WO2025074006A1

WO2025074006A1 - Dielectric heating aerosol-generating device with an interdigitated electrode arrangement

Info

Publication number: WO2025074006A1
Application number: PCT/EP2024/078164
Authority: WO
Inventors: Oleg Mironov
Original assignee: Philip Morris Products SA
Current assignee: Philip Morris Products SA
Priority date: 2023-10-05
Filing date: 2024-10-07
Publication date: 2025-04-10
Anticipated expiration: 2026-04-05

Abstract

Provided is an aerosol-generating device (120) for dielectrically heating an aerosol-forming substrate (110). The device (120) comprises an oscillation circuit (150) and an electrode arrangement coupled to the oscillation circuit. The electrode arrangement forms a load capacitor for dielectrically heating the aerosol-forming substrate. The electrode arrangement comprises a first electrode interdigitated.

Description

Dielectric Heating Aerosol-generating Device With An Interdigitated Electrode Arrangement

The present disclosure relates to aerosol-generating devices, and specifically to aerosolgenerating devices configured to heat an aerosol-forming substrate by dielectric heating. The disclosure also relates to dielectric heating circuits for use in a dielectric heating aerosol-generating device and an aerosol-generating system.

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 aerosol-forming 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.

According to the present disclosure, there is provided an aerosol-generating device including any one or more of the features described below.

The aerosol-generating device may comprise an oscillation circuit. The oscillation circuit may comprise a switching unit and a feedback loop connected across the switching unit. The feedback loop may comprise two electrical contacts configured to interconnect with an electrode arrangement that forms a load capacitor for dielectrically heating the aerosol-forming substrate. The aerosolgenerating device may further comprise any of the features described below alone or in combination with any other feature of the disclosure.

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.

According to an example of the disclosure, provided is an aerosol-generating device for dielectrically heating an aerosol-forming substrate. The device comprises an oscillation circuit comprising a switching unit configured for inverting operation and a feedback loop connected across the switching unit. The feedback loop comprises two electrical contacts configured to interconnect with an electrode arrangement that forms a load capacitor for dielectrically heating the aerosolforming substrate. The feedback loop is configured to perform resonant oscillating operation. The feedback loop is configured to provide a 180° phase shift between an output signal of the switching unit and an input switching signal of the switching unit.

The oscillation circuits of the present disclosure enable more efficient dielectric heating of an aerosol-forming substrate by facilitating the coupling of a load capacitor electrode arrangement within the feedback loop of the oscillation circuit. The resonant oscillating operation of the feedback loop is able to generate high peak voltages across the load capacitor at high frequencies to deliver power to an aerosol-forming substrate within the electrode arrangement while maintaining the supply voltage across the switching unit, thereby keeping switching losses to a minimum. The oscillation circuits of the present disclosure may be configured to be self-oscillating; that is, the oscillation circuit itself controls the phase with which the external power acts on it.

Where the switching unit is configured for inverting operation, the feedback unit is configured to provide a 180° phase shift between an output signal of the switching unit and an input switching signal of the switching unit. This allows for effective resonant oscillating operation to occur.

In some examples, the feedback loop further comprises the electrode arrangement coupled between the two electrical contacts. In some examples, the electrode arrangement is coupled to, or configured to be coupled to a resonant cavity for housing an aerosol-forming substrate to be dielectrically heated via the electrode arrangement.

According to an example of the disclosure, provided is an aerosol-generating device for dielectrically heating an aerosol-forming substrate. The device comprises an oscillation circuit comprising a switching unit and a feedback loop connected to the switching unit. The feedback loop comprises a first inductor having no more than five turns. The first inductor is connected in series with one of two electrical contacts configured to interconnect with an electrode arrangement that forms a load capacitor for dielectrically heating the aerosol-forming substrate.

At the operation frequency of the oscillation circuit, the first inductor in the feedback loop is configured to deliver a 90° phase shift between an output signal of the switching unit and an input switching signal of the switching unit. A further 90° phase shift may be provided by a capacitive element, as described in further detail below. By providing an inductor with no more than five turns, the required phase shift for effective resonant oscillating operation may be achieved while also minimizing the presence of parasitic inductance and capacitance in the feedback loop which negatively impact efficient dielectric heating of the aerosol-forming substrate and cause additional power losses that do not contribute to the dielectric heating.

In an example, the first inductor comprises no more than three turns. In preferred examples, the inductor has less than three turns, and preferably no more than one turn. In some examples, the first inductor may have less than one turn, for example, a half turn or omega-shaped inductor. In an example, a diameter of the turn(s) of the first inductor is less than 15 mm and more than 3 mm, preferably less than 12 mm and more than 5 mm.

According to an example of the disclosure, there is provided an aerosol-generating device for dielectrically heating an aerosol-forming substrate. The device comprises an oscillation circuit. The oscillation circuit comprises a switching unit and a feedback loop connected across the switching unit. The feedback loop comprises a series connection of a first inductor, two electrical contacts configured to interconnect with an electrode arrangement that forms a load capacitor for heating the aerosol-forming substrate, and a second inductor.

Providing a first inductor coupled to a first side of the load capacitor and a second inductor coupled to a second side of the load capacitor enables more symmetrical voltages to be generated across the load capacitor, while also providing a 90° phase shift for effective resonant oscillating operation.

In some examples, the second inductor may comprise the same number of turns as the first inductor to facilitate the symmetrical generation of voltages across the load capacitor. In some examples, the turn(s) in the second inductor have the same diameter as those in the first inductor.

In some examples, the first inductor and the second inductor are inductively coupled to one another to form a mutual inductance. In order to achieve high peak voltages across the load capacitor, a high inductance is needed in the feedback loop. However, a high inductance also limits the maximum oscillation frequency attained in the feedback loop, and therefore, the power deliverable to the load capacitor. Inductively coupling the first inductor with the second inductor creates a slightly distributed inductor having an amplified effective inductance. Utilising an inductive coupling between the first and second inductors therefore enables the use of inductors having lower inductance values to mitigate the limitations on the achievable oscillation frequency in the feedback loop, while also providing a high effective inductance to amplify the peak voltages generated across the load capacitor.

In an example, the mutual inductive coupling between the first and second inductor may be between 40% and 70% (or has an inductive coupling coefficient from 0.4 to 0.7), and preferably greater than 50% (or has an inductive coupling coefficient greater than 0.5). In an example, the mutual inductive coupling between the first and second inductors may be achieved by the close proximity between the first and second inductors. In alternative examples, a mutual inductive coupling between the first and second inductors is achieved with the use of a magnetic core extending through both the first and second inductors. The use of a magnetic core may facilitate a stronger inductive coupling between the first and second inductors than that achievable based on close proximity alone.

In an example, a coil axis of the first inductor is arranged to be in parallel with and offset from a coil axis of the second inductor to minimize a capacitive coupling between the first and second inductors. In an example, the first and second inductors are formed as planar inductors.

In an example, a coil axis of the first inductor is arranged to coaxially align with a coil axis of the second inductor.

In an example, a planar extension of the first inductor intersects the second inductor.

According to an example of the disclosure, provided is an aerosol-generating device for dielectrically heating an aerosol-forming substrate. The device comprises an oscillation circuit. The oscillation circuit comprises a switching unit and a feedback loop connected to the switching unit. The feedback loop comprises a series connection of a first inductor and two electrical contacts configured to interconnect with an electrode arrangement that forms a load capacitor for heating the aerosol-forming substrate. The oscillation circuit further comprises a delay element configured to impede the switching speed of the switching unit. Specifically, the delay element may delay a switching signal received by the switching unit.

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

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

In an example, the oscillation circuit is configured to operate a frequency of between 100MHz-2.5GHz, and preferably between 500MHz-1 ,5GHz.

In operation, the oscillation frequency in the feedback loop will increase towards a certain resonance frequency based on the passive properties of the components in the feedback loop. However, as the oscillation frequency increases beyond a certain threshold, the feedback loop starts to lose the inductive properties that provide the necessary phase shift for effective resonant oscillating operation. Furthermore, as the oscillation frequency exceeds a certain threshold, the impedance of the feedback loop increases, reducing the dielectric heating efficiency in the load capacitor. By providing a delay element configured to impede the switching speed of the switching unit, the maximum oscillation frequency may be limited to a frequency range in which the feedback loop behaves inductively and has a low impedance for efficient dielectric heating.

In some examples, a biasing unit is coupled to an input terminal of the switching unit via the delay element. In some examples, the delay element is coupled to ground by a capacitor.

In an example, the first inductor and the two electrical contacts for coupling with the load capacitor form a resonant circuit. In such examples, the delay element may be configured such that an oscillation frequency of the oscillation circuit is limited to a frequency below a parallel resonant frequency fpAR (also known as the antiresonant frequency) of the resonant circuit, but above a series resonant frequency fsER (or resonant frequency) of the resonant circuit.

In an example, the time delay imposed by the delay element is between 5% to 35% of the period of the parallel resonant frequency fpAR of the resonant circuit.

In an example, the time delay imposed by delay element is between 35% and 90% of a difference between the period of the parallel resonant frequency fpAR and the period of the series resonant frequency fsER, preferably between 50% and 85% of a difference between the period of the parallel resonant frequency fpAR and the period series resonant frequency fsER.

In an example, the delay element is configured to impose a time delay of between 50 and 500 picoseconds, preferably between 150 and 350 picoseconds, more preferably between 200 and 300 picoseconds.

In an example, the delay element comprises a low-pass filter.

In some examples, the delay element has an inductive behaviour. Advantageously, inductive delay elements may provide the required time delay without impacting the wave shape of the oscillations in the circuit. In an example, the delay element comprises a meandering electrically conductive element. In an example, the meandering electrically conductive element comprises between two and twelve meandering branches, preferably between three and ten meandering branches, more preferably three meandering branches. In an example, the meandering electrically conductive element comprises one of an omega-shaped coil, a single planar coil, a flat inductor, a wavy line, a zig-zag line, or a sawtooth line.

In an example, the oscillation circuit further comprises the electrode arrangement fixedly interconnected to the two electrical contacts to form the load capacitor, the load capacitor including or being configured to removably receive an aerosol-forming substrate. This enables an article comprising an aerosol-forming substrate to be inserted directly into a heating area in close proximity with the electrode arrangement or in a cavity within the electrode arrangement. In an alternative example, the oscillation circuit further comprises the electrode arrangement removably interconnected to the two electrical contacts to form the load capacitor, the load capacitor including or being configured to removably receive an aerosol-forming substrate. In such examples, the electrode arrangement may form part of an article comprising an aerosolforming substrate. In other examples, the electrode arrangement may be removable to facilitate easy insertion of an article comprising an aerosol-forming substrate in a heater area on or within the electrode arrangement prior to connection with the oscillation circuit.

In an example, the oscillation circuit is configured such that, during operation, a peak AC voltage across the two electrical contacts is greater than a supply voltage of the oscillation circuit. In some examples, the oscillation circuit is configured such that, during operation, the peak AC voltage across the two electrical contacts is greater than five times the supply voltage of the oscillation circuit. Advantageously, providing a higher voltage across the load capacitor than the supply voltage enables more power to be delivered to an aerosol-forming substrate with lower switching losses in the switching unit, and therefore directly impacts the efficiency of the aerosolgenerating device. In examples of the present disclosure, this may be achieved without the use of any voltage transformers by relying solely on resonant oscillating operation within the feedback loop. In an example, the peak AC voltage across the two electrical contacts at the operating frequency of the oscillation circuit is from 50V to 500V, more preferably 100V to 400V, even more preferably 120V to 350V, wherein the DC supply voltage to the oscillation circuit is between 6V to 15V.

