FIELD OF THE INVENTION

The present invention relates to an aerosol generating system including an aerosol generating device and a consumable article.

BACKGROUND

The popularity and use of reduced-risk or modified-risk devices (also known as vaporisers) has grown rapidly in the past few years as an aid to assist habitual smokers wishing to quit using traditional tobacco products such as cigarettes, cigars, cigarillos, and rolling tobacco. Various devices and systems are available that heat or warm aerosolisable substances as opposed to burning tobacco in conventional tobacco products.

A commonly available reduced-risk or modified-risk device is the heated substrate aerosol generation device or heat-not-burn device. Devices of this type generate an aerosol or vapour by heating a consumable article containing an aerosol substrate such as moist leaf tobacco to a temperature typically in the range of 150°C to 300°C. Heating an aerosol substrate, but not combusting or burning it, releases an aerosol that comprises the components sought by the user but not the undesirable by-products of combustion. In addition, the aerosol produced by heating the tobacco or other aerosolisable material does not typically comprise the burnt or bitter taste that may result from combustion which can be unpleasant for the user.

Currently available aerosol generating devices can use one of a number of different approaches to provide heat to the aerosol generating substrate. One such approach is to provide an aerosol generating device which employs an induction heating system. In this case, an induction coil is provided in the device and an inductively heatable susceptor is utilised to heat the aerosol generating substrate. For example, the inductively heatable susceptor may be located within the consumable article. 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 conduction, to the aerosol generating substrate. An aerosol is subsequently generated as the aerosol generating substrate is heated.

In order to improve the consistency and/or efficiency of aerosol generation, it is desirable to supply variable amounts of heat energy to different portions of the consumable article. However, this is difficult to achieve in inductively heatable aerosol generating systems.

An object of the present invention is to address this problem.

SUMMARY OF INVENTION

According to an aspect of the invention, there is provided an aerosol generating system comprising: a consumable article comprising: a rod of aerosol generating material; and an inductively heatable susceptor disposed within the rod of aerosol generating material, wherein the susceptor extends along the length of the rod of aerosol generating material, and wherein the susceptor comprises a first segment and a second segment which are connected by a connecting portion having a reduced cross-sectional area with respect to the first segment and the second segment; and an aerosol generating device comprising: a housing arranged to define a heating chamber for receiving the consumable article; a first inductor and a second inductor arranged to at least partially surround the heating chamber and spaced along the length of the heating chamber, wherein the first inductor and the second inductor are arranged to at least partially surround the first segment and the second segment respectively when the consumable article is received within the heating chamber; a power source configured to supply electricity to the first inductor and the second inductor; and a control circuitry configured to selectively control the supply of electricity to each of the first inductor and the second inductor.

In this way, the heat which is inductively generated in the first and second segments of the susceptor may be localised to each segment, thereby allowing controlled heating of particular regions of the consumable article. Susceptors are required to be made from electrically conductive materials, such as steel, copper, aluminium or brass. According to the Wiedemann-Franz law, the electrical conductivity of metals is proportional to their thermal conductivity, such that susceptors are typically also good thermal conductors. As a result, during induction heating of a susceptor, the generated heat is distributed evenly across the susceptor. This prevents susceptors from being used to heat different regions of a consumable article to different temperatures.

However, by providing a portion of reduced cross-sectional area which separates the first and second segments of the susceptor, the transfer of heat is limited between the first and second segments. This prevents the first and second segments from rapidly attaining thermal equilibrium, such that the first and second segments may be held at different temperatures for a prolonged period of time. Specifically, by providing first and second inductors configured to heat the first and second segments respectively, the first and second segments may be supplied with different amounts of heat energy without rapidly equilibrating. Accordingly, the portion of aerosol generating substrate surrounding the first segment may be supplied with a different amount of heat energy to the portion of aerosol generating substrate surrounding the second segment. Variable and localised heating of the aerosol substrate may be desirable to improve the heating efficiency of the device, ensure a consistent aerosol generating operation, and tune the sensory experience for the consumer. Furthermore, by utilising a single susceptor having a portion of reduced cross-sectional area, the consumable article may be manufactured in a simple and cost-effective manner.

