heating element comprises at least two electrodes, which are separated by at least one gap, and has a cylindrical or tubular shape, wherein the gap between the electrodes increases in a direction of a cylindrical axis.

Example Ex112. The aerosol-generating system according to any of Ex100 to Ex111, wherein the dielectric heating element comprises cylindrical segments or strips forming a cylindrical or tubular heater having a cylindrical axis, and wherein the spatially varying profile changes over time in a direction transverse to the cylindrical axis.

Example Ex113. The aerosol-generating system according to any of Ex107 or Ex108, wherein the at least two electrodes are arranged opposite to each other, wherein a distance across the longitudinal axis increases linearly from a first end towards a second end.

Example Ex114. The aerosol-generating system according to any of Ex107 or Ex108, wherein the at least two electrodes are arranged opposite to each other, wherein a distance across the longitudinal axis increases logarithmically from a first end towards a second end.

Example Ex115. The aerosol-generating system according to any of Ex100 to Ex114, wherein the oscillation circuit comprises a resonant feedback circuit including the dielectric heating element, so that the oscillation circuit is self-resonating.

Example Ex116. The aerosol-generating system according to any of Ex100 to Ex115, wherein the oscillation circuit comprises an oscillation unit for controlling the switching unit with a defined switching frequency.

Example Ex117. The aerosol-generating system according to Ex116, wherein the oscillation unit comprises a DC-to-AC converter or a stripline oscillator.

Example Ex118. The aerosol-generating system according to any of Ex100 to Ex117, further comprising a temperature determining unit for measuring a value indicative of one or more temperatures of the aerosol-forming substrate; and wherein the controller is operable for controlling the temperature of the aerosol-forming substrate by changing the parameter or configuration of the aerosol-generating device based on a signal from the temperature determining unit.

Example Ex119. The aerosol-generating system according to Ex118, wherein the temperature determining unit comprises at least two temperature sensors which are arranged distanced away from each other along a defined direction.

Example Ex120. The aerosol-generating system according to Ex118, wherein the change of the parameter or configuration of the aerosol-generating device includes enabling or disabling the switching unit by respectively making or breaking a connection between the power source and the switching unit.

Example Ex121. The aerosol-generating system according to any of Ex118 to Ex120, wherein the change of the parameter or configuration of the aerosol-generating device includes enabling or disabling the switching unit by using a biasing circuit to respectively enable or disable a switching of a transistor of the switching unit by moving the switching unit into an inoperable range of voltage or current.

Example Ex122. The aerosol-generating system according to any of Ex118 to Ex121 , wherein the change of the parameter or configuration of the aerosol-generating device includes enabling or disabling the switching unit by respectively enabling or disabling the resonant feedback circuit.

Example Ex123. The aerosol-generating system according to any of Ex118 to Ex118, wherein the change of the parameter or configuration of the aerosol-generating device includes changing a switching frequency of the switching unit.

Example Ex124. The aerosol-generating system according to any of Ex118 to Ex119, wherein the change of the parameter or configuration of the aerosol-generating device includes controlling by the controller a DC supply voltage provided by the power source based on a signal from the temperature determining unit.

Example Ex125. The aerosol-generating system according to Ex124, further comprising a voltage controlling unit electrically interconnected with the power source, configured to provide the DC supply voltage with a time-variable level.

Example Ex126. The aerosol-generating system according to Ex125, wherein the voltage control unit includes a DC-DC converter, preferably a boost, buck, half-bridge, or full bridge converter, a voltage regulator, a charge pump circuit, or a combination thereof.

Example Ex127. The aerosol-generating system according to any of Ex124 to Ex126, wherein the DC supply voltage is provided as the output voltage of a voltage regulator or of a DC- DC converter.

Example Ex128. The aerosol-generating system according to any of Ex118 to Ex127, wherein the change of the parameter or configuration of the aerosol-generating device is performed so that the oscillation circuit is enabled when the temperature of the aerosol-forming substrate is below a first threshold value, and the oscillation circuit is disabled when the temperature of the aerosol-forming substrate is above a second threshold value.

Example Ex129. The aerosol-generating system according to any of Ex118 to Ex128, wherein the change of the parameter or configuration of the aerosol-generating device is performed by controlling the heating of the aerosol-forming substrate in a pulse width modulation, PWM, operation, wherein a ratio of a heating pulse width to a non-heating pulse width is changed based on a signal from the temperature determining unit.

Example Ex130. The aerosol-generating system according to any of Ex118 to Ex129, wherein the signal from the temperature determining unit is compared to a defined set value, and wherein the change of the parameter or configuration of the aerosol-generating device is performed in response to a result of the comparison, so that a closed loop temperature control is performed.

Example Ex131. The aerosol-generating system according to any of Ex118 to Ex130, wherein the controller is operable to control the temperature of the aerosol-forming substrate by first applying a preheating phase to reach a first target temperature at which at least one component of the aerosol-forming substrate vaporizes or at which a maintenance heat level is reached.

Example Ex132. The aerosol-generating system according to Ex131 , wherein the controller is operable to control the temperature of the aerosol-forming substrate to perform, after performing the preheating phase, a puff heating phase where the temperature is maintained at least at a second target temperature.

Example Ex133. The aerosol-generating system according to any of Ex131 or Ex132, wherein the controller is operable to provide a first heating power during the preheating phase, the first heating power being higher than a second heating power provided during the puff heating phase.

Example Ex134. The aerosol-generating system according to any of Ex131 to Ex133, wherein the controller is operable to provide to the oscillation circuit, during the preheating phase, at least 70% of a maximum supply voltage of the power source, preferably more than 80% of the maximum supply voltage of the power source.

Example Ex135. The aerosol-generating system according to any of Ex132 to Ex134, wherein the controller is operable to provide to the oscillation circuit, during the puff heating phase, between 40% and 60% of a maximum supply voltage of the power source, preferably around 50% of the maximum supply voltage of the power source.

Example Ex136. The aerosol-generating system according to any of Ex100 to Ex135, wherein the aerosol-forming substrate comprises a solid matrix containing an aerosol former.

Example Ex137. The aerosol-generating system according to any of Ex100 to Ex136, wherein the dielectric heating element is formed as a separate insertable part or as an integral part of the aerosol-generating device.

Example Ex138. The aerosol-generating system according to any of Ex118 to Ex137, wherein the temperature determining unit is at least partly received within the solid matrix. Example Ex139. The aerosol-generating system according to any of Ex118 to Ex138, wherein the temperature determining unit is formed to encompass at least a part of the solid matrix.

Example Ex140. The aerosol-generating system according to any of Ex118 to Ex139, wherein the temperature determining unit includes a temperature sensor that is operable to capture a temperature of an element of the aerosol-generating device that has dielectric properties.

Example Ex141. The aerosol-generating system according to any of Ex118 to Ex140, wherein the dielectric heating element comprises at least two electrodes that are placed on a dielectric carrier film or material, and wherein the temperature determining unit is operable to capture the temperature of the dielectric carrier film or material.

Example Ex142. The aerosol-generating system according to any of Ex118 to Ex140, wherein the dielectric heating element comprises at least two electrically conductive electrodes and wherein the temperature determining unit is operable to capture a temperature of at least one of the electrodes.

Example Ex143. The aerosol-generating system according to any of Ex118 to Ex142, wherein the temperature determining unit comprises a thermistor, a resistance-based temperature detector, a thermocouple, a fiber-optic temperature sensor, or a thermopile.

Example Ex144. The aerosol-generating system according to any of Ex118 to Ex138, wherein the temperature determining unit comprises a non-contact temperature sensor arranged for detecting a heat radiation indicative of the temperature of the aerosol-forming substrate.

Example Ex145. The aerosol-generating system according to Ex144, wherein the temperature determining device comprises an infrared temperature sensor, an infrared camera, a pyrometer, a pyroelectric sensor, a time-of-flight sensor, or a combination thereof.

Example Ex146. The aerosol-generating system according to any of Ex140 to Ex145, wherein an aerosol-generating article comprising the aerosol-forming substrate includes a plate or surface exposed towards the temperature sensor, the plate or surface having an increased thermal radiation emissivity compared to the rest of the aerosol-forming substrate.

Example Ex147. The aerosol-generating system according to any of the Ex118 to Ex146, wherein the temperature determining unit comprises a temperature probe arranged for penetrating the aerosol-forming substrate, when the aerosol-forming substrate is arranged in operational connection with the dielectric heating element.

Example Ex148. The aerosol-generating system according to any of Ex118 to Ex147, wherein the temperature determining unit comprises a dielectric resonator or antenna for detecting an electric field at the aerosol-forming substrate, and wherein the controller is operable to derive the temperature of the aerosol-forming substrate from the detected electric field.

Example Ex149. The aerosol-generating system according to any of Ex118 to Ex148, wherein the temperature determining unit is operable to determine the temperature of the aerosolforming substrate based on a heating cavity temperature, a DC supply voltage, and/or a DC supply current. Example Ex150. The aerosol-generating system according to any of Ex118 to Ex149, wherein the controller comprises a trained artificial intelligence network for deriving the temperature of the aerosol-forming substrate.

Example Ex151. The aerosol-generating system according to any of Ex118 to Ex150, wherein the temperature determining unit comprises a current sensor for monitoring changes of a DC supply current, and wherein the controller is operable to derive the temperature of the aerosolforming substrate from the detected changes in the DC supply current.

Example Ex152. The aerosol-generating system according to any of Ex118 to Ex151 , wherein the temperature determining unit comprises at least one temperature marker, the temperature marker transitioning from a first physical state into a second physical state when reaching a defined marker temperature.

Example Ex153. The aerosol-generating system according to Ex152, wherein the temperature marker comprises a magnetic susceptor having a Curie temperature defining the marker temperature, wherein a magnetic characteristic of the temperature marker changes when reaching the marker temperature.

Example Ex154. The aerosol-generating system according to Ex152, wherein the temperature marker comprises a dielectric marker, the dielectric marker changing a dielectric characteristic when reaching the marker temperature.

Example Ex155. The aerosol-generating system according to Ex154, wherein the dielectric marker comprises water and the marker temperature is an evaporation temperature of water.

Example Ex156. The aerosol-generating system according to any of Ex100 to Ex155, wherein the aerosol-generating device comprises a flexible low-dielectric carrier film and wherein at least a part of the oscillation circuit is formed on the flexible low-dielectric carrier film.

Example Ex157. The aerosol-generating system according to Ex156, wherein a temperature determining unit is formed on or within the low-dielectric carrier film.

Example Ex158. An aerosol-generating device for dielectrically heating an aerosolforming substrate, the aerosol-generating device comprising: a power source; an oscillation circuit powered by the power source; a dielectric heating element fed by the oscillation circuit, the dielectric heating element being arranged for dielectrically heating the aerosol-forming substrate by dipole rotation when subjected to an electric field caused by the dielectric heating element; and a controller for controlling heating of the aerosol-forming substrate by changing a parameter or configuration of the aerosol-generating device, wherein the dielectric heating element is shaped such that opposing electrodes have a variable, preferably increasing, distance towards each other along a given direction between the two opposing electrodes, wherein the controller is configured to change the parameter to cause a spatially and temporally varying profile of the electric field strength in a space or volume for receiving the aerosolforming substrate along the given direction, wherein the spatially varying profile changes over time in response to the changing of the parameter or configuration of the aerosol-generating device.

Example Ex159. The aerosol-generating device according to Example Ex158, wherein the device is adapted according to any one of the Examples Ex2 to Ex54.

