EP4373331A1

EP4373331A1 - An induction heating assembly for an aerosol generating device

Info

Publication number: EP4373331A1
Application number: EP22735485.9A
Authority: EP
Inventors: Grzegorz Aleksander PILATOWICZ
Original assignee: JT International SA
Current assignee: JT International SA
Priority date: 2021-07-23
Filing date: 2022-07-05
Publication date: 2024-05-29
Also published as: JP2024526527A; CN117615677A; WO2023001547A1; KR20240036611A

Abstract

An induction heating assembly (11) for an aerosol generating device (10) comprises a heating chamber (18) for receiving at least part of an aerosol generating substrate (102), an induction coil (58) positioned externally of the heating chamber (18) for generating an electromagnetic field, an inductively heatable susceptor (48) positioned inside the heating chamber (18) at a periphery (31) thereof externally of the aerosol generating substrate (102), and a temperature sensor (64) in thermal contact with the inductively heatable susceptor (48). The inductively heatable susceptor (48) is arranged with respect to the induction coil (58) to be inductively heated by the generated electromagnetic field and has a geometric feature (70) arranged to shield the temperature sensor (64) from the generated electromagnetic field.

Description

AN INDUCTION HEATING ASSEMBLY FOR AN AEROSOL GENERATING DEVICE

Technical Field The present disclosure relates generally to an induction heating assembly for an aerosol generating device, and more particularly to an induction heating assembly for heating an aerosol generating substrate to generate an aerosol for inhalation by a user of the aerosol generating device. Embodiments of the present disclosure also relate to an aerosol generating device comprising an induction heating assembly. The present disclosure is particularly applicable to a portable (hand-held) aerosol generating device. Such devices heat, rather than bum, an aerosol generating substrate, e.g., tobacco or other suitable materials, by conduction, convection, and/or radiation to generate an aerosol for inhalation by a user. The present disclosure is particularly concerned with an inductively heated aerosol generating device.

Technical Background

The popularity and use of reduced-risk or modified-risk devices (also known as aerosol generating devices or vapour generating devices or personal vaporizers) has grown rapidly in recent years as an alternative to the use of traditional tobacco products. Various devices and systems are available that heat or warm aerosol generating substances to generate an aerosol for inhalation by a user.

A commonly available reduced-risk or modified-risk device is the heated substrate aerosol generating device, or so-called heat-not-bum device. Devices of this type generate an aerosol or vapour by heating an aerosol generating substrate to a temperature typically in the range 150°C to 300°C. Heating the aerosol generating substrate to a temperature within this range, without burning or combusting the aerosol generating substrate, generates a vapour which typically cools and condenses to form an aerosol for inhalation by a user of the device.

Currently available aerosol generating devices can use one of a number of different approaches to heat to the aerosol generating substrate. One such approach is to provide an aerosol generating device which employs an induction heating system. In such a device, an induction coil is provided in the device and an inductively heatable susceptor is provided to heat the aerosol generating substrate. Electrical energy is supplied to the induction coil when a user activates the device which in turn generates an alternating electromagnetic field. The susceptor couples with the electromagnetic field and generates heat which is transferred, for example by one or more of conduction, radiation and convection to the aerosol generating substrate and an aerosol is generated as the aerosol generating substrate is heated.

It is generally desirable to rapidly heat an aerosol generating substrate to, and to maintain the aerosol generating substrate at, a temperature sufficiently high to generate a vapour. The temperature of the aerosol generating substrate must be carefully controlled to generate a vapour aerosol with suitable characteristics and, thus, it is desirable to be able to accurately control the heating temperature. The present disclosure seeks to address this need.

Summary of the Disclosure

According to a first aspect of the present disclosure, there is provided an induction heating assembly for an aerosol generating device, the induction heating assembly comprising: a heating chamber for receiving at least part of an aerosol generating substrate; an induction coil positioned externally of the heating chamber for generating an electromagnetic field; an inductively heatable susceptor positioned inside the heating chamber at a periphery thereof externally of heating the aerosol generating substrate, the inductively heatable susceptor being arranged with respect to the induction coil to be inductively heated by the generated electromagnetic field; a temperature sensor in thermal contact with the inductively heatable susceptor; wherein the inductively heatable susceptor has a geometric feature arranged to shield the temperature sensor from the generated electromagnetic field. According to a second aspect of the present disclosure, there is provided an aerosol generating device comprising an induction heating assembly according to the first aspect. The induction heating assembly may further comprise a power source arranged to provide power to the induction coil.

The induction heating assembly is configured to heat an aerosol generating substrate, without burning the aerosol generating substrate, to volatise at least one component of the aerosol generating substrate and thereby generate a heated vapour which cools and condenses to form an aerosol for inhalation by a user of the aerosol generating device. The aerosol generating device is typically a hand-held, portable, device.