In an example, the impedance of the feedback loop at the operation frequency is matched with the impedance of the switching unit, which improves the efficiency of the oscillation circuit.

In an example, the feedback loop is 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 is 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 reduces noise and ground influences for more predictable operation in the feedback loop.

In an example, the feedback loop is connected across an output terminal and a biasing terminal of the switching unit. In some examples, the output terminal of the switching unit is coupled to the supply voltage via a radio frequency choke. The choke acts to block high frequency alternating currents while passing direct current and low frequency alternating current.

In an example, the feedback loop is configured to operate as an inductive load at an operating frequency of the oscillation circuit to provide approximately a 90° phase shift. As described above, this can be achieved by providing one or more inductors in series with the load capacitor in the feedback loop. In an example, the feedback loop further comprises a capacitive element providing for a 90° phase shift at an operating frequency of the oscillation circuit. In an example, the capacitive element comprises a capacitor connected to ground. The combination of the inductive load and capacitive element in the feedback loop provides a 180° phase shift, which, in combination with an inverting switching unit, provides effective resonant oscillating operation for dielectric heating.

In an example, the oscillation circuit further comprises a capacitor connected between an output terminal of the switching unit and ground, the capacitor having a capacitance value that is bigger than a maximal intrinsic capacitance of the switching unit. This reduces the influence of the variation of the intrinsic properties of the switching unit due to factors such as temperature and operating frequency on the operation of the feedback loop.

In an example, the feedback loop comprises a resonant circuit including the two electrical contacts, such that in operation, the load capacitor is part of the resonant circuit. In some examples, the resonant circuit comprises one of a parallel resonant circuit, a series resonant circuit, or a combination of parallel and series resonant circuits. In an example, the feedback loop comprises a parallel resonant circuit which, in use, is electrically stimulated by the output signal of the switching unit. In such examples, the output signal of the switching unit may be a switched voltage across a transistor. In some examples, the impedance of the resonant circuit at the operation frequency of the oscillation circuit is between 0.5Q and 8Q, preferably between 1 Q and 5Q, and more preferably, between 1 ,5Q and 3Q.

In an example, the switching device comprises a single transistor. In some examples, the transistor may be a bipolar junction transistor (BJT), and the feedback loop may be connected between the collector or emitter and the base of the BJT. In other examples, the transistor may be a field effect transistor (FET) and the feedback loop may be connected between the drain or source and the gate of the FET.

In an example, the oscillation circuit is configured such that the ratio of the dielectric heating losses in the load capacitor to the switching losses in the switching unit is greater than 1 1 :9, preferably greater than 13:7. Current dielectric heaters typically have heating efficiencies in the region of 50%. However, dielectric heating aerosol-generating devices incorporating the above mentioned features (e.g., incorporating the appropriate feedback loop and delay element) can achieve heating efficiencies up to 70%, which is comparable to induction heating systems known in the art.

The electrode arrangement comprises a first electrode and a second electrode. In operation, the second electrode has an opposite polarity to the first electrode. In some examples, the first and second electrodes may be flat plate electrodes configured to heat an aerosol-forming substrate situated between the first and second electrode plates. In some examples, the first and second electrode plates may be slightly bent or rounded at the edges to create a smoother electric field distribution around the boundaries of the electrode plates. In some examples, the electrode plates may be curved. The curved electrode plates may have a radius of 15mm or greater.

According to an example of the disclosure, there is provided an aerosol-generating device for dielectrically heating an aerosol-forming substrate. The device comprises an oscillation circuit and an electrode arrangement coupled to the oscillation circuit. The electrode arrangement forms a load capacitor for heating the aerosol-forming substrate. The electrode arrangement comprises a first electrode interdigitated with a second electrode.

The term interdigitated relates to an electrode arrangement comprising a first electrode having a first polarity and a second electrode having a second polarity which is the opposite of the first polarity, wherein at least a portion of the first electrode separates two portions of the second electrode. 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. The electrode arrangement may take on any form, providing that an electric field can be generated across an aerosol-forming substrate in the vicinity of the electrode arrangement.

In an example, the electrode arrangement may form a flat plate for heating an aerosol-forming substrate situated on a surface of the electrode arrangement. In some examples, the flat plate comprises a first electrode and a second electrode which is at least partially interdigitated with the first electrode. In some examples, the first electrode may comprise a first plurality of electrode portions and the second electrode may comprise a second plurality of electrode portions, wherein each of the first plurality of electrode portions are separated by one of the second plurality of electrode portions.

In some examples, the electrode arrangement may comprise a first plate and a second plate, wherein the electrode arrangement is configured to heat an aerosol-forming substrate situated between the first plate and the second plate. In an example, the first plate comprises a first electrode and a second electrode which is at least partially interdigitated with the first electrode. In some examples, the second plate may also comprises a first electrode and a second electrode which is at least partially interdigitated with the first electrode. In some examples, the first electrode may comprise a first plurality of electrode portions and the second electrode may comprise a second plurality of electrode portions, wherein each of the first plurality of electrode portions are separated by one of the second plurality of electrode portions.

In other examples, the electrode arrangement may be cylindrical and define a central cavity for heating an aerosol-forming substrate situated within the cavity.

In one example, the electrode arrangement may comprise a first electrode and a second electrode each comprising a cylindrical segment configured to interdigitate with a cylindrical segment of the other electrode around a cylindrical axis. In some examples, the first electrode comprises a first plurality of cylindrical segments and the second electrode comprises a second plurality of cylindrical segments, wherein each of the first plurality of cylindrical segments are positioned around the cylindrical axis separated by one of the second plurality of cylindrical segments.

In another example, the first electrode comprises a first plurality of axially aligned electrode rings and the second electrode comprises a second plurality of axially aligned electrode rings, wherein each of the first plurality of electrode rings are separated by one of the second plurality of electrode rings.

In some examples, the first electrode comprises a plurality of axially aligned electrode rings and the second electrode comprises a rod or pin extending through the plurality of axially aligned electrode rings.

In some examples, the first electrode comprises a first plurality of electrode rods or pins and the second electrode comprises a second plurality of electrode rods or pins, wherein each of the first plurality of electrode rods or pins and second plurality of electrode rods or pins are alternately positioned in a grid to form an electrode array. Such examples may create a highly uniform electric field through an aerosol-forming substrate, and may be particularly suited to dielectrically heating a liquid aerosol-forming substrate in a reservoir. In some examples, the density of the electrode array may provide a wicking effect on a liquid aerosol-forming substrate to draw more liquid aerosolforming substrate from the reservoir into the electrode array as the aerosol is generated.

In some examples, the distance between the first electrode and the second electrode may vary across the electrode arrangement. This may further facilitate a more uniform electric field distribution through an aerosol-forming substrate.

According to an example of the disclosure, provided is an aerosol-generating device for dielectrically heating an aerosol-forming substrate. The device comprises an oscillation circuit and an electrode arrangement coupled to the oscillation circuit. The electrode arrangement forming a load capacitor for heating the aerosol-forming substrate. The electrode arrangement comprises a first electrode coaxially aligned with a second electrode.

Advantageously, the use of coaxially aligned electrodes may provide more a more uniform electric field, and therefore more uniform dielectric heating through an aerosol-forming substrate situated within the electrode arrangement.

In an example, the first electrode comprises a tubular body having a hollow center and the second electrode comprises a rod or pin situated within the hollow center of the first electrode. In such examples, an article comprising an aerosol-forming substrate may be inserted into the electrode arrangement between the first and second electrode. In some examples, the tubular body of the first electrode may comprise one or more openings. The one or more openings may enable the aerosol generated by the dielectric heating to escape the electrode arrangement to an airflow channel. In another example, the first electrode comprises a tubular body having a hollow center and the second electrode comprises a tubular body having a hollow center, wherein the second electrode is situated within the hollow center of the first electrode. In an example, the tubular body of the second electrode comprises one or more openings. Such examples enable the inner electrode to define a central airflow passage for the generated aerosol to escape the electrode arrangement.

In an example, the first electrode comprises a plurality of axially aligned electrode rings and the second electrode comprises a rod or pin extending through the plurality of axially aligned electrode rings. In such examples, gaps between the electrode rings may enable aerosol to escape from the electrode arrangement to an airflow channel.

In some examples in which either or both the first and second electrodes comprise a plurality of electrode portions, the aerosol-generating device may be configured to provide partial or sectional heating of an aerosol-forming substrate by selectively energizing one or more of the plurality of electrode portions. This enables an aerosol-generating device to switch between different electric field distribution patterns between the first and second electrodes to adjust the heating profile across the aerosol-forming substrate. This sectional heating approach may be used to compensate for geometry and heat transfer properties of the electrode arrangement (and also other components of the aerosol-generating device) and the aerosol-forming substrate in order to avoid localized overheating or underheating in the aerosol-forming substrate.

In some examples, the above described electrode arrangements may be coupled to a forced oscillation circuit, wherein the power that sustains the oscillation motion is modulated externally.

In an example, the oscillation circuit further comprises one of a variable capacitor, a variable inductor, a voltage regulator, a transistor voltage biasing element.

In an example, the aerosol-generating device further comprises a temperature sensor configured to detect a temperature indicative of the temperature of an aerosol-forming substrate within or adjacent to the load capacitor. In an example, the temperature sensor may be a contact sensor configured to directly measure the temperature of the aerosol-forming substrate or a component in the vicinity of the aerosol-forming substrate. In another example, the temperature sensor may be a non-contact sensor configured to capture heat radiation from the aerosol-forming substrate or a component in the vicinity of the aerosol-forming substrate. In an example, the noncontact temperature sensor is configure to capture heat radiation from a component that increases or homogenized the heat radiation and has greater thermal conductive properties than the aerosolforming substrate.

In an example, the aerosol-generating device further comprises an E-field sensor configured to measure the strength of an E-field in the vicinity of the aerosol-forming substrate. In examples in which the oscillation circuit comprises a first and second inductor sharing a mutual inductive coupling, the aerosol-generating device may further comprise an H-field sensor configure to measure the strength of a magnetic field in the vicinity of the first and second inductors.

In some examples, the aerosol-generating device further comprises a frequency sensing device configured to measure the frequency of an alternating electric field detected across an electrode assembly. In an example, the frequency sensing device comprises a resonant cavity (or resonator) situated within or in the vicinity of the electrode arrangement.

In an example, the aerosol-generating device may be configured to control the power delivered to the aerosol-forming substrate based on a measured frequency of an alternating electric field detected across an electrode assembly. In another example, the aerosol-generating device may be configured to control the power delivered to the aerosol-forming substrate based on a detected temperature of the aerosol-forming substrate. The temperature generated via dielectric heating by the oscillation circuit, inside or at the substrate that is located in the heating zone of the load capacitor, for example after a pre-heating phase, can be in a range between 80°C to 365°C, more preferably between 80°C to 320°C, and more preferably between 100°C to 240°C, and more preferably between 180°C to 220°C. Preferably, the temperature of the substrate is kept lower than a temperature where pyrolysis could occur in the material composition of the aerosol forming substrate. Preferably, the temperature is such that one or more active ingredients of the substrate are vaporized and thereafter aerosolized, for example simultaneously or sequentially during a heating session, for example a heating session for a duration of one puff or inhalation, for example a duration in a range between 0.5 seconds to 10 seconds, or a heating session for a duration that covers multiple puffs or inhalation, for example a duration of more than 10 seconds and less than 10 minutes, or preferably, more than 30 seconds and less than 6 minutes. In some examples, a controller of the aerosol-generating device or the settings of the oscillation circuit can be configured such that they control or set the temperature to such a range between 80°C to 365°C, more preferably between 80°C to 320°C, or more preferably 180°C to 220°C by open-loop control, or closed-loop control.