It will be understood that the first inductor and the second inductor are spaced apart in the length direction of the heating chamber. In other words, the inductors do not occupy or share the same longitudinal position along the heating chamber. Advantageously, this means that field lines produced by each inductor are concentrated in a single segment of the susceptor respectively, e.g. the field lines produced by the first inductor are concentrated in the first segment, and the field lines produced by the second inductor are concentrated in the second segment.

Preferably, each inductor is an induction coil. Preferably, the first and second inductor are arranged to (entirely) surround the first and second segments of the susceptor respectively.

Preferably, the first inductor and the second inductor do not overlap. In particular, the first and second inductors (and third inductor etc.) are arranged such that the first and second inductors (and third inductor etc.) do not overlap in a direction perpendicular to the length of the heating chamber (i.e. in a radial direction). In this way, overlapping field lines are avoided and each inductor is configured to provide localised heating to a single respective segment.

Preferably, the first inductor is arranged to surround the first segment of the susceptor but does not surround the second segment of the susceptor (or any other segments), and the second inductor is arranged to surround the second segment of the susceptor but does not surround the first segment of the susceptor (or any other segments).

Preferably, the susceptor is formed as an elongate sheet. The term “sheet” may be understood as referring to a planar shape having a thickness many times smaller than its length or breadth. For example, the elongate sheet may be substantially cuboidal or rectangular. In this way, the ease of manufacturability of the consumable article is further improved.

Preferably, the reduced cross-sectional area of the connecting portion is provided by a notch in the susceptor. In this way, notches may be formed along the side of a uniform length of susceptor material, prior to the length of susceptor material being cut into a number of susceptors. Accordingly, the ease of manufacturability of the susceptor is further improved.

In one example, the notch(es) may be formed in one side of the susceptor only.

Preferably, each notch may extend across a distance of 20% to 90% of the width of the susceptor. For example, each notch may extend across a distance of 30%, 40%, 50%, 60%, 70% or 80% of the width of the susceptor. A longer notch optimises the reduction in heat transfer between segments and leads to more efficient heating of the particular regions of the aerosol substrate. However, a longer notch will also increase the fragility of the susceptor, thereby increasing the manufacturing difficulty of the susceptor.

Preferably, the reduced cross-sectional area of the connecting portion is provided by a pair of opposing notches in the susceptor. In this way, the consumable article may be symmetrically heated about its longitudinal axis.

Preferably, each notch comprises opposing parallel sides. In other words, each notch may be a rectangular or cuboidal notch.

Alternatively, each notch has a concave shape. In other words, each notch may be a curved notch, e.g. a semi-circular or hemispherical notch.

Preferably, the susceptor comprises a third segment which is connected to the second segment by another connecting portion having a reduced cross-sectional area with respect to the second segment and the third segment, wherein the aerosol generating device comprises a third inductor arranged to at least partially surround the heating chamber and spaced from the first inductor and the second inductor along the length of the heating chamber, wherein the third inductor is arranged to at least partially surround the third segment when the consumable article is received within the heating chamber, wherein the power source is further configured to supply electricity to the third inductor, and wherein the control circuitry is further configured to selectively control the supply of electricity to the third inductor.

The skilled person will appreciate that the susceptor may include a plurality of segments, wherein adjacent segments are each connected by a respective connecting portion. For example, the susceptor may comprise four, five, six, seven, etc. segments. The aerosol generating device may comprise a corresponding number of induction coils each configured to heat a respective segment of the plurality of segments.

Preferably, the segments are periodically (e.g. evenly) spaced along the length of the susceptor. In this way, the ease of manufacturability of the consumable article is further improved. Preferably, the susceptor comprises (or consists of) stainless steel and a Ni-Fe alloy. For example, the susceptor may be a laminate of stainless steel and Ni-Fe alloy.

According to a second aspect of the invention, there is provided a consumable article for an aerosol generating device, comprising: a rod of aerosol generating material; and an inductively heatable susceptor disposed within the rod of aerosol generating material, wherein the susceptor extends along the length of the rod of aerosol generating material, wherein the susceptor comprises a first segment and a second segment which are connected by a connecting portion having a reduced cross-sectional area with respect to the first segment and the second segment, wherein the reduced cross-sectional area of the connecting portion is provided by a notch in the susceptor, and wherein the notch is substantially devoid of aerosol generating material.

