Dielectric system with an electrode displacement mechanism for temperature regulation

Abstract

There is provided an aerosol-generating device comprising a heating chamber configured to at least partly receive an aerosol-forming substrate, a dielectric heating element comprising at least two electrodes, wherein the dielectric heating element, in operation, heats the aerosol-forming substrate through dipole rotation caused by an alternating electric field generated within the heating chamber by the at least two electrodes, and an electrode displacement mechanism designed to adjust a distance between the at least two electrodes in dependence of a temperature of the aerosol-forming substrate, thereby modifying an electric field strength of the alternating electric field in the heating chamber.

Description

[0001] Dielectric system with an electrode displacement mechanism for temperature regulation

[0002] The present invention relates to an aerosol-generating device, and specifically to an aero- sol-generating device configured to heat an aerosol-forming substrate by dielectric heating. The present disclosure further relates to an aerosol-generating system comprising an aerosol-generating device and to a method to manufacture an aerosol-generating device.

[0003] 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.

[0004] 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.

[0005] Systems that dielectrically heat an aerosol-forming substrate have been proposed, which advantageously provide a more uniform heating of the aerosol-forming substrate. However, known dielectric heating systems may be 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. This high degree of complexity is particularly noticeable when aiming for safe and accurate temperature regulation of the aerosol-forming substrate.

[0006] It would be desirable to provide a device and system that dielectrically heats an aerosolforming substrate with greater efficiency, while still being realisable in a compact or handheld system, wherein the temperature regulation is improved.

[0007] Device:

[0008] According to a first aspect of the present invention, there is provided an aerosol-generating device comprising a heating chamber configured to at least partly receive an aerosol-forming substrate, a dielectric heating element comprising at least two electrodes, wherein the dielectric heating element, in operation, heats the aerosol-forming substrate through dipole rotation caused by an alternating electric field generated within the heating chamber by the at least two electrodes, and an electrode displacement mechanism designed to adjust a distance between the at least two electrodes in dependence of a temperature of the aerosol-forming substrate. By adjusting the distance between the at least two electrodes, an electric field strength or amplitude of the alternating electric field in the heating chamber can be modified, and consequently the heating energy delivered to the aerosol-forming substrate, and therefore the temperature of the aerosol-forming substrate. Thus, by having an electrode displacement mechanism that changes the arrangement of the electrodes itself, the temperature of the aerosol-forming substrate can be controlled without necessarily changing a configuration or parameters of the electrical circuitry in order to achieve the necessary voltages and frequencies, thereby making the device less complex and at the same time more reliable and safe against overheating.

[0009] As used herein, the term “heating chamber” relates to a chamber with a specific structure to receive and / or hold the aerosol-forming substrate within the device. The heating chamber may have a tubular shape with a diameter that is substantially the same as a diameter of the aerosolforming substrate or an insertion portion of an aerosol-generating article having the aerosol-forming substrate. The heating chamber may be defined by the electrodes. Alternatively, the heating chamber may have its own rigid structure defined by walls arranged between the electrodes and the aerosol-forming substrate / article.

[0010] The electrode displacement mechanism may include a temperature-sensitive material that reversibly changes one or more of its dimensions, for example through expansion, contraction, bending, and / or volumetric phase change, in dependence of the temperature of the aerosol-forming substrate. Hence, a change in a dimension of the temperature-sensitive material may cause a direct adjustment of the spacing (distance) between at least two electrodes. This passive displacement concept may allow for a safe and smart solution of dis-placing electrodes, without the need for complex control circuits. Examples of suitable temperature-sensitive materials include bimetallic elements, placed on or forming at least a part of the at least two electrodes, auxetic materials, or phase-change wax compositions (such as thermal wax actuators) that undergo dimensional changes when heated.

[0011] Electrodes:

[0012] The at least two electrodes of the dielectric heating element may be arranged within or in close proximity to the heating chamber.

[0013] The at least two electrodes may be shaped as electrode plates opposed to each other, so as to receive and / or hold the aerosol-forming substrate therebetween.

[0014] The at least two electrodes may comprise one or more pairs of interdigitated electrodes. The one or more pairs of interdigitated electrodes may be arranged as parallel strips along a longitudinal extension of a tubular structure, to receive and / or hold the aerosol-forming substrate therebetween. The tubular structure may be configured to expand in radius and retract in radius upon being subject to temperature change, preferably to increase radius with hotter temperature and decrease radius with colder temperature. The tubular structure may comprise an auxetic sleeve material.

[0015] The at least two electrodes may be shaped as two facing semi-spheres with gap areas arranged therebetween.

[0016] The at least two electrodes may be arranged in a cantilever-based arrangement, where at least one of the at least two electrodes is formed as a cantilever, to approach or retract from the other electrode as a function of temperature.

[0017] Oscillation Circuit

[0018] The aerosol-generating device may further comprise an RF voltage source including an RF oscillation circuit configured to provide an RF voltage to the at least two electrodes.

[0019] The RF oscillation circuit may be configured to operate the at least two electrodes at a radio frequency in the ultra-high frequency range (UHF), or in a range from 100 MHz to 2 GHz, preferably from 300 MHz to 1 GHz.

[0020] The at least two electrodes may form a load capacitor that is part of the RF oscillation circuit.

[0021] The RF oscillation circuit may comprise an inverting switching unit with a feedback loop connected between the input and the output of the switching unit, wherein the load capacitor and an inductor is part of the feedback loop. Moreover, the RF oscillation circuit may comprise a delay element for setting a switching frequency of the inverting switching unit. The delay element may be configured to impede the switching speed of the switching unit. Specifically, the delay element may delay a switching signal received by the switching unit.

[0022] 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. The 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.

[0023] 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.

[0024] Bimetallic Electrode Arrangement - Structure and Shape:

[0025] The electrode displacement mechanism may comprise a bimetallic arrangement. The bimetallic arrangement may comprise at least two different layers of metal having different thermal expansion coefficients, so when heated, one metal expands more than the other, causing at least one electrode of the at least two electrodes to bend or curve. The at least one of the at least two electrodes may be at least partially made of the bimetallic arrangement.

[0026] A first layer of the two different layers may be made by / of steel and a second layer may be made by / of brass.

[0027] The at least two different layers may be formed of one or more foils.

[0028] Each of the at least two different layers may extend along a longitudinal direction of the device, which corresponds to a length direction of the elongated heating chamber.

[0029] The electrodes themselves may be the electrode displacement mechanism, for example bimetallic electrodes with each layer having a different coefficient of thermal expansion (CTE).

[0030] Bimetallic Electrode Arrangement - Movement:

[0031] The two different layers may be designed such that an electrode deflection occurs as a snap action or a smooth action in more gradual steps than the snap action depending on the temperature. For example, the two different layers may be designed such that when a temperature threshold is reached, the electrodes deflect as a snap action almost instantly and / or smoothly deflect below the temperature threshold.

[0032] Bimetallic Electrode Arrangement - Displacement:

[0033] At least one electrode of the at least two electrodes may be arranged in a cantilever-based arrangement, to approach or retract from the other electrode as a function of temperature.

[0034] A “cantilever-based arrangement” as used herein relates to an arrangement where an elongated electrode is anchored at one end and free to move at the other.

[0035] The at least two electrodes may comprise two facing electrodes made of the bimetallic arrangement, and are formed as a cantilever, to symmetrically bend relative to a central axis, which corresponds to a length direction of the electrodes.

[0036] The at least two electrodes may comprise the bimetallic arrangement, and may be configured to symmetrically bend or curve relative to a central axis, which corresponds to a longitudinal (length) direction of the electrodes that have an elongated form.

[0037] The bimetallic arrangement may be configured to curve inward (i.e., concave) or outward (i.e., convex).

[0038] The at least two electrodes, preferably formed as plates, may be arranged to flex against the substrate or aerosol-forming article, such that the substrate or aerosol-forming article is compressed somewhat to yield to the movement of the electrodes.

[0039] Passively and / or Actively actuated Actuators:

[0040] The electrode displacement mechanism may comprise an actuator with a movable element to engage with the at least two electrodes, so as to adjust the distance between the at least two electrodes upon activation in dependence of the temperature of the aerosol-forming substrate.

[0041] Linear Actuator: The actuator may be a linear actuator comprising a piston as movable element. The piston may be configured to engage with at least one of the at least two electrodes such as to adjust a distance between the at least two electrodes by linear movement.

[0042] Actively Actuated Actuator (Electromechanical Actuator):

[0043] The aerosol-generating device may comprise a sensing arrangement to measure a temperature of the aerosol-forming substrate, a temperature inside the heating chamber, or a value indicative of the temperature of the aerosol-forming substrate. The aerosol-generating device may comprise a controller configured to cause movement of the movable element of the actuator based on a signal from the sensing arrangement.

[0044] The sensing arrangement may comprise a temperature detector, for example a resistive positive-temperature coefficient (PTC) or negative temperature coeffcient (NTC) temperature detector comprising a temperature sensitive resistive track. The resistive track may be arranged in the heating chamber. The resistive track may be arranged in contact with the aerosol-forming substrate.

[0045] The sensing arrangement may comprise an infrared sensor to measure infrared radiation or other heat radiation emitted by the aerosol-forming substrate in operation, or another type of optical temperature sensor, for example a temperature sensor that is based on the time-of-flight (ToF) optical principle.

[0046] Passively Aactuated Actuator (Thermal Actuation Device):

[0047] The actuator comprises a thermal actuation device including a temperature-sensitive material.

[0048] The temperature-sensitive material may include an auxetic material of reversibly changing one or more dimensions as a function of temperature.

