Cavity arrangement for heat losses mitigation

Abstract

There is provided an aerosol-generating device for dielectrically heating an aerosol-forming substrate of an aerosol-forming article to generate an aerosol therefrom. The device comprising: an electromagnetic field generator configured to generate radio-frequency (RF) electromagnetic radiation, a peripheral layer defining a resonant cavity, the peripheral layer being made of an electrically conductive material to confine the RF electromagnetic radiation within the resonant cavity, and a dielectric filling arranged within an interior of the resonant cavity, the dielectric filling defining a substrate cavity for receiving the aerosol-forming substrate. The peripheral layer has a peripheral layer thickness from 1 to 1000 micrometers, preferably from 2 to 500 micrometers, more preferably from 5 to 250 micrometers.

Description

[0001] Cavity Arrangement for Heat Losses Mitigation

[0002] 1. Technical field

[0003] The present disclosure relates to aerosol-generating devices, and specifically to aerosolgenerating devices configured to heat an aerosol-forming substrate by dielectric or microwave heating. More specifically, the present disclosure targets aerosol-generating devices having a dielectric heating system based on resonant cavity technology. The disclosure also relates to a method of manufacturing an aerosol-generating device and a use of an electrically conductive coating layer to generate an aerosol-generating device.

[0004] 2. Background

[0005] 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 heating occurs as a result of eddy currents induced by a magnetic field and magnetic hysteresis losses of the magnetic movements in a susceptor heating element.

[0006] 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.

[0007] Systems that dielectrically heat an aerosol-forming substrate have been proposed, using a resonant cavity that is fed with a microwave from a wave source via a microwave coupler, which advantageously provide uniform heating of the aerosol-forming substrate. For example, see WO 2021 / 013477 A1 and WO 2022 / 128290 A1 , these references are herewith incorporated by reference in their entirety.

[0008] Dielectric heating, which is also often referred to as microwave heating, electric heating, or radio-frequency heating, generally refers to heating that arises as a result of dipole rotation of a to-be-heated material or substance that is subjected to an alternating electric field, and particularly a high-frequency alternating electric field. When an alternating electric field is applied to materials or substances containing polar molecules (i.e. molecules having an electrical dipole moment), the polar molecules align themselves in the electric field and rotate when the electric field alternates to maintain alignment with the electric field. This rotation (dipole rotation) results in heating of the materials or substances in the alternating electric field. In prior art aerosol-generating devices using a resonant cavity, a peripheral wall made from a relatively thick piece of a machined electrically conductive material, such as copper, is used to define the resonant cavity. However, such a relatively thick wall has several drawbacks: besides adding weight and costs to a handheld device, it also suffers from energy loss due to high thermal conductivity, and the time required to cool the copper is relatively long because of the limited surface area for heat dissipation.

[0009] It would be preferable to provide a system that dielectrically heats an aerosol-forming substrate using a resonant cavity with greater efficiency, while still being realizable in a compact or handheld system.

[0010] 3. Summary

[0011] According to a first aspect, there is provided an aerosol-generating device for dielectrically heating an aerosol-forming substrate of an aerosol-forming article to generate an aerosol therefrom. The device comprises: an electromagnetic field generator configured to generate radio-frequency (RF) electromagnetic radiation, a peripheral layer defining a resonant cavity, the peripheral layer being made of an electrically conductive material to confine the RF electromagnetic radiation within the resonant cavity, and a dielectric filling arranged within an interior of the resonant cavity, the dielectric filling defining a substrate cavity for receiving the aerosol-forming substrate. The peripheral layer has a peripheral layer thickness from 1 to 1000 micrometers, preferably from 2 to 500 micrometers, more preferably from 5 to 250 micrometers. Preferably, the peripheral layer may have a peripheral layer thickness from 5 to 100 micrometers, more preferably from 5 to 20 micrometers, in particular from 5 to 10 micrometers.

[0012] These thickness ranges of the peripheral layer are advantageous because they are designed as a function of the skin depth (5) of the operating frequency of the RF electromagnetic field used in the present aerosol-generating device for heating. The RF electromagnetic field has an operating frequency from 300 MHz to 300 GHz, preferably of about 2.4 GHz or 4.8 GHz. Specifically, the thickness ranges of the peripheral layer are designed to be at least equal to the skin depth (5). This ensures that the RF field penetrates sufficiently into the material, allowing for adequate interaction. To avoid unnecessary material usage, the thickness of the peripheral layer is designed not to exceed a practical limit where additional thickness no longer contributes to the interaction with the RF field, but only adds unnecessary weight. This limit may be set to no more than 10 times the skin depth.

[0013] In preferred embodiments, the peripheral layer thickness may range from TT times the skin depth 5 to 3TT times the skin depth 5, preferably from 1.5TT times the skin depth 5 to 2.5TT times the skin depth 5, in particular the peripheral layer thickness may be about 2TT times the skin depth 5. The use of such thicknesses ensures absorption and interaction of the RF electromagnetic field within the material of the peripheral layer. Using multiples of TT for the peripheral layer thickness in terms of skin depth 6 may leverage the inherent periodicity and phase characteristics of electromagnetic waves, thereby enhancing the efficiency and predictability of RF material performance.

[0014] The peripheral layer may be contact with the dielectric filling.

[0015] Housing and Thermal insulation layer

[0016] The aerosol-generating device may comprise a housing for the resonant cavity. The housing may comprise a thermal insulation layer that surrounds the peripheral layer. The thermal insulation layer may be made of a less thermally conductive material than the electrically conductive material of the peripheral layer.

[0017] The thermal insulation layer may be in contact with the peripheral layer.

[0018] The use of a less thermally conductive material that circumscribes the resonant cavity has the effect of reducing the heat that is drained out.

[0019] A thermal conductivity of the thermally conductive material may be from T 103to 20 103times, preferably from 1.5-103to 2 103times, more preferably from 1.7-103to 1.9-103times less than a thermal conductivity of the electrically conductive material of the peripheral layer.

[0020] The thermal insulation layer may be made of a non-electrically conductive material. For example, the thermal insulation layer may comprise a plastic material, such as but not limited to polyetheretherketone (PEEK).

[0021] By having electrically non-conductive layers, namely the dielectric filling and the thermal insulation layer, such as an air gap or solid thermal insulation layer, arranged adjacent to and / or in contact with respective outer or inner surfaces of the resonant cavity I electrically conductive peripheral layer may enable the use of a thin electrically conductive peripheral layer (thickness from 1 to 1000 micrometers, preferably from 2 to 500 micrometers, more preferably from 5 to 250 micrometers) forming the resonant cavity while enhancing electromagnetic and thermal efficiency. These layers may help suppress eddy currents and reduce thermal conduction. In particular, the concept can offer the following three advantages (l-lll):

[0022] I. Reduce the electric losses due to eddy currents and skin effect. When the resonant cavity is fed by a microwave (2.45 GHz), eddy currents are induced in the electrically conductive peripheral layer due to the electromagnetic fields generated within the resonant cavity, creating relatively high losses. The thin peripheral layer can reduce these losses.

