Dielectric heating aerosol-generating device with air gap and shielding

Abstract

Dielectric heating aerosol-generating device with air gap and shielding The present invention relates to an aerosol-generating device that comprises a heating chamber which is arranged to at least partly receive an aerosol-forming substrate, a dielectric heater including at least two electrode plates forming a capacitor, the at least two electrodes and the heating chamber being arranged to heat the aerosol-forming substrate by an alternating dielectric field caused between the at least two electrode plates when arranged at least partially inside the heating chamber, a shell at least partly encompassing the heating chamber, and a retaining mechanism which is arranged within the shell so that the heating chamber is suspended within the shell, with a gap between the shell and the heating chamber.

Description

[0001] Dielectric heating aerosol-generating device with air gap and shielding

[0002] The present invention relates to an aerosol-generating device, and specifically to an aerosol-generating device configured to heat an aerosol-forming substrate by dielectric heating. The present disclosure further relates to an aerosol-generating system comprising an aerosolgenerating 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 aerosolforming substrate more remote from the heating element.

[0005] Systems that dielectrically heat an aerosol-forming substrate have been proposed, which advantageously provide uniform heating of the aerosol-forming substrate. However, known dielectric heating systems are less efficient than inductive heating systems and require complex electrical circuitry in order to achieve the necessary voltages and frequencies for dielectric heating of an aerosol-forming substrate.

[0006] Dielectric heating aerosol-generating devices may use switching units, e.g. a transistor, for generating the radio frequency (RF) electromagnetic radiation for dielectrically heating the substrate via at least one pair of electrodes arranged so that the substrate functions as a dielectric therebetween. As well known in the field, shielding of the capacitive plates or electrodes is crucial for any commercially available device, for electromagnetic compliance and safety. Further, the transistor produces heat which needs to be dissipated in a manner that is not harmful to a user.

[0007] It would be desirable to provide a device and system that dielectrically heats an aerosolforming substrate with greater efficiency, while still being realizable in a compact or handheld system, wherein the electromagnetic shielding of the capacitive plates and the heat management of the switching unit are improved.

[0008] According to an aspect of the present invention, there is provided an aerosol-generating device comprises a heating chamber which is arranged to at least partly receive an aerosolforming substrate, a dielectric heater including at least two electrode plates forming a capacitor, the at least two electrodes and the heating chamber being arranged to heat the aerosol-forming substrate by an alternating dielectric field caused between the at least two electrode plates when arranged at least partially inside the heating chamber, a shell at least partly encompassing the heating chamber, and a retaining mechanism which is arranged within the shell so that the heating chamber is suspended within the shell, with a gap between the shell and the heating chamber.

[0009] An advantage of this idea is that the heating chamber can at least partially be encompassed by a low-k insulating material, such as air or vacuum, which does not heat up during operation of the dielectric heater. Advantageously, a solid heat insulation material having a higher dielectric constant than air or vacuum can be avoided which would be subjected to e-field radiation and could cause additional undesired heat. Of course, also any other low-dielectric gas or vacuum may also be used instead of air.

[0010] According to an advantageous example, the gap is at least partly filled with air. Air has a relative permittivity (i.e. dielectric constant) close to vacuum and is thus heated up by the dielectric heater to a much lower extent than any solid thermal insulator. In addition, air or vacuum has a relatively high thermal resistivity or relatively low thermal conductivity (a thermal conductivity of about 0.025 W / (m K)) and provides an effective means of heat insulation and minimized generation of dielectric losses. Thus, empty spaces for thermal insulation are advantageous to avoid or reduce the use of solid thermally insulating layers that — while they may have good thermal insulation properties — can heat up when exposed to an RF electric field radiation from the dielectric heater. Thus, air or vacuum may be used as a thermal insulation layer. It should be pointed out that vacuum will in many cases be a too expensive solution to be implemented, requiring vacuum sealing. However, also air has the advantage that no or very low amounts of heat will be caused by exposure to the alternating electric field given the low polar nature of air.

[0011] Instead of the thermal conductivity, also the R-value can be taken into account. As this is generally known, the R-value, or resistance value, in the context of thermal insulation, refers to a measure of how well a material resists the flow of heat. It is used to rate the insulation effectiveness of various materials. The higher the R-value, the better the material insulates against heat transfer.

[0012] The R-value is the thermal resistance per unit area and is defined by the following equation: R=L / k with:

[0013] R... thermal resistance (R-value)

[0014] L... thickness of the material, measured in meters k... thermal conductivity of the material, measured in W / (mK)

[0015] According to a further advantageous example, the heating chamber comprises a wall made of low-dielectric material, and wherein the at least two electrode plates are arranged on an outer surface or on an inner surface of the wall. Thus, the electrodes have a secure mechanical support and may also be formed by thin films or printed structures. According to a further advantageous example, the shell comprises a thermally insulating body with an electrically conductive inner and / or outer shielding layer. Providing an electrically conductive shielding layer is important for ensuring the required electromagnetic compatibility during operation.

[0016] According to a further advantageous example, the thermally insulating body comprises a polymer material, preferably polyether ether ketone, PEEK. The advantage of choosing such a material is that it can be fabricated in a cost efficient matter and at the same time has satisfactory thermal insulation properties and also having a relatively low relative permittivity.

[0017] According to a further advantageous example, the inner and / or outer shielding layer comprises at least one of aluminium, copper, and an Al-Cu alloy, or other alloys including either Al or Cu. These metals are well established and have excellent electrical conductivity. Various technologies can be used for fabricating and assembling the inner and / or outer shielding layer.

[0018] According to a further advantageous example, wherein the inner and / or outer shielding layer comprises a flexible printed circuit board, PCB, which is arranged adjacent to an outer and / or inner surface of the thermally insulating body, respectively.

[0019] According to a further advantageous example the inner and / or outer shielding layer comprises a coating deposited onto an outer and / or inner surface of the thermally insulating body, respectively, by adhesion.

[0020] According to a further advantageous example, the inner and / or outer shielding layer comprises a coating deposited onto an outer and / or inner surface of the thermally insulating body, respectively, by an additive coating process, preferably chemical vapor deposition, CVD, or physical vapor deposition, PVD.

[0021] According to a further advantageous example, at least one shielding layer is supported by the retaining mechanism within the shell. With this geometry, the shielding layer can be thermally insulated by a low-k material like air or vacuum.

[0022] According to a further advantageous example, the at least two electrodes oppose each other for heating the aerosol-forming substrate therebetween. This is a particularly energy efficient and space saving architecture. In particular, the electrodes may form part of a load capacitor of an oscillation circuit.

[0023] According to a further advantageous example, the retaining mechanism includes at least one spacer, column, or body having a low dielectric constant, the spacer having a width of less than 2 mm. By using a spacer material with a low dielectric constant, it can be ensured that the spacer itself is not heated up during the dielectric heating operation.

[0024] According to another example, the retaining mechanism can be formed by a highly porous body, for example a solid foam. Preferably, the porosity or void fraction is more than 90%, more preferably more than 95%. For example, the retaining mechanism comprises a highly porous body, and the gap is formed by voids of the porous body. According to a further advantageous example, the retaining mechanism comprises a low-k dielectric material. In particular, according to various examples, the retaining mechanism may comprise at least one of quartz glass, fluorine-doped silicon dioxide, organosilicate glass (OSG), carbon-doped oxide (CDO), porous silicon dioxide, porous organosilicate glass, carbon doped oxide, polyimide, polynorbornene, benzocyclobutene, polytetrafluoroethylene (PTFE), hydrogen silsesquioxane, methylsilsesquioxane, oxycarbosilane, carbon doped oxide (CDO), and material with Si, C, O, and H (SiCOH).

