Dielectric heating aerosol-generating device with heat sink structure for heat management of switching unit

Abstract

Dielectric heating aerosol-generating device with heat sink structure for heat management of switching unit 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 aerosol-generating device and to a method to manufacture an aerosol-generating device. An aerosol-generating device comprises a heating chamber which is arranged to at least partly receive an aerosol-forming substrate, wherein the heating chamber comprises a dielectric heating element, which in operation heats the aerosol-forming substrate by dipole rotation when subjected to an alternating electric field inside the heating chamber, an oscillation circuit comprising a switching unit, wherein the dielectric heating element is fed by the oscillation circuit, a shell forming an inner volume that at least partly encompasses the heating chamber, the shell configured to insulate heat within the inner volume, wherein the switching unit is arranged within the inner volume and in thermal contact with the heating chamber, so that in operation heat losses of the switching unit are for at least a substantial part dissipated into the heating chamber.

Description

[0001] Dielectric heating aerosol-generating device with heat sink structure for heat management of switching unit

[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. Such a transistor produces heat which needs to be evacuated within the device.

[0007] It would be desirable to provide a device and system that dielectrically heats an aerosolforming substrate with greater efficiency, while still being realisable in a compact or handheld system, wherein the heat management of the switching unit and the overall energy efficiency is improved.

[0008] According to an aspect of the present invention, there is provided an aerosol-generating device comprising a heating chamber which is arranged to at least partly receive an aerosolforming substrate, wherein the heating chamber comprises a dielectric heating element, which in operation heats the aerosol-forming substrate by dipole rotation when subjected to an alternating electric field inside the heating chamber, an oscillation circuit comprising a switching unit, wherein the dielectric heating element is fed by the oscillation circuit, a shell forming an inner volume that at least partly encompasses the heating chamber, the shell configured to insulate heat within the inner volume, wherein the switching unit is arranged within the inner volume and in thermal contact with the heating chamber, so that in operation heat losses of the switching unit are for at least a substantial part dissipated into the heating chamber. Thus, the inner volume forms a contiguous volumetric structure allowing a heat from the dielectric heating element and the oscillation circuit to spread within the inner volume.

[0009] By forming a heater space which is thermally insulated from the exterior environment and by including both the oscillation circuit and the heating chamber inside one united or identical insulated volume, the losses of the oscillation circuit (which may amount to 30% - 50% of the consumed energy) can be directed towards the heating chamber and can be used for heating the aerosol-forming substrate. Advantageously, the heat generated by the heating device including the heat losses is fully (or at least to a significant amount) concentrated within a common insulated volume that also includes the heating chamber for the aerosol-forming substrate. Thus, the energy of the battery can be used more efficiently. Moreover, the confinement of the heat losses within the inner volume allows a passive heating by means of the oscillation circuit losses. These losses are brought close to the heating chamber and thus allow a preheating of the aerosol forming substrate. Consequently, the preheating time can be reduced. Finally, an effective heat management of the switching unit (e.g. transistor) of the oscillation circuit can be achieved and the switching unit is thus effectively protected against overheating.

[0010] Aspects of the herein described invention may not necessarily be limited to a dielectric heating arrangement, but could also be used for heating arrangements where an oscillator is used that has a relatively high switching frequency, e.g. switching frequencies of more than 1MHz, for example for inductive heating arrangements or combinations of inductive and dielectric heating arrangements. For example, according to yet another aspect of the present invention, an aerosolgenerating device or system could be provided, having a heating chamber which is arranged to receive an aerosol-forming substrate, wherein the heating chamber has an inductive heating coil wound around an axis of extension of the heating chamber, which in operation can heat one or more susceptors that are arranged in the aerosol-forming substrate or at the heating chamber, such that the aerosol-forming substrate can be inductively heated by an alternating magnetic field that induces currents in the one or more susceptors, an oscillation circuit comprising a switching unit, wherein the inductive heating coil is fed by the oscillation circuit, a shell forming an inner volume that at least partly encompasses the heating chamber, the shell configured to insulate heat within the inner volume, wherein the switching unit is arranged within the inner volume and in thermal contact with the heating chamber, so that in operation heat losses of the switching unit are for at least a substantial part dissipated into the heating chamber.

[0011] Advantageously, the shell may include an electrically conductive element forming an electromagnetic shielding layer.

[0012] As this is known in the field, electromagnetic shielding of the oscillation circuit is important for any commercially available device for electromagnetic compliance and safety. Surrounding the oscillation circuit and in particular the electrodes that operate for dielectric heating of the aerosol-forming substrate, may further have the advantage that such an electromagnetic shielding layer usually also functions as a heat reflective layer. The shell may have the double function of being an electromagnetic shielding layer and of confining the generated heat within the inner volume.

[0013] The shell may include at least one heat reflection layer. The at least heat reflection layer may be arranged at an inner surface of the shell. In particular, a separate layer which is electrically conductive and heat reflective may be deposited on the shell. This can be done on the outside of the shell as well as on the inner surface. The outer surface is more easily accessible for fabrication of the heat reflection layer. On the other hand, depositing the heat reflection layer on the inner surface has the advantage that the heat is kept inside the inner volume more effectively.

[0014] The shell may include an inner airspace or vacuum chamber to provide for a low-dielectric thermal insulation. As this is known, air or vacuum provides an effective means of heat insulation. Thus, empty spaces for thermal insulation are advantageous to avoid or reduce the use of solid thermally insulating layers that — while they 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 first thermal insulation layer. It should be pointed out that vacuum will in many cases be a too expensive solution to be implemented. 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.

[0015] The shell may comprise a thermally insulating body with a thermally conductive inner shielding layer. This structure has the advantage that the shell may be connected to a heat sink structure for effectively dissipating the generated heat around the heating chamber.

[0016] The thermally insulating body may comprise a plastic material, preferably polyether ether ketone, PEEK. Plastic material can be fabricated cost efficiently and is recyclable after use.

[0017] For instance, the shell may have a thermal conductivity of less than 2 W / mK, preferably less than 1 W / mK.

[0018] For realizing a capacitor-type dielectric heater, the heating chamber may comprise at least two opposing electrodes arranged for heating the aerosol-forming substrate, wherein the switching unit is connected to the electrodes. This is a particularly energy efficient and space saving architecture.

[0019] In particular, the electrodes may form a part of a load capacitor of the oscillation circuit.

[0020] Further, the one or more inductor, the load capacitor, and the switching unit may be arranged inside the inner volume in order to effectively use any heat losses generated by the oscillation circuit.

