WO2025073961A1

WO2025073961A1 - Oscillator unit for dielectric heating - measure depletion of dielectric material

Info

Publication number: WO2025073961A1
Application number: PCT/EP2024/078049
Authority: WO
Inventors: 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 for dielectrically heating an aerosol-forming substrate of an aerosol-forming article. The aerosol-generating device comprising a power source; and an oscillation circuit, the oscillation circuit including: a switching unit; and a resonant oscillating feedback circuit connected between an input and an output of the switching unit, the resonant oscillating feedback circuit including a dielectric heating element which is arranged for dielectrically heating the substrate. In operation, an electrical parameter associated with a capacitance of the dielectric heating element is measured to determine a property of the substrate.

Description

Oscillator unit for dielectric heating - Measure Depletion of Dielectric Material

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 also relates to a system comprising the aerosol-generating device. The disclosure also relates to a method of dielectrically heating an aerosol-forming substrate of an aerosolforming article by means of an aerosol-generating device and to a method for calibrating same.

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 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.

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, there is provided an aerosol-generating device for dielectrically heating an aerosol-forming substrate of an aerosol-forming article. The aerosol-generating device comprises a power source and an oscillation circuit. The oscillation circuit includes a switching unit, a resonant oscillating feedback circuit connected between an input and an output of the switching unit, the resonant oscillating feedback circuit including a dielectric heating element which is arranged for dielectrically heating the substrate, wherein, in operation, an electrical parameter associated with a capacitance of the dielectric heating element is measured to determine a property of the substrate. The oscillation circuit may allow for more efficient dielectric heating by maximizing losses in the dielectric heating element because the dielectric heating element is an element of a resonating feedback loop of the oscillation circuit so as to enable for relatively higher peak AC voltage across the dielectric heating element as compared to the voltage supplied by the power source. Determining a property of the substrate may enable for more efficient heating as operation can be adapted to present circumstances. The heating of the aerosol-forming substrate may lead to a change in the resonant frequency due to decrease of the relative permittivity of the substrate and hence the capacitance of the dielectric heating element, as the dielectric heating element is part of the oscillating circuit (in particular of its feedback loop) that is self-oscillating at a resonant frequency of the oscillation circuit. Said change in the capacitance and resonant frequency may be indicative of substrate depletion.

The dielectric heating element may be removably received as a part of the aerosol-forming article, one-time insertable, or integrated within the resonant oscillating feedback circuit of the aerosol-generating device.

The electrical parameter may be a value indicative of the relative permittivity of a material that forms the substrate, and wherein the property of the substrate that is determined includes a depletion of the substrate.

The aerosol-generating device may further include a probe or antenna to measure a frequency of oscillation of the oscillation circuit.

The probe or antenna may measure an electric field at the aerosol-forming substrate, and wherein a controller associated with the probe or antenna may be operable to derive a parameter associated with the frequency of oscillation of the oscillation circuit from the detected electric field.

The probe or antenna may include a transverse electromagnetic (TEM) transmission line, a microstrip, an inductor, or an antenna.

The aerosol-generating device may further include a power sensing system to detect a power consumption value drawn from the power source, and wherein the power consumption value may be used as the electrical parameter associated with the capacitance of the dielectric heating element.

The detected power consumption value may be indicative for the resonant frequency of the oscillation circuit, because a change in the resonant frequency may be proportional to the power loss of the dielectric heating element. This relationship may enable to derive the substrate depletion based on the power consumption value drawn from the power source rather than from a frequency measurement device. Using a power sensing system instead of a frequency measurement device, like an antenna or probe, may enable for a compact product.

The power consumption value may be indicative of a supply current, in particular a DC supply current, drawn from the power source. As the DC supply current that is fed to the oscillation circuit may be most likely variable, the value enables to measure or to gain knowledge of the substrate depletion.

The power sensing system may comprise a shunt to derive the supply current.

The shunt may be connected between the switching unit and the power source.

The frequency of oscillation of the oscillation circuit is not obtained from detected current and/or voltage values from an electric circuit forming the oscillation circuit or the resonant oscillating feedback circuit.

Feeding of the dielectric heating element may be done by auto-oscillation at resonance, at very high frequencies, that may not be able to be obtained by time based analysis of the current/voltage.

The probe or antenna may include a resonant cavity.

The resonant cavity may have a resonant frequency that is greater than an operational range of frequencies of oscillation of the oscillation circuit, and may comprise impurities or mechanical imperfections, to have a spread-out frequency response such that an operational range of frequencies of oscillation of the oscillation circuit is covered by said spread-out frequency response.

The resonant cavity may comprise a quarter wavelength coaxial cavity resonator, preferably a quarter wavelength coaxial cavity resonator with an inner wire, wherein the inner wire may have an impurity-doped insulator.

The resonant cavity may have a resonant frequency of in between 8 GHz to 12 GHz, preferably about 10 GHz.

The resonant cavity may have a quarter wavelength of in between 6.3 mm to 9.4 mm, preferably about 7.5 mm.

The switching unit may include a frequency measurement device to measure a switching frequency of a transistor of the switching unit.

The aerosol-generating device may further comprise a signal processing unit to convert an output provided by the resonant cavity to a signal that is receivable by a controller associated with the resonant cavity.

The signal processing unit may comprise a rectifier connected to the resonant cavity to generate a DC signal from the output of the cavity resonator, and an impedance element, preferably a resistor, on which the DC signal is applied, and a voltage sensor to measure a voltage over the impedance element that is fed to the controller.

The resonant cavity may be removably or integratedly placed into an area which is penetrated by an electric field of the dielectric heating element during operation of the dielectric heating element.

The area may be a peripheral area of the dielectric heating element. The area may be a heating cavity for receiving the aerosol-forming substrate, wherein the resonant cavity may be placed therein such as to avoid obstructing the aerosol-forming substrate.

The frequency of oscillation of the oscillation circuit may be in a range between 10 MHz and 100 GHz, preferably between 100 MHz to 1.5 GHz, in particular between 200 MHz to 900 MHz.

These frequency ranges may allow for the use of less expensive components and a straightforward circuit design. Furthermore, in these frequency ranges, the electric field strength may be reduced, thereby reducing the risk of electric breaks so that the substrate remains stable.

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.

The probe or antenna may be formed on or within the flexible low-dielectric carrier film.

The aerosol-generating device may further comprise a data processor, the data processor configured to determine a depletion level as the property of the substrate based on a relationship with the frequency of oscillation of the oscillation circuit.

The use of frequency of oscillation of the oscillation circuit, that is the self-oscillating frequency of the oscillation circuit, in the relationship to obtain the depletion level of the substrate is advantageous as several possible ways of measurements are existing that are indicative of said frequency and thus of substrate depletion. In other words, the relationship may or may not actually take into account the frequency in a direct way. In this regard, substrate depletion may be derived from the self-oscillating frequency of the oscillation circuit that is measured by, for example, an antenna or, in an alternative embodiment, can be determined by having information on the power consumption (voltage/current) of the oscillation circuit, which is indicative and dependent of the self-oscillating frequency of the oscillation circuit.

There are patent applications existing about depletion level measurements for liquid cartridges in the e-vapor space, where two electrode plates are stimulated with a frequency, to determine the capacity and thereafter the liquid level. One of these patents is WO2018114849A1.

In contrast, in the present application, the depletion measurement and dielectric heating principle may be integrated, as the electrodes (in particular electrode plates) are used for heating, and at the same time are a functional part of the resonant circuit impacting the resonant frequency. There may be no separate capacitive liquid level measurement.

In other words, the electrodes may be used for both, the depletion measurement (e.g., via measurement of power consumption value) and the dielectric heating. The depletion measurement may be performed simultaneously or time delayed with the dielectric heating.

Having the relationship pre-stored in the data processor may enable for more efficient operation, because the relationship may be subject to calibration at factory level. The relationship may associate an increase of the frequency with an increase of the depletion level.

An increase of the depletion level or the frequency may be indicative of a decrease in the relative permittivity of the substrate and hence a decrease of the capacity of the dielectric heating element due to a reduction of a share of an aerosol forming material compared to a share of a carrier material, such as tobacco-based or cellulose material, in the aerosol-forming substrate during heating operation.

A variation of the frequency upon consumption from full substrate to a maximum depletion level is in between 3% to 25%, preferably between 5% to 20%, in particular between 7% to 15%.

These frequency ranges allow for an improved determination of depletion, because the variation from full substrate to empty substrate is relatively high and could be further increased by using liquid filler or aerosolization agents or materials (e.g. water, PPG, glycerin) in the substrate that have a substantially higher dielectric constant than the tobacco material.