[0049] The thermal actuation device may include a material chamber filled with the temperaturesensitive material, such as wax, arranged to change its volume in dependence of a temperature of the aerosol-forming substrate. The volume change associated with the temperature of the aerosol-forming substrate may cause movement of the movable element of the actuator, for example in a piston-like arrangement or expandable material chamber.

[0050] The material chamber or other arrangement may be arranged within or in close proximity to the heating chamber, to achieve a thermal connection between the aerosol-forming substrate and the temperature-sensitive material when the aerosol-forming substrate is received in the heating chamber.

[0051] The movable element may be in contact with at least one electrode and the temperaturesensitive material, and is made of a thermally conductive material, such as a metal, so as to achieve a thermal connection and low thermal resistance between the aerosol-forming substrate and the temperature-sensitive material. The actuator may comprise at least one of a wax motor, a wax thermostatic element, and / or a thermostatic actuator.

[0052] Temperature-Sensitive Tubular Structure:

[0053] The at least two electrodes may comprise one or more pairs of interdigitated electrodes arranged as parallel strips along a longitudinal extension of a temperature-sensitive tubular structure to receive and / or hold the aerosol-forming substrate therebetween. The temperature-sensitive tubular structure may be made of a temperature-sensitive material configured to expand in radius and retract in radius upon being subject to temperature change. The temperature-sensitive tubular structure may increase its radius with increasing temperature and decrease its radius with decreasing temperature.

[0054] The tubular structure may be formed of an auxetic sleeve material that reversibly expands its radius and retracts its radius upon being subject to temperature change.

[0055] Substrate Holding Mechanism:

[0056] The aerosol-generating device may further comprise a substrate holding mechanism configured to hold the aerosol-forming substrate in operation and / or when received in the heating chamber.

[0057] The substrate holding mechanism may be formed by the at least two electrodes.

[0058] The at least two electrodes may exert a holding pressure on the substrate at any temperature within a range of 0°C to 400°C.

[0059] The at least two electrodes may comprise four electrodes comprising a first couple / pair of electrodes where at least one of the first couple of electrodes forms the electrode displacement mechanism. A second couple / pair of electrodes may be configured to hold the aerosol-forming substrate in operation and / or when received in the heating chamber.

[0060] The substrate holding mechanism may be realized by a heating chamber structure that does not include the at least two electrodes.

[0061] The substrate holding mechanism can be made of a low-dielectric material, for example a high temperature polymer such as polyether ether ketone (PEEK), ceramic material, quartz glass, or another high temperature resistive material with a relatively low relative permittivity, preferably from 1.1 to 10, preferably from 1.5 to 8, in particular from 2 to 5

[0062] As used herein, the term “relative permittivity” refers to the real part of the complex, frequency-dependent relative permittivity, measured at a temperature of 20 degrees Celsius, in an alternating electric field with at a very low frequency (VLF) of 1 Kilohertz or less, as defined in the international standard IEC 62631-2-1 :2018. It will be appreciated that the frequency value of 1 Kilohertz is included here solely as a general reference and other definitions may use different frequencies.

[0063] Heat-Insulated Volume: The aerosol-generating device may further comprise a heat-insulated volume thermally connected to the heating chamber (for example, by an air gap). At least one of the at least two electrodes is at least partially arranged within the heat-insulated volume so as to be subject to a temperature change of the aerosol-forming substrate arranged in the heating chamber in use, to provide for thermal conductivity of the temperature inside the heat-insulated volume.

[0064] The actuator and / or the movable element of the actuator may be at least partially arranged within the heat-insulated volume, so as to be subject to a temperature change and low thermal resistance to thermal distribution of the aerosol-forming substrate arranged in the heating chamber in use.

[0065] The heat-insulated volume may surround the heating chamber and is arranged in distance to it, preferably by spacers or by an actuator of the electrode displacement mechanism.

[0066] The heat-insulated volume may have a tubular structure. The tubular structure may be a temperature-sensitive tubular structure. The tubular structure may be made of a temperature sensitive auxetic material.

[0067] System:

[0068] According to a second aspect of the present invention, there is provided an aerosol-generating system comprising an aerosol-generating article comprising an aerosol-forming substrate; and an aerosol-generating device according to the first aspect for dielectrically heating the aero- sol-forming substrate.

[0069] The at least two electrodes of the aerosol-generating device may be positioned at a distance from the external periphery of the aerosol-forming substrate, preferably with a distance in a range from 0.1 millimeters to 0.8 millimeters, preferably from 0.2 millimeters to 0.6 millimeters, in particular from 0.3 millimeters to 0.4 millimeters.

[0070] The at least two electrodes of the aerosol-generating device may be arranged in contact or in close proximity with the aerosol-forming substrate or article.

[0071] The aerosol-forming substrate may comprise a tobacco material.

[0072] The aerosol-forming substrate may be a solid aerosol-forming substrate.

[0073] The aerosol-forming substrate may comprise a liquid material.

[0074] Manufacturing Method:

[0075] According to a third aspect of the present invention, there is provided a method for manufacturing an aerosol-generating device, preferably according to the first aspect. The method comprises providing an electrode displacement mechanism designed to adjust a distance between at least two electrodes for dielectrically heating an aerosol-forming substrate therebetween in dependence of a temperature of the aerosol-forming substrate.

[0076] The electrode displacement mechanism may comprise one or more of the following electrode displacement mechanisms A to D: A. A bimetallic arrangement, wherein at least one of: the bimetallic arrangement is attached to at least one of the at least two electrodes, and / or at least one of the at least two electrodes is at least partially made of the bimetallic arrangement.

[0077] B. A thermal actuation device configured to convert thermal energy into a mechanical movement, preferably a linear movement, for adjusting a distance between the at least two electrodes in response to a temperature change of the aerosol-forming substrate.

[0078] C. A temperature-sensitive tubular structure having the at least two electrodes arranged thereon, and configured to convert thermal energy into a mechanical movement, preferably a radial movement, for adjusting a distance between the at least two electrodes in response to a temperature change of the aerosol-forming substrate.

[0079] D. A sensing arrangement to measure a temperature of the aerosol-forming substrate, a temperature inside the heating chamber, or a value indicative of said temperature; an electromechanical actuator configured to convert electric energy into mechanical movement, preferably a linear movement, for adjusting a distance between the at least two electrodes, and a controller configured to control the electromechanical actuator based on a signal from the sensing arrangement.

[0080] The invention is defined in the claims. However, below there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein.

[0081] Example Ex. 1 An aerosol-generating device comprising a heating chamber configured to at least partly receive an aerosol-forming substrate, a dielectric heating element comprising at least two electrodes, wherein the dielectric heating element, in operation, heats the aerosol-forming substrate through dipole rotation caused by an alternating electric field generated within the heating chamber by the at least two electrodes, and an electrode displacement mechanism designed to adjust a distance between the at least two electrodes in dependence of a temperature of the aerosol-forming substrate, thereby modifying an electric field strength of the alternating electric field in the heating chamber.

[0082] Example Ex1.1. The aerosol-generating device according to the preceding example, wherein the at least two electrodes of the dielectric heating element are arranged within or in close proximity to the heating chamber.

[0083] Example Ex1 .2. The aerosol-generating device according to any of the preceding examples, wherein the at least two electrodes are shaped as electrode plates opposed to each other, so as to receive and / or hold the aerosol-forming substrate therebetween.

[0084] Example Ex1.3. The aerosol-generating device according to Examples Ex1 or Ex1.1 , wherein the at least two electrodes comprise one or more pairs of interdigitated electrodes Example Ex1.3.1. The aerosol-generating device according to the preceding example, wherein the one or more pairs of interdigitated electrodes are arranged as parallel strips along a longitudinal extension of a tubular structure, to receive and / or hold the aerosol-forming substrate therebetween

[0085] Example Ex1.3.1.1. The aerosol-generating device according to the preceding example, wherein the tubular structure is configured to expand in radius and retract in radius upon being subject to temperature change, preferably to increase radius with hotter temperature and decrease radius with colder temperature,

[0086] Example Ex1.3.1.2. The aerosol-generating device according to any of Examples

[0087] Ex1.1.1 to Ex1.3.1.1 , wherein the tubular structure comprises an auxetic sleeve material.

[0088] Example Ex1.4. The aerosol-generating device according to Examples Ex1 or Ex1.1 , wherein the at least two electrodes are shaped as two facing semi-spheres with gap areas arranged therebetween.

[0089] Example Ex1 .5. The aerosol-generating device according to any one of the preceding examples, wherein the at least two electrodes are arranged in a cantilever-based arrangement, wherein at least one of the at least two electrodes is formed as a cantilever, to approach or retract from the other electrode as a function of temperature.

[0090] Example Ex1 .6. The aerosol-generating device according to any one of the preceding examples, wherein the aerosol-generating device further comprise an RF voltage source including an RF oscillaton circuit configured to provide an RF voltage to the at least two electrodes.

[0091] Example Ex1.6.1. The aerosol-generating device according to the preceding example, wherein the RF oscillation circuit is configured to operate the at least two electrodes at a radio frequency in the ultra-high frequency range (UHF), or in a range from 100 MHz to 2 GHz, preferably from 300 MHz to 1 GHz.

[0092] Example Ex1.6.2. The aerosol-generating device according to example Ex1.6 or Ex1.6.1 , wherein the at least two electrodes form a load capacitor that is part of the RF oscillation circuit.

[0093] Example Ex1.6.2.1. The aerosol-generating device according to the preceding example, wherein the RF oscillation circuit comprises an inverting switching unit with a feedback loop connected between the input and the output of the switching unit, wherein the load capacitor and an inductor is part of the feedback loop.

