Patent Publication Number: US-2023148670-A1

Title: An Aerosol Generating Article and an Aerosol Generating System

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to aerosol generating articles, and more particularly to an aerosol generating article for use with an aerosol generating device for heating the aerosol generating article to generate an aerosol for inhalation by a user. Embodiments of the present disclosure also relate to an aerosol generating system comprising an aerosol generating device and an aerosol generating article. 
     TECHNICAL BACKGROUND 
     Devices which heat, rather than burn, an aerosol generating substance (liquid or non-liquid) to produce an aerosol for inhalation have become popular with consumers in recent years. Such devices can use one of a number of different approaches to provide heat to the aerosol generating substance. 
     One approach is to provide an aerosol generating device which employs a resistive heating system. In such a device, a resistive heating element is provided to heat the aerosol generating substance and thereby generate a vapour which typically cools and condenses to form an aerosol for inhalation by a user of the device. 
     Another approach is to provide an aerosol generating device which employs an induction heating system. In such a device, an induction coil and a susceptor are provided. 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 substance thereby generating a vapour which typically cools and condenses to form an aerosol for inhalation by a user of the device. 
     Embodiments of the present disclosure seek to provide optimum heating of the aerosol generating substance which is necessary for effective aerosol generation. 
     SUMMARY OF THE DISCLOSURE 
     According to a first aspect of the present disclosure, there is provided an aerosol generating article for use with an aerosol generating device including a magnetic field generator, the aerosol generating article comprising:
         first and second discrete compartments configured to contain respectively a first aerosol generating substance and a second aerosol generating substance; and   an inductively heatable susceptor configured to be inductively heated by the magnetic field generator, the inductively heatable susceptor having a first part positioned in the first compartment and a second part positioned in the second compartment.       

     The aerosol generating article is intended for use with an aerosol generating device for heating the first and second aerosol generating substances, without burning the aerosol generating substances, to volatise at least one component of the first and second aerosol generating substances and thereby generate a vapour which cools and condenses to form an aerosol for inhalation by a user of the aerosol generating device. 
     According to a second aspect of the present disclosure, there is provided an aerosol generating system comprising:
         a magnetic field generator comprising a substantially helical induction coil having a longitudinal axis; and   an aerosol generating article according to the first aspect, wherein:
           the first and second compartments are positioned inside the helical induction coil; and   the first part of the inductively heatable susceptor extends in a direction substantially parallel to the longitudinal axis of the induction coil and the second part of the inductively heatable susceptor extends in a direction that intersects the first part.   
               

     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 provision of first and second aerosol generating substances in corresponding first and second discrete compartments, along with an inductively heatable susceptor having first and second parts, enables the first and second aerosol generating substances to be individually heated. This in turn allows the heating of the first and second aerosol generating substances to be adapted for the particular substances so that an aerosol with improved characteristics can be generated for an enhanced user experience. 
     The first and second parts of the inductively heatable susceptor may be configured to be heated to first and second temperatures respectively. One of the first and second temperatures may be higher than the other of the first and second temperatures. The first and second aerosol generating substances may have different vaporisation temperatures and heating of the first and second parts of the inductively heatable susceptor to different first and second temperatures may, thus, provide for the generation of an aerosol with improved characteristics. 
     In some embodiments, the first and second aerosol generating substances may comprise respectively first and second aerosol generating liquids, and the first temperature may be higher than the boiling temperature of the first aerosol generating liquid and the second temperature may be higher than the boiling temperature of the second aerosol generating liquid. 
     In some embodiments, one of the first and second aerosol generating substances may comprise a nicotine source which releases nicotine vapour when heated, and the other one of the first and second aerosol generating substances may comprise a delivery enhancing compound. The delivery enhancing compound releases a second vapour when heated. The nicotine vapour reacts with the second vapour in the gas phase to form an aerosol comprising nicotine salt particles that is delivered to the downstream end of the aerosol generating device/system to be inhaled by the user. 
     The nicotine source may comprise one or more of nicotine, a nicotine salt, or a nicotine derivative. The nicotine source may comprise natural nicotine or synthetic nicotine. The nicotine source may comprise pure nicotine, a solution of nicotine, or a liquid tobacco extract. The delivery enhancing compound may comprise an acid such as pyruvic acid or lactic acid. 