A minimum depletion level may be indicative for an initial state of the aerosol-forming substrate, and wherein a maximum depletion level may be indicative for a state where at least a portion, preferably between 50% and 100%, in particular between 80 to 95%, of the aerosol forming material that may be present in an initial state may be evaporated or aerosolized.

The relationship may comprise a mapping function MF that maps a parameter associated with the frequency of oscillation of the oscillation circuit to a predefined or predetermined depletion level.

The mapping function MF may comprise a look-up table, correspondence table, algorithm, regression mapping, or trained artificial intelligence network.

The parameter may be indicative of the self-resonant frequency of the oscillation circuit.

The parameter may comprise a power consumption value.

This relationship may enable to derive the substrate depletion based on the power consumption value drawn from the power source rather than from a frequency measurement device. Using a power sensing system instead of a frequency measurement device, like an antenna or probe, may enable for a compact product.

The power consumption value may comprise one or more of a DC supply current and a DC supply voltage.

The DC supply voltage may be controlled to a fixed value and the parameter is indicative of a DC supply current.

In this respect, while the voltage DC level provided by the power source may be fixed, the voltage DC level provided by an output of a DC-DC converter may be variable.

The mapping function may associate an increase of the power consumption value with an increase of the depletion level. The aerosol-generating device may further comprise a memory, wherein the mapping function may be pre-stored at the memory, wherein the mapping function may be indicative of a correlation of different power consumption patterns, such as DC currents and/or DC voltages obtained from a power source of a calibration device or the aerosol-generating device, with measured frequencies of oscillation of the oscillation circuit.

The parameter may further comprise a heating duration of a present heating session.

The heating duration may include one or more of a time from the start of the present heating session or a number of puffs made during the present heating session.

The parameter may further comprise a heating temperature; and/or a humidity level.

The heating temperature may comprise at least one of a temperature of the air in the cavity for receiving the aerosol-forming substrate and a substrate temperature.

The data processor may be configured to output a control signal for enabling heating operation when the depletion level of the aerosol-forming substrate is below a threshold value or to disable heating operation when the depletion level of the aerosol-forming substrate exceeds a threshold value.

A threshold value may be indicative that the substrate is empty, and wherein disabling heating operation may comprise shut-off or ramp-down heating operation when the depletion level of the aerosol-forming substrate exceeds the threshold value.

The control signal may be used for substrate recognition.

The dielectric heating element may be a load capacitor CL.

The load capacitor CL may include electrodes, such as electrode plates Ei, E2, for receiving the substrate therebetween.

The resonant oscillating feedback circuit may be a self-resonant oscillating feedback circuit.

The resonant oscillating feedback circuit may comprise at least a first inductor Li, the first inductor Li being connected in series with a load capacitor CL as the dielectric heating element.

The resonant oscillating feedback circuit may comprise a first inductor Li and a second inductor L2, wherein the inductors Li, L2 may be connected in series with the load capacitor CL that is connected therebetween.

The first inductor Li and the second inductor L2 may be distributed relative to each other so that a mutual inductance 2M may be generated between them.

The mutual inductance 2M may be in a range between 7nH and 30nH, more preferably between 10nH and 20nH.

The at least two inductors each may comprise less than 5 windings, preferably 1 or 2 windings. The aerosol-generating device may further comprise a controller for controlling the oscillation circuit to cause heating of the substrate by changing a parameter or configuration of the aerosol-generating device.

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 not include any control action to change a switching frequency of a transistor of the switching 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 oscillating feedback circuit.

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.

The change of the parameter or configuration of the aerosol-generating device may be based on a signal from the data processor.

The change of the parameter or configuration of the aerosol-generating device may be performed so that the oscillation circuit may be enabled when a depletion level is below a 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 temperature above an aerosolization temperature of an aerosol forming material, and thereafter performing a puff heating phase where the temperature may be maintained constant.

The controller may be operable to control temperature of the heating element during a puff heating phase in a temperature range in between 150° and 400°, preferably in between 180° and 300°, in particular in between 220° and 240°.

The resonant oscillating feedback circuit may comprise at least a first inductor Li connected to a load capacitor CL as the dielectric heating element, wherein the resonant oscillating feedback circuit may be self-resonating at the self-resonant frequency of an LC circuit formed by the at least first inductor Li and the load capacitor CL during heating operation.

The aerosol-generating device may further comprise an indication means to output a status related to the depletion level or a fill level of the substrate to a user.

The indication means may comprise one or more of a display, vibrating feedback means and acoustic signal means.

The status may be indicative that the substrate is deemed empty.

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 DL, or a delay element as its principal timing element. The delay-line oscillator may be set to oscillate by inverting the output of the delay line DL or the delay element and feeding that signal back to the input of the delay line DL or the 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 resonant oscillating feedback circuit may further comprise a second capacitor C2, the second capacitor C2 being connected between the resonant oscillating feedback circuit and ground, such that the second capacitor C2 may provide a phase shift of the feedback voltage of 90°.

According to a second aspect, there is provided a system comprising an aerosol-generating article comprising an aerosol-forming substrate and an aerosol-generating device, preferably the aerosol-generating device according to the first aspect, for dielectrically heating the aerosolforming substrate.

The aerosol-generating article may have the form of a stick or plate.

The aerosol-forming substrate may comprise a solid material.

The aerosol-forming substrate may comprise a carrier material and an aerosol forming material.

The carrier material may have a relative permittivity that is lower than a relative permittivity of the aerosol forming material.

A relative permittivity of the carrier material may be in between 3 to 30 times lower, preferably 5 to15 times lower than a relative permittivity of the aerosol forming material.

The carrier material may comprise tobacco, a tobacco substitute, or a cellulose based material.

The carrier material may comprise a solid material.

The carrier material may comprise a tobacco-based material.

The carrier material may comprise alkaloids, such as nicotine.

The carrier material may comprise a flavoring material.

The tobacco-based material may have a relative permittivity in between 1 to 8, preferably in between 2 to 4, in particular in between 2.3 to 2.7.

The aerosol forming material may comprise a liquid or gel-like aerosol forming material. The aerosol forming material may comprise a mix between polypropylene glycol (PPG) and glycerin.

The aerosol forming substrate may comprise water.

The aerosol forming material may have a relative permittivity in between 10 to 60, preferably 14 to 43, in particular 28 to 32.

An aerosol ization temperature of the aerosol forming material may be below an aerosolization temperature of the carrier material.

According to a third aspect, there is provided a method of dielectrically heating an aerosolforming substrate of an aerosol-forming article by means of an aerosol-generating device. The method comprises the following steps: providing power from a power source to an oscillation circuit of the aerosol-generating device, the oscillation circuit including: a switching unit; a resonant oscillating feedback circuit connected between an input and an output of the switching unit, the resonant oscillating feedback circuit including a dielectric heating element which is arranged for heating the substrate; measuring an electrical parameter associated with a capacitance of the dielectric heating element to determine a property of the substrate.

The method may further comprise determining the property of the substrate, wherein the determination may include mapping the measured electrical parameter to the property of the substrate by means of a mapping function that is preferably pre-stored on the aerosol-generating device.

The method may further comprise performing an action with the aerosol-generating device based on the determined property of the substrate.

The electrical parameter may include a power consumption value, preferably a DC supply current, drawn from the power source, and wherein the determined property of the substrate may include a depletion level of the substrate.

The action may comprise at least one of shutting-off heating operation, ramping-down heating operation, and indicating to a user that the substrate is deemed empty, when the depletion level exceeds a threshold value.

The method steps may be performed by an aerosol-generating device according to the first aspect.

According to a fourth aspect, there is provided a method of calibrating an aerosol-generating device. The method comprises the following steps: providing power from a power source to an oscillation circuit of the aerosol-generating device, the oscillation circuit including: a switching unit; and a resonant oscillating feedback circuit including two opposed electrodes Ei, E2 with an aerosol-forming substrate therebetween for heating the substrate; measuring a frequency of the electric field between the electrodes, correlating the measured frequency to the provided power, and storing the obtained relationship in a mapping function of the aerosol-generating device.

The resonant oscillating feedback circuit may be connected between an input and an output of the switching unit.

The method steps may be performed by an aerosol-generating device or by a separate calibration device.

The aerosol-generating device may be an aerosol-generating device according to the first aspect.

According to a fifth aspect, there is provided a resonant cavity to measure a frequency of oscillation of an oscillation circuit of an aerosol-generating device.

The aerosol-generating device with respect to the fifth aspect may be the aerosolgenerating device according to the first aspect.