Example Ex160. A method of dielectrically heating an aerosol-forming substrate by means of an aerosol-generating device, the method comprising the following steps: dielectrically heating the aerosol-forming substrate by dipole rotation when subjected to an electric field caused by a dielectric heating element, wherein the dielectric heating element is comprised in an oscillation circuit of the aerosol-generating device, the oscillation circuit being fed by a power source; controlling heating of the aerosol-forming substrate by changing a parameter or configuration of the aerosol-generating device; wherein the dielectric heating element is shaped such that opposing electrodes have a variable, preferably increasing, distance towards each other along a given direction between the two opposing electrodes, wherein the controller is configured to change the parameter to cause a spatially and temporally varying profile of the electric field strength in a space or volume for receiving the aerosolforming substrate along the given direction, wherein the profile changes over time in response to the changing of the parameter or configuration of the aerosol-generating device.

Example Ex161. The method according to Example Ex160, wherein the method is adapted according to any one of the Examples Ex56 to Ex99.

Example Ex162. An aerosol-generating system comprising: an aerosol-generating article comprising an aerosol-forming substrate, and an aerosol-generating device for dielectrically heating the aerosol-forming substrate, the aerosol-generating device comprising: a power source; an oscillation circuit powered by the power source; a dielectric heating element fed by the oscillation circuit, the dielectric heating element being arranged for heating the aerosol-forming substrate by dipole rotation when subjected to an electric field caused by the dielectric heating element; a controller for controlling heating of the aerosol-forming substrate by changing a parameter or configuration of the aerosol-generating device; wherein the dielectric heating element is shaped such that opposing electrodes have a variable, preferably increasing, distance towards each other along a given direction between the two opposing electrodes, wherein the controller is configured to change the parameter to cause a spatially and temporally varying profile of the electric field strength at in a space or volume for receiving the aerosol-forming substrate along the given direction, wherein the profile changes over time in response to the changing of the parameter or configuration of the aerosol-generating device.

Example Ex163. The system according to Example Ex162, wherein the system is adapted according to any one of the Examples Ex101 to Ex157.

Brief Description of Drawings

The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic illustration of a dielectric heating aerosol-generating system according to embodiments of the disclosure;

Figure 2 is a schematic illustration of an oscillation circuit for use in the dielectric heating aerosol-generating system of Figure 1 , according to embodiments of the disclosure;

Figure 3A is a schematic illustration of an oscillation circuit showing two different phaseshifting elements, one exemplarily implemented as a resonance circuit, one exemplarily implemented as a capacitive element, to achieve a 180° phase shift;

Figure 3B is a schematic illustration of an oscillation circuit showing two different phaseshifting elements, one exemplarily implemented as a resonant circuit having parallel resonance properties, one exemplarily implemented as a capacitive element, to achieve a 180°-phase shift;

Figure 3C is a schematic illustration of an oscillation circuit having a resonant cavity;

Figure 4 illustrates an oscillation circuit diagram according to embodiments of the disclosure;

Figure 5A-F illustrate how a Quartz-mimicking or Quartz equivalent circuit may be derived, as a non-limiting example of a parallel-resonant circuit, according to embodiments of the disclosure;

Figure 6 illustrates a frequency analyzer plot of a parallel resonant circuit showing the effect of the switching frequency on the phase shift and impedance of a parallel resonant circuit;

Figures 7A-C are isometric illustrations of inductor pairs sharing a mutual inductive coupling for use in the oscillation circuit of Figures 2 to 4, according to embodiments of the disclosure;

Figures 8A-D are isometric and schematic illustrations of flat interdigitated electrode arrangements for use in the oscillation circuit of Figures 2 to 4, according to embodiments of the disclosure;

Figure 9 shows an isometric and schematic illustration of a tubular interdigitated electrode arrangement for use in the oscillation circuit of Figures 2 to 4 configured to dielectrically heat an aerosol-forming substrate 110, according to embodiments of the disclosure;

Figure 10 shows a schematic illustration of an interdigitated electrode arrangement with a varying electrode separation distance, according to embodiments of the disclosure;

Figures 11A-C show a schematic illustration of an electrode arrangement with an increasing electrode distance along a longitudinal axis, according to embodiments of the disclosure; Figures 12A and 12B show a schematic illustration of another electrode arrangement with an increasing electrode distance along a longitudinal axis, according to embodiments of the disclosure;

Figure 13 is a schematic illustration of a temperature sensing arrangement for detecting a temperature progression of an aerosol-forming substrate situated with the electrode arrangement, according to embodiments of the disclosure;

Figures 14A and 14B show a schematic illustration of another electrode arrangement that causes a varying heating zone in a radial direction, according to embodiments of the disclosure;

Figures 15A-D show schematic illustrations of tubular interdigitated electrode arrangements for use in the oscillation circuit of Figures 2 to 4 configured to dielectrically heat an aerosol-forming substrate 110;

Figure 16 is a schematic illustration of a temperature sensing system for detecting a temperature of an aerosol-forming substrate situated with the electrode arrangement, according to embodiments of the disclosure;

Figure 17 is a schematic illustration of an electrode arrangement and two inductively coupled inductors formed on a quartz glass substrate, according to embodiments of the disclosure;

Figure 18 is a schematic illustration of a temperature sensing system for detecting a temperature of an aerosol-forming substrate situated with the electrode arrangement, according to embodiments of the disclosure;

Figure 19 is a schematic illustration of a control system utilizing a temperature sensing system for controlling the power delivered to an aerosol-forming substrate based on a detected aerosol-forming substrate temperature;

Figure 20 is a schematic illustration of a control system utilizing a temperature sensing system for controlling the power delivered to an aerosol-forming substrate based on a detected aerosol-forming substrate temperature, according to a further embodiment of the disclosure;

Figure 21 is an alternative schematic illustration of an oscillation circuit for use in the aerosolgenerating system of Figure 1, according to embodiments of the disclosure;

Figure 22 is a schematic illustration of a control system utilizing a frequency sensing system for controlling the power delivered to an aerosol-forming substrate based on a frequency of an alternating electric field detected across an electrode assembly, according to embodiments of the disclosure.

Detailed Description

The above and other features and advantages of example embodiments will become more apparent by describing in detail, example embodiments with reference to the attached drawings. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. Example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. Accordingly, while example embodiments are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but to the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of example embodiments. Like numbers refer to like elements throughout the description of the figures.

Figure 1 is a schematic illustration of a dielectric heating aerosol-generating system 100 according to an embodiment of the disclosure. The system 100 comprises an article 105 comprising an aerosol-forming substrate 110 and an aerosol-generating device 120 for heating the aerosolforming substrate 110. The aerosol-generating device 120 comprises a first electrode 130 and a second electrode 135 separated by a cavity 140 for receiving the article 105. The cavity 140 and the article 105 are sized such that the aerosol-forming substrate 110 is in contact with or in close proximity to both the first electrode 130 and the second electrode 135 when received within the cavity 140. Moreover, the first electrode 130 and the second electrode 135 form part of a feedback loop of an oscillation circuit 150 via a first and second electrical contact 160, 165.

In other examples, the first electrode 130 and the second electrode 135 may form part of the article 105 comprising the aerosol-forming substrate 110. In such embodiments, a cavity between the first and second electrical contacts 160, 165 is sized such that, when the aerosol-forming article 105 is housed within the cavity 140, an electrical connection is made between the first electrode 130 and the first electrical contact 160, and the second electrode 135 and the second electrical contact 165.

In some embodiments, the width of the article 105 comprising the aerosol-forming substrate 110 is slightly greater than the spacing between the first electrode 130 and the second electrode 135, such that the distal end of the aerosol-generating substrate 110 is slightly compressed between the first electrode 130 and the second electrode 135. In some embodiments, the article 105, in an initial, uncompressed form, has a width between 5-30% larger than the distance between the first electrode 130 and the second electrode 135. This may reduce or prevent the build-up of air between the first electrode 130 and the second electrode 135 when the aerosol-forming article 105 is received in the cavity 140, and decrease a distance between first and second electrodes 130, 135 for dielectric heating, thereby improving dielectric properties of the load capacitor CL and the accuracy of any measurements or determinations of the dielectric properties of the aerosol-forming substrate 110 performed by the aerosol-generating device 120.

The aerosol-forming substrate 110 may comprise tobacco-based or non-tobacco based materials having an aerosol forming material therein and one or more active agents or ingredients, such as nicotine, pharmaceutical, botanicals, flavorants, liquid substrates with one or more active agents or ingredients, or a combination thereof. The aerosol-forming substrate 110 can also be a liquid aerosol-forming substrate and thereby the aerosol-forming article 105 can be in the form of a cartridge, capsule, or liquid container, and the electrodes 130, 135 can be configured as a wicking element or capillary element for liquid transfer. For example, it is possible that first and second electrodes 130, 135 form a capillary structure that is part of the aerosol-forming article 105 or reaches into an inner volume of the aerosol-forming article 105 that can heat and vaporize a liquid aerosolforming substrate 110 located in the inner volume. For example, the first and second electrodes 130, 135 can be embodied as parallelly arranged plates separated by a distance that forms a capillary channel, for example in a range between 0.1 mm to 2 mm, depending on the desired capillary strength or rise. The first and second electrodes can be arranged as two matrices or arrays of pinlike, rod-like, or tab-like electrodes with opposite polarity, the two matrices or arrays interposed between each other, forming a capillary structure therebetween, for example with an average distance between neighboring pin-like electrodes being in a range between 0.1 mm to 2 mm, depending on the desired capillary strength or rise. In another variant, the wicking element can be a separate element that is interposed between two electrodes 130, 135, for example flat or slightly curved electrodes 130, 135.

The aerosol-generating device 120 further comprises a power supply 170 and a controller 180 electrically coupled to the oscillation circuit 150. In this embodiment, the power supply 170 can be a rechargeable lithium ion battery, for example with one or more lithium ion battery cells, and the aerosol-generating device 120 comprises a power connector that enables the aerosol-generating device 120 to be connected to a mains power supply for recharging the power supply. Providing the aerosol-generating device 120 with a power supply, such as a battery, enables the aerosolgenerating device 120 to be portable and used outdoors or in locations in which a mains power supply is not available. In use, power is supplied to the oscillation circuit 150 from the power supply 170 when a user activates the aerosol-generating device 120. In this embodiment, the aerosolgenerating device 120 is activated by a user pressing an activation button (not shown) that can be provided on an external surface of the aerosol-generating device 120. It will be appreciated that in other embodiments, the aerosol-generating device 120 may be activated in another manner, such as on detection of a user drawing on a mouthpiece (not shown) by a puff sensor provided on the mouthpiece, or a user holding the aerosol-generating device 120. When power is supplied to the oscillation circuit 150, the oscillation circuit 150 generates an alternating electric field across the first and second electrodes 130, 135 to dielectrically heat the aerosol-forming substrate 110 in the cavity 140, releasing volatile compounds.

The controller 180 may cause dielectric heating of the aerosol-forming substrate 110 that is located between the two electrodes 130, 135 with an average dielectric heating power density in a range between 1W/cm³ to 25W/cm³, preferably between 1.5W/cm³ and 15W/cm³ per volume of substrate material during a time period of less than 15 minutes. In particular, during a heat-up phase, the average dielectric heating power density may be controlled or set to be in a range between 7W/cm³ to 25W/cm³, preferably between 8W/cm³ to 20W/cm³. During a target heating phase (also called maintenance heating phase) during consumption, the average dielectric heating power density is in a range between 1W/cm³ to 7W/cm³, preferably between 1W/cm³ to 5W/cm³. In a nonlimiting example, these power densities may be used in heat-not-burn (HnB) applications.