[0023] II. Reduce costs for manufacturing the resonant cavity as the highly-conductive material typically used to form the resonant cavity (peripheral layer), like aluminum, silver or copper, is pricey; and

[0024] III. Reduce the thermal capacity of the electrically conductive peripheral layer, to avoid storing heat and energy therein that would require more power to heat-up a heating chamber to reach operational temperature, additional cooling, and might reduce the overall energy efficiency. The thermal insulation layer may have the form of an air gap. The air gap may be adjacent to the peripheral layer. The air gap may be filled with gas or vacuum.

[0025] The thermal insulation layer may have a melting temperature from 150 to 500°C, preferably from 175 to 400°C, in particular from 200 to 350°C.

[0026] The housing may be an elongated housing, preferably a cylindrical housing.

[0027] The housing may be configured to be handheld.

[0028] The thermal insulation material may be made of or comprise a solid material. The solid material of the thermal insulation layer may be in contact with the peripheral layer. The solid material may provide for more structural integrity and robustness of the relatively thin peripheral layer.

[0029] The use of solid material in the thermal insulation layer may act, at least partially, as a heat shield that reflects heat generated within the resonant cavity, thereby improving heating efficiency and loss of heat I energy in free air. This arrangement may retain the benefits of having a relatively thin peripheral layer while reducing the overall heat conduction and energy loss compared to having a thick piece of machined copper and / or an air gap between the outer shell of the housing and the resonant cavity.

[0030] The thermal insulation layer may comprise one or more air channels machined in the solid material, so as to extend along a longitudinal and / or circumferential direction of the thermal insulation layer. The one or more air channels may have the form of a groove with an opening towards the peripheral layer.

[0031] The thermal insulation material may comprise a plastic material, preferably a thermoplastic polymer that belongs to the family of polyaryletherketones (PAEK). Preferably, the thermal insulation layer comprises or is made of polyetheretherketone (PEEK).

[0032] PEEK may possess good electrical insulating properties, which remain relatively stable over a wide range of temperatures and environmental conditions compared to many standard plastics.

[0033] Alternatively or additionally, the thermal insulation layer comprises or is made of polyetherimide (PEI).

[0034] The aerosol-generating device may comprise at least one additional thermal insulation layer arranged between the thermal insulation layer that comprises the solid material and at least one of the dielectric filling and / or an outer shell of the housing. The at least one additional thermal insulation layer may have the form of an air gap. The air gap may be filled with gas or vacuum.

[0035] Coated peripheral layer (electrically conductive coating layer)

[0036] The peripheral layer may be formed as a coating layer.

[0037] Using a coating layer instead of a solid wall in a resonant cavity may reduce material usage due to the reduction of waste products generated during machining (e.g. milling or turning) and weight while enhancing durability. An outer surface of the dielectric filling may be coated with the electrically conductive material to form the peripheral layer, or at least a portion thereof.

[0038] An inner surface of the thermal insulation layer is coated with the electrically conductive material to form the peripheral layer, or at least a portion thereof.

[0039] The peripheral layer may be a peripheral coating multilayer. The peripheral coating multilayer may comprise a first coating layer attached to the outer surface of the dielectric filling and a second coating layer attached to the inner surface of the thermal insulation layer, so that in an attached state of the aerosol-generating device, the first and second coating layers are electrically connected to each other.

[0040] The advantage of using a coated multilayer may be twofold: it reduces heat generation in the peripheral layer by minimizing eddy current formation through its laminated structure, while simultaneously enhancing interaction with the RF field due to the establishment of a relatively thin, homogeneously distributed coating on both the thermal insulation layer and the dielectric filling.

[0041] The peripheral layer may comprise a first coating part on the outer surface of the dielectric filling and a second coating part on the inner surface of the thermal insulation layer, wherein the first coating part having a first interlocking feature, such as a recess or a protrusion, and the second coating part having a second interlocking feature complementary to the first interlocking feature, so that in an attached state of the aerosol-generating device, the first and second interlocking features engage with each other to be electrically connected to each other.

[0042] The advantage of a peripheral layer comprising a first coating part with an interlocking feature on the dielectric filling and a second complementary coating part on the thermal insulation layer is that it ensures secure and reliable electrical connectivity, while reducing wear of the materials due to relative rotational movements between the components (e.g., between the dielectric filling and the thermal insulation layer) of the device when a user removes or inserts the aerosol-forming article.

[0043] The electrically conductive material of the peripheral layer may comprise or may be made of a metal or a metal alloy. The metal or the metal alloy may comprise or may be made of silver. In other examples, copper may be used. The use of silver is advantageous as it has an electrical and thermal conductivity higher compared to copper, thereby making it ideal for high-performance and specialized applications, albeit at a higher cost.

[0044] The peripheral layer may be an electrically conductive paint or an electrically conductive paste.

[0045] Preferably, the peripheral layer may be a silver paint.

[0046] Resonant Cavity The resonant cavity may have an inner diameter from 10 to 35 millimeters, or more preferably from 15 to 25 millimeters.

[0047] The resonant cavity may have a cylindrical shape.

[0048] The resonant cavity may have a rectangular cuboid shape.

[0049] The resonant cavity may have an oval, round, or rectangular cross-section along the insertion direction

[0050] The resonant cavity may have a shape corresponding to a hollow cylinder.

[0051] The resonant cavity may be configured as a quarter wavelength resonator.

[0052] The aerosol-generating device may comprise a resonant circuit including the resonant cavity, for example as an element of the resonant circuit.

[0053] Dielectric filling

[0054] The dielectric filling may act as a wave matching circuit to reduce a wavelength of the RF electromagnetic radiation generated by the electromagnetic field generator to a reduced wavelength of an RF electromagnetic radiation field form within the resonant cavity, the reduced wavelength ranges from 1 to 50 millimeters, preferably from 5 to 25 millimeters, in particular from 10 to 20 millimeters.

[0055] The provision of the dielectric filling having a relative permittivity erof greater than one within the interior of the resonant cavity may have a beneficial effect of reducing the resonant frequency of the resonant cavity compared to the same resonant cavity lacking any filling (i.e. relative to a resonant cavity which is entirely hollow and contains only air). In general terms, for a resonant cavity of a given size, the greater the relative permittivity erof the filling, the smaller the resonant frequency of the resonant cavity. Therefore, where the resonant cavity has a size consistent with the aerosol-generating device being handheld and portable, the filling which is used can be selected to tune the resonant frequency of the resonant cavity to correspond with an operation frequency for the RF electromagnetic radiation generated by the electromagnetic field generator.

[0056] The reduced wavelength may be at or within + / -10% of a length of the substrate cavity or aerosol-forming substrate.

[0057] The dielectric filling may be a relative permittivity greater than 1.