[0021] Provided that the heat generating components are miniaturized enough to be fitted within the inner volume, the principles of the present disclosure may also be applied to the concept where a resonant cavity is used. In this case, the heating chamber may comprise a resonant cavity and the oscillation circuit may form an electromagnetic field generator configured to generate radio-frequency, RF, electromagnetic radiation within the resonant cavity.

[0022] For mechanically supporting the electrodes of the dielectric heating element, the heating chamber has inner walls, which comprise a material with a low dielectric constant, preferably a glass, preferably quartz glass, or polyimide.

[0023] Further, the switching unit may be attached to a heat sink, the heat sink being in thermal contact with the heating chamber or a heat sink and the walls of the heating chamber may form a unitary element of heat conductive material. This structure offers the advantage of even more effectively gathering the heat generated by the switching unit and dissipating the heat within the insulated inner volume.

[0024] A particularly space saving way of realizing a heat sink structure for an oscillation circuit, that comprises at least one inductor, is to attach the inductor to a heat sink and / or to design the inductor to form a heat sink of the switching unit.

[0025] The heat sink may comprise at least one of copper, silver, aluminium, graphene, and carbon-based material, or a combination, composite, or alloy of these materials. These materials have a high thermal conductivity, are robust, and have a low weight density.

[0026] The aerosol-generating device may comprise a power source external to the shell, supplying power via or through the shell to the oscillation circuit inside the inner volume of the shell. In particular, for larger batteries or accumulators, this ensures that the inner volume does not have to be excessively large.

[0027] Further, the aerosol-generating device may comprise a support unit (or retaining mechanism) which is arranged within the shell so that the heating chamber is supported within the shell, wherein an air gap is provided between the shell and the heating chamber. Thus, the air forms an additional heat insulation to confine the heat losses of the oscillation circuit within the inner volume. Of course, also any other low-dielectric gas or vacuum may also be used instead of air.

[0028] In particular, the retaining mechanism may include at least one spacer having a low dielectric constant. 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.

[0029] The shell may be at least partly electrically conductive and may be connected to ground, thereby providing an electromagnetic shielding layer configured to shield the surrounding environment from electromagnetic radiation emitted during the heating process.

[0030] 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.

[0031] Accordingly, the heating chamber may have a circular cross-section, or a polygonal, e. g. rectangular cross-section. For achieving a particularly effective heat transfer from the switching unit, the oscillation circuit may comprise at least one inductor, and the at least one inductor is attached to a housing covering the switching unit.

[0032] Further, 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.

[0033] Furthermore, the inner volume arranged inside the shell may include a first area comprising the heating chamber, and a second area comprising the oscillator with a load capacitor and the at least one inductor of a resonant circuit, wherein a heat-conductive structure is arranged between the first area and the second area for improved heat exchange. Such a compartmentalization has the advantage that the electronic components are protected from environmental influences, such as dust and humidity, while at the same time no thermal separation occurs.

[0034] In order to achieve a particularly effective and fast heat transfer to the aerosol-forming substrate, electrodes of the load capacitor may be arranged inside the heating chamber, preferably placed on or in contact with the heat-conductive structure.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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 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; providing an oscillation circuit comprising a switching unit, wherein the heating element is fed by the oscillation circuit; arranging a shell to at least partly encompass the heating chamber, the shell being configured to insulate heat within an inner volume formed by the shell; wherein the switching unit is arranged within the inner volume of the shell and in thermal contact with the heating chamber, so that in operation heat losses of the switching unit are for at least a substantial part dissipated into the heating chamber.

[0040] The switching unit may be attached to a heat sink, the heat sink being in thermal contact with the heating chamber.

[0041] Furthermore, the oscillation circuit may comprise at least one inductor, wherein the inductor is attached to a heat sink and / or forms a heat sink.

[0042] The heat sink may comprise at least one of copper, silver, aluminium, graphene, and carbon-based material.

[0043] The at least one inductor may be attached to a housing covering the switching unit.

[0044] Further, the switching unit may comprise a metal-oxide semiconductor transistor, MOSFET, preferably a laterally-diffused metal-oxide semiconductor, LDMOS, transistor.

[0045] In particular, the at least one inductor may be in direct contact with the backside metal of the MOSFET for efficient heat sinking properties.

[0046] Further, an insulated volume arranged inside the shell may include a first area comprising the heating chamber, and a second area comprising the oscillator with a load capacitor and two inductors, wherein a heat-conductive structure is arranged between the first area and the second area.

[0047] Electrodes of the load capacitor may also be arranged inside the heating chamber, preferably placed on or in contact with the heat-conductive structure.

[0048] Furthermore, it should be noted that a material forming the walls of the heating chamber may have a thermal resistivity of at least 1 m K / W, preferably more than 4 m K / W (that would be PEEK), even more preferably more than 10 m K / W. This is different from the material of known metal or plastic separation walls.

[0049] 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.

[0050] 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.

[0051] As used herein, the term “puff” means the action of a user drawing an aerosol into their body through their mouth or nose.

[0052] As used herein, the term “relative permittivity” refers to the real part of the complex, frequency-dependent relative permittivity, measured at a temperature of 20 degrees Celsius, in an alternating electric field with at a very low frequency (VLF) of 1 Kilohertz or less, as defined in the international standard IEC 62631-2-1 :2018. It will be appreciated that the frequency value of 1 Kilohertz is included here solely as a general reference and other definitions may use different frequencies.

[0053] 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.

[0054] Example Ex1. An aerosol-generating device comprising a heating chamber which is arranged to at least partly receive an aerosol-forming substrate, wherein the heating chamber comprises a dielectric heating element, which in operation heats the aerosol-forming substrate by dipole rotation when subjected to an alternating electric field inside the heating chamber, an oscillation circuit comprising a switching unit, wherein the dielectric heating element is fed by the oscillation circuit, a shell forming an inner volume that at least partly encompasses the heating chamber, the shell configured to insulate heat within the inner volume, wherein the switching unit is arranged within the inner volume and in thermal contact with the heating chamber, so that in operation heat losses of the switching unit are for at least a substantial part dissipated into the heating chamber.

[0055] Example Ex2. The aerosol-generating device according to Ex1 , wherein the shell includes an electrically conductive element that forms an electromagnetic shielding layer.

[0056] Example Ex3. The aerosol-generating device according to any one of the preceding examples, wherein the shell includes at least one heat reflection layer.

[0057] Example Ex4. The aerosol-generating device according to Ex3, wherein the at least one heat reflection layer is arranged at an inner surface of the shell. Example Ex5. The aerosol-generating device according to any one of the preceding examples, wherein the shell includes an inner airspace or vacuum chamber to provide for a low- dielectric thermal insulation.