In general terms, a vapour is a substance in the gas phase at a temperature lower than its critical temperature, which means that the vapour can be condensed to a liquid by increasing its pressure without reducing the temperature, whereas an aerosol is a suspension of fine solid particles or liquid droplets, in air or another gas. It should, however, be noted that the terms ‘aerosol’ and ‘vapour’ may be used interchangeably in this specification, particularly with regard to the form of the inhalable medium that is generated for inhalation by a user.

The geometric feature is arranged to concentrate the generated electromagnetic field away from the temperature sensor, and the temperature sensor is thus shielded from the generated electromagnetic field. In particular, the geometric feature is shaped to (i.e. has a shape and/or volume arranged to) concentrate the generated electromagnetic field away from the temperature sensor. The geometric feature is formed from a susceptor material, and may be at least partly formed in or by the inductively heatable susceptor. The inductively heatable susceptor is not positioned in the aerosol generating substrate (i.e., it does not act as an internal heating element) but is instead positioned externally of the aerosol generating substrate, and thus the temperature sensor is also positioned externally of the aerosol generating substrate (e.g., between the aerosol generating substrate and the induction coil) where the electromagnetic field concentration may be at its highest. By shielding the temperature sensor from the generated electromagnetic field, the effect of the generated electromagnetic field on the temperature sensor is minimised. In particular, inductive heating of the temperature sensor is substantially or entirely avoided, thereby ensuring that an accurate measurement of the temperature of the inductively heatable susceptor can be obtained by the temperature sensor. This in turn ensures that the heating of the aerosol generating substrate can be accurately controlled.

Optional features will now be set out. These are applicable singly or in any combination with any aspect of the present disclosure.

The temperature sensor may be received within the geometric feature. The effect of the electromagnetic field on the temperature sensor is thereby minimised, resulting in a more accurate measurement of the temperature of the inductively heatable susceptor.

The temperature sensor may be a thermocouple and may comprise a first thermocouple wire which may be received within the geometric feature and may comprise a second thermocouple wire which may be received within the geometric feature. The geometric feature has a shape and/or volume operable to receive the first and second thermocouple wires. By arranging the first and second thermocouple wires within the geometric feature, the effect of the generated electromagnetic field on the first and second thermocouple wires is minimised, resulting in a more accurate measurement of the temperature of the inductively heatable susceptor.

The induction coil may extend around the heating chamber. The heating chamber may have a longitudinal axis defining a longitudinal direction The induction coil may be a helical coil which may extend around the heating chamber about the longitudinal axis. By providing an induction coil which extends helically around the heating chamber, reliable heating of the inductively heatable susceptor by the generated electromagnetic field can be assured.

The inductively heatable susceptor may be elongate in the longitudinal direction of the heating chamber. The elongate inductively heatable susceptor is heated efficiently in the presence of the generated electromagnetic field and the elongate shape ensures that the aerosol generating substrate is heated rapidly and uniformly along its length. The energy efficiency of the aerosol generating device is thereby maximised.

The inductively heatable susceptor may have an inner surface and may have an outer surface. The heating chamber may comprise a chamber wall that defines an interior volume of the heating chamber. There may be an outer air gap between the inductively heatable susceptor (e.g., an outer surface of the inductively heatable susceptor) and the chamber wall and, when an aerosol generating substrate (or an aerosol generating article comprising the aerosol generating substrate) is received in the heating chamber, there may be an inner air gap between the inductively heatable susceptor (e.g., an inner surface of the inductively heatable susceptor) and the aerosol generating substrate (or the aerosol generating article comprising the aerosol generating substrate). An efficient transfer of heat from the inductively heatable susceptor to the aerosol generating substrate may, therefore, be realised.

The induction heating assembly may comprise a holder positioned inside the heating chamber. The inductively heatable susceptor may be mounted on the holder. The use of a holder may facilitate positioning of the inductively heatable susceptor in the heating chamber at the periphery of the heating chamber and externally of the aerosol generating substrate so that the inductively heatable susceptor is positioned externally adjacent to, but does not penetrate, the aerosol generating substrate.

The geometric feature may comprise a groove which may be formed in the inner surface or the outer surface of the inductively heatable susceptor. The groove may extend in the longitudinal direction. The temperature sensor may be positioned in the groove. The temperature sensor and its component parts, e.g., first and second thermocouple wires, can be fully accommodated in the groove, thus ensuring that the effect of the generated electromagnetic field on the temperature sensor and its component parts is minimised, and resulting in a more accurate measurement of the temperature of the inductively heatable susceptor. The groove can also be formed easily in the inner surface or the outer surface of the inductively heatable susceptor, thereby improving the manufacturability of the induction heating assembly. The groove may extend in the longitudinal direction from the location of the temperature sensor to an end of the inductively heatable susceptor. Component parts of the temperature sensor, such as first and second thermocouple wires, can be accommodated in the groove.

