Induction-heated aerosol generator for use with an aerosol-generating article - Patent Application 20070122997

Abstract

The aerosol generating system comprises an induction heating aerosol generator (1) and an aerosol-generating article (2). The article comprises an aerosol-forming substrate (25) and a flat, particularly sheet-like, susceptor (22) disposed within the evaporation portion of the article. The apparatus comprises an induction heating arrangement including a DC power supply (12) and a DC / AC inverter. The DC / AC inverter includes a power switching amplifier having at least one transistor switch (111), at least one transistor switch driver circuit (112), and an LC load network (113) comprising at least a capacitor and a cylindrical helical induction coil (L2). The interior space of the induction coil is configured to removably receive at least the evaporation portion of the aerosol-generating article. The cylindrical helical induction coil has a non-circular, flattened, or elliptical cross-sectional shape comprising, particularly, two opposing flat sections connected by two opposing at least partially curved sections.

Description

[Technical Field]

[0001] The present invention relates to an inductively heated aerosol generating device for use with an aerosol-generating article. The present invention further relates to an aerosol generating system comprising such a device and such an article. [Background technology]

[0002] Aerosol-generating devices and systems used to generate inhalable aerosols by inductively heating an aerosol-forming substrate are generally known in the prior art. Such systems and devices may include an induction heating arrangement including an induction coil for generating an alternating magnetic field. The magnetic field is used to induce at least one of heat-generating eddy currents or hysteresis losses in a susceptor disposed in thermal proximity or direct physical contact with the aerosol-forming substrate, which is capable of forming an inhalable aerosol upon heating. The susceptor and substrate may be part of an aerosol-generating article receivable within the interior space of the induction coil. In particular, the substrate may be a liquid aerosol-forming substrate stored within a liquid reservoir of the article. The reservoir may be in fluid communication with a susceptor located within an evaporation portion of the article, and the aerosol-forming liquid may be evaporated by interaction of the susceptor with the alternating magnetic field of the induction coil. Alternatively, the aerosol-forming substrate may be a solid or gel-like aerosol-forming substrate in thermal proximity or in direct physical contact with the susceptor, with both the susceptor and the substrate being contained in the evaporation portion of the article. Alternatively, the susceptor may be part of the aerosol-generating device.

[0003] In some articles, the susceptor may have a flat shape, such as a sheet-like shape, that provides a large surface-to-mass ratio, which is beneficial for efficiently utilizing the heat generated by the susceptor and for enhancing heat transfer from the susceptor to the aerosol-forming substrate.

[0004] During a user experience, the induction heating arrangement may be operated continuously or on demand, particularly in an intermittent mode such as every puff. While the susceptor may be permanently maintained at a temperature level sufficient to form a satisfactory amount of aerosol during a continuous mode of operation, achieving a sufficient temperature level within a short period of time may be a challenge when the heating system is operated intermittently, such as at the user's request.

[0005] It would therefore be desirable to have an aerosol-generating apparatus and aerosol-generating system for inductively heating an aerosol-forming substrate that has the advantages of prior art solutions but alleviates their limitations. It may be desirable to have an aerosol-generating apparatus and aerosol-generating system for inductively heating an aerosol-forming substrate in close thermal proximity or direct physical contact with a susceptor, particularly a flat, sheet-like susceptor, each of which allows for greater heating efficiency, particularly allowing sufficient temperature levels to be achieved within a shorter period of time. Summary of the Invention

[0006] According to the present invention, there is provided an induction heating aerosol generating device for use with an aerosol-generating article. The article comprises an aerosol-forming substrate and a flat, particularly sheet-like, susceptor disposed within the evaporation portion of the article and configured to heat the aerosol-forming substrate by interaction of the susceptor with an alternating magnetic field provided by the aerosol generating device. The device comprises an induction heating arrangement including a DC power source and power electronics including a DC / AC inverter connected to the DC power source. The DC / AC inverter includes a power switching amplifier having at least one transistor switch, at least one transistor switch driver circuit associated with the transistor switch, and an LC load network including at least a capacitor and a cylindrical helical induction coil. The interior space of the induction coil is configured to removably receive at least the evaporation portion of the aerosol-generating article. The cylindrical helical induction coil has a non-circular, flattened transverse cross-sectional shape comprising, particularly, two opposing flat sections connected by two opposing at least partially curved sections.

[0007] As used herein, the term "aerosol-generating device" refers to an electrically operated device capable of interacting with an aerosol-forming substrate, particularly at least one aerosol-generating article including an aerosol-forming liquid, and a susceptor, such as for generating an aerosol by inductively heating the substrate through interaction of the susceptor with an alternating magnetic field provided by the device. The aerosol-generating device is preferably a smoking device for generating an aerosol that can be directly inhaled by a user through the user's mouth. Specifically, the aerosol-generating device is a handheld aerosol-generating device.

[0008] According to the present invention, it has been found that the heating efficiency of an induction-heated aerosol generator having an induction coil intended to heat a flat, particularly sheet-like, susceptor can be improved by adapting the geometry of the magnetic field within the interior space of the induction coil in which the susceptor is placed to the flat shape of the susceptor. In particular, it has been found that flattening the cross-sectional shape of the induction coil can reduce the radial distance between the induction coil and the major surfaces (principal surfaces) of the flat susceptor (i.e., the major surfaces of the susceptor that determine the shape of the flat susceptor), provided that the susceptor is arranged so that its major surfaces face or are aligned, particularly substantially parallel, with two opposing flat sections of the cross-sectional shape of the outer periphery of the induction coil, i.e., so that the plane defined by the shape of the flat susceptor is aligned, particularly substantially parallel, with the plane defined by the two opposing flat sections of the outer periphery of the induction coil (the plane defined by the two opposing flat sections of the outer periphery of the induction coil contains the main axis of symmetry, as defined below). As the radial distance is reduced, the magnetic field strength at the susceptor increases, which in turn results in an increase in heating efficiency. Therefore, the level of heat generated in the susceptor for a given level of power passing through the induction coil is increased, which in particular allows the desired temperature level to be reached in a shorter period of time.

[0009] The efficiency of the induction heated aerosol generator is advantageously further enhanced due to the use of a cylindrical helical induction coil, which allows for the generation of a homogeneous alternating magnetic field.

[0010] The non-circular flattened transverse cross-sectional shape of the induction coil preferably comprises a minor axis of symmetry and a major axis of symmetry. The minor axis of symmetry may extend between two opposing flat sections of the induction coil. Conversely, the major axis of symmetry may extend between two opposing at least partially curved sections of the induction coil.

[0011] The ratio of the maximum distance along the major axis of symmetry between two opposing at least partially curved sections to the maximum distance along the minor axis of symmetry between two opposing flat sections is preferably in the range of 1.2 to 3, in particular 1.5 to 2.5, which is particularly advantageous with regard to a good match between the geometry of the magnetic field and the flat shape of the susceptor to be heated.

[0012] In order to arrange the induction coil as close as possible to the inner space of the induction coil in which the susceptor is placed, the maximum distance along the minor axis of symmetry between the two opposing flat sections may be in the range of 4 mm to 7 mm, in particular 5 mm to 6 mm.