The resonant cavity may be used in the calibration method according to the fourth aspect to measure frequency of the electric field between the electrodes.

The aerosol-generating device may further comprise a signal processing unit to convert an output provided by the resonant cavity to a signal that is receivable by a controller associated with the resonant cavity. The signal processing unit may comprise a rectifier connected to the resonant cavity to generate a DC signal from the output of the cavity resonator, and an impedance element, preferably a resistor, on which the DC signal is applied, and a voltage sensor to measure a voltage over the impedance element that is fed to the controller.

The area may be a peripheral area of the dielectric heating element.

The area may be a heating cavity for receiving the aerosol-forming substrate, wherein the resonant cavity may be placed therein such as to avoid obstructing the aerosol-forming substrate.

In an example, the feedback loop may be 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 examples, 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 “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.

As used herein, the term "data processor" refers to a component of a controller of the aerosol-generating device or, in some embodiments, may refer to a separate entity.

As used herein, the term “power sensing system” relates to a measurement device or circuit that enables for detection of one or more of current, voltage and power values. As used herein, the term “electric field strength” refers to the electric field strength across electrodes, preferably electrode plates, of a capacitor for dielectric heating. The electric field strength increases proportionally with voltage, in particular the effective voltage, also called the voltage strength, of the alternating voltage applied to the capacitor, and inversely proportional with a distance between its electrodes.

As used herein, the term “resonant oscillating feedback (loop) circuit” refers to a resonant circuit of a feedback loop of the oscillation circuit.

As used herein, the term “power source” refers to a power supply.

As used herein, the term “target heating phase” (also called “maintenance heating phase) refers to a “nominal heating operation” where the consumer is using the device for inhalation. During the target heating phase an aerosol-forming substrate may be heated, preferably according to a heating profile, to reach or maintain a target aerosolization temperature for inhalation.

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 of an aerosol-forming article, the aerosol-generating device comprising a power source; and an oscillation circuit, the oscillation circuit including: a switching unit; a resonant oscillating feedback circuit including a dielectric heating element which is arranged for dielectrically heating the substrate; wherein, in operation, an electrical parameter associated with a capacitance of the dielectric heating element is measured to determine a property of the substrate.

Example Ex2: The aerosol-generating device according to Example Ex1 , wherein the dielectric heating element is removably received as a part of the aerosol-forming article, one-time insertable, or integrated within the resonant oscillating feedback circuit of the aerosol-generating device.

Example Ex3: The aerosol-generating device according to Example Ex1 or Ex2, wherein the electrical parameter is a value indicative of the relative permittivity of a material that forms the substrate, and wherein the property of the substrate that is determined includes a depletion of the substrate.

Example Ex4: The aerosol-generating device according to any of the preceding examples, wherein the aerosol-generating device further includes a probe or antenna to measure a frequency of oscillation of the oscillation circuit. Example Ex5: The aerosol-generating device according to Example Ex4, wherein the probe or antenna measures an electric field at the aerosol-forming substrate, and wherein a controller associated with the probe or antenna is operable to derive a parameter associated with the frequency of oscillation of the oscillation circuit from the detected electric field.

Example Ex6: The aerosol-generating device according to Example Ex4 or Ex5, wherein the probe or antenna includes a transverse electromagnetic (TEM) transmission line, a microstrip, an inductor, or an antenna.

Example Ex7: The aerosol-generating device according to any of the preceding examples, wherein the aerosol-generating device further includes a power sensing system to detect a power consumption value drawn from the power source, and wherein the power consumption value is used as the electrical parameter associated with the capacitance of the dielectric heating element.

Example Ex8: The aerosol-generating device according to Example Ex7, wherein the power consumption value is indicative of a supply current, in particular a DC supply current, drawn from the power source. As the DC supply current that is fed to the oscillation circuit may be most likely variable, the value enables to measure or to gain knowledge of the substrate depletion.

Example Ex9: The aerosol-generating device according to Example Ex7 or Ex8, wherein the power sensing system comprises a shunt to derive the supply current.

Example Ex10: The aerosol-generating device according to Example Ex9, wherein the shunt is connected between the switching unit and the power source..

Example Ex11 : The aerosol-generating device according to Example Ex4, wherein the probe or antenna includes a resonant cavity.

Example Ex12: The aerosol-generating device according to Example Ex11 , wherein the resonant cavity has a resonant frequency that is greater than an operational range of frequencies of oscillation of the oscillation circuit, and comprises impurities or mechanical imperfections, to have a spread-out frequency response such that an operational range of frequencies of oscillation of the oscillation circuit is covered by said spread-out frequency response.

Example Ex13: The aerosol-generating device according to Example Ex11 or Ex12, wherein the resonant cavity comprises a quarter wavelength coaxial cavity resonator, preferably a quarter wavelength coaxial cavity resonator with an inner wire, wherein the inner wire has an impurity-doped insulator.

Example Ex14: The aerosol-generating device according to any of Examples Ex11 to Ex13, wherein the resonant cavity has a resonant frequency of in between 8 GHz to 12 GHz, preferably about 10 GHz.

Example Ex15: The aerosol-generating device according to any of Examples Ex11 to Ex14, wherein the resonant cavity has a quarter wavelength of in between 6.3 mm to 9.4 mm, preferably about 7.5 mm. Example Ex16: The aerosol-generating device according to any of the preceding examples, wherein the switching unit includes a frequency measurement device to measure a switching frequency of a transistor of the switching unit.

Example Ex17: The aerosol-generating device according to any of the preceding examples, further comprising a signal processing unit to convert an output provided by the resonant cavity to a signal that is receivable by a controller associated with the resonant cavity.

Example Ex18: The aerosol-generating device according to Example Ex17, wherein the signal processing unit comprises: a rectifier connected to the resonant cavity to generate a DC signal from the output of the cavity resonator, and an impedance element, preferably a resistor, on which the DC signal is applied, and a voltage sensor to measure a voltage over the impedance element that is fed to the controller.

Example Ex19: The aerosol-generating device according to any of Examples Ex11 to Ex15, wherein the resonant cavity is removably or integratedly placed into an area which is penetrated by an electric field of the dielectric heating element during operation of the dielectric heating element.

Example Ex20: The aerosol-generating device according to Example Ex19, wherein the area is a peripheral area of the dielectric heating element.

Example Ex21 : The aerosol-generating device according to Example Ex19, wherein the area is a heating cavity for receiving the aerosol-forming substrate, wherein the resonant cavity is placed therein such to avoid obstructing the aerosol-forming substrate.

Example Ex22: The aerosol-generating device according to any of the preceding examples, wherein the frequency of oscillation of the oscillation circuit is in a range between 10 MHz and 100 GHz, preferably between 100 MHz to 1.5 GHz, in particular between 200 MHz to 900 MHz.

Example Ex23: 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 Ex24: The aerosol-generating device according to Example Ex23, wherein the probe or antenna is formed on or within the flexible low-dielectric carrier film, or antenna is formed on or within the flexible low-dielectric carrier film.

Example Ex25: The aerosol-generating device according to any of Examples Ex3 to Ex24, further comprising a data processor, the data processor configured to determine a depletion level as the property of the substrate based on a relationship with the frequency of oscillation of the oscillation circuit.

Example Ex26: The aerosol-generating device according to Example Ex25, wherein the relationship associates an increase of the frequency with an increase of the depletion level. Example Ex27: The aerosol-generating device according to Example Ex25 or Ex26, wherein an increase of the depletion level or the frequency is indicative of a decrease in the relative permittivity of the substrate and hence a decrease of the capacity of the dielectric heating element due to a reduction of a share of an aerosol forming material compared to a share of a carrier material, such as tobacco-based or cellulose material, in the aerosol-forming substrate during heating operation.

Example Ex28: The aerosol-generating device according to any of Examples Ex25 to Ex27, wherein a variation of the frequency upon consumption from full substrate to a maximum depletion level is in between 3% to 25%, preferably between 5% to 20%, in particular between 7% to 15%.

Example Ex29: The aerosol-generating device according to any of Examples Ex25 to Ex28, wherein a minimum depletion level is indicative for an initial state of the aerosol-forming substrate, and wherein a maximum depletion level is indicative for a state where at least a portion, preferably between 50% and 100%, in particular between 80 to 95%, of the aerosol forming material that is present in an initial state is evaporated or aerosolized.

Example Ex30: The aerosol-generating device according to any of Examples Ex25 to Ex29, wherein the relationship comprises a mapping function MF that maps a parameter associated with the frequency of oscillation of the oscillation circuit to a predefined or predetermined depletion level.