In yet another exemplary embodiment, the aerosol-generating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 35W/cm³ and 35kW/cm³. The aerosol-generating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 50W/cm³ and 10 kW/cm³, between 50W/cm³ and 2.5kW/cm³ or between 50W/cm³ and 1 ,25kW/cm³. The aerosol-generating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 170W/cm³ and 2.5kW/cm³, between 250W/cm³ and 2.5kW/cm³ or between 500W/cm³ and 2.5kW/cm³. Preferably, the aerosol-generating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 1 kW/cm³ and 2kW/cm³. In a non-limiting example, these power densities may be used for heating and vaporizing liquids during a puff in a puff-on-demand application, for example for a duration in a range between 0.5 seconds to 10 seconds.

For such puff-on-demand applications, the dielectric heating losses per volume may be substantially higher than the ones of HnB applications with minute-long heating sessions. However, the heated volume may be smaller (~10 mm³ in puff-on-demand applications versus -300 mm³ in HnB applications).

The aerosol-generating system 100 is also configured for measuring a dielectric property of the aerosol-forming article 105 or the aerosol-forming substrate 110 using the electrodes 130, 135 that are employed for dielectric heating of the aerosol-forming substrate 110. In some examples, the first and second electrodes 130, 135 can be used for dielectric measurements, either during the heating process or separately to the heating process. In this embodiment, the aerosol-generating system 100 can be configured to determine the presence of the aerosol-forming article 105 between the first electrode 130 and the second electrode 135. The aerosol-generating system can be configured to measure a dielectric property, for example an instant value, timely-evolution, or change of a dielectric property, for example to determine whether the aerosol-forming article 105 meets specific criteria or is an authentic substrate. The aerosol-generating system in this example is also configured to control the heating of the aerosol-forming substrate 110 based on the measured dielectric property of the aerosol-forming article 105.

Figure 2 is a schematic illustration of an oscillation circuit 250 for use in the aerosolgenerating system 100 of Figure 1 , according to an embodiment of the disclosure. Oscillation circuit 250 comprises a switching unit 260 interconnected with a resonator feedback loop 270 to provide for a self-oscillating signal to the switching unit 260. The feedback loop 270 is connected between an input and an output of the switching unit 260. The switching unit 260 comprises a single transistor, such as a bipolar junction transistor (BJT) or a field effect transistor (FET).

The oscillation circuit 250 can further comprise a choke 280 that acts on an input to the feedback loop 270 to provide for a stimulation signal, for example a stimulation voltage. The oscillation circuit also comprise a biasing unit 290 acting on the feedback loop 270 for providing a variable or controllable biasing signal, for example a biasing voltage for setting the operating conditions. In the variant shown, the feedback signal can be described as a voltage. The output voltage UOUT of the switching unit 260 is coupled to the feedback loop 270 providing a feedback switching signal in the form of a voltage UIN to the switching unit 260. The configuration of the feedback loop 270 is such that the output signal, e.g. the voltage UOUT of the switching unit 260 can undergo a phase change and arrives inverted at the input UIN of the switching unit 260 for resonant oscillation. In other configurations, a current could be used as the feedback signal with a switching unit 260 comprising a BJT.

The feedback loop 270 is configured to be self-oscillating and will oscillate at or close to a given resonance frequency determined by the values of the passive components of the feedback loop 270. Feedback loop 270 is configured to provide a 180- phase shift from the output UOUT to input UIN of switching unit 260 for oscillation, and in addition, the transistor T is configured for inverting operation.

As shown in Figures 3A and 3B, feedback loop 270 includes a resonant circuit 272 comprising the load capacitor CL providing for a first 90° phase shift or quarter wave shift to the feedback signal. Feedback loop 270 further includes a capacitive element 274 providing for a second 90°-phase shift or quarter wave shift to the feedback signal, such that the feedback signal reaching the input of the switching unit 260 is inverted and phase-shifted by 180°. Switching unit 260 is itself configured for inverted switching operation to provide a 180-phase shift between the input UIN and the output UOUT of the switching unit 260.

Resonant circuit 272 comprises the first and second electrodes 130, 135, together forming a load capacitor CL. When an aerosol-forming substrate 110 is situated between the first and second electrodes 130, 135, it forms part of the load capacitor CL. Importantly, the load capacitor CL is formed in the feedback loop 270, and not at a separate output or part of a separate circuitry that is connected to the switching unit 260. This enables a high-frequency oscillating voltage to be created across the electrodes of load capacitor CL, which is needed for sufficient and efficient dielectric heating of the aerosol-forming substrate 110, without having an additional output or circuit to the already resonating feedback loop 270, which would create unnecessary losses and circuit complexity. The resonant circuit 272 may comprise a series resonator circuit or a parallel resonator circuit, examples of which are described in greater detail below.

In an alternative embodiment, resonant circuit 272 may include a resonant cavity 272, as illustrated in Figure 3C. The resonant circuit 272 including resonant cavity may have an interior volume configured to receive an aerosol-forming substrate 110, for example having an opening for inserting an aerosol-forming substrate 110. In an example, the resonant circuit 272 including resonant cavity can be configured as a A/4 resonator. The resonant circuit 272 including resonant cavity may be configured to behave like an RLC circuit. The inductor L and the capacitor C are arranged in parallel to each other, to have a parallel resonance or a frequency close to the parallel resonance that can be stimulated by the switching unit 260. Resonant circuit 272 including cavity may be coupled to the feedback loop 270 using one or more of a capacitive coupling, an inductive antenna coupling (magnetic coupling), a direct electric coupling, or a window coupling (e.g. coupling with a loop).

The resonant circuit 272 including resonant cavity can have any shape, but preferably has a cylindrical shape or a rectangular parallelepiped shape. In one embodiment, the resonant cavity can be configured as a split-ring resonator.

Figure 4 illustrates an oscillation circuit 350 according to a non-limiting, exemplary embodiment of the disclosure. Oscillation circuit 350 comprises a switching unit 260 in the form of a transistor T having an intrinsic capacitance Cj. Moreover, transistor T is configured for inverting operation, for example as an inverting common source FET, MOSFET, or a common emitter BJT. The source terminal of transistor T can be coupled to a DC power supply via a choke 280. Between the gate and source terminals of transistor T extends a feedback loop 270. The feedback loop 270 comprises a resonant circuit 272 including a load capacitor CL having a first and second electrode 130, 135 separated by an aerosol-forming substrate 110. In the variant shown, the resonator circuit 272 is also connected to ground via a delay line DL and a capacitor C2 connected in series to the delay line DL. The circuit 350 further comprises a biasing unit 290 coupled to the gate terminal of the transistor T via the delay line DL. AS shown in Figure 4, the biasing unit 290 is electrically connected between the delay line DL and the capacitor C2, so that the biasing unit 290 is somewhat isolated from the high oscillation frequency of the feedback loop 270. The delay line could be placed elsewhere, for example somewhere else in the feedback loop.

The delay line DL is a time delay element, for example an element that has inductive behavior, for slowing down the arriving voltage wave from the feedback loop 270 during a period of the oscillation. This allows to tune the resonant circuit 272 to a desired switching and oscillation frequency, in order to move the oscillation frequency away from the natural resonant frequency given by the resonant circuit 272. This ensures that oscillation circuit 350 remains in a predefined frequency operating range to provide for the requisite inverted or 90- phase-shifted feedback and also to make sure that the feedback loop has a low impedance to provide for a high gain, as described in greater detail below.

The oscillation circuit 350 is shown with electrical contacts 160, 165 that are arranged on each side of the load capacitor CL. In some embodiments, the first and second electrodes 130, 135 may be removable from the oscillation circuit 350, or may form part of the aerosol-forming article 110. In such embodiments, electrical contacts 160, 165 provide an electrical connection between the first and second electrode 130, 135 and the feedback loop 270. In embodiments where the load capacitor CL is fixed within the feedback loop 270, for example, such that an aerosol-forming substrate 110 can be inserted and removed to and from a cavity formed in between the first and second electrodes 130, 135, electrical contacts 160, 165 provide electrical connections from the first and second electrodes to the next components in the feedback loop 270, e.g. inductors Li and L2. With respect to the power supply voltage, a DC power supply voltage is provided that is preferably in a range that is suitable for battery operation with one or more standard battery cells. Preferably, the DC power supply voltage is below 14V. For example, it is possible to operate the oscillation circuit 350 on a single battery cell, for example an 18650 battery cell (Li-Ion), or a similar battery cell, that provides for 3.2V to 3.9V. However, more preferably, a voltage of one battery cell of an exemplary 3.5V to 7V for power supply can be boosted, for example by a DC-DC converter (e.g. a boost circuit), or a voltage doubler. Alternatively or in addition, two or more battery cells can be used in series, or other configurations or arrangements that allows to increase a voltage from one or more battery cell can be used. It is also possible to have a controllable output voltage (e.g. DC- DC converter, voltage regulator), to control the temperature of heating by a change to the DC supply voltage, or to boost the voltage (for example to 10-12V) for maximum power at the preheating stage, to speed up the preheating stage with the goal to reach the aerosolization temperature quickly. Control of the DC supply voltage is one way that makes it possible to rapidly change heating power despite the oscillation circuit 350 freely oscillating.

A capacitor Ci is arranged in parallel to the transistor T and therefore in parallel with the intrinsic capacitor of the transistor T (e.g. a field effect transistor). This facilitates a less voltagedependent oscillation and frequency, stabilizes the oscillation, and also improves the overall dielectric heating efficiency. Capacitance of capacitor Ci is chosen to be larger than the maximal intrinsic capacitor Ci of transistor T at the operating conditions, so that the variation of the intrinsic transistor based on frequency, temperature, etc. has much less or negligible influence on the feedback loop 270. For example, in a non-limiting embodiment, the value can be in a range between 2pF to 100pF, more preferably in a range between 5pF and 50pF.

Capacitive element 274 comprises a capacitor C2 arranged at the output or end of the resonant circuit 272. In one embodiment, capacitive element 274 comprises more than one capacitor. As described above, capacitive element 274 has the function of providing a 90- phase shift to the feedback voltage of feedback loop 270 with minimized losses or other undesired effects, and it therefore needs to have a high-quality factor or Q factor, preferably above 1000 at 100MHz. The capacitance value for C2 of the capacitive element 274 should be relatively high as compared to Ci, for example in a range between 500pF to 100nF, more preferably between 1nF and 50nF, which leads to a low impedance of capacitive element 274. In a variant, the capacitive element 274 can be implemented as a RC network to provide for the 90- phase shift, for example using two single- resistor-capacitor networks, having two capacitors in the feedback loop, each capacitor connected to ground via a resistor.

Resonant circuit 272, together with capacitive element 274, provides for a 180- phase shift and a voltage gain from the output UOUT to the input UIN, and transistor T (for example a FET) is configured for inverting operation, thereby also providing for another 180- phase shift. This results in a resonant or close-to resonant oscillation and an amplified voltage UL across the electrodes 130 and 135 of the load capacitor CL, as compared to the DC supply voltage. When operating close to resonance, the resonant circuit 272 circuit behaves inductively, having a high Q factor. Furthermore, the feedback loop 270 is impedance-matched with the transistor T, at an impedance of approximately 500mQ to 8Q, preferably around 2Q, to provide for a high gain, leading to an increased voltage across the load capacitor CL. Also, preferably, this gain is achieved without the use of an additional voltage or current amplifying passive element, such as a tapped inductor or a transformer located in the circuit that forms the feedback loop 270, as such passive elements are difficult and lossy to operate and design at frequencies greater than 50 MHz. Preferably, the impedances of the resonant circuit and capacitor C2 add up to match the impedance of the transistor T, more preferably the resonant circuit is substantially impedance-matched with the transistor.