In embodiments in which the groove is formed in the inner surface of the inductively heatable susceptor, the temperature sensor may be recessed from the inner surface. In embodiments in which the groove is formed in the outer surface of the inductively heatable susceptor, the temperature sensor may be recessed from the outer surface. By recessing the temperature sensor from the inner surface or the outer surface of the inductively heatable susceptor, the effect of the generated electromagnetic field on the temperature sensor and its component parts is minimised, resulting in a more accurate measurement of the temperature of the inductively heatable susceptor.

The groove may be covered by an electrically conductive and non-magnetically permeable material strip which may enclose the temperature sensor in the groove. The material strip should ideally have a high electrical conductivity (i.e., a low electrical resistivity) so that when eddy currents (e.g., generated in the adjacent inductively heatable susceptor) pass through it, very little heat is generated in the material strip.

The geometric feature may comprise a channel which may be arranged on the inner surface or the outer surface of the inductively heatable susceptor. The channel may extend in the longitudinal direction. The temperature sensor may be positioned in the channel. The temperature sensor and its component parts, e.g., first and second thermocouple wires, can be fully accommodated in the channel, thus ensuring that the effect of the generated electromagnetic field on the temperature sensor and its component parts is minimised, and resulting in a more accurate measurement of the temperature of the inductively heatable susceptor. The channel can also be formed easily on the inner surface or the outer surface of the inductively heatable susceptor, thereby improving the manufacturability of the induction heating assembly. The channel may extend in the longitudinal direction from the location of the temperature sensor to an end of the inductively heatable susceptor. Component parts of the temperature sensor, such as first and second thermocouple wires, can be accommodated in the channel.

The channel may be formed by a pair of side walls which may extend in the longitudinal direction. The side walls may comprise an electrically conductive and magnetically permeable material. The side walls can be configured and dimensioned to maximise the shielding effect of the channel on the temperature sensor. The side walls should ideally be spaced from the temperature sensor by a sufficient distance that heat generated in the side walls (e.g., by virtue of eddy currents and/or magnetic hysteresis losses) does not affect the temperature sensor (and, thus, the measured temperature) and is instead transferred to the inductively heatable susceptor.

The channel may be covered by an electrically conductive and non-magnetically permeable material strip which may enclose the temperature sensor in the channel. As noted above, the material strip should ideally have a high electrical conductivity (i.e., a low electrical resistivity) so that when eddy currents (e.g., generated in the adjacent inductively heatable susceptor) pass through it, very little heat is generated in the material strip.

The induction heating assembly may comprise a plurality of said inductively heatable susceptors which may be mounted on the holder and which may extend around the inner surface of the chamber wall. By providing a plurality of inductively heatable susceptors, more rapid and uniform heating of an aerosol generating substrate may be achieved.

The chamber wall may include a coil support structure which may be formed in or on an outer surface for supporting the induction coil. The coil support structure facilitates mounting of the induction coil and allows the induction coil to be positioned optimally with respect to the inductively heatable susceptor. The inductively heatable susceptor is, therefore, heated efficiently, thereby improving the energy efficiency of the induction heating assembly and the aerosol generating device. The provision of the coil support structure also facilitates manufacture and assembly of the induction heating assembly.

The coil support structure may comprise a coil support groove. The coil support groove may extend helically around the outer surface of the chamber wall. The coil support groove is particularly suitable for receiving a helical induction coil. Thus, the helical induction coil may extend around the heating chamber. The induction coil may comprise a Litz wire or a Litz cable. It will, however, be understood that other materials could be used. The circular cross-section of a helical induction coil may facilitate the insertion of the aerosol generating substrate into the heating chamber and may ensure uniform heating of the inductively heatable susceptor and, thus, the aerosol generating substrate.

The induction coil may be arranged to operate in use with a fluctuating electromagnetic field having a magnetic flux density of between approximately 20mT and approximately 2.0T at the point of highest concentration.

The heating chamber may be substantially tubular and the or each inductively heatable susceptor may be mounted on the holder so that it extends around the periphery of the substantially tubular heating chamber. The heating chamber may be substantially cylindrical and the or each inductively heatable susceptor may be mounted on the holder so that it extends around the periphery of the substantially cylindrical heating chamber. Thus, the heating chamber may be configured to receive a substantially cylindrical aerosol generating substrate which may be advantageous as, often, aerosol generating substrates in the form of aerosol generating articles are packaged and sold in a cylindrical form. The induction heating assembly may comprise two inductively heatable susceptors. Each of the inductively heatable susceptors may be elongate in the longitudinal direction and may have a substantially semi-circular cross-section.