[0058] The dielectric filling may have a relative permittivity from 2 to 300, preferably from 5 to 200, in particular from 5 to 100.

[0059] The dielectric filling may be made of a non-electrically conductive material. For example, the dielectric filling may comprise or is made of ceramic material.

[0060] The dielectric filling may comprise or is made of ceramic material.

[0061] The dielectric filling may be detachably attachable from the housing.

[0062] By having a removable dielectric filling, the dielectric filling can be replaced by a filling of a different material with a different relative permittivity that matches the aerosol-forming article / substrate for enhanced heating. In other words, the use of a detachable dielectric filling may serve to use different aerosol-forming articles with different properties (e.g. diameters) and / or aerosol-forming substrates of different material with the same device.

[0063] Substrate cavity

[0064] The substrate cavity may have a length from 5 to 50 millimeters, or more preferably from 10 to 20 millimeters.

[0065] The substrate cavity may have an inner diameter from 3 to 15 millimeters, or more preferably from 5 to 10 millimeters.

[0066] The substrate cavity may have a cylindrical shape.

[0067] The substrate cavity may have a rectangular cuboid shape.

[0068] The substrate cavity may have an oval, round, or rectangular cross-section along an insertion direction of the aerosol-forming substrate.

[0069] The substrate cavity may match at least one or more of a cross-sectional area and a length of the aerosol-forming substrate.

[0070] RF electromagnetic field generator and Antenna

[0071] The RF electromagnetic field generator may comprise a solid state RF transistor.

[0072] The use of a solid state RF transistor may allow the aerosol-generating device to be compact. The conventional means for producing the RF frequency radiation for heating, such as in domestic microwave ovens, is a magnetron. Magnetrons are bulky and require high voltages to operate. Furthermore, magnetrons have a relatively unstable frequency output and have a relatively short service life. A RF transistor can provide for consistent operation over many more usage cycles and requires much lower operating voltages. Advantageously, one or more solid state RF transistors may be configured to generate and amplify the RF electric field. Using a single transistor to provide both the generating and amplification of the RF electric field allows for the aerosol-generating device to be compact. The solid state RF transistor may be, for example, a LDMOS transistor, a GaAs FET, a SiC MESFET or a GaN HFET.

[0073] The RF electromagnetic field generator may be configured to generate a frequency from 300 MHz to 300 GHz, preferably from 900 MHz to 30 GHz, more preferably from 900 MHz to 5 GHz, in particular of about 2.4 GHz or 4.8 GHz.

[0074] The aerosol-generating device may comprise at least one of a waveguide and an antenna configured to convey the RF electromagnetic radiation generated by the electromagnetic field generator to the resonant cavity.

[0075] Parameter measurement

[0076] The aerosol-generating device may comprise a probe or antenna to measure a parameter of the electric field generated in the substrate cavity (also called substrate chamber). The parameter measured by the probe or antenna may be the frequency of the electric field generated in the substrate cavity. The control electronics may be associated with the probe or antenna and configured to derive the load-dependent parameter from the measured parameter of the electric field.

[0077] The probe or antenna may include at least one of: a transverse electromagnetic (TEM) transmission line, a microstrip, an inductor, or an antenna.

[0078] The probe or antenna may include another resonant cavity or another transmission line, or both.

[0079] The probe or antenna may comprise a quarter wavelength coaxial cavity resonator, preferably comprising an inner wire, wherein the inner wire has an impurity-doped insulator.

[0080] The aerosol-generating device may comprise a signal processing unit configured to convert an output provided by the resonant cavity or both to a signal that is receivable by the control electronics.

[0081] Manufacturing method

[0082] According to a second aspect, there is provided a method to manufacture an aerosol generating device, preferably according to the first aspect, the aerosol generating device comprising an electromagnetic field generator configured to generate radio-frequency (RF) electromagnetic radiation, the method comprises:

[0083] Providing a peripheral layer defining a resonant cavity and a dielectric filling defining a substrate cavity for receiving an aerosol-forming substrate, so that the dielectric filling is arranged within an interior of the resonant cavity. The peripheral layer being made of an electrically conductive material to confine the RF electromagnetic radiation within the resonant cavity. The peripheral layer has a layer thickness from 1 to 1000 micrometers, preferably from 2 to 500 micrometers, more preferably from 5 to 250 micrometers.

[0084] Preferably, the peripheral layer may have a peripheral layer thickness from 5 to 100 micrometers, more preferably from 5 to 20 micrometers, in particular from 5 to 10 micrometers.

[0085] The method may comprise providing a housing that surrounds the resonant cavity.

[0086] The method may comprise providing a thermal insulation layer circumscribing the resonant cavity. The thermal insulation layer may form the most inner part of the housing. The thermal insulation layer may be formed as a sleeve for receiving the dielectric filling.

[0087] The peripheral layer may be arranged between the dielectric filling and thermal insulation layer and may be in contact, preferably attached, e.g. coated, to one or more of said two portions.

[0088] The method may comprise coating an inner surface of the thermal insulation layer of the housing for the resonant cavity, thereby generating the resonant cavity. Alternatively or additionally, the method may comprise coating an outer surface of the dielectric filling with the electrically conductive material of the peripheral layer, thereby generating the resonant cavity. The coating may comprise painting or a deposition process, preferably at least one of physical vapor Deposition (PVD) and chemical vapor deposition (CVD).

[0089] The aerosol-generating device according to the first aspect of the invention may be manufactured according to the method of the second aspect of the invention.

[0090] Use

[0091] According to a third aspect, there is provided a use of an electrically conductive coating layer to generate a resonant cavity in an aerosol generating device for dielectrically heating an aerosol-forming substrate, preferably according to the first aspect.

[0092] The electrically conductive coating layer may have a layer thickness from 1 to 1000 micrometers, preferably from 2 to 500 micrometers, more preferably from 5 to 250 micrometers.

[0093] The electrically conductive coating layer may have a peripheral layer thickness from 5 to 100 micrometers, more preferably from 5 to 20 micrometers, in particular from 5 to 10 micrometers.

[0094] An inner surface of a thermal insulation layer of a housing for the resonant cavity, and / or an outer surface of the dielectric filling may be coated with an electrically conductive material, thereby generating the electrically conductive coating layer.

[0095] The peripheral layer of the aerosol-generating device according to the first aspect of the invention may be used as electrically conductive coating layer according to the use of the third aspect of the invention.

[0096] According to a fourth aspect, there may be provided an aerosol-generating device for dielectrically heating an aerosol-forming substrate of an aerosol-forming article to generate an aerosol therefrom, the device comprising: an electromagnetic field generator configured to generate radio-frequency (RF) electromagnetic radiation, a peripheral layer defining a resonant cavity, the peripheral layer being made of an electrically conductive material to confine the RF electromagnetic radiation within the resonant cavity, and a dielectric filling arranged within an interior of the resonant cavity, the dielectric filling defining a substrate cavity for receiving the aerosol-forming substrate, the peripheral layer in contact with the dielectric filling, and a non- conductive outer layer in contact with the peripheral layer, or an air gap adjacent to the peripheral layer, wherein the peripheral layer has a peripheral layer thickness from 1 to 1000 micrometers, preferably from 2 to 500 micrometers, more preferably from 5 to 250 micrometers.