The combination of capacitor Ci , the feedback loop with resonant circuit 272 and capacitive element 274 can also be described as a bandpass filter or Pi or TT network that generates a 180- phase shift. In the illustrated embodiment, the resonant circuit 272 of the feedback loop 270 is not connected to ground, but is suspended with ends at each capacitor Ci and C2, thereby not having a direct ground connection at either end of resonant circuit 272, reducing stray elements and ground influences for more predictable operation.

At the operating frequency, the resonant circuit 272 including load capacitor CL acts as an inductive load providing a first 90° phase shift, also referred to as a quarter-wave phase shift, and capacitive element 274 exemplarily including a high quality factor capacitor C2 connected to ground, provides for the second 90° phase shift or quarter-wave phase shift.

Oscillation circuit 350 can be described or characterized as a Pierce oscillation circuit with a modified feedback loop 270, where the physical Quartz element is replaced by a Quartz-mimicking or Quartz electric equivalent circuit to provide for an inverting feedback to the switching unit 260 that also operates in an inverted mode. In some embodiments, oscillation circuit 272 can be based on other resonant feedback loop oscillation circuit configurations, for example, but not limited to, the use of a Colpitts or Hartley type oscillator, using an inverting transistor T.

Figures 5A to 5F illustrate how a Quartz-mimicking or Quartz equivalent circuit may be derived using a variant of a parallel resonator circuit PRC, that can serve as an exemplary and nonlimiting embodiment as resonant circuit 272. A Quartz-mimicking or Quartz equivalent circuit can have a parallel resonance at a given frequency. This can be seen as a circuit with two branches, one representing the mechanical oscillation and one representing the electric behavior, as illustrated in figure 5A and 5B. The mechanical oscillation is represented by a first branch having load capacitor CL and an inductor LTOT. The electric oscillation is represented by a second branch arranged in parallel to the first branch, having a Capacitor CE. This configuration leads to a series connection of two capacitors CL and CE (seen around the loop formed by the two branches) so that CE will decrease the overall capacitive value of the equivalent circuit. Also, this circuit provides an inductive phase shift of about 90 within certain defined frequency range.

Referring now to Figure 5C, one branch of the parallel resonator circuit PRC comprises an inductor LTOT and the load capacitor CL connected in series of the first branch. This branch can be improved by splitting LTOT into two inductors Li and L2 on each side of the load capacitor CL, as shown in Figure 5D, to provide a split inductor or split-coil design and a more symmetric application of the voltage UL across the load capacitor CL, thereby improving dielectric heating efficiency. To provide for parallel resonance, the capacitor CE of the second branch can be replaced with an inductor (as shown in Figure 5F) due to capacitor CE‘S minimal capacitive effect on CL.

In a non-limiting example starting from the split inductor Li and L2 of the resonant circuit of Figure 5D, inductors Li and L2 can be mutually magnetically coupled to form a mutual inductance M, thereby forming the parallel circuit branch or second branch of the resonant circuit 272, as shown in Figure 5E. The mutual magnetic coupling can be achieved by the close proximity of the two inductors Li and L2 with alignment of winding axis of the coils, or by use of a mutual magnetic core, or both. This has the advantage of providing a parallel-resonator circuit PRC without the use of additional wires for the second branch, and without additional windings or separate magnetic cores for a second parallelly-arranged inductor. This also allows for a symmetric arrangement that favors and facilitates the inductive coupling of the two inductors Li, L2 and the balancing of the voltage UL over load capacitor CL. The symmetry of the two branches in either direction with first branch Li - CL - L2 and the second branch with inductor LE, representing the two mutual inductance values, facilitates the symmetrical balancing of the voltage over the electrodes of the load capacitor CL, which consequently reduces losses created at the load capacitor CL. This split inductor principle can also be referred to as a split coil resonator.

The resonant circuit 272 could also be implemented as shown in the Figure 5F, where the mutual inductance M (seen two times due to the mutuality) is replaced by a separate inductive element, for example inductor LE.

The values of components in this resonant circuit 272 are preferably chosen to be in the following exemplary and non-limiting ranges. LTOT can be a range between 10nH to 50nH, more preferably between 15nH and 40nH, which is the equivalent of Li plus L2, LE could be in a range between 7nH and 30nH, more preferably between 10nH and 20nH, and the value of the load capacitor can be in a range between 0.5pF to 5pF, more preferably between 1 pF to 3pF.

The resonant circuit 272 can be configured as another type of tank circuit providing for the 90- phase shift in a given frequency range. In one embodiment, the resonant circuit 272 can be implemented as a series resonant circuit, having the load capacitor CL connected in series with one or more inductive elements, configured to provide for an inductive response or 90°- phase shift in a given frequency range that is suitable for dielectric heating.

In order to produce the required dielectric losses in the load capacitor CL, a high frequency is needed. The dielectric losses will increase somewhat proportionally to the frequency (in this case the oscillation frequency f_s of the oscillation circuit) of the alternating voltage applied to the load capacitor CL. However, higher switching frequencies f_s lead to greater switching losses in the transistor. Where very high switching frequencies are used, e.g. 1 GHz or more, expensive circuit designs are necessary to make the circuit operable (e.g. GaN transistors, GHz-type circuit design e.g.).

To compensate for a lower switching frequency, a higher oscillation AC voltage UL (for example measured by the RMS or peak voltage) can be provided across the load capacitor CL to deliver the necessary power to the load capacitor CL. When a balance has to be struck between increasing the switching frequency f_s and increasing the voltage over the load capacitor CL in order to increase the heating power (and therefore dielectric losses PL in the load capacitor CL which can include the aerosol-forming substrate 110), the voltage increase has a stronger effect on the heating power than frequency increase, as voltage has a second order relationship with power. The dielectric losses in load capacitor CL are also dependent on the distance separating the two electrodes 130 and 135, which influences the electric field strength EF across the aerosol-forming substrate 110.

As an example, a decreasing efficiency occurs with increasing switching frequency f_s, an exponentially increasing transistor price is the consequence of an increased switching frequency f_s to ensure operability, and a decreasing electric field strength occurs with increasing switching frequency f_s.

For mobile portable designs of dielectric heater that are handled by a human, safety considerations with respect to voltage insulation and potential dielectric breakdown due to contamination and general inhomogeneous material of the substrate material S of the aerosolforming substrate 110 are a serious concern. Therefore, there are working ranges for switching frequency fs and electric field strength EF, for a hand-held and human-operated portable device. The electric field strength is dependent on voltage UL applied to capacitor CL and a maximal distance d between the first and second electrodes 130, 135.

It is preferable that the switching frequency is limited to a certain range, firstly to ensure sufficient power losses PL across the load capacitor CL, and secondly to avoid excessive switching losses. Limiting the value of f_s enables the use of straightforward circuit design, for example, but not limited to, the use of a LDMOS or other standard transistor used for RF circuits. Preferably, the switching frequency should be in a range between 100MHz and 1.2GHz, more preferably between 150MHZ to 1GHz, more preferably between 200MHz and 900MHz. At the same time, the maximal- value of electric field strength between the electrodes of the load capacitor CL should be limited to a reasonable value that allows for simple electric insulation materials and designs, taking into account impurities and inhomogeneous substrate designs, the use of thin electrodes that may be located in close proximity to each other (for example but not limited to 1 mm-10 mm), potential exposure or close proximity to human body, and potential improper human manipulation. Preferably the average electric field strength across the electrodes of the load capacitor is maximally 120V/mm, more preferably maximally 100V/mm, even more preferably maximally 80V/mm.

Preferably, at nominal heating operation (not during a start-up or warm-up phase that lasts less than 30 seconds where the efficiency can be lower), the heating efficiency should be at least 60% (desired power losses PL versus all the other losses, which can include switching losses of transistor T, losses caused by biasing circuit and choke, inductive-resistive losses of the inductors Li and L2, capacitive-resistive losses from capacitors Ci and C2, and resistive losses of electrodes E1 and E2 and the wiring. As an example, the overall power could be 10W, while the effective power or heating losses PL should be 6W or more, with 4W or less of non-heating losses or other heating losses not caused in the substrate 110 between the first and second electrodes 130, 135. More than 6-7W of power losses is not desirable for a handheld device, and more preferably there should be less than 5W, at nominal heating conditions or other operation that can last for more than 30 seconds.

To have a proper inverting effect and a 180° phase shift on the feedback loop 270 between UIN and UOUT, the oscillation circuit 350 must remain in a frequency operating range where the behavior of the feedback loop 270 is highly inductive. In the example comprising a parallel resonator circuit (PRC), the series resonance frequency fsER (resonant frequency) is relatively close to the parallel resonance frequency fpAR (also referred to as the antiresonant frequency). If the oscillation frequency fs of the PRC exceeds the parallel resonance frequency f_PAR, the feedback loop 270 will act capacitively and not provide the necessary phase inversion to the loop 270. Furthermore, the equivalent impedance of the circuit will increase to an extent that is too high for efficient dielectric heating as the requisite gain is not providing for.

Oscillations in the feedback loop 270 will be naturally drawn towards the parallel resonance frequency of the resonant circuit 272. However, the addition of a delay line DL can introduce a slight time delay limiting the oscillation frequency below the parallel resonance frequency. Figure 6 shows a frequency analyzer plot of an exemplary resonant circuit 272, specifically a plot of a parallel resonator circuit PRC showing the relationship between the oscillation frequency (with a series resonance at 855 MHz and a parallel resonance at 1.246 GHz), the phase shift across the PRC (with a relatively flat inductive 90° frequency response between the two resonant frequencies) and the effective impedance of the PRC. More specifically, it can be seen from Figure 6 that the 90° phase shift starts dropping before the parallel resonance frequency fp_AR is reached. After the parallel resonance frequency fpAR is reached, the phase shift response drops below 0° to capacitive behavior and the impedance is very high, e.g. 2.4kQ. The ideal operating frequency range is closer to the series resonance frequency fsER where the phase shift is still 90° and the impedance response is low, preferably an impedance that is less than 2Q, more preferably less than 1Q. The parallel resonance frequency fpAR can be above 1GHz, e.g. 1GHz to 1.5GHz, while the actual switching frequency f_s can be below 1GHz, and this lower switching frequency is caused by the delay line DL.