[0058] Example Ex6. The aerosol-generating device according to any one of the preceding examples, wherein the shell comprises a thermally insulating body with a thermally conductive inner shielding layer.

[0059] Example Ex7. The aerosol-generating device according to Ex6, wherein the thermally insulating body comprises a plastic material, preferably polyether ether ketone, PEEK.

[0060] Example Ex8. The aerosol-generating device according to any one of the preceding examples, wherein the shell has a thermal conductivity of less than 2 W / mK, preferably less than 1 W / mK.

[0061] Example Ex9. The aerosol-generating device according to any one of the preceding examples, wherein the heating chamber comprises at least two opposing electrodes arranged for heating the aerosol-forming substrate, and wherein the switching unit is connected to the electrodes.

[0062] Example Ex10. The aerosol-generating device according to Ex9, wherein the electrodes form a part of a load capacitor of the oscillation circuit.

[0063] Example Ex11. The aerosol-generating device according to Ex10, wherein the oscillation circuit further comprises one or more inductors, and wherein the one or more inductor, the load capacitor, and the switching unit are arranged inside the inner volume.

[0064] Example Ex12. The aerosol-generating device according to any one of the preceding examples, wherein the heating chamber comprises a resonant cavity and the oscillation circuit forms an electromagnetic field generator configured to generate radio-frequency, RF, electromagnetic radiation within the resonant cavity.

[0065] Example Ex13. 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 a glass, preferably quartz glass, or polyimide.

[0066] Example Ex14. The aerosol-generating device according to any one of the preceding examples, wherein the switching unit is attached to a heat sink, the heat sink being in thermal contact with the heating chamber or wherein a heat sink and the walls of the heating chamber form a unitary element of heat conductive material.

[0067] Example Ex15. The aerosol-generating device according to any one of the preceding examples, wherein the oscillation circuit comprises at least one inductor, wherein the inductor is attached to a heat sink and / or forms a heat sink of the switching unit.

[0068] Example Ex16. The aerosol-generating device according to Ex15, wherein the heat sink comprises at least one of copper, silver, aluminum, graphene, and carbon-based material.

[0069] Example Ex17. The aerosol-generating device according to any one of the preceding examples, wherein the aerosol-generating device comprises a power source external to the shell, supplying power via or through the shell to the oscillation circuit inside the inner volume of the shell.

[0070] Example Ex18. The aerosol-generating device according to any one of the preceding examples, wherein the aerosol-generating device comprises a support unit which is arranged within the shell so that the heating chamber is supported within the shell and wherein an air gap is provided between the shell and the heating chamber.

[0071] Example Ex19. The aerosol-generating device according to Ex18, wherein the support unit includes at least one spacer having a low dielectric constant.

[0072] Example Ex20. 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 layer configured to shield the surrounding environment from electromagnetic radiation emitted during the heating process.

[0073] Example Ex21. The aerosol-generating device according to any one of the preceding examples, wherein the heating chamber has a cylindrical shape.

[0074] Example Ex22. The aerosol-generating device according to any of the preceding examples, wherein the heating chamber has a rectangular parallelepiped shape.

[0075] Example Ex23. 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.

[0076] Example Ex24. The aerosol-generating device according to any one of the preceding examples, wherein the oscillation circuit comprises at least one inductor, and wherein the at least one inductor is attached to a housing covering the switching unit.

[0077] Example Ex25. The aerosol-generating device according to any one of the preceding examples, wherein the switching unit comprises a metal-oxide semiconductor transistor, MOSFET, preferably a laterally-diffused metal-oxide semiconductor, LDMOS, transistor.

[0078] Example Ex26. The aerosol-generating device according to any one of the preceding examples, wherein the inner volume arranged inside the shell includes a first area comprising the heating chamber, and a second area comprising the oscillator with a load capacitor and at least one inductor, wherein a heat-conductive structure is arranged between the first area and the second area for improved heat exchange.

[0079] Example Ex27. The aerosol-generating device according to Ex26, wherein electrodes of the load capacitor are arranged inside the heating chamber, preferably placed on or in contact with the heat-conductive structure.

[0080] Example Ex28. 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. Example Ex29. 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 receive an aerosol-forming substrate, wherein the heating chamber comprises a heating element, which in operation heats the aerosolforming substrate by dipole rotation when subjected to an alternating electric field inside the heating chamber, providing an oscillation circuit comprising a switching unit, wherein the heating element is fed by the oscillation circuit, arranging a shell to at least partly encompass the heating chamber, the shell being configured to insulate heat within an inner volume formed by the shell, wherein the switching unit is arranged within the inner volume of the shell and in thermal contact with the heating chamber, so that in operation heat losses of the switching unit are for at least a substantial part dissipated into the heating chamber.

[0081] Example Ex30. The method according to Ex29, wherein the switching unit is attached to a heat sink, the heat sink being in thermal contact with the heating chamber.

[0082] Example Ex31 . The method according to example Ex29 or Ex30, wherein the oscillation circuit comprises at least one inductor, wherein the inductor is attached to a heat sink and / or forms a heat sink.

[0083] Example Ex32. The method according to any one of examples Ex29 to Ex31 , wherein the heat sink comprises at least one of copper, silver, aluminium, graphene, and carbon-based material.

[0084] Example Ex33. The method according to example E31 or Ex32, wherein the at least one inductor is attached to a housing covering the switching unit.

[0085] Example Ex34. The method according to any one of examples Ex29 to Ex33, wherein the switching unit comprises a metal-oxide semiconductor transistor, MOSFET, preferably a laterally- diffused metal-oxide semiconductor, LDMOS, transistor.

[0086] Example Ex35. The method according to any one of examples Ex31 to Ex34, wherein the at least one inductor is in direct contact with the backside metal of the MOSFET for efficient heat sinking properties.

[0087] Example Ex36. The method according to any one of examples Ex29 to Ex35, wherein the inner volume arranged inside the shell includes a first area comprising the heating chamber, and a second area comprising the oscillator circuit with a load capacitor and two inductors, wherein a heat-conductive structure is arranged between the first area and the second area.

[0088] Example Ex37. The method according to Ex36, wherein electrodes of the load capacitor are arranged inside the heating chamber, preferably placed on or in contact with the heat- conductive structure.