     The aerosol generating device/system may comprise a reaction chamber located downstream of both the first and second compartments. The reaction chamber may be configured to receive the released nicotine vapour and second vapour and allow them to react to form the aerosol for inhalation. The reaction chamber may form part of the aerosol generating device and may typically be located between an aerosol generating space (e.g. a cavity) adapted to receive the aerosol generating article and a mouthpiece. Alternatively, the reaction chamber may form a part of the aerosol generating article. 
     Each of the first and second aerosol generating substances may comprise a solid matrix and the first and second parts of the inductively heatable susceptor may be secured in the solid matrix. The first and second parts of the inductively heatable susceptor are held securely in place in the solid matrix. In addition, such an arrangement may facilitate uniform heat transfer from the first and second parts of the inductively heatable susceptor respectively to the first and second aerosol generating substances and/or may facilitate manufacture of the aerosol generating article. 
     The solid matrix may comprise at least one of a porous ceramic and foam material. The foam material may be a mousse and may comprise tobacco. Thus, the mousse may comprise a tobacco mousse, a reconstituted tobacco (RTB) mousse or an e-liquid mousse. 
     The foam material may comprise a plurality of fine particles (e.g. tobacco particles). The tobacco particles may have a particle size between 50 and 180 μm. The foam material may further comprise an aerosol forming agent such as propylene glycol, glycerol or a combination thereof. The aerosol forming agent can further comprise water. The foam material may further comprise a solvent and/or an acid and/or an ester. The foam material may further comprise a foam forming agent. The foam forming agent may be non-protein containing polysaccharide. The foam forming agent may be selected from the group consisting of agar, gellan gum, lecithin, polyglycerol esters of fatty acids, glycerol esters of fatty acids, sorbitan esters of fatty acids, and/or mixtures thereof, without being limited thereto. The foam material may comprise a foam stabilizing agent. The foam stabilizing agent may comprise cellulose gum, hydroxyalkylated carbohydrates, derivatives thereof, e.g. salts thereof, preferably alkali metal salts thereof, e.g. sodium and/or potassium salts thereof, and mixtures thereof. 
     The first and second parts of the inductively heatable susceptor may be positioned in use with respect to the magnetic field generator so that the first part is heated to the first temperature more rapidly than the second part is heated to the second temperature. Controlling the rate of heating of the first and second parts of the inductively heatable susceptor may provide for the generation of an aerosol with improved characteristics. The rate of heating of the first and second parts of the inductively heatable susceptor may be controlled by varying any one or more of the shape and/or size of the first and second parts of the inductively heatable susceptor, the positions and/or orientations of the first and second parts of the inductively heatable susceptor with respect to the magnetic field generator, or the material from which the first and second parts of the inductively heatable susceptor are formed. 
     The first and second parts of the inductively heatable susceptor may be configured to have different orientations from each other with respect to the magnetic field generator. The use of different orientations may be employed to control the rate of heating of the first and second parts of the inductively heatable susceptor. For example, the first and second parts may be oriented so that there is a stronger electromagnetic coupling between the first part and the magnetic field generator than between the second part and the magnetic field generator. Thus, the first part may be heated to a first temperature which is higher than the second temperature to which the second part is heated and/or the first part may be heated to the first temperature more rapidly than the second part is heated to the second temperature. 
     The first part of the inductively heatable susceptor may comprise an inductively heatable material and the second part of the inductively heatable susceptor may comprise a non-inductively heatable material. With this arrangement, the second part of the inductively heatable susceptor is configured to be heated conductively by heat generated in the first part. Such an arrangement may provide for conductive heating of the second part to a second temperature which is lower than the first temperature achieved by inductively heating the first part and/or may provide for a slower rate of heating of the second part relative to the first part. 
     The inductively heatable susceptor may comprise a plate susceptor which may be shaped so that the second part extends from the first compartment into the second compartment. This may facilitate manufacture of the susceptor, and thereby facilitate manufacture of the aerosol generating article. 
     The first and second compartments may be separated by a substantially fluid-impermeable partition wall. The first and second aerosol generating substances can be reliably contained within their respective first and second discrete compartments by the fluid-impermeable partition wall. 
     The partition wall may comprise a thermally insulating material. The thermally insulating material may be configured to minimise heat transfer between the first and second compartments. By minimising heat transfer between the first and second compartments, the heating of the first and second aerosol generating substances by the first and second parts of the inductively heatable susceptor can be carefully controlled to provide for the generation of an aerosol with the desired characteristics. 