[0013] Similarly, the maximum distance along the longitudinal axis of symmetry between two opposing at least partially curved sections may be in the range of 7 mm to 10 mm, in particular 8 mm to 9 mm.

[0014] Preferably, the two opposing flat sections are substantially parallel to one another. A parallel configuration is particularly useful for matching the magnetic field shape to a susceptor having a sheet-like shape. In particular, each of the two opposing flat sections may be substantially straight.

[0015] The shape of the two at least partially curved sections is selected to provide a smooth transition between the two opposing flat sections and ensure a smooth bend. Preferably, the at least partially curved section is one of substantially semicircular, substantially semi-oval, substantially semi-elliptical, or substantially parabolic.

[0016] In particular, each of the two opposing planar sections (connecting the two opposing planar sections) may be tangent to the two opposing planar sections (respectively), so that the transition between the two opposing planar sections is particularly smooth.

[0017] Preferably, the non-circular flattened transverse cross-sectional shape of the induction coil is oval. As used herein, the term "oval" defines a shape consisting of two semicircles connected by parallel lines tangent to their endpoints. Thus, the induction coil may have an oval cylindrical shape.

[0018] Generally, a cylindrical helical induction coil can be formed by one or more turns of coil wire. For example, the induction coil can have 3 to 6 turns, in particular 4 to 5 turns. The number of turns does not necessarily have to be an integer; it can be any number between two integers.

[0019] The coil wire may preferably have a circular cross section.

[0020] The coil wire may be one of a solid wire, a stranded wire, and a litz wire.

[0021] Because induction coils are driven by AC current, the current through the coil wire flows only near the outer surface of the coil wire. Therefore, the diameter of the coil wire does not need to be large to carry a large current. To achieve a compact coil design with a sufficiently large number of turns per unit of length, it can be beneficial if the coil wire has a diameter in the range of 0.8 mm to 1.5 mm, and especially 1 mm to 1.2 mm.

[0022] The induction coil preferably has an axial length extension similar to the axial length extension of the susceptor measured in the same direction when received within the interior space of the induction coil. The induction coil may have an axial length in the range of 4 millimeters to 12 millimeters, particularly 5 millimeters to 8 millimeters.

[0023] It is preferable to have a gap between adjacent turns of the induction coil. That is, the pitch of the helical induction coil may be greater than the axial extension of the cross-section of the coil wire, as seen in the longitudinal cross-section of the induction coil. In particular, if the coil wire has a circular cross-section, the pitch of the helical induction coil may be greater than the diameter of the coil wire. As a result, the coil wire of adjacent turns does not contact each other. This allows the coil wire to be used without wire insulation. Nevertheless, the coil wire may be insulated. For example, the coil wire may be coated copper wire, e.g., enamel-coated copper wire. In addition, the gap between adjacent turns of the induction coil serves to improve heat dissipation, thus leading to less resistive power loss in the coil winding. The gap between adjacent turns also helps to reduce undesirable ring / crossover effects. The (center-to-center) distance between adjacent portions of the coil wire of adjacent turns may be within a range of 1.1 to 1.4 times, particularly 1.2 to 1.3 times, the axial extension of the cross-section of the coil wire, as seen in the longitudinal cross-section of the induction coil. In particular, when the coil wire has a circular cross section, the distance between adjacent portions of the coil wire of adjacent turns (center to center) is in the range of 1.1 to 1.4 times, and especially 1.2 to 1.3 times, the diameter of the coil wire. These ranges have been proven to provide a sufficiently long distance that still allows for a compact coil design, i.e., a sufficiently large number of turns per unit of length.

[0024] The aerosol generating device may further comprise a magnetic flux concentrator disposed around the induction coil and configured to distort the alternating magnetic field of the induction coil towards the interior space of the induction coil in use.

[0025] In particular, the magnetic flux concentrator may include a sleeve portion circumferentially surrounding the induction coil and additional annular protrusions at each axial end of the sleeve portion that protrude radially inward beyond the sleeve portion, such that the induction coil is axially disposed between the annular protrusions. Advantageously, the annular protrusions at each axial end of the sleeve portion that protrude radially inward beyond the sleeve portion result in a concentration or focus of the magnetic field within the interior space of the induction coil. Therefore, the level of heat generated within the susceptor for a given level of power passing through the induction coil is increased compared to an induction coil without a magnetic flux concentrator or an induction coil that only has a sleeve-shaped magnetic flux concentrator without annular protrusions at each axial end. This also helps increase heating efficiency, particularly reaching a desired temperature level in a shorter period of time. In addition, the magnetic flux concentrator acts as a magnetic shield, capable of reducing the extent to which the magnetic field propagates beyond the induction coil.

[0026] Preferably, the magnetic flux concentrator comprises or is made of one or more layers of magnetic flux concentrator foil. According to a preferred configuration of the magnetic flux concentrator, each of the annular protruding portions may be made of one or more layers of magnetic flux concentrator foil, and the one or more layers of the annular protruding portion extend radially outward at least to, and preferably beyond, the outer periphery of the induction coil. On top of the annular protruding portion, a sleeve portion may be made of one or more layers of magnetic flux concentrator foil surrounding the induction coil and each of the annular protruding portions. According to an alternative configuration of the magnetic flux concentrator, the sleeve portion may be made of one or more layers of magnetic flux concentrator foil surrounding the induction coil, while each of the annular protruding portions may be made of one or more layers of magnetic flux concentrator foil and terminate radially flush with the outer periphery of the sleeve portion.

[0027] At least one of the annular protruding portions, preferably the more distal annular protruding portion, may include a recess or feed-through opening for passing a connecting lead of the induction coil. If the magnetic flux concentrator is formed by winding a magnetic flux concentrator foil, the recess or feed-through opening may be cut into the annular protruding portion after winding the magnetic flux concentrator foil.

[0028] Like the induction coil, the magnetic flux concentrator may have a non-circular flat transverse cross-sectional shape that corresponds to the non-circular flat transverse cross-sectional shape of the induction coil, i.e., a non-circular flat transverse cross-sectional shape that comprises, in particular consists of, two opposing flat sections connected by two opposing at least partially curved sections. In particular, the cross-sectional shape of the magnetic flux concentrator may be oval.

[0029] The aerosol generating device may further comprise a coil support on which the induction coil and, if present, the magnetic flux concentrator are supported.

[0030] The coil support may comprise a support tube, in particular a cylindrical support tube, with the induction coil disposed around the outer periphery of the support tube.

[0031] The interior space of the support tube may form a receiving cavity for removably receiving at least a portion, in particular at least an evaporative portion, of an aerosol-generating article with which the device is configured to be used.

[0032] The coil support may include a circumferential collar at each axial end of the support tube to provide axial lateral constraint for the coil windings.

[0033] At least one of the collars may include a recess or feed-through opening for passing a connecting lead for the induction coil.