[0089] The invention will be further described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic illustration of a dielectric heating aerosol-generating system according to embodiments of the disclosure;

[0090] 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;

[0091] 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;

[0092] 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;

[0093] Figure 4 illustrates an oscillation circuit diagram according to embodiments of the disclosure;

[0094] 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;

[0095] 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;

[0096] Figure 7 is a schematic cross-sectional view of an aerosol-generating device according to a first example;

[0097] Figure 8 is a schematic cross-sectional view of an aerosol-generating device according to another example;

[0098] Figure 9 is a schematic cross-sectional view of an aerosol-generating device according to a further example;

[0099] Figure 10 is a schematic cross-sectional view of an aerosol-generating device according to a further example;

[0100] Figure 11 is a schematic cross-sectional view of an aerosol-generating device according to a further example; and

[0101] Figure 12 is a schematic cross-sectional view of an aerosol-generating device according to a further example.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] The aerosol-generating device 120 may have an outer casing 121 which is configured to be handheld.

[0106] 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.

[0107] 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.

[0108] 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 aerosol-forming article 105 or reaches into an inner volume of the aerosol-forming article 105 that can heat and vaporize a liquid aerosol-forming substrate 110 located in the inner volume 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 2 mm, depending on the desired capillary strength or rise. The first and second electrodes 130, 135 can be arranged as two matrices or arrays of pin-like, rod-like, or tab-like electrodes with opposite polarity, the two matrices or arrays interposed between each other, forming a capillary structure therebetween, for example with an average distance between neighboring pin-like electrodes being in a range between 0.1 mm to 2 mm, depending on the desired capillary strength or rise. In another variant, the wicking element can be a separate element that is interposed between two electrodes 130, 135, for example flat or slightly curved electrodes 130, 135.

[0109] 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.

[0110] 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 120. When power is supplied to the oscillation circuit 150, the oscillation circuit 150 generates an alternating electric field across the first and second electrodes 130, 135 to dielectrically heat the aerosol-forming substrate 110 in the heating chamber 140, releasing volatile compounds.

[0111] The controller 180 may cause dielectric heating of the aerosol-forming substrate 110 that is located between the two electrodes 130, 135 for a heat-not-burn operation, using 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.

[0112] 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 / cm3in a puff-on-demand heating operation. The aerosolgenerating 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.

[0113] 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.

[0114] 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.

[0115] 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% of plant leaf lamina, more preferably, at least 50% of plant leaf lamina, still more preferably at least 75% of plant leaf lamina and most preferably at least 90% of plant leaf lamina.

[0116] 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.

[0117] 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.

[0118] The aerosol-forming substrate 110 of the aerosol-forming article 105 may comprise an aerosol former. Where the aerosol-forming substrate 110 comprises cut filler, the cut filler may be soaked with aerosol former. Soaking the cut filler can be done by spraying or by other suitable application methods.

[0119] Preferably, the aerosol former comprises one or more of glycerine, for example vegetable glycerine (VG), and / or propylene glycol (PG), or equivalent aerosol formers. 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 aerosolgenerating 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.

[0120] 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.

[0121] 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.

[0122] Suitable aerosol-forming substrates and articles comprising cut filler include those described in W02022 / 074240 and / or W02022 / 074158, these references herewith incorporated by reference in their entirety.

[0123] 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 aerosolgenerating system 100 can include reconstituted tobacco, such as one or more sheets of homogenized tobacco material made by a cast leaf process.

[0124] 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 a homogenised tobacco material may have a tobacco content of at least about 40% by weight on a dry weight basis or of at least about 50% by weight on a dry weight basis. In other embodiments, the homogenised tobacco material may have a tobacco content of about 70% or more by weight on a dry weight basis, such as between 70% and 80% by weight on a dry weight basis.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] Suitable non-tobacco fibres for inclusion in the aerosol-forming substrate 110, to strengthen the material, are known in the art and include, but are not limited to: cellulose fibers; soft-wood fibres; hard-wood fibres; jute fibres and combinations thereof. For example, the aerosol-forming substrate 110 may comprise between 2% and 6% non-tobacco fibres by weight on a dry weight basis, such as between 3% and 5% non-tobacco fibres by weight on a dry weight basis, preferably about 4% non-tobacco fibres by weight on a dry weight basis. Preferably, the non-tobacco fibres are cellulose fibres.

[0129] The aerosol-forming substrate 110 may comprise an aerosol former. Preferably, the aerosol former comprises one or more of glycerine, for example VG (Vegetable Glycerin), and 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-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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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).

[0136] The oscillation circuit 250 can further comprise a choke 280 that acts on an input to the feedback loop 270 to provide for a stimulation signal, for example a stimulation voltage. The oscillation circuit 250 also comprises a biasing unit 290 acting on the feedback loop 270 for providing a variable or controllable biasing signal, for example a biasing voltage for setting the operating conditions. In the variant shown, the feedback signal can be described as a voltage. The output voltage UOUT of the switching unit 260 is coupled to the feedback loop 270 providing a feedback switching signal in the form of an input voltage UIN to the switching unit 260. The configuration of the feedback loop 270 is such that the output signal, e.g. the output voltage UOUT of the switching unit 260 can undergo a phase change and arrives inverted at the input voltage UIN of the switching unit 260 for resonant oscillation. In other configurations, a current could be used as the feedback signal with the switching unit 260 comprising a BJT.

[0137] 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.

[0138] As shown in Figures 3A and 3B, the feedback loop 270 includes a resonant circuit 272 comprising the load capacitor CL providing for a first 90° phase shift or quarter wave shift to the feedback signal. The feedback loop 270 further includes a capacitive element 274 providing for a second 90° phase shift or quarter wave shift to the feedback signal, such that the feedback signal reaching the input of the switching unit 260 is inverted and phase-shifted by 180°. The switching unit 260 is itself configured for inverted switching operation to provide the 180° phase shift between the input voltage UIN and the output voltage UOUT of the switching unit 260.

[0139] 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.

[0140] 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.

[0141] The delay line DL is a time delay element, for example an element that has inductive behavior, for slowing down the arriving voltage wave from the feedback loop 270 during a period of the oscillation. This allows to tune the resonant circuit 272 to a desired switching and oscillation frequency, to move the oscillation frequency away from the natural resonant frequency given by the resonant circuit 272. This ensures that oscillation circuit 350 remains in a predefined frequency operating range to provide for the requisite inverted or 90° phase shifted feedback and also to make sure that the feedback loop 270 has a low impedance to provide for a high gain, as described in greater detail below.

[0142] The oscillation circuit 350 is shown with electrical contacts 160, 165 that are arranged on each side of the load capacitor CL. In some embodiments, the first and second electrodes 130, 135 may be removable from the oscillation circuit 350, or may form part of the aerosol-forming article 110. In such embodiments, the electrical contacts 160, 165 provide an electrical connection between the first and second electrodes 130, 135 and the feedback loop 270. In embodiments where the load capacitor CL is fixed within the feedback loop 270, for example, such that an aerosol-forming substrate 110 can be inserted and removed to and from a 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.