[0025] According to a further advantageous example, the material that forms the retaining mechanism has a dielectric constant below 3.3, more preferably below 3. The lowest possible value is, of course, 1.

[0026] According to a further advantageous example, the retaining mechanism includes islands that are embedded into the wall of the shell, serving as anchoring points for the at least two electrodes. By such a geometry, a particularly smooth surface of the respective wall and a secure attachment of the electrodes can be achieved. Moreover, when providing the islands as anchoring points for the electrodes, the electrodes can be mounted to be surrounded by air as an insulator. Thus, undesired heat generation due to dielectric heating by the electric field can be avoided during operation. This can be further improved by arranging the electrodes so that the electrodes are not in direct contact with the shell or walls of the heating chamber.

[0027] According to a further advantageous example, the retaining mechanism includes at least one spacer comprising at least one of polyimide, ceramic material, temperature resistant material, and porous material, for example a solid foam having a high porosity value.

[0028] According to a further advantageous example, the shell may at least partly electrically conductive and may be connected to ground, thereby providing an electromagnetic shielding configured to shield the surrounding environment from electromagnetic radiation emitted during the heating process.

[0029] The heating chamber may have any suitable form to easily accommodate an aerosolforming substrate. Advantageously, the heating chamber may have a cylindrical shape, or a rectangular parallelepiped shape.

[0030] Accordingly, the heating chamber may have a circular cross-section, or a polygonal, e. g. rectangular cross-section.

[0031] For ensuring a particularly efficient energy transfer from the electrodes to the aerosolforming substrate as well as an efficient mechanical fixation of the article, the heating chamber may comprise at least two opposing electrodes formed as flat springs for fixing the aerosol-forming substrate.

[0032] According to a further advantageous example, wherein a gap is formed between the flat springs and the shell. Thus, the electrodes are insulated by a very low-k material (in other words, a material having a low relative permittivity) such as air. According to a further advantageous example, the shell is hollow to form an air or vacuum space therein. Thus, it can be avoided that the thermally insulating material is heated up excessively due to dielectric heating by the electric field during the dielectric heating process. The walls of the heating chamber and the shell may also integrally form a void for containing air or a vacuum.

[0033] According to a further advantageous example, the aerosol-generating device comprises the oscillation circuit comprising a switching unit, wherein the heating element is fed by the oscillation circuit. For instance, the switching unit may comprise a metal-oxide semiconductor transistor, MOSFET, preferably a laterally-diffused metal-oxide semiconductor, LDMOS, transistor. LDMOS technology offers the advantages of high voltage handling capability, high power density, low on- resistance, high linearity, and high gain. To achieve these advantages, a LDMOS transistor is structurally different from a conventional MOSFET by the fact that the former has a laterally diffused channel, a thicker drain drift region, a buried drain contact, a thicker gate oxide, and a larger layout. The thick and highly-doped drift region in LDMOS can withstand higher electric field and therefore, the device can work at high voltages without breakdown. Also, higher doping concentration reduces the resistance of the device, which results in lower power dissipation and higher efficiency. Moreover, the lateral diffusion regions benefit from spreading of the electric field and help reduce breakdowns. In summary, the amalgamation of a highly-doped drift region and a lateral diffusion region marks LDMOS devices well-suited for high-power and high-efficiency RF amplification.

[0034] According to a further advantageous example, the oscillation circuit further may comprise a delay element configured to impede the switching speed of the switching unit. Specifically, the delay element may delay a switching signal received by the switching unit.

[0035] An oscillation circuit comprising a delay element is sometimes referred to as a delay-line oscillator. The delay-line oscillator is a form of electronic oscillator that uses a delay line, or delay element as its principal timing element. A delay-line oscillator may be set to oscillate by inverting the output of the delay line or delay element and feeding that signal back to the input of the delay line or delay element with appropriate amplification.

[0036] 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.

[0037] According to a further advantageous example, the heating chamber has inner walls, which comprise a material with a low relative permittivity, preferably quartz glass, or PEEK. Thus, easy cleaning of the heating chamber can be achieved and the heating chamber can be isolated from other elements that are subject to heating, to avoid contamination.

[0038] According to a further advantageous example, the inner walls of the heating chamber are coated at least partly with an inert protective layer.

[0039] According to a further aspect of the present invention, there is provided an aerosolgenerating device comprising a heating chamber which is arranged to at least partly receive an aerosol-forming substrate so that in operation the aerosol-forming substrate is heated by dipole rotation when subjected to an alternating electric field inside the heating chamber, a shell at least partly encompassing the heating chamber, wherein the shell is at least partly electrically conductive and forms an electromagnetic shielding configured to shield the surrounding environment from electromagnetic radiation emitted during the heating process. Such an electromagnetic shielding ensures the shielding of the capacitive plates or electrodes, which is crucial for any commercially available device, for electromagnetic compliance and safety.

[0040] According to a further aspect of the present invention, there is provided a system comprising an aerosol-generating article comprising a solid aerosol-forming substrate; and an aerosolgenerating device according to any one of the aspects and examples above for dielectrically heating the solid aerosol-forming substrate.

[0041] According to a further aspect of the present invention, there is provided a method to manufacture an aerosol-generating device, preferably according to any of the aspects and examples described above, the method comprising providing a heating chamber which is arranged to at least partly receive an aerosol-forming substrate, wherein the heating chamber comprises a heating element, which in operation heats the aerosol-forming substrate by dipole rotation when subjected to an alternating electric field inside the heating chamber, arranging a shell to at least partly encompass the heating chamber, wherein a retaining mechanism is provided, the retaining mechanism being arranged within the shell so that the heating chamber is suspended within the shell, with a gap between the shell and the heating chamber.

[0042] The gap may at least partly be filled with air.

[0043] According to a further advantageous example, the heating chamber comprises a wall made of low-dielectric material, and wherein the at least two electrode plates are arranged on an outer surface or on an inner surface of the wall. Thus, the electrodes have a secure mechanical support and may also be formed by thin films or printed structures.

[0044] According to a further advantageous example, the shell comprises a thermally insulating body with an electrically conductive inner and / or outer shielding layer. Providing an electrically conductive shielding layer is important for ensuring the required electromagnetic compatibility during operation.

[0045] According to a further advantageous example, the thermally insulating body comprises a plastic material, preferably polyether ether ketone (PEEK). The advantage of choosing such a material is that it can be fabricated in a cost efficient matter and at the same time has satisfactory thermal insulation properties, as well as chemical stability when subject to electric fields.

[0046] According to a further advantageous example, the inner and / or outer shielding layer comprises at least one of aluminium, copper, an Al-Cu alloy, or an alloy based on Al or Cu. These metals are well established and have excellent electrical conductivity. Various technologies can be used for fabricating and assembling the inner and / or outer shielding layer.

[0047] According to a further advantageous example, wherein the inner and / or outer shielding layer comprises a flexible printed circuit board, PCB, which is arranged adjacent to an outer and / or inner surface of the thermally insulating body, respectively.

[0048] According to a further advantageous example, the inner and / or outer shielding layer comprises a coating deposited onto an outer and / or inner surface of the thermally insulating body, respectively, by adhesion.

[0049] According to a further advantageous example, the inner and / or outer shielding layer comprises a coating deposited onto an outer and / or inner surface of the thermally insulating body, respectively, by an additive coating process, preferably chemical vapor deposition, CVD, or physical vapor deposition, PVD.

[0050] According to a further advantageous example, at least one shielding layer is supported by the retaining mechanism within the shell. With this geometry, the shielding layer can be electrically insulated by a low-k material like air or vacuum.