The heating chamber and/or the holder may comprise a substantially non-electrically conductive and non-magnetically permeable material. For example, the heating chamber and/or the holder may comprise a heat-resistant plastics material, such as poly ether ether ketone (PEEK). The heating chamber and/or the holder is/are not heated by the electromagnetic field generated by the induction coil during operation of the aerosol generating device, ensuring that energy input into the inductively heatable susceptor is maximised. This in turn helps to ensure that the energy efficiency of the induction heating assembly and the aerosol generating device is maximised. The aerosol generating device also remains cool to the touch, ensuring that user comfort is maximised.

The temperature sensor may be selected from the group consisting of a thermocouple, a thermistor and a resistance temperature detector (RTD). Other types of temperature sensor may, however, be employed.

The inductively heatable susceptor may comprise a metal. The metal is typically selected from the group consisting of stainless steel and carbon steel. The inductively heatable susceptor could, however, comprise any suitable material including one or more, but not limited, of aluminium, iron, nickel, stainless steel, carbon steel, and alloys thereof, e.g., Nickel Chromium or Nickel Copper. With the application of an electromagnetic field in its vicinity, the inductively heatable susceptor generates heat due to eddy currents and magnetic hysteresis losses resulting in a conversion of energy from electromagnetic to heat.

The aerosol generating device may include a controller, e.g., comprising control circuitry, which may be configured to operate at a high frequency. The power source and circuitry may be configured to operate at a frequency of between approximately 80 kHz and 1 MHz, possibly between approximately 150 kHz and 250 kHz, and possibly at approximately 200 kHz. The power source and circuitry could be configured to operate at a higher frequency, for example in the MHz range, depending on the type of inductively heatable susceptor that is used.

The aerosol generating substrate may comprise any type of solid or semi-solid material. Example types of aerosol generating solids include powder, granules, pellets, shreds, strands, particles, gel, strips, loose leaves, cut filler, porous material, foam material or sheets. The aerosol generating substrate may comprise plant derived material and in particular, may comprise tobacco. It may advantageously comprise reconstituted tobacco, for example including tobacco and any one or more of cellulose fibres, tobacco stalk fibres and inorganic fillers such as CaC03.

Consequently, the aerosol generating device may be referred to as a “heated tobacco device”, a “heat-not-bum tobacco device”, a “device for vaporising tobacco products”, and the like, with this being interpreted as a device suitable for achieving these effects. The features disclosed herein are equally applicable to devices which are designed to vaporise any aerosol generating substrate.

The aerosol generating substrate may form part of an aerosol generating article and may be circumscribed by a paper wrapper.

The aerosol generating article may be formed substantially in the shape of a stick, and may broadly resemble a cigarette, having a tubular region with an aerosol generating substrate arranged in a suitable manner. The aerosol generating article may include a filter segment, for example comprising cellulose acetate fibres, at a proximal end of the aerosol generating article. The filter segment may constitute a mouthpiece filter and may be in coaxial alignment with the aerosol generating substrate. One or more vapour collection regions, cooling regions, and other structures may also be included in some designs. For example, the aerosol generating article may include at least one tubular segment upstream of the filter segment. The tubular segment may act as a vapour cooling region. The vapour cooling region may advantageously allow the heated vapour generated by heating the aerosol generating substrate to cool and condense to form an aerosol with suitable characteristics for inhalation by a user, for example through the filter segment.

The aerosol generating substrate may comprise an aerosol former. Examples of aerosol- formers include polyhydric alcohols and mixtures thereof such as glycerine or propylene glycol. Typically, the aerosol generating substrate may comprise an aerosol- former content of between approximately 5% and approximately 50% on a dry weight basis. In some embodiments, the aerosol generating substrate may comprise an aerosol- former content of between approximately 10% and approximately 20% on a dry weight basis, and possibly approximately 15% on a dry weight basis.

Upon heating, the aerosol generating substrate may release volatile compounds. The volatile compounds may include nicotine or flavour compounds such as tobacco flavouring.

Brief Description of the Drawings

Figure 1 is a diagrammatic cross-sectional view of an aerosol generating system comprising an aerosol generating device and an aerosol generating article ready to be positioned in a heating chamber of the aerosol generating device;

Figure 2 is a diagrammatic cross-sectional view of the aerosol generating system of Figure 1, showing the aerosol generating article positioned in the heating chamber of the aerosol generating device;

Figure 3 is a diagrammatic cutaway perspective view of a first example of an induction heating assembly of the aerosol generating device of Figures 1 and 2, showing a holder and inductively heatable susceptors positioned in the heating chamber;

Figure 4 is a diagrammatic perspective view of the holder and the inductively heatable susceptors;

Figure 5 is an exploded view of the holder and the inductively heatable susceptors of Figure 4;

Figures 6 and 7 are diagrammatic perspective views of part of a first example of an inductively heatable susceptor having a groove formed in the outer surface of the inductively heatable susceptor;

Figures 8 and 9 are diagrammatic perspective views of part of a second example of an inductively heatable susceptor having a groove formed in the inner surface of the inductively heatable susceptor; and

Figures 10 and 11 are diagrammatic perspective views of part of a third example of an inductively heatable susceptor having a channel arranged on the outer surface of the inductively heatable susceptor. Detailed Description of Embodiments

Embodiments of the present disclosure will now be described by way of example only and with reference to the accompanying drawings. Referring initially to Figures 1 and 2, there is shown diagrammatically an example of an aerosol generating system 1. The aerosol generating system 1 comprises an aerosol generating device 10 and an aerosol generating article 100 for use with the device 10. The aerosol generating device 10 comprises a main body 12 housing various components of the aerosol generating device 10. The main body 12 can have any shape that is sized to fit the components described in the various embodiments set out herein and to be comfortably held by a user unaided, in a single hand.