[0034] Like the induction coil, the outer periphery of the support tube can also have a non-circular flattened cross-sectional shape comprising, and particularly consisting of, two opposing flat sections connected by two opposing at least partially curved sections. That is, the exterior (outer surface) of the support tube along its periphery can include, and particularly consist of, two opposing flat outer portions connected by two opposing at least partially curved outer portions. In this configuration, the induction coil is wound around the periphery of the support tube such that the non-circular flattened cross-sectional shape of the induction coil follows the non-circular flattened cross-sectional shape of the periphery of the support tube.

[0035] Preferably, the non-circular flattened transverse cross-sectional shape of the support tube is elliptical, especially when the transverse cross-sectional shape of the induction coil is elliptical. Thus, the support tube and induction coil may have an elliptical cylindrical shape, i.e., a flattened cylinder shape with two opposing planar side wall portions parallel to each other and two opposing side hemispherical wall portions between the two opposing planar side wall portions.

[0036] When the outer periphery of the support tube has a non-circular flattened cross-sectional shape as described above, each of the collars, if present, may have a non-circular flattened cross-sectional shape corresponding to the non-circular flattened cross-sectional shape of the outer periphery of the support tube. In particular, each collar may have an oval cross-sectional shape.

[0037] To stabilize the coil winding, the outer periphery of the support tube may be provided with a wire recess pattern into which the coil wire is received. The wire recess pattern is preferably selected to correspond to the desired winding pattern of the induction coil. Since the induction is a cylindrical helical induction coil, the wire recess pattern is also preferably a helical wire recess pattern.

[0038] Furthermore, the wire recess pattern allows for a further reduction in the radial distance between the induction coil and the susceptor location within the induction coil's internal space. As already mentioned above, reducing the radial distance increases the magnetic field strength at the susceptor location, which in turn increases heating efficiency. Therefore, the level of heat generated within the susceptor for a given level of power passing through the induction coil is increased, which, in addition to the non-circular, flattened cross-sectional shape of the support tube's outer periphery, further serves to reach the desired temperature level within a shorter period of time. The greater the recess depth of the wire recess pattern, the better the magnetic field strength at the susceptor location within the induction coil's internal space. For example, when the coil wire has a circular cross section, the recess depth of the radial wire recess pattern is preferably within the range of 0.2 to 0.8 times, particularly 0.3 to 0.5 times, the diameter of the coil wire.

[0039] The outer periphery of the support tube may further include a flux concentrator recess for each of the annular protruding portions of the flux concentrator, into which the radially inner end of the respective annular protruding portion is received, thereby providing a secure support for the annular protruding portions, which helps prevent displacement of the flux concentrators, which could otherwise lead to undesirable changes in the inductance of the induction coil and undesirable changes in the magnetic field density within the interior space of the induction coil.

[0040] For easy and inexpensive manufacture, the coil support may include or be made of plastic. If the induction heating module must comply with certain regulatory requirements, the coil support may include or be made of bisphenol A-free plastic.

[0041] According to the present invention, the heating arrangement comprises a power supply electronic circuit comprising a DC / AC inverter connected to a DC power source, the DC / AC inverter comprising a power switching amplifier having at least one transistor switch, at least one transistor switch driver circuit associated with the transistor switch, and an LC load network comprising at least one capacitor. In this respect, it has further been found that the use of a switching power amplifier is beneficial in terms of good heating efficiency for a given, particularly limited, power available from a DC power source such as a battery.

[0042] Preferably, the switching power amplifier is a single-ended switching power amplifier, which is less complex than a power amplifier in a push-pull configuration.

[0043] In particular, the power switching amplifier may comprise a single transistor switch, which also reduces the complexity of the amplifier.

[0044] The switching power amplifier is preferably one of a class C power amplifier, a class D power amplifier, and a class E power amplifier.

[0045] When the DC / AC inverter includes a Class E power amplifier, the switching power amplifier may include a transistor switch, a transistor switch supply circuit for supplying a switching signal (gate-source voltage) to the transistor switch, and an LC load network including a shunt capacitor and a series connection of a capacitor and an inductor, where the inductor corresponds to an induction coil used to generate an alternating magnetic field for induction heating. The transistor switch may include a field-effect transistor (FET), for example, a metal-oxide semiconductor field-effect transistor (MOSFET). Furthermore, the switching power amplifier may include a choke for supplying a DC supply voltage from a DC power source to the LC load network.

[0046] When the DC / AC inverter includes a class-D power amplifier, the switching power amplifier may include two transistors connected to a DC power source, two switching elements for switching the two transistors on and off, a first capacitor, and an LC load network including a series connection of a capacitor and an inductor, where the inductor corresponds to an induction coil used to generate an alternating magnetic field for induction heating. The switching element is controllable / controlled at high frequency in a manner that ensures that one of the two transistors is off when the other of the two transistors is on. Additionally, there may be a second capacitor arranged symmetrically to the first capacitor.

[0047] The aerosol generating device may comprise a device housing in which the induction heating arrangement and DC power supply are located or disposed.

[0048] The aerosol generating device, and in particular the device housing, may be provided with an insertion opening providing access to the interior space of the induction coil or the interior space of the support tube of the induction heating module to allow an aerosol-generating article to be inserted therein.

[0049] The aerosol-generating device may further comprise a receiving cavity for removably receiving at least the evaporated portion of the aerosol-generating article. The receiving cavity may be located at least partially within the interior space of the induction coil or, in some cases, the interior space of the support tube. In particular, the receiving cavity may be at least partially formed by the interior space of the induction coil or the support tube, in some cases, particularly by the interior space of the support tube. The induction coil may be arranged to surround at least a portion of the receiving cavity, in particular to surround at least the evaporated portion of the aerosol-generating article, when the aerosol-generating article is received within the receiving cavity.

[0050] The aerosol generating device may be configured to operate continuously after activation of the system or intermittently, such as with each puff.

[0051] The LC network may further include a shunt capacitor in parallel with the transistor switch. Additionally, the DC / AC converter may include a choke inductor for providing a DC supply voltage from the DC power source.

[0052] The aerosol generating device is preferably configured to generate a high-frequency fluctuating magnetic field. As referred to herein, the high-frequency fluctuating magnetic field may have a frequency in the range of 500 kHz (kilohertz) to 30 MHz (megahertz), particularly 5 MHz (megahertz) to 15 MHz (megahertz), and preferably 5 MHz (megahertz) to 10 MHz (megahertz).

[0053] The aerosol-generating device may further comprise a controller configured to control operation of the device. In particular, the controller may be configured to control operation of the induction heating arrangement, preferably in a closed-loop configuration, to control heating of the aerosol-forming substrate to a predetermined operating temperature. Depending on at least one of the type of aerosol-forming substrate to be heated, the configuration of the susceptor, and the arrangement of the susceptor relative to the aerosol-forming substrate, the operating temperature may be in the range of 180°C to 370°C, in particular 180°C to 240°C, or 280°C to 370°C.