Ideally, the oscillation frequency fs should be set to be below the parallel resonance frequency fpAR but above the series resonance frequency fsER, to make sure that two conditions are fulfilled, firstly (i) that the resonant circuit behaves inductively to provide a 90° phase shift, and secondly (ii) to make sure that the impedance of the resonant circuit (an therefore the feedback loop 270) is low, as illustrated in the graphs of FIG. 6. For example, a resulting impedance of the feedback loop at the oscillation frequency fs of the oscillation circuit can be in a range of approximately 10OmQ to 2Q. Preferably, the delay line DL is configured such that the oscillation frequency fs is closer to the series resonance frequency fsER than to the parallel resonance frequency fp_AR, thereby maintaining a low resonant circuit impedance while operating at a frequency range where the resonant circuit provides the 90° phase shift. The time delay caused by delay line DL needs to be relatively short, as the series resonance and the parallel resonance of a parallel oscillating circuit PRC are close to each other, relative to the overall frequency range. Preferably, the delay caused by delay line DL that acts of feedback loop 270 should be in a range between 5% to 35% of the period of the parallel resonance frequency f_PAR, providing that the above two conditions (i) and (ii) are fulfilled. In an embodiment, the delay caused by the delay line DL that acts on feedback loop 270 is in a range between 35% and 90% of a difference between the period of the parallel resonance frequency f_PAR and the period of the series resonance frequency fsER, again providing that the above two conditions (i) and (ii) are fulfilled, more preferably a range between 50% and 85%. For example, taking the illustration of FIG. 6 and as a non-limiting numerical example, assuming that a parallel resonance frequency is at 1.25GHz, therefore having a period of 800ps (picoseconds), and a series resonance is at 855MHZ, and therefore a period of 1169ps, there is a difference of 369ps between the period of f_PAR and fsER. The time delay caused by delay line DL can be in the above range, for example at 70% of the period difference between f_PAR and fsER, thereby being 258ps, thereby making sure that the feedback loop 270 has the desired inductive behavior and low impedance that is necessary to provide inverting feedback at high gain.

Preferably, the delay line is implemented as a meandering conductive element having dominantly inductive behavior, for example a meandering element having from two (2) to twelve (12) meandering branches, more preferably from three (3) to eight (8) meandering branches. Such implementations exhibit minimal stray inductive and capacitive behavior. Various delay line structures can be used to provide the desired function, for example an Omega-shaped coil, single planar coil, flat inductor, wavy line, zig-zag line, or a sawtooth line. It is also possible to provide the required delay line functionality by a specific transmission line design. For example, it is possible that the physical element of the delay line DL is implemented as a conductor in a printed circuit board, for example implemented as a microstrip patch antenna. In some embodiments, a low-pass filter may be used as the delay line DL, however this will have an impact on the shape of the oscillating voltage, whereas a delay line DL that provides for a short time delay by inductive effect will not impact the wave shape. In the embodiment illustrated in Figure 4, delay line DL is placed between the feedback loop output of the resonant circuit 272 and capacitive element 274, but other arrangements are also possible.

Figures 7A-C are isometric illustrations of a split coil resonator having a mutual inductive coupling for use in the oscillation circuit of Figures 2 to 4, according to embodiments of the disclosure. In the example of Figure 7A, the two inductors Li and L2, are each formed as a single winding, e.g. a single loop coil. The winding central axis of each coil substantially coincides with each other, and the plane formed by each single-winding inductor is parallel to the other, and is also in close proximity. This establishes a mutual inductance between inductors Li and L2 without a magnetic core Me. If necessary, the mutual inductance M can be further increased by adding a magnetic core Me that traverses or at least partially traverses each winding of Li and L2 to reach a desired inductance level. In this respect, a distance between the two planes in which the windings are arranged can be increased, to minimize the capacitive effect between them. Preferably the windings of inductors Li and L2 are wound in the same direction around the coinciding winding central axis of, or in case a core Me is present, around the core Me or the central axis. This way, the magnetic flux caused by both coils Li and L2 is enhanced, rather than cancelled out. In other words, the two inductors Li and L2 appear as a continuously wound coil around a magnetic core Me, or around the winding central axis in case no core is used, with two winding regions forming two inductor coils Li , L2.

Figure 7B illustrates an alternative split coil resonator arrangement, wherein instead of one full loop coil for Li and L2, an omega-shaped loop is used. Other winding shapes are also possible while providing substantially the same functionality.

In some examples, it is possible to use a smaller diameter of inductor coils Li, L2, but have several loops or turns. Preferably the number of turns in each inductor coil Li, L2 is no more than five (5), preferably less than three turns, and preferably no more than one turn. To further reduce the capacitive coupling between Li and L2, the inductors Li , L2 of the split coil resonator of Figure 7B are arranged as planar coils in an omega-shape, single winding, or double winding coils, both on the same surface or plane, and are therefore not aligned in parallel to each other. This is desirable since the capacitive effect between the two inductors Li and L2 can provide for unwanted additional dielectric losses. In this embodiment, the magnetic coupling by core Me is achieved via a u-shaped core with each leg traversing a center of each planar coil Li , L2.

Both Figures 7A and 7B show an embodiment of the resonant circuit 272 as a complete parallel resonant circuit PRC by virtue of the second branch being created by the mutual inductance M between inductors Li and L2.

It is also possible that the mutual inductance M between Li and L2 are created by simple proximity of the two inductor coils Li and L2, without the use of a magnetic core Me as illustrated in Figure 7C, or by inter-winding the coils of inductors Li and L2. The electrode arrangement of Figure 7C comprises parallelly arranged electrode plates E1 and E2 having curved edges to reduce hotspots in the electric field formed around the boundaries of the electrode plates.

Figures 7A and 7B illustrate electrode arrangements comprising a pair of electrode plates 130, 135 aligned in parallel, however other electrode arrangements are also possible.

Figures 8A-D are schematic illustrations of flat interdigitated electrode arrangements for use in the oscillation circuit of Figures 2 to 4, according to embodiments of the disclosure. The use of interdigitated electrodes allows for a more homogenous electric field generation, which can be used to avoid hot spots across an aerosol-forming substrate. Figure 8A shows an electrode arrangement comprising two electrodes. A first electrode comprises one or more extended portions and a second electrode comprises a corresponding one or more recessed portions for receiving the one or more extended portions of the first electrode. In other some examples, both the first and second electrodes each comprise a combination of extended portions and recessed portions configured to align with corresponding recessed portions and extended portions in the opposing electrode.

Figures 8B and 8C show electrode arrangements comprising a plurality of electrodes for each polarity wherein each electrode is positioned adjacent to electrodes of the opposite polarity.

The shape and geometry of the electrodes may vary however, it is preferable that the edges and corners of the electrodes are rounded, e.g. having a radius in range of about 0.15 mm to 2.5 mm, to “soften” the peaks of the electric field at the edges and corners.

As shown in Figure 8D, it is possible to make an interdigitated electrode arrangement for one- side flat aerosol-forming substrate 110. However, dielectric heating may be improved by providing a second electrode arrangement identical to the electrode arrangement shown in Figure 8D on an opposite side of the aerosol-forming substrate 110. The electrodes of the second electrode arrangement can be configured to align with electrodes of the first electrode arrangement having an opposite polarity.

As shown in Figure 9, the interdigitated electrode arrangement may comprise a first and second electrode Ei , E2 configured to interdigitate together around a cylindrical axis to form a tubular structure. In this embodiment, there are two pairs of three digits of the electrodes having a diameter between 5 mm to 9 mm. The tangential distance between the electrodes of opposite polarity can be between 0.5 mm to 2 mm, preferably between 0.7 mm to 1.7 mm. A rod shaped aerosol-forming substrate can be arranged inside the electrode arrangement.

According to the present disclosure, the tangential distance of the electrodes varies along the longitudinal axis of the electrode arrangement. This is schematically indicated by the two exemplary distances di and d2 wherein di < d2. By this progressive increase of the tangential distance of the adjacently polarized electrodes E1, E2 along the longitudinal axis, the electric field strength shows a decreasing intensity gradient along the longitudinal axis in this direction. As indicated by the arrow in Figure 9, for a given oscillating voltage on the electrodes E1 and E2, the electric field strength will decrease from the left to the right side of the cylindrical interdigitated electrode arrangement, with an electric field strength at di (smaller distance) being larger than at d2 (larger distance).

Thus, the heating energy applied to the substrate to be heated, and consequently also the temperature, will also decrease in this direction. By increasing a power supplied to the heater (for example by increasing a DC supply voltage), it is possible to move a zone that is heated to a target temperature towards the right side, e. g. towards an area where the electrodes are more spaced apart from each other. This allows to generate a progressive zoned heating, for example to heat a cylindrical substrate from the left to the right (as indicated by the arrow in Figure 9).

For example, at a given AC voltage UL applied to the electrodes E1 and E2, if the distance d between the electrodes E1 and E2 is decreased, the electric field strength EF is increased proportionally, but the losses at the load PL increase in square. In particular, the power losses PL generated in the load capacitor CL are given by the following equation (1).

P_L = 2nf_sE₀E”E^V (1) wherein:

PL loss at load fs oscillation frequency so dielectric constant (relative permittivity) s” imaginary part of the complex permittivity

EF electric field strength

V volume of the substrate material S

In other words, the electrodes of the heating element are shaped so that by changing a parameter or configuration of the aerosol-generating device, such as the DC supply voltage, a travelling of an isotherm can be achieved. This travelling heating zone leads to a more homogenous composition of the generated aerosol over time because not all the substrate is heated to a particular temperature at once. This is particularly advantageous when different ingredients are present in the substrate, which have different evaporation temperatures. For instance, menthol evaporates at 160°C, water at 100°C.

The inventors of the present disclosure have also found that despite the increased heating energy over time no dangerous overheating will occur. The reason is that in those regions where the heating zone has already passed through, the substrate has been depleted by evaporation of the aerosol, leading to a decrease of the dielectric constant. Thus, a further increase of the temperature is counteracted in these regions.

Of course, the distance between the electrodes Ei and E2 does not have to change linearly. Rather, the distance may vary in any desired pattern to generate a particular temperature profile. For instance, for any arrangement of the electrodes E1 and E2, the distance can change logarithmically to compensate for the exponential change of heating power with the distance between the electrodes.

For instance, Figure 10 illustrates an embodiment in which the distance between electrodes of opposite polarity varies across different regions of the electrode arrangement. This may be advantageous to modify the strength of the electric field in different regions of the electrode arrangement, thereby modifying the heating power delivered to different regions of an aerosolforming substrate 110 heated using the electrode arrangement. For any arrangement of the electrodes E1 and E2, the distance can change logarithmically to compensate for the exponential change of heating power with the distance between the electrodes.

According to this embodiment, the electrodes have a progressively increasing gap which is not straight and generates a heating zone travelling along a direction opposing the direction y. For instance, the electrodes can be fabricated on a flexible PCB, which can be rolled to form a tubular electrode arrangement. According to a further embodiment, the electrodes Ei and E2 may also be arranged to have an increasing radial distance across to the longitudinal axis. Figures 11A and 11 B illustrate the travelling of the isotherm along the substrate S in a schematic longitudinal cut view of an electrode arrangement with two obliquely arranged planar electrode plates E1 and E2. As shown in this Figure, at a first instant of time, a first voltage ULI is applied between the electrodes E1 , E2 and at a following instant of time, a second voltage Ui_2 is applied between the electrodes E1 and E2, ULI being smaller than UL2.

Due to the particular form of the electrodes, an expanding heat zone HZ1 (defined by a temperature in the volume that is above a certain value, for example 200°C to 220°C) can be observed. The heat zone HZ1 expands towards an area between the electrodes that has a greater distance between each other because the temperature increases when the power losses increase, e.g. by increasing a voltage UL across the capacitor CL. This expanded heat zone is shown as heat zone HZ2.

The heat zone HZ2 may also be smaller than shown in Figure 11 B. As shown in Figure 11 C, for a higher voltage UL2, the heat zone HZ2 may have essentially the same longitudinal dimension as the heat zone HZ1. In other words, when increasing the voltage, a heated area may travel over time from regions with a smaller distance between the electrodes E1 and E2 towards regions with a larger distance between the electrodes E1 and E2. It should be noted that the temporal variation of the spatially varying temperature profile is not mainly due to heat propagation, but due to the controlled changing of the parameter or configuration of the aerosol-generating device, e. g. the voltage across the electrodes.