A first end 14 of the aerosol generating device 10, shown towards the bottom of Figures 1 and 2, is described for convenience as a distal, bottom, base or lower end of the aerosol generating device 10. A second end 16 of the aerosol generating device 10, shown towards the top of Figures 1 and 2, is described as a proximal, top or upper end of the aerosol generating device 10. During use, the user typically orients the aerosol generating device 10 with the first end 14 downward and/or in a distal position with respect to the user’s mouth and the second end 16 upward and/or in a proximate position with respect to the user’s mouth.

The aerosol generating device 10 comprises an induction heating assembly 11 positioned in the main body 12. The induction heating assembly 11 comprises a heating chamber 18. The heating chamber 18 defines an interior volume in the form of a cavity 20 having a substantially cylindrical cross-section for receiving an aerosol generating article 100. The heating chamber 18 has a longitudinal axis defining a longitudinal direction and is formed of a heat-resistant plastics material, such as polyether ether ketone (PEEK). The aerosol generating device 10 further comprises a power source 22, for example one or more batteries which may be rechargeable, and a controller 24.

The heating chamber 18 is open towards the second end 16 of the aerosol generating device 10. In other words, the heating chamber 18 has an open first end 26 towards the second end 16 of the aerosol generating device 10. The heating chamber 18 is typically held spaced apart from the inner surface of the main body 12 to minimise heat transfer to the main body 12.

The aerosol generating device 10 can optionally include a sliding cover 28 movable transversely between a closed position (see Figure 1) in which it covers the open first end 26 of the heating chamber 18 to prevent access to the heating chamber 18 and an open position (see Figure 2) in which it exposes the open first end 26 of the heating chamber 18 to provide access to the heating chamber 18. The sliding cover 28 can be biased to the closed position in some embodiments.

The heating chamber 18, and specifically the cavity 20, is arranged to receive a correspondingly shaped generally cylindrical or rod-shaped aerosol generating article 100. Typically, the aerosol generating article 100 comprises a pre-packaged aerosol generating substrate 102. The aerosol generating article 100 is a disposable and replaceable article (also known as a “consumable”) which may, for example, contain tobacco as the aerosol generating substrate 102. The aerosol generating article 100 has a proximal end 104 (or mouth end) and a distal end 106. The aerosol generating article 100 further comprises a mouthpiece segment 108 positioned downstream of the aerosol generating substrate 102. The aerosol generating substrate 102 and the mouthpiece segment 108 are arranged in coaxial alignment inside a wrapper 110 (e.g., a paper wrapper) to hold the components in position to form the rod-shaped aerosol generating article 100.

The mouthpiece segment 108 can comprise one or more of the following components (not shown in detail) arranged sequentially and in co-axial alignment in a downstream direction, in other words from the distal end 106 towards the proximal (mouth) end 104 of the aerosol generating article 100: a cooling segment, a center hole segment and a filter segment. The cooling segment typically comprises a hollow paper tube having a thickness which is greater than the thickness of the wrapper 110. The center hole segment may comprise a cured mixture containing cellulose acetate fibres and a plasticizer, and functions to increase the strength of the mouthpiece segment 108. The filter segment typically comprises cellulose acetate fibres and acts as a mouthpiece filter. As heated vapour flows from the aerosol generating substrate 102 towards the proximal (mouth) end 104 of the aerosol generating article 100, the vapour cools and condenses as it passes through the cooling segment and the center hole segment to form an aerosol with suitable characteristics for inhalation by a user through the filter segment.

The heating chamber 18 has a side wall (or chamber wall) 30 extending between a base 32, located at a second end 34 of the heating chamber 18, and the open first end 26. The side wall 30 and the base 32 are connected to each other and can be integrally formed as a single piece. In the illustrated embodiment, the side wall 30 is tubular and, more specifically, cylindrical. In other embodiments, the side wall 30 can have other suitable shapes, such as a tube with an elliptical or polygonal cross section. In yet further embodiments, the side wall 30 can be tapered.

In the illustrated embodiment, the base 32 of the heating chamber 18 is closed, e.g., sealed or air-tight. That is, the heating chamber 18 is cup shaped. This can ensure that air drawn from the open first end 26 is prevented by the base 32 from flowing out of the second end 34 and is instead guided through the aerosol generating substrate 102.