     The inductively heatable susceptor may extend through the partition wall. Thus, the first part can be located in the first compartment and the second part can be located in the second compartment in a convenient manner which may facilitate manufacture of the aerosol generating article. 
     The second part of the inductively heatable susceptor may extend in a direction which is substantially perpendicular to the first part. This may allow for a stronger electromagnetic coupling between the first part of the inductively heatable susceptor and the magnetic field generator, for example whilst allowing the second part to easily extend through the partition wall from the first compartment into the second compartment. 
     The aerosol generating system according to the second aspect may further comprise an aerosol generating device in which the magnetic field generator is incorporated. The aerosol generating device may include a cavity having a longitudinal axis, and the helical induction coil may extend around the cavity such that the longitudinal axes of the helical induction coil and the cavity are substantially parallel. With such an arrangement, the first part of the inductively heatable susceptor may be substantially parallel to a longitudinal axis of the induction coil when the aerosol generating article is positioned in the cavity. This in turn may ensure a strong electromagnetic coupling between the first part of the inductively heatable susceptor and the induction coil, possibly enabling the first part to be heated to a first temperature which is higher than the second temperature to which the second part is heated and/or possibly enabling the first part to be heated to the first temperature more rapidly than the second part is heated to the second temperature. 
     The induction coil may comprise any suitable material, for example a Litz wire or a Litz cable. 
     The inductively heatable susceptor may comprise at least one of a metal material, a metal alloy material, a ceramic material, a carbon material, and a polymeric fibre material coated with a metal material. The inductively heatable susceptor may comprise one or more, but not limited, of aluminium, iron, nickel, stainless 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 may generate heat due to eddy currents and/or magnetic hysteresis losses resulting in a conversion of energy from electromagnetic to heat. 
     The first and/or second aerosol generating substance(s) may comprise an aerosol generating liquid. 
     The first and/or second aerosol generating substance(s) may comprise a non-liquid aerosol generating substance, for example 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 leaves, cut filler, porous material, foam material or sheets. The non-liquid aerosol generating material may comprise plant derived material and in particular, may comprise tobacco. It may advantageously comprise reconstituted tobacco. 
     The first and/or second aerosol generating substance(s) may comprise an aerosol-former. Examples of aerosol-formers include polyhydric alcohols and mixtures thereof such as glycerine or propylene glycol. Typically, the first and/or second aerosol generating substance(s) may comprise an aerosol-former content of between approximately 5% and approximately 50% on a dry weight basis. In some embodiments, the first and/or second aerosol generating substance(s) 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 first and second aerosol generating substances may release volatile compounds. The volatile compounds may include nicotine or flavour compounds such as tobacco flavouring. 
     The magnetic field generator may be arranged to operate in use with a fluctuating electromagnetic field having a magnetic flux density of between approximately 20 mT and approximately 2.0 T at the point of highest concentration. 
     The magnetic field generator may include a power source and 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 500 kHz, 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. 
     In embodiments in which the first and second aerosol generating substances comprise a non-liquid aerosol generating material, the aerosol generating article may comprise an air-permeable shell which includes the first and second discrete compartments. The air-permeable shell may comprise an air permeable material which is electrically insulating and non-magnetic. The material may have a high air permeability to allow air to flow through the material with a resistance to high temperatures. Examples of suitable air permeable materials include cellulose fibres, paper, cotton and silk. The air-permeable material may also act as a filter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagrammatic cross-sectional view of an aerosol generating device; 
         FIG.  2    is a diagrammatic cross-sectional view of a first example of an aerosol generating article for use with the aerosol generating device of  FIG.  1   ; and 
         FIG.  3    is a diagrammatic cross-sectional view of a second example of an aerosol generating article for use with the aerosol generating device of  FIG.  1   . 
     
    
    
     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  FIG.  1   , there is shown diagrammatically an example of an aerosol generating device  10  for use with a “pod-type” aerosol generating article, and in particular the first and second examples of the aerosol generating articles  1 ,  2  illustrated in  FIGS.  2  and  3   . The aerosol generating device  10  has a proximal end  12  and a distal end  14  and comprises a device body  16  which includes a power source  18  and a controller  20  which may be configured to operate at high frequency. The power source  18  typically comprises one or more batteries which could, for example, be inductively rechargeable. 