In some examples, the configuration and dimensioning of the oscillation circuit is selected to passively limit the temperature of the aerosol-forming substrate to a range between 80°C to 365°C, more preferably between 80°C to 320°C, or more preferably 180°C to 220°C, without the use of active temperature control.

The disclosure further provides an aerosol-generating system comprising an aerosolgenerating device according to any of the above examples and an article comprising an aerosolforming substrate. The article is arranged relative to the electrode arrangement to enable dielectric heating of the aerosol-forming substrate. According to a seventh aspect, the disclosure provides an aerosol-generating device dielectric heating circuit. The circuit comprises a low-dielectric constant carrier material comprising a first electrode configured to form a part of a load capacitor, a second electrode configured to form another part of the load capacitor, and a first inductor electrically coupled to the first electrode. The low dielectric constant carrier material is configured receive an aerosol-forming substrate between or in the vicinity of the first electrode and the second electrode for dielectric heating. Dielectric constant may also be referred to as the relative permittivity of the material. The term low-dielectric constant or low relative permittivity as used herein refers to properties of a material measured at room temperature at a very low frequency (VLF), preferably below 1 kHz, e.g. as defined in the international standard IEC 62631 -2-1 :2018.

In an alternative example, the carrier material may not be a low-dielectric material but may comprise a flex PCB configured to be wrapped around a heating chamber that is formed of a rigid, low-dielectric, high-temperature resistant, non-conductive material. This utilizes cost-effective PCB as the carrier material that can be wrapped around an element that forms the heating chamber, to thereby isolate the PCB from the heating chamber. The PCB may be attached to the heating chamber by an adhesive, for example a scotch tape around the PCB. To reduce the amount of PCB substrate material that can be dielectrically heated, sections between the first and second electrodes can be cut out to form openings. In some examples, both the carrier material and the heating chamber may be formed of a low-dielectric material.

Providing dielectric heating circuit components on a low dielectric carrier material may facilitate simple large scale manufacturing of dielectric heating circuits for dielectric heating aerosolgenerating devices.

In an example, the low dielectric constant carrier material forms or is configured to form a cavity for receiving an aerosol-forming substrate between the first electrode and the second electrode for dielectric heating.

In an example, the low dielectric carrier material comprises a flexible portion configured to be bent or rolled such that the cavity is formed between the first electrode and the second electrode. In an example, the low dielectric constant carrier material comprises a flexible printed circuit board (“flex PCB”) or a combined rigid and flex PCB. The low dielectric constant carrier material may comprise one or more conductive layers that form at least one of the first or second electrodes. The low dielectric constant carrier material may comprise one or more conductive layers that form the first inductor. The one or more conductive layers can be made of copper (Cu) or aluminum (Al) or another conductive material. The one or more conductive layers may have a thickness in a range between 5 mm to 100 mm, more preferably between 12 mm to 70 mm, more preferably between 18mm to 35mm, more preferably about 35 mm. A track or trace width for the conductor layers that form the first inductor and the electrical interconnections is preferably in a range between 0.5 mm to 8 mm, more preferably 1 .5 mm to 6 mm.

In an example, the low dielectric constant carrier material may comprise one or more of polyimide, PET (Polyethylene terephthalate), FR4, Polytetrafluoroethylene (PTFE), or liquid crystal polymers (LCP). The low dielectric constant carrier material may have a thickness in a range between 5 mm to 150 mm, and preferably about 25mm, 35mm, or 50mm, and for example 30 mm for the outer cover layers.

In an example, the flexible portion of the heating circuit may be bent or folded such that the first and second electrodes oppose each other in parallel or parallel-oblique planar fashion, to form a planar heating zone therebetween. In another embodiment, the section of the heating circuit where first and second electrodes are located can be rolled to form a cylindrical heating zone inside the rolled, cylindrical heater circuit, thereby having the first and second electrodes arranged as elements of cylindrical segments or flat strips around a cylindrical heating zone. The cylindrical diameter of the rolled heating circuit can be in a range between 6 mm to 14 mm to accommodate an aerosol-forming article therebetween. The width of the planar extension of the rolled heating circuit can be in a range between 18.85 mm to 44 mm plus about 5 mm to 10 mm, for example to provide for an overlapping strip that can be used for bonding of the tubular ends to a cylindrically-shaped heater.

In an example, the first and second electrodes may have a length such that they fully or partially cover a length of the low dielectric constant carrier material, for example a length along the insertion direction, for example in a range between 5 mm to 30mm.

In an example, the first electrode and the second electrode each comprise cylindrical segments that are configured to oppose each other around a cylindrical axis when the flexible-low dielectric constant substrate is bent or rolled.

In an example, the first electrode comprises a hollow center with an inner diameter, and a second electrode having an outer diameter smaller than the inner diameter of the first electrode such that the second electrode can fit within the hollow center of the first electrode when the flexible-low dielectric substrate is bent or rolled.

In an example, the first electrode and the second electrode are configured to interdigitate together as the flexible low-dielectric constant substrate is bent or rolled.

In one example, the low dielectric constant carrier material may comprise a single dielectric layer and a single conductive layer. In another example, the low dielectric constant carrier material may comprise multiple dielectric or conductive layer. The multi-layer example may comprise a double-sided flex PCB, or a four (4) layer flex PCB, or an adhesiveless polyimide double sided copper clad laminate.

In some examples, the flexible low-dielectric constant substrate comprises an insulating layer located between the heating zone and the conductive layer that forms one or more of the first and second electrodes. The insulating layer may provide for an electric insulation of the first or second electrodes to prevent electric shocks and dielectric breakdown, and also protection of the heating zone to avoid contact of the aerosol-forming article with the first and second electrodes. The insulating layer may have a low dielectric constant value to avoid dielectric heating losses in the insulating layer. Preferably, the insulating layer should be designed to be thick enough to provide for sufficient electrical field strength and voltage breakdown, thin enough to avoid too much material being parasitically heated, and have a low dielectric constant at the intended operation frequency of the dielectric heating aerosol-generating device. Preferably the dielectric constant of the insulation layer is below 3.2 at the operation frequency of the dielectric heating aerosol-generating device, more preferably below 3. In an example, the insulation layer may have a thickness in a range between 25 mm to 70 mm.

In an example, the overall thickness of the heating circuit is less than 500 mm, more preferably less than 400 mm.

In some examples, the region of the low-dielectric constant carrier material the one or more inductors may be stiffened, for example with an additional stiffening layer, to form a rigid or semirigid PCB structure. In some examples, the section of the low-dielectric constant carrier material comprising the first and second electrodes may be formed to be more flexible than the section comprising the first inductor.

In another example, the low-dielectric constant carrier material comprises a quartz body. The quartz body may comprise a hollowed out portion defining the cavity for receiving an aerosol-forming substrate between the first electrode and the second electrode for dielectric heating. In an example, the low-dielectric carrier material comprises an optical measurement device for measuring aerosol diffusion for puff detection. Advantageously, a quartz carrier material may provide a transparent protective layer for an optical measurement device. The optical measurement device may comprise an optical emitter or light source and an optical receiver or photo-sensitive device. In an example, walls of the quartz carrier material may include optical channels with a different refractive index than the quartz to act as waveguides or lightguides. In an example, the waveguides may be embedded into the quartz carrier material, for example as channels, conduits, or holes, and can be filled with a transparent material having a different refractive index to the quartz. The light guides can be used to guide light towards and away cavity for illumination or measurement purposes.

In an example, the low-dielectric constant carrier material may comprise a material that has a low-dielectric constant (low relative permittivity), high-temperature resistivity (about 400°C), electrically non-conductive properties, and preferably is also food-grade microwave-safe, for example a plastic, ceramic, or glass. A portion of the low-dielectric constant carrier material comprising the first and second electrodes may be structurally shaped to form a space or cavity that can be used as a heating chamber. The dielectric heating element, for example electrode pairs forming the load capacitor, and/or the inductor can be placed on a surface or embedded inside the low-dielectric constant carrier material. In other examples, the low-dielectric constant carrier material may be a relatively soft, bendable material, for example a thin layer (e.g. less than 200pm) of low- dielectric (e.g. low relative permittivity) high-temperature resistant polymer, for example polyimide such as Kapton, for example PEI (Polyetherimide), more preferably PEEK (Polyether Ether Ketone) to thereby allow to bendably, foldably, or rollably form a heating chamber. This enables the low- dielectric constant carrier material to form a heater module/element, or at least a part thereof, by printed circuit board (PCB) manufacturing techniques.

In some examples, the low-dielectric constant carrier material comprises low-dielectric microwave ceramics that can form a heating chamber and at the same time can be used as a substrate for the first and second electrodes and the inductor. In an example, the low-dielectric constant carrier material comprises one or more temperature sensors for measuring thermal radiation. In some examples, the one or more temperature sensors may comprise one or more temperature sensing tracks made from a material having a temperature dependent resistance configured to measure a temperature inside or adjacent to the load capacitor formed by the first and second electrodes. In this respect, resistance temperature detector (RTD) technology can be used and integrated to the low-dielectric carrier material. The conductor tracks may be formed based on known printing techniques (e.g. flex PCB manufacturing techniques). In some examples, the one or more temperature sensing tracks are formed from of PT100 or PT1000 sensing material. In some examples, a first portion of a temperature sensing track may be made of a first material and a second portion of the temperature sensing track may be formed of a second material having less temperature-dependent resistivity than the first material - e.g., a lower temperature coefficient of resistance (TCR). For example, the second material may comprise one of copper, aluminum. The second material may have a larger cross-section than the first material. The first material may be made of a high TCR material such as steel, or other alloy. In some examples, the first portion of the temperature sensing track may be the temperature sensing portion of the temperature sensing track. In some examples, the temperature sensing track may be provided on the surface of the low- dielectric constant carrier material in the vicinity of the load capacitor. In other examples, the temperature sensing track may be embedded in the low-dielectric constant carrier material in the vicinity of the load capacitor. In some examples, the temperature sensing track may be provided on the low-dielectric constant carrier material below the first electrode, or the second electrode, or both. In an example, the low-dielectric constant carrier material comprises one or more time-of-flight sensors for measuring stick presence.

The above described low-dielectric constant carrier materials may further comprise a second inductor electrically interconnected to the second electrode. The second inductor may be configured to form a mutual inductive coupling with the first inductor. In some examples, the second inductor may be provided on an opposite side of the low-dielectric constant carrier material to the first inductor. In some examples, the low-dielectric constant carrier material may comprise a magnetic core extending through low-dielectric constant carrier material through the first and second inductors to facilitate a stronger mutual inductive coupling. The first and second inductor may comprise any of the features described above in relation to inductors.

The above described low-dielectric constant carrier materials may further comprise any other components of the above described oscillation circuits, including but not limited to, further components of the feedback loop, the switching unit, the delay element and or the biasing unit.

The low-dielectric constant carrier material may comprise additional functional or structural layers, for example a metallic layer that can serve both as heat shielding and reflecting layer, and as electromagnetic shielding layer. Preferably, the heat shielding and reflecting layer covers an entire surface extension of the first and second electrodes. In another variant, an additional sensing layer can be provided to integrate temperature sensors and interconnection tracks for the measurement signals and sensor power supply lines.

It is to be appreciated that the features of the above examples of the disclosure are complementary with one another, except where stated otherwise, and so features of different examples may be readily implemented in the oscillation circuits of other examples. Further optional examples of the disclosure are set out below.