The varying temperature profile is a result of the temporally and spatially varying electric field strength. More specifically, the dielectric heating element is shaped such that opposing electrodes have a variable, preferably increasing, distance towards each other along a given direction between the two opposing electrodes, wherein the controller is configured to change the parameter to cause a spatially and temporally varying profile of the electric field strength in a space or volume for receiving the aerosol-forming substrate along the given direction, wherein the spatially varying profile changes over time in response to the changing of the parameter or configuration of the aerosolgenerating device. Thus, it is possible to increase or decrease the heating power (e.g. a supply voltage or a switching frequency) to thereby move a given electric field strength profile along the given direction (axis). This allows to move a heating zone, spatial heating profile, or point along the given direction.

In an embodiment, the end or area where the two electrodes E1 , E2 are closer to each other forms the downstream side (which may be referred to as the mouthpiece side or inhalation side), while the end or area where the two electrodes E1 , E2, are farther apart from each other forms the upstream side, along an airflow path of an aerosol-generating device.

Thereby, the portion of the substrate S that is first depleted from aerosol-former (for example HZ1) can act as a filter for the aerosol generated thereafter, for example by portion of the substrate (HZ2) that is further upstream. Referencing Figures 11A-11 C, the upstream side would be the bottom end, while the downstream side would be the upper end. The substrate S could be either a flat- long itudi nally shaped substrate or a cylindrical stick, or have other shapes that define an extension along an airflow path.

In other words, the two electrodes Ei, E2 can be arranged having changing distance relative to each other along an imaginary axis that is located in the middle between the two electrodes, and the electrodes can be powered with an increasing or decreasing dielectric heating power (e.g. increasing or decreasing supply voltage and/or frequency) to move a given average electric field strength along the imaginary axis.

Furthermore, as the temperature depends on what kind of substrate S is located between the two electrodes E1 , E2, the present disclosure provides an electric field strength profile, that can be moved along the imaginary axis.

Furthermore, as will be explained in more detail with reference to Figure 12, the distance between the electrodes E1 and E2 can change logarithmically to compensate for the exponential change of heating power with the distance between the electrodes E1 and E2.

As illustrated by Figures 12A and 12B, the electrodes do not necessarily have to have a linear increase in their distance across to the longitudinal axis. With a linear increase of the distance, the power losses show an exponential decrease.

To fully or at least partially compensate for this exponential decrease of power losses as a function of the distance d between the two opposite-polarity electrodes plates E1 and E2, the distance between the two plates E1, E2 can be increased logarithmically in a direction in which the heating zone HZ is intended to expand. This is illustrated in Figure 12B. Such an arrangement allows to achieve a linear or close to linear response of the increase in voltage and the progression of the heating zone HZ (in the variant shown, the heating zone expands towards the right).

As shown in Figure 12A, if d4 is two times d1 , the heating energy at d1 will be four (4) times higher than at d4 (due to the exponential increase). As the substrate S should not be heated above a certain temperature, for example no more than 350°C to 365°C, the increase between d1 and d4 should be such that the maximal temperature of the first heating zone HZ1 does not exceed a range between 350°C to 365°C. Preferably, the increase in distance should not be more than root of 2, e .g. 1.41 , preferably in a range between 1.1 and 1.41 , more preferably in a range between 1.15 and 1.3.

Also, with a logarithmic instead of a linear increase of the distances for each equidistant step, it is possible to achieve a somewhat linear progression of the heating zone’s isothermal line as a function of the applied voltage UL.

Figure 13 schematically illustrates a further example of an aerosol-generating device with a heating element 1000 that has electrodes according to any of the arrangements illustrated above. In order to determine a temperature of the cavity 140, at least two temperature sensing units 1950A, 1950B are provided. A controller 1880 receives output signals from these temperature sensing units and may control a heating operation of the heating element 1000 based on these output signals. Of course, more than two temperature sensing units also may be provided along the cavity 140. Advantageously, the temperature sensing units 1950A, 1950B are located at or close to each extremity of the heating element 1000, which may for instance be tubular.

In particular, the two temperature sensing units 1950A, 1950B are distanced from each other along the direction, in which the heating zone travels. The two or more temperature sensing units 1950A, 1950B are preferably integrated into the carrier film. This allows to perform a precise control of the progression of the heating zone that lies above a target temperature.

Figures 14A and 14B illustrate the principle according to the present disclosure applied to a cylindrical or tubular aerosol-forming substrate 110. According to this embodiment, a first alternating voltage ULI is applied between the electrodes Ei , E2 at a first instant of time and at a following instant of time, a second alternating voltage Ui_2 is applied between the electrodes E1 and E2, ULI being smaller than Ui_2. Thereby, a given electric field strength value moves radially inwards towards the inner core of the aerosol-forming substrate 110, such that the penetration depth of the heat zone HZ1 to HZ2 towards an inner core of the aerosol-forming substrate 110 is expanded. In other words, the isotherm travels in a direction across to the radial axis over time.

Generally, the heating power per volume of substrate material [W/cm³] depends on the electric field strength, but also linearly depends on the dielectric constant of the substrate material that is heated. An aerosol-forming substrate 110 includes usually high dielectric aerosol-former, such as but not limited to glycerine and sometimes polypropylene glycol (PPG). The dielectric constant of the substrate 110 may therefore have a high dielectric constant value of exemplarily 10 or more when it is in the unconsumed state, and the dielectric constant of the substrate 110 may decrease to less than 3 upon heating and depletion. Therefore, with the given exemplary and non-limiting numerical example, the heating power per volume can decrease by a factor 3 or more for a given volume of substrate material. These numbers are only exemplary values to illustrate the effect of depletion and the change in heating power for a given electric field strength. In the present application, this effect may provide an inherent automatic safety feature as already mentioned above. The effect can be used to avoid overheating at the side or end of the electrodes where the electrode gap is the smallest, as that will be the location where the electric field strength is the strongest. If the electric field strength (or voltage) changes over time along the one given direction along the electrodes, to progressively increase the electric field strength with a decrease of electric field strength along the given direction, the substrate 110 and the velocity of motion of the electric field in the given direction can be used to cause a substantial depletion at a given temperature. This will cause the quite substantial decrease of the dielectric constant, and therefore less heating will be caused at the side where electrodes are closest, i.e. the upper end in Figures 11A-C and the left side in Figures 12A-B.

By having such substrate, the travelling temperature profile will form a bump or peak that moves from the small gap side to the large gap side along the given direction, with the temperature being the highest where the aerosolization temperature is caused, as the depletion will cause the substantial dielectric constant drop, and despite being exposed to a higher electric field.

In other words, the temperature profile may not be solely increasing in the one direction, but can move in that direction, and can have a bump-like temperature profile. Advantageously, the highest temperature is about 200°C to 220°C as the desired aerosolization temperature that can move towards the one direction.

Figures 15A-D show isometric and schematic illustrations of tubular interdigitated electrode arrangements for use in the oscillation circuit of Figures 2 and 3 configured to dielectrically heat an aerosol-forming substrate 110 positioned in a central cavity formed by the electrode arrangement. The electrode arrangement in Figures 15A-B comprises a series of axially aligned electrode bands positioned adjacent to electrode bands having opposing polarities. In such embodiments, the aerosol-forming substrate 110 is not positioned directly between opposing electrodes, although it is still influenced by the presence of the alternating electric field in its proximity to cause dielectric heating of the aerosol-forming substrate 110. Stronger and more uniform heating of the aerosolforming substrate 110 may be achieved using the electrode arrangement shown in Figures 15C-D, which is configured such that electrical field between opposing polarity electrodes is strongest across the aerosol-forming substrate 110.

Figure 16 is a schematic illustration of an electrode arrangement formed on a low dielectric flexible carrier material, according to embodiments of the disclosure. The arrangement comprises a first and second electrodes Ei, E2 formed on a flexible low dielectric carrier material 1145. Flexible low dielectric carrier material 1145 may comprise a polyimide. In some embodiments, the flexible low dielectric carrier material 1145 comprises a polyimide having a dielectric constant below 3.0, which may be produced by either changing its structure to lower the dielectric constant, or with use of low-dielectric fillers. For example, the intrinsic structure of the polyimide may be modified using one or more of fluorine-containing groups, non-planar large conjugated structures, alicyclic structures, or adding low-dielectric fillers such as fluorinated graphene, mica.

While the embodiment of Figure 16 shows an interdigitated electrode arrangement similar to those described above, other electrode arrangements may also be used. Furthermore, the first and second electrodes E1, E2 do not need to be provided on the flexible low dielectric carrier material 1145 in a specific position, orientation, or with any fixed separation distance from each other. In some embodiments, the first and second electrodes E1 , E2 are provided on the flexible low dielectric carrier material 1145 in a first position in which the first and second electrodes E1, E2 are not in alignment, then the flexible low dielectric carrier material 1145 is bent or rolled to move the first and second electrodes E1, E2 to a second position in which they are aligned. Although not shown in Figure 12, the flexible low dielectric carrier material 1145 may further comprise a first inductor Li and/or a second inductor L2.

The low dielectric flexible carrier material 1145 further comprises a temperature sensor 1950 configured to detect a temperature of an aerosol-forming substrate positioned between the first and second electrodes Ei, E2. A signal indicative of the detected temperature is received by the microcontroller 1880. Based on the detected temperature, the microcontroller 1880 or another microprocessor may control the heating operation of the aerosol-generating device as will become more apparent from Figures 18 and 19 below.

In some embodiments, the low dielectric flexible carrier material 1145 described above may comprise additional components or sections of the oscillation circuits described above, including a switching unit transistor T, and other passive components such as capacitors Ci , C2, the delay line DL, and sensors (optical, magnetic-field, electric-field). In this respect, most or all components of the oscillation circuit could be placed onto the same low dielectric flexible carrier material 1145, including switching transistor, resonant circuit, and capacitive element, for example as surface-mounted elements, for high volume manufacturing and testing.

In some embodiments, the temperature sensor 1950 may comprise a sensor which either penetrates or is physically coupled to the surface of the aerosol-forming substrate, as illustrated in Figure 16.

Another way to capture a value indicative of the temperature of the aerosol-forming substrate 110 is by measuring the temperature of the insulation/substrate material on which the electrode arrangement is placed.

For example, as discussed above, the carrier material for mounting the opposing electrodes E1, E2 can be polyimide or PEEK or another high-temperature plastic material, and the electrodes can be embedded or placed on a surface of such carrier material. While the dielectric constant (or relative permittivity) of such material could be lower than the aerosol-forming substrate 110, it is still dielectric and therefore will heat up, following a heating curve that is substantially proportional to the heating curve of the aerosol-forming substrate. This enables the temperature sensing system to determine a value indicative of the aerosol-forming substrate temperature based on a measured temperature of the carrier material on which the load capacitor CL is placed. This may be measured using a semiconductor temperature sensor directly placed onto the carrier material, and with wiring (or another communicative coupling) that leads to a controller/microprocessor 1880.

Referring now to the embodiment of Figure 16, a temperature of the carrier material can be measured at an area between two electrodes E1 , E2 of opposite polarity, with a temperature sensor 1950 placed on a carrier material that is used to mount both electrodes E1 , E2. In some embodiments, a separate element is provided having a dielectric value that is similar to that of the aerosol-forming substrate 110, with a temperature sensor in measuring contact to measure a value indicative of the aerosol-forming substrate temperature.