[0051] According to a further advantageous example, the at least two electrodes oppose each other for heating the aerosol-forming substrate therebetween. This is a particularly energy efficient and space saving architecture. In particular, the electrodes may form a part of a load capacitor of the oscillation circuit.

[0052] According to a further advantageous example, the retaining mechanism includes at least one spacer or column having a low dielectric constant, the spacer having a width of less than 2mm. By using a spacer material with a low dielectric constant, it can be ensured that the spacer itself is not heated up during the dielectric heating operation.

[0053] According to a further advantageous example, the retaining mechanism comprises a low-k dielectric material. In particular, according to various examples, the retaining mechanism may comprise at least one of quartz glass, fluorine-doped silicon dioxide, organosilicate glass (OSG), carbon-doped oxide (CDO), porous silicon dioxide, porous organosilicate glass, carbon doped oxide, polyimide, polynorbornene, benzocyclobutene, polytetrafluoroethylene (PTFE), hydrogen silsesquioxane, methylsilsesquioxane, oxycarbosilane, carbon doped oxide (CDO), and material with Si, C, O, and H (SiCOH).

[0054] According to a further advantageous example, the retaining mechanism has a dielectric constant below 3.3, more preferably below 3. The lowest possible value is, of course, 1 . According to a further advantageous example, the retaining mechanism includes islands that are embedded into the wall of the shell, serving as anchoring points for the at least two electrodes. By such a geometry, a particularly smooth surface of the respective wall and a secure attachment of the electrodes can be achieved. Moreover, when providing the islands as anchoring points for the electrodes, the electrodes can be mounted to be surrounded by air as an insulator. Thus, undesired heat generation due to the electric field can be avoided during operation. This can be further improved by arranging the electrodes so that the electrodes are not in direct contact with the shell or walls of the heating chamber.

[0055] According to a further advantageous example, the retaining mechanism includes at least one spacer comprising at least one of polyimide, ceramic material, temperature resistant material, and porous material.

[0056] According to a further advantageous example, the shell may at least partly electrically conductive and may be connected to ground, thereby providing an electromagnetic shielding configured to shield the surrounding environment from electromagnetic radiation emitted during the heating process.

[0057] The heating chamber may have any suitable form to easily accommodate an aerosolforming substrate. Advantageously, the heating chamber may have a cylindrical shape a rectangular parallelepiped shape.

[0058] Accordingly, the heating chamber may have a circular cross-section, or a polygonal, e. g. rectangular cross-section.

[0059] For ensuring a particularly efficient energy transfer from the electrodes to the aerosolforming substrate as well as an efficient mechanical fixation of the article, the heating chamber may comprise at least two opposing electrodes formed as flat springs for fixing the aerosol-forming substrate.

[0060] According to a further advantageous example, wherein a gap is formed between the flat springs and the shell. Thus, the electrodes are insulated by a very low-k material such as air.

[0061] According to a further advantageous example, the shell is hollow to form an air or vacuum space therein. Thus, it can be avoided that the thermally insulating material is heated up excessively due to the electric field during the dielectric heating process. The walls of the heating chamber and the shell may also integrally form a void for containing air or a vacuum.

[0062] According to a further advantageous example, the aerosol-generating device comprises an oscillation circuit comprising a switching unit, wherein the heating element is fed by the oscillation circuit.

[0063] According to a further advantageous example, the heating chamber has inner walls, which comprise a material with a low dielectric constant, preferably quartz glass, or polyimide. Thus, easy cleaning of the heating chamber can be achieved. According to a further advantageous example, the inner walls of the heating chamber are coated at least partly with an inert protective layer.

[0064] As used herein, the term “aerosol-generating device” relates to a device that interacts with an article comprising an aerosol-forming substrate to generate an aerosol.

[0065] As used herein, the term “aerosol-forming substrate” relates to a substrate capable of releasing volatile compounds that can form an aerosol. Such volatile compounds can be released by heating the aerosol-forming substrate.

[0066] As used herein, the term “puff” means the action of a user drawing an aerosol into their body through their mouth or nose.

[0067] 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 I EC 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.

[0068] 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.

[0069] Example Ex1 . An aerosol-generating device comprising: a heating chamber which is arranged to at least partly receive an aerosol-forming substrate, a dielectric heater including at least two electrode plates forming a capacitor, the at least two electrodes and the heating chamber being arranged to heat the aerosol-forming substrate by an alternating dielectric field caused between the at least two electrode plates when arranged at least partially inside the heating chamber, a shell at least partly encompassing the heating chamber, and a retaining mechanism which is arranged within the shell so that the heating chamber is suspended within the shell, with a gap between the shell and the heating chamber.

[0070] Example Ex2. The aerosol-generating device according to example Ex1 , wherein the gap is at least partly filled with air.

[0071] Example Ex3. The aerosol-generating device according to any one of the preceding examples, wherein the heating chamber comprises a wall made of low-dielectric material, and wherein the at least two electrode plates are arranged on an outer surface or on an inner surface of the wall.

[0072] Example Ex4. The aerosol-generating device according to any one of the preceding examples, wherein the shell comprises a thermally insulating body with an electrically conductive inner and / or outer shielding layer. Example Ex5. The aerosol-generating device according to example Ex4, wherein the thermally insulating body comprises a polymer material, preferably polyether ether ketone, PEEK.

[0073] Example Ex6. The aerosol-generating device according to example Ex4 or Ex5, wherein the inner and / or outer shielding layer comprises at least one of aluminum, copper, and an Al-Cu alloy.

[0074] Example Ex7. The aerosol-generating device according to any one of examples Ex4 to Ex6, wherein the inner and / or outer shielding layer comprises a flexible printed circuit board, PCB, which is arranged adjacent to an outer and / or inner surface of the thermally insulating body, respectively.

[0075] Example Ex8. The aerosol-generating device according to any one of examples Ex4 to Ex7, wherein the inner and / or outer shielding layer comprises a coating deposited onto an outer and / or inner surface of the thermally insulating body, respectively, by adhesion.

[0076] Example Ex9. The aerosol-generating device according to any one of examples Ex4 to Ex7, wherein the inner and / or outer shielding layer comprises a coating deposited onto an outer and / or inner surface of the thermally insulating body, respectively, by an additive coating process, preferably chemical vapor deposition, CVD, or physical vapor deposition, PVD.

[0077] Example Ex10. The aerosol-generating device according to any one of the preceding examples, wherein at least one shielding layer is supported by the retaining mechanism within the shell.

[0078] Example Ex11. The aerosol-generating device according to any one of the preceding examples, wherein the at least two electrodes oppose each other for heating the aerosol-forming substrate therebetween.

[0079] Example Ex12. The aerosol-generating device according to any one of the preceding examples, wherein the retaining mechanism includes at least one spacer or column having a low relative permittivity, the spacer having a width of less than 2 mm.

[0080] Example Ex13. The aerosol-generating device according to any one of the preceding examples, wherein the retaining mechanism comprises a low-k dielectric material.

[0081] Example Ex14. The aerosol-generating device according to example Ex13, wherein the retaining mechanism comprises at least one of quartz glass, fluorine-doped silicon dioxide, organosilicate glass (OSG), carbon-doped oxide (CDO), porous silicon dioxide, porous organosilicate glass, carbon doped oxide, polyimide, polynorbornene, benzocyclobutene, polytetrafluoroethylene (PTFE), hydrogen silsesquioxane, methylsilsesquioxane, oxycarbosilane, carbon doped oxide (CDO), and material with Si, C, O, and H (SiCOH).