Referring in particular to Figures 3 to 5, the induction heating assembly 11 comprises a holder 36 (or frame) positioned in the cavity 20 of the heating chamber 18 and which is also formed of a heat-resistant plastics material, such as polyether ether ketone (PEEK). The holder 36 is not shown in Figures 1 and 2 for simplicity. The holder 36 has a proximal end 38 and a distal end 40 and comprises a rim 42 at the proximal end 38 which cooperates with a circumferential lip 44 at the open first end 26 of the heating chamber 18 (best seen in Figure 3). The holder 36 includes two longitudinally extending susceptor mounts 46 which extend from the rim 42 towards the distal end 40 of the holder 36. Two elongate substantially semi-circular inductively heatable susceptors 48 in the form of curved plates are mounted on the holder 36 by the susceptor mounts 46 so that together, the inductively heatable susceptors 48 form a susceptor with a tubular form. Each of the inductively heatable susceptors 48 has an inner surface 48a and an outer surface 48b. The inductively heatable susceptors 48, and more particularly the inner surface 48a, may be spaced from the aerosol generating substrate 102 to form an inner air gap that permits air to flow between the inner surface 48a of the inductively heatable susceptors 48 and an outer surface of the wrapper 110 of the aerosol generating article 100.

The side wall 30 of the heating chamber 18 has an inner surface 50 and an outer surface 52, and the inductively heatable susceptors 48 are positioned at a periphery 31 of the heating chamber 18. More specifically, the inductively heatable susceptors 48 extend around the inner surface 50 of the side wall 30. The outer surface 48b of the inductively heatable susceptors 48 faces, but is spaced apart from, the inner surface 50 of the side wall 30 to form an outer air gap that permits air to flow between the outer surface 48b of the inductively heatable susceptors 48 and the inner surface 50 of the side wall 30.

The induction heating assembly 11 comprises an electromagnetic field generator 56 for generating an electromagnetic field. The electromagnetic field generator 56 comprises a substantially helical induction coil 58. The induction coil 58 has a circular cross- section and extends helically around the substantially cylindrical heating chamber 18. The induction coil 58 can be energised by the power source 22 and controller 24. The controller 24 includes, amongst other electronic components, an inverter which is arranged to convert a direct current from the power source 22 into an alternating high- frequency current for the induction coil 58.

The side wall 30 of the heating chamber 18 includes a coil support structure 60 formed in the outer surface 52. In the illustrated example, the coil support structure 60 comprises a coil support groove 62 which extends helically around the outer surface 52. The induction coil 58 is positioned in the coil support groove 62 and is, thus, securely and optimally positioned with respect to the inductively heatable susceptors 48.

Referring to Figures 6 to 11, the induction heating assembly 11 further comprises a temperature sensor 64, which may for example be a thermocouple, a thermistor, a resistance temperature detector (RTD) or any other suitable temperature sensor. The temperature sensor 64 is operatively coupled to the controller 24 and is in thermal contact with the inductively heatable susceptor 48 to allow the temperature of the inductively heatable susceptor 48 to be measured. In the illustrated examples, the temperature sensor 64 comprises first and second connecting wires 66, 68 which connect the temperature sensor 64 to the controller 24. In the case of a thermocouple, the first and second connecting wires 66, 68 may comprise first and second thermocouple wires. The inductively heatable susceptor 48 has a geometric feature 70 which is arranged to shield the temperature sensor 64 from the electromagnetic field generated by the induction coil 58 by concentrating the generated electromagnetic field away from the temperature sensor 64. It should be noted that the geometric feature 70 is omitted from Figures 1 to 5 for simplicity.

Referring to Figures 6 and 7, there is shown a first example of an inductively heatable susceptor 48 in which the geometric feature 70 comprises a groove 72 formed in the outer surface 48b of the inductively heatable susceptor 48. The groove 72 extends in the longitudinal direction from a position at which the temperature sensor 64 is located to an end of the inductively heatable susceptor 48. The temperature sensor 64 is positioned in the groove 72 so that it is recessed from the outer surface 48b. In the example of Figure 7, the groove 72 is covered by an electrically conductive and non- magnetically permeable material strip 74. The material strip 74 encloses the temperature sensor 64 and the first and second connecting wires 66, 68 in the groove 72 and comprises a material having a high electrical conductivity (i.e., a low electrical resistivity) so that when eddy currents generated in the adjacent inductively heatable susceptor 48 pass through it, very little heat is generated in the material strip 74.