Examples

Ex 1 . An aerosol-generating device for dielectrically heating an aerosol-forming substrate, the device comprising an oscillation circuit.

Ex 2. The aerosol-generating device according to Ex1 , wherein the oscillation circuit comprises: a switching unit; and a feedback loop connected to the switching unit, the feedback loop comprising two electrical contacts configured to interconnect with an electrode arrangement that forms a load capacitor for dielectrically heating the aerosol-forming substrate.

Ex 5. The aerosol-generating device according to Ex2, wherein the switching unit is configured for inverting operation, wherein the feedback loop is configured to perform resonant oscillating operation and configured to provide a 180° phase shift between an output signal of the switching unit and an input switching signal of the switching unit. Ex 6. The aerosol-generating device according to any of Ex2 to Ex5, wherein the feedback loop comprises a capacitive element providing for a 90 degrees phase shift to a signal from the feedback loop.

Ex 7. The aerosol-generating device according to Ex6, wherein the capacitive element comprises a capacitor connected to ground.

Ex 8. The aerosol-generating device according to any of Ex2 to Ex7, wherein the feedback loop with the two electrical contacts is configured to operate as an inductive load at an operating frequency of the oscillation circuit.

Ex 9. The aerosol-generating device according to any of Ex2 to Ex8, wherein the feedback loop comprises a resonant circuit comprising the two electrical contacts, the resonant circuit providing for a 90 degrees phase shift circuit at an operating frequency of the oscillation circuit.

Ex 10. The aerosol-generating device according to Ex9, wherein the resonant circuit comprises one of a parallel resonant circuit, a series resonant circuit, or a combination thereof.

Ex 1 1. The aerosol-generating device according to Ex9, wherein the feedback loop comprises a parallel resonant circuit with the two electrical contacts connected in parallel with an inductor, the parallel resonant circuit being electrically stimulated by the output signal of the switching unit.

Ex 12. The aerosol-generating device according to Ex11 , wherein the output signal of the switching unit is a switched voltage across a transistor.

Ex 13. The aerosol-generating device according to any of Ex2 to Ex12, wherein the feedback loop is suspended between a power supply and ground.

Ex 14. The aerosol-generating device according to any of Ex2 to Ex13, wherein the switching device comprises a single transistor.

Ex 15. The aerosol-generating device according to any of Ex2 to Ex14, wherein the transistor is an bipolar junction transistor (BJT) and the feedback loop is connected between the collector or emitter and the base of the BJT. Ex 16. The aerosol-generating device according to any of Ex2 to Ex14, wherein the transistor is an field effect transistor (FET) and the feedback loop is connected between the drain or source and gate of the FET.

Ex 17. The aerosol-generating device according to any of Ex15 or 16, further comprising a capacitor connected between the base or gate of the transistor and electrical ground.

Ex 18. The aerosol-generating device according to any of Ex2 to Ex17, further comprising an RF choke inductor between the an output terminal of the switching unit and a supply voltage of the oscillation circuit.

Ex 19. The aerosol-generating device according to any preceding Ex, wherein the oscillation circuit is self-oscillating.

Ex 20. The aerosol-generating device according to any of Ex2 to Ex19, wherein the feedback loop does not comprise a voltage transformer.

Ex 21 . The aerosol-generating device according to any preceding Ex, wherein the oscillation circuit is configured such that the ratio of the dielectric heating losses in the load capacitor to the switching losses in the switching unit is greater than 11 :9, preferably greater than 13:7.

Ex 22. The aerosol-generating device according to any preceding Ex, wherein the oscillation circuit is configured to operate a frequency of between 100MHz-2.5GHz.

Ex 23. The aerosol-generating device according to any of Ex2 to Ex22, further comprising a capacitor connected between an output terminal of the switching unit and ground, the capacitor having a capacitance value that is bigger than an intrinsic capacitance of the switching unit.

Ex 24. The aerosol-generating device according to any of Ex2 to Ex23, wherein the oscillation circuit is configured such that, during operation, a peak AC voltage across the two electrical contacts is greater than a supply voltage of the oscillation circuit.

Ex 25. The aerosol-generating device according to Ex24, wherein the oscillation circuit is configured such that, during operation, the peak AC voltage across the two electrical contacts is greater than five times the supply voltage of the oscillation circuit. Ex 26. The aerosol-generating device according to any of Ex2 to Ex25, wherein the oscillation circuit further comprises a delay element configured to impede a switching speed of the switching unit.

Ex 27. The aerosol-generating device according to Ex26, wherein the two electrical contacts form a resonant circuit, wherein the delay element is configured such that an oscillation frequency of the oscillation circuit is below a parallel resonant frequency fPAR of the resonant circuit and above a series resonant frequency fSER of the resonant circuit.

Ex 28. The aerosol-generating device according to Ex27, wherein the time delay caused by delay element is between 5% to 35% of the period of the parallel resonant frequency fPAR of the resonant circuit.

Ex 29. The aerosol-generating device according to claim Ex27, wherein the time delay caused by delay element is between 35% and 90% of a difference between the period of the parallel resonant frequency fPAR and the period of the series resonant frequency fSER, preferably between 50% and 85% of a difference between the period of the parallel resonant frequency fPAR and the period of the series resonant frequency fSER of the resonant circuit.

Ex 30. The aerosol-generating device according to any of Ex26 to Ex29, wherein the delay element is configured to impose a time delay of between 50 and 500 picoseconds, preferably between 150 and 350 picoseconds, more preferably between 200 and 300 picoseconds.

Ex 31 . The aerosol-generating device according to any of Ex26 to Ex30, wherein the delay element comprises a low-pass filter.

Ex 32. The aerosol-generating device according to any of Ex26 to Ex30, wherein the delay element comprises a meandering electrically conductive element.

Ex 33. The aerosol-generating device according to Ex32, wherein the meandering electrically conductive element comprises between two and twelve meandering branches, preferably between three and ten meandering branches, more preferably three meandering branches.

Ex 34. The aerosol-generating device according to any of Ex32 or Ex33, wherein the meandering electrically conductive element comprises one of an omega-shaped coil, a single planar coil, a flat inductor, a wavy line, a zig-zag line, or a sawtooth line. Ex 35. The aerosol-generating device according to any of Ex2 to Ex34, wherein the feedback loop comprises a first inductor connected in series with one of the two electrical contacts.

Ex 36. The aerosol-generating device according to Ex35, wherein the first inductor comprises no more than five turns.

Ex 37. The aerosol-generating device according to any Ex36, wherein the first inductor comprises no more than three turns.

Ex 38. The aerosol-generating device according to any Ex37, wherein the first inductor comprises no more than one turns.

Ex 39. The aerosol-generating device according to any of Ex35 to Ex38, wherein the feedback loop further comprises a second inductor, wherein the two electrical contacts are connected in series between the first inductor and the second inductor.

Ex 40. The aerosol-generating device according to Ex39, wherein the second inductor comprises the same number of turns as the first inductor.

Ex 41. The aerosol-generating device according to any of Ex39 to Ex40, wherein a coil axis of the first inductor is arranged to be in parallel with and offset from a coil axis of the second inductor.

Ex 42. The aerosol-generating device according to any of Ex39 to Ex41 , wherein the first inductor and the second inductor are formed as planar inductors.

Ex 43. The aerosol-generating device according to any of Ex39 to Ex41 , wherein a coil axis of the first inductor is arranged to coaxially align with a coil axis of the second inductor.

Ex 44. The aerosol-generating device according to any of Ex39 to Ex43, wherein the feedback loop is configured such that a mutual inductive coupling is formed between the first inductor and the second inductor.

Ex 45. The aerosol-generating device according to Ex44, wherein the mutual inductive coupling is between 40% and 70%, and optionally between 50% and 60%. Ex 46. The aerosol-generating device according to any of Ex44 to Ex45, wherein the mutual inductive coupling between the first inductor and the second inductor is achieved without a magnetic core.

Ex 47. The aerosol-generating device according to any of Ex44 to Ex45, further comprising a magnetic core extending through the first inductor and the second inductor to provide the mutual inductive coupling.

Ex 48. The aerosol-generating device according to any of Ex2 to Ex47, wherein the feedback loop has substantially the same impedance as the switching unit.

Ex 49. The aerosol-generating device according to any of Ex2 to Ex48, further comprising the electrode arrangement fixedly interconnected to the two electrical contacts and to form the load capacitor, the load capacitor including or being configured to removably receive an aerosol-forming substrate.

Ex 50. The aerosol-generating device according to any of Ex2 to Ex48, further comprising the electrode arrangement removably interconnected to the two electrical contacts to form the load capacitor, the load capacitor including or being configured to removably receive an aerosol-forming substrate.

Ex 51 . The aerosol-generating device according to Ex49 or Ex50, wherein the electrode arrangement comprises a first electrode coaxially aligned with a second electrode.

Ex 52. The aerosol-generating device according to Ex51 , wherein the first electrode comprises a tubular body having hollow center and the second electrode comprises a rod or pin situated within the hollow center of the first electrode.

Ex 53. The aerosol-generating device according to Ex52, wherein the tubular body of the first electrode comprises one or more openings.

Ex 54. The aerosol-generating device according to any of Ex51 to Ex53, wherein the first electrode comprises a tubular body having a hollow center and the second electrode comprises a tubular body having a hollow center, wherein the second electrode is situated within the hollow center of the first electrode. Ex 55. The aerosol-generating device according to Ex54, wherein the tubular body of the second electrode comprises one or more openings.

Ex 56. The aerosol-generating device according to any of Ex51 to Ex53, wherein the first electrode comprises a plurality of axially aligned electrode rings and the second electrode comprises a rod or pin extending through the plurality of axially aligned electrode rings.

Ex 57. The aerosol-generating device according to Ex56, wherein the device is configured to independently energize one or more of the plurality of axially aligned electrode rings for providing sectional dielectric heating.

Ex 58. The aerosol-generating device according to Ex57, wherein the device is configured to independently energize each of the plurality of axially aligned electrode rings for providing sectional dielectric heating.

Ex 59. The aerosol-generating device according to Ex49 or Ex50, wherein the electrode arrangement comprises a first electrode interdigitated with a second electrode.

Ex 60. The aerosol-generating device according to Ex59, wherein the electrode arrangement forms a flat plate.

Ex 61 . The aerosol-generating device according to any of Ex59 to Ex60, wherein the first electrode and the second electrode each comprise a plurality of electrode portions, wherein the electrode arrangement comprises: a first plate comprising a first electrode portion interdigitated with a second electrode portion; and a second plate comprising a first electrode portion interdigitated with a second electrode portion.

Ex 62. The aerosol-generating device according to any of Ex59 to Ex61 , wherein the first electrode and the second electrode each comprise a cylindrical segment configured to interdigitate with the cylindrical segment of the other electrode around a cylindrical axis.

Ex 63. The aerosol-generating device according to Ex62, wherein the first electrode comprises a first plurality of cylindrical segments and the second electrode comprises a second plurality of cylindrical segments, wherein each of the first plurality of cylindrical segments are positioned around the cylindrical axis separated by one of the second plurality of cylindrical segments. Ex 64. The aerosol-generating device according to Ex63, wherein the device is configured to independently energize one or more of the first plurality cylindrical segments for providing sectional dielectric heating.

Ex 65. The aerosol-generating device according to Ex64, wherein the device is further configured to independently energize one or more of the second plurality cylindrical segments for providing sectional dielectric heating.