[0097] 4. Terms and Definitions

[0098] As used herein, the term “aerosol-generating device” refers to a device that interacts with an aerosol-forming substrate of an aerosol-forming article to generate an aerosol. Preferably, the aerosol-generating device is a smoking device that interacts with an aerosol-forming substrate of an aerosol-forming article to generate an aerosol that is directly inhalable into a user’s lungs through the user's mouth. The aerosol-generating device may be a holder for a smoking article. Preferably, the aerosol-forming article is a smoking article that generates an aerosol that is directly inhalable into a user’s lungs through the user's mouth. More, preferably, the aerosolforming article is a smoking article that generates a nicotine-containing aerosol that is directly inhalable into a user’s lungs through the user's mouth.

[0099] As used herein, the term “aerosol-generating system” refers to a combination of an aerosolgenerating device and an aerosol-forming article, in which the aerosol-forming article and the aerosol-generating device cooperate to generate and deliver an aerosol to a user of the system.

[0100] As used herein, the term “aerosol-forming substrate” refers to a substrate consisting of or comprising an aerosol-forming material that is capable of releasing volatile compounds upon heating to generate an aerosol.

[0101] As used herein, the term “solid insulation layer” refers to a thermal insulation layer material that comprises a solid material, preferably a plastic material, more preferably a thermoplastic polymer that belongs to the family of polyaryletherketones (PAEK), in particluar polyetheretherketone (PEEK) and / or polyetherimide (PEI).

[0102] As used herein, the term “radio frequency (RF)” means a frequency between 300 MHz and 300 GHz, preferably between 300 MHz and 100 GHz, and includes microwaves. Preferably, the RF electromagnetic field has a frequency between 500 MHz and 50 GHz, more preferably between 900 MHz and 30 GHz. The RF electromagnetic field may have a frequency between 900 Mhz and 5 GHz. In one embodiment the RF electromagnetic field has a frequency of about 2.4GHz or 4.8 GHz.

[0103] As used herein, the term “skin depth 5“ determines how deeply an RF electromagnetic field penetrates into the peripheral layer. In particular, the skin depth 5 may be defined as the distance at which the RF field strength decreases to 1 / e (about 37%) of its original value and may be given by the formula:

[0104] 8 = - - —

[0105] 2-rrf where:

[0106] - p is the resistivity of the electrically conductive material of the peripheral layer,

[0107] - po is the permeability in vacuum,

[0108] - pris the relative permeability of the electrically conductive material of the peripheral layer,

[0109] - f is the frequency of the RF electromagnetic field.

[0110] 5. List of non-limiting examples

[0111] The invention is defined in the claims. However, below there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein. Example Ex1. An aerosol-generating device for dielectrically heating an aerosol-forming substrate of an aerosol-forming article to generate an aerosol therefrom, the device comprising: an electromagnetic field generator configured to generate radio-frequency (RF) electromagnetic radiation, a peripheral layer defining a resonant cavity, the peripheral layer being made of an electrically conductive material to confine the RF electromagnetic radiation within the resonant cavity, and a dielectric filling arranged within an interior of the resonant cavity, the dielectric filling defining a substrate cavity for receiving the aerosol-forming substrate, wherein the peripheral layer has a peripheral layer thickness from 1 to 1000 micrometers, preferably from 2 to 500 micrometers, more preferably from 5 to 250 micrometers.

[0112] Example Ex1.1. An aerosol-generating device according to the preceding example, wherein the peripheral layer has a peripheral layer thickness from 5 to 100 micrometers, more preferably from 5 to 20 micrometers, in particular from 5 to 10 micrometers.

[0113] Example Ex1.2. An aerosol-generating device according to any one of the preceding examples, wherein the resonant cavity has an inner diameter from 10 to 35 millimeters, or more preferably from 15 to 25 millimeters.

[0114] Example Ex1.3. An aerosol-generating device according to any one of the preceding examples, wherein the resonant cavity has a cylindrical shape.

[0115] Example Ex1.4. An aerosol-generating device according to any one of the preceding examples, wherein the resonant cavity has a rectangular cuboid shape

[0116] Example Ex1.5. An aerosol-generating device according to any one of the preceding examples, wherein the resonant cavity has an oval, round, or rectangular cross-section along the insertion direction

[0117] Example Ex1.6. An aerosol-generating device according to any one of the preceding examples, wherein the resonant cavity has a shape corresponding to a hollow cylinder

[0118] Example Ex1.7. An aerosol-generating device according to any one of the preceding examples, wherein the resonant cavity is configured as a quarter wavelength resonator.

[0119] Example Ex1.8. An aerosol-generating device according to any one of the preceding examples, further comprising a resonant circuit including the resonant cavity, for example as an element of the resonant circuit.

[0120] Example Ex1.9. An aerosol-generating device according to any one of the preceding examples, wherein the dielectric filling acts as a wave matching circuit to reduce a wavelength of the RF electromagnetic radiation generated by the electromagnetic field generator to a reduced wavelength of an RF electromagnetic radiation field from within the resonant cavity, the reduced wavelength ranges from 1 to 50 millimeters, preferably from 5 to 25 millimeters, in particular from 10 to 20 millimeters.

[0121] Example Ex1.10. An aerosol-generating device according to any one of the preceding examples, wherein the reduced wavelength is at or within + / -10% of a length of the substrate cavity.

[0122] Example Ex1.11. An aerosol-generating device according to any of the preceding examples, wherein the dielectric filling has a relative permittivity greater than 1.

[0123] Example Ex1.12. An aerosol-generating device according to any one of the preceding examples, wherein the dielectric filling has a relative permittivity from 2 to 300, preferably from 5 to 200, in particular from 5 to 100.

[0124] Example Ex1.13. An aerosol-generating device according to any one of the preceding examples, wherein the dielectric filling comprises or is made of ceramic material.

[0125] Example Ex1.14. An aerosol-generating device according to any one of the preceding examples, wherein the dielectric filling is detachably attachable from a housing of the device.

[0126] Example Ex1.15. An aerosol-generating device according to any one of the preceding examples, wherein the substrate cavity has a length from 5 to 50 millimeters, or more preferably from 10 to 20 millimeters.

[0127] Example Ex1.16. An aerosol-generating device according to any one of the preceding examples, wherein the substrate cavity has an inner diameter from 3 to 15 millimeters, or more preferably from 5 to 10 millimeters.

[0128] Example Ex1.17. An aerosol-generating device according to any one of the preceding examples, wherein the substrate cavity has a cylindrical shape.