     The aerosol generating device  10  is generally cylindrical and comprises a generally cylindrical aerosol generating space  22 , for example in the form of a cavity, at the proximal end  12  of the aerosol generating device  10 . The cylindrical aerosol generating space  22  is arranged to receive a correspondingly shaped generally cylindrical aerosol generating article  1 ,  2  as described below in connection with  FIGS.  2  and  3   . 
     The aerosol generating device  10  comprises a magnetic field generator  24  for generating an electromagnetic field. The magnetic field generator  24  comprises a substantially helical induction coil  26 . The induction coil  26  has a circular cross-section, extends around the cylindrical aerosol generating space  22  and has a longitudinal axis. The induction coil  26  can be energised by the power source  18  and controller  20 . The controller  20  includes, amongst other electronic components, an inverter which is arranged to convert a direct current from the power source  18  into an alternating high-frequency current for the induction coil  26 . 
     The aerosol generating device  10  includes one or more air inlets  28  in the device body  16  which allow ambient air to flow into the aerosol generating space  22 . The aerosol generating device  10  also includes a mouthpiece  30  having an air outlet  32 . The mouthpiece  30  is removably mounted on the device body  16  at the proximal end  12  to allow access to the aerosol generating space  22  for the purposes of inserting or removing an aerosol generating article  1 ,  2 . 
     Referring to  FIG.  2   , there is shown a first example of an aerosol generating article  1  for use with the aerosol generating device  10 . The induction coil  26  of the aerosol generating device  10  is also shown in  FIG.  2    to clearly indicate how the aerosol generating article  1  is positioned relative to the induction coil  26  when the aerosol generating article  1  is positioned in the aerosol generating space  22 . 
     As noted above, the aerosol generating article  1  is a “pod-type” article and has a substantially circular bottom wall  40 , a substantially circular top wall  42  and substantially cylindrical side wall  44 . The bottom wall  40  and the top wall  42  are typically air-permeable and can include a plurality of openings or perforations or can comprise a material with a porous structure which allows air to flow through the bottom wall  40  and the top wall  42  without the need for the openings or perforations. 
     The aerosol generating article  1  comprises first and second compartments  46 ,  48 . The first and second compartments  46 ,  48  are discrete compartments which are separated by a partition wall  50  that can be substantially fluid-impermeable. 
     The first and second compartments  46 ,  48  contain respectively a first aerosol generating substance  52  and a second aerosol generating substance  54 , and in some embodiments one of the first and second aerosol generating substances  52 ,  54  can comprise a nicotine source and the other of the first and second aerosol generating substances  52 ,  54  can comprise a delivery enhancing compound, such as pyruvic acid or lactic acid. In the illustrated first example, one of the first and second aerosol generating substances  52 ,  54  is a type of solid or semi-solid material and typically comprises plant derived material, and in particular tobacco. One or both of the first and second aerosol generating substances  52 ,  54  may also comprise an aerosol-former. 
     The aerosol generating article  1  includes an inductively heatable susceptor  56  which is configured to be inductively heated by the magnetic field generator  24 , and in particular by the induction coil  26 . The inductively heatable susceptor  56  comprises a first part  58  positioned in the first compartment  46  and a second part  60  positioned in the second compartment  48 . The inductively heatable susceptor  56  comprises a plate susceptor which is generally L-shaped, with the second part  60  extending in a direction which is substantially perpendicular to the first part  58 . In the first example of the aerosol generating article  1 , the second part  60  of the inductively heatable susceptor  56  extends through the partition wall  50  from the first compartment  46  into the second compartment  48 . 
     In a first implementation, the first and second parts  58 ,  60  of the inductively heatable susceptor  56  both comprise an inductively heatable material. As will be understood by one of ordinary skill in the art, when the induction coil  26  is energised during use of the aerosol generating device  10 , an alternating and time-varying electromagnetic field is produced. This couples with the first and second parts  58 ,  60  of the inductively heatable susceptor  56  and generates eddy currents and/or magnetic hysteresis losses in the inductively heatable susceptor  56  causing the first and second parts  58 ,  60  to heat up. The heat is transferred from the first part  58  of the inductively heatable susceptor  56  to the first aerosol generating substance  52  in the first compartment  46 , for example by conduction, radiation and convection. In a similar manner, the heat is transferred from the second part  60  of the inductively heatable susceptor  56  to the second aerosol generating substance  54  in the second compartment  48 , for example by conduction, radiation and convection. Thus, the first and second aerosol generating substances  52 ,  54  are heated independently by the corresponding first and second parts  58 ,  60  of the inductively heatable susceptor  56 . The partition wall  50  can comprise a thermally insulating material that is configured to minimise heat transfer between the first and second compartments  46 ,  48 , so that the heating of the first and second aerosol generating substances  52 ,  54  can be carefully controlled. 