Example Ex31 : The aerosol-generating device according to Example Ex30, wherein the mapping function MF comprises a look-up table, correspondence table, algorithm, regression mapping, trained artificial intelligence network.

Example Ex32: The aerosol-generating device according to Example Ex30 or Ex31 , wherein the parameter is indicative of the self-resonant frequency of the oscillation circuit.

Example Ex33: The aerosol-generating device according to any of Examples Ex30 to Ex32, wherein the parameter comprises a power consumption value.

Example Ex34: The aerosol-generating device according to Example Ex33, wherein the power consumption value comprises one or more of a DC supply current and a DC supply voltage.

Example Ex35: The aerosol-generating device according to Example Ex33 or Ex34, wherein the DC supply voltage is controlled to a fixed value and the parameter is indicative of a DC supply current. In this respect, while the voltage DC level provided by the power source may be fixed, the voltage DC level provided by an output of a DC-DC converter may be variable.

Example Ex36: The aerosol-generating device according to any of Examples Ex33 to Ex35, wherein the mapping function associates an increase of the power consumption value with an increase of the depletion level.

Example Ex37: The aerosol-generating device according to any of Examples Ex33 to Ex36, further comprising a memory, wherein the mapping function is pre-stored at the memory, wherein the mapping function is indicative of a correlation of different power consumption patterns, such as DC currents and/or DC voltages obtained from a power source of a calibration device or the aerosol-generating device, with measured frequencies of oscillation of the oscillation circuit.

Example Ex38: The aerosol-generating device according to any of Examples Ex33 to Ex37, wherein the parameter further comprises a heating duration of a present heating session.

Example Ex39: The aerosol-generating device according to Example Ex38, wherein the heating duration includes one or more of a time from the start of the present heating session or a number of puffs made during the present heating session.

Example Ex40: The aerosol-generating device according to any of Examples Ex33 to Ex39, wherein the parameter further comprises a heating temperature; and/or a humidity level.

Example Ex41 : The aerosol-generating device according to Example Ex40, wherein the heating temperature comprises at least one of a temperature of the air in the cavity for receiving the aerosol-forming substrate and a substrate temperature.

Example Ex42: The aerosol-generating device according to any of Examples Ex25 to Ex41 , wherein the data processor is configured to output a control signal for enabling heating operation when the depletion level of the aerosol-forming substrate is below a threshold value or to disable heating operation when the depletion level of the aerosol-forming substrate exceeds a threshold value.

Example Ex43: The aerosol-generating device according to Example Ex42, wherein a threshold value is indicative that the substrate is empty, and wherein disabling heating operation comprises shut-off or ramp-down heating operation when the depletion level of the aerosolforming substrate exceeds the threshold value.

Example Ex44: The aerosol-generating device according to Example Ex42 or Ex43, wherein the control signal is used for substrate recognition.

Example Ex45: The aerosol-generating device according to any of the preceding examples, wherein the dielectric heating element is a load capacitor CL.

Example Ex46: The aerosol-generating device according to Example Ex45, wherein the load capacitor CL includes electrodes, such as electrode plates Ei , E2, for receiving the substrate there between.

Example Ex47: The aerosol-generating device according to any of the preceding examples, wherein the resonant oscillating feedback circuit is a self-resonant oscillating feedback circuit.

Example Ex48: The aerosol-generating device according to any of the preceding examples, wherein the resonant oscillating feedback circuit comprises at least a first inductor Li, the first inductor Li being connected in series with a load capacitor CL as the dielectric heating element.

Example Ex49: The aerosol-generating device according to any of the preceding examples, wherein the resonant oscillating feedback circuit comprises the first inductor Li and a second inductor L2, wherein the inductors Li , L2 are connected in series with the load capacitor CL that is connected therebetween.

Example Ex50: The aerosol-generating device according to Example Ex49, wherein the first inductor Li and the second inductor L2 are distributed relative to each other so that a mutual inductance 2M is generated between them.

Example Ex51 : The aerosol-generating device according to Example Ex50, wherein the mutual inductance 2M is in a range between 7nH and 30nH, more preferably between 10nH and 20nH.

Example Ex52: The aerosol-generating device according to any of Examples Ex49 to Ex51 , wherein the at least two inductors each comprise less than 5 windings, preferably 1 or 2 windings.

Example Ex53: The aerosol-generating device according to any of the preceding examples, further comprising a controller for controlling the oscillation circuit to cause heating of the substrate by changing a parameter or configuration of the aerosol-generating device.

Example Ex54: The aerosol-generating device according to Example Ex53, 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 Ex55: The aerosol-generating device according to Example Ex53 or Ex54, wherein the change of the parameter or configuration of the aerosol-generating device does not include any control action to change a switching frequency of a transistor of the switching unit.

Example Ex56: The aerosol-generating device according to any of Examples Ex53 to Ex55, 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 oscillating feedback circuit.

Example Ex57: The aerosol-generating device according to any of Examples Ex53 to Ex56, 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.

Example Ex58: The aerosol-generating device according to any of Examples Ex53 to Ex57, wherein the change of the parameter or configuration of the aerosol-generating device is based on a signal from the data processor.

Example Ex59: The aerosol-generating device according to any of Examples Ex53 to Ex57, wherein the change of the parameter or configuration of the aerosol-generating device is performed so that the oscillation circuit is enabled when a depletion level is below a threshold value.56Examples

Ex60: The aerosol-generating device according to any of Examples Ex53 to Ex59, wherein the controller is operable to control the temperature of the aerosol-forming substrate by first applying a preheating phase to reach a temperature above an aerosol ization temperature of an aerosol forming material, and thereafter performing a puff heating phase where the temperature is maintained constant.

Example Ex61 : The aerosol-generating device according to any of Examples Ex43 to Ex60, wherein the controller is operable to control temperature of the heating element during a puff heating phase in a temperature range in between 150° and 400°, preferably in between 180° and 300°, in particular in between 220° and 240°.

Example Ex62: The aerosol-generating device according to any of the preceding examples, wherein the resonant oscillating feedback circuit comprises at least the first inductor Li connected to the load capacitor CL as the dielectric heating element, wherein the resonant oscillating feedback circuit is self-resonating at the self-resonant frequency of the LC circuit formed by the at least first inductor Li and the load capacitor CL during heating operation.

Example Ex63: The aerosol-generating device according to any of Examples Ex25 to Ex62, further comprising an indication means to output a status related to the depletion level or a fill level of the substrate to a user.

Example Ex64: The aerosol-generating device according to Example Ex63, wherein the indications means comprises one or more of a display, vibrating feedback means and acoustic signal means.

Example Ex65: The aerosol-generating device according to Example Ex63 or Ex64, wherein the status is indicative that the substrate is deemed empty.

Example Ex66: The aerosol-generating device according to any of the preceding examples, wherein the oscillation circuit further comprises a delay line DL, the delay line DL branching out from a path of the resonant oscillating feedback circuit.

Example Ex67: The aerosol-generating device according to any of the preceding examples, wherein the resonant oscillating feedback circuit further comprises a second capacitor C2, the second capacitor C2 being connected between the resonant oscillating feedback circuit and ground, such that the second capacitor C2 provides a phase shift of the feedback voltage of 90°.

Example Ex68: A system comprising an aerosol-generating article comprising an aerosol-forming substrate; and an aerosol-generating device according to any one of the preceding examples for dielectrically heating the aerosol-forming substrate.

Example Ex69: The system according to Example Ex68, wherein the aerosol-generating article has the form of a stick or plate.

Example Ex70: The system according to Example Ex68 or Ex69, wherein the aerosolforming substrate comprises solid material. Example Ex71 : The system according to any of Examples Ex68 to Ex70, wherein the aerosol-forming substrate comprises a carrier material and an aerosol forming material.

Example Ex72: The system according to Example Ex71 , wherein the carrier material has a relative permittivity that is lower than a relative permittivity of the aerosol forming material.

Example Ex73: The system according to Example Ex71 or Ex72, wherein a relative permittivity of the carrier material is in between 3 to 30 times lower, preferably 5 to15 times lower than a relative permittivity of the aerosol forming material.

Example Ex74: The system according to any of Examples Ex71 to Ex73, wherein the carrier material comprises tobacco, a tobacco substitute, or a cellulose based material.

Example Ex75: The system according to any of Examples Ex71 to Ex74, wherein the carrier material comprises solid material.

Example Ex76: The system according to any of Examples Ex71 to Ex75, wherein the carrier material comprises at least one of tobacco-based material, alkaloids, such as nicotine, and flavoring material.