[0082] Example Ex15. The aerosol-generating device according to any one of the preceding examples, wherein the retaining mechanism has a relative permittivity below 3.3, more preferably below 3. Example Ex16. The aerosol-generating device according to any one of the preceding examples, wherein the retaining mechanism includes islands that are embedded into the wall of the heating chamber or into a wall of the shell, serving as anchoring points for the at least two electrodes, and / or wherein the retaining mechanism includes at least one pin-like structure, walls, and / or a body or layer comprising a material with a porosity of more than 90%, more preferably of more than 95%.

[0083] Example Ex17. The aerosol-generating device according to any one of the preceding examples, wherein the electrodes are not in direct contact with the shell.

[0084] Example Ex18. The aerosol-generating device according to any one of the preceding examples, wherein the retaining mechanism includes at least one spacer comprising at least one of polyimide, ceramic material, temperature resistant material, and porous material.

[0085] Example Ex19. The aerosol-generating device according to any one of the preceding examples, wherein the shell is at least partly electrically conductive and is connected to ground, thereby providing an electromagnetic shielding configured to shield the surrounding environment from electromagnetic radiation emitted during the heating process.

[0086] Example Ex20. The aerosol-generating device according to any one of the preceding examples, wherein the heating chamber has a cylindrical shape.

[0087] Example Ex21. The aerosol-generating device according to any one of the preceding examples, wherein the heating chamber has a rectangular parallelepiped shape.

[0088] Example Ex22. The aerosol-generating device according to any one of the preceding examples, wherein the heating chamber has a circular cross-section or wherein the heating chamber has a polygonal cross-section.

[0089] Example Ex23. The aerosol-generating device according to any one of the preceding examples, wherein the heating chamber comprises at least two opposing electrodes formed as flat springs for fixing the aerosol-forming substrate.

[0090] Example Ex24. The aerosol-generating device according to example Ex23, wherein a gap is formed between the flat springs and the shell.

[0091] Example Ex25. The aerosol-generating device according to any one of the preceding examples, wherein the shell is hollow to form an air or vacuum space therein.

[0092] Example Ex26. The aerosol-generating device according to any one of the preceding examples, wherein the aerosol-generating device comprises an oscillation circuit comprising a switching unit, wherein the heating element is fed by the oscillation circuit.

[0093] Example Ex27. The aerosol-generating device according to any one of the preceding examples, wherein the heating chamber has inner walls, which comprise a material with a low dielectric constant, preferably quartz glass, or polyimide.

[0094] Example Ex28. The aerosol-generating device according to example Ex27, wherein the inner walls of the heating chamber are coated at least partly with an inert protective layer. Example Ex29. An aerosol-generating device comprising: a heating chamber which is arranged to at least partly receive an aerosol-forming substrate so that in operation the aerosol-forming substrate is heated by dipole rotation when subjected to an alternating electric field inside the heating chamber, a shell at least partly encompassing the heating chamber, wherein the shell is at least partly electrically conductive and forms an electromagnetic shielding configured to shield the surrounding environment from electromagnetic radiation emitted during the heating process.

[0095] Example Ex30. A system comprising an aerosol-generating article comprising a solid aerosol-forming substrate; and an aerosol-generating device according to any one of the preceding examples for dielectrically heating the solid aerosol-forming substrate.

[0096] Example Ex31. A method to manufacture an aerosol-generating device, preferably according to any one of the preceding examples, the method comprising: providing a heating chamber which is arranged to at least partly receive an aerosol-forming substrate, wherein the heating chamber comprises a heating element, which in operation heats the aerosol-forming substrate by dipole rotation when subjected to an alternating electric field inside the heating chamber, arranging a shell to at least partly encompass the heating chamber, wherein a retaining mechanism is provided, the retaining mechanism being arranged within the shell so that the heating chamber is suspended within the shell, with a gap between the shell and the heating chamber.

[0097] Example Ex32. The method according to Ex31 , wherein the gap is at least partly filled with air.

[0098] Example Ex33. The method according to example Ex31 or Ex32, wherein the heating chamber comprises a wall made of low-dielectric material, and wherein the at least two electrode plates are arranged on an outer surface or on an inner surface of the wall.

[0099] Example Ex34. The method according to any one of examples Ex31 to Ex33, wherein the shell comprises a thermally insulating body with an electrically conductive inner and / or outer shielding layer.

[0100] Example Ex35. The method according to example Ex34, wherein the thermally insulating body comprises a plastic material, preferably polyether ether ketone, PEEK.

[0101] Example Ex36. The method according to example Ex34 or 35, wherein the inner and / or outer shielding layer comprises at least one of aluminum, copper, and an Al-Cu alloy.

[0102] Example Ex37. The method according to any of examples Ex34 to Ex36, wherein the inner and / or outer shielding layer comprises a flexible printed circuit board, PCB, which is arranged adjacent to an outer and / or inner surface of the thermally insulating body, respectively. Example Ex38. The method according to any of examples Ex34 to Ex37, wherein the inner and / or outer shielding layer comprises a coating deposited onto an outer and / or inner surface of the thermally insulating body, respectively, by adhesion.

[0103] Example Ex39. The method according to any of examples Ex34 to Ex37, wherein the inner and / or outer shielding layer comprises a coating deposited onto an outer and / or inner surface of the thermally insulating body, respectively, by an additive coating process, preferably chemical vapor deposition, CVD, or physical vapor deposition, PVD.

[0104] Example Ex40. The method according to any of examples Ex31 to Ex39, wherein at least one shielding layer is supported by the retaining mechanism within the shell.

[0105] Example Ex41. The method according to any of examples Ex31 to Ex40, wherein the at least two electrodes oppose each other for heating the aerosol-forming substrate therebetween.

[0106] Example Ex42. The method according to any of examples Ex31 to Ex41, wherein the retaining mechanism includes at least one spacer or column having a low dielectric constant, the spacer having a width of less than 2mm.

[0107] Example Ex43. The method according to any of examples Ex31 to Ex42, wherein the retaining mechanism comprises a low k dielectric material.

[0108] Example Ex44. The method according to example Ex43, wherein the retaining mechanism comprises at least one of quartz glass, fluorine-doped silicon dioxide, organosilicate glass (OSG), carbon-doped oxide (CDO), porous silicon dioxide, porous organosilicate glass, carbon doped oxide, polyimide, polynorbornene, benzocyclobutene, polytetrafluoroethylene (PTFE), hydrogen silsesquioxane, methylsilsesquioxane, oxycarbosilane, carbon doped oxide (CDO), and material with Si, C, O, and H (SiCOH).

[0109] Example Ex45. The method according to any one of examples Ex31 to Ex44, wherein the retaining mechanism has a dielectric constant below 3.3, more preferably below 3 and above 1.

[0110] Example Ex46. The method according to any one of examples Ex31 to Ex45, wherein the retaining mechanism includes islands that are embedded into the wall of the shell, serving as anchoring points for the at least two electrodes.

[0111] Example Ex47. The method according to any one of examples Ex31 to Ex46, wherein the electrodes are not in direct contact with the shell.

[0112] Example Ex48. The method according to any one of examples Ex31 to Ex47, wherein the retaining mechanism includes at least one spacer comprising at least one of polyimide, ceramic material, temperature resistant material, and porous material.

[0113] Example Ex49. The method according to any one of examples Ex31 to Ex48, wherein the shell is at least partly electrically conductive and is connected to ground, thereby providing an electromagnetic shielding configured to shield the surrounding environment from electromagnetic radiation emitted during the heating process. Example Ex50. The method according to any one of examples Ex31 to Ex49, wherein the heating chamber has a cylindrical shape.