Referring to Figures 8 and 9, there is shown a second example of an inductively heatable susceptor 48 in which the geometric feature 70 comprises a groove 72 formed in the inner surface 48a of the inductively heatable susceptor 48. The groove 72 extends in the longitudinal direction from a position at which the temperature sensor 64 is located to an end of the inductively heatable susceptor 48. The temperature sensor 64 is positioned in the groove 72 so that it is recessed from the inner surface 48a. In the example of Figure 9, the groove 72 is covered by an electrically conductive and non- magnetically permeable material strip 74. The material strip 74 encloses the temperature sensor 64 and the first and second connecting wires 66, 68 in the groove 72 and comprises a material having a high electrical conductivity as discussed above.

Referring to Figures 10 and 11, there is shown a third example of an inductively heatable susceptor 48 in which the geometric feature 70 comprises a channel 76 arranged on the outer surface 48b of the inductively heatable susceptor 48. The channel 76 extends in the longitudinal direction from a position at which the temperature sensor 64 is located to an end of the inductively heatable susceptor 48. The channel 76 is formed by a pair of longitudinally extending side walls 76a. The side walls 76a comprise an electrically conductive and magnetically permeable material, and may be formed of the same material as the inductively heatable susceptor 48. The side walls 76a are spaced from the temperature sensor 64 by a sufficient distance to minimise heat transfer from the side walls 76a to the temperature sensor 64 which could affect the temperature measurement. In the example of Figure 11, the channel 76 is covered by an electrically conductive and non-magnetically permeable material strip 74. The material strip 74 encloses the temperature sensor 64 and the first and second connecting wires 66, 68 in the channel 76 and comprises a material having a high electrical conductivity as discussed above.

In order to use the aerosol generating device 10, a user displaces the sliding cover 28 (if present) from the closed position shown in Figure 1 to the open position shown in Figure 2. The user then inserts an aerosol generating article 100 through the open first end 26 into the heating chamber 18, and more specifically into the holder 36 positioned in the heating chamber 18, so that the aerosol generating substrate 102 is received in the cavity 20 and so that the proximal end 104 of the aerosol generating article 100 is positioned at the open first end 26 of the heating chamber 18, with at least part of the mouthpiece segment 108 projecting from the open first end 26 to permit engagement by a user’s lips. Upon activation of the aerosol generating device 10 by a user, the induction coil 58 is energised by the power source 22 and controller 24 which supply an alternating electrical current to the induction coil 58, and an alternating and time-varying electromagnetic field is thereby generated by the induction coil 58. This couples with the inductively heatable susceptors 48 and generates eddy currents and/or magnetic hysteresis losses in the susceptors 48 causing them to heat up. The heat is transferred from the inductively heatable susceptors 48 to the aerosol generating substrate 102, for example by conduction, radiation and convection. This results in heating of the aerosol generating substrate 102 without combustion or burning, and a vapour is thereby generated. The generated vapour cools and condenses to form an aerosol which can be inhaled by a user of the aerosol generating device 10 through the mouthpiece segment 108, and more particularly through the filter segment.

The vaporisation of the aerosol generating substrate 102 is facilitated by the addition of air from the surrounding environment, for example through the open first end 26 of the heating chamber 18, the air being heated as it flows through an inner airflow path defined by the inner air gap between the inner surface 48a of each inductively heatable susceptor 48 and outer surface of the wrapper 110 and through an outer airflow path defined by the outer air gap between the outer surface 48b of each inductively heatable susceptor 48 and the inner surface 50 of the side wall 30. More particularly, when a user sucks on the filter segment, air is drawn into the heating chamber 18 through the open first end 26 as illustrated by the arrows A in Figure 2 and the air is heated as it flows through the heating chamber 18 from the open first end 26 towards the closed second end 34 along the inner airflow path and the outer airflow path. When the heated air reaches the closed second end 34 of the heating chamber 18, it turns through approximately 180° and enters the distal end 106 of the aerosol generating article 100. The heated air is then drawn through the aerosol generating article 100 as illustrated by the arrow B in Figure 2, from the distal end 106 towards the proximal (mouth) end 104. This results in heating of the aerosol generating substrate 102 without combustion or burning, and a vapour is thereby generated. As noted above, the generated vapour cools and condenses to form an aerosol which can be inhaled by a user of the aerosol generating device 10 through the mouthpiece segment 108, and more particularly through the filter segment.

A user can continue to inhale aerosol all the time that the aerosol generating substrate 102 is able to continue to produce a vapour, e.g., all the time that the aerosol generating substrate 102 has vaporisable components left to vaporise into a suitable vapour. The controller 24 can adjust the magnitude of the alternating electrical current passed through the induction coil 58 to ensure that the temperature of the inductively heatable susceptors 48, and in turn the temperature of the aerosol generating substrate 102, does not exceed a threshold level. Specifically, at a particular temperature, which depends on the constitution of the aerosol generating substrate 102, the aerosol generating substrate 102 will begin to bum. This is not a desirable effect and temperatures above and at this temperature are avoided.