[0129] Example Ex1.18. An aerosol-generating device according to any one of the preceding examples, wherein the substrate cavity has a rectangular cuboid shape.

[0130] Example Ex1.19. An aerosol-generating device according to any one of examples Ex1 to Ex1.17, wherein the substrate cavity has an oval, round, or rectangular cross-section along an insertion direction of the aerosol-forming substrate.

[0131] Example Ex1.20. An aerosol-generating device according to any one of the preceding examples, wherein the substrate cavity matches at least one or more of a cross-sectional area and a length of the aerosol-forming substrate.

[0132] Example Ex1.21. An aerosol-generating device according to any one of the preceding examples, wherein the RF electromagnetic field generator comprises a solid state RF transistor.

[0133] Example Ex1.22. wherein the RF electromagnetic field generator is configured to generate a frequency from 300 MHz to 300 GHz, preferably from 900 MHz to 30 GHz, more preferably from 900 MHz to 5 GHz, in particular of about 2.4 GHz or 4.8 GHz. Example Ex1.23. The aerosol-generating device according to any one of the preceding examples, further comprising at least one of a waveguide and an antenna configured to convey the RF electromagnetic radiation generated by the electromagnetic field generator to the resonant cavity.

[0134] Example Ex1.24. An aerosol-generating device according to any one of the preceding examples, further comprising a probe or antenna to measure a parameter of the electric field generated in the substrate cavity (also called substrate chamber).

[0135] Example Ex1.24.1. An aerosol-generating device according to the preceding example, wherein the parameter measured by the probe or antenna is the frequency of the electric field generated in the substrate cavity.

[0136] Example Ex1.24.2. An aerosol-generating device according to any one of examples Ex1.24 to Ex1.24.1 , wherein the control electronics is associated with the probe or antenna and configured to derive the load-dependent parameter from the measured parameter of the electric field.

[0137] Example Ex1.24.3. An aerosol-generating device according to any one of examples Ex1.24 to Ex1.24.2, wherein the probe or antenna includes at least one of: a transverse electromagnetic (TEM) transmission line, a microstrip, an inductor, or an antenna.

[0138] Example Ex1.24.4. An aerosol-generating device according to any one of examples Ex1.24 to Ex1.24.3, wherein the probe or antenna includes another resonant cavity or another transmission line, or both.

[0139] Example Ex1.24.5. An aerosol-generating device according to any one of examples Ex1 .24 to Ex1 .24.4, wherein the probe or antenna comprises a quarter wavelength coaxial cavity resonator, preferably comprising an inner wire, wherein the inner wire has an impurity-doped insulator.

[0140] Example Ex1.25. An aerosol-generating device according to any one of the preceding examples, further comprising a signal processing unit configured to convert an output provided by the resonant cavity or both to a signal that is receivable by the control electronics.

[0141] Example Ex2. An aerosol-generating device according to any one of the preceding examples, wherein the peripheral layer thickness is designed to be equal to or greater than a skin depth 5 of the electrically conductive material of the peripheral layer at an operation frequency of the RF electromagnetic radiation, and / or wherein the peripheral layer thickness is designed to be equal to or smaller than 10 times the skin depth 5.

[0142] Example Ex2.1 . An aerosol-generating device according to the preceding example, wherein the peripheral layer thickness ranges from TT times the skin depth 5 to 3TT times the skin depth 5, preferably from 1 .5TT times the skin depth 5 to 2.5TT times the skin depth 5, in particular the peripheral layer thickness is about 2TT times the skin depth 5. Example Ex3. An aerosol-generating device according to any one of the preceding examples, comprising a housing for the resonant cavity, wherein the housing comprises a thermal insulation layer that surrounds the peripheral layer, wherein the thermal insulation layer is made of a less thermally conductive material than the peripheral layer.

[0143] Example Ex3.1 . An aerosol-generating device according to the preceding example, wherein the housing is an elongated housing, preferably a cylindrical housing.

[0144] Example Ex3.2.An aerosol-generating device according to any one of examples Ex3 to Ex3.1 , wherein the housing is configured to be handheld.

[0145] Example Ex3.3.An aerosol-generating device according to any one of examples Ex3 to Ex3.2, wherein a thermal conductivity of the thermally conductive material is from 1 ■ 103to 20103times, preferably from 1.5-103to 2 103times, more preferably from 1.7-103to 1.9-103times less than a thermal conductivity of the electrically conductive material of the peripheral layer.

[0146] Example Ex3.4.An aerosol-generating device according to any one of examples Ex3 to Ex3.3, wherein the thermal insulation layer is made of a non-electrically conductive material.

[0147] Example Ex3.5.An aerosol-generating device according to any one of examples Ex3 to Ex3.4, wherein the thermal insulation layer has the form of an air gap.

[0148] Example Ex3.5.1. The aerosol-generating device according to the preceding example, wherein the air gap is filled with gas or vacuum.

[0149] Example Ex4. An aerosol-generating device according to any one of examples Ex3 to Ex3.3, wherein the thermal insulation material comprises a solid material, preferably a plastic material, more preferably a thermoplastic polymer that belongs to the family of polyaryletherketones (PAEK), in particluar polyetheretherketone (PEEK) and / or polyetherimide (PEI).

[0150] Example Ex4.1 . An aerosol-generating device according to the preceding example, wherein the thermal insulation layer comprises one or more air channels machined in the solid material, so as to extend along a longitudinal and / or circumferential direction of the thermal insulation layer.

[0151] Example Ex4.2. An aerosol-generating device according to the preceding example, wherein the one or more air channels have the form of a groove with an opening towards the peripheral layer.

[0152] Example Ex4.3. An aerosol-generating device according to any one of examples Ex4 to Ex4.2, wherein the thermal insulation layer has a melting temperature from 150 to 500°C, preferably from 175 to 400°C, in particular from 200 to 350°C.

[0153] Example Ex4.4. An aerosol-generating device according to any one of examples Ex4 to Ex4.3, further comprising at least one additional thermal insulation layer arranged between the thermal insulation layer comprising the solid material and at least one of the dielectric filling and / or an outer shell of the housing, wherein the at least one additional thermal insulation layer has the form of an air gap, preferably filled with gas or vacuum.

[0154] Example Ex5. An aerosol-generating device according to any one of the preceding examples, wherein the peripheral layer is formed as a coating layer.

[0155] Example Ex5.1 . An aerosol-generating device according to the preceding example, wherein the peripheral layer is an electrically conductive paint or electrically conductive paste.

[0156] Example Ex6. An aerosol-generating device according to any one of the preceding examples, wherein an outer surface of the dielectric filling is coated with the electrically conductive material to form at least a portion of the peripheral layer.

[0157] Example Ex7. An aerosol-generating device according to any one of examples Ex4 to Ex6, wherein an inner surface of the thermal insulation layer is coated with the electrically conductive material to form at least a portion of the peripheral layer.