Thus, a value indicative of the temperature of the dielectric substrate material is captured by measuring the temperature of the material of the carrier substrate or film where the electrodes are placed on. For example, the insulation and/or carrier material for the opposing electrodes can be polyimide or PEEK or other high-temperature plastic material, and the electrodes can be embedded or placed on a surface of such insulation material. While the dielectric constant or relative permittivity of such material could be lower than the substrate material, it is still dielectric (2.8 to 4.0) and therefore will heat up, for example following a heating curve that is substantially proportional to the heating curve of the substrate. This allows to measure a value indicative of the substrate temperature by measuring a temperature of the insulation/carrier material of the electrodes of the load capacitor CL, for example by a semiconductor temperature sensor directly placed onto the insulator/carrier material, and with wiring that leads to a controller/microprocessor. As a non-limiting example, taking the interdigitated electrodes Ei, E2, a temperature of the insulator/carrier material can be measured at an area between two electrodes of opposite polarity, with a temperature sensor placed on a common insulator/carrier that is used for both electrodes E1, E2. It is also possible that a separate element is provided that has a dielectric value that is similar to the one of the aerosol-forming substrate S, with a temperature sensor in measuring contact therewith, to measure a value indicative of the substrate temperature S.

The temperature sensor is configured to measure temperatures in the region of 100-200°C, and may comprise one or more of thermocouples, thermistors, resistance-based temperature detectors (RTDs, PT100), thermoelements, fiber-optic temperature sensors. In some embodiments, the temperature sensor comprises one or more non-contact sensors such as an NIR sensor.

In some embodiments, the temperature sensing system may be configured to measure a temperature of the electrodes or of the air inside the cavity, however, since these are not dielectric they will heat-up following a different temperature profile based on heat transfer from the aerosolforming substrate. A controller may receive a measured temperature of the electrodes or the air around the aerosol-forming substrate and calculate or deduce a value indicative of the substrate temperature, for example using one or more of a formula, look-up table, and or artificial intelligence network training.

Instead of or in addition to temperature sensors, which output a signal indicative of the temperature over a larger range of temperature, also one or more temperature markers may be employed. A temperature marker signifies herein a sensing element which changes a physical state when transitioning past a defined marker temperature. The change in physical state is then transduced into an electrical output signal.

A first example of a temperature marker comprises a susceptor material with a particular Curie temperature. The Curie temperature may be between about 200°C and about 450°C, preferably between about 240°C and about 400°C, for example about 280°C. As a general rule, whenever a value is mentioned throughout this application, this is to be understood such that the value is explicitly disclosed. However, a value is also to be understood as not having to be exactly the particular value due to technical considerations.

Once the susceptor material has reached its Curie temperature, its magnetic properties change. At the Curie temperature the susceptor material reversibly changes from a ferromagnetic phase to a paramagnetic phase. By inductively energizing the susceptor by means of an inductor coil this phase-change of the susceptor material may be detected. For example a control unit, associated to a power supply of a device, may be capable of detecting when the susceptor material has reached its Curie temperature by monitoring the values of the current absorbed by the inductor.

Also a dielectric temperature marker can be used according to the present disclosure. As is generally known, the dielectric constant of a polar material changes over temperature not continuously, but with stepwise discontinuities. The temperature of the discontinuities is dependent on the polar material and can be used as a marker temperature by detecting the abrupt change of the dielectric constant. There are several discontinuities in the dielectric constant as temperature changes. For instance, the dielectric constant changes abruptly at phase boundaries of the polar material.

As a specific example, water content can be used as a marker to detect an exact moment when a threshold temperature of 100°C is reached.

According to a further example, one type of temperature marker can mark a lower temperature of a desired range, and one other type of temperature marker could mark a higher temperature of the same range. Thus, it is possible to detect when the reference temperature of the marker is exceeded or otherwise breached.

The published International applications WO2015/177294 A1 , WO2018/041924 A1 , W02020/064686 A1 describe the use of magnetic temperature markers having a Curie temperature to change the magnetic characteristics at a given temperature. The contents of the above three applications are all incorporated by reference as if fully set forth herein in their entirety.

Another way of physically implementing the electrode arrangements described above is to use quartz glass (either fused quartz or fused Silica) as a substrate material, and to place electrodes on a surface of a quartz glass using a deposition process. Figure 17 is a schematic illustration of an electrode arrangement and two inductively coupled inductors Li, L2 formed on a quartz glass substrate 1345, according to embodiments of the disclosure.

In the illustrated embodiment, a first and second electrode 1330, 1335 is arranged on an outer surface of a cylindrical quartz glass substrate 1345 with the inner cylindrical volume defining a cavity 1340 for receiving an article 1305 comprising an aerosol-forming substrate 1310. The first and second inductors Li, L2 are positioned on opposite sides of the quartz glass substrate 1345, with a magnetic core Me extending through the center of the first and second inductors Li , L2, strengthening the mutual inductive coupling between them.

In an alternative embodiment, the first and second electrodes 1330, 1335 may be positioned on an inner surface of two opposing quartz glass surfaces, where an aerosol-forming substrate 1310 may be inserted therebetween.

In the embodiment of Figure 17, cavity 1340 is formed with the quartz glass substrate 1345, which serves as a transparent protective layer for an optical measurement device 1350 (for example optocouplers) for measuring aerosol diffusion for puff detection, temperature sensors for measuring thermal radiation, and time-of-f light sensors for measuring stick presence. Optical measurement device 1350 may comprise an optical emitter or light source 1354, an optical receiver or photosensitive device 1353, and the walls of the quartz glass substrate 1345 can include optical channels with a different refractive index than the quartz glass to act as waveguides or lightguides 1351 and 1352. Waveguides 1351 and 1352 may be embedded into the quartz glass substrate 1345, for example as channels, conduits, or holes, and can be filled with a transparent material having a different refractive index to the quartz glass substrate 1345. The light guides 1351 and 1352 can be used to guide light towards and away from cavity 1340 for illumination or measurement purposes.

Quartz glass provides for optical transmission into the ultraviolet and infrared spectrum, and advantageously exhibits low thermal expansion so is able to endure repeated heating cycles without damage or degradation. The smooth surfaces achievable with quartz glass provide a cavity 1340 with cleanable surfaces that can also reduce the accumulation of contaminants. In addition, quartz glass has good thermal insulation properties that allows to provide heat insulation around the cavity 1340, for concentrating the heat within the aerosol-forming substrate 1310.

Advantageously quartz glass has a lower dielectric constant (also referred to the relative permittivity) than other glass materials, reducing the extent of parasitic heating from the dielectric heating circuit and generated electric field.

Quartz glass can also be machined or otherwise processed to form different shapes and arrangements. This allows to integrate other aspects with the electrode arrangement that is formed by the glass structure, including ribs, grooves, and channels for optimizing airflow through the aerosol-generating device. In some embodiments, the upstream air intake comes from ribs and grooves that are arranged to be in parallel with a rotational axis of a heating chamber comprising the electrode arrangement. In such embodiments, it is possible to provide for a heating chamber that is defined by glass walls, allowing for external sensing of parameters (temperature, airflow, puffs, etc.) with optical means for example optical measurement device 1350, permitting easy cleaning and reduced deposition of contaminants to the inner surfaces, and also allows the integration of inductive cores and windings of inductors.

Figure 18 is a schematic illustration of a further temperature sensing system for detecting a temperature of an aerosol-forming substrate 110 situated with the electrode arrangement, according to embodiments of the disclosure. The system comprises a temperature sensor 1850 communicatively coupled to a controller 1880. The temperature sensor 1850 is configured to detect in a non-contact manner a temperature of an aerosol-forming substrate 110 situated between electrodes of an electrode arrangement and subject to dielectric heating as described above.

In an embodiment, the aerosol-forming substrate temperature is measured or approximated by the temperature sensing system. The measured or approximated temperature value may be fed to a temperature control loop unit configured for controlling power supplied to the aerosol-forming substrate.

As illustrated in Figure 18, one way to measure the temperature is by using a non-contact sensor (such as a near infrared sensor (NIR)), to capture heat radiation from the aerosol-forming substrate 110, or from a plate/device 1890 at the aerosol-forming substrate 110 material that increases or homogenizes the heat radiation and has greater thermal conductive properties than the aerosol-forming substrate 110.

Figure 19 is a schematic illustration of a control system utilizing a temperature sensing system for controlling the power delivered to an aerosol-forming substrate 110 based on a detected aerosol-forming substrate temperature. The control system comprises a controller configured to receive aerosol-forming substrate temperature data from a temperature sensing device, as described above. Where the controller determines that the aerosol-forming substrate temperature exceeds a predetermined upper threshold, the controller cuts the power to an oscillation circuit using a DC/DC cut off so that a fixed and variable temperature may be delivered to the aerosol-forming substrate.

In an alternative embodiment, the controller may be configured to use pulse width modulation (PWM) to vary the on and off duty ratio of the oscillation circuit pulses based on a measured or estimated temperature.

As an alternative to cutting the power supply from the oscillation circuit, the biasing voltage of the switching unit can be manipulated to put the transistor outside of a range where oscillation occurs. Either the biasing or DC voltage, or the DC supply voltage could be increased or lowered, to increase or lower the heating power delivered to the load capacitor CL until a measured temperature of the aerosol-forming substrate reaches a target temperature or is within a target temperature range.

In an alternative embodiment, the feedback loop of the oscillation circuit may be disrupted, for example by electrical or mechanical means.

In some embodiments, the control system is configured to control the power delivered to the aerosol-forming substrate in two stages; a first stage where the aerosol-forming substrate temperature is ramped up as fast as possible, and a second stage where the aerosol-forming substrate is maintained at a target aerosolization temperature.

The first stage is performed by maximizing the DC supply voltage to, for example 10V to 12V. Once the target aerosolization temperature is reached, for example in a range between 80°C to 365°C, preferably 180°C to 320°C, more preferably 180°C to 220°C., the heating power is decreased by reducing the supply voltage to a lower value, for example around 6.4V to 7.6V. During the ramp- up time of the first stage of the temperature control, the overall power consumption can be 10W- 15W, preferably with an efficiency of at least 65%, and upon reaching aerosolization temperature of the aerosol former, the temperature can be controlled to 180°-220°, for example to achieve constant aerosol delivery for a given session duration.

Upon aerosolization of the aerosol-forming substrate, there will typically be a change in DC supply current, as the dielectric constant of the aerosol-forming substrate will drop. The dielectric constant can therefore be used as a value that is indicative of the temperature of the aerosol-forming substrate. In some embodiments, an artificial intelligence network is used to determine the temperature of the aerosol-forming substrate based on one or more of the heating cavity temperatures, the DC supply voltage, or the DC supply current.

Figure 20 illustrates a more detailed block diagram of the control system utilizing a temperature sensing system for controlling the power delivered to an aerosol-forming substrate 110 based on a detected aerosol-forming substrate temperature. In particular, this Figure shows the selfoscillating circuit of Figure 3A in an exemplary application environment. A power supply 2020 powers the oscillating circuit and is in particular connected to the switching unit 260 via a DC/DC converter 2010. A microprocessor 2030 receives the temperature signal from the resonant circuit 272. The microprocessor 2030 may further receive a signal indicative of the power, current, and/or voltage provided by the DC/DC converter 2010. The microprocessor 2030 outputs a control signal to the DC/DC converter 2010.

As an alternative to cutting the power supply from the dielectric heater circuit, also the biasing voltage could be moved to put the switching unit 260 outside of a range where oscillation happens with the biasing or DC voltage, or the DC supply voltage could be increased or lowered, to thereby increase or lower the heating power at the load capacitor CL to control the temperature based on a measured value, in comparison to a desired set value.