[0054] The controller may comprise a microprocessor (e.g., a programmable microprocessor), a microcontroller, or an application specific integrated circuit (ASIC) or other electronic circuit capable of providing control. The controller may comprise further electronic components, in particular parts of a DC / AC inverter and / or a power amplifier. In particular, the induction heating module may be at least partially part of the controller.

[0055] The aerosol generating device may further include a puff detector, such as a microphone or pressure sensor, for detecting a user puff, i.e., the onset of a user experience when the user initiates a puff on the device. The puff detector may be operably connected to the controller, such that detection of the occurrence of a puff by the puff detector may trigger delivery of power to the induction coil for generating the aerosol. That is, the controller may be configured to initiate operation of the heating arrangement, in particular generation of the alternating magnetic field, in response to the puff detector detecting the occurrence of a user puff.

[0056] According to the present invention, a DC power supply is configured to provide a DC supply voltage and a DC supply current to the induction heating arrangement, and preferably the DC power supply is a battery, such as a lithium iron phosphate battery. The DC power supply may have a capacity sufficient to allow continuous generation of aerosol for approximately six minutes, or a multiple of six minutes. Similarly, the power supply may have a capacity sufficient to allow a predetermined number of puffs or discontinuous operation of the induction heating arrangement.

[0057] The present invention further relates to an aerosol-generating system comprising an aerosol-generating device according to the invention and as described herein, the system further comprising an aerosol-generating article for use in the aerosol-generating device, the article comprising an aerosol-forming substrate and a flat, in particular sheet-like, susceptor, the susceptor being arranged in an evaporation portion of the article and configured to heat the aerosol-forming substrate by interaction of the susceptor with an alternating magnetic field provided by the aerosol-generating device.

[0058] As used herein, the term "aerosol-generating system" refers to the combination of an aerosol-generating article as further described herein and an aerosol-generating device according to the present invention as described herein, in which the article and device cooperate to generate a respirable aerosol.

[0059] The term "aerosol-generating article" as used herein refers to an article comprising at least one aerosol-forming substrate that, when heated, releases a volatile compound capable of forming an aerosol. The aerosol-generating article is preferably a heated aerosol-generating article, i.e., an aerosol-generating article comprising at least one aerosol-forming substrate that is intended to be heated, rather than combusted, to release a volatile compound capable of forming an aerosol. The aerosol-generating article may be a consumable product, in particular a consumable product that is discarded after a single use. Preferably, the article may comprise a liquid aerosol-forming substrate, i.e., an aerosol-forming liquid. Alternatively, the article may comprise a solid aerosol-forming substrate or a gel-like aerosol-forming substrate, or a combination thereof.

[0060] As used herein, the term "aerosol-forming substrate" generally refers to a substrate formed from or containing an aerosol-forming material capable of releasing volatile compounds upon heating to generate an aerosol. The aerosol-forming substrate is intended to be heated, rather than combusted, to release the aerosol-forming volatile compounds. The aerosol-forming substrate may be a solid aerosol-forming substrate, a liquid aerosol-forming substrate, a gel-like aerosol-forming substrate, or any combination thereof. The aerosol-forming substrate is preferably a liquid aerosol-forming substrate, i.e., an aerosol-forming liquid. The aerosol-forming liquid may contain both solid and liquid aerosol-forming materials or components. The aerosol-forming substrate, particularly the aerosol-forming liquid, may contain a tobacco-containing material containing volatile tobacco flavor compounds that are released from the substrate upon heating. Alternatively, or additionally, the aerosol-forming substrate, particularly the aerosol-forming liquid, may contain a non-tobacco material. The aerosol-forming substrate, particularly the aerosol-forming liquid, may further contain an aerosol former. Examples of suitable aerosol formers are glycerin and propylene glycol. The aerosol-forming substrate, particularly the aerosol-forming liquid, may also contain other additives and ingredients (such as nicotine or flavorings). In particular, the aerosol-forming liquid may contain water, solvents, ethanol, plant extracts, and natural or artificial flavors. The aerosol-forming liquid may be an aqueous aerosol-forming liquid or an oil-based aerosol-forming liquid. The aerosol-forming substrate may also be a paste-like material, a sachet of porous material containing the aerosol-forming substrate, or loose tobacco mixed with, for example, a gelling agent or adhesive, which may contain a common aerosol former such as glycerin, which is compressed or molded into a plug.

[0061] As used herein, the term "susceptor element" refers to an element capable of converting electromagnetic energy into heat when subjected to a varying magnetic field. This can be the result of at least one of hysteresis loss or eddy currents induced in the susceptor, depending on the electrical and magnetic properties of the susceptor material. Hysteresis loss occurs in ferromagnetic or ferrimagnetic susceptors due to magnetic domains in the susceptor material switching under the influence of the changing magnetic field. Eddy currents may be induced if the susceptor is conductive. In the case of a conductive ferromagnetic or ferrimagnetic susceptor, heat can be generated due to both eddy currents and hysteresis loss.

[0062] Thus, the susceptor element may be formed from any material that can be inductively heated to a temperature sufficient to generate an aerosol from the aerosol-forming substrate. Preferred susceptors include metal or carbon. Preferred susceptors may include ferromagnetic materials, such as ferritic iron, or ferromagnetic steel or stainless steel. Suitable susceptors may be or include aluminum. Preferred susceptors may be formed from 400 series stainless steel, such as grade 410, grade 420, or grade 430 stainless steel.

[0063] The susceptor may have a variety of geometric configurations depending, inter alia, on the type of aerosol-forming substrate.

[0064] The flat, particularly sheet-like, susceptor may include or be a susceptor blade, susceptor strip, or susceptor plate. In particular, when the substrate is a liquid, i.e., an aerosol-forming liquid, the susceptor may include or be a mesh susceptor.

[0065] In any of these configurations, the susceptor advantageously has the ability to perform both the functions of drawing (delivering) and heating the aerosol-forming liquid. According to any of the foregoing configurations, the susceptor may be considered a liquid-delivery susceptor.

[0066] If the aerosol-forming substrate is a liquid substrate, the article may comprise a liquid reservoir for storing the aerosol-forming liquid. The susceptor is preferably in fluid communication with the liquid reservoir in which the aerosol-forming liquid is stored.

[0067] Further features and advantages of the aerosol generation system are described with respect to the induction heating module and aerosol generator of the present invention and apply equally.

[0068] As used herein, the terms "radial" and "axial" refer to the cylindrical geometry of a cylindrical induction coil.

[0069] The present invention is defined in the claims. However, below 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 described above, for example, with any one or more features of other examples, embodiments, or aspects described herein.