[0094] Example Ex1 .6.2.1 .1 . The aerosol-generating device according to the preceding example, wherein the RF oscillation circuit comprises a delay element for setting a switching frequency of the inverting switching unit.

[0095] Example Ex2. The aerosol-generating device according to any one of the preceding examples, wherein the electrode displacement mechanism comprises a bimetallic arrangement, the bimetallic arrangement comprises at least two different layers of metal having different thermal dilatation coefficients, so when heated, one metal expands more than the other, causing at least one electrode of the at least two electrodes to bend or curve.

[0096] Example Ex2.1. The aerosol-generating device according to the preceding example, wherein the at least one of the at least two electrodes is at least partially made of the bimetallic arrangement.

[0097] Example Ex2.2. The aerosol-generating device according to any one of Examples Ex2 to Ex2.1 , wherein a first layer of the two different layers is made by steel and a second layer is made by brass.

[0098] Example Ex2.2.1. The aerosol-generating device according to the preceding example, wherein each of the at least two different layers is formed of one or more foils.

[0099] Example Ex2.2.2. The aerosol-generating device according to any one of Examples Ex2.2 to Ex2.2.1 , wherein each of the at least two different layers extends along a longitudinal direction of the device, which corresponds to a length direction of the elongated heating chamber.

[0100] Example Ex2.3. The aerosol-generating device according to any one of the preceding examples, wherein the two different layers are designed such that an electrode deflection occurs as a snap action or a smooth action in more gradual steps than the snap action depending on the temperature.

[0101] Example Ex2.3.1. The aerosol-generating device according to the preceding example, wherein the two different layers are designed such that when a temperature threshold is reached, the electrodes deflect as a snap action almost instantly and / or smoothly deflect below the temperature threshold.

[0102] Example Ex3. The aerosol-generating device according to any one of Examples Ex2 to Ex2.3.1 , wherein the at least one of the at least two electrodes is arranged in a cantilever-based arrangement, to approach or retract from the other electrode as a function of temperature.

[0103] Example Ex4. The aerosol-generating device according to any one of Examples Ex2 to Ex3, wherein the at least two electrodes comprise the bimetallic arrangement, and are configured to symmetrically bend or curve relative to a central axis, which corresponds to a longitudinal direction of the electrodes that have an elongated form.

[0104] Example Ex4.1. The aerosol-generating device according to the preceding example, wherein the bimetallic arrangement is configured to curve inward or outward.

[0105] Example Ex5. The aerosol-generating device according to any one of the preceding examples, wherein the electrode displacement mechanism comprises an actuator with a movable element to engage with the at least two electrodes, so as to adjust the distance between the at least two electrodes upon activation in dependence of the temperature of the aerosol-forming substrate. Example Ex6. The aerosol-generating device according to any one of the preceding examples, wherein the actuator is a linear actuator comprising a piston as a movable element, the piston configured to engage with at least one of the at least two electrodes such as to adjust a distance between the at least two electrodes by linear movement.

[0106] Example Ex7. The aerosol-generating device according to any one of Examples Ex5 and Ex6, comprising a sensing arrangement to measure a temperature of the aerosol-forming substrate, a temperature inside the heating chamber, or a value indicative of the temperature of the aerosol-forming substrate, and a controller configured to cause movement of the movable element of the actuator based on a signal from the sensing arrangement.

[0107] Example Ex7.1. The aerosol-generating device according to the preceding example, wherein the sensing arrangement comprises a resistive temperature detector comprising a temperature sensitive resistive track, preferably arranged in the heating chamber.

[0108] Example Ex7.2. The aerosol-generating device according to Example Ex7, wherein the sensing arrangement comprises an infrared sensor to measure infrared radiation emitted by the aerosol-forming substrate in operation.

[0109] Example Ex8. The aerosol-generating device according to any one of Examples Ex5 and Ex6, wherein the actuator comprises a thermal actuation device including a temperature-sensitive material.

[0110] Example Ex8.1. The aerosol-generating device according to the preceding example, wherein the temperature-sensitive material can include an auxetic material of reversibly changing one or more dimensions as a function of temperature.

[0111] Example Ex9. The aerosol-generating device according to any one of Examples Ex8 and Ex8.1 , wherein the thermal actuation device includes a material chamber filled with the temperature-sensitive material, such as wax, arranged to change its volume in dependence of a temperature of the aerosol-forming substrate.

[0112] Example Ex9.1. The aerosol-generating device according to the preceding example, wherein the material chamber is arranged within or in close proximity to the heating chamber, to achieve a thermal connection between the aerosol-forming substrate and the temperature-sensitive material when the aerosol-forming substrate is received in the heating chamber.

[0113] Example Ex9.1.1. The aerosol-generating device according to the preceding example, wherein the movable element is in contact with the at least one electrode and the temperaturesensitive material, and is made of thermally conductive material, such as a metal, so as to achieve a thermal connection between the aerosol-forming substrate and the temperature-sensitive material. Example Ex9.1.2. The aerosol-generating device according to Examples Ex9.1 or Ex9.1.1 , wherein the actuator comprises at least one of a wax motor, a wax thermostatic element, and / or a thermostatic actuator

[0114] Example Ex10. The aerosol-generating device according to any one of the preceding examples, wherein the at least two electrodes comprise one or more pairs of interdigitated electrodes arranged as parallel strips along a longitudinal extension of a temperature-sensitive tubular structure to receive and / or hold the aerosol-forming substrate therebetween, wherein the temperature-sensitive tubular structure is made of a temperature-sensitive material configured to expand in radius and retract in radius upon being subject to temperature change, preferably to increase radius with increasing temperature and decrease radius with decreasing temperature.

[0115] Example Ex10.1. The aerosol-generating device according to the preceding example, wherein the tubular structure is formed of an auxetic sleeve material that reversibly expands in radius and retracts its radius upon being subject to temperature change.

[0116] Example Ex11 . The aerosol-generating device according to any of the preceding examples, comprising a substrate holding mechanism configured to hold the aerosol-forming substrate when received in the heating chamber.

[0117] Example Ex11.1. The aerosol-generating device according to the preceding example, wherein the substrate holding mechanism is formed by the at least at least two electrodes .

[0118] Example Ex11.2. The aerosol-generating device according to Example Ex11 , wherein the at least two electrodes comprise four electrodes comprising a first couple of electrodes where at least one of the first couple of electrodes forms the electrode displacement mechanism, and a second couple of electrodes configured to hold the aerosol-forming substrate in operation.

[0119] Example Ex11 .3. The aerosol-generating device according to Example Ex11 , wherein the substrate holding mechanism is realized by a heating chamber structure that does not include the at least two electrodes.

[0120] Example Ex12. The aerosol-generating device according to any one of the preceding examples, comprising a heat-insulated volume thermally connected to the heating chamber, wherein at least one of the at least two electrodes is at least partially arranged within the heat- insulated volume so as to be subject to a temperature change of the aerosol-forming substrate arranged in the heating chamber in use.

[0121] Example Ex12.1. The aerosol-generating device according to the preceding example, wherein the actuator and / or the movable element of the actuator is at least partially arranged within the heat-insulated volume, so as to be subject to a temperature change of the aerosolforming substrate arranged in the heating chamber in use. Example Ex12.2. The aerosol-generating device according to any one of Examples Ex12 and Ex12.1 , wherein the heat-insulated volume surrounds the heating chamber and is arranged in distance to it, preferably by spacers or by the actuator of the electrode displacement mechanism.

[0122] Example Ex12.3. The aerosol-generating device according to any one Examples Ex12 to Ex12.2, wherein the heat-insulated volume has a tubular structure, preferably made of a temperature sensitive auxetic material.

[0123] Example Ex13. An aerosol-generating system comprising an aerosol-generating article comprising an aerosol-forming substrate; and an aerosol-generating device according to any one of the preceding examples for dielectrically heating the aerosol-forming substrate.

[0124] Example Ex13.1. The aerosol-generating system according to the preceding example, wherein the at least two electrodes of the aerosol-generating device are positioned at a distance from the external periphery of the aerosol-forming substrate, preferably with a distance in a range from 0.1 millimeters to 0.8 millimeters, preferably from 0.2 millimeters to 0.6 millimeters, in particular from 0.3 millimeters to 0.4 millimeters.

[0125] Example Ex13.2. The aerosol-generating system according to any one of Examples Ex13 and Ex13.1 , wherein the at least two electrodes of the aerosol-generating device are arranged in contact with the aerosol-forming substrate or the article.

[0126] Example Ex13.3. The aerosol-generating system according to any one of Examples Ex13 to Ex13.2, wherein the aerosol-forming substrate comprises a tobacco material.

[0127] Example Ex13.4. The aerosol-generating system according to any one of Examples Ex13 to Ex13.3, wherein the aerosol-forming substrate is a solid aerosol-forming substrate.

[0128] Example Ex14. A method of manufacturing an aerosol-generating device, preferably according to any one of Examples Ex12 to Ex12.3, comprises providing an electrode displacement mechanism designed to adjust a distance between at least two electrodes for dielectrically heating an aerosol-forming substrate therebetween in dependence of a temperature of the aerosol-forming substrate.

[0129] Example Ex15. The method according to the preceding example, wherein the electrode displacement mechanism comprises one or more of the following electrode displacement mechanisms A to D:

[0130] A. A bimetallic arrangement, wherein at least one of: the bimetallic arrangement is attached to at least one of the at least two electrodes, and / or at least one of the at least two electrodes is at least partially made of the bimetallic arrangement.

[0131] B. A thermal actuation device configured to convert thermal energy into a mechanical movement, preferably a linear movement, for adjusting a distance between the at least two electrodes in response to a temperature change of the aerosol-forming substrate. C. A temperature-sensitive tubular structure having the at least two electrodes arranged thereon, and configured to convert thermal energy into a mechanical movement, preferably a radial movement, for adjusting a distance between the at least two electrodes in response to a temperature change of the aerosol-forming substrate.