[0114] Example Ex51. The method according to any one of examples Ex31 to Ex50, wherein the heating chamber has a rectangular parallelepiped shape.

[0115] Example Ex52. The aerosol-generating device according to any one of examples Ex31 to Ex51 , wherein the heating chamber has a circular cross-section or wherein the heating chamber has a polygonal cross-section.

[0116] Example Ex53. The method according to any one of examples Ex31 to Ex52, wherein the heating chamber comprises at least two opposing electrodes formed as flat springs for fixing the aerosol-forming substrate.

[0117] Example Ex54. The method according to Ex53, wherein a gap is formed between the flat springs and the shell.

[0118] Example Ex55. The method according to any one of examples Ex31 to Ex54, wherein the shell is hollow to form an air or vacuum space therein.

[0119] Example Ex56. The method according to any one of examples Ex31 to Ex55, wherein the aerosol-generating device comprises an oscillation circuit comprising a switching unit, wherein the heating element is fed by the oscillation circuit.

[0120] Example Ex57. The method according to any one of examples Ex31 to Ex56, wherein the heating chamber has inner walls, which comprise a material with a low dielectric constant, preferably quartz glass, or polyimide.

[0121] Example Ex58. The method according to example Ex57, wherein the inner walls of the heating chamber are coated at least partly with an inert protective layer.

[0122] The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

[0123] Figure 1 is a schematic illustration of a dielectric heating aerosol-generating system according to embodiments of the disclosure;

[0124] 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;

[0125] 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;

[0126] 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;

[0127] Figure 4 illustrates an oscillation circuit diagram according to embodiments of the disclosure; 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;

[0128] 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;

[0129] Figure 7 is a schematic cross-sectional view of an aerosol-generating device according to a first example;

[0130] Figure 8 is a schematic cross-sectional view of an aerosol-generating device according to a second example;

[0131] Figure 9 is a schematic cross-sectional view of an aerosol-generating device according to a further example;

[0132] Figure 10 is a schematic cross-sectional view of an aerosol-generating device according to a further example; and

[0133] Figure 11 is a further schematic cross-sectional view of the aerosol-generating device according to Figure 10; and

[0134] Figure 12 is a further schematic cross-sectional view of the aerosol-generating device according to Figure 10 with an aerosol-generating substrate inserted.

[0135] 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.

[0136] 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.

[0137] Figure 1 is a schematic illustration of a dielectric heating aerosol-generating system 100 according to an embodiment of the disclosure. The system 100 comprises an article 105 comprising an aerosol-forming substrate 110 and an aerosol-generating device 120 for heating the aerosol-forming substrate 110. The aerosol-generating device 120 comprises a first electrode 130 and a second electrode 135 separated by a heating chamber 140 for 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 form part of a feedback loop 270 of an oscillation circuit 150 via a first electrical contact 160 and a second electrical contact 165.

[0138] The aerosol-generating device 120 may have an outer casing 121 which is configured to be handheld.

[0139] 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.

[0140] 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 build-up 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.

[0141] The aerosol-forming substrate 110 may comprise tobacco-based or non-tobacco based materials having an aerosol forming material therein and one or more active agents or ingredients, such as nicotine, pharmaceutical, botanicals, flavorants, liquid substrates with one or more active agents or ingredients, or a combination thereof. The aerosol-forming substrate 110 can also be a liquid aerosol-forming substrate and thereby the aerosol-forming article 105 can be in the form of a cartridge, capsule, 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 aerosolforming article 105 or reaches into an inner volume of the aerosol-forming article 105 that can heat and vaporize a liquid aerosol-forming substrate 110 located in the inner volume 302. For example, the first and second electrodes 130, 135 can be embodied as parallelly arranged plates separated by a distance that forms a capillary channel, for example in a range between 0.1 mm to 2mm, depending on the desired capillary strength or rise. The first and second electrodes 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 0.1mm to 2mm, depending on the desired capillary strength or rise. In another variant, the wicking element can be a separate element that is interposed between two electrodes 130, 135, for example flat or slightly curved electrodes 130, 135.

[0142] 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.

[0143] 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 aerosol-generating 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.

[0144] The controller 180 may cause dielectric heating of the aerosol-forming substrate 110 that is located between the two electrodes 130, 135 with an average dielectric heating power density in a range between 1 W / cm3to 25 W / cm3, preferably between 1.5 W / cm3and 15 W / 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 7 W / cm3to 25 W / cm3, preferably between 8 W / cm3to 20 W / cm3. During a target heating phase (also called maintenance heating phase) during consumption, the average dielectric heating power density is in a range between 1 W / cm3to 7 W / cm3, preferably between 1 W / cm3to 5 W / cm3. In a non-limiting example, these power densities may be used in heat-not-burn applications. In yet another exemplary embodiment, the aerosol-generating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 35 W / cm3and 35 kW / cm3. The aerosol-generating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 50 W / cm3and 10 kW / cm3, between 50 W / cm3and 2.5 kW / cm3or between 50 W / cm3and 1 .25 kW / cm3. The aerosol-generating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 170 W / cm3and 2.5 kW / cm3, between 250 W / cm3and 2.5 kW / cm3or between 500 W / cm3and 2.5 kW / cm3. Preferably, the aerosol-generating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 1 kW / cm3and 2 kW / cm3. In a non-limiting example, these power densities may be used for heating and vaporizing liquids during a puff in a puff-on-demand application.

[0145] The aerosol-generating system 100 is also configured for measuring a dielectric property of the aerosol-forming article 105 or the aerosol-forming substrate 110 using the electrodes 130, 135 that are employed for dielectric heating of the aerosol-forming substrate 110. In some examples, the first and second electrodes 130, 135 can be used for dielectric measurements, either during the heating process (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-forming 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-forming 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-forming article 105.

[0146] In one exemplary embodiment, the material composition of the substrate 110 of the aerosol-forming article 105 that can be dielectrically heated by the aerosol-generating system 100 can include tobacco powder or tobacco cut filler.

[0147] As used herein, the term “cut filler” is used to describe a blend of shredded plant material, such as tobacco plant material, including, in particular, one or more of leaf lamina, processed stems and ribs, homogenised plant material. Preferably, the cut filler comprises at least 25 percent of plant leaf lamina, more preferably, at least 50 percent of plant leaf lamina, still more preferably at least 75 percent of plant leaf lamina and most preferably at least 90 percent of plant leaf lamina.

[0148] The cut filler suitable to be used with 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. 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.

[0149] The aerosol-forming substrate 110 of the aerosol-forming article 105 may comprise an aerosol former. Where the aerosol-forming substrate 110 comprises a cut filler, the cut filler may be soaked with aerosol former. Soaking the cut filler can be done by spraying or by other suitable application methods.

[0150] 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 aerosol-forming substrate 110 may comprise any amount of aerosol former. For example, the aerosol-forming substrate 110 may comprise between 5 weight percent aerosol former and 25 weight percent aerosol former. For example, the aerosol-forming substrate 110 may comprise between 10 weight percent aerosol former and 20 weight percent aerosol former, or between 15 weight percent aerosol former and 20 weight percent aerosol former. Preferably, the aerosol-generating substrate 110 comprises about 18 weight percent aerosol former. The weight percentages of aerosol former are given as a dry weight basis of the cut filler, with the balance being tobacco.

[0151] 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.

[0152] The aerosol-forming substrate 110 can have different shapes, for example a cuboid shape, rectangular parallelepiped shape, pouch-shaped, or may be cylindrically shaped, and is preferably substantially cylindrically shaped, having a length of between 10 mm and 15 mm, such as between 11 mm and 14 mm, preferably about 12 mm, and having a diameter of between 4.5 mm and 8 mm, such as between 6.5 mm and 7.5 mm, preferably about 7 mm.