As another alternative, it is possible to disable the resonant feedback loop FL, for example by electrical or mechanical means. For example, the circuit could be mechanically disrupted, magnetized, etc.

In terms of a temperature profile, one could control the power delivered to the substrate S in two stages. A first stage is a stage where the substrate temperature is ramped up as fast as possible. This stage may also be called a pre-heating phase. Then, a second stage follows at which the delivered power is reduced. This phase may be referred to as a puff heating phase. In some examples, this phase is also called target heating phase or maintenance heating phase.

This can be done by maximizing the DC supply voltage. For instance, for the specific selfresonating circuit shown in Figure 20, the only way to decrease the temperature ramp-up time (by increasing the heating power once the circuit is on and running) is to increase the DC supply voltage to a maximal desired value, e. g. between 10V to 12V, and once the aerosol ization temperature is reached, for example in a range between 80°C to 365°C, preferably 180°C to 320°C, more preferably 180°C to 220°C., the heating power is decreased for reducing the supply voltage to a lower value, for example around 6.4V to 7.6V (e. g. double the nominal cell voltage of each of two lithium-ion battery cells put in series). For an exact timing when to switch from upper DC supply voltage level to the lower level, it is advantageous have accurate feedback on the temperature of the substrate by measurement. In particular, during the first stage (pre-heating phase), the average dielectric heating power density may be controlled or set to be in a range between 7W/cm³ to 25W/cm³, and during the second stage (puff heating phase) during consumption, the average dielectric heating power density is in a range between 1W/cm³ to 7W/cm³. In other words, during the pre-heating phase at least 70% of a maximum supply voltage of the power source, preferably more than 80% of the maximum supply voltage of the power source are supplied to the oscillation circuit. Then, during the puff heating phase, between 40% and 60% of a maximum supply voltage of the power source, preferably around 50% of the maximum supply voltage of the power source is supplied to the oscillation circuit as a reduced power.

However, upon aerosolization of the Glycerol-based aerosol-former, once could expect to see a change in DC supply current, as the dielectric constant will drop. This can also be used as a value that is indicate of the temperature. One could use a trained artificial intelligence network or model to determine the temperature of the substrate itself based on a heating cavity temperature, power DC supply voltage, DC supply current.

During the ramp-up time, the overall power consumption can be 10W-15W, preferably with an efficiency of at least 65%, and upon reaching aerosolization temperature of the aerosol former, the temperature can be controlled to 200°C to 220°C, for example to achieve constant aerosol delivery for a given session duration.

Furthermore, it is common that the substrate includes a certain percentage of water, for example caused from environmental humidity. Water is known to have a high dielectric value (about 80). The water content therefore will most likely increase the overall dielectric constant of the aerosolforming substrate, as the other material will have a lower dielectric constant. When starting a heating session, during the heating ramp-up phase, one can therefore observe a DC feeding current that increases until the vaporization temperature of water has been reached (about 100°C). Thereafter, due to the removal of water, the DC feeding current will drop again until the aerosolization temperature is reached (about 200°C). The presence of water will therefore have an impact on the capacitance value of CL, and will most likely slow down the switching frequency f_s. This leads to a reduction of the possible heating power. To compensate for this effect, one can maximize the DC feed voltage to the start-up phase.

It will be appreciated that many of the embodiments described above do not rely on the use of a self-oscillating oscillation circuit, and can therefore be implemented using a forced oscillation circuit such as that illustrated in Figure 21 , while still providing the described function and advantages. Specifically, an oscillation unit may be coupled to a switching unit or buffer to convert a DC supply voltage to an AC signal fed to a resonant or quasi-resonant load circuit comprising the load capacitor.

In an embodiment, the switching unit comprises one of a single transistor architecture, halfbridge or full-bridge architecture. In such embodiments, zero current switching techniques may be used to reduce or minimize switching losses, using a parallel or series resonant circuit or tank circuit. In an embodiment, the oscillation unit is implemented as a stripline oscillator.

The heating and depletion of the aerosol-forming substrate leads to a change in the resonant frequency due to decrease of the dielectric constant and hence the capacity [Farad] of the capacitor, as the load capacitor CL is part of the resonant circuit 272 that can be self-oscillating at or close to a resonance frequency.

In one embodiment, a frequency sensor is used to correlate different power consumption patterns (e.g. DC current that is fed from the power source by power analysis) with the frequency of oscillation for a particular oscillation circuit and aerosol-forming substrate type. A control system can then use a power consumption value (DC supply current, voltage, both) as a parameter that is indicative of a depletion of a substrate.

Figure 22 is a schematic illustration of a control system utilizing a frequency sensing system for control the power delivered to an aerosol-forming substrate based on a frequency of an alternating electric field detected or estimated across an electrode assembly, according to embodiments of the disclosure. The system comprises a resonant cavity (or resonator, e.g., quarter wavelength resonator) having a peak resonance frequency above the switching frequency of the oscillating feedback loop. The resonant cavity is prepared, for example by the use of impurities or mechanical imperfections, to provide a wide range frequency response showing a variation between the different frequencies, such that the operational range of frequencies is covered by a resonance response. In one embodiment, the resonator comprises a quarter wavelength coaxial cavity resonator with an inner wire. The resonator comprises an impurity-doped insulator. The resonator is situated at a location within the electric field generated by the load capacitor CL, for example at a peripheral area of the load capacitor CL, or an area of the heating cavity that would not obstruct the aerosol-forming substrate.

The resonator is connected via a direct electric coupler to a rectifier for generating a DC signal. The generated DC signal is fed to a resistor/impedance to be measured by a voltage measurement device. The voltage measurements are transmitted to a controller/microprocessor for calibration/further processing.

In alternative embodiment, the system may utilize one or more of resonant antennas, microstrips, waveguides, for high-frequency sensing.

The embodiments described above are exemplary embodiments only, and various other embodiments according with this disclosure are also envisaged.

For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term “about”. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In this context, therefore, a number A is understood as A ± 5% of A.

Claims

CLAIMS:

1. An aerosol-generating device for dielectrically heating an aerosol-forming substrate, the aerosol-generating device comprising: a power source; an oscillation circuit powered by the power source; a dielectric heating element fed by the oscillation circuit, the dielectric heating element being arranged for dielectrically heating the aerosol-forming substrate by dipole rotation when subjected to an electric field caused by the dielectric heating element; and a controller for controlling heating of the aerosol-forming substrate by changing a parameter or configuration of the aerosol-generating device, wherein the dielectric heating element is shaped such that opposing electrodes have a variable, preferably increasing, distance towards each other along a given direction between the two opposing electrodes, wherein the controller is configured to change the parameter to cause a spatially and temporally varying profile of the electric field strength in a space or volume for receiving the aerosol-forming substrate along the given direction, wherein the spatially varying profile changes over time in response to the changing of the parameter or configuration of the aerosol-generating device.

2. The aerosol-generating device according to claim 1 , wherein the dielectric heating element is shaped so that in operation an electric field strength has a varying intensity along at least one defined direction.

3. The aerosol-generating device according to any of claims 1 or 2, wherein the spatially varying profile is such that a predetermined temperature in operation moves along at least one direction.

4. The aerosol-generating device according to any of claims 1 to 3, wherein the controller is configured to set or control a timely displacement rate of the spatially varying profile to a predetermined value or predetermined curve.

5. The aerosol-generating device according to any of the claims 1 to 4, wherein changing of the parameter or configuration of the aerosol-generating device comprises increasing a supply voltage to the oscillation circuit.

6. The aerosol-generating device according to any of the preceding claims, wherein the dielectric heating element comprises at least two electrodes arranged to accommodate the aerosol-forming substrate in a heating cavity, the heating cavity defining a longitudinal axis, wherein the at least two electrodes have a distance from each other which increases along the longitudinal axis, wherein the at least two electrodes are arranged in a tubular arrangement forming a cylindrical heating cavity therein, the at least two electrodes having opposite polarity forming a gap between each other, and wherein the gap has a width which increases along the longitudinal axis of the tubular arrangement.

7. The aerosol-generating device according to any of the preceding claims, wherein the dielectric heating element comprises interdigitated or strip electrodes in a flat configuration and separated by at least one gap, wherein in a given direction the width of the gap increases.

8. The aerosol-generating device according to any of the preceding claims, wherein the oscillation circuit comprises a resonant feedback circuit including the dielectric heating element, so that the oscillation circuit is self-resonating.

9. The aerosol-generating device according to any of the preceding claims, further comprising a temperature determining unit for measuring a value indicative of one or more temperatures of the aerosol-forming substrate; and wherein the controller is operable for controlling the temperature of the aerosol-forming substrate by changing the parameter or configuration of the aerosol-generating device based on a signal from the temperature determining unit.

10. The aerosol-generating device according to claim 9, wherein the change of the parameter or configuration of the aerosol-generating device includes controlling by the controller a DC supply voltage provided by the power source based on a signal from the temperature determining unit, wherein the voltage control unit includes a DC-DC converter, preferably a boost, buck, halfbridge, or full bridge converter, a voltage regulator, a charge pump circuit, or a combination thereof.

11. The aerosol-generating device according to claim 9 or 10, wherein the temperature determining unit includes a temperature sensor that is operable to capture a temperature of an element of the aerosol-generating device that has dielectric properties.

12. The aerosol-generating device according to any of the claims 9 to 11 , wherein the dielectric heating element comprises at least two electrodes that are placed on a dielectric carrier film or material, and wherein the temperature determining unit is operable to capture the temperature of the dielectric carrier film or material.

13. The aerosol-generating device according to any of the claims 9 to 12, wherein the temperature determining unit comprises at least one temperature marker, the temperature marker transitioning from a first physical state into a second physical state when reaching a defined marker temperature.

14. A method of dielectrically heating an aerosol-forming substrate by means of an aerosolgenerating device, the method comprising the following steps: dielectrically heating the aerosol-forming substrate by dipole rotation when subjected to an electric field caused by a dielectric heating element, wherein the dielectric heating element is comprised in an oscillation circuit of the aerosol-generating device, the oscillation circuit being fed by a power source; controlling heating of the aerosol-forming substrate by changing a parameter or configuration of the aerosol-generating device; wherein the dielectric heating element is shaped such that opposing electrodes have a variable, preferably increasing, distance towards each other along a given direction between the two opposing electrodes, wherein the controller is configured to change the parameter to cause a spatially and temporally varying profile of the electric field strength in a space or volume for receiving the aerosol-forming substrate along the given direction, wherein the profile changes over time in response to the changing of the parameter or configuration of the aerosol-generating device.

5. An aerosol-generating system comprising: an aerosol-generating article comprising an aerosol-forming substrate, and an aerosol-generating device for dielectrically heating the aerosol-forming substrate, the aerosol-generating device comprising: a power source; an oscillation circuit powered by the power source; a dielectric heating element fed by the oscillation circuit, the dielectric heating element being arranged for heating the aerosol-forming substrate by dipole rotation when subjected to an electric field caused by the dielectric heating element; a controller for controlling heating of the aerosol-forming substrate by changing a parameter or configuration of the aerosol-generating device; wherein the dielectric heating element is shaped such that opposing electrodes have a variable, preferably increasing, distance towards each other along a given direction between the two opposing electrodes, wherein the controller is configured to change the parameter to cause a spatially and temporally varying profile of the electric field strength in a space or volume for receiving the aerosol-forming substrate along the given direction, wherein the profile changes over time in response to the changing of the parameter or configuration of the aerosol-generating device.