[0132] D. A sensing arrangement to measure a temperature of the aerosol-forming substrate, a temperature inside the heating chamber, or a value indicative of said temperature; an electromechanical actuator configured to convert electric energy into mechanical movement, preferably a linear movement, for adjusting a distance between the at least two electrodes, and a controller configured to control the electromechanical actuator based on a signal from the sensing arrangement.

[0133] The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

[0134] Figure 1 is a schematic illustration of a dielectric heating aerosol-generating system according to embodiments of the disclosure;

[0135] 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;

[0136] Figure 3A is a schematic illustration of an oscillation circuit showing two different phaseshifting elements, one exemplarily implemented as a resonance circuit, one exemplarily implemented as a capacitive element, to achieve a 180° phase shift;

[0137] Figure 3B is a schematic illustration of an oscillation circuit showing two different phaseshifting elements, one exemplarily implemented as a resonant circuit having parallel resonance properties, one exemplarily implemented as a capacitive element, to achieve a 180° phase shift;

[0138] Figure 4 illustrates an oscillation circuit diagram according to embodiments of the disclosure;

[0139] Figures 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;

[0140] 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;

[0141] Figures 7A-C illustrate a schematic illustration of a bimetallic electrode arrangement having two opposed electrode plates for use in the dielectric heating aerosol-generating system of Figure 1 , according to embodiments of the disclosure;

[0142] Figure 8 illustrates a schematic illustration of a bimetallic electrode arrangement having tubular interdigitated electrodes for use in the dielectric heating aerosol-generating system of Figure 1 , according to embodiments of the disclosure; Figure 9 illustrates a schematic illustration of a bimetallic electrode arrangement having two facing semi-spheres electrodes with gap areas arranged therebetween for use in the dielectric heating aerosol-generating system of Figure 1 , according to embodiments of the disclosure;

[0143] Figures 10A-B illustrate a schematic illustration of a passively actuated actuator for displacing electrodes having a temperature-sensitive material that reversibly changes its volume upon being subject to temperature change caused by a temperature change of the aerosol-forming substrate for use in the dielectric heating aerosol-generating system of Figure 1 , according to embodiments of the disclosure;

[0144] Figure 11 illustrates a schematic illustration of an actively actuated actuator for displacing electrodes based on a measured temperature of the aerosol-forming substrate for use in the dielectric heating aerosol-generating system of Figure 1 , according to embodiments of the disclosure; and

[0145] Figure 12 illustrates a schematic illustration of a passively actuated actuator in form of a tubular structure for displacing electrodes wherein the electrodes comprise pairs of interdigitated electrodes arranged as parallel strips along a longitudinal extension of the tubular structure, wherein the tubular structure is made of a temperature-sensitive material configured to expand in radius and retract in radius upon being subject to a temperature change of the aerosol-forming substrate for use in the dielectric heating aerosol-generating system of Figure 1 , according to embodiments of the disclosure.

[0146] Description of Drawings

[0147] The above and other features and advantages of example embodiments will become more apparent by describing in detail, example embodiments with reference to the attached drawings. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. Example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.

[0148] Accordingly, while example embodiments are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but to the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of example embodiments. Like numbers refer to like elements throughout the description of the Figures.

[0149] 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 aerosol-generating article 105 comprising an aerosol-forming substrate 110 and an aerosol-generating device 120 for heating the aerosol-forming substrate 110. The aerosol-generating device 120 comprises a dielectric heating element formed by an electrode arrangement comprising a first electrode 130 and a second electrode 135 separated by a heating chamber 140 for removably receiving the article 105. The heating chamber 140 and the article 105 are sized such that the aerosol-forming substrate 110 is in contact or in close proximity to both the first electrode 130 and the second electrode 135 when received within the heating chamber 140. Moreover, the first electrode 130 and the second electrode 135 can form part of a feedback loop of an oscillation circuit 150 via a first electrical contact 160 and a second electrical contact 165. In the shown embodiment, the electrodes 130, 135 are in direct contact with the aerosol-generating article 105 having the aero- sol-forming substrate 110, thereby holding the aerosol-forming substrate 110 in place.

[0150] In other configurations, the heating chamber 140 comprises an alternative substrate holding mechanism, for example a heating chamber structure (not shown), such as a heating chamber sleeve, with walls made of a material with relatively low relative permittivity, such as PEEK, that is arranged between the aerosol-forming substrate 110, in particular an outer periphery of the article 105, and the electrodes 130, 135. In such configuration, the electrodes 130, 135 are positioned at a distance from the external periphery of the aerosol-forming substrate 110, preferably with a distance in a range from 0.1 millimeters to 0.8 millimeters, preferably from 0.2 millimeters to 0.6 millimeters, in particular from 0.3 millimeters to 0.4 millimeters.

[0151] In other examples, the first electrode 130 and the second electrode 135 may form part of the article 105 comprising the aerosol-forming substrate 110. In such embodiments, a heating chamber 140 between the first and second electrical contacts 160, 165 is sized such that, when the aerosol-forming article 105 is housed within the heating chamber 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.

[0152] 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 2-20% larger than the distance between the first electrode 130 and the second electrode 135. This may reduce or prevent the buildup of air between the first electrode 130 and the second electrode 135 when the aerosol-forming article 105 is received in the heating chamber 140, and decrease a distance between first and second electrodes 130, 135 for dielectric heating, thereby improving dielectric properties of a 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.

[0153] 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.

[0154] The aerosol-forming substrate 110 can also be a liquid aerosol-forming substrate and thereby the aerosol-generating article 105 can be in the form of a cartridge, capsule, pouch, token, or liquid container, and the electrodes 130, 135 can be configured as a wicking element, liquid transfer element, or capillary element for liquid transfer. For example, it is possible that first and second electrodes 130, 135 are arranged to have a liquid transfer element therebetween to expose the liquid transfer element to the alternating electric field, or first and second electrodes 130, 135 itself form a capillary structure that is part of the aerosol-generating article 105 or reaches into an inner volume of the aerosol-generating article 105 that can heat and vaporize a liquid aerosol-forming substrate 110 located in the inner volume. For example, the first and second electrodes 130, 135 can be embodied as parallelly arranged plates separated by a distance that forms a capillary channel, for example in a range between 0.1 mm to 2 mm, preferably 1 mm to 2 mm, depending on the desired capillary strength or rise. The first and second electrodes 130, 135 can be arranged as two matrices or arrays of pin-like, rod-like, or tab-like electrodes with opposite polarity, the two matrices or arrays interposed between each other, forming a capillary structure therebetween, for example with an average distance between neighboring pin-like electrodes being in a range between 0.1 mm to 2 mm, depending on the desired capillary strength or rise. In another variant, the wicking element can be a separate element that is interposed between two electrodes 130, 135, for example flat or slightly curved electrodes 130, 135.

[0155] The aerosol-generating device 120 further comprises a power supply 170 and a controller 180 electrically coupled to the oscillation circuit 150. In this embodiment, the power supply 170 can be a rechargeable lithium ion battery, for example with one or more lithium ion battery cells, and the aerosol-generating device 120 comprises a power connector that enables the aerosolgenerating device 120 to be connected to a mains power supply for recharging the power supply. Providing the aerosol-generating device 120 with a power supply, such as a battery, enables the aerosol-generating device 120 to be portable and used outdoors or in locations in which a mains power supply is not available.

[0156] 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, or by the user inserting an aerosolgenerating article 105 to the aerosol-generating device. 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 heating chamber 140, releasing volatile compounds.

[0157] The controller 180 may cause dielectric heating of the aerosol-forming substrate 110 that is located between the two electrodes 130, 135 with an average dielectric heating power density in a range between 1W / cm3to 25W / cm3, preferably between 1.5W / cm3and 15W / cm3per volume of substrate material during a time period of less than 15 minutes. In particular, during a heat-up phase, the average dielectric heating power density may be controlled or set to be in a range between 7W / cm3to 25W / cm3, preferably between 8W / cm3to 20W / cm3. During a target heating phase (also called maintenance heating phase) during consumption, the average dielectric heating power density is in a range between 1W / cm3to 7W / cm3, preferably between 1W / cm3to 5W / cm3. In a non-limiting example, these power densities may be used in heat-not-burn applications.

[0158] In yet another exemplary embodiment, the aerosol-generating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 35W / cm3and 35kW / cm3. The aerosol-generating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 50W / cm3and 10 kW / cm3, between 50W / cm3and 2.5kW / cm3or between 50W / cm3and 1.25kW / cm3. The aerosolgenerating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 170W / cm3and 2.5kW / cm3, between 250W / cm3and 2.5kW / cm3or between 500W / cm3and 2.5kW / cm3. Preferably, the aerosol-generating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 1 kW / cm3and 2kW / cm3. In a non-limiting example, these power densities may be used for heating and vaporizing liquids during a puff in a puff-on-demand application.

[0159] The aerosol-generating system 100 is also configured for measuring a dielectric property of the aerosol-generating article 105 or the aerosol-forming substrate 110 using the electrodes 130, 135 that are employed for dielectric heating of the aerosol-forming substrate 110. In some examples, the first and second electrodes 130, 135 can be used for dielectric measurements, either during the heating process (for example during the pre-heating phase or the main heating phase) or separately to the heating process. In this embodiment, the aerosol-generating system 100 can be configured to determine the presence of the aerosol-generating article 105 between the first electrode 130 and the second electrode 135. The aerosol-generating system 100 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-generating article 105 meets specific criteria or is an authentic substrate. The aerosol-generating system 100 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-generating article 105.