[0153] Suitable aerosol-forming substrates and articles comprising a cut filler include those described in W02022 / 074240 and / or W02022 / 074158, these references herewith incorporated by reference in their entirety.

[0154] In another exemplary embodiment, the material composition of the aerosol-forming substrate 110 of the aerosol-forming article 105 that can be dielectrically heated by the aerosol- generating system 100 can include reconstituted tobacco, such as one or more sheets of homogenized tobacco material made by a cast leaf process.

[0155] Where the aerosol-forming substrate 110 comprises a homogenised tobacco material, the tobacco material preferably comprises particulate tobacco obtained by grinding or otherwise comminuting tobacco leaf lamina. Such homogenised tobacco material may have a tobacco content of at least about 40% by weight on a dry weight basis or of at least about 50% by weight on a dry weight basis. In other embodiments, the homogenised tobacco material may have a tobacco content of about 70% or more by weight on a dry weight basis, such as between 70% and 80% by weight on a dry weight basis.

[0156] 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.

[0157] 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.

[0158] Suitable extrinsic binders for inclusion in the aerosol-forming substrate 110 are known in the art and include, but are not limited to: gums such as, for example, guar gum, xanthan gum, arabic gum and locust bean gum; cellulosic binders such as, for example, hydroxypropyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose and ethyl cellulose; polysaccharides such as, for example, starches, organic acids, such as alginic acid, conjugate base salts of organic acids, such as sodium-alginate, agar and pectins; and combinations thereof. For example, the aerosol-forming substrate 110 may comprise between 1 % and 5% extrinsic binder by weight on a dry weight basis, such as between 1.5% and 3.5% extrinsic binder by weight on a dry weight basis, preferably about 2% extrinsic binder by weight on a dry weight basis. Preferably, the extrinsic binder is guar gum.

[0159] 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 aerosolforming 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.

[0160] 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 aerosol-forming substrate 110 may comprise between 10 weight percent aerosol former and 20 weight percent aerosol former, or between 15 weight percent aerosol formerand 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.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] Figure 2 is a schematic illustration of an oscillation circuit 250 for use in the aerosolgenerating system 100 of Figure 1 , according to an embodiment of the disclosure. The oscillation circuit 250 comprises a switching unit 260 interconnected with a resonator feedback loop 270 to provide for a self-oscillating signal to the switching unit 260. The switching unit 260 comprises a single transistor, such as a bipolar junction transistor (BJT) or a field effect transistor (FET).

[0167] The oscillation circuit 250 can further comprises 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.

[0168] 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.

[0169] 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 UIN and the output voltage UOUT of the switching unit 260.

[0170] 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.

[0171] 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.

[0172] The delay line DL is a time delay element, for example an element that has inductive behavior, for slowing down the arriving voltage wave from the feedback loop 270 during a period of the oscillation. This allows to tune the resonant circuit 272 to a desired switching and oscillation frequency, to move the oscillation frequency away from the natural resonant frequency given by the resonant circuit 272. This ensures that the oscillation circuit 350 remains in a predefined frequency operating range to provide for the requisite inverted or 90° phase shifted feedback and also to make sure that the feedback loop 270 has a low impedance to provide for a high gain, as described in greater detail below.

[0173] 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. 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 aerosolization temperature quickly. Control of the DC supply voltage is one way that makes it possible to rapidly change heating power despite the oscillation circuit 350 freely oscillating.

[0174] 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 the capacitor Ci is chosen to be larger than the maximal intrinsic capacitor Ci of the transistor T at the operating conditions, so that the variation of the intrinsic transistor based on frequency, temperature, etc. has much less or negligible influence on the feedback loop 270. For example, in a non-limiting embodiment, the value can be in a range between 2 pF to 100 pF, more preferably in a range between 5 pF and 50 pF.

[0175] A capacitive element 274 comprises a capacitor C2 arranged at the output or end of the resonant circuit 272. In one embodiment, the capacitive element 274 comprises more than one capacitor. As described above, the capacitive element 274 has the function of providing a 90° phase shift to the feedback voltage of the feedback loop 270 with minimized losses or other undesired effects, and it therefore needs to have a high-quality factor or Q factor, preferably above 1000 at 100 MHz. The capacitance value for the capacitor C2 of the capacitive element 274 should be relatively high as compared to the capacitor Ci , for example in a range between 500 pF to 100 nF, more preferably between 1 nF and 50 nF, 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.

[0176] 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 voltage input 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 80, preferably around 20, to provide for a high gain, leading to an increased voltage across the load capacitor CL. Also, preferably, this gain is achieved without the use of an additional voltage or current amplifying passive element, such as a tapped inductor or a transformer located in the circuit that forms the feedback loop 270, as such passive elements are difficult and lossy to operate and design at frequencies greater than 50 MHz. Preferably, the impedances of the resonant circuit 272 and 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.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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 the 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.

[0183] 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.

[0184] 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 10 nH to 50 nH, more preferably between 15 nH and 40 nH, which is the equivalent of Li plus L2, LE could be in a range between 7 nH and 30 nH, more preferably between 10 nH and 20 nH, and the value of the load capacitor can be in a range between 0.5 pF to 5 pF, more preferably between 1 pF to 3 pF.

[0185] 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. T o have a proper inverting effect and a 180° phase shift on the feedback loop 270 between the input voltage UIN and output voltage UOUT, the oscillation circuit 350 must remain in a frequency operating range where the behavior of the feedback loop 270 is highly inductive. In the example comprising a parallel resonator circuit (PRC), the series resonance frequency fsER (resonant frequency) is relatively close to the parallel resonance frequency 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 feedback loop 270. Furthermore, the equivalent impedance of the circuit will increase to an extent that is too high for efficient dielectric heating as not providing for the requisite gain.

[0186] 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. 2.4 kQ. 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 2 Q, more preferably less than 1 Q. The parallel resonance frequency fpAR can be above 1 GHz, e.g. 1 GHz to 1.5 GHz, while the actual switching frequency fs can be below 1 GHz, and this lower switching frequency is caused by the delay line DL.

[0187] 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 Figures 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 100 mil to 2 Q. 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 FIG. 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 855 MHZ, 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.

[0188] 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.

[0189] Now turning to Figure 7, various aspects of heat insulation and electromagnetic shielding for a capacitor-type dielectric heater like the one described above will be explained. As well known in the field, shielding of the capacitive plates or electrodes 130, 135 is crucial for any commercially available device, for electromagnetic compliance and safety. In addition to shielding, given that only air and vacuum do not heat when subject to an electric field, a shielding arrangement may also be combined with a solution where air gaps are used for thermal insulation purposes.

[0190] In particular, as shown in Figure 7, a heating chamber 140 for receiving an aerosol-forming substrate is delimited by heating chamber walls 304. Two electrodes 130, 135 are arranged on an outer surface of the heating chamber walls 304. The electrodes are operable to form a capacitor CL for dielectric heating of the aerosol-forming substrate 110. The heating chamber 140 is encompassed by a shell 300. On the inside of this shell 300, an electrically conductive shielding layer 326 is arranged. An air gap 324 is provided between the shell 300 and the heating chamber 140. The air gap 324 may also be referred to as an empty space or void.