In this way, the thermal conduction between the first and second segments is further reduced due to the absence of aerosol generating material within the notch. Advantageously, this improves the capability of the susceptor to be held at different temperatures, thereby providing improved localised heating of the aerosol generating material. In addition, this configuration prevents the overheating of aerosol generating material within each notch, and improves the consistency of the aerosol generating operation.

The skilled person will appreciate that the consumable article of the second aspect may be used within the aerosol generating system of the first aspect.

Preferably, the reduced cross-sectional area of the connecting portion is provided by a pair of opposing notches in the susceptor, wherein each notch is substantially devoid of aerosol generating material.

The skilled person will appreciate that each notch may be described as being substantially filled with an (air) void.

Preferably, each notch comprises opposing parallel sides. Alternatively, each notch has a concave shape. BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention are now described, by way of example, with reference to the drawings, in which:

Figure 1 is a schematic view of an aerosol generating system comprising an aerosol generating device and a consumable article according to an embodiment of the invention;

Figure 2 is a schematic view illustrating the consumable article containing a susceptor and the surrounding induction coils of the aerosol generating device;

Figure 3 is a schematic view of the susceptor of the consumable article;

Figure 4A to 4C are schematic views of alternative susceptors according to alternative embodiments of the invention; and

Figure 5 is a schematic view of a susceptor disposed in an aerosol generating substrate of a consumable article according to another embodiment of the invention.

DETAILED DESCRIPTION

As described herein, a vapour is generally understood to refer to 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.

Figure 1 illustrates a schematic cross-sectional view of an aerosol generating system 10 comprising an aerosol generating device 20 and a consumable article 40 for use with the aerosol generating device 20. The aerosol generating device 20 is a heat-not-burn device, which may also be referred to as a tobacco-vapour device. The consumable article 40 comprises an aerosol generating substrate 48, such as tobacco. The aerosol generating device 20 is configured to heat, without burning, the consumable article 40 to form an aerosol from the aerosol generating substrate 48 for inhalation by a user of the aerosol generating device 20.

The aerosol generating device 20 comprises a housing 22 configured to hold various components of the aerosol generating device 20. The housing 22 can have any shape that is sized to fit the components described herein and to be comfortably held by a user unaided, in a single hand.

The aerosol generating device 20 has a first end 23 shown towards the bottom of Figure 1 , which may also be described as a distal, bottom, base or lower end of the aerosol generating device 20. The aerosol generating device 20 has an opposed second end 25 shown towards the top of Figure 1 , which may also be described as a proximal, top or upper end of the aerosol generating device 20. During use, the user typically orients the aerosol generating device 20 with the first end 23 downward and/or in a distal position with respect to the user’s mouth and the second end 25 upward and/or in a proximate position with respect to the user’s mouth.

The aerosol generating device 20 comprises a heating chamber 24 positioned in the housing 22. That is, the housing 22 is arranged to define the heating chamber 24 which forms an interior volume for receiving the consumable article 40. The heating chamber 24 has a longitudinal axis defining a longitudinal direction. The longitudinal direction of the heating chamber 24 aligns with the length direction of the aerosol generating device 20, i.e. the direction defined between the first end 23 and the second end 25 of the aerosol generating device 20.

The heating chamber 24 is open towards the second end 25 of the aerosol generating device 20. In other words, the heating chamber 24 has an opening 26 towards the second end 25 of the aerosol generating device 20. In use, the user may insert the consumable article 40 through the opening 26 in the heating chamber 24 such that the consumable article 40 is positioned within the heating chamber 24. The length of the heating chamber 24 is configured such that a portion of the consumable article 40 protrudes through the opening 26 (i.e. out of the heating chamber 24) and can be received in the mouth of the user.

The heating chamber 24 is arranged to receive a correspondingly shaped consumable article 40. In this example, the heating chamber 24 is arranged to receive a generally cylindrical or rod-shaped consumable article 40. Thus, the heating chamber 24 is also tubular, e.g. substantially cylindrical. However, the skilled person will appreciate that the shape of the heating chamber 24 is not limited to being tubular. For example, the heating chamber 24 may be formed to define a cuboidal, conical, hemi-spherical or other shaped cavity, and be configured to receive a complementary shaped consumable article.