[0160] In one exemplary embodiment, the material composition of the substrate 110 of the aerosolgenerating article 105 that can be dielectrically heated by the aerosol-generating device 120 can include tobacco powder or tobacco cut filler.

[0161] As used herein, the term “cut filler” is used to describe to a blend of shredded plant material, such as tobacco plant material, including, in particular, one or more of leaf lamina, processed stems and ribs, homogenised plant material. Preferably, the cut filler comprises at least 25% of plant leaf lamina, more preferably, at least 50% of plant leaf lamina, still more preferably at least 75% of plant leaf lamina and most preferably at least 90% of plant leaf lamina.

[0162] The cut filler suitable to be used in the present invention generally may a resemble cut filler used for conventional smoking articles. The cut width of the cut filler preferably is between 0.3 millimeters and 2.0 millimeters, more preferably, the cut width of the cut filler is between 0.5 millimeters and 1 .2 millimeters and most preferably, the cut width of the cut filler is between 0.6 millimeters and 0.9 millimeters.

[0163] The aerosol-generating substrate 110 may comprise between 80 milligrams and 400 milligrams of the cut filler. For example, the aerosol-generating substrate 110 may comprise between 100 milligrams and 300 milligrams of the cut filler, between 100 milligrams and 250 milligrams of the cut filler, between 125 milligrams and 200 milligrams of the cut filler, or between 140 milligrams and 180 milligrams of the cut filler, such as about 150 milligrams of the cut filler.

[0164] The aerosol-forming substrate 110 of the aerosol-generating article 105 may comprise an aerosol former. Where the aerosol-forming substrate 110 comprises cut filler, the cut filler may be soaked with the aerosol former. Soaking the cut filler can be done by spraying or by other suitable application methods. Preferably, the aerosol former comprises one or more of glycerine, for example vegetable glycerine (VG), and / or propylene glycol (PG). The aerosol former may consist of glycerine or propylene glycol or of a combination of glycerine and propylene glycol. The aero- sol-forming substrate 110 may comprise any amount of aerosol former.

[0165] For example, the aerosol-forming substrate 110 may comprise between 5 weight percent aerosol former and 25 weight percent aerosol former. For example, the aerosol-forming substrate 110 may comprise between 10 weight percent aerosol former and 20 weight percent aerosol former, or between 15 weight percent aerosol former and 20 weight percent aerosol former. Preferably, the aerosol-generating substrate 110 comprises about 18 weight percent aerosol former. The weight percentages of aerosol former are given as a dry weight basis of the cut filler, with the balance being tobacco.

[0166] The aerosol-forming substrate 110 may have a density of no more than 0.45 grams per cubic centimetre, no more than 0.4 grams per cubic centimetre, no more than 0.36 grams per cubic centimetre, no more than 0.3 grams per cubic centimetre, or no more than 0.25 grams per cubic centimetre. The aerosol-forming substrate 110 may have a density of at least 0.1 grams per cubic centimetre. For example, the aerosol-forming substrate 110 may have a density of at least 0.15 grams per cubic centimetre, at least 0.2 grams per cubic centimetre, or at least 0.28 grams per cubic centimetre.

[0167] The aerosol-forming substrate 110 can have different shapes, for example a cuboid shape, rectangular parallelepiped shape, pouch-shaped, or may be cylindrically shaped, and is preferably substantially cylindrically shaped, having a length of between 10 mm and 15 mm, such as between 11 mm and 14 mm, preferably about 12 mm, and having a diameter of between 4.5 mm and 8mm, such as between 6.5 mm and 7.5 mm, preferably about 7 mm.

[0168] Suitable aerosol-forming substrates and articles comprising cut filler include those described in W02022 / 074240 and / or W02022 / 074158, these references herewith incorporated by reference in their entirety.

[0169] In another exemplary embodiment, the material composition of the aerosol-forming substrate 110 of the aerosol-generating article 105 that can be dielectrically heated by the aerosolgenerating device 120 can include reconstituted tobacco, such as one or more sheets of homogenized tobacco material made by a cast leaf process. Where the aerosol-forming substrate 110 comprises homogenised tobacco material, the tobacco material preferably comprises particulate tobacco obtained by grinding or otherwise comminuting tobacco leaf lamina. Such a homogenised tobacco material may have a tobacco content of at least about 40% by weight on a dry weight basis or of at least about 50% by weight on a dry weight basis. In other embodiments, the homogenised tobacco material may have a tobacco content of about 70% or more by weight on a dry weight basis, such as between 70% and 80% by weight on a dry weight basis.

[0170] In yet another exemplary embodiment, the aerosol-forming substrate 110 can include a plurality of tobacco beads or granules. For example, the mean diameter of the plurality of beads or granules may be between 0.5 millimetres and 10 millimetres. The substrate 110 may comprise between 2 beads and 200 beads or granules, or between 5 beads and 200 beads or granules, or between 10 beads and 100 beads or granules, or between 20 beads and 75 beads or granules, or between 30 beads and 50 beads or granules, or between 40 beads and 50 beads or granules. The total weight of the plurality of beads or granules in the aerosol-generating article 105 may be between 50 mg and 350 mg, or between 100 mg and 300 mg, or between 125 mg and 250 mg, or between 150 mg and 200 mg. The beads or granules may comprise tobacco, an aerosol former and a hydrocolloid binder.

[0171] The aerosol-forming substrate 110 may comprise one or more intrinsic binders, that are tobacco endogenous binders, one or more extrinsic binders, that are tobacco exogenous binders, or a combination thereof to help agglomerate the particulate tobacco. Alternatively, or in addition, the aerosol-forming substrate 110 may comprise other additives including, but not limited to, tobacco and non-tobacco fibres, aerosol- formers, humectants, plasticisers, flavourants, fillers, aqueous and non-aqueous solvents and combinations thereof.

[0172] Suitable extrinsic binders for inclusion in the aerosol-forming substrate 110 are known in the art and include, but are not limited to: gums such as guar gum, xanthan gum, arabic gum and locust bean gum; cellulosic binders such as hydroxypropyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose and ethyl cellulose; polysaccharides such as starches, organic acids, such as alginic acid, conjugate base salts of organic acids, such as sodium-algi- nate, agar and pectins; and combinations thereof. For example, the aerosol-forming substrate 110 may comprise between 1% and 5% extrinsic binder by weight on a dry weight basis, such as between 1.5% and 3.5% extrinsic binder by weight on a dry weight basis, preferably about 2% extrinsic binder by weight on a dry weight basis. Preferably, the extrinsic binder is guar gum.

[0173] Suitable non-tobacco fibres for inclusion in the aerosol-forming substrate 110, to strengthen the material, are known in the art and include, but are not limited to: cellulose fibers; soft-wood fibres; hard-wood fibres; jute fibres and combinations thereof. For example, the aerosol-forming substrate 110 may comprise between 2% and 6% non-tobacco fibres by weight on a dry weight basis, such as between 3% and 5% non-tobacco fibres by weight on a dry weight basis, preferably about 4% non-tobacco fibres by weight on a dry weight basis. Preferably, the non-tobacco fibres are cellulose fibres.

[0174] The aerosol-forming substrate 110 may comprise an aerosol former. Preferably, the aerosol former comprises one or more of glycerine, for example VG (Vegetable Glycerine), and PG (Propylene Glycol). The aerosol former may consist of glycerine or propylene glycol or of a combination of glycerine and propylene glycol. The aerosol-forming substrate 110 may comprise any amount of aerosol former. For example, the aerosol-forming substrate 110 may comprise between 5 weight percent aerosol former and 25 weight percent aerosol former. For example, the aerosolforming substrate 110 may comprise between 10 weight percent aerosol former and 20 weight percent aerosol former, or between 15 weight percent aerosol former and 20 weight percent aerosol former. Preferably, the aerosol-forming substrate 110 comprises about 18 weight percent aerosol former. The weight percentages of aerosol former are given as a dry weight basis of the aerosol-forming substrate 110.

[0175] Preferably, the aerosol-forming substrate 110 has a weight of between 220 milligrams and 350 milligrams. For example, the aerosol-forming substrate 110 may have a weight between 240 milligrams and 320 milligrams, between 250 milligrams and 310 milligrams, between 240 milligrams and 280 milligrams, or between 290 milligrams and 330 milligrams.

[0176] The aerosol-forming substrate 110 may have a density of no more than 0.75 grams per cubic centimetre, no more than 0.68 grams per cubic centimetre, no more than 0.67 grams per cubic centimetre, no more than 0.59 grams per cubic centimetre, or no more than 0.56 grams per cubic centimetre. The aerosol-forming substrate 110 may have a density of at least 0.5 grams per cubic centimetre. For example, the aerosol-forming substrate 110 may have a density of at least 0.55 grams per cubic centimetre, at least 0.56 grams per cubic centimetre, or at least 0.64 grams per cubic centimetre.

[0177] The aerosol-forming substrate 110 can have different shapes, for example a cuboid shape, rectangular parallelepiped shape, pouch-shaped, or may be cylindrically or substantially cylindrically shaped.

[0178] For example, the aerosol-forming substrate can be preferably substantially cylindrically shaped, having a length of between 10 mm and 15 mm, such as between 11 mm and 14 mm, preferably about 12 mm, and having a diameter of between 4.5 mm and 8 mm, such as between 6.5 mm and 7.5 mm, preferably about 7 mm, and can preferably have substrate volumes in a range between 0.16 cubic centimeters to 0.75 cubic centimeters. In yet another exemplary embodiment, the aerosol-forming substrate 110 can be a non-tobacco-based substrate and / or a substantially tobacco free substrate. The aerosol-generating substrate 110 may be a cellulose-based substrate, for example as described in W02020 / 207733, WO2023 / 126494, and / or WO2022 / 248378, these references herewith incorporated by reference in their entirety.