[0191] The use of at least one air gap 324 presents the advantage that no or only a very low amount of heat will be caused by exposure to the alternating electric field, given the low polar nature of air. As this is known in the art, the relative permittivity (also referred to as dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of vacuum. A dielectric is an insulating material, and the dielectric constant of an insulator measures the ability of the insulator to store electric energy in an electrical field. The lowest possible dielectric constant is thus the value for vacuum, namely by definition sr=1. Air also has a dielectric constant close to 1 [sr=1.00058986±0.00000050 (under standard conditions, for a frequency of 900 kHz)].

[0192] Technically, vacuum space could be used as a thermal insulation space inside the gap 324, but this is more costly to implement. In this respect, the present invention attempts to use empty spaces for thermal insulation, in order to avoid or reduce the use of solid thermally insulating layers that may have good thermal insulation properties, but can heat up when exposed to RF electric field radiation from the dielectric heater. Other suitable gases having a low dielectric constant, like nitrogen or helium, may of course also be used.

[0193] Figure 7 shows a cross-sectional view of the dielectric heater in an insertion direction, having exemplarily a cylindrically-shaped heating chamber 140 and a circular cross-section thereof, for example to receive a stick-like aerosol-forming article. But other shapes are also possible for the heating chamber 140, for example having a polygonal, rectangular, oval, square, etc. cross-section. Also, in the variant shown in Figure 7, two cylindrically shaped segments are shown for the electrodes 130, 135, but other configurations or numbers of electrodes are also possible.

[0194] As can be seen from Figure 7, the heating chamber 140 is delimited by the heating chamber walls 304. The heating chamber walls 304 are electrically insulating and provide a mechanical support for the first and second electrodes 130, 135. For example, the heating chamber walls 304 may be formed from a low dielectric material that can easily be cleaned, such as glass, preferably quartz glass, or polyimide. Also, an additional layer can be provided on the inner surface 310 to facilitate cleaning. Alternatively, the heating chamber walls 304 may also be formed directly by the electrodes 130, 135.

[0195] Further, the heating chamber walls 304 are supported inside the shell 300 by means of a heating chamber support unit 306. For instance, the heating chamber support unit 306 may comprise a plurality of spacers 308. For instance, a plurality of low dielectric spacers 308, e.g. four or six, may be arranged around the circumference of the heating chamber walls 304 for holding the heating chamber 140 in space. New materials such as polyimide or ceramic have been developed for 5G connectors that are low-dielectric, temperature resistant, porous, etc. Ideally, to reduce thermal conductivity, the spacers 308 have a small diameter, e.g. less than 1 mm, preferably less than 0.5 mm, and more specifically less than 0.3 mm.

[0196] There may be provided a first group of spacers 308 and a second group of spacers 309, the first and the second groups of spacers being distanced from each other in a longitudinal direction of the heating chamber 140. Thus, the heating chamber 140 is held firmly within the shell 300.

[0197] In a variant, the heating chamber support unit 306 can be made of a porous layer or solid foam, for example a foam with a very high porosity, for example a porosity of over 90%, preferably over 95%. This allows to have an element with a very high air content to reduce to overall relative permittivity of the support unit. Preferably, the material chosen for the porous body or solid foam has a low relative permittivity itself, for example less than 4, preferably less than 3.5.

[0198] With reference to Figure 7, the heating chamber 140 is surrounded by a cylindrical heating chamber wall 304. The heating chamber wall 304 is electrically insulating and mechanically supports two electrodes, the first electrode 130 and the second electrode 135. The two electrodes 130, 135 are operable to generate an electric field inside the heating chamber 140.

[0199] The heating chamber walls 304 are mechanically supported by the heating chamber support unit 306. The heating chamber support unit 306 comprises, according to the embodiment shown in Figure 7, a total of six spacers 308-1 , 308-2, 308-3, 308-4, 308-5, 308-6. Of course, also more or less than six spacers 308 can be used according to the present disclosure. It is only important that the heating chamber support unit 306 does not significantly obstruct the air convection and heat radiation inside the insulated volume 302.

[0200] The spacers 308 are distributed around the circumference of the heating chamber 140. It should be noted that according to Figure 7, the spacers 308 are not distributed evenly. However, of course, also an equidistant distribution of the spacers 308 around the heating chamber 140 is possible.

[0201] According to the present disclosure, the thermally insulating shell 300 surrounds the heating chamber 140, forming a closed inner volume 302, which may also form an air gap. In order to provide an electromagnetic shielding, a shielding layer 326 can be arranged on the inner surface of the shell 300.

[0202] In summary, Figure 7 schematically represents a dielectric heating arrangement, including a cylindrical heating chamber 140, which may of course also have any other shape. The eating chamber walls 304, having a cylindrical (or other) shape, form the heating cavity 140. The heating chamber walls 304 may be made of a low dielectric material that can be easily cleaned (for instance glass, quartz glass, polyimide, etc.) and can be coated with an additional layer for easy cleaning. The heating chamber walls 304 are optional, there can also be a direct contact between the electrodes 130, 135 and the aerosol-forming article. The electrodes 130, 135 form the plates of a load capacitor CL. The air space (or air gap) 324 functions as a first thermal insulation layer.

[0203] The low dielectric spacers 308-1 to 308-6 are provided for holding the heating cavity 140 in space. As mentioned above, the spacers 308 may comprise a low-dielectric, temperature resistant, porous, etc. material, e.g. polyimide or ceramic. In order to reduce the thermal conductivity, the spacers 308 have a small diameter, e.g. less than 1 mm, less than 0.5 mm, less than 0.3 mm, and more than 0.1 mm.

[0204] A shielding layer 326 is provided, which has a high electrical conductivity, is thin, and has no or at least only few edges. Materials with high heat reflective properties and good electric conductivity are e.g. aluminum, copper, or alloys comprising aluminum and / or copper.

[0205] A non-conductive solid thermal insulation layer is formed by the shell 300, comprising e.g. PEEK or a similar material.

[0206] According to the present disclosure as illustrated in Figure 8, the shielding layer 326 is not necessarily arranged on the inner surface of the shell 300, but may also be provided on the outer surface. In particular, Figure 8 shows a variant where the shielding layer 326 is arranged outside on top of the solid thermal insulation layer formed by the shell 300. The shielding layer 326 can be rolled around or into the cylinder formed by the solid thermal insulation layer 300, for example as a flex PCB layer, or can be deposited by a coating process (adhesion, additive process such as CVD, PVD) and can be very thin, e.g. less than 100 pm. It is also possible that the shielding layer 326 is suspended in the air between two air gap layers.

[0207] Moreover, as shown in Figure 9, not only one first shielding layer 326 may be provided, but a second shielding layer 328 may also be provided. In this case, the first shielding layer 326 is arranged on the inner surface of the shell 300, whereas the second shielding layer 328 is deposited on the outer surface of the shell 300, functioning as an outer heat insulation layer. Advantageously, the shielding layers 326, 328 both not only function as electrically conductive protection against electromagnetic disturbances, but also serve the purpose of heat reflectors, which reflect back the heat into the insulated volume 302. The design shown exemplarily in Figures 7 to 9 may also be adapted to be suitable for rectangular or token like consumables. In this case, the conductive elements, namely the electrodes 130, 135, and the shielding layer 326, do not have any sharp edges or corners. It is also important to note that an electric connection of the shielding layer 326 to ground Vcc has to be provided for proper operation with the oscillation circuit 150 as disclosed in Figure 4.

[0208] Referring now to Figures 10 to 12, a further advantageous example of the present disclosure will be explained.