[0143] 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 a 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 allow 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.

[0144] 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 2pF to 100pF, more preferably in a range between 5pF and 50pF.

[0145] 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 100MHz. The capacitance value for the capacitor C2 of the capacitive element 274 should be relatively high as compared to the capacitor Ci, for example in a range between 500pF to 100nF, more preferably between 1nF and 50nF, which leads to a low impedance of the capacitive element 274. In a variant, the capacitive element 274 can be implemented as a RC network to provide for the 90° phase shift, for example using two single-resistor-capacitor networks, having two capacitors in the feedback loop 270, each capacitor connected to ground via a resistor.

[0146] The resonant circuit 272, together with the capacitive element 274, provides for a 180° phase shift and a voltage gain from the output voltage UOUT to the input voltage UIN, and the transistor T (for example a FET) is configured for inverting operation, thereby also providing for another 180° phase shift. This results in a resonant or close-to resonant oscillation and an amplified voltage UL across the electrodes 130 and 135 of the load capacitor CL, as compared to the DC supply voltage. When operating close to resonance, the resonant circuit 272 behaves inductively, having a high Q factor. Furthermore, the feedback loop 270 is impedance-matched with the transistor T, at an impedance of approximately 500mQ to 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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 total inductance 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.

[0152] 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.

[0153] 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.

[0154] The values of components in this resonant circuit 272 are preferably chosen to be in the following exemplary and non-limiting ranges. The total inductance LTOT can be a range between 10nH to 50nH, more preferably between 15nH and 40nH, which is the equivalent of Li plus L2, LE could be in a range between 7nH and 30nH, more preferably between 10nH and 20nH, and the value of the load capacitor can be in a range between 0.5pF to 5pF, more preferably between 1 pF to 3pF.

[0155] 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.

[0156] T o have a proper inverting effect and a 180° phase shift on the feedback loop 270 between 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.

[0157] Oscillations in the feedback loop 270 will be naturally drawn towards the parallel resonance (antiresonant) frequency of the resonant circuit 272. However, the addition of the delay line DL can introduce a slight time delay limiting the oscillation frequency below the parallel resonance frequency. Figure 6 shows a frequency analyzer plot of an exemplary resonant circuit 272, specifically a plot of a parallel resonator circuit PRC showing the relationship between the oscillation frequency (with a series resonance at 855 MHz and a parallel resonance at 1.246 GHz), the phase shift across the PRC (with a relatively flat inductive 90° frequency response between the two resonant frequencies) and the effective impedance of the PRC. More specifically, it can be seen from Figure 6 that the 90° phase shift starts dropping before the parallel resonance frequency fpAR is reached. After the parallel resonance frequency fPAR, the phase shift response drops below 0° to capacitive behavior and the impedance is very high, e.g. 2.4kQ. The ideal operating frequency range is closer to the series resonance frequency fsER where the phase shift is still 90° and the impedance response is low, preferably an impedance that is less than 2Q, more preferably less than 1 Q. The parallel resonance frequency fpAR can be above 1GHz, e.g. 1GHz to 1.5GHz, while the actual switching frequency fs can be below 1GHz, and this lower switching frequency is caused by the delay line DL.

[0158] 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 FIG. 6. For example, a resulting impedance of the feedback loop 270 at the oscillation frequency fs of the oscillation circuit can be in a range of approximately 100mQ to 2Q. Preferably, the delay line DL is configured such that the oscillation frequency fs is closer to the series resonance frequency fsER than to the parallel resonance frequency fPAR, thereby maintaining a low resonant circuit impedance while operating at a frequency range where the resonant circuit provides the 90° phase shift. The time delay caused by the delay line DL needs to be relatively short, as the series resonance and the parallel resonance of a parallel oscillating circuit PRC are close to each other, relative to the overall frequency range. Preferably, the delay caused by the delay line DL that acts on the feedback loop 270 should be in a range between 5% to 35% of the period of the parallel resonance frequency fpAR, providing that the above two conditions (i) and (ii) are fulfilled. In an embodiment, the delay caused by the delay line DL that acts on the feedback loop 270 is in a range between 35% and 90% of a difference between the period of the parallel resonance frequency fpAR and the period of the series resonance frequency fSER, again providing that the above two conditions (i) and (ii) are fulfilled, more preferably a range between 50% and 85%. For example, taking the illustration of Figure 6 and as a non-limiting numerical example, assuming that a parallel resonance frequency fpAR is at 1.25 GHz, therefore having a period of 800ps (picoseconds), and a series resonance frequency fsER is at 855MHZ, and therefore a period of 1169ps, there is a difference of 369ps between the periods of fpAR and fsER. The time delay caused by the delay line DL can be in the above range, for example at 70% of the period difference between fpAR and 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.

[0159] 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.

[0160] In any case, the switching unit, e.g. the transistor 260, generates heat losses which have to be dissipated. As shown in Figure 7, according to embodiments of the present disclosure, the heat generated by the transistor 260 is not dissipated to the outside environment of the aerosolgenerating device 120, or somewhere inside the outer casing 121 of the aerosol-generating device 120, but is effectively used for heating the inside of the heating chamber 140. To achieve this confinement of the heating losses, the heating chamber 140 is surrounded by a shell 300 which forms an outer heat insulation layer. The shell 300 defines an inner volume 302 and insulates any heat generated within the inner volume 302, so that the heat remains inside the inner volume 302 and can be used to heat the heating chamber 140. The inner volume 302 can therefore also be referred to as an insulated volume.

[0161] The shell 300 can be made from a material having a high thermal resistivity, resistance, or R-value (also referred to as thermal insulance), expressed in m2K / W.

[0162] 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.

[0163] The R-value is the thermal resistance per unit area and is defined by the following equation:

[0164] R=L / k with:

[0165] R... thermal resistance (R-value)

[0166] L... thickness of the material, measured in meters k... thermal conductivity of the material, measured in W / (mK)

[0167] The thermal conductivity k of the material of the shell 300 should be preferably less than 1 , more preferably less than 0.6, even more preferably less than 0.3, expressed in W / (mK). Moreover, an average wall thickness of the shell 300 is preferably such that sufficient thermal insulation is provided, and is in average at least 1 mm thick, preferably in average more than 1.5 mm thick, more preferably more than 2.0 mm thick. An electrode arrangement, referred to as an “applicator” 314 is formed by an assembly of the capacitive plates (or electrodes) 130, 135 producing the alternating electric field. The electrodes 130, 135 may of course not only be straight, but may also be curved structures.