The aerosol generating device 20 comprises a plurality of induction coils 32 - 36 which act as electromagnetic field generators for generating an electromagnetic field. The induction coils 32 - 36 will be described in more detail with reference to Figure 2.

The aerosol generating device 20 further comprises a power source 28 such as one or more batteries which may be rechargeable, and control circuitry 30 such as a microcontroller (MCU). The control circuitry 30 is configured to selectively control the supply of electricity from the power source 28 to the plurality of induction coils 32 - 36.

Figure 2 illustrates a schematic view of the consumable article 40 showing its internal structure and components. In the illustrated state, the consumable article 40 has been received within the heating chamber 24 of the aerosol generating device 20 but, for ease of illustration, only the induction coils 32 - 36 of the aerosol generating device 20 are shown.

The consumable article 40 is a disposable and replaceable article, which may also be referred to as an aerosol generating article or heat-not-burn stick. The consumable article 40 has a proximal end 42 (or mouth end) and an opposed distal end 44. The length direction of the consumable article 40 is defined between the proximal end 42 and the distal end 44. The consumable article 40 comprises an aerosol generating substrate 48 located adjacent the distal end 44. Particularly, the aerosol generating substrate 48 is a rod of aerosol generating material, such as a rod of tobacco. The consumable article 40 further comprises a mouthpiece segment 46 positioned downstream of the aerosol generating substrate 48, i.e. adjacent the proximal end 42. The mouthpiece segment 46 comprise a filter which typically comprises cellulose acetate fibres. The aerosol generating substrate 48 and the mouthpiece segment 42 may be separated by further structural or filter elements, such as a polymer film filter for cooling the aerosol and a hollow acetate film. The aerosol generating substrate 48 and the mouthpiece segment 42 (and other components) are arranged in coaxial alignment inside a wrapper, e.g. a paper wrapper, to hold the components in position to form the rod-shaped consumable article 40.

The consumable article 40 further comprises a susceptor 50 disposed within the aerosol generating substrate 48. That is, the susceptor 50 is surrounded by the aerosol generating substrate 48. The susceptor 50 is an inductively heatable element which, on application of an electromagnetic field in its vicinity, generates heat due to eddy currents and magnetic hysteresis losses resulting in a conversion of energy from electromagnetic to heat. The susceptor 50 is formed from a material suitable for being inductively heated. For example, the susceptor 50 may be made from metal such as aluminium, iron, nickel, stainless steel, carbon steel, and alloys thereof, e.g. nickel chromium, nickel copper, or nickel iron. Preferably, the susceptor 50 comprises a laminate of stainless steel and a nickel iron alloy.

The susceptor 50 is formed as an elongate sheet, i.e. a strip of material having a thickness many times smaller than its length or width. The susceptor 50 is arranged to extend along at least a portion of the length of the aerosol generating substrate 48 (and consumable article 40) such that, in use, the susceptor 50 is aligned substantially parallel with the longitudinal axis of the heating chamber 24. In alternative examples, the susceptor 50 may be formed in alternative shapes, such as a rod-shape. As further illustrated in Figure 3, the susceptor 50 comprises a plurality of segments 52 - 56. Specifically, the susceptor 50 comprises a first segment 52, a second segment 54, and a third segment 56, but the skilled person will appreciate the number of segments may vary in accordance with the number of induction coils 32 - 36, as discussed further below. The susceptor 50 further comprises a plurality of connecting portions 58. Each segment 52 - 56 is connected to the adjacent segment 52 - 56 by a respective connecting portion 58. For example, the first segment 52 is connected to the second segment 54 by a connecting portion 58 and the second segment 54 is connected to the third segment 56 by another connecting portion 58. The connecting portions 58 have a smaller cross- sectional area (i.e. in a plane perpendicular to the length of the susceptor 50) than each adjacent segment 52 - 56. That is, the connecting portions 58 are narrower regions of the susceptor 50 which are spaced along the length of the susceptor 50.

The skilled person will appreciate that the segments 52 - 56 and the connecting portions 58 are formed from the same material, and simply describe different regions of the susceptor 50.