Example Ex77: The system according to Example Ex74, wherein the tobacco-based material has a relative permittivity in between 1 to 8, preferably in between 2 to 4, in particular in between 2.3 to 2.7.

Example Ex78: The system according to any of Examples Ex68 to Ex77, wherein the aerosol forming material comprises a liquid or gel-like aerosol forming material.

Example Ex79: The system according to any of Examples Ex68 to Ex78, wherein the aerosol forming material comprises a mix between polypropylene glycol (PPG) and glycerin.

Example Ex80: The system according to any of Examples Ex68 to Ex79, wherein the aerosol forming substrate comprises water.

Example Ex81 : The system according to any of Examples Ex68 to Ex80, wherein the aerosol forming material has a relative permittivity in between 10 to 60, preferably 14 to 43, in particular 28 to 32.

Example Ex 82: The system according to any of Examples Ex68 to Ex81 , wherein an aerosolization temperature of the aerosol forming material is below an aerosolization temperature of the carrier material.

Example Ex83: A method of dielectrically heating an aerosol-forming substrate of an aerosol-forming article by means of an aerosol-generating device, the method comprising the following steps: providing power from a power source to an oscillation circuit of the aerosol-generating device, the oscillation circuit including: a switching unit; a resonant oscillating feedback circuit including a dielectric heating element which is arranged for heating the substrate; measuring an electrical parameter associated with a capacitance of the dielectric heating element to determine a property of the substrate.

Example Ex84: The method according to Example Ex83, further comprising determining the property of the substrate, wherein the determination includes mapping the measured electrical parameter to the property of the substrate by means of a mapping function that is preferably prestored on the aerosol-generating device.

Example Ex85: The method according to Example Ex83 or Ex84, further comprising performing an action with the aerosol-generating device based on the determined property of the substrate.

Example Ex86: The method according to any of Examples Ex83 to Ex85, wherein the electrical parameter includes a power consumption value, preferably a DC supply current, drawn from the power source, and wherein the determined property of the substrate includes a depletion level of the substrate.

Example Ex87: The method according to Example Ex85 or Ex86, wherein the action comprises at least one of shutting-off heating operation, ramping-down heating operation, and indicating to a user that the substrate is deemed empty, when the depletion level exceeds a threshold value.

Example Ex88: The method according to any of Examples Ex83 to Ex87, wherein the method steps are performed by an aerosol-generating device according to any of Examples Ex1 to Ex65.

Example Ex89: A method of calibrating an aerosol-generating device, the method comprising the following steps: providing power from a power source to an oscillation circuit of the aerosol-generating device, the oscillation circuit including: a switching unit; and a resonant oscillating feedback circuit including two opposed electrodes Ei, E2 with an aerosol-forming substrate there between for heating the substrate; measuring a frequency of the electric field between the electrodes, correlating the measured frequency to the provided power, and storing the obtained relationship in a mapping function of the aerosol-generating device.

Example Ex90: The method according to Example Ex89, wherein the method steps are performed by an aerosol-generating device according to any of Examples Ex1 to Ex60 or by a separate calibration device. Example Ex91 : The method according to Example Ex89 or Ex90, wherein aerosolgenerating device is an aerosol-generating device according to any of Examples Ex1 to Ex60.

Example Ex92: The aerosol-generating device according to any one of Examples Ex1 to Ex67, wherein the resonant oscillating feedback circuit is connected between an input and an output of the switching unit.

Example Ex93: The method according to any one of Examples Ex83 to Ex88, wherein the resonant oscillating feedback circuit is connected between an input and an output of the switching unit.

Example Ex94: The method according to any one of Examples Ex89 to Ex91 , wherein the resonant oscillating feedback circuit is connected between an input and an output of the switching unit.

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 cavity having parallel resonance properties, one exemplarily implemented as a capacitive element, to achieve a 180° phase shift;

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 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, according to embodiments of the disclosure;

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

Figures 11A-D show isometric and 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;

Figures 12a-c are schematic illustrations of electrode arrangements for dielectrically heating liquid aerosol-forming substrates configured to function as both a heater and wicking element, according to embodiments of the disclosure;

Figure 13 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 14 is a schematic illustration of a control system utilizing a power sensing system for controlling the power delivered to an aerosol-forming substrate based on a detected power consumption value drawn from the power source, according to an embodiment of the disclosure;

Figure 15 is a schematic illustration of a control system utilizing a power sensing system to determine a depletion level, according to an embodiment of the disclosure;

Figure 16 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 across an electrode assembly, according to an embodiment of the disclosure;

Figure 17 is a schematic illustration of a spread-out frequency response provided by a frequency sensing system, in particular a resonant cavity that is prepared, for example by the use of impurities or mechanical imperfections, such that the operational range of frequencies is covered by a resonant response;

Figure 18 is a schematic illustration of a control system utilizing a frequency sensing system to determine a depletion level, according to an embodiment of the disclosure;

Figure 19 is a schematic illustration of a method of dielectrically heating an aerosol-forming substrate, according to an embodiment of the disclosure;

Figure 20 is a schematic diagram that shows the different progression of the switching losses against electric field strength and cost of transistor.

Specific 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 aerosol-forming 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 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 aerosolforming 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% to 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 aerosolforming 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 aerosol-forming 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 130, 135 can be arranged as two matrices or arrays of pin-like, 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 aerosolgenerating 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 aerosol-generating 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 aerosol-generating 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 aerosolforming 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 1 W/cm³ to 25 W/cm³, preferably between 1 .5 W/cm³ and 15 W/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 8 W/cm³ to 20 W/cm³. 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 7 W/cm³, preferably between 1 W/cm³ to 5 W/cm³. In a non-limiting 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 35 W/cm³ and 35 kW/cm³. The aerosol-generating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 50 W/cm³ and 10 kW/cm³, between 50 W/cm³ and 2.5 kW/cm³ or between 50 W/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 170 W/cm³ and 2.5kW/cm³, between 250 W/cm³ and 2.5 kW/cm³ or between 500 W/cm³ and 2.5 kW/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 2 kW/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 aerosolforming article 105 between the first electrode 130 and the second electrode 135. The aerosolgenerating 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 aerosolgenerating system 100 in this example is also configured to control the heating of the aerosolforming substrate 110 based on the measured dielectric property of the aerosol-forming article 105.

In one exemplary embodiment, the material composition of the substrate 110 of the aerosolforming article 105 that can be dielectrically heated by the aerosol forming device 120 can include tobacco powder or tobacco cut filler.

As used herein, the term “cut filler” is used to describe to a blend of shredded plant material, such as tobacco plant material, including, in particular, one or more of leaf lamina, processed stems and ribs, homogenised plant material. Preferably, the cut filler comprises at least 25 percent of plant leaf lamina, more preferably, at least 50 percent of plant leaf lamina, still more preferably at least 75 percent of plant leaf lamina and most preferably at least 90 percent of plant leaf lamina.

The cut filler suitable to be used with the present invention generally may resemble cut filler used for conventional smoking articles. The cut width of the cut filler preferably is between 0.3 millimeters and 2.0 millimeters, more preferably, the cut width of the cut filler is between 0.5 millimeters and 1 .2 millimeters and most preferably, the cut width of the cut filler is between 0.6 millimeters and 0.9 millimeters.

The aerosol-generating substrate 110 may comprise between 80 milligrams and 400 milligrams of cut filler. For example, the aerosol-generating substrate 110 may comprise between 100 milligrams and 300 milligrams of cut filler, between 100 milligrams and 250 milligrams of cut filler, between 125 milligrams and 200 milligrams of cut filler, or between 140 milligrams and 180 milligrams of cut filler, such as about 150 milligrams of cut filler.

The aerosol-forming substrate 110 of the aerosol-forming article 105 may comprise an aerosol former. Where the aerosol-forming substrate 110 comprises cut filler, the cut filler may be soaked with aerosol former. Soaking the cut filler can be done by spraying or by other suitable application methods.

Preferably, the aerosol former comprises one or more of glycerine and propylene glycol (PPG). The aerosol former may consist of glycerine or propylene glycol or of a combination of glycerine and propylene glycol. The aerosol-forming substrate 110 may comprise any amount of aerosol former. For example, the aerosol-forming substrate 110 may comprise between 5 weight percent aerosol former and 25 weight percent aerosol former. For example, the aerosol-forming substrate 110 may comprise between 10 weight percent aerosol former and 20 weight percent aerosol former, or between 15 weight percent aerosol former and 20 weight percent aerosol former. Preferably, the aerosol-generating substrate 110 comprises about 18 weight percent aerosol former. The weight percentages of aerosol former are given as a dry weight basis of the cut filler, with the balance being tobacco.