[0168] As can be seen from Figure 7, the inner volume 302 forms a contiguous volumetric structure which allows any heat generated by any part of the dielectric heating element and the oscillation circuit to spread within the inner volume 302 with little thermal resistance or obstruction. Advantageously, the electrodes E1 , E2 of the load capacitor CL, the two inductors Li, L2, and the transistor 260 can also all be arranged within the inner volume 302, as producing additional electric losses to the switching losses caused by the switching element, e.g, transistor 260. This geometry allows at least a significant part of the heat generated by the transistor 260 to be diverted into the heating chamber 140 via heat conduction and heat radiation. As shown in Figure 7, the heating chamber 140 and / or inner volume 302 is open at one end, such that an aerosolforming article can be inserted through the open end into heating chamber 140. However, it is also possible that the heating chamber 140 can be closed and opened by a lid or cap (not shown), for example a pivotable, rotatable, or slidable lid that is movable between an open and a closed position, or by a removable mouthpiece, tray, or other configuration. The lid or cap can also be made to have thermal insulating properties, similar or analogous to shell 300. Such arrangement would allow for further heat insulation and concentration inside heating chamber 140. According to an aspect of the herein presented invention, a heater space is provided, thermally insulated from an exterior environment or the remaining interior of the aerosolgenerating device, where both the oscillator (that can generate substantial losses, e.g. 25-50%) and the heating chamber 140 (for removably receiving the aerosol-forming article with the substrate) are arranged inside the same and / or united volume, forming a thermally-unitary volume (referred to as insulated volume or inner volume 302). According to an aspect of the present invention, as much as possible of the generated heat, including the heat losses, can be concentrated into a common insulated volume 302 that also includes the heating chamber 140 for the aerosol-forming substrate 110.

[0169] As mentioned above, the resonant dielectric circuit may include an inductive element, for example the two matching split inductors Li, L2 directly connected to the transistor 260. Such inductors Li, L2 may be formed from a material that has a certain thermal mass and high thermal conductivity, preferably a thermal conductivity of above 100, more preferably above 150, expressed in W / (mK), forming a heat sink and heat radiator structure. Advantageously, such inductors Li, L2 act as a heat sink for the transistor 260, to redirect the switching losses that generate heat from the transistor 260 to the heating chamber 140, all within the insulated volume 302.

[0170] According to an aspect of the invention, the inductors Li , L2 are therefore used as heat sink to provide thermal management of the transistor 260.

[0171] To this purpose, inductors may be advantageously machined in a relatively heavy, bulky form, not necessarily being a wire, but rather a machined inductor, for example from a material having high thermal conductivity, e.g. copper. Of course, the inductors may also be formed from a thicker wire, having a certain surface, a certain mass, such to be used as a heat sink. Such a wire may e.g. have a diameter of about 1 mm.

[0172] Further, bulky inductors may be in thermal attachment to the element that forms the transistor 260 in addition to the electric attachment for the resonant circuit, for example thermally attached to the transistor casing or transistor substrate die, playing the role of a heat sink.

[0173] As can be seen from Figure 7, the heating chamber 140 is delimited by heating chamber walls 304. The heating chamber walls 304 are electrically insulating and can provide mechanical support for the first and second electrodes 130, 135. For example, the heating chamber walls 304 may be formed from a low dielectric materials that can easily be cleaned and can resist the heating temperatures, such as glass, preferably quartz glass, a high-temperature polymer, for example polyether ether ketone (PEEK), or a ceramic material. 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. The provision of heating chamber walls 304 within the shell 300 allows to provide a sealed volume for the heating chamber 140 relative to the volume where the electronic components with switching unit 260 are located, to avoid any contamination of the heating chamber 140 by harmful and potentially harmful constituents (HPHC) that could emanate from the transistor 260 and other components.

[0174] For example, as shown in Figure 8, it is possible to provide for two volumes within the inner volume 302 of the shell 300, one for the switching unit 260, and one for the heating chamber 140, with a separation provided by heat sink structure 316 as a filling, wall, barrier, or other structural element that physically separates the two volumes, but still provides a thermal contact and low thermal resistivity between the two volumes. Preferably, the material chosen for heat sink 316 is electrically highly resistive, has a low relative permittivity (preferably between 2-4), but has a low thermal resistance, to allow for heat exchange within the entire volume of the shell 300. In the variant shown in Figure 8, the inductors Li and L2 can be in thermal contact with the material that forms the heat sink 316, shown as a filling, and in the variant shown, the entire internal volume of the shell 300 other than the heating chamber 140 is filled or occupied by the heat sink structure 316, to have a good thermal heat exchange between the switching unit 260, and the heating chamber 140. Air paths or vents 322 can be provided that lead to the heating chamber 140, and an additional protective wall 304 to keep any HPHC out of the heating chamber 140 can be provided, in the form of the heating chamber walls 304, for example a coating made of glass such as quartz glass, ceramic, or suitable high-temperature polymer, preferably PEEK.

[0175] 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, six, or more, may be arranged around the circumference of the heating chamber walls 304 for holding the heating chamber 140 in space. For instance, new materials such as low-dielectric polymer, such as PEEK, 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, more specifically less than 0.3 mm. With the provision of spacers, it is possible to establish an air gap or air space between the electrodes 130, 135 and the shell 300, so that the alternating electric field generated by electrodes 130, 135 is more removed from the material of shell 300. Despite a material chosen for the shell 300 having a low relative permittivity (around 3 or more), air would still have substantially lower relative permittivity with (slightly more than 1). This allows to further reduce unnecessary dielectric heating losses by the electric field.

[0176] 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 308, 309 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.

[0177] Due to the limited space, the power source 312 (e.g. a battery) is arranged outside the inner volume 302, and essentially only the transistor and the inductors are arranged inside the volume 302, and the electric interconnection to transistor. Any other component that could produce fumes and HPHC should be avoided.

[0178] According to a further aspect of the present disclosure, the improved heat loss management can provide thermal enhancement since the transistor 260 heats first, before the applicator 314 and hence before the heating of the substrate of the aerosol-forming article.

[0179] In Figure 7, it can be seen that the coils of the inductors Li, L2 are electrically connected with the resonant circuit 272 to the transistor 260, but also physically to a heat-generating surface of the transistor 260, for example by a thermal connection to the transistor packaging or die.

[0180] As a consequence, the inductors Li, L2 may not only be used as a heat sink, but also as a thermal bridge and conductor for preheating the applicator 314 by the heat generated by the transistor 260. The transistor 260 may dissipate approximately 1.5 - 2 W during the preheating phase, before the first puff. Thereby a significant amount of heating energy can be concentrated inside the heating chamber 140. In addition, the inductors Li, L2 can also generate electric losses during operation, and these are also dissipated into the heating chamber 140.