[0070] Example 1: An induction heating aerosol generating apparatus for use with an aerosol-generating article, the article comprising an aerosol-forming substrate and a flat, particularly sheet-like, susceptor, disposed in an evaporation portion of the article and configured to heat the aerosol-forming substrate by interaction of the susceptor with an alternating magnetic field provided by the aerosol-generating apparatus; the apparatus comprising a DC power source and an induction heating arrangement, the heating arrangement comprising power supply electronics including a DC / AC inverter connected to the DC power source, the DC / AC inverter comprising a power switching amplifier having at least one transistor switch, at least one transistor switch driver circuit associated with the transistor switch, and an LC load network comprising at least a capacitor and a cylindrical spiral induction coil, the interior space of the induction coil being configured to removably receive at least the evaporation portion of the aerosol-generating article, the cylindrical spiral induction coil having a non-circular flat transverse cross-sectional shape including, particularly consisting of, two opposing flat sections connected by two opposing at least partially curved sections. Example 2: 2. The induction heating arrangement of example 1, wherein the non-circular flattened transverse cross-sectional shape comprises a minor axis of symmetry and a major axis of symmetry. Example 3: The induction heating arrangement of Example 2, wherein the ratio of the maximum distance along the major axis of symmetry between the two opposing at least partially curved sections to the maximum distance along the minor axis of symmetry between the two opposing flat sections is in the range of 1.2 to 3, in particular 1.5 to 2.5. Example 4: An induction heating arrangement as described in either Example 2 or Example 3, wherein the maximum distance along the minor axis of symmetry between two opposing flat sections is in the range of 4 millimeters to 7 millimeters, specifically 5 millimeters to 6 millimeters. Example 5: An induction heating arrangement according to any one of Examples 2 to 4, wherein the maximum distance along the longitudinal axis of symmetry between two opposing at least partially curved sections is in the range of 7 millimeters to 10 millimeters, specifically 8 millimeters to 9 millimeters. Example 6: 6. The induction heating arrangement of any one of Examples 1-5, wherein the two opposing flat sections are parallel to each other. Example 7: 7. The induction heating arrangement of any one of Examples 1-6, wherein each of the two opposing flat sections is substantially straight. Example 8: 8. The induction heating arrangement of any one of Examples 1-7, wherein each of the two opposing at least partially curved sections is one of a substantially semicircular, a substantially semi-oval, a substantially semi-elliptical, or a substantially parabolic shape. Example 9: 9. The induction heating arrangement according to any one of Examples 1 to 8, wherein the non-circular flat transverse cross-sectional shape of the induction coil is oval. Example 10: The induction heating arrangement according to any one of Examples 1 to 9, wherein the induction coil has an oval cylindrical shape. Example 11: 11. The induction heating arrangement of any one of Examples 1-10, wherein the induction coil is formed by one or more turns of coil wire, the coil wire having a circular cross section. Example 12: 12. The induction heating arrangement according to any one of embodiments 1 to 11, wherein the switching power amplifier is a single-ended switching power amplifier. Example 13: 13. The induction heating arrangement of any one of Examples 1-12, wherein the switching power amplifier is one of a class C power amplifier, a class D power amplifier, and a class E power amplifier. Example 14: 14. The induction heating arrangement according to any one of Examples 1 to 13, wherein the induction heating arrangement is configured to generate an alternating magnetic field in the range of 500 kHz to 30 MHz, in particular 5 MHz to 15 MHz, preferably 5 MHz to 10 MHz. Example 15: An aerosol-generating system comprising an aerosol-generating device according to any one of Examples 1 to 14 and an aerosol-generating article for use with the aerosol-generating device, the article comprising an aerosol-forming substrate and a flat, in particular sheet-like, susceptor, which is arranged in the evaporation section and is configured to heat the aerosol-forming substrate by interaction of the susceptor with an alternating magnetic field provided by the aerosol-generating device.

[0071] The embodiments will now be further described with reference to the figures. [Brief explanation of the drawings]

[0072] [Figure 1] FIG. 1 shows an exemplary embodiment of an aerosol generation system according to the present invention in longitudinal cross section. [Figure 2] FIG. 2 shows a detailed longitudinal cross-section of the aerosol generation system according to FIG. [Figure 3] FIG. 3 shows a detail of the aerosol generation system according to FIG. 1 in a longitudinal perspective cross-sectional view. [Figure 4] FIG. 4 shows details of the coil support used in the aerosol generating device according to FIG. [Figure 5] FIG. 5 shows details of an induction heating arrangement used in the aerosol generating device according to FIG. [Figure 6] FIG. 6 shows further details of the coil support used in the aerosol generating device according to FIG. [Figure 7] FIG. 7 shows details of a first embodiment of a power supply electronic circuit that can be used in the aerosol generating device according to FIG. [Figure 8] FIG. 8 shows details of a second embodiment of power supply electronics that can alternatively be used in the aerosol generating device according to FIG. DETAILED DESCRIPTION OF THE INVENTION

[0073] 1-3 show schematic cross-sectional views of an aerosol-generating system 1 according to an exemplary embodiment of the present invention. System 1 is configured to generate an inhalable aerosol by inductively heating a susceptor in thermal contact with a liquid aerosol-forming substrate 25, hereinafter also referred to as aerosol-forming liquid 25. System 1 comprises two main components: an aerosol-generating article 2 and an aerosol-generating device 1 for use with article 2. While article 2 comprises a susceptor 22 and an aerosol-forming liquid 25 to be heated, device 1 comprises a receiving cavity 16 for receiving article 2 and an induction heating arrangement 10 configured to generate an alternating magnetic field for inductively heating susceptor 22 and thus vaporizing aerosol-forming liquid 25 in article 2 when aerosol-forming liquid 25 is inserted into cavity 16 of device 1.

[0074] 1 , which shows the device 1 and the article 2 separated from each other, the aerosol generating device 1 comprises a substantially rod-shaped body having a substantially cylindrical device housing 15. Within the distal portion 4, the device 1 comprises a power source 12, e.g., a lithium-ion battery, and an electrical circuit 11 including a controller 160 for controlling the operation of the device 1, in particular for controlling the heating process. Within the proximal portion 5 opposite the distal portion 4, the device 1 comprises a receiving cavity 16 and at least part of an induction heating arrangement 10. The receiving cavity 16 is an open cavity with an insertion opening 19 at the proximal end of the device 1 to allow the article 2 to be inserted into the receiving cavity 16.

[0075] The induction heating arrangement 10 includes an induction coil 13 for generating an alternating magnetic field within the cavity 16. The induction coil 13 is a cylindrical helical coil that circumferentially surrounds the cylindrical receiving cavity 16. In this embodiment, the induction coil 13 has an axial length of approximately 8 millimeters and is formed by a single layer of 4.25 turns of a coil wire having a circular cross section. The turns of the induction coil 13 extend along the extended length of the cavity 16. It is preferable that there be a gap between adjacent turns of the induction coil 13. That is, the pitch of the helical induction coil 13 may be greater than the diameter of the coil wire. As a result, adjacent turns of the coil wire do not contact each other, which allows the coil wire to be used without wire insulation. Nevertheless, the coil wire in this embodiment is an enamel-coated copper wire with a diameter of 1.1 millimeters. In addition, the gap between adjacent turns of the induction coil serves to improve heat dissipation, thus leading to less resistive power loss in the coil winding. In this embodiment, the distance (center to center) between adjacent portions of the coil wire of adjacent turns is about 1.1 times the diameter of the coil wire. These ranges have been proven to provide a sufficiently long distance that still allows for a compact coil design, i.e., a sufficiently large number of turns per unit of length.