Ex 66. The aerosol-generating device according to any of Ex59 to Ex61 , wherein the first electrode comprises a first plurality of axially aligned electrode rings and the second electrode comprises a second plurality of axially aligned electrode rings, wherein each of the first plurality of electrode rings are separated by one of the second plurality of electrode rings.

Ex 67. The aerosol-generating device according to Ex66, wherein the device is configured to independently energize one or more of the first plurality of electrode rings for providing sectional dielectric heating.

Ex 68. The aerosol-generating device according to Ex67, wherein the device is further configured to independently energize one or more of the second plurality of electrode rings for providing sectional dielectric heating.

Ex 69. An aerosol-generating system comprising: an aerosol-generating device according to any preceding Ex; and a load capacitor comprising an aerosol-forming substrate.

Ex 70. An aerosol-generating device dielectric heating circuit, the circuit comprising: a first electrode configured to form a first part of a load capacitor; a second electrode configured to form a second part of the load capacitor; and a first inductor electrically coupled to the first electrode, wherein the first electrode, the second electrode and the first inductor are situated on a low- dielectric constant carrier material, wherein the low dielectric constant carrier material is configured to removably receive an aerosol-forming substrate between or adjacent to the first electrode and the second electrode for dielectric heating. Ex 71 . A method of manufacturing a dielectric heater for an aerosol-generating device, the method comprising: providing a first electrode configured to form a part of a load capacitor C1 on a flexible low- dielectric substrate; providing a second electrode configured to form another part of the load capacitor C1 on the low- dielectric substrate; electrically coupling a planar inductor L1 to the first electrode; and bending or rolling the low-dielectric substrate such that the first electrode and the second electrode at least partially face each other.

Any of all the features of the above described oscillation circuit may be provided on a single low dielectric constant carrier material.

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-b are a schematic illustrations 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 degrees phase shift;

Figure 3c 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 degrees 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 11 A-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;

Figure 12A-D are schematic illustrations of an electrode arrangement having variable polarity control, according to embodiments of the disclosure;

Figure 13a-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 14A-C are isometric illustrations of coaxial electrode arrangements for use in the oscillation circuit of Figures 2 to 4, according to embodiments of the disclosure;

Figure 15 is a schematic illustration of an electrode arrangement and inductor formed on a low dielectric flexible substrate, according to embodiments of the disclosure;

Figure 16A is a schematic illustration of an electrode arrangement and two inductively coupled inductors formed on a low dielectric flexible substrate, according to embodiments of the disclosure;

Figure 16B is a schematic illustration of the electrode arrangement of figure 16A comprising a temperature sensing system for measuring a temperature at different locations with the electrode arrangement, according to embodiments of the disclosure;

Figure 16C is a schematic illustration of electrode arrangements provided on a flexible carrier material for installing around a low-dielectric chamber comprising a substrate for dielectric heating, according to embodiments of the disclosure;

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

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

Figure 19 is a schematic illustration of an alternative temperature sensing system for detecting a temperature of an aerosol-forming substrate situated with the electrode arrangement, according to embodiments of the disclosure; Figure 20 is a schematic illustration of a control system utilizing a temperature sensing system for control the power delivered to an aerosol-forming substrate based on a detected aerosolforming substrate temperature;

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

Figure 22 is a schematic illustration of a control system utilizing a frequency sensing system for 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 embodiments of the disclosure.

Specific Description

Figure 1 is a schematic illustration of a dielectric heating aerosol-generating system 100 according to an embodiment of the disclosure. The system 100 comprises an article 105 comprising an aerosol-forming substrate 110 and an aerosol-generating device 120 for heating the aerosolforming substrate 110. The aerosol-generating device 120 comprises a first electrode 130 and a second electrode 135 separated by a cavity 140 for receiving the article 105. The cavity 140 and the article 105 are sized such that the aerosol-forming substrate 1 10 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 1 10. In such embodiments, a cavity between the first and second electrical contacts 160, 165 is sized such that, when the aerosol-forming article 105 is housed within the cavity 140, an electrical connection is made between the first electrode 130 and the first electrical contact 160, and the second electrode 135 and the second electrical contact 165.

In some embodiments, the width of the article 105 comprising the aerosol-forming substrate 110 is slightly greater than the spacing between the first electrode 130 and the second electrode 135, such that the distal end of the aerosol-generating substrate 110 is slightly compressed between the first electrode 130 and the second electrode 135. In some embodiments, the article 105, in an initial, uncompressed form has a width between 5-30% larger than the distance between the first electrode 130 and the second electrode 135. This may reduce or prevent the build-up of air between the first electrode 130 and the second electrode 135 when the aerosol-forming article 105 is received in the cavity 140, and decrease a distance between first and second electrodes 130, 135 for dielectric heating, thereby improving dielectric properties of the load capacitor CL and the accuracy of any measurements or determinations of the dielectric properties of the aerosol-forming substrate 110 performed by the aerosol-generating device 120. The aerosol-forming substrate 110 may comprise tobacco-based or non-tobacco based materials having an aerosol forming material therein and one or more active agents or ingredients, such as nicotine, pharmaceutical, botanicals, flavorants, liquid substrates with one or more active agents or ingredients, or a combination thereof. The aerosol-forming substrate 110 can also be a liquid aerosol-forming substrate and thereby the aerosol-forming article 105 can be in the form of a cartridge, capsule, or liquid container, and the electrodes 130, 135 can be configured as a wicking element or capillary element for liquid transfer. For example, it is possible that first and second electrodes 130, 135 form a capillary structure that is part of the aerosol-forming article 105 or reaches into an inner volume of the aerosol-forming article 105 that can heat and vaporize a liquid aerosolforming substrate 110 located in the inner volume. For example, the first and second electrodes 130, 135 can be embodied as parallelly arranged plates separated by a distance that forms a capillary channel, for example in a range between 0.1 mm to 2mm, depending on the desired capillary strength or rise. The first and second electrodes can be arranged as two matrices or arrays of pinlike, rod-like, or tab-like electrodes with opposite polarity, the two matrices or arrays interposed between each other, forming a capillary structure therebetween, for example with an average distance between neighboring pin-like electrodes being in a range between 0.1 mm to 2mm, depending on the desired capillary strength or rise. In another variant, the wicking element can be a separate element that is interposed between two electrodes 130, 135, for example flat or slightly curved electrodes 130, 135.

The aerosol-generating device 120 further comprises a power supply 170 and a controller 180 electrically coupled to the oscillation circuit 150. In this embodiment, the power supply 170 can be a rechargeable lithium ion battery, for example with one or more lithium ion battery cells, and the aerosol-generating device 120 comprises a power connector that enables the aerosol-generating device 120 to be connected to a mains power supply for recharging the power supply. Providing the aerosol-generating device 120 with a power supply, such as a battery, enables the aerosolgenerating device 120 to be portable and used outdoors or in locations in which a mains power supply is not available.

In use, power is supplied to the oscillation circuit 150 from the power supply 170 when a user activates the aerosol-generating device 120. In this embodiment, the 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 aerosol-forming substrate 110 in the cavity 140, releasing volatile compounds.

The aerosol-generating system 100 is also configured for measuring a dielectric property of the aerosol-forming article 105 or the aerosol-forming substrate 1 10 using the electrodes 130, 135 that are employed for dielectric heating of the aerosol-forming substrate 110. In some examples, the first and second electrodes 130, 135 can be used for dielectric measurements, either during the heating process or separately to the heating process. In this embodiment, the aerosol-generating system 100 can be configured to determine the presence of the aerosol-forming article 105 between the first electrode 130 and the second electrode 135. The aerosol-generating system can be configured to measure a dielectric property, for example an instant value, timely-evolution, or change of a dielectric property, for example to determine whether the aerosol-forming article 105 meets specific criteria or is an authentic substrate. The aerosol-generating system in this example is also configured to control the heating of the aerosol-forming substrate 110 based on the measured dielectric property of the aerosol-forming article 105.

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

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

The feedback loop 270 is configured to be self-oscillating and will oscillate at or close to a given resonance frequency determined by the values of the passive components of the feedback loop 270. Feedback loop 270 is configured to provide a 180° phase shift from the output UOUT to input UIN of switching unit 260 for oscillation, and in addition, the transistor T is configured for inverting operation. As shown in Figures 3a and 3b, feedback loop 270 includes a resonant circuit 272 comprising the load capacitor CL providing for a first 90 degrees phase shift or quarter wave shift to the feedback signal. Feedback loop 270 further includes a capacitive element 274 providing for a second 90 degrees 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 degrees. Switching unit 260 is itself configured for inverted switching operation to provide a 180 degree phase shift between the input UIN and the output UOUT of the switching unit 260.

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

In an alternative embodiment, resonant circuit 272 may include a resonant cavity 272, as illustrated in Figure 3c. The resonant circuit 272 including resonant cavity may have an interior volume configured to receive an aerosol-forming substrate 1 10, for example having an opening for inserting an aerosol-forming substrate 1 10. In an example, the resonant circuit 272 including resonant cavity can be configured as a A/4 resonator. The resonant circuit 272 including resonant cavity may be configured to behave like an RLC circuit. The inductor L and the capacitor C are arranged in parallel to each other, to have a parallel resonance or a frequency close to the parallel resonance that can be stimulated by the switching unit 260. Resonant circuit 272 including cavity may be coupled to the feedback loop 270 using one or more of a capacitive coupling, an inductive antenna coupling (magnetic coupling), a direct electric coupling, or a window coupling (e.g. coupling with a loop).

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

Figure 4 illustrates an oscillation circuit 350 according to a non-limiting, exemplary embodiment of the disclosure. Oscillation circuit 350 comprises a switching unit 260 in the form of a transistor T having an intrinsic capacitance Ci. Moreover, transistor T is configured for inverting operation, for example as an inverting common source FET, MOSFET, or a common emitter BJT. The source terminal of transistor T can be coupled to a DC power supply via a choke 280. Between the gate and source terminals of transistor T extends a feedback loop 270. The feedback loop 270 comprises a resonant circuit 272 including a load capacitor CL having a first and second electrode 130, 135 separated by an aerosol-forming substrate 110. In the variant shown, the resonator circuit 272 is also connected to ground via a delay line D and a capacitor C2 connected in series to the delay line D . 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 D 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 oscillation circuit 350 remains in a predefined frequency operating range to provide for the requisite inverted or 90° phase shifted feedback and also to make sure that the feedback loop has a low impedance to provide for a high gain, as described in greater detail below.

The oscillation circuit 350 is shown with electrical contacts 160, 165 that are arranged on each side of the load capacitor CL. In some embodiments, the first and second electrodes 130, 135 may be removable from the oscillation circuit 350, or may form part of the aerosol-forming article 110. In such embodiments, electrical contacts 160, 165 provide an electrical connection between the first and second electrode 130, 135 and the feedback loop 270. In embodiments where the load capacitor CL is fixed within the feedback loop 270, for example, such that an aerosol-forming substrate 1 10 can be inserted and removed to and from a cavity formed in between the first and second electrodes 130, 135, electrical contacts 160, 165 provide electrical connections from the first and second electrodes to the next components in the feedback loop 270, e.g. inductors Li and L₂.