[0181] Such losses may be suitably channeled in order to preheat aerosol-forming article and the capacitor plates 130, 135 reaching, for example, a temperature of approximately 50 degrees Celsius or more. It is important to stress that during this state of operation, dielectric heat is generated in the aerosol-forming substrate 110 of the article 105 and the applicator 314 additionally receives the heat from the heat conduction of the split inductors Li, L2 acting as a heat sink and any heat conductive elements.

[0182] The applicator 314 (that is the electrodes 130, 135 with the supporting structure) is preheated by channeling the power losses, mostly switching losses of the transistor 260 to thereby reduce the inherent heat-up time.

[0183] Thus, by dissipating the heat losses of the transistor 260 via the inductors Li, L2, the overall efficiency of the device (by, in this case, externally heating the heating chamber 140) is improved. The electrodes 130, 135 are preheated by the losses produced by the transistor 260. This would amount to a dual heating scheme by mere passive means, including external radiative heat from the losses and internal dielectric heat from the alternating electric field of the electrodes 130, 135.

[0184] In order to efficiently dissipate the heat losses caused by the switching of the transistor 260, according to the embodiment of Figure 7, the inductors Li, L2 can be made of a highly heat- conductive material, e.g. copper, and are connected to the electrodes 130, 135 without interrupting any thermal bridges by providing a rigid thermal connection between the inductors Li , L2 and the electrodes 130, 135. According to another aspect of the invention, the oscillator circuit that can be placed inside the volume 302 can also be powering an inductive coil for inductive heating. Thereby, the electrodes 130, 135 could be functionally replaced by one or more inductive heating coils.

[0185] Figure 7 schematically shows the bulky structure of the inductors, serving as a heat sink for the transistor 260 as well as a heat vector for the electrodes 130, 135. Thus, passive heating can be achieved mostly via transistor switching losses, bringing these losses close to the electrodes 130, 135 to perform a preheating operation. Due to the nature of the RF current flowing through the inductor coils, there will be also electric losses caused by the coils, that can further speed up the heating process.

[0186] Now turning to Figure 9, a further advantageous example of the present disclosure is shown. According to this embodiment, the thermal distribution is further supported by heat conductive elements or heat sink structures 316 (comprising for instance copper, silver, aluminum, graphene, other carbon-based material). The heat sink structure 316 is arranged to contact an element of the casing or the die of the transistor 260 of the oscillator, in order to move the heat into the heating chamber 140. The heat sink structure 316 may dissipate heat generated by the transistor 260 mainly by heat radiation or convection, but also via heat conduction directly to one of the electrodes 130, 135. Mainly, the aim is not heating up the electrodes 130, 135, but spreading the heat throughout the heating chamber 140, to make sure the aerosol-forming substrate is subject to external convective heat, and not only internal dielectric heat. To this end, a thermal connection 318 which provides heat conduction is arranged between one of the electrodes 130, 135 and the heat sink structure 316. Further, an end face 320 of the heating chamber walls 304 of the heating chamber 140 has venting apertures 322 through which a heat exchange via heat convection is possible.

[0187] Turning back to Figure 8, it can be seen that a much more expansive heat sink structure 316 can be provided and that the venting apertures 322 may be led through this heat sink structure 316. The venting apertures 322 form channels which may be covered with a microwave- safe and easy to clean material, such as glass, preferably quartz glass, a high-temperature polymer, for example polyether ether ketone (PEEK), or a ceramic material.

[0188] In the scheme proposed in Figure 8, the heat sink structure 316, also just called “heat sink” in the following, is an additional element. Similar to the example of Figure 7, the arrangement shown in Figure 8 includes a heating chamber 140, arranged inside an insulated volume (also called “inner volume”) 302. Heating chamber walls 304 are provided as a mechanical support for the electrodes 130, 135 and may have a cylindrical (or any other) shape, to form the heating chamber 140. The heating chamber walls 304 are, for instance, made of a low dielectric material that can be easily cleaned (e.g. glass, quartz glass, polyimide, etc.). The electrodes 130, 135 can form the load capacitor CL. Furthermore, around the electrodes 130, 135, an air space 324 or air gap is provided as a first thermal insulation layer.

[0189] Low dielectric spacers 308 are provided for holding the heating chamber 140 in space. As already mentioned, new materials, such as polyimide or ceramic, have been developed for 5G connectors that are low-dielectric (polyimide, ceramic), temperature resistant, porous, etc. Furthermore, a shielding layer 326 may be arranged at the inner surface of the shell 300, at an outer surface of shell 300, or both. The shielding layer 326 has high electrical conductivity, is comparatively thin, and has no or only few edges and / or sharp corners. Advantageously, the shielding layer 326 has heat reflective properties.

[0190] The shell 300 forms an outer heat insulation layer and comprises a non-conductive thermal insulation layer having a high thermal resistivity, for example PEEK or similar, for forming the insulated volume 302. According to the example shown in Figure 8, the battery 312 is arranged outside of the insulated volume 302.

[0191] Furthermore, an RF oscillation circuit 150 is arranged inside the insulated volume 302, the oscillation circuit 150 being operable to generate an RF E-field between the electrodes 130, 135.

[0192] According to an aspect of the present disclosure, a heat sink 316 is arranged in close contact with the transistor 260 of the oscillation circuit 150, for spreading heat inside the insulated volume 302. The heat sink 316 may have any suitable shape, and may also extend into the heating chamber 140 or may at least partly surround the heating chamber 140.

[0193] Further, the inductors Li , L2 and the heat sink 316 may also be merged into a single integral structural component. A quite thick metallic structure can be used playing the role of the coupled inductors Li, L2 and, in addition, the heat sink function. In other words, according to one aspect of the present disclosure, it is proposed to execute the inductors Li, L2 in a way such that they function as a heat sink structure 316.

[0194] When using an oscillation circuit according to Figure 4, the inductors Li and L2 are electrically connected to the electrodes 130, 135 with one end. The other end of the first electrode 130 is connected with its other end to the transistor 260.

[0195] Thus, instead of making the inductors Li , L2 very light and little with almost no heat transfer, one aspect of the present disclosure is to make them heavy and use them as a heat sink for the transistor 260, to increase their thermal capacity, such as to convey transistor switching losses and other electric losses to the electrodes 130, 135 and to the heating chamber 140 for preheating.