The connecting portions 58 are defined by one or more notches 60 which are formed in the susceptor 50. The notches 60 preferably extend through the entire thickness of the susceptor 50 (i.e. in a direction perpendicular to the length and width of the susceptor 50). Each notch 60 may also be referred to as a slit, indentation, incision, or recess formed in the exterior of the susceptor 50. Each notch 60 is laterally positioned along the length of the susceptor 50. That is, each notch 60 is formed in the side or edge of the susceptor 50, e.g. perpendicular to the length and thickness of the susceptor 50. Each notch 60 is created by removing a portion of material from the susceptor 50, e.g. using a cutting tool.

The notches 60 form the respective connecting portions 58 having a smaller cross- sectional area than the adjacent segments 52 - 56. The cross-sectional area available for heat to longitudinally flow between adjacent segments 52 - 56 is therefore reduced. Advantageously, by utilising a single susceptor 50 having notches 60 to reduce heat flow, rather than disposing multiple separate susceptors within the consumable article 40, the manufacturing efficiency of the consumable article 40 is improved. In particular, the susceptor 50 may be formed from a length (or ribbon) of susceptor material which is then cut to form a plurality of susceptors 50. The notches 60 may be formed along the length of susceptor material prior to being cut into individual susceptors 50.

In the depicted embodiment of Figures 2 and 3, adjacent segments 52 - 56 are spaced from each other by an opposing pair of notches 60. That is, the connecting portion 58 between the first segment 52 and the second segment 54 is formed by two notches 60 provided on opposite sides of the susceptor 50. Similarly, the connecting portion 58 between the second segment 54 and the second segment 56 is formed by two notches 60 provided on opposite sides of the susceptor 50. Advantageously, this ensures that the consumable article 40 may be symmetrically heated about its longitudinal axis.

Each notch 60 comprises opposing parallel sides, i.e. sides which are arranged perpendicular to the length of the consumable article 50, thereby forming rectangular or cuboidal notches. However, the skilled person will appreciate that the shape and arrangement of the notches 60 may vary. Alternative examples are discussed below with reference Figures 4A to 4C.

In Figure 2, each notch 60 is illustrated as being filled with aerosol generating material. However, as discussed with reference to Figure 5 below, the notches 60 may instead by occupied by air.

The induction coils 32 - 36 are arranged such that, when the consumable article 40 is received within the heating chamber 24, the induction coils 32 - 36 surround the aerosol generating substrate 48 and susceptor 50 contained therein. More specifically, each induction coil 32 - 36 is arranged to surround a respective segment 52 - 56 of the susceptor 50. A first induction coil 32 is arranged to surround the first segment 52, a second induction coil 34 is arranged to surround the second segment 54, and a third induction coil 36 is arranged to surround the third segment 56. The induction coils 32 - 36 will be understood to be spaced apart in the length direction of the heating chamber. That is, the first induction coil 32, the second induction coil 34, and the third induction coil 36 do not overlap in a radial direction of the heating chamber.

The skilled person will appreciate the number of induction coils 32 - 36 may be varied in accordance with the number of segments 52 - 56 of the susceptor 50, and that each induction coil 32 - 36 may be arranged around a respective segment 52 - 56 of the susceptor 50.

Each induction coil 32 - 36 extends helically around the (tubular) heating chamber 24. Each induction coil 32 - 36 can be energised by the power source 28 and control circuitry 30. The control circuitry 30 includes, amongst other electronic components, an inverter which is arranged to convert a direct current from the power source 28 into an alternating high-frequency current for the induction coils 32 - 36.

Upon activation of the aerosol generating device 20 by a user, the induction coils 32 - 36 may be energised by the power source 28 and control circuitry 30 which can supply an alternating electrical current through the induction coils 32 - 36, such that an alternating and time-varying electromagnetic field is produced by the induction coils 32 - 36. This couples with the inductively heatable susceptor 50 received within the heating chamber 24 and generates eddy currents and/or magnetic hysteresis losses in the susceptor 50 causing the susceptor 50 to heat up. The heat is then transferred from the inductively heatable susceptor 50 to the aerosol generating substrate 48, for example by conduction, radiation and convection. This results in heating of the aerosol generating substrate 48 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 20 through the mouthpiece segment 46, and more particularly through the filter.