     The first and second aerosol generating substances  52 ,  54  are heated by the corresponding first and second parts  58 ,  60  of the inductively heatable susceptor  56  without being burned. The heating of the first and second aerosol generating substances  52 ,  54  releases one or more volatile compounds and generates first and second vapours (e.g. a nicotine vapour and a second vapour) which tend to mix and which may react as they flow through the air outlet  32  and which cool and condense to form an aerosol which can be inhaled by a user of the aerosol generating device  10  through the mouthpiece  30 . 
     In the first implementation, the first and second parts  58 ,  60  of the inductively heatable susceptor  56  are configured to have different orientations from each other with respect to the induction coil  26 , for example by virtue of the L-shaped geometry of the inductively heatable susceptor  56 , when the aerosol generating article  1  is positioned in the aerosol generating space  22 . In particular, the first part  58  of the inductively heatable susceptor  56  is configured so that it extends in a direction that is substantially parallel to the longitudinal axis of the induction coil  26 , thereby ensuring a strong electromagnetic coupling between the first part  58  and the induction coil  26 . Conversely, the second part  60  of the inductively heatable susceptor  56  is configured so that it extends in a direction that is substantially perpendicular to the longitudinal axis of the induction coil  26  to provide a weaker electromagnetic coupling between the second part  60  and the induction coil  26 . The stronger electromagnetic coupling between the first part  58  of the inductively heatable susceptor  56  and the induction coil  26  may enable the first part  58  to be inductively heated to a first temperature which is higher than a second temperature to which the second part  60  is inductively heated by virtue of the weaker electromagnetic coupling between the second part  60  and the induction coil  26 . Alternatively or in addition, the first part  58  may be heated to the first temperature more rapidly than the second part  60  is heated to the second temperature by virtue of the stronger electromagnetic coupling between the first part  58  and the induction coil  26 . By heating the first and second parts  58 ,  60  to different first and second temperatures and/or at different rates, the heating within the first and second discrete compartments  46 ,  48  can be adapted for the different first and second aerosol generating substances  52 ,  54  so that an aerosol with improved characteristics can be generated. 
     In a second implementation, the first part  58  of the L-shaped inductively heatable susceptor  56  comprises an inductively heatable material and the second part  60  of the inductively heatable susceptor  56  comprises a non-inductively heatable material. Accordingly, when the induction coil  26  is energised during use of the aerosol generating device  10 , the electromagnetic field generated by the induction coil  26  couples with the first part  58  of the inductively heatable susceptor  56  and inductively heats the first part  58  to a first temperature in the manner described above. A proportion of the heat generated in the first part  58  is transferred to the first aerosol generating substance  52  in the first compartment  46 , for example by conduction, radiation and convection. A proportion of the heat generated in the first part  58  is also transferred by conduction to the second part  60 , so that the second part  60  is heated conductively to a second temperature by the heat generated in the first part  56 . Because the second part  60  is heated conductively, rather than inductively, the second part  60  is typically heated to a lower second temperature than the first temperature to which the first part  58  is inductively heated and/or the second part  60  is heated at a slower rate than the first part  58 . 
     Referring to  FIG.  3   , there is shown a second example of an aerosol generating article  2  for use with the aerosol generating device  10 . The induction coil  26  of the aerosol generating device  10  is also shown in  FIG.  3    to clearly indicate how the aerosol generating article  2  is positioned relative to the induction coil  26  when the aerosol generating article  2  is positioned in the aerosol generating space  22 . The aerosol generating article  2  is similar to the aerosol generating article  1  described above with reference to  FIG.  2   , and corresponding components are identified using the same reference numerals. 