[0209] Figure 10 shows a different embodiment for a flat-type or cuboid shaped consumable article 105 in a cross-sectional view cut along a longitudinal axis 303. The article 105 is shown in a position before being introduced into the heating chamber 140. The article 105 can be slid into the heating chamber 140 in a direction along the longitudinal axis 303 of the heating chamber 140 as indicated by arrows 301. The walls 304 of the heat chamber 140 are integrally formed with the shell 300 to form one hollow thermal insulation layer. Preferably, a first air gap 324 is formed within the void of the hollow insulation layer. The first air gap 324 may, of course, also be filled with any other suitable gas or may be evacuated to at least form a partial vacuum.

[0210] According to this embodiment, the electrode plates 130, 135 are arc-shaped and curved towards the central longitudinal axis 303 of the heating chamber 140, or otherwise arranged to reach into the heating chamber 140. The electrode plates 130, 135 are arranged in parallel to be able to flex and directly contact the consumable article 105, in order to heat the substrate 110 therein by dielectric heating.

[0211] The electrodes 130, 135 may have spring elastic properties, so that they are flexibly and reversibly bendable to apply a pressure across to the longitudinal axis 303 onto the consumable article 105. The electrodes 130, 135 thus act like two leaf springs and have an initial distance D2 from each other. The article 105 has a thickness D1 in a direction across to the longitudinal axis 303. Upon insertion of the article 105 in the insertion direction 301 , the electrodes 130, 135 can flex within a second air space or air gap 325, to increase their initial distance D2 to D1. According to this embodiment, mechanical contact of the electrodes 130, 135 with the walls 304 of the heating chamber 140 is avoided. This allows to have a precise and close distance of the electrodes 130, 135 to the substrate 110.

[0212] Low dielectric and low thermal conductive islands 308, 309 are arranged to be embedded into the walls 304 which form a solid thermal insulation layer, having the function of the spacers described above. Thus, it can be ensured that the heating chamber 140 has smooth, flat surfaces to avoid aerosol deposits and allow easy cleaning. Instead of a solid material, it is also possible that a highly porous body is used for the islands 308, 309, for example a solid foam, as explained above.

[0213] As shown in Figures 10 to 12, the walls 304 and the shell 300 may form an integral insulation layer 305 that can be hollow to form the first air gap 324. However, also two separate layers can be provided, one to form the walls 304 of the heating chamber 140, and an outer wall or shell 300 to form the first air gap 324. The electrodes 130, 135 may have any shape that allows to flex and any dimensions to correspond substantially to the surface area of the aerosol-generating substrate 110, when inserted into the heating chamber 140.

[0214] Similar to the embodiments shown in Figures 7 to 9, the shielding layer 326 can be outside of the solid thermally insulating shell 300, inside, or at other positions, for example by being deposited onto the solid thermally insulating shell 300 on the inside, outside, or both.

[0215] Figure 11 illustrates an exemplary shape of the first electrode 130 in a cross-sectional view of the arrangement of Figure 10 rotated by 90°. The second electrode 135 (not visible) may be shaped correspondingly. The electrodes 130, 135 may have contact arms 336 which are mechanically suspended from the islands 308, 309. The arms 336 allow a facilitated elastic deformation of the electrodes 130, 135 upon insertion of the article 105.

[0216] Figure 12 shows a further cross-sectional view of the heating chamber 140 and the surrounding solid thermal insulation 305 with the inserted article 105. As can be seen in detail in this Figure, an end face 320 of the heating chamber 140 comprises a stop, e.g. a spring 334, against which the article 105 rests in the mounted state. Moreover, first and second contacts 330, 332 are connected to the first and second electrodes 130, 135, respectively. The first and second contacts 330, 332 are led outside the shell 300 to be connected to the inductor Li, L2 as shown in Figure 10.

[0217] In summary, the solution proposed by the present invention advantageously proposes one or more air gap layers around the heating chamber 140 for thermal insulation, in order to avoid that a solid heat insulation material will be subjected to e-field radiation and will cause additional undesired heat. To this purpose, advantageously, the shielding layer or screen 326 or the solid thermal insulation holds suspended the electrodes 130, 135 by means of a plurality of spacers 308, 309. Thus, a circumferential air gap creating an air insulation layer is established around the heating chamber 140. As mentioned above, the term “air gap” is to be understood as a void that is evacuated or filled with any low-k gas or fluid.

[0218] Furthermore, the aerosol-generating device 120 may comprise an outer casing 121 protecting the aerosol-generating device and to be touched by the user.

[0219] It should also be noted that the first and second electrodes 130, 135 are preferably directly connected to the oscillator. The wiring of the first and second electrodes 130, 135 may lead through the air gap and through the shielding.

Claims

CLAIMS1 . An aerosol-generating device comprising: a heating chamber which is arranged to at least partly receive an aerosol-forming substrate, a dielectric heater including at least two electrode plates forming a capacitor of an oscillator circuit, the oscillator circuit configured to provide an RF voltage to the at least two electrode plates, the at least two electrodes and the heating chamber being arranged to heat the aerosol-forming substrate by an alternating dielectric field caused between the at least two electrode plates by the RF voltage when arranged at least partially inside the heating chamber, a shell at least partly encompassing the heating chamber, and a retaining mechanism which is arranged within the shell so that the heating chamber is suspended within the shell, with a gap formed between the shell and the heating chamber.

2. The aerosol-generating device according to claim 1 , wherein the gap is at least partly filled with air.

3. The aerosol-generating device according to any one of the preceding claims, wherein the heating chamber comprises a wall made of low-dielectric material, and wherein the at least two electrode plates are arranged on an outer surface or on an inner surface of the wall.

4. The aerosol-generating device according to any one of the preceding claims, wherein the shell comprises a thermally insulating body with an electrically conductive inner and / or outer shielding layer.

5. The aerosol-generating device according to any one of the preceding claims, wherein at least one shielding layer is supported by the retaining mechanism within the shell.

6. The aerosol-generating device according to any one of the preceding claims, wherein the retaining mechanism includes at least one spacer or column having a low relative permittivity, the spacer having a width of less than 2 mm.

7. The aerosol-generating device according to any one of the preceding claims, wherein the retaining mechanism comprises a highly porous body, and the gap is formed by voids of the porous body.

8. The aerosol-generating device according to any one of the preceding claims, wherein the retaining mechanism includes islands that are embedded into the wall of the heating chamber or into a wall of the shell, serving as anchoring points for the at least two electrodes, and / or wherein the retaining mechanism includes at least one pin-like structure, walls, and / or a body or layer comprising a material with a porosity of more than 90%, more preferably of more than 95%.

9. The aerosol-generating device according to any one of the preceding claims, wherein the electrodes are not in direct contact with the shell.

10. The aerosol-generating device according to any one of the preceding claims, wherein the shell is at least partly electrically conductive and is connected to ground, thereby providing an electromagnetic shielding configured to shield the surrounding environment from electromagnetic radiation emitted during the heating process.11 . The aerosol-generating device according to any one of the preceding claims, wherein the heating chamber comprises at least two opposing electrodes formed as flat springs for fixing the aerosol-forming substrate.

12. The aerosol-generating device according to claim 11 , wherein a gap is formed between the flat springs and the shell.

13. The aerosol-generating device according to any one of the preceding claims, wherein the shell is hollow to form an air or vacuum space therein.

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

15. A method to manufacture an aerosol-generating device according to any one of claims 1 to 13, the method comprising: providing a heating chamber which is arranged to at least partly receive an aerosol-forming substrate, wherein the heating chamber comprises a heating element, which in operation heats the aerosol-forming substrate by dipole rotation when subjected to an alternating electric field inside the heating chamber, and arranging a shell to at least partly encompass the heating chamber,wherein a retaining mechanism is provided, the retaining mechanism being arranged within the shell so that the heating chamber is suspended within the shell, with a gap between the shell and the heating chamber.

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