The aerosol-forming substrate 110 may have a density of no more than 0.45 grams per cubic centimetre, no more than 0.4 grams per cubic centimetre, no more than 0.36 grams per cubic centimetre, no more than 0.3 grams per cubic centimetre, or no more than 0.25 grams per cubic centimetre. The aerosol-forming substrate 110 may have a density of at least 0.1 grams per cubic centimetre. For example, the aerosol-forming substrate 110 may have a density of at least 0.15 grams per cubic centimetre, at least 0.2 grams per cubic centimetre, or at least 0.28 grams per cubic centimetre.

The aerosol-forming substrate 110 can have different shapes, for example a cuboid shape, rectangular parallelepiped shape, pouch-shaped, or may be cylindrically shaped, and is preferably substantially cylindrically shaped, having a length of between 10 mm and 15 mm, such as between 11 mm and 14 mm, preferably about 12 mm, and having a diameter of between 4.5 mm and 8 mm, such as between 6.5 mm and 7.5 mm, preferably about 7 mm.

Suitable aerosol-forming substrates and articles comprising cut filler include those described in W02022/074240 and/or W02022/074158, these references herewith incorporated by reference in their entirety.

In another exemplary embodiment, the material composition of the aerosol-forming substrate 110 of the aerosol-forming article 105 that can be dielectrically heated by the aerosol forming device 120 can include reconstituted tobacco, such as one or more sheets of homogenized tobacco material made by a cast leaf process.

Where the aerosol-forming substrate 110 comprises homogenised tobacco material, the tobacco material preferably comprises particulate tobacco obtained by grinding or otherwise comminuting tobacco leaf lamina. Such homogenised tobacco material may have a tobacco content of at least about 40% by weight on a dry weight basis or of at least about 50% by weight on a dry weight basis. In other embodiments, the homogenised tobacco material may have a tobacco content of about 70% or more by weight on a dry weight basis, such as between 70% and 80% by weight on a dry weight basis.

In yet another exemplary embodiment, the aerosol-forming substrate 110 can include a plurality of tobacco beads or granules. For example, the mean diameter of the plurality of beads or granules may be between 0.5 millimetres and 10 millimetres. The substrate 110 may comprise between 2 beads and 200 beads or granules, or between 5 beads and 200 beads or granules, or between 10 beads and 100 beads or granules, or between 20 beads and 75 beads or granules, or between 30 beads and 50 beads or granules, or between 40 beads and 50 beads or granules. The total weight of the plurality of beads or granules in the aerosol-generating article 105 may be between 50 mg and 350 mg, or between 100 mg and 300 mg, or between 125 mg and 250 mg, or between 150 mg and 200 mg. The beads or granules may comprise tobacco, an aerosol former and a hydrocolloid binder.

The aerosol-forming substrate 110 may comprise one or more intrinsic binders that is tobacco endogenous binders, one or more extrinsic binders that is tobacco exogenous binders, or a combination thereof to help agglomerate the particulate tobacco. Alternatively, or in addition, the aerosol-forming substrate 110 may comprise other additives including, but not limited to, tobacco and non-tobacco fibres, aerosol- formers, humectants, plasticisers, flavorants, fillers, aqueous and non-aqueous solvents and combinations thereof.

Suitable extrinsic binders for inclusion in the aerosol-forming substrate 110 are known in the art and include, but are not limited to: gums such as, for example, guar gum, xanthan gum, arabic gum and locust bean gum; cellulosic binders such as, for example, hydroxypropyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose and ethyl cellulose; polysaccharides such as, for example, starches, organic acids, such as alginic acid, conjugate base salts of organic acids, such as sodium-alginate, agar and pectins; and combinations thereof. For example, the aerosol-forming substrate 110 may comprise between 1% and 5% extrinsic binder by weight on a dry weight basis, such as between 1.5% and 3.5% extrinsic binder by weight on a dry weight basis, preferably about 2% extrinsic binder by weight on a dry weight basis. Preferably, the extrinsic binder is guar gum.

Suitable non-tobacco fibres for inclusion in the aerosol-forming substrate 110, to strengthen the material, are known in the art and include, but are not limited to: cellulose fibers; soft-wood fibres; hard-wood fibres; jute fibres and combinations thereof. For example, the aerosol-forming substrate 110 may comprise between 2% and 6% non-tobacco fibres by weight on a dry weight basis, such as between 3% and 5% non-tobacco fibres by weight on a dry weight basis, preferably about 4% non-tobacco fibres by weight on a dry weight basis. Preferably, the non-tobacco fibres are cellulose fibres.

The aerosol-forming substrate 110 may comprise an aerosol former. Preferably, the aerosol former comprises one or more of glycerine and propylene glycol. The aerosol former may consist of glycerine or propylene glycol or of a combination of glycerine and propylene glycol. The aerosol-forming substrate 110 may comprise any amount of aerosol former. For example, the aerosol-forming substrate 110 may comprise between 5 weight percent aerosol former and 25 percent aerosol former. For example, the aerosol-forming substrate 110 may comprise between 10 weight percent aerosol former and 20 weight percent aerosol former, or between 15 weight percent aerosol former and 20 weight percent aerosol former. Preferably, the aerosol-forming substrate 110 comprises about 18 weight percent aerosol former. The weight percentages of aerosol former are given as a dry weight basis of the aerosol-forming substrate 110. Preferably, the aerosol-forming substrate 110 has a weight of between 220 milligrams and 350 milligrams. For example, the aerosol-forming substrate 110 may have a weight between 240 milligrams and 320 milligrams, between 250 milligrams and 310 milligrams, between 240 milligrams and 280 milligrams, or between 290 milligrams and 330 milligrams.

The aerosol-forming substrate 110 may have a density of no more than 0.75 grams per cubic centimetre, no more than 0.68 grams per cubic centimetre, no more than 0.67 grams per cubic centimetre, no more than 0.59 grams per cubic centimetre, or no more than 0.56 grams per cubic centimetre. The aerosol-forming substrate 110 may have a density of at least 0.5 grams per cubic centimetre. For example, the aerosol-forming substrate 110 may have a density of at least 0.55 grams per cubic centimetre, at least 0.56 grams per cubic centimetre, or at least 0.64 grams per cubic centimetre.

The aerosol-forming substrate 110 may be cylindrically shaped, and is preferably substantially cylindrically shaped, having a length of between 10 mm and 15 mm, such as between 11 mm and 14 mm, preferably about 12 mm, and having a diameter of between 4.5 mm and 8 mm, such as between 6.5 mm and 7.5 mm, preferably about 7 mm, and can preferably have substrate volumes in a range between 0.16 cubic centimeters to 0.75 cubic centimeters.

In yet another exemplary embodiment, the aerosol-forming substrate 110 can be a non- tobacco-based substrate and/or a substantially tobacco free substrate. The aerosol-generating substrate 110 may be a cellulose-based substrate, for example as described in W02020/207733, WO2023/ 126494, and/or WO2022/248378, these references herewith incorporated by reference in their entirety.

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. The 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 an input voltage UIN to the switching unit 260. The configuration of the feedback loop 270 is such that the output signal, e.g. the output voltage UOUT of the switching unit 260 can undergo a phase change and arrives inverted at the input voltage 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. The feedback loop 270 is configured to provide a 180° phase shift from the output voltage UOUT to the input voltage UIN of the switching unit 260 for oscillation, and in addition, the transistor T is configured for inverting operation.

As shown in Figures 3a and 3b, the 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. The 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°. The switching unit 260 is itself configured for inverted switching operation to provide a 180° phase shift between the input voltage UIN and the output voltage UOUT of the switching unit 260.

The 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, the 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. The resonant circuit 272 including resonant 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 0. Moreover, the 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 the transistor T can be coupled to a DC power supply via a choke 280. Between the gate and source terminals of transistor T, a feedback loop 270 extends. 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 DL could be placed elsewhere, for example somewhere else in the feedback loop 270.

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, to move the oscillation frequency away from the natural resonant frequency given by the resonant circuit 272. This ensures that the 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 270 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, the electrical contacts 160, 165 provide an electrical connection between the first and second electrodes 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, the electrical contacts 160, 165 provide electrical connections from the first and second electrodes 130, 135 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 10V-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.

The 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 the capacitor Ci is chosen to be larger than the maximal intrinsic capacitor Ci of the 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.