[0076] The induction coil 13 is part of the induction module 30, which, in addition to the induction coil 13, further comprises a coil support 17 disposed within the device housing 15 for supporting the induction coil 13. The coil support 17 is shown in detail in FIG. 4. The coil support 17 comprises a cylindrical support tube 32 and circumferential collars 33 at each axial end of the support tube 32. The more distal collars 33 include recesses or feed-through openings 34 for passing connecting leads 60 to the induction coil 13, as shown in FIG. 5. As can be seen from FIGS. 1-3, the interior space of the support tube 32 at least partially defines the receiving cavity 16 of the device 1 for removably receiving at least a portion of the aerosol-generating article 2. That is, the inner surface of the support tube 32 along its inner circumference forms at least a portion of the inner surface of the receiving cavity 16. For easy and inexpensive manufacture, the coil support 17 may be made of plastic. If the induction heating module 30 must comply with certain regulatory requirements, the coil support 17 may be made of, for example, a bisphenol A-free plastic.

[0077] In addition to induction coil 13, induction heating arrangement 10 includes power supply electronics that are at least partially integrated within electrical circuit 11 and may be coupled to induction coil 13 via connecting electrical pads 131 (see FIG. 1 ). In combination with induction coil 13, power supply electronics functions to generate a high-frequency alternating current that passes through induction coil 13, which causes induction coil 31 to generate a high-frequency varying magnetic field within the interior space of induction coil 12 and thus within cavity 16, as indicated by the dashed line in FIG. 2 . The frequency of the high-frequency varying magnetic field may be in the range of 500 kHz (kilohertz) to 30 MHz (megahertz), particularly 5 MHz (megahertz) to 15 MHz (megahertz), and preferably 5 MHz (megahertz) to 10 MHz (megahertz). As described in further more detail below, the alternating magnetic field is used to induce at least one of heat-generating eddy currents or hysteresis losses in susceptor 22 of article 2 to vaporize aerosol-forming liquid 25 contained within article 2.

[0078] Next to the device 1, FIG. 1 also shows details of an aerosol-generating article 2. In this embodiment, the article 2 is a cartridge having the shape of a mushroom seed that can be coupled to the device 1. At its distal end, the article 2 comprises an elongated evaporation portion 29 configured to be inserted into the receiving cavity 16 of the device 1, as shown in FIGS. 2 and 3 . Within the evaporation portion 29, the article 2 comprises a susceptor 22 disposed therein, such that when the evaporation portion 29 of the article 2 is inserted into the cavity 16, the susceptor 22 is located within the interior space of the induction coil 13. Therefore, the susceptor 22 can be subjected to an alternating magnetic field generated by the induction coil 13 during operation of the heating arrangement 10 in order to be heated.

[0079] In this embodiment, the susceptor 22 is a flat sheet-like mesh made of induction-heated ferromagnetic stainless steel. Thus, the susceptor 22 may also be viewed as a sheet-like mesh susceptor 22 capable of performing both the functions of drawing (transporting) and heating the aerosol-forming liquid 25. Because the material of the susceptor 22 at hand is both conductive and magnetic, the alternating electromagnetic field of the induction coil 13 can induce both heat-generating eddy currents and hysteresis losses in the susceptor material.

[0080] The susceptor mesh 22 is in fluid communication with the aerosol-forming liquid 25 contained in the reservoir 24 of the article 2 by way of a porous suction element 28. The porous suction element 28 is configured to directly contact the liquid 25 in the reservoir 24 and transport the liquid 25 to the mesh susceptor 22. The susceptor mesh 22 is therefore continuously humidified. Upon inserting the article 2 into the cavity 16 (see FIGS. 2 and 3) and activating the heating arrangement 10, the mesh susceptor 22 is heated to a temperature sufficient to vaporize the aerosol-forming liquid 25 in contact with the mesh susceptor 22.

[0081] As can be further seen in particular in FIG. 1 , mesh susceptor 22 is disposed within airflow channel 26 that passes through article 2 along its central axis. Airflow channel 26 has an air inlet at the distal end of article 2 and an outlet at the proximal end of article 2. The outlet is formed by mouthpiece 21, through which a user may inhale. Thus, when a user inhales through mouthpiece 21 during use of the system, air is entrained into airflow channel 26 via the air inlet and passes along mesh susceptor 22. There, vaporized material of the aerosol-forming liquid is entrained within the airflow through airflow channel 26. The airflow containing the vaporized material then passes further downstream within airflow channel 26 toward mouthpiece 21 while being cooled, such as to form an aerosol that exits article 2 through the outlet in mouthpiece 21.

[0082] The aerosol generating device 1 according to this embodiment further comprises a puff detector 14 for detecting a puff taken by the user. The puff detector 14 is operatively connected to the power supply electronics such that detection of a puff by the puff detector 14 triggers the delivery of power to the induction coil 13 to generate the aerosol. To this extent, the aerosol generating device 1 according to this embodiment may be referred to as a puff-on-demand device. Once the user stops puffing, the power supply to the induction coil is interrupted so as not to generate an aerosol that would otherwise be used unnecessarily. That is, the induction heating arrangement is operated intermittently according to the user's request.

[0083] While the susceptor may be permanently maintained at a temperature level sufficient to form a satisfactory amount of aerosol during a continuous mode of operation, achieving a sufficient temperature level within a short period of time may be a challenge when the heating arrangement is operated intermittently, such as at the user's request (puff on demand).

[0084] To achieve higher heating efficiency, particularly to achieve a sufficient temperature level within a shorter period of time, it has been found that adapting the geometry of the magnetic field within the interior space of the induction coil 13 in which the susceptor 22 is installed to the flat, sheet-like shape of the susceptor 22 can be advantageous. In particular, it has been found that by flattening the transverse cross-sectional shape of the induction coil 13, the radial distance between the induction coil 13 and the main surface of the flat susceptor 22 can be reduced. Reducing the radial distance increases the magnetic field strength at the susceptor, which in turn results in increased heating efficiency. Therefore, the level of heat generated within the susceptor for a given level of power passing through the induction coil is increased, thereby making it possible, in particular, to reach the desired temperature level within a shorter period of time. Therefore, in this embodiment, the outer periphery of the support tube 32 has a non-circular, flat transverse cross-sectional shape (see dashed lines in FIG. 4 ) consisting of two opposing flat sections 32.1 connected by two opposing, at least partially curved sections 32.2. Because the induction coil 13 is wound around the outer periphery of the support tube 32, the cross-sectional shape of the induction coil 13 follows the non-circular flattened cross-sectional shape of the outer periphery of the support tube 32. That is, the cylindrical helical induction coil 13 also has a non-circular flattened cross-sectional shape (see the dotted line on the right side of Figure 5) consisting of two opposing flat sections 13.1 connected by two opposing at least partially curved sections 13.2.

[0085] In this embodiment, the non-circular flattened cross-sectional shape of the support tube 32 and induction coil 13 is elliptical, i.e., it is made up of two semicircles 13.2, 32.2 connected by parallel lines 13.1, 32.1 tangent to their end points. Thus, the induction coil 13 and support tube 17 have an elliptical cylindrical shape.