[0179] Figure 2 is a schematic illustration of an oscillation circuit 250 for use in the aerosol-generating system 100 of Figure 1 , according to an embodiment of the disclosure. The oscillation circuit 250 comprises a switching unit 260 interconnected with a resonator feedback loop 270 to provide for a self-oscillating signal to the switching unit 260. The switching unit 260 comprises a single transistor, such as a bipolar junction transistor (BJT) or a field effect transistor (FET).

[0180] 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 250 also comprises 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. An output voltage UOUT of the switching unit 260 is coupled to the feedback loop 270 providing a feedback switching signal in the form of an input voltage UIN to the switching unit 260. The configuration of the feedback loop 270 is such that the output signal, e.g. the output voltage UOUT of the switching unit 260 can undergo a phase change and arrives inverted at the input voltage UIN of the switching unit 260 for resonant oscillation. In other configurations, a current could be used as the feedback signal with the switching unit 260 comprising a BJT.

[0181] The feedback loop 270 is configured to be self-oscillating and will oscillate at or close to a given resonance frequency determined by the values of the passive components of the feedback loop 270. The feedback loop 270 is configured to provide a 180° phase shift from the output voltage UOUT to input voltage UIN of the switching unit 260 for oscillation, and in addition, the transistor T is configured for inverting operation.

[0182] As shown in Figures 3a and 3b, the feedback loop 270 includes a resonant circuit 272 comprising the load capacitor CL providing for a first 90° phase shift or quarter wave shift to the feedback signal. The feedback loop 270 further includes a capacitive element 274 providing for a second 90°phase shift or quarter wave shift to the feedback signal, such that the feedback signal reaching the input of the switching unit 260 is inverted and phase-shifted by 180°. The switching unit 260 is itself configured for inverted switching operation to provide the 180° phase shift between the input voltage UIN and the output voltage UOUT of the switching unit 260.

[0183] The resonant circuit 272 comprises the first and second electrodes 130, 135, together forming the load capacitor CL. When the 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 the 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.

[0184] Figure 4 illustrates an oscillation circuit 350 according to a non-limiting, exemplary embodiment of the disclosure. The oscillation circuit 350 comprises a switching unit 260 in the form of a transistor T having an intrinsic capacitance Cj. Moreover, the transistor T is configured for inverting operation, for example as an inverting common source FET, MOSFET, or a common emitter BJT. The source terminal of the transistor T can be coupled to a DC power supply via a choke 280. Between the gate terminal and source terminal of the transistor T extends a feedback loop 270. The feedback loop 270 comprises the resonant circuit 272 including the load capacitor CL having the first and second electrodes 130, 135 separated by the aerosol-forming substrate 110. In the variant shown, the resonator circuit 272 is also connected to ground via a delay line DL and a capacitor C2 connected in series to the delay line DL. The oscillation circuit 350 further comprises a biasing unit 290 coupled to the gate terminal of the transistor T via the delay line DL. AS shown in Figure 4, the biasing unit 290 is electrically connected between the delay line DL and the capacitor C2, so that the biasing unit 290 is somewhat isolated from the high oscillation frequency of the feedback loop 270. The delay line DL could be placed elsewhere, for example somewhere else in the feedback loop 270.

[0185] The delay line DL is a time delay element, for example an element that has inductive behavior, for slowing down the arriving voltage wave from the feedback loop 270 during a period of the oscillation. This allows to tune the resonant circuit 272 to a desired switching and oscillation frequency, to move the oscillation frequency away from the natural resonant frequency given by the resonant circuit 272. This ensures that oscillation circuit 350 remains in a predefined frequency operating range to provide for the requisite inverted or 90° phase shifted feedback and also to make sure that the feedback loop 270 has a low impedance to provide for a high gain, as described in greater detail below.

[0186] 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 105. In such embodiments, the electrical contacts 160, 165 provide an electrical connection between the first and second electrodes 130, 135 and the feedback loop 270. In embodiments where the load capacitor CL is fixed within the feedback loop 270, for example, such that an aerosol-forming substrate 110 can be inserted and removed to and from a heating chamber 140 formed in between the first and second electrodes 130, 135, the electrical contacts 160, 165 provide electrical connections from the first and second electrodes 130, 135 to the next components in the feedback loop 270, e.g. inductors Li and L2.

[0187] 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 cells 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 aero- solization 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.

[0188] A capacitor Ci is arranged in parallel to the transistor T and therefore in parallel with the intrinsic capacitor of the transistor T (e.g. a field effect transistor). This facilitates a less voltagedependent oscillation and frequency, stabilizes the oscillation, and also improves the overall dielectric heating efficiency. Capacitance of capacitor Ci is chosen to be larger than the maximal intrinsic capacitor Ci of transistor T at the operating conditions, so that the variation of the intrinsic transistor based on frequency, temperature, etc. has much less or negligible influence on the feedback loop 270. For example, in a non-limiting embodiment, the value can be in a range between 2pF to 100pF, more preferably in a range between 5pF and 50pF.

[0189] A 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, the capacitive element 274 has the function of providing a 90° phase shift to the feedback voltage of the feedback loop 270 with minimized losses or other undesired effects, and it therefore needs to have a high-quality factor or Q factor, preferably above 1000 at 100MHz. The capacitance value for C2 of the capacitive element 274 should be relatively high as compared to Ci , for example in a range between 500pF to 100nF, more preferably between 1nF and 50nF, which leads to a low impedance of the capacitive element 274. In a variant, the capacitive element 274 can be implemented as a RC network to provide for the 90° phase shift, for example using two single-resistor-capacitor networks, having two capacitors in the feedback loop 270, each capacitor connected to ground via a resistor.

[0190] The resonant circuit 272, together with the capacitive element 274, provides for a 180° phase shift and a voltage gain from the output voltage UOUT to the input voltage UIN, and the transistor T (for example a FET) is configured for inverting operation, thereby also providing for another 180° phase shift. This results in a resonant or close-to resonant oscillation and an amplified voltage UL across the electrodes 130 and 135 of the load capacitor CL, as compared to the DC supply voltage. When operating close to resonance, the resonant circuit 272 behaves inductively, having a high Q factor. Furthermore, the feedback loop 270 is impedance-matched with the transistor T, at an impedance of approximately 500mQ to 8Q, preferably around 2Q, to provide for a high gain, leading to an increased voltage across the load capacitor CL. Also, preferably, this gain is achieved without the use of an additional voltage or current amplifying passive element, such as a tapped inductor or a transformer located in the circuit that forms the feedback loop 270, as such passive elements are difficult and lossy to operate and design at frequencies greater than 50 MHz. Preferably, the impedances of the resonant circuit 272 and the capacitor C2 add up to match the impedance of the transistor T, more preferably the resonant circuit 272 is substantially impedance-matched with the transistor T.

[0191] The combination of the capacitor Ci , the feedback loop 270 with the resonant circuit 272 and the capacitive element 274 can also be described as a bandpass filter or Pi or TT network that generates a 180° phase shift. In the illustrated embodiment, the resonant circuit 272 of the feedback loop 270 is not connected to ground, but is suspended with ends at each capacitor Ci and C2, thereby not having a direct ground connection at either end of resonant circuit 272, reducing stray elements and ground influences for more predictable operation.

[0192] At the operating frequency, the resonant circuit 272 including the load capacitor CL acts as an inductive load providing a first 90° phase shift, also referred to as a quarter-wave phase shift, and the capacitive element 274 exemplarily including a high quality factor capacitor C2 connected to ground, provides for a second 90° phase shift or quarter-wave phase shift.

[0193] The oscillation circuit 350 can be described or characterized as a Pierce oscillation circuit with a modified feedback loop 270, where the physical Quartz element is replaced by a Quartzmimicking or Quartz electric equivalent circuit to provide for an inverting feedback to the switching unit 260 that also operates in an inverted mode. In some embodiments, the resonant 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.

[0194] Figures 5A to 5F illustrate how a Quartz-mimicking or Quartz equivalent circuit may be derived using a variant of a parallel resonator circuit PRC, that can serve as an exemplary and non-limiting embodiment as a resonant circuit 272. A Quartz-mimicking or Quartz equivalent circuit can have a parallel resonance at a given frequency. This can be seen as a circuit with two branches, one representing the mechanical oscillation and one representing the electric behavior, as illustrated in Figures 5A and 5B. The mechanical oscillation is represented by a first branch having the load capacitor CL and an inductor LTOT. The electric oscillation is represented by a second branch arranged in parallel to the first branch, having a capacitor CE. This configuration leads to a series connection of two capacitors CL and CE (seen around the loop formed by the two branches) so that the capacitor CE will decrease the overall capacitive value of the equivalent circuit. Also, this circuit provides an inductive phase shift of about 90° within certain defined frequency range.

[0195] 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 the LTOT into two inductors Li and L2 on each side of the load capacitor CL, as shown in Figure 5D, to provide a split inductor or split-coil design and a more symmetric application of the voltage UL across the load capacitor CL, thereby improving dielectric heating efficiency. To provide for parallel resonance, the capacitor CE of the second branch can be replaced with an inductor (as shown in Figure 5F) due to the capacitor CE‘S minimal capacitive effect on the capacitor CL.