     The aerosol generating article  2  comprises first and second compartments  46 ,  48  separated by a partition wall  50  and an inductively heatable susceptor  56  having first and second parts  58 ,  60 . The first compartment  46  contains a first aerosol generating substance  52  and the first part  58  of the inductively heatable susceptor  56 . The second compartment  48  contains a second aerosol generating substance  54  and the second part  60  of the inductively heatable susceptor  56 . 
     Each of the first and second aerosol generating substances  52 ,  54  comprises a solid matrix  62 ,  64  and the first and second parts  58 ,  60  of the inductively heatable susceptor  56  are secured respectively in each solid matrix  62 ,  64 . Each solid matrix  62 ,  64  typically comprises at least one of a porous ceramic and a foam material, for example in the form of a reconstituted tobacco mousse or an e-liquid mousse, which ensures that the first and second parts  58 ,  60  of the inductively heatable susceptor  56  are held securely in place in the respective first and second compartments  46 ,  48 . 
     The first and second parts  58 ,  60  of the inductively heatable susceptor can be separate inductively heatable parts which are separated from each other in the first and second compartments  46 ,  48  and both of the first and second parts  58 ,  60  can comprise an inductively heatable material. When the aerosol generating article  2  is positioned in the aerosol generating space  22  during use of the aerosol generating device  10  and the induction coil  26  is energised, an alternating and time-varying electromagnetic field is produced. This couples with the first and second parts  58 ,  60  of the inductively heatable susceptor  56  and generates eddy currents and/or magnetic hysteresis losses in the inductively heatable susceptor  56  causing the first and second parts  58 ,  60  to heat up independently. The heat is transferred from the first part  58  of the inductively heatable susceptor  56  to the first aerosol generating substance  52  in the first compartment  46 , for example by conduction, radiation and convection. In a similar manner, the heat is transferred from the second part  60  of the inductively heatable susceptor  56  to the second aerosol generating substance  54  in the second compartment  48 , for example by conduction, radiation and convection. Thus, the first and second aerosol generating substances  52 ,  54  are heated independently by the corresponding first and second parts  58 ,  60  of the inductively heatable susceptor  56 . 
     The first and second aerosol generating substances  52 ,  54  are heated by the corresponding first and second parts  58 ,  60  of the inductively heatable susceptor  56  without being burned. The heating of the first and second aerosol generating substances  52 ,  54  releases one or more volatile compounds and generates first and second vapours which tend to mix as they flow through the air outlet  32  and which cool and condense to form an aerosol which can be inhaled by a user of the aerosol generating device  10  through the mouthpiece  30 . 
     As will be apparent from  FIG.  3   , the first and second parts  58 ,  60  of the inductively heatable susceptor  56  are plate susceptors and are both arranged so that they extend in a direction substantially parallel to the longitudinal axis of the induction coil  26 , which is the optimum orientation for coupling with the electromagnetic field generated by the induction coil  26 . In addition, the first part  58  is positioned closer to an inner circumference of the induction coil  26  than the second part  60  and due to the fact that the magnetic flux density increases from a minimum along a central longitudinal axis of the induction coil  26  to a maximum close to the inner circumference of the induction coil  26 , the first part  58  of the inductively heatable susceptor  56  is inductively heated to a first temperature which is higher than a second temperature to which the second part  60  is inductively heated. Alternatively or in addition, the first part  58  may be heated to the first temperature more rapidly than the second part  60  is heated to the second temperature by virtue of its closer proximity to the inner circumference of the induction coil  26 . As explained above, by heating the first and second parts  58 ,  60  to different first and second temperatures and/or at different rates, the heating within the first and second compartments  46 ,  48  can be adapted for the different first and second aerosol generating substances  52 ,  54  so that an aerosol with improved characteristics can be generated. 
     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. For example, the L-shaped inductively heatable susceptor  56  described in connection with the first example of  FIG.  2    could be employed in the second example of  FIG.  3   , such that the first and second parts  58 ,  60  are secured in a solid matrix  62 ,  64  provided in each of the first and second compartments  46 ,  48 . In this case, both the first and second parts  58 ,  60  of the inductively heatable susceptor  56  could comprise an inductively heatable material or the first part  58  could comprise an inductively heatable material whilst the second part  60  could comprise a non-inductively heatable material which is heated conductively by the first part  58 . Conversely, an inductively heatable susceptor  56  comprising separate first and second parts  58 ,  60  as described in connection with the second example of  FIG.  3    could be employed in the first example of  FIG.  2   . 
     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”.