[0158] Example Ex8. An aerosol-generating device according to any one of examples Ex4 to Ex7, wherein the peripheral layer is a peripheral coating multilayer, comprising a first coating layer attached to the outer surface of the dielectric filling and a second coating layer attached to the inner surface of the thermal insulation layer, so that in an attached state of the aerosol-generating device, the first and second coating layers are electrically connected to each other.

[0159] Example Ex9. An aerosol-generating device according to any one of examples Ex4 to Ex8, wherein the peripheral layer comprises a first coating part on the outer surface of the dielectric filling and a second coating part on the inner surface of the thermal insulation layer, wherein the first coating part having a first interlocking feature, such as a recess or a protrusion, and the second coating part having a second interlocking feature complementary to the first interlocking feature, so that in an attached state of the aerosol-generating device, the first and second interlocking features engage with each other to be electrically connected to each other.

[0160] Example Ex10. An aerosol-generating device according to any one of the preceding examples, wherein the electrically conductive material of the peripheral layer comprises or is made of a metal or a metal alloy.

[0161] Example Ex11 . An aerosol-generating device according to the preceding example, wherein the metal or the metal alloy comprises or is made of silver.

[0162] Example Ex11.1. An aerosol-generating device according to the preceding example, wherein the peripheral layer is a silver paint.

[0163] Example Ex12. A method to manufacture an aerosol generating device, preferably according to any one of the preceding examples, the aerosol generating device comprising an electromagnetic field generator configured to generate radio-frequency (RF) electromagnetic radiation, the method comprises: Providing a peripheral layer defining a resonant cavity and a dielectric filling defining a substrate cavity for receiving an aerosol-forming substrate, so that the dielectric filling is arranged within an interior of the resonant cavity, wherein the peripheral layer being made of an electrically conductive material to confine the RF electromagnetic radiation within the resonant cavity, and wherein the peripheral layer has a peripheral layer thickness from 1 to 1000 micrometers, preferably from 2 to 500 micrometers, more preferably from 5 to 250 micrometers.

[0164] Example Ex12.1 . A method according to the preceding example, wherein the peripheral layer has a peripheral layer thickness from 5 to 100 micrometers, more preferably from 5 to 20 micrometers, in particular from 5 to 10 micrometers.

[0165] Example Ex12.2. A method according to any one of examples Ex12 to Ex12.1 , further comprises providing a housing that surrounds the resonant cavity

[0166] Example Ex13. A method according to any one of examples Ex12 to Ex12.2, comprising coating an inner surface of a thermal insulation layer of a housing for the resonant cavity, and / or an outer surface of the dielectric filling with the electrically conductive material of the peripheral layer, thereby generating the resonant cavity.

[0167] Example Ex14. A method according to any one of examples Ex12 to Ex13, wherein the coating comprises painting or a deposition process, preferably at least one of physical vapor Deposition (PVD) and chemical vapor deposition (CVD).

[0168] Example Ex15. Use of an electrically conductive coating layer to generate a resonant cavity in an aerosol generating device for dielectrically heating an aerosol-forming substrate, preferably according to any of examples Ex1 to Ex11.1.

[0169] Example Ex15.1. Use of an electrically conductive coating layer according to the preceding example, wherein the electrically conductive coating layer has a layer thickness from 1 to 1000 micrometers, preferably from 2 to 500 micrometers, more preferably from 5 to 250 micrometers.

[0170] Example Ex15.2. Use of an electrically conductive coating layer according to examples Ex15 to Ex15.1 , wherein the electrically conductive coating layer has a peripheral layer thickness from 5 to 100 micrometers, more preferably from 5 to 20 micrometers, in particular from 5 to 10 micrometers.

[0171] Example Ex15.3. Use of an electrically conductive coating layer according to examples Ex15 to Ex15.2, wherein an inner surface of a solid thermal insulation layer of a housing for the resonant cavity, and / or an outer surface of the dielectric filling is coated with an electrically conductive material, thereby generating the electrically conductive coating layer.

[0172] Example Ex16. An aerosol-generating device according to any one of examples Ex1 to Ex11.1 , wherein the peripheral layer is in contact with the dielectric filling, and further comprising a non-electrically conductive outer layer in contact with the peripheral layer, or an air gap adjacent to the peripheral layer,

[0173] 6. Example Ex16.1. An aerosol-generating device according to the preceding example, wherein the non-electrically conductive outer layer is made of a solid thermal insulation material, for example but not limited to PEEK or PEI. Brief Description of Drawings

[0174] The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

[0175] Figure 1 is a schematic illustration of an aerosol-generating system having an aerosolgenerating device as known from the prior art.

[0176] Figure 2 is a schematic illustration of a portion of an aerosol-generating device according to a first embodiment of the invention, which may be used in the aerosol-generating system of Figure 1.

[0177] Figure 3 is a schematic illustration of a portion of an aerosol-generating device according to a second embodiment of the invention, which may be used in the aerosol-generating system of Figure 1.

[0178] Figure 4 is a schematic illustration of a portion of an aerosol-generating device according to a third embodiment of the invention, which may be used in the aerosol-generating system of Figure 1.

[0179] Figure 5 is a schematic illustration of a portion of an aerosol-generating device according to a fourth embodiment of the invention, which may be used in the aerosol-generating system of Figure 1.

[0180] 7. Detailed Description

[0181] The above and other features and advantages of example embodiments will become more apparent by describing in detail with reference to the attached drawings. However, specific structural and functional details disclosed herein are merely representative for purposes of describing the example embodiments. The example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.

[0182] Accordingly, while the example embodiments are capable of various modifications and alternative forms, the 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 the example embodiments to the particular forms disclosed, but to the contrary, the example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of example embodiments. Like numbers refer to like elements throughout the description of the Figures. Figure 1 is a schematic illustration of an aerosol-generating system 100 as known from the prior art using radiofrequency (RF) electromagnetic radiation, sometimes referred to as dielectric heating. The aerosol-generating system 100 has an aerosol-generating device 200 and an aerosol-forming article 300 comprising an aerosol-forming substrate 301.

[0183] The aerosol-generating device 200 may have an elongate housing 201. The elongate housing 201 accommodates a power source 202, control electronics 203, a radio-frequency (RF) electromagnetic field generator 204 and a resonant cavity 205. For example, the electromagnetic field generator 204 can include a solid state transistor. The power source 202 is coupled to the control electronics 203 and the RF electromagnetic field generator 204 to provide power thereto. In the illustrated example, the power source 202 is a rechargeable battery, such as a lithium-ion battery. However, in alternative examples, other suitable power sources may be used; for example, an alternative form of battery or a capacitor. An outer shell of the elongate housing 201 that is visible to a user in normal use is made of plastic, metal, preferably aluminum, or any suitable material acting as an outer shell of the housing, e.g. that is waterproof and relatively rigid.