With respect to the power supply voltage, a DC power supply voltage is provided, that is preferably in a range that is suitable for battery operation with one or more standard battery cells. Preferably, the DC power supply voltage is below 14V. For example, it is possible to operate the oscillation circuit 350 on a single battery cell, for example an 18650 battery cell (Li-Ion), or a similar battery cell, that provides for 3.2V to 3.9V. However, more preferably, a voltage of one battery cell of an exemplary 3.5V to 7V for power supply can be boosted, for example by a DC-DC converter (e.g. a boost circuit), or a voltage doubler. Alternatively or in addition, two or more battery cells can be used in series, or other configurations or arrangements that allows to increase a voltage from one or more battery cell can be used. It is also possible to have a controllable output voltage (e.g. DC- DC converter, voltage regulator), to control the temperature of heating by a change to the DC supply voltage, or to boost the voltage (for example to 10-12V) for maximum power at the preheating stage, to speed up the preheating stage with the goal to reach the aerosolization temperature quickly. Control of the DC supply voltage is one way that makes it possible to rapidly change heating power despite the oscillation circuit 350 freely oscillating.

A capacitor Ci is arranged in parallel to the transistor T and therefore in parallel with the intrinsic capacitor of the transistor T (e.g. a field effect transistor). This facilitates a less voltagedependent oscillation and frequency, stabilizes the oscillation, and also improves the overall dielectric heating efficiency. Capacitance of capacitor Ci is chosen to be larger than the maximal intrinsic capacitor Ci of transistor T at the operating conditions, so that the variation of the intrinsic transistor based on frequency, temperature, etc. has much less or negligible influence on the feedback loop 270. For example, in a non-limiting embodiment, the value can be in a range between 2pF to 10OpF, more preferably in a range between 5pF and 50pF.

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

Resonant circuit 272, together with capacitive element 274, provides for a 180° phase shift and a voltage gain from the output UOUT to the input UIN, and transistor T (for example a FET) is configured for inverting operation, thereby also providing for another 180° phase shift. This results in a resonant or close-to resonant oscillation and an amplified voltage UL across the electrodes 130 and 135 of the load capacitor CL, as compared to the DC supply voltage. When operating close to resonance, the resonant circuit 272 circuit behaves inductively, having a high Q factor. Furthermore, the feedback loop 270 is impedance-matched with the transistor T, 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.

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

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

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

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

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

In a non-limiting example starting from the split inductor Li and L₂ of the resonant circuit of Figure 5D, inductors Li and L₂ can be mutually magnetically coupled to form a mutual inductance M, thereby forming the parallel circuit branch or second branch of the resonant circuit 272, as shown in Figure 5E. The mutual magnetic coupling can be achieved by the close proximity of the two inductors L1 and L2 with alignment of winding axis of the coils, or by use of a mutual magnetic core, or both. This has the advantage of providing a parallel-resonator circuit PRC without the use of additional wires for the second branch, and without additional windings or separate magnetic cores for a second parallelly-arranged inductor. This also allows for a symmetric arrangement that favors and facilitates the inductive coupling of the two inductors Li, L₂ and the balancing of the voltage UL over load capacitor CL. The symmetry of the two branches in either direction with first branch Li - CL - L₂ and the second branch with inductor L_E, 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, L_E could be in a range between 7nH and 30nH, more preferably between 10nH and 20nH, and the value of the load capacitor can be in a range between 0.5pF to 5pF, more preferably between 1 pF to 3pF.

The resonant circuit 272 can be configured as another type of tank circuit providing for the 90° phase shift in a given frequency range. In one embodiment, the resonant circuit 272 can be implemented as a series resonant circuit, having the load capacitor CL connected in series with one or more inductive elements, configured to provide for an inductive response or 90 degrees 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 voltage applied to the load capacitor CL. However, higher switching frequencies f_s lead to greater switching losses in the transistor. Where very high switching frequencies are used, e.g. 1 GHz or more, expensive circuit designs are necessary to make the circuit operable (e.g. GaAn transistors, GHz-type circuit design e.g.).

To compensate for a lower switching frequency, a higher oscillation AC voltage UL (for example measured by the RMS or peak voltage) can be provided across the load capacitor CL to deliver the necessary power to the load capacitor CL. When a balance has to be struck between increasing the switching frequency f_s and increasing the voltage over the load capacitor CL in order to increase the heating power (and therefore dielectric losses PL in the load capacitor CL which can include the aerosol-forming substrate 110), the voltage increase has a stronger effect on the heating power than frequency increase, as voltage has a second order relationship with power. The dielectric losses in load capacitor CL are also dependent on the distance separating the two electrodes 130 and 135, which influences the electric field strength E_F across the aerosol-forming substrate 1 10.

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 E_F, for a hand-held and human-operated portable device The electric field strength is dependent on voltage UL applied to capacitor CL and a maximal distance d between the first and second electrodes 130, 135.

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

Preferably, during 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 Ei 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 1 10 between the first and second electrodes 130, 135. More than 6-7W of power losses is not desirable for a handheld device. Preferably the aerosol-generating device is configured such that there are less than 5W of losses during nominal heating operation or any other operation lasting for more than 30 seconds. The average dielectric heating power density provided by the aerosol-generating device may be in a range between 1 W/cm3 to 25W/cm3 per volume of aerosol-forming substrate material over a time period of less than 15 minutes, preferably between 1.5W/cm3 and 15W/cm3. During an initial start-up phase, the average dielectric heating power density may be controlled or set to operate in a range between 7W/cm3 to 25W/cm3. During a nominal (maintenance) heating phase, the average dielectric heating power density may be controlled or set to operate in a range between 1 W/cm3 to 7W/cm3. Preferably, during the start-up phase, the average dielectric heating power density is controlled or set to operate in a range between 8W/cm3 to 20W/cm3. Preferably, during the nominal heating phase the average dielectric heating power density is controlled or set to operate in a range between 1 W/cm3 to 5W/cm3.

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

Oscillations in the feedback loop 270 will be naturally drawn towards the parallel resonance (antiresonant) frequency of the resonant circuit 272. However, the addition of a delay line D can introduce a slight time delay limiting the oscillation frequency below the parallel resonance frequency. Figure 6 shows a frequency analyzer plot of an exemplary resonant circuit 272, specifically a plot of a parallel resonator circuit PRC showing the relationship between the oscillation frequency (with a series resonance at 855 MHz and a parallel resonance at 1 .246 GHz), the phase shift across the PRC (with a relatively flat inductive 90° degrees 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 f_PAR is reached. After the parallel resonance frequency fp_AR, the phase shift response drops below 0° to capacitive behavior and the impedance is very high, e.g. 2.4kO. 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. The impedance of the resonant circuits at the operating frequency of the oscillation circuit may be between 0.5Q and 10O, preferably between 10 and 50, and more preferably, between 1.50 and 30. The parallel resonance frequency f_PAR can be above 1 GHz, e.g. 1 GHz to 1.5GHz, while the actual switching frequency fs can be below 1 GHz, and this lower switching frequency is caused by the delay line DL.

Ideally, the oscillation frequency fs should be set to be below the parallel resonance frequency f_PAR but above the series resonance frequency fsER, to make sure that two conditions are fulfilled, firstly (i) that the resonant circuit behaves inductively to provide a 90° phase shift, and secondly (ii) to make sure that the impedance of the resonant circuit (an therefore the feedback loop 270) is low, as illustrated in the graphs of FIG. 6. For example, a resulting impedance of the feedback loop at the oscillation frequency fs of the oscillation circuit can be in a range of approximately 10OmQ to 2Q. Preferably, the delay line DL is configured such that the oscillation frequency fs is closer to the series resonance frequency fsER than to the parallel resonance frequency 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 delay line DL needs to be relatively short, as the series resonance and the parallel resonance of a parallel oscillating circuit PRC are close to each other, relative to the overall frequency range. Preferably, the delay caused by delay line DL that acts of feedback loop 270 should be in a range between 5% to 35% of the period of the parallel resonance frequency f_PAR, providing that the above two conditions (i) and (ii) are fulfilled. In an embodiment, the delay caused by the delay line DL that acts on feedback loop 270 is in a range between 35% and 90% of a difference between the period of the parallel resonance frequency f_PAR and the period of the series resonance frequency fsER, again providing that the above two conditions (i) and (ii) are fulfilled, more preferably a range between 50% and 85%. For example, taking the illustration of FIG. 6 and as a non-limiting numerical example, assuming that a parallel resonance frequency is at 1 .25 GHz, therefore having a period of 800ps (picoseconds), and a series resonance is at 855MHZ, and therefore a period of 1 169ps, there is a difference of 369ps between the period of f_PAR and fsER. The time delay caused by delay line DL can be in the above range, for example at 70% of the period difference between f_PAR and fsER, thereby being 258ps, thereby making sure that the feedback loop 270 has the desired inductive behavior and low impedance that is necessary to provide inverting feedback at high gain.

Preferably, the delay line is implemented as a meandering conductive element having dominantly inductive behavior, for example a meandering element having from two (2) to twelve (12) meandering branches, more preferably from three (3) to eight (8) meandering branches. Such implementations exhibit minimal stray inductive and capacitive behavior. Various delay line structures can be used to provide the desired function, for example an Omega-shaped coil, single planar coil, flat inductor, wavy line, zig-zag line, or a sawtooth line. It is also possible to provide the required delay line functionality by a specific transmission line design. For example, it is possible that the physical element of the delay line DL is implemented as a conductor in a printed circuit board, for example implemented as a microstrip patch antenna. In some embodiments, a low-pass filter may be used as the delay line DL, however this will have an impact on the shape of the oscillating voltage, whereas a delay line DL that provides for a short time delay by inductive effect will not impact the wave shape. In the embodiment illustrated in Figure 4, delay line DL is placed between the feedback loop output of the resonant circuit 272 and capacitive element 274, but other arrangements are also possible. Figures 7A-C are isometric illustrations of a split coil resonator having a mutual inductive coupling for use in the oscillation circuit of Figures 2 to 4, according to embodiments of the disclosure. In the example of Figure 7A, the two inductors Li and L₂, are each formed as a single winding, e.g. a single loop coil. The winding central axis of each coil substantially coincides with each other, and the plane formed by each single-winding inductor is parallel to the other, and is also in close proximity. This establishes a mutual inductance between inductors Li and L₂ without a magnetic core M_c. 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 M_c is present, around the core M_c 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 M_c, 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). 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 M_c is achieved via a u-shaped core with each leg traversing a center of each planar coil Li, L₂.

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

It is also possible that the mutual inductance M between Li and L₂ are created by simple proximity of the two inductor coils Li and L₂, without the use of a magnetic core M_c as illustrated in Figure 7C, or by inter-winding the coils of inductors Li and L₂. The electrode arrangement of Figure 7C comprises parallelly arranged electrode plates Ei 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 1 10. 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, thehe tubular structure can have a diameter between 5mm to 9mm. The tangential distance between the electrodes of opposite polarity can be between 0.5 mm to 3 mm, preferably between 0.7 mm to 12.2 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 1 10 positioned in a central cavity formed by the electrode arrangement. The electrode arrangement in Figures 1 1 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 1 10 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 1 1 B, which is configured such that electrical field between opposing polarity electrodes is strongest across the aerosol-forming substrate 1 10. Figures 1 1 C-D illustrate how the plurality of electrode portions from the electrode arrangements of Figure 11 A-B may be electrically connected to achieve an interdigitated configuration.