The capacitive element 274 comprises a capacitor C2 arranged at the output or end of the resonant circuit 272. In one embodiment, the capacitive element 274 comprises more than one capacitor. As described above, the capacitive element 274 has the function of providing a 90° phase shift to the feedback voltage of the 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 the capacitor C2 of the capacitive element 274 should be relatively high as compared to the capacitor Ci, for example in a range between 500pF to 100nF, more preferably between 1 nF 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.

The resonant circuit 272, together with the capacitive element 274, provides for a 180° phase shift and a voltage gain from the output voltage UOUT to the input voltage UIN, and the 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 80, preferably around 20, 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 272 and capacitor C2 add up to match the impedance of the transistor T, more preferably the resonant circuit 272 is substantially impedance-matched with the transistor T.

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

The 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 Quartzmimicking 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, the 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 non-limiting 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 Figures 5A and 5B. The mechanical oscillation is represented by a first branch having a 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 the capacitor 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 the capacitor CE‘S minimal capacitive effect on the capacitor CL.

In a non-limiting example starting from the split inductors Li and L2 of the resonant circuit 272 of Figure 5D, the 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 the 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 CL can be in a range between 0.5pF to 5pF, more preferably between 1pF 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 T. 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 the 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, Figure 20 shows a schematic diagram depicting various curves of switching losses against electric field strength and transistor cost with non-limiting and non-exclusive numerical values for given dielectric losses PL and given geometry/arrangement of electrodes Ei and E2. The diagram shows a decreasing efficiency with increasing switching frequency f_s, an exponentially increasing transistor price for an increased switching frequency f_s to ensure operability, and a decreasing electric field strength 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 the voltage UL (i.e. , voltage strength of the alternating voltage) applied to the capacitor CL and a maximal distance d between the first and second electrodes 130, 135.

It is preferable that the switching frequency f_s 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 switching frequency 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 f_s should be in a range between 100 MHz and 1.2 GHz, more preferably between 150 MHZ to 1 GHz, more preferably between 200 MHz and 900 MHz. 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 120 V/mm, more preferably maximally 100 V/mm, even more preferably maximally 80 V/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 the input voltage UIN and the output voltage 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 f_PAR (also called antiresonant frequency). If the oscillation (switching) 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 feedback loop 270. Furthermore, the equivalent impedance of the circuit will increase to an extent that is too high for efficient dielectric heating as not providing for the requisite gain.

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 f_PAR. 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 (switching) frequency fs (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 fpAR is reached. After the parallel resonance frequency f_PAR, 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 1 Q. The parallel resonance frequency fp_AR can be above 1 GHz, e.g. 1 GHz to 1.5 GHz, while the actual switching frequency fs can be below 1 GHz, and this lower switching frequency fs is caused by the delay line DL.

Ideally, the oscillation (switching) 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 Figure 6. For example, a resulting impedance of the feedback loop 270 at the oscillation (switching) frequency fs of the oscillation circuit can be in a range of approximately 100mQ to 2Q. Preferably, the delay line DL is configured such that the oscillation (switching) frequency fs is closer to the series resonance frequency fsER than to the parallel resonance frequency f_PAR, 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 the 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 the delay line DL that acts of the 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 the feedback loop 270 is in a range between 35% and 90% of a difference between the period of the parallel resonance frequency fpAR 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 Figure 6 and as a non-limiting numerical example, assuming that a parallel resonance frequency fpAR is at 1.25 GHz, therefore having a period of 800 ps (picoseconds), and a series resonance frequency fsER is at 855 MHZ, and therefore a period of 1169 ps, there is a difference of 369 ps between the periods of fpAR and fsER. The time delay caused by the delay line DL can be in the above range, for example at 70% of the period difference between fpAR and f_SER, thereby being 258 ps, 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 DL 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, the 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 (3) turns, and preferably no more than one (1) 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 the 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 the 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.

Alternatively, as shown in Figure 9, the interdigitated electrode arrangement may comprise a first and second electrode 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. Preferably, the tubular structure can have a diameter between 5 mm to 9 mm. The tangential distance between the electrodes of opposite polarity can be between 0.5 mm to 3 mm, preferably between 0.7 mm to 2.2 mm.

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 aerosol-forming substrate 110 heated using the electrode arrangement, to provide for sectional, zoned or partial heating.

Figures 11 A-B 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 11 A-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, but is still heated by the presence of the alternating electric field in its proximity. Stronger and more uniform heating of the aerosol-forming substrate 110 may be achieved using the electrode arrangement shown in Figure 11 B, which is configured such that electrical field between opposing polarity electrodes is strongest across the aerosol-forming substrate 110. Figures 11C-D illustrate how the plurality of electrode portions from the electrode arrangements of Figures 11 A-B may be electrically connected to achieve an interdigitated configuration.

Figures 12a-c illustrate alternative electrode arrangements for use as both a heater assembly and wicking element for dielectrically heating a liquid aerosol-forming substrate. The arrangement of Figure 12a comprises a reservoir housing a liquid aerosol-forming substrate 110 and a plurality of electrode plates situated adjacent to electrode plate of the opposite polarity. The arrangement functions by generating an alternating electric field across adjacent electrode plates to dielectrically heat liquid aerosol-forming substrate situated between the adjacent electrodes. The distance between adjacent electrode plates may be selected such that the channel between adjacent electrode plates has a capillary effect drawing the liquid aerosol-forming substrate into the channel. Figures 12b-c illustrate a similar electrode arrangement which uses an array of interlocking electrode pins rather than electrode plates. Instead of pins, blades, tabs, rods, or cylinders could also be used. As better seen in Figure 12c, the array of interlocking electrode pins is configured such that adjacent electrode pins have an opposite polarity. Such electrode arrangements are particularly suited for providing uniform heating of the aerosol-forming substrate and avoiding localised overheating of the aerosol-forming substrate, which can lead to the generation of a poor quality aerosol. As with the embodiment in Figure 12a, the distance between adjacent electrode pins in the electrode array may be selected such that the region between adjacent electrode pins has a capillary effect, drawing the liquid aerosol-forming substrate into the electrode array.

Figure 13 is a schematic illustration of a control system utilizing a temperature sensing system for control 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. 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 (called heat-up phase or pre-heating phase) where the aerosol-forming substrate temperature is ramped up as fast as possible, and a second stage (called target heating phase) where the aerosol-forming substrate is maintained at a target aerosol ization temperature.

The first stage is performed by maximizing the DC supply voltage to, for example 10 V to 12 V. 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 6.4 V to 7.6 V. During the ramp-up time of the first stage of the temperature control, the overall power consumption can be 10 W-15 W, preferably with an efficiency of at least 65%, and upon reaching aerosolization temperature of the aerosol former, the temperature can be controlled to 180°C- 220°C, 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 aerosolforming 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 14 illustrates a block diagram of a control system utilizing a power sensing system for controlling the power delivered to an aerosol-forming substrate 110 based on a detected power consumption value (DC supply current, DC supply voltage, or both). In some examples, the microprocessor 2030 may further receive a temperature signal from the resonant circuit 272. In particular, this Figure shows the self-oscillating 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. The microprocessor 2030 receives a signal indicative of the power, current, and/or voltage provided by the DC/DC converter 2010 or the power supply 2020. In an example, the power sensing system comprises a shunt connected between the switching unit 260 and the power supply 2020 (power source), in particular between the switching unit 260 and the DC/DC converter 2010, to derive a voltage that is indicative for the DC supply current. In some examples, the power sensing system further comprises a voltage sensor to measure the voltage across the shunt and to feed the result indicative for the DC supply current to the microprocessor 2030. The microprocessor 2030 outputs a control signal to the DC/DC converter 2010.

Where the controller determines that the aerosol-forming substrate is depleted, the controller disables heating operation. For example, the controller cuts the power to the oscillation circuit using a DC/DC cut off so that no further power is supplied to the oscillating circuit and its amplitude slowly decreases, thereby also causing the temperature delivered to the aerosol- forming substrate to fall successively. 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 lower the heating power at the load capacitor CL. AS another alternative, it would be 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.

Figure 15 is a more detailed block diagram of the control system utilizing the power sensing system to determine a depletion level, according to an embodiment of the disclosure. The determined depletion level DL may be used, by the microprocessor 2030 to enable heating operation only when the depletion level DL is below a threshold value. As used in the embodiment, said threshold value is indicative for a maximum depletion level where the aerosol-forming substrate is depleted. A minimum depletion level (at around DL= 0%) is indicative for an initial state of the aerosol-forming substrate 110, i.e. before the substrate is subject to heating.