[0086] Due to the parallel oval and semicircular portions, the non-circular, flattened cross-sectional shape of the induction coil 13 and support tube 32 has a minor axis of symmetry and a major axis of symmetry. As shown by the dashed arrows for the induction coil 13 in FIG. 5, the minor axis of symmetry extends between the two opposing flat sections 13.1 of the induction coil 13, while the major axis of symmetry extends between the two opposing curved sections 13.2 of the induction coil. The ratio of the maximum distance along the major axis of symmetry between the two opposing at least partially curved sections 13.2, 32.2 to the maximum distance along the minor axis of symmetry between the two opposing flat sections 13.1, 32.1 is preferably in the range of 1.2 to 3, particularly 1.5 to 2.5. These ratios are particularly advantageous for achieving a good match between the magnetic field geometry and the flat shape of the susceptor 22 to be heated.

[0087] To further improve heating efficiency, the induction heating arrangement 10 of this embodiment includes a magnetic flux concentrator 50 disposed around the induction coil 13 and configured to distort the alternating magnetic field of the induction heating arrangement 10 toward the interior space of the induction coil 13 during use. To this end, the magnetic flux concentrator 50 has a specific configuration including a sleeve portion 52 circumferentially surrounding the induction coil 13, and additionally annular protruding portions 51 at each axial end of the sleeve portion 52 that protrude radially inward beyond the sleeve portion 52, so that the induction coil 13 is axially disposed between the annular protruding portions 51, as can be particularly seen in FIGS. 1 and 2. Thus, as seen in a longitudinal cross-section through the magnetic flux concentrator 50 along the length axis of the induction coil 13 (see FIGS. 1 and 2), the magnetic flux concentrator 50 has a U- or C-shape, with the sleeve portion 52 being part of the base of the U- or C-shape and the annular protruding portions 51 being part of the arms or legs of the U- or C-shape. To this extent, it has been found that the magnetic field density at the susceptor 22 can be increased by distorting the magnetic field toward the interior space of the induction coil 13 using the magnetic flux concentrator 50 shaped as described above. In particular, the annular protrusions 51 at each axial end of the sleeve portion 52, which protrude radially inward beyond the sleeve portion 52, lead to a concentration or focusing of the magnetic field within the interior space of the induction coil 13. Therefore, the level of heat generated within the susceptor 22 for a given level of power passing through the induction coil 13 is increased compared to an induction coil without a magnetic flux concentrator or with only a sleeve-shaped magnetic flux concentrator without annular protrusions at each axial end. In addition, the magnetic flux concentrator 50 acts as a magnetic shield, capable of reducing the extent to which the magnetic field propagates beyond the induction coil 13. Therefore, the magnetic flux concentrator 50 can help reduce undesired heating of other sensitive components of the system or sensitive items external to the apparatus 1.

[0088] To ensure sufficient concentration of the magnetic field, the annular protrusion 51 should extend radially inward beyond the outer periphery of the induction coil 13, whereas the concentration of the magnetic field may be sufficient if the annular protrusion 51 extends radially inward at most to the inner periphery of the induction coil 13, i.e., if the annular protrusion does not protrude radially inward beyond the inner periphery of the induction coil 13.

[0089] In this embodiment, the magnetic flux concentrator 50 is constructed from magnetic flux concentrator foil. More specifically, each annular protrusion 51 is made of magnetic flux concentrator foil that is spirally wound on the coil support 17 in multiple layers, such that it extends radially outward beyond the outer periphery of the induction coil 13. Over the annular protrusion 51, a sleeve portion 52 is formed of several layers of the same magnetic flux concentrator foil material, such that it surrounds the induction coil 13 and each annular protrusion 51. As an example, a flexible three-layer ferrite sheet, available from Laird Corporation under the trade name MHLL6060-300, including a ferrite layer sandwiched between an adhesive layer and a cover layer, can be used as the magnetic flux concentrator foil. MHLL6060-300 has a foil thickness of approximately 90 micrometers, a real permeability of approximately 130, and an imaginary permeability of approximately 5 at a frequency of 13.56 MHz. 1-3 each have a height dimension (radial) of 2 millimeters and a width dimension (axial) of 2 millimeters. Sleeve portion 52 has a thickness dimension (radial) of approximately 180 micrometers and a width dimension (axial) of 10 millimeters. Thus, using a foil material having a foil thickness of 90 micrometers would require approximately 22 wraps to form a 2 millimeter high annular protrusion portion 51 and approximately 2 wraps to form a 180 micrometer thick sleeve portion 52.

[0090] The sleeve portion 52 is radially separated from the induction coil 13 by a radial gap having a width (radial extension) in the range of 0.5 mm to 1.5 mm, in particular 0.8 mm to 1 mm. Advantageously, the radial gap may help to avoid heat loss from the induction coil to the sleeve portion, reducing losses in the induction coil and increasing losses in the heated susceptor 22, i.e., increasing the heating efficiency of the aerosol generation device 1. Similarly, each of the annular protruding portions 51 is axially separated from the induction coil 13 by an axial gap. The radial gap and / or the axial gap may be a void or gap at least partially filled with a filler material.

[0091] Like the support tube 32 and induction coil 13, the magnetic flux concentrator 50 may also have a non-circular flattened cross-sectional shape that corresponds to the non-circular flattened cross-sectional shapes of the support tube 32 and induction coil 13. In particular, the cross-sectional shape of the magnetic flux concentrator 50 may be oval.

[0092] 6, the more distal annular protruding portion 51 includes a recess or feed-through opening 501 for passing connecting leads 60 for the induction coil. The recess or feed-through opening 501 may be cut into the annular protruding portion 51 after winding the flux concentrator foil.

[0093] To further increase the heating efficiency, the outer periphery of the support tube 32 in this embodiment is provided with a helical wire recess pattern 39, as shown in Figures 4 and 6, into which the coil wire is received. Advantageously, the wire recess pattern 39 allows for a further reduction in the radial distance between the induction coil 13 and the susceptor position within the interior space of the induction coil 13. As already mentioned above, a reduced radial distance increases the magnetic field strength at the susceptor position, which in turn increases the heating efficiency.

[0094] The greater the depth of the recesses in the wire recess pattern 39, the better the magnetic field strength at the position of the susceptor within the internal space of the induction coil 13. For example, when the coil wire has a circular cross section, the radial depth of the recesses in the wire recess pattern 39 is preferably within a range of 0.2 to 0.8 times, particularly 0.3 to 0.5 times, the diameter of the coil wire. The radial distance between the induction coil 13 and the inner periphery of the coil support 17 may be 0.1 to 1 mm, particularly 0.2 to 0.5 mm, and preferably approximately 0.3 mm, as shown in FIG. 6. This ensures that the radial distance between the induction coil 13 and the internal space of the support tube 32 is particularly short, allowing the susceptor 22 to be accommodated. That is, the radial distance a between the inner periphery of the support tube 32 and the bottom of the recess pattern 39 is 0.1 to 1 mm, particularly 0.2 to 0.5 mm, and preferably approximately 0.3 mm.