[0184] The resonant cavity 205 is defined by a peripheral wall 206, which is generally cylindrical in form. For the illustrated example, the peripheral wall 206 is formed of copper. The resonant cavity 205 is arranged so that the length of the resonant cavity 205 lies generally along a longitudinal axis 207 of the elongate housing 201. The resonant cavity 205 defines a blind cavity, with an opening 208 at one end of the cavity and an opposite end 209 of the cavity being closed.

[0185] A dielectric filling 210 formed of ceramic material, such as alumina, is provided within the resonant cavity 205. The dielectric filling 210 is provided as an annular sleeve circumscribing a substrate cavity 211 within the resonant cavity 205. The dielectric filling 210 has a relative permittivity £rgreater than 1 . The provision of the dielectric filling 210 having a relative permittivity £rof greater than one within the interior of the resonant cavity 205 has been found to have a beneficial effect of reducing the resonant frequency of the resonant cavity 205 compared to the same resonant cavity lacking any filling (i.e. relative to a resonant cavity which is entirely hollow and contains only air). In general terms, for a resonant cavity 205 of a given size, the greater the relative permittivity £rof the filling, the smaller the resonant frequency of the resonant cavity 205. So, where the resonant cavity has a size consistent with the aerosol-generating device 200 being handheld and portable, the filling which is used can be selected to tune the resonant frequency of the resonant cavity 205 to correspond with an operation frequency for the RF electromagnetic radiation generated by the electromagnetic field generator 204. Having the dielectric filling 210 arranged within the interior of the resonant cavity 205 so as to circumscribe the substrate cavity 211 helps to keep the substrate 301 positioned away from the peripheral layer 206 of the resonant cavity 205. This, in turn, helps to increase coupling of the aerosol-forming substrate 301 with any standing waves of the RF electromagnetic radiation established within the resonant cavity. These advantages can be achieved without having to the use RF electromagnetic radiation at excessively high frequencies, therefore reducing the design complexity for electromagnetic field generation. An antenna 212 extends from the RF electromagnetic field generator 204 into the interior of the resonant cavity 205. In other words, the dielectric filling 210 acts as a minifying glass that allows to receive an RF wave via the antenna 212 having a certain length (for example 12,5 cm at an operation frequency of 2,4 GHz) into a wave having a length of, for example, between 10 to 20 millimeters (substantially matching a length of the aerosol-forming substrate 301) which is ultimately obtained within the resonant cavity 205.

[0186] The aerosol-forming article 300 is received in the substrate cavity 211 via the opening 208. Airflow inlets (not shown) may be provided in the elongate housing 201 to allow air to be drawn into the aerosol-generating device 200, through the substrate cavity 211 and out through a mouthpiece of the aerosol-forming article 300.

[0187] Typically, as shown in Figure 1 , the peripheral wall 206 defining the resonant cavity 205 is made from a relatively thick piece of a machined electrically conductive material, such as copper.

[0188] Copper has several advantages, such as excellent electrical conductivity and ease of machining. However, such a relatively thick wall has several drawbacks: besides adding weight to a handheld device, it also suffers from energy loss due to high thermal conductivity, and the time required to cool the copper is relatively long because of the limited surface area for heat dissipation. To address this issue, as shown in Figures 2 to 5, a relative thin electrically conductive peripheral layer 213 that forms a resonant cavity 214 is considered. The thickness of the peripheral layer 213 is designed as a function of the skin depth 5 of an operation frequency of the RF electromagnetic field. In particular, the thickness of the peripheral layer is designed to be at least equal to the skin depth 5. This ensures that the RF field penetrates sufficiently into the material, allowing for adequate interaction. To avoid unnecessary material usage, the thickness of the peripheral layer 213 may not exceed a practical limit. This limit may be set to no more than 10 times the skin depth 5, or 2 times TT the skin depth 5. For example, the peripheral layer 213 has a peripheral layer 213 thickness from 1 to 1000 micrometers, preferably from 2 to 500 micrometers, more preferably from 5 to 250 micrometers. Normally, 5 to 10 micrometers peripheral layer thickness is sufficient for frequencies of the RF electromagnetic field as disclosed herein. Between the peripheral layer 213 and the outer shell of the housing 201 , there is provided a thermal insulation layer 215, 315.

[0189] Arranging electrically non-conductive layers, namely the dielectric filling 210 and the thermal insulation layer, such as the air gap 315 or the solid thermal insulation layer 215, adjacent to and / or in contact with respective outer or inner surfaces of the resonant cavity 214 may enable the use of a thin electrically conductive peripheral layer 213 (thickness from 1 to 1000 micrometers, preferably from 2 to 500 micrometers, more preferably from 5 to 250 micrometers) forming the resonant cavity 214 while enhancing electromagnetic and thermal efficiency. These layers may help suppress eddy currents and reduce thermal conduction. In particular, the concept can offer the following three advantages (l-lll):

[0190] I. Reduce the electric losses due to Eddy currents. When the resonant cavity 214 is fed by a microwave (2.45 GHz), eddy currents are induced in the electrically conductive peripheral layer 213 due to the electromagnetic fields generated within the resonant cavity 214, creating relatively high losses. The thin peripheral layer 213 can reduce these losses.

[0191] II. Reduce costs for manufacturing the resonant cavity 214, as the highly-conductive material typically used to form the resonant cavity 214 (peripheral layer 213), like aluminum, silver or copper, is pricey; and

[0192] III. Reduce the thermal capacity of the electrically conductive peripheral layer 213, to avoid storing heat and energy therein that would require additional cooling, and might reduce the overall energy efficiency.

[0193] In the embodiment shown in Figure 3, a thermal insulation layer in form of an air gap 315 between the peripheral layer 213 and the outer shell of the housing 201 may be provided. The air gap 315 may be arranged adjacent to the peripheral layer 213, such that a medium of the air gap 315 is filled with, for example but not limited to gas, such as air, or vacuum, is in contact with the peripheral layer 213.

[0194] In an alternative embodiment, as shown in Figures 2, 4 and 5, the peripheral layer 213 is surrounded by a thermal insulation layer, i.e., a solid thermal insulation layer 215, made of or comprising a solid material that is less-thermally conductive than the peripheral layer 213. The solid thermal insulation layer 215 may be in contact with the peripheral layer 213. This arrangement would retain the benefits of the electrically conductive material while reducing the overall heat conduction and energy loss. Although not shown in Figure 3, this arrangement may also be supplemented with the solid thermal insulation layer 215. The solid thermal insulation layer 215 is provided as an annular sleeve circumscribing the resonant cavity 214. In the present example, the solid thermal insulation layer 215 is made of polyetheretherketone (PEEK). PEEK has a lower thermal conduction (-0.25 W / nr K) and is lighter when compared to the copper (-401 W / m K), so during the aerosolization process it drains less energy and is better suited for handheld devices. Although it is preferable that the solid thermal insulation layer 215 comprises PEEK, it is envisaged that in some embodiments the wave source may comprise another plastic material or other suitable solid thermal insulation layer materials capable to withstand temperatures in a range between 200 to 350°C, and can preferably be coated.