Figure 12A-D are schematic illustrations of an electrode arrangement having variable polarity control, according to embodiments of the disclosure. By the use of an analog signal demultiplexer or analog signal switch or an equivalent circuit, it is possible to selectively connect one or more pairs of electrodes to an oscillating feedback loop to deliver sectional heating to the load capacitor CL. In the illustrated embodiment, adjacent electrodes can be switched to have the same polarity, or opposing electrodes can be switched and reconfigured to the same polarity. This enables an oscillation circuit to switch between different electric field distribution patterns between the electrodes to adjust the heating profile across the aerosol-forming substrate 1 10. In the embodiment shown in Figures 12A to 12B, the electrodes form cylindrical segments that can be arranged around a cylindrically-shaped cavity for different electric-field patterns. This principle also works for other numbers of electrode pairs, e.g. two (2) pairs, three (3) pairs, or four (4) pairs, etc., and for sectional, zoned, or partial heating of areas or volumes of an aerosol-forming substrate 1 10. The analog signal switch or analog signal demultiplexer can be implemented electronically, mechanically, or electro- mechanically. For example, a semiconductor-based or solid state switch or demultiplexer can be based on JFET switches or a bilateral parallelly-arranged CMOS switch, combining PMOS and NMOS. An electromechanical based switch or demultiplexer can be based on a microelectromechanical systems (MEMS), for example using a RF MEMS switching technology, and a mechanical switch or demultiplexer can be based on relays, for example RF micro-relays. In some embodiments, more than one oscillation circuit may be used. For example, a separate oscillation circuit may be provided for each pair of electrodes in the electrode arrangement.

Figure 12D illustrates how electrodes of the electrode arrangement from the system of Figure 12C may be independently energized to provide sectional, zoned, or partial heating of a cylindrical substate 110. In the illustrated embodiment, there are four (4) opposing electrodes, each neighboring pair of electrodes configured to be connected to an oscillation circuit 150, 250, 350, or another type of oscillation circuit. This enables the selective heating of a segment area or zone of the cylindrical substrate 110 with heating zones HZ that can be moved by 90 degrees for each electrode pair. The size of the heating zones may be modified by changing the geometry of the electrodes or the number of electrode pairs in the electrode arrangement. For this configuration shown in Figure 12D and for other configurations that are intended to heat cylindrical consumables, an aerosol-forming article 105 comprising an aerosol-forming substrate 1 10 may form a hollow cylinder, having an interior hollow cylindrical volume. This aerosolforming article geometry may be beneficial since lower dielectric losses occur at areas that are located farther away from two electrode plates Ei and E₂ having opposite polarity. The inner hollow cylinder can have a diameter of that is in a range between 20% and 80% less that the outer diameter of the aerosol-forming article 105, more preferably in a range between 25% and 60% less that the outer diameter of the aerosol-forming article 105, even more preferably between 25% and 45% less that the outer diameter of the aerosol-forming article 105. In one embodiment, the inner core of the cylindrical aerosol-forming article 105 may be filled with an aerosol-forming material or a filler material that has a higher dielectric constant than the aerosol-forming material of the outer cylinder portion. In some embodiments, the inner core of the aerosol-forming article 105 could have a higher content of an aerosol-forming carrier liquid, such as glycerol or polypropene glycol (PPG), having high dielectric constants. Such an arrangement can increase the dielectric losses in the core area for further aerosol generation, or provide a filler material that could generated additional heat by dielectric losses, the heat capable of propagating from the inner core to the lateral sides into the outer cylindrical portion.

As another variant, it is also possible that a penetrating pin, rod, or blade is provided with the aerosol forming device 100, arranged centrally in the heating cavity. The penetrating pin, rod, or blade can be made or coated with a material having a high dielectric constant. The penetrating pin, rod, or blade can be configured and arranged such that it penetrates substantially into a central axis of the aerosol-forming substrate 110, when the aerosol-forming article 105 is inserted into the cavity. Preferably, the material chosen for the pin, rod, blade or the coating thereof should have a high dielectric constant, for example above 20, be non-conductive, and have good heat radiation properties and thermal stability, for example but not limited high-entropy or high dielectric ceramics. Such pin, rod, or blade could act as a passive heater that would heat up in the oscillating electric fields, improving the heating performance in the center of the cylindrical aerosol-forming article 105.

Figures 13A to 13C-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 13a comprises a reservoir housing a liquid aerosol-forming substate 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 substate into the channel. Figures 13b-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 13c, 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 13a, 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 substate into the electrode array.

Figure 14 shows isometric illustrations of coaxial electrode arrangements for use in the oscillation circuit of Figures 2 and 3, according to embodiments of the disclosure. The electrode arrangement of Figure 14A comprises a first electrode tube, pin, or rod Ei and a second electrode E₂ tube having a larger diameter than the first electrode tube, pin or rod Ei. The electrode arrangement is configured such that an aerosol-forming substrate may be situated between the first electrode Ei and second electrode E₂when coaxially aligned. Aerosol generated from the aerosolforming substrate 110 can escape in a direction that is parallel to the rotational or cylindrical axis of the substrate, or can also escape laterally from the cylindrically shaped second electrode E₂. However, it is also possible that the first electrode Ei can comprise one or more openings leading to a central airflow channel running through the centre of the first electrode Ei allowing the generated aerosol to escape laterally via the centrally-arranged electrode arrangement.

In another embodiment illustrated in Figure 14B, the first electrode Ei may be in the form of a rod situated within a tubular electrode E₂. In a variant, in order to enable generated aerosol to escape laterally by the electrode arrangement, the second electrode E₂ may comprise one or more openings, similar to the first electrode Ei of Figure 14A. Alternatively, the tubular electrode E₂ may not extend entirely around the first electrode Ei, thereby creating another region for generated aerosol to laterally escape the electrode arrangement. In the electrode arrangement illustrated in Figure 14B, tubular electrode E₂ comprises two electrode portions separated by a gap enabling zoned or sectional heating across the length of an aerosol-forming substrate 1 10 situated between the electrodes Ei and E₂. The two electrode portions of tubular electrode E₂ may share the same polarity or they may be independently energized with the use of an analog signal demultiplexer 11 10 or by the use of selectively applying signals of different oscillators 150, 250, 350 to provide sectional, zoned or partial heating of an aerosol-forming substrate situated between the first electrode Ei and the tubular electrode E₂.

Figure 14C illustrates another electrode arrangement in which the tubular or rod-like electrode E₂ comprises a plurality of electrode bands axially aligned with each other and coaxially aligned with a first electrode Ei. Similarly, to the electrode arrangement illustrated in Figure 14B, separation gaps can be provided between each of the plurality of electrode bands to enable generated aerosol to escape the electrode arrangement. The plurality of electrode bands of the tubular electrode E₂ may be independently oscillated to provide sectional, zoned or partial heating of an aerosol-forming substrate 110 situated between the first electrode Ei and the tubular or rod-like electrode E₂. Figure 14C also illustrates how the electrode arrangement can be integrated with an aerosol-generating device. A DC power supply 1090 is coupled to an oscillation circuit 1 100 which is directly connected to the first electrode Ei. In order to enable the plurality of electrode bands of the tubular electrode E₂ to be independently energized, the plurality of electrode bands can be connected to the oscillation circuit 1100 via an analog signal demultiplexer or analog signal switch 1110 and microprocessor 1120.

Figure 15 is a schematic illustration of an electrode arrangement and inductor formed on a low dielectric constant flexible carrier material, according to embodiments of the disclosure. The arrangement comprises a first and second electrode 1130, 1135 formed on a flexible low dielectric carrier material 1145. Flexible low dielectric constant carrier material 1 145 may comprise a polyimide, or other flexible, electrically insulating, high-temperature, and low dielectric material. In some embodiments, the flexible low dielectric constant carrier material 1 145 comprises a polyimide having a dielectric constant below 3.0, which may be produced by either changing its structure to lower the dielectric constant, or with use of low-dielectric fillers. For example, the intrinsic structure of the polyimide may be modified using one or more of fluorine-containing groups, non-planar large conjugated structures, alicyclic structures, or adding low-dielectric fillers such as fluorinated graphene, mica.

While the embodiment of Figure 15 shows an interdigitated electrode arrangement similar to those described above, other electrode arrangements may also be used. Furthermore, the first and second electrodes 1 130, 1135 do not need to be provided on the flexible low dielectric constant carrier material 1145 in a specific position, orientation, or with any fixed separation distance from each other. In some embodiments, the first and second electrodes 1 130, 1 135 are provided on the flexible low dielectric constant carrier material 1 145 in a first position in which the first and second electrodes 1130, 1 135 are not in alignment, then the flexible low dielectric constant carrier material 1145 is bent or rolled to move the first and second electrodes 1130, 1 135 to a second position in which there are aligned. The flexible low dielectric carrier material 1145 further comprises a first inductor Li electrically coupled to the first electrode 1 130 via a first electrical contact 1160. Although not shown in Figure 15, the flexible low dielectric constant carrier material 1 145 may also comprise a second inductor L₂ electrically coupled to the second electrode 1135 via a second electrical contact 1160. The second inductor L₂ may be provided on the opposite side of the flexible low dielectric constant carrier material 1 145 to the first inductor Li. Providing the electrode arrangement of the load capacitor CL, and other components of an oscillation circuit feedback loop on a single flexible carrier material may simplify the manufacturing process and reduce parasitic effects in the oscillation circuit.

Figure 16A is a schematic illustration of an electrode arrangement and two inductively coupled inductors Li, L₂ formed on a low dielectric constant flexible carrier material 1245, according to embodiments of the disclosure. Similarly to the arrangement in Figure 15, the arrangement comprises a first and second electrode 1230, 1235 formed on a flexible low dielectric constant carrier material 1245. The flexible low dielectric constant carrier material 1245 further comprises a first inductor Li electrically coupled to the first electrode 1230 and a second inductor L₂ electrically coupled to the second electrode 1235. The second inductor L₂ is provided on the opposite side of the flexible low dielectric constant carrier material 1245 to the first inductor Li aligned with the first inductor Li . In the illustrated embodiment, the first and second inductors Li, L₂ have an omega shape. The low dielectric constant flexible carrier material 1245 further comprises a perforation that traverses both the first and second centre of the first and second inductors Li and L₂. With this perforation, a magnetic core M_c can be positioned to extend through the centre of the first and second inductors Li, L₂, strengthening the mutual inductive coupling between them. In order to facilitate the close positioning of the two omega-shaped inductors Li and L₂, one interconnector may extend to the opposite side of the flexible low dielectric constant carrier material 1245 with a via or other traversing interconnector. In this embodiment, the electrodes 1230 and 1235 can be placed on one side of the low dielectric constant flexible substrate 1245, and thereby that portion of the substrate can be rolled to a certain radius so that the respective ends will match, while the inductors Li and L₂ are arranged on opposite sides of the substrate for alignment and inductive coupling to create a mutual inductance. This facilitates the formation of a cylindrical heating cavity with an integrated electric insulation layer. In some embodiments, further electrical insulation is provided to cover the metallic layers that form the electrodes, the interconnects, and the one or more inductors. Such electrical insulation could include an additional layer of flexible low dielectric constant carrier material, or could arise by fully embedding conductive structures into the flexible low dielectric constant carrier material 1245.

The low dielectric constant flexible carrier material 1245 can further comprise a temperature sensor 1250 configured to detect a temperature of an aerosol-forming substrate positioned between the first and second electrode 1230, 1235. Figure 16B illustrates an embodiment wherein temperature sensor 1250 comprises a temperature sensing track running between the first and second electrode 1230, 1235. The temperature sensing track comprises a first portion 1250a and a second portion 1250b. The first portion 1250a is formed from PT 1000 and the second portion 1250b is formed from PT100. The first portion 1250a and the second portion 1250b are each coupled to measurement terminals 1255a, 1255b, respectively, via return lines. The return lines may be formed from copper. Figure 16C illustrates embodiments in which the flexible carrier material 1245 is not a low dielectric material, but rather comprises a flex PCB configured to be wrapped around a heating chamber 1260 that is formed of a rigid, low-dielectric, high-temperature resistant, non-conductive material 1265. The flexible carrier material 1245 comprises a first electrode E1 and a second electrode E2 configured to be positioned on opposite sides of the heating chamber 1260 when the flexible carrier material 1245 is wrapped around the heating chamber 1260. In an examples, each of the first electrode E1 and the second electrode E2 may comprise a plurality of electrodes in order to form a plurality of electrode pairs around the heating chamber 1260.