To assist with this, the controller 24 is configured to receive an indication of the temperature of the aerosol generating substrate 102, and more specifically the inductively heatable susceptors 48, from the temperature sensor 64 and to use the temperature indication to control the magnitude of the alternating electrical current supplied to the induction coil 58. The heating of the aerosol generating substrate 102 can, therefore, be accurately controlled, in particular because the geometric feature 70 (e.g., groove 72 or channel 76) shields the temperature sensor 64 from the generated electromagnetic field and thereby minimises or prevents inductive heating of the temperature sensor 64.

Although exemplary embodiments have been described in the preceding paragraphs, it should be understood that various modifications may be made to those embodiments without departing from the scope of the appended claims. Thus, the breadth and scope of the claims should not be limited to the above-described exemplary embodiments.

Any combination of the above-described features in all possible variations thereof is encompassed by the present disclosure unless otherwise indicated herein or otherwise clearly contradicted by context. Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

Claims

1. An induction heating assembly (11) for an aerosol generating device (10), the induction heating assembly (11) comprising: a heating chamber (18) for receiving at least part of an aerosol generating substrate (102); an induction coil (58) positioned externally of the heating chamber (18) for generating an electromagnetic field; an inductively heatable susceptor (48) positioned inside the heating chamber (18) at a periphery (31) thereof externally of the aerosol generating substrate (102), the inductively heatable susceptor (48) being arranged with respect to the induction coil (58) to be inductively heated by the generated electromagnetic field; a temperature sensor (64) in thermal contact with the inductively heatable susceptor (48); wherein the inductively heatable susceptor (48) has a geometric feature (70) arranged to shield the temperature sensor (64) from the generated electromagnetic field.

2. An induction heating assembly according to claim 1, wherein the temperature sensor (64) is received within the geometric feature (70).

3. An induction heating assembly according to claim 2, wherein the temperature sensor (64) is a thermocouple and comprises a first thermocouple wire (66) received within the geometric feature (70) and a second thermocouple wire (68) received within the geometric feature (70).

4. An induction heating assembly according to any preceding claim, wherein the induction coil (58) extends around the heating chamber (18).

5. An induction heating assembly according to claim 4, wherein the heating chamber (18) has a longitudinal axis defining a longitudinal direction, the inductively heatable susceptor (48) is elongate in the longitudinal direction of the heating chamber (18), and the inductively heatable susceptor (48) has an inner surface (48a) and an outer surface (48b).

6. An induction heating assembly according to claim 5, wherein the heating chamber (18) comprises a chamber wall (30) that defines an interior volume of the heating chamber (18), and wherein, when an aerosol generating substrate (102) is received in the heating chamber (18), there is an inner air gap between the inner surface (48a) of the inductively heatable susceptor (48) and the aerosol generating substrate (102) and an outer air gap between the outer surface (48b) of the inductively heatable susceptor (48) and the chamber wall (30).

7. An induction heating assembly according to claim 5 or claim 6, wherein the geometric feature (70) comprises a groove (72) formed in the inner surface (48a) or the outer surface (48b) of the inductively heatable susceptor (48), the groove (72) extends in the longitudinal direction, and the temperature sensor (64) is positioned in the groove (72).

8. An induction heating assembly according to claim 7, wherein the groove (72) extends in the longitudinal direction from the location of the temperature sensor (64) to an end of the inductively heatable susceptor (48).

9. An induction heating assembly according to claim 7 or claim 8, wherein, when the groove (72) is formed in the inner surface (48a) of the inductively heatable susceptor (48), the temperature sensor (64) is recessed from the inner surface (48a).

10. An induction heating assembly according to claim 7 or claim 8, wherein, when the groove (72) is formed in the outer surface (48b) of the inductively heatable susceptor (48), the temperature sensor (64) is recessed from the outer surface (48b).

11. An induction heating assembly according to any of claims 7 to 10, wherein the groove (72) is covered by an electrically conductive and non-magnetically permeable material strip (74) to enclose the temperature sensor (64) in the groove (72).

12. An induction heating assembly according to claim 5 or claim 6, wherein the geometric feature (70) comprises a channel (76) arranged on the inner surface (48a) or the outer surface (48b) of the inductively heatable susceptor (48), the channel (76) extends in the longitudinal direction, and the temperature sensor (64) is positioned in the channel (76).

13. An induction heating assembly according to claim 12, wherein the channel (76) extends in the longitudinal direction from the location of the temperature sensor (64) to an end of the inductively heatable susceptor (48).

14. An induction heating assembly according to claim 12 or claim 13, wherein the channel (76) is formed by a pair of side walls (76a) extending in the longitudinal direction, the side walls (76a) comprising an electrically conductive and magnetically permeable material.

15. An induction heating assembly according to any of claims 12 to 14, wherein the channel (76) is covered by an electrically conductive and non-magnetically permeable material strip (74) to enclose the temperature sensor (64) in the channel (76).