[0196] In a non-limiting example starting from the split inductors Li and L20f the resonant circuit 272 of Figure 5D, the inductors Li and L2 can be mutually magnetically coupled to form a mutual inductance M, thereby forming the parallel circuit branch or second branch of the resonant circuit 272, as shown in Figure 5E. The mutual magnetic coupling can be achieved by the close proximity of the two inductors Li and L2 with alignment of winding axis of the coils, or by use of a mutual magnetic core, or both. This has the advantage of providing a parallel-resonator circuit PRC without the use of additional wires for the second branch, and without additional windings or separate magnetic cores for a second parallelly-arranged inductor. This also allows for a symmetric arrangement that favors and facilitates the inductive coupling of the two inductors Li, L2 and the balancing of the voltage UL over the load capacitor CL. The symmetry of the two branches in either direction with first branch Li - CL - L2 and the second branch with an inductor LE, representing the two mutual inductance values, facilitates the symmetrical balancing of the voltage over the electrodes of the load capacitor CL, which consequently reduces losses created at the load capacitor CL. This split inductor principle can also be referred to as a split coil resonator.

[0197] The resonant circuit 272 could also be implemented as shown in Figure 5F, where the mutual inductance M (seen two times due to the mutuality) is replaced by a separate inductive element, for example the inductor LE.

[0198] The values of components in this resonant circuit 272 are preferably chosen to be in the following exemplary and non-limiting ranges. The LTOT can be a range between 10nH to 50nH, more preferably between 15nH and 40nH, which is the equivalent of Li plus L2, 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.

[0199] The resonant circuit 272 can be configured as another type of tank circuit providing for the 90° phase shift in a given frequency range. In one embodiment, the resonant circuit 272 can be implemented as a series resonant circuit, having the load capacitor CL connected in series with one or more inductive elements, configured to provide for an inductive response or 90° phase shift in a given frequency range that is suitable for dielectric heating.

[0200] T o have a proper inverting effect and a 180° phase shift on the feedback loop 270 between UIN and UOUT, the oscillation circuit 350 must remain in a frequency operating range where the behavior of the feedback loop 270 is highly inductive. In the example comprising a parallel resonator circuit (PRC), the series resonance frequency fsER (resonant frequency) is relatively close to the parallel resonance frequency fpAR (antiresonant frequency). If the oscillation frequency fs of the PRC exceeds the parallel resonance frequency fPAR, the feedback loop 270 will act capacitively and not provide the necessary phase inversion to the loop 270. Furthermore, the equivalent impedance of the circuit will increase to an extent that is too high for efficient dielectric heating as not providing for the requisite gain.

[0201] 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 the delay line DL can introduce a slight time delay limiting the oscillation frequency below the parallel resonance frequency. Figure 6 shows a frequency analyzer plot of an exemplary resonant circuit 272, specifically a plot of a parallel resonator circuit PRC showing the relationship between the oscillation frequency (with a series resonance at 855 MHz and a parallel resonance at 1.246 GHz), the phase shift across the PRC (with a relatively flat inductive 90° frequency response between the two resonant frequencies) and the effective impedance of the PRC. More specifically, it can be seen from Figure 6 that the 90° phase shift starts dropping before the parallel resonance frequency fpAR is reached. After the parallel resonance frequency fPAR, the phase shift response drops below 0° to capacitive behavior and the impedance is very high, e.g. 2.4kQ. The ideal operating frequency range is closer to the series resonance frequency fsER where the phase shift is still 90° and the impedance response is low, preferably an impedance that is less than 20, more preferably less than 10. The parallel resonance frequency fPAR can be above 1GHz, e.g. 1GHz to 1.5GHz, while the actual switching frequency fs can be below 1GHz, and this lower switching frequency is caused by the delay line DL.

[0202] Ideally, the oscillation frequency fs should be set to be below the parallel resonance frequency fpAR but above the series resonance frequency fsER, to make sure that two conditions are fulfilled, firstly (i) that the resonant circuit 272 behaves inductively to provide a 90° phase shift, and secondly (ii) to make sure that the impedance of the resonant circuit 272 (an therefore the feedback loop 270) is low, as illustrated in the graphs of Figure 6. For example, a resulting impedance of the feedback loop 270 at the oscillation frequency fs of the oscillation circuit can be in a range of approximately 100mQ to 2Q. Preferably, the delay line DL is configured such that the oscillation frequency fs is closer to the series resonance frequency fsER than to the parallel resonance frequency fPAR, thereby maintaining a low resonant circuit impedance while operating at a frequency range where the resonant circuit provides the 90° phase shift. The time delay caused by the delay line DL needs to be relatively short, as the series resonance and the parallel resonance of a parallel oscillating circuit PRC are close to each other, relative to the overall frequency range. Preferably, the delay caused by the delay line DL that acts of the feedback loop 270 should be in a range between 5% to 35% of the period of the parallel resonance frequency fPAR, providing that the above two conditions (i) and (ii) are fulfilled. In an embodiment, the delay caused by the delay line DL that acts on the feedback loop 270 is in a range between 35% and 90% of a difference between the period of the parallel resonance frequency fPAR and the period of the series resonance frequency fsER, again providing that the above two conditions (i) and (ii) are fulfilled, more preferably a range between 50% and 85%. For example, taking the illustration of Figure 6 and as a non-limiting numerical example, assuming that a parallel resonance frequency fPAR is at 1.25 GHz, therefore having a period of 800ps (picoseconds), and a series resonance is frequency fsER at 855MHZ, and therefore a period of 1169ps, there is a difference of 369ps between the period of fPAR and fsER. The time delay caused by the delay line DL can be in the above range, for example at 70% of the period difference between fPAR and 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 DL is implemented as a meandering conductive element having dominantly inductive behavior, for example a meandering element having from two (2) to twelve (12) meandering branches, more preferably from three (3) to eight (8) meandering branches. Such implementations exhibit minimal stray inductive and capacitive behavior. Various delay line structures can be used to provide the desired function, for example an Omega-shaped coil, single planar coil, flat inductor, wavy line, zig-zag line, or a sawtooth line. It is also possible to provide the required delay line functionality by a specific transmission line design. For example, it is possible that the physical element of the delay line DL is implemented as a conductor in a printed circuit board, for example implemented as a microstrip patch antenna. In some embodiments, a low-pass filter may be used as the delay line DL, however this will have an impact on the shape of the oscillating voltage, whereas a delay line DL that provides for a short time delay by inductive effect will not impact the wave shape. In the embodiment illustrated in Figure 4, the delay line DL is placed between the feedback loop output of the resonant circuit 272 and the capacitive element 274, but other arrangements are also possible.

[0203] Figures 7 to 9 illustrate schematic illustrations of bimetallic electrode arrangements acting as a dielectric heating element for use in the dielectric heating aerosol-generating system 100 of Figure 1. In these Figures, a deflection of the electrodes 130, 135, when subject to a temperature increase change caused by the aerosol-forming substrate 110 during heating, is indicated in dashed lines.

[0204] In Figures 7A-C, a bimetallic electrode arrangement having two opposed electrode plates 230, 235 is shown. The electrode plates 230, 235 are opposed to each other, so as to receive and / or hold the aerosol-forming substrate 110 therebetween and are at least partially arranged within or in close proximity to the heating chamber 140, so as to be subject to a temperature change caused by the aerosol-forming substrate 110 during heating. The electrode plates 230, 235 comprise at least two different layers 231 , 232 of metal having different thermal dilatation coefficients, so when subject to a temperature change caused by the aerosol-forming substrate 110 during heating, one metal expands more than the other, causing the bimetallic arrangement to bend or curve. Via the bimetallic arrangement, if the temperature of the aerosol-forming substrate 110 goes beyond a safety or predefined threshold, the electrode plates 230, 235 deflect such as to increase their distance which, consequently, determines a reduction in the electric field strength acting on the aerosol-forming substrate 110. By reducing the electric field strength, the heating power provided to the aerosol-forming substrate 110 decreases analogous with the temperature of the aerosol-forming substrate 110.

[0205] In some examples, the electrode plates 230, 235 are arranged to flex against the substrate 110 (e.g., in the form of a pouch, cuboid, etc.) so that the substrate 110 can be compressed somewhat to yield to the movement of the electrodes 230, 235 while still allowing the electrodes 230, 235 to exert pressure (e.g., a holding pressure) on the substrate 110 at any temperature within a range of 0°C to 400°C. That is, when the temperature of the substrate 110 increases or is too high, the electrodes 230, 235 increase the distance from each other, thereby reducing pressure exerted by them on the substrate 110. On the contrary, when the temperature of the substrate 110 decreases or is too low, the electrodes 230, 235 decrease the distance from each other, thereby increasing pressure exerted by them on the substrate 110. While in this embodiment, the pressure on the substrate 110 is directly exerted by the electrodes 230, 235, there are alternative embodiments existing where the pressure is exerted via a holding structure / arrange- ment, such as movable walls of the heating chamber 140. In Figure 7A, the electrode plates 230, 235 are designed in a cantilever-based arrangement, meaning each electrode plate 230, 235 is supported only at one end, allowing the other end to move freely, preferably symmetrically to a central axis, which corresponds to a length direction of the electrodes 230, 235. This setup enables the electrode plates 230, 235 to function as cantilevers, which can bend or deflect due to a temperature change of the aerosol-forming substrate 110, and at the same time enable to hold the aerosol-forming substrate 110 in place.

[0206] In other configurations, holding of the aerosol-forming substrate 110 is achieved by walls (not shown) of the heating chamber structure arranged between the aerosol-forming substrate 110 and the electrodes 130, 135.

[0207] In Figure 7B, the electrode plates 230, 235 are configured to curve inward (i.e. , concave) with respect to the central axis and outward (i.e., convex) in Figure 7C.