In some embodiments, the low dielectric constant flexible carrier materials 1145, 1245 described above may comprise additional components or sections of the oscillation circuits described above, including a switching unit transistor T, and other passive components such as capacitors Ci, C2, the delay line DL, and sensors (optical, magnetic-field, electric-field), or circuit footprints for mounting such components. In this respect, most or all components of the oscillation circuit could be placed onto the same low dielectric constant flexible carrier material 1245, including switching transistor, resonant circuit, and capacitive elements, for example as surface-mounted elements, for high volume manufacturing and testing.

In the electrode arrangements of both Figure 15 and 16, the second inductor L₂ may be offset from the first inductor Li on the opposite side of the low dielectric constant flexible carrier material to reduce the parasitic capacitance between the two inductors Li, L₂.

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

In the illustrated embodiment, a first and second electrode 1330, 1335 is arranged on an outer surface of a cylindrical quartz glass substrate 1345 with the inner cylindrical volume defining a cavity 1340 for receiving an article 1305 comprising an aerosol-forming substrate 1310. Similar to the embodiments described above with respect to Figure 16, first and second inductors Li, L₂ are positioned on opposite sides of the quartz glass substrate 1345, with a magnetic core M_c extending through the center of the first and second inductors Li, L₂, strengthening the mutual inductive coupling between them.

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

In the embodiment of Figure 17, cavity 1340 is formed from the quartz glass substrate 1345, which provides an effective transparent protective layer for an optical measurement device 1350 provided on a surface of the quartz glass substrate 1345 (for example optocouplers) for measuring aerosol diffusion for puff detection. One or more temperature sensors may be provided on the quartz glass substrate 1345 for measuring thermal radiation. In the embodiment illustrated in Figure 17, a temperature sensing track 1360 is embedded within a heating region of the quartz glass substrate 1345. In other embodiments, temperature sensing track 1360 may be provided across an inner surface of cavity 1340. Temperature sensing track 1360 may comprise the same features described in relation to temperature sensing track 1250 in Figure 16b.

One or more time-of-flight sensors may be provided on the quartz glass substrate 1345 for measuring stick presence. Optical measurement device 1350 may comprise an optical emitter or light source 1354 and an optical receiver or photo-sensitive device 1353. The walls of the quartz glass substrate 1345 can include optical channels with a different refractive index than the quartz glass, to act as waveguides or lightguides 1351 and 1352. Waveguides 1351 and 1352 may be embedded into the quartz glass substrate 1345, for example as channels, conduits, or holes, and can be filled with a transparent material having a different refractive index to the quartz glass substrate 1345. The light guides 1351 and 1352 can be used to guide light towards and away cavity 1340 for illumination or measurement purposes.

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

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

Quartz glass can also be machined or otherwise processed to form different shapes and arrangements. Additional features beneficial to the electrode arrangement may be formed directly into the glass structure, such as ribs, grooves, and channels for optimizing airflow through the aerosol-generating device. In some embodiments, the upstream air intake comes from ribs and grooves that are arranged to be in parallel with a rotational axis of a heating chamber comprising the electrode arrangement. In such embodiments, it is possible to provide for a heating chamber that is defined by glass walls, allowing for external sensing of parameters (temperature, airflow, puffs, etc.) with optical means, such as an optical measurement device 1350. This permits easy cleaning and reduced deposition of contaminants to the inner surfaces, and also allows the integration of inductive cores and windings of inductors. Figure 18 is a schematic illustration of a temperature sensing system for detecting a temperature of an aerosol-forming substrate 1 10 situated within the electrode arrangement, according to embodiments of the disclosure. The system comprises a heat sensor 1850 communicatively coupled to a controller 1880. The heat sensor 1850 is configured to detect in a noncontact manner a temperature of an aerosol-forming substrate 110 situated between electrodes of an electrode arrangement and subject to dielectric heating as described above.

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

As illustrated in Figure 18, one way to measure the temperature is by using a non-contact sensor (such as a near infrared sensor (NIR)), to capture heat radiation from the aerosol-forming substrate 1 10, or from a plate/device 1890 at the aerosol-forming substrate 110 material that increases or homogenizes the heat radiation and has greater thermal conductive properties than the aerosol-forming substrate 110.

In other embodiments, the heat sensor 1850 may comprise a sensor which either penetrates or is physically coupled to the surface of the aerosol-forming substrate, as illustrated in Figure 19.

Another way to capture a value indicative of the temperature of the aerosol-forming substrate 1 10 is by measuring the temperature of the insulation/substrate material on which the electrode arrangement is placed, for example by measuring a temperature of the low dielectric constant flexible carrier material 1245.

For example, as discussed above with respect to Figures 15 and 16 the carrier material for mounting the opposing electrodes Ei, E₂ can be polyimide or PEEK or another high-temperature plastic material. The electrodes can be embedded or placed on a surface of such carrier material. While the dielectric constant (or relative permittivity) of such material could be lower than the aerosolforming substrate 1 10, it is still dielectric and therefore will heat, following a heating curve that is substantially proportional to the heating curve of the aerosol-forming substrate. This enables the temperature sensing system to determine a value indicative of the aerosol-forming substrate temperature based on a measured temperature of the carrier material on which the load capacitor CL is placed. This may be measured using a semiconductor temperature sensor directly placed onto the carrier material, and with wiring (or another communicative coupling) that leads to a controller/microprocessor 1880.

Referring now to the embodiment of Figure 19, a temperature of the carrier material can be measured at an area between two electrodes Ei, E₂ of opposite polarity, with a temperature sensor 1950 placed on a carrier material that is used to mount both electrodes Ei , E₂. In some embodiments, a separate element is provided having a dielectric value that is similar to that of the aerosol-forming substrate 1 10, with a temperature sensor in to measure a value indicative of the aerosol-forming substrate temperature.

The temperature sensor is configured to measure temperatures in the region of 100-250°C, and may comprise one or more of thermocouples, thermistors, resistance-based temperature detectors (RTDs, PT100), thermoelement, fiber-optic temperature sensors. In some embodiments, the temperature sensor comprises one or more non-contact sensors such as an NIR sensor.

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

Figure 20 is a schematic illustration of a control system utilizing a temperature sensing system 1510 for control of the power delivered to an aerosol-forming substrate 1 10 based on a detected aerosol-forming substrate temperature. The control system comprises a controller 1520 configured to receive aerosol-forming substrate temperature data from a temperature sensing device 1510, as described above. Where the controller 1520 determines that the aerosol-forming substrate temperature exceeds a predetermined upper threshold, the controller 1520 cuts the power from a power supply 1530 to an oscillation circuit 1540 using a DC/DC cut off 1550, so that a fixed and variable temperature may be delivered to the aerosol-forming substrate.

In an alternative embodiment, the controller 1520 may be configured to use pulse width modulation (PWM) to vary the on and off duty ratio of the on-time versus the off-time of oscillation circuit 1540 based on a measured or estimated temperature.

As an alternative to cutting the power supply 1530 from the oscillation circuit 1540, the biasing voltage 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 1540 may be disrupted, for example by electrical or mechanical means.

In some embodiments, the control system is configured to control the power delivered to the aerosol-forming substrate in two stages; a first stage where the aerosol-forming substrate temperature is ramped up as fast as possible (also referred to as the preheat or preheating stage), and a second stage where the aerosol-forming substrate is maintained at a target aerosolisation temperature. The first stage is performed by maximizing the DC supply voltage to, for example 10V to 12V. Once the target aerosolization temperature is reached, for example in a range 150°C-250°C, more preferably 150°C-220°C, the heating power is decreased by reducing the supply voltage to a lower value, for example around 6.4V to 7.6V. During the ramp-up time of the first stage of the temperature control, the overall power consumption can be 10W-15W, preferably with an efficiency of at least 65%, and upon reaching aerosolization temperature of the aerosol former, the temperature can be controlled to 150°-220°, for example to achieve constant aerosol delivery for given session duration.

Upon aerosolization of the aerosol-forming substrate, there will typically be a change in DC supply current, as the dielectric constant of the aerosol-forming substrate will drop. The dielectric constant can therefore be used as a value that is indicative of the temperature of the aerosol-forming substrate.

In some embodiments, a trained 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.

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

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

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

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

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

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

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

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

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

Claims

1 . An aerosol-generating device for dielectrically heating an aerosol-forming substrate, the device comprising: an oscillation circuit; and an electrode arrangement coupled to the oscillation circuit, the electrode arrangement forming a load capacitor for dielectrically heating the aerosol-forming substrate, the electrode arrangement comprising a first electrode interdigitated with a second electrode.

2. The aerosol-generating device according to claim 1 , wherein the electrode arrangement is fixedly coupled to the oscillation circuit to form the load capacitor, the load capacitor including or being configured to removably receive an aerosol-forming substrate.

3. The aerosol-generating device according to claim 1 , wherein the electrode arrangement is removably coupled to the oscillation circuit to form the load capacitor, the load capacitor including or being configured to removably receive an aerosol-forming substrate.

4. The aerosol-generating device according to any preceding claim, wherein the electrode arrangement forms a flat plate.

5. The aerosol-generating device according to any of claims 1 to 3, wherein the first electrode and the second electrode each comprise a plurality of electrode portions, wherein the electrode arrangement comprises: a first plate comprising a first electrode portion interdigitated with a second electrode portion; and a second plate comprising a first electrode portion interdigitated with a second electrode portion.

6. The aerosol-generating device according to any of claims 1 to 3, wherein the first electrode and the second electrode each comprise a cylindrical segment configured to interdigitate with the cylindrical segment of the other electrode around a cylindrical axis.

7. The aerosol-generating device according to claim 6, wherein the first electrode comprises a first plurality of cylindrical segments and the second electrode comprises a second plurality of cylindrical segments, wherein each of the first plurality of cylindrical segments are positioned around the cylindrical axis separated by one of the second plurality of cylindrical segments.

8. The aerosol-generating device according to claim 7, wherein the device is configured to independently energize one or more of the first plurality cylindrical segments for providing sectional dielectric heating.

9. The aerosol-generating device according to claim 8, wherein the device is further configured to independently energize one or more of the second plurality cylindrical segments for providing sectional dielectric heating.

10. The aerosol-generating device according to any of claims 1 to 3, wherein the first electrode comprises a first plurality of axially aligned electrode rings and the second electrode comprises a second plurality of axially aligned electrode rings, wherein each of the first plurality of electrode rings are separated by one of the second plurality of electrode rings.

1 1. The aerosol-generating device according to claim 10, wherein the device is configured to independently energize one or more of the first plurality of electrode rings for providing sectional dielectric heating.

12. The aerosol-generating device according to claim 11 , wherein the device is further configured to independently energize one or more of the second plurality of electrode rings for providing sectional dielectric heating.

13. The aerosol-generating device according to any preceding claim, wherein the oscillation circuit is configured to self-oscillate.

14. The aerosol-generating device according to claim 13, wherein the oscillation circuit comprises a switching unit and a feedback loop across the switching unit, wherein the electrode arrangement is situated in the feedback loop.

15. An aerosol-generating system comprising: an aerosol-generating device according to any preceding claim; and an aerosol-forming substrate situated within or adjacent to the electrode arrangement.