More particularly, the control circuitry 30 is configured to control the supply of current to each induction coil 32 - 36 independently. For example, the control circuitry 30 can supply different amounts of power (or no power) to each of the first induction coil 32, the second induction coil 34, and the third induction coil 36. In this way, the electromagnetic field generated by each induction coil 32 - 36 may be selectively controlled, such that differing amounts of heat energy may be generated in each corresponding segment 52 - 56 of the susceptor 50. As the segments 52 - 56 are separated by the notches 60, i.e. the connecting portions 58 reduce the cross-sectional area available for heat transfer between each segment 52 - 56, each segment 52 - 56 may be held at different temperatures. Thus, the portions of aerosol generating substrate 48 adjacent and surrounding each segment 52 - 56 may receive different levels of heating. It will be appreciated the induction coils 32 - 36 are each arranged to provide localised heating to only one of the segments 52 - 56 respectively, e.g. the first induction coil 32 is arranged to surround the first segment 52 only, the second induction coil 34 is arranged to surround the second segment 54 only, and the third induction coil 36 is arranged to surround the third segment 56 only.

For example, it may be desirable to heat the central portion of aerosol generating substrate 48 surrounding the second segment 54 to a higher temperature than the portions of aerosol generating substrate 48 surrounding first segment 52 and the third segment 56. Thus, the control circuitry 30 may supply a higher current to the second induction coil 34, and a lower current to the first induction coil 32 and the third induction coil 36.

Figures 4A - 4C illustrate a number of other susceptors 50 according to alternative embodiments of the invention.

Figure 4A illustrates a susceptor 70 having a notch 60 formed in one side of the susceptor 50 only. That is, the notch 60 does not have a corresponding notch on the opposing side of the susceptor 70, such that the susceptor 70 is asymmetric about its length. Advantageously, only forming a notch (or notches) along one side of the susceptor 70 may simply the manufacturing process.

Figure 4B illustrates a susceptor 80 having a pair of notches 60 formed on opposing sides of the susceptor 80. Unlike the susceptor 50 illustrated in Figures 2 and 3, the susceptor 80 in this embodiment has a single pair of opposing notches 60 and thus only a first segment 52 and a second segment 54. Accordingly, the susceptor 80 is configured to be received in an aerosol generating device 20 having a first induction coil 32 and a second induction coil 34 arranged to surround the first segment 52 and the second segment 54 respectively.

The skilled person will appreciate the number of segments 52 - 56 of each embodiment may be varied. The number of induction coils 32 -36 may also be varied in accordance with the number of segments 52 - 56.

Figure 4C illustrates a susceptor 90 having a plurality of notches 60 laterally formed along the length of the susceptor 90. Unlike the other embodiments, the notches 60 are formed having a concave shape. In other words, the notches 60 each have a curved interior surface. In the depicted embodiment, each notch 60 has a corresponding notch 60 on the opposite side of the susceptor 90, and the plurality of notches 60 define a first segment, 52, second segment 54, third segment 56, fourth segment 57, and fifth segment 58. However, the skilled person will again appreciate that, in alternative embodiments, any number or arrangement of concave notches 60 may be formed in the susceptor 90.

Figure 5 is a schematic view of a susceptor 100 according to another embodiment of the invention. The susceptor 100 comprises corresponding features to the susceptor 50 of Figures 2 and 3, except that each notch 60 is devoid of (i.e. does not contain) aerosol generating material. That is, each connecting portion 58 is partially surrounded by one or more air voids 62 which respectively fill each notch 60 such that each air void 62 acts as barrier to prevent heat transfer between adjacent segments 52 - 56 of the susceptor 100. The air void 62 may also be described as an air gap.

In the susceptor 50 shown in Figures 2 and 3, it is possible that some heat may be transferred between adjacent segments 52 - 56 across the aerosol generating material disposed in each notch 60, e.g. by conduction, convection, or radiation. Hence, by configuring the susceptor 100 such that there is no aerosol generating material within each notch 60, but instead each notch 60 only contains air, the heat transfer between segments 52 - 56 may be further reduced. It will be appreciated that each of the previously described susceptors 60, 70, 80 or variations thereof may also be adapted to include air voids 62 within each notch 60.