[0208] In contrast to the embodiments shown in Figures 7A-C, Figure 8 illustrates a schematic illustration of a bimetallic electrode arrangement having a pair of interdigitated electrodes 330, 335 arranged to interdigitate together around a cylindrical axis to form a tubular structure configured to receive and / or hold the aerosol-forming substrate 110 therebetween. In particular, the interdigitated electrodes 330, 335 comprise a respective ring element 332, 337 from which an electrode digit 331 , 336 extends towards the respective other ring element in an interdigitated fashion. Preferably, the ring elements 332, 337 and / or the tubular structure can have a diameter between 5 mm to 9 mm. In the illustrated embodiment, there is one pair of electrodes with different polarity and each of them having one electrode digit 331 , 336. In other embodiments, more than one pair of electrodes and / or more than one electrode digit may be present for a respective electrode. Likewise, the interdigitated electrodes 330, 335 can also be arranged in a plate-like (i.e. flat) structure in other configurations.

[0209] Alternatively, as shown in Figure 9, a bimetallic electrode arrangement having two facing semi-spheres electrodes 430, 435 with gap areas 440, 445 therebetween can be used. The semispheres electrodes 430, 435 are dimensioned to receive and / or hold the aerosol-forming substrate 110 therebetween. In such configuration, an electric field strength between gap areas is higher compared to an electric field strength between the spherical portions. By opening up the semi-spheres electrodes 430, 435 on their end portions, the maximum electric field strength applied to the aerosol-forming substrate 110 can be significantly reduced while requiring only a small amount of deflection. This may be beneficial in terms of portion-wise heating of the aerosol-forming substrate 110. For example, with ongoing depletion of the aerosol-forming substrate 110 on its periphery, the semi-spheres electrodes 430, 435 open up at their ends and cause a relatively uniform heating of a middle portion of the aerosol-forming substrate 110.

[0210] Figures 10-11 illustrate schematic illustrations of an electrode displacement mechanism comprising an actuator 510, 610, with a movable element to engage with at least one electrode so as to adjust the distance between the at least two electrodes 130, 135 upon activation in dependence of the temperature of the aerosol-forming substrate 110 for use in the dielectric heating aerosol-generating system 100 of Figure 1. In these embodiments, the actuators 510, 610 are formed as linear actuators comprising a piston 512, 612 as a movable element to adjust a distance between the at least two electrodes 130, 135 by linear movement. While Figures 10A-B refer to a configuration where a passively actuated actuator 510 in form of a thermal actuation device is used, Figure 11 shows an embodiment where an actively actuated actuator 610 in form of an electromechanical actuator, particularly a microactuator, is used.

[0211] As used herein, the term “passive actuation” refers to an activation scheme where the actuator is directly driven by expansion or retraction of a temperature sensitive material that reversibly changes one or more of its dimensions as a function of temperature. The term “active actuation” refers to an activation scheme where the actuator is driven with the use of a control circuit based on direct or indirect temperature measurements of the aerosol-forming substrate 110.

[0212] With reference to Figures 10A-B, the passively actuated actuator 510 and the electrodes 130, 135 are arranged within a common heat-insulated volume 520, so as to be subject to a temperature change of the aerosol-forming substrate 110 through the convection and conduction of heat when received and heated in the heating chamber 140. The passively actuated actuator 510 comprises a material chamber 514 filled with the temperature-sensitive material, such as wax, that changes its volume in response to a temperature increase in the heat-insulated volume 520, thereby extracting the piston 512 and thus increasing a distance between the electrodes 130, 135.

[0213] Alternatively, the passively actuated actuator 510 is arranged outside the heat-insulated volume 520. In this embodiment, the piston 512 is made of a material with relatively high thermal conductivity, for example a metal, such as aluminum or copper, to transfer heat from the electrodes to the temperature-sensitive material within the material chamber 514. In Figure 11 , there is illustrated a sensing arrangement 620 to measure a temperature inside the heating chamber 140 and a controller 630 configured to cause movement of the movable element of the actively actuated actuator 610 based on a signal from the sensing arrangement 620. In examples, the sensing arrangement 620 comprises a resistive temperature detector comprising a temperature sensitive resistive track (not shown). In other examples, the sensing arrangement 620 comprises an infrared sensor to measure infrared radiation emitted by the aerosol-forming substrate in operation that is indicative of the temperature of the aerosol-forming substrate. In the shown embodiment, the actively actuated actuator 610 is a micro-actuator based on piezoelectric (piezo) materials configured to convert electrical energy supplied by the power supply 170 into mechanical motion with relatively high accuracy and responsiveness. The actuator may be controlled by the controller 360 in a feedback loop configuration with the sensing arrangement 620.

[0214] Figure 12 illustrates a schematic illustration of an electrode displacement mechanism having a passively actuated actuator in form of a temperature-sensitive tubular structure 710 for use in the dielectric heating aerosol-generating system of Figure 1. In this embodiment, one or more pairs of interdigitated electrodes 721 , 722 are arranged as parallel strips along a longitudinal extension of the temperature-sensitive tubular structure 720. The temperature-sensitive tubular structure is made of a temperature-sensitive material configured to expand in radius r1 and retract in radius r2 upon being subject to a temperature change of the aerosol-forming substrate 110 arranged within the temperature-sensitive tubular structure 720. In embodiments, the temperature-sensitive tubular structure 710 is formed of an auxetic sleeve material that reversibly expands in radius and retracts its radius upon being subject to temperature change.

Claims

CLAIMS1 . An aerosol-generating device comprising a heating chamber configured to at least partly receive an aerosol-forming substrate, a dielectric heating element comprising at least two electrodes, wherein the dielectric heating element, in operation, heats the aerosol-forming substrate through dipole rotation caused by an alternating electric field generated within the heating chamber by the at least two electrodes, and an electrode displacement mechanism designed to adjust a distance between the at least two electrodes in dependence of a temperature of the aerosol-forming substrate, thereby modifying an electric field strength of the alternating electric field in the heating chamber, wherein the electrode displacement mechanism comprises a temperature-sensitive material that reversibly changes one or more of its dimensions in dependence of the temperature of the aerosol-forming substrate.

2. The aerosol-generating device according to the preceding claim, wherein the electrode displacement mechanism comprises a bimetallic arrangement, the bimetallic arrangement comprises at least two different layers of metal having different thermal dilatation coefficients, so that when heated, one metal expands more than the other, causing at least one electrode of the at least two electrodes to bend or curve.

3. The aerosol-generating device according to claim 2, wherein the at least one electrode of the at least two electrodes is arranged in a cantilever-based arrangement, to approach or retract from the other electrode as a function of temperature.

4. The aerosol-generating device according to claim 2 or 3, wherein the at least two electrodes comprise the bimetallic arrangement, and are configured to symmetrically bend or curve relative to a central axis, which corresponds to a longitudinal direction of the electrodes that have an elongated form.

5. The aerosol-generating device according to any one of the preceding claims, wherein the electrode displacement mechanism comprises an actuator with a movable element to engage with the at least two electrodes, so as to adjust the distance between the at least two electrodes upon activation in dependence of the temperature of the aerosol-forming substrate.

6. The aerosol-generating device according to the preceding claim, wherein the actuator is a linear actuator comprising a piston as a movable element, the piston configured to engage with at least one of the at least two electrodes such as to adjust a distance between the at least two electrodes by linear movement.

7. The aerosol-generating device according to claim 5 or 6, wherein the actuator comprises a thermal actuation device including the temperature-sensitive material.

8. The aerosol-generating device according to the preceding claim, wherein the thermal actuation device includes a material chamber filled with the temperature-sensitive material, such as wax, arranged to change its volume in dependence of a temperature of the aero- sol-forming substrate.

9. The aerosol-generating device according to any one of the preceding claims, wherein the at least two electrodes comprise one or more pairs of interdigitated electrodes arranged as parallel strips along a longitudinal extension of a temperature-sensitive tubular structure to receive and / or hold the aerosol-forming substrate therebetween, wherein the temperature-sensitive tubular structure is made of the temperature-sensitive material configured to expand in radius and retract in radius upon being subject to temperature change, preferably to increase radius with increasing temperature and decrease radius with decreasing temperature.

10. The aerosol-generating device according to any one of the preceding claims, comprising a substrate holding mechanism configured to hold the aerosol-forming substrate when received in the heating chamber.11 . The aerosol-generating device according to any one of the preceding claims, comprising a heat-insulated volume thermally connected to the heating chamber, wherein at least one of the at least two electrodes is at least partially arranged within the heat-insulated volume so as to be subject to a temperature change of the aerosol-forming substrate arranged in the heating chamber in use.

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

13. A method of manufacturing an aerosol-generating device, preferably according to any one of the preceding claims, wherein the method comprises providing an electrode displace-merit mechanism designed to adjust a distance between at least two electrodes for dielectrically heating an aerosol-forming substrate therebetween in dependence of a temperature of the aerosol-forming substrate, the electrode displacement mechanism comprising a temperature-sensitive material that reversibly changes one or more of its dimensions in dependence of the temperature of the aerosol-forming substrate.

14. The method according to the preceding claim, wherein the electrode displacement mechanism comprises one or more of the following electrode displacement mechanisms A to C:A. A bimetallic arrangement, wherein at least one of: the bimetallic arrangement is attached to at least one of the at least two electrodes, and / or at least one of the at least two electrodes is at least partially made of the bimetallic arrangement.B. A thermal actuation device configured to convert thermal energy into a mechanical movement, preferably a linear movement, for adjusting a distance between the at least two electrodes in response to a temperature change of the aerosol-forming substrate.C. A temperature-sensitive tubular structure having the at least two electrodes arranged thereon, and configured to convert thermal energy into a mechanical movement, preferably a radial movement, for adjusting a distance between the at least two electrodes in response to a temperature change of the aerosolforming substrate.

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