[0095] 2 and 6 , the outer periphery of the support tube 32 may further include a flux concentrator recess 38 for each of the annular protruding portions 51 of the flux concentrator 50, in which the radially inner end of the respective annular protruding portion 51 is received. Thus, the annular protruding portions 51 are securely supported, which helps prevent displacement of the flux concentrator 50, which could otherwise lead to undesirable changes in the inductance of the induction coil 13 and undesirable changes in the magnetic field density within the interior space of the induction coil 13.

[0096] FIG. 7 shows further details of the power supply electronics that can be used in the induction heating arrangement 10, and in particular in the aerosol generating device shown in FIGS. 1-3. According to this embodiment, the induction heating arrangement 10 comprises a DC / AC inverter connected to the DC power supply 12 shown in FIG. 1. The DC / AC inverter includes a class E power amplifier, which in turn includes the following components: a transistor switch 111 comprising a field-effect transistor (FET), e.g., a metal-oxide semiconductor field-effect transistor (MOSFET), a transistor switch supply circuit indicated by arrow 112 for supplying a switching signal (gate-source voltage) to the transistor switch 111, and an LC load network 113 comprising a shunt capacitor C1 and a series connection of a capacitor C2 and an inductor L2. Inductor L2 corresponds to the induction coil 13 shown in FIGS. 1-3 that is used to generate an alternating magnetic field in the cavity 16. In addition, a choke L1 is provided for supplying a DC supply voltage +V_DC from the DC power supply 12. 7, the ohmic resistance R representing the total equivalent resistance or total resistive load 114 when the system is in use, i.e. when an item 2 is inserted into the cavity 16 of the device 1, is the sum of the ohmic resistance of the induction coil 13 marked L2 and the ohmic resistance of the susceptor 22. Otherwise, when no item is inserted into the cavity 16, the equivalent resistance or resistive load 114 corresponds only to the ohmic resistance of the induction coil 13.

[0097] FIG. 8 shows another embodiment of power supply electronics that can alternatively be used in the aerosol generating device shown in FIGS. 1-3 to provide a high-frequency oscillating current to the induction coil 13. The configuration shown in FIG. 8 corresponds to a class D amplifier configuration. Here, a DC power supply 12 is connected to two transistors 1210 and 1212. Two switching elements 1220 and 1222 are provided to switch the two transistors 1210 and 1212 on and off. The switching elements 1220 and 1222 are controlled at high frequency in a manner that ensures that one of the two transistors 1210 and 1212 is off when the other is on. The induction coil 13 used to generate the alternating magnetic field for induction heating is again represented by L2, while the combined ohmic resistance of the induction coil 13 and susceptor 22 is represented by R. The values of C1 and C2 can be selected to maximize the efficient dissipation of power within the susceptor element. Capacitor C1 is not required to configure the architecture as class D and may therefore be omitted.

[0098] For purposes of this specification and the appended claims, unless otherwise indicated, all numbers expressing amounts, quantities, percentages, and the like are understood to be modified in all instances by the term "about." Also, all ranges include the disclosed maximum and minimum points, and include any intermediate ranges therein, which may or may not be specifically recited herein. Thus, in this context, the number A is understood as A ± 5%. Within this context, the number A may be considered to include a numerical value that is within the typical standard error for measurement of the property that the number A modifies. In some cases, as used in the appended claims, the number A may deviate by the percentages recited above, provided that the amount by which A deviates does not materially affect the basic and novel characteristics of the claimed invention. Also, all ranges include the disclosed maximum and minimum points, and include any intermediate ranges therein, which may or may not be specifically recited herein.

Claims

1. Aerosol generating system comprising an aerosol generating article and an induction heating aerosol generating device for use with the aerosol generating article, wherein the article comprises an aerosol-forming liquid and a flat, particularly sheet-like susceptor disposed in the evaporating portion of the article and configured to heat the aerosol-forming liquid through interaction between the susceptor and an alternating magnetic field provided by the aerosol generating device, the device comprising a DC power supply and an induction heating arrangement, the heating arrangement comprising a power supply electronic circuit comprising a DC / AC inverter connected to the DC power supply, the DC / AC inverter comprising a power switching amplifier having at least one transistor switch, at least one transistor switch driver circuit associated with the transistor switch, and an LC load network comprising at least a capacitor and a cylindrical helical induction coil, the internal space of the induction coil configured to removably receive at least the evaporating portion of the aerosol generating article, and the cylindrical helical induction coil having a non-circular, flattened cross-sectional shape comprising, in particular, two opposing flat sections connected by two opposing, at least partially curved sections.

2. The aerosol generating system according to claim 1, wherein the non-circular, flattened cross-sectional shape includes a symmetrical minor axis and a symmetrical major axis.

3. The aerosol generating system according to claim 2, wherein the ratio of the maximum distance along the major axis of symmetry between the two opposing at least partially curved sections to the maximum distance along the minor axis of symmetry between the two opposing flat sections is in the range of 1.2 to 3, particularly 1.5 to 2.

5.

4. The aerosol generating system according to claim 2, wherein the maximum distance along the symmetrical minor axis between the two opposing flat sections is in the range of 4 mm to 7 mm, particularly 5 mm to 6 mm.

5. The aerosol generating system according to claim 2, wherein the maximum distance along the symmetrical major axis between the two opposing at least partially curved sections is in the range of 7 mm to 10 mm, particularly 8 mm to 9 mm.

6. The aerosol generating system according to claim 1, wherein the two opposing flat sections are parallel to each other.

7. The aerosol generating system according to claim 1, wherein each of the two opposing flat sections is substantially straight.

8. The aerosol generating system according to claim 1, wherein each of the two opposing at least partially curved sections is substantially semicircular, substantially semi-elliptical, substantially semi-elliptical, or substantially parabolic.

9. The aerosol generating system according to claim 1, wherein the non-circular, flattened cross-sectional shape of the induction coil is oval.

10. The aerosol generating system according to claim 1, wherein the induction coil has an oval cylindrical shape.

11. The induction coil formed by one or more windings of a coil wire, wherein the coil wire has a circular cross-section, according to claim 1.

12. The aerosol generation system according to claim 1, wherein the switching power amplifier is a single-ended switching power amplifier.

13. The aerosol generation system according to claim 1, wherein the switching power amplifier is one of a Class C power amplifier, a Class D power amplifier, and a Class E power amplifier.

14. The aerosol generating system according to claim 1, wherein the induction heating arrangement is configured to generate an alternating magnetic field in the range of 500 kHz to 30 MHz, particularly 5 MHz to 15 MHz, preferably 5 MHz to 10 MHz.

15. The aerosol generating system according to any one of claims 1 to 14, wherein the flat susceptor is positioned such that when the evaporated portion of the aerosol generating article is received within the internal space of the induction coil, the main surface of the flat susceptor aligns with the two opposing flat sections of the cross-sectional shape of the induction coil.

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