[0196] Furthermore, the insulated volume 312 may also be separated into two areas, a first area operating as the heating chamber 140, and a second area provided for the oscillation circuit with the load capacitor CL and the inductors Li L2, with a heat-conductive separation wall between the first and second areas. In another variant, the electrodes 130, 135 of the load capacitor CL are arranged inside the heating chamber walls 304, for example placed on or in contact with a heat- conductive separation wall forming the heating chamber walls 304. This may for instance be seen in Figure 8.

[0197] All elements of the aerosol-generating device may advantageously be designed such that the junction temperature of the transistor 260 never exceeds a threshold value. For example, the heat sink 316 and / or the inductors Li, L2 can be designed such that the heat sinking and heat conduction are sufficient to avoid temperatures of the junction exceeding a certain threshold. This temperature threshold for the junction of the transistor 260 can be somewhat lower than the heating temperature of the aerosol-forming substrate 110. Exemplarily, for the design illustrated in Figure 9, the heat sink 316 may be a copper plate of 2 cm x 1 .2 cm which reaches a temperature of about 85 degrees Celsius during preheating. The inductors Li, L2 may reach a temperature of 100 degrees Celsius, which is then used to preheat the electrodes 130, 135.

[0198] For example, the mass of the inductors Li, L2 may be around 2-3 grams, and this will be distributed within air gaps for insulation, and thus the inductors Li , L2 fundamentally act as a heat sink.

[0199] Furthermore, the thermal inertia or thermal capacity of the heat sink 316 may also be calculated and its temperature rise for a given dielectric heating power evolution.

[0200] Still with reference to the scheme of Figure 9, different arrangements of the heating chambers 140 and heat sink structure 316 may be proposed. In particular, the heat sink 316 may also be electrically and / or thermally interconnected to the shielding layer 326. That would allow to create a combined external heater by combining heat propagation and electromagnetic shielding in one. In this case, the shell 300 forming an outer heat insulation layer may be heat resistive to deal with the elevated temperatures caused by the external heater formed by the heating chamber 140 and the heat sink structure 316.

[0201] Figures 10 to 12 illustrate various further embodiments of the aerosol-generating device 120, showing cross-sectional views of the area comprising the heating chamber 140.

[0202] Figure 10 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. However, other shapes are also possible for the heating chamber 140, for example rectangular, oval, square, etc. Also, in variant shown in Figure 10, two cylindrically-shaped segments are shown for the electrodes 130, 135, but other configurations or number of electrodes are also possible.

[0203] With reference to Figure 10, the heating chamber 140 is surrounded by a cylindrical heating chamber wall 300. The heating chamber wall 300 is electrically insulating and mechanically supports two electrodes, a first electrode 130 and a second electrode 135. The two electrodes 130, 135 are operable to generate an electric field inside the heating chamber 140.

[0204] The heating chamber walls 304 are mechanically supported by a heating chamber support unit 306. The heating chamber support unit 306 comprises, according to the embodiment shown in Figure 10, 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.

[0205] The spacers 308 are distributed around the circumference of the heating chamber 140. It should be noted that according to Figure 9, 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. According to the present disclosure, a 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.

[0206] According to the present disclosure as illustrated in Figure 11 , the shielding layer 326 is not arranged on the inner surface of the shell 300, but on the outer surface. In particular, Figure 11 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] Finally, as shown in Figure 12, 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.

Claims

CLAIMS1 . An aerosol-generating device comprising an outer casing, a heating chamber which is arranged to at least partly receive an aerosol-forming substrate, wherein the heating chamber comprises heating chamber walls and a dielectric heating element, which in operation heats the aerosol-forming substrate by dipole rotation when subjected to an alternating electric field inside the heating chamber, an oscillation circuit comprising a switching unit, wherein the dielectric heating element is fed by the oscillation circuit, inside the outer casing, a shell forming an inner volume that at least partly encompasses the heating chamber walls, the shell configured to insulate heat within the inner volume, wherein the switching unit is arranged within the inner volume and in thermal contact with the heating chamber, so that in operation heat losses of the switching unit are for at least a substantial part dissipated into the heating chamber.

2. The aerosol-generating device according to claim 1 , wherein the shell includes an electrically conductive element that forms an electromagnetic shielding layer.

3. The aerosol-generating device according to any one of the preceding claims, wherein the shell includes at least one heat reflection layer.

4. The aerosol-generating device according to claim 3, wherein the at least one heat reflection layer is arranged at an inner surface of the shell.

5. The aerosol-generating device according to any one of the preceding claims, wherein the shell includes an inner airspace or vacuum chamber to provide for a low-dielectric thermal insulation.

6. The aerosol-generating device according to any one of the preceding claims, wherein the heating chamber comprises at least two opposing electrodes arranged for heating the aerosol-forming substrate, and wherein the switching unit is connected to the electrodes.

7. The aerosol-generating device according to claim 6, wherein the electrodes form a part of a load capacitor of the oscillation circuit.

8. The aerosol-generating device according to claim 7, wherein the oscillation circuit further comprises one or more inductors, and wherein the one or more inductor, the load capacitor, and the switching unit are arranged inside the inner volume.

9. The aerosol-generating device according to any one of the preceding claims, wherein the switching unit is attached to a heat sink, the heat sink being in thermal contact with the heating chamber or wherein a heat sink and the walls of the heating chamber form a unitary element of heat conductive material.

10. The aerosol-generating device according to any one of the preceding claims, wherein the oscillation circuit comprises at least one inductor, wherein the inductor is attached to a heat sink and / or forms a heat sink of the switching unit.

11. The aerosol-generating device according to any one of the preceding claims, wherein the aerosol-generating device comprises a support unit which is arranged within the shell so that the heating chamber is supported within the shell and wherein an air gap is provided between the shell and the heating chamber.

12. The aerosol-generating device according to claim 11 , wherein the support unit includes at least one spacer having a low dielectric constant.

13. The aerosol-generating device according to any one of the preceding claims, wherein the inner volume arranged inside the shell includes a first area comprising the heating chamber, and a second area comprising the oscillator with a load capacitor and at least one inductor, wherein a heat-conductive structure is arranged between the first area and the second area for improved heat exchange.

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, preferably according to any one of the preceding claims, the method comprising: providing a heating chamber which is arranged to receive an aerosol-forming substrate, wherein the heating chamber comprises heating chamber walls and 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,providing an oscillation circuit comprising a switching unit, wherein the heating element is fed by the oscillation circuit, and arranging a shell inside an outer casing, to at least partly encompass the heating chamber walls, the shell being configured to insulate heat within an inner volume formed by the shell, wherein the switching unit is arranged within the inner volume of the shell and in thermal contact with the heating chamber, so that in operation heat losses of the switching unit are for at least a substantial part dissipated into the heating chamber.

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