Generally, when an aerosol-forming substrate, for example including a tobacco-based material and an aerosol forming material, is subject to heating, the dielectric constant of the load capacitor CL that holds the aerosol-forming substrate will decrease. This is because the tobacco material has a lower dielectric constant as compared to the rather liquid or gel-like aerosol forming material (for example a mix between polypropylene glycol (PPG) and glycerin), and the liquid or gel-like aerosol forming material will evaporate or aerosolize. PPG has a dielectric constant of 14- 20, and glycerin has a dielectric constant of 42.5. 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 of the load capacitor CL, as the load capacitor CL is part of the resonant circuit that is self-oscillating at a resonance frequency.

A variation of the measured frequency upon consumption from full substrate to a maximum depletion level is in between 3% to 25%, preferably between 5% to 20%, in particular between 7% to 15%. This could be increased by using liquid filler or aerosolization agents or materials (e.g. water, PPG, glycerin) in the substrate that have a substantially higher dielectric constant than the tobacco material.

In particular, an increase of the depletion level DL and the resonance frequency is indicative of a decrease in the dielectric constant of the substrate and hence a decrease of the capacity of the dielectric heating element due to a reduction of a share of an aerosol forming material.

The change in resonance frequency in turn is proportional to the power loss of the load capacitor CL. Hence, it is possible to measure the power consumption to have an indication of depletion of the substrate. In this respect, it is possible to simply use a frequency sensor for calibration purposes, for example at a factory level, to correlate different power consumption patterns (e.g. of DC supply current that is fed from a power source of a calibration device) with the frequency of oscillation. Thereafter, the aerosol-generating device itself may not need to have a frequency sensor or frequency sensing system anymore.

Accordingly, based on previously made frequency measurements and calibration, a mapping function MF as illustrated in Figure 15 may be generated and pre-stored at the aerosolgenerating device so that it is possible to use a power consumption value (DC supply current, DC supply voltage, or both) as a parameter that is indicative of substrate depletion.

Figure 16 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. 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 control ler/microprocessor for calibration/further processing. In particular, said system may be used as a calibration system to generate the mapping function MF as discussed with respect to Figure 15.

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

Figure 18 is a schematic illustration of the control system utilizing the power sensing system to determine a depletion level DL based on a frequency of an alternating electric field detected across an electrode assembly, according to an embodiment of the disclosure.

In contrast to the embodiment discussed with respect to Figure 15, the system includes a frequency detection unit FD to derive a frequency of the alternating electric field that is generated by the load capacitor CL and detected by the power sensing system. The derived frequency is then fed to a pre-stored mapping function MF that maps the derived frequency, in particular a resonant frequency of the oscillation circuit 150, to a depletion level DL. The determined depletion level DL may be used, by the microprocessor 2030 to enable heating operation only when the depletion level DL is below a threshold value. As used in the embodiment, said threshold value is indicative for a maximum depletion level where the aerosolforming substrate is depleted. A minimum depletion level (at around DL= 0%) is indicative for an initial state of the aerosol-forming substrate 110, i.e. before the substrate is subject to heating.

The system may utilize one or more of resonant antennas, microstrips, waveguides, for high-frequency sensing.

It will be appreciated that the embodiments described above are exemplary embodiments only, and various other embodiments according with this disclosure are also envisaged.

Figure 19 is a schematic illustration of a method of dielectrically heating an aerosol-forming substrate 110, according to an embodiment of the disclosure. The method is performed by the aerosol generating device 120 having the self-oscillating circuit of Figure 3A and the control system of Figure 14 in an exemplary application environment. However, the method is not limited to the use of the control system of Figure 14. In alternative examples, to control system of Figure 15 may be used instead. The method includes the following steps:

In a first step, power, particularly DC power, is provided from the power supply 2020 (power source) to the oscillation circuit 150 of the aerosol-generating device 120, the oscillation circuit 150 includes the switching unit 260 and the feedback loop 270 of the oscillation circuit 150 including a load capacitor CL. (dielectric heating element) which is arranged for heating the aerosol-forming substrate 110.

In a second step, an electrical parameter associated with a capacitance of the load capacitor CL is measured and based thereon.

In a third step, a property of the aerosol-forming substrate 110 is determined. In the present example, the electrical parameter includes a power consumption value, in particular a DC supply current, that is drawn from the power supply 2020 and measured as explained with respect to Figure 14. The determined property of the substrate includes a depletion level DL of the aerosolforming substrate 110 that is determined by mapping the measured DC supply current (or power consumption value, or DC supply voltage, or DC voltage at the DC/DC converter 2010) to the depletion level by means of the mapping function MF as shown in Figure 15. In an alternative example, the depletion level is determined by mapping the frequency of an alternating electric field detected across the electrodes of the load capacitor CL (see Figure 16) to the depletion level by means of the mapping function MF as shown in Figure 18.

In a fourth step, an action is performed by the aerosol-generating device 120 based on the determined property of the substrate. The action may comprise at least one of shutting-off heating operation, ramping-down heating operation, and indicating to a user that the aerosol-forming substrate 110 is deemed empty, when the depletion level exceeds a threshold value that is indicative for a nearly empty aerosol-forming substrate 110.

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 of an aerosol-forming article, the aerosol-generating device comprising a power source; and an oscillation circuit, the oscillation circuit including: a switching unit; a resonant oscillating feedback circuit connected between an input and an output of the switching unit, the resonant oscillating feedback circuit including a dielectric heating element which is arranged for dielectrically heating the substrate; wherein, in operation, an electrical parameter associated with a capacitance of the dielectric heating element is measured to determine a property of the substrate.

2. The aerosol-generating device according to the preceding claim, wherein the aerosolgenerating device further includes a power sensing system to detect a power consumption value drawn from the power source, wherein the power consumption value is used as the electrical parameter associated with the capacitance of the dielectric heating element.

3. The aerosol-generating device according to claim 2, wherein the power consumption value is indicative of a supply current, in particular a DC supply current, drawn from the power source.

4. The aerosol-generating device according to any of the preceding claims, wherein the frequency of oscillation of the oscillation circuit is in a range between 10 MHz and 100 GHz, preferably between 100 MHz to 1.5 GHz, in particular between 200 MHz to 900 MHz.

5. The aerosol-generating device according to any of the preceding claims, wherein the electrical parameter is a value indicative of the relative permittivity of a material that forms the substrate, and wherein the property of the substrate that is determined includes a depletion of the substrate, wherein the aerosol-generating device further comprises a data processor, wherein the data processor is configured to determine the depletion level of the substrate based on a relationship with the frequency of oscillation of the oscillation circuit.

6. The aerosol-generating device according to the preceding claim, wherein a variation of the frequency upon consumption from full substrate to a maximum depletion level is in between 3% to 25%, preferably between 5% to 20%, in particular between 7% to 15%.

7. The aerosol-generating device according to claim 5 or claim 6, wherein the relationship comprises a mapping function MF that maps a parameter associated with the frequency of oscillation of the oscillation circuit to a predefined or predetermined depletion level.

8. The aerosol-generating device according to the preceding claim, wherein the parameter comprises a power consumption value, preferably a DC supply current drawn from the power source.

9. A system comprising an aerosol-generating article comprising an aerosol-forming substrate; and an aerosol-generating device according to any one of the preceding claims for dielectrically heating the aerosol-forming substrate.

10. The system according to the preceding claim, wherein the aerosol-forming substrate comprises solid material.

11. A method of dielectrically heating an aerosol-forming substrate of an aerosol-forming article by means of an aerosol-generating device, the method comprising the following steps: providing power from a power source to an oscillation circuit of the aerosol-generating device, the oscillation circuit including: a switching unit; a resonant oscillating feedback circuit connected between an input and an output of the switching unit, the resonant oscillating feedback circuit including a dielectric heating element which is arranged for heating the substrate; measuring an electrical parameter associated with a capacitance of the dielectric heating element to determine a property of the substrate.

12. The method according to the preceding claim, further comprising determining the property of the substrate, wherein the determination includes mapping the measured electrical parameter to the property of the substrate by means of a mapping function that is preferably pre-stored on the aerosol-generating device, and wherein the electrical parameter includes a power consumption value, preferably a DC supply current, drawn from the power source, and wherein the determined property of the substrate includes a depletion level of the substrate.

13. A method of calibrating an aerosol-generating device, the method comprising the following steps: providing power from a power source to an oscillation circuit of the aerosol-generating device, the oscillation circuit including: a switching unit; and a resonant oscillating feedback circuit including two opposed electrodes with an aerosol-forming substrate there between for heating the substrate, measuring a frequency of the electric field between the electrodes, correlating the measured frequency to the provided power, and storing the obtained relationship in a mapping function of the aerosol-generating device.