[0195] In the illustrated examples, the peripheral layer 213 is formed as a coating layer made of electrically conductive material, such as silver, copper, gold or another material substantially opaque to RF electromagnetic radiation. Various techniques may be employed for the coating. Among the most common and effective coating processes for the present disclosure are painting, physical vapor deposition (PVD), and chemical vapor deposition (CVD).

[0196] As will be described in more detail in the following with respect to Figures 2 to 5, the peripheral layer 213 defining the resonant cavity 214 may be generated by at least one of coating at least a portion of an inner surface of the solid thermal insulation layer 215 and / or the dielectric filling 210.

[0197] Figure 2 shows an arrangement where an inner surface of the solid thermal insulation layer 215 is coated with the electrically conductive material to form the peripheral layer 213.

[0198] Figure 3 shows another arrangement where an outer surface of the dielectric filling 210 is coated with the conductive material to form the peripheral layer 213.

[0199] Figure 4 and Figure 5 show a cross-sectional view of a portion of an aerosol-generating device 200. In these arrangements, the peripheral layer 213 is composed of two matching layers or parts respectively.

[0200] Figure 4 shows a peripheral coating multilayer structure, wherein the peripheral layer 213 comprises a first coating layer 217 coated on the outer surface of the dielectric filling 210 and a second coating layer 218 coated on the inner surface of the solid thermal insulation layer 215, so that in the shown attached state of the aerosol-generating device 200, the first coating layer 217 and the second coating layer 218 are electrically connected to each other. As illustrated, the second coating layer 218 is provided as an annular sleeve configured to receive and to circumscribe the first coating layer 217.

[0201] Figure 5 shows a peripheral multipart structure, wherein the peripheral layer 213 comprises a first coating part 219 on the outer surface of the dielectric filling 210 and a second coating part 220 on the inner surface of the solid thermal insulation layer 215. The first coating part 219 includes a first interlocking feature while the second coating part 220 includes a second interlocking feature complementary to the first interlocking feature. When the aerosol-generating device 200 is in the shown attached state, the first and second interlocking features engage with each other, establishing a firm and rotation-proof mechanical connection and an electrical connection. In the present example, the interlocking features are generated by coating only a halfportion of both the peripheral inner surface of the solid thermal insulation layer 215 and of the outer surface of the dielectric filling 210.

Claims

CLAIMS1. An aerosol-generating device for dielectrically heating an aerosol-forming substrate of an aerosol-forming article to generate an aerosol therefrom, the device comprising: an electromagnetic field generator configured to generate radio-frequency (RF) electromagnetic radiation, a peripheral layer defining a resonant cavity, the peripheral layer being made of an electrically conductive material to confine the RF electromagnetic radiation within the resonant cavity, a dielectric filling arranged within an interior of the resonant cavity, the dielectric filling defining a substrate cavity for receiving the aerosol-forming substrate, and a housing for the resonant cavity, the housing comprising a thermal insulation layer that surrounds the peripheral layer, wherein the thermal insulation layer is made of a non-electrically conductive material with a lower thermal conductivity than the peripheral layer, wherein the peripheral layer has a peripheral layer thickness from 1 to 1000 micrometers, preferably from 2 to 500 micrometers, more preferably from 5 to 250 micrometers.

2. An aerosol-generating device according to the preceding claim, wherein the peripheral layer thickness is designed to be equal to or greater than a skin depth 5 of the electrically conductive material of the peripheral layer at an operation frequency of the RF electromagnetic radiation, and / or wherein the peripheral layer thickness is designed to be equal to or smaller than 10 times the skin depth 5.

3. An aerosol-generating device according to any one of the preceding claims, wherein the thermal insulation layer has the form of an air gap.

4. An aerosol-generating device according to claim 1 or claim 2, wherein the thermal insulation material comprises a solid material, preferably a plastic material, more preferably a thermoplastic polymer that belongs to the family of polyaryletherketones (PAEK), in particluar polyetheretherketone (PEEK) and / or polyetherimide (PEI).

5. An aerosol-generating device according to any one of the preceding claims, wherein the peripheral layer is formed as a coating layer.

6. An aerosol-generating device according to any one of the preceding claims, wherein an outer surface of the dielectric filling is coated with the electrically conductive material to form at least a portion of the peripheral layer.

7. An aerosol-generating device according to any one of claims 4 to 6, wherein an inner surface of the thermal insulation layer is coated with the electrically conductive material to form at least a portion of the peripheral layer.

8. An aerosol-generating device according to any one of claims 4 to 7, wherein the peripheral layer is a peripheral coating multilayer, comprising a first coating layer attached to the outer surface of the dielectric filling and a second coating layer attached to the inner surface of the thermal insulation layer, so that in an attached state of the aerosol-generating device, the first and second coating layers are electrically connected to each other.

9. An aerosol-generating device according to any one of claims 4 to 8, wherein the peripheral layer comprises a first coating part on the outer surface of the dielectric filling and a second coating part on the inner surface of the thermal insulation layer, wherein the first coating part having a first interlocking feature, such as a recess or a protrusion, and the second coating part having a second interlocking feature complementary to the first interlocking feature, so that in an attached state of the aerosol-generating device, the first and second interlocking features engage with each other to be electrically connected to each other.

10. An aerosol-generating device according to any one of the preceding claims, wherein the electrically conductive material of the peripheral layer comprises or is made of a metal or a metal alloy.

11. An aerosol-generating device according to the preceding claim, wherein the metal or the metal alloy comprises or is made of silver.

12. A method to manufacture an aerosol generating device, preferably according to any of the preceding claims, the aerosol generating device comprising an electromagnetic field generator configured to generate radio-frequency (RF) electromagnetic radiation, the method comprises:Providing a peripheral layer defining a resonant cavity, a housing for the resonant cavity, and a dielectric filling defining a substrate cavity for receiving an aerosol-forming substrate, so that the dielectric filling is arranged within an interior of the resonant cavity, wherein the peripheral layer being made of an electrically conductive material to confine the RF electromagnetic radiation within the resonant cavity,wherein the housing comprises a thermal insulation layer that surrounds the peripheral layer, the thermal insulation layer being made of a non-electrically conductive material with a lower thermal conductivity than the peripheral layer, and wherein the peripheral layer has a peripheral layer thickness from 1 to 1000 micrometers, preferably from 2 to 500 micrometers, more preferably from 5 to 250 micrometers.

13. The method according to the preceding claim, comprising coating an inner surface of a thermal insulation layer of a housing for the resonant cavity, and / or an outer surface of the dielectric filling with the electrically conductive material of the peripheral layer, thereby generating the resonant cavity.

14. The method according to the preceding claim, wherein the coating comprises painting or a deposition process, preferably at least one of physical vapor Deposition (PVD) and chemical vapor deposition (CVD).

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