Patent Publication Number: US-2022211109-A1

Title: An Aerosol Generating System, An Aerosol Generating Device And An Aerosol Generating Article

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to an aerosol generating system and/or an aerosol generating device, and more particularly to an aerosol generating system and/or an aerosol generating device for use with an aerosol generating article to generate an aerosol for inhalation by a user. Embodiments of the present disclosure also relate to a plate-shaped aerosol generating article. 
     TECHNICAL BACKGROUND 
     Devices which heat, rather than burn, an aerosol generating material 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 material. One such approach is to provide an aerosol generating device which employs an induction heating system and into which an aerosol generating article, comprising aerosol generating material, can be removably inserted by a user. In such a device, an induction coil is provided with the device and an inductively heatable susceptor is provided typically with the aerosol generating 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 material and an aerosol is generated as the aerosol generating material is heated. 
     Embodiments of the present disclosure seek to provide an improved aerosol generating system and device. 
     SUMMARY OF THE DISCLOSURE 
     According to a first aspect of the present disclosure, there is provided an aerosol generating system comprising an aerosol generating device and an aerosol generating article including aerosol generating material and an inductively heatable susceptor, wherein the aerosol generating device comprises:
         an electromagnetic field generator including a first planar coil and a second planar coil;   a heating chamber for receiving the aerosol generating article, the heating chamber being positioned between the first and second planar coils and including an air inlet and an air outlet; and   an airflow path extending between the air inlet and the air outlet.       

     According to a second aspect of the present disclosure, there is provided an aerosol generating device for heating an aerosol generating article including aerosol generating material and an inductively heatable susceptor, wherein the aerosol generating device comprises:
         an electromagnetic field generator including a first planar coil and a second planar coil;   a heating chamber for receiving the aerosol generating article, the heating chamber being positioned between the first and second planar coils and including an air inlet and an air outlet; and   an airflow path extending between the air inlet and the air outlet.       

     The aerosol generating system/device is adapted to heat the aerosol generating material, without burning the aerosol generating material, to volatise at least one component of the aerosol generating material and thereby generate a vapour or aerosol for inhalation by a user of the aerosol generating system/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. 
     As used herein, the term “planar coil” means a spirally wound coil with a winding axis which is perpendicular to the surface in which the coil lies. The planar coils may lie in a flat plane. Thus, the planar coils may essentially be flat coils. The planar coils may lie on a curved plane. For example, the planar coils may be wound in a flat Euclidean plane and may thereafter be manipulated (e.g. bent) to lie on a curved plane. 
     The provision of an electromagnetic field generator comprising first and second planar coils allows the dimensions of the aerosol generating device to be minimised, in particular as compared to conventional aerosol generating devices which comprise an electromagnetic field generator that utilises a helical induction coil extending around the heating chamber. 
     The first and second planar coils may be arranged to generate electromagnetic fields that penetrate the heating chamber in different directions. This may provide improved coupling of the electromagnetic fields with the inductively heatable susceptor, thereby ensuring improved heating of the inductively heatable susceptor whilst maximising energy efficiency. Improved heating of the inductively heatable susceptor in turn leads to improved heating of the aerosol generating material, thereby maximising the amount of aerosol that is generated and providing an improved user experience. 
     The heating chamber may include an opening through which the aerosol generating article may be inserted into the heating chamber. The aerosol generating article can be easily inserted into, and removed from, the heating chamber via the opening. The aerosol generating article may be inserted into the heating chamber along a direction that is parallel with a longitudinal axis of the heating chamber. 
     The aerosol generating article may comprise a substantially cylindrical or rod-shaped aerosol generating article. The aerosol generating article may have any suitable cross section, e.g., a circular or elliptical cross section. Thus, the heating chamber may be arranged to receive a substantially cylindrical or rod-shaped aerosol generating article. The aerosol generating article can, thus, be manufactured using apparatus and methods that are used to manufacture conventional smoking articles having a cylindrical form. Further, the ability of the heating chamber to receive a substantially cylindrical or rod-shaped aerosol generating article is advantageous as, often, aerosol generating articles are packaged and sold in a cylindrical form. The aerosol generating article may include an integral filter through which a user may inhale an aerosol released upon heating. Thus, the device may be arranged to accommodate aerosol generating articles that include an integral filter. 
     The aerosol generating article may comprise an inductively heatable susceptor extending along the longitudinal axis or longitudinal direction thereof. 
     The inductively heatable susceptor may extend from a first end to a second end of the aerosol generating material. 
     The aerosol generating article may comprise a plurality of inductively heatable susceptors, each susceptor extending along the longitudinal axis or longitudinal direction thereof. Such an aerosol generating article may be easy to manufacture. Each susceptor may be provided in the form of a sheet or strip, which may give efficient heating and facilitate manufacture of the aerosol generating article. 
     The aerosol generating article may be substantially plate-shaped. The cross-section of the heating chamber may have major surfaces and side surfaces and the first and second planar coils may be positioned outwardly of the major surfaces of the heating chamber. With this arrangement, a larger proportion of the electromagnetic fields generated by the first and second planar coils penetrate the heating chamber and, hence, the major surfaces of the plate-shaped aerosol generating article allowing improved coupling of the electromagnetic fields with the inductively heatable susceptor and, hence, ensuring improved heating of the inductively heatable susceptor. The plate-shaped form of the aerosol generating article also ensures that the inductively heatable susceptor is located close to the first and second planar coils which further ensures improved coupling of the electromagnetic fields with the inductively heatable susceptor and maximises energy input into the inductively heatable susceptor. The use of a plate-shaped aerosol generating article also allows the dimensions of the aerosol generating system/device to be minimised to provide a compact system/device. 
     The aerosol generating device may be arranged to accommodate aerosol generating articles (e.g. plate-shaped aerosol generating articles) which do not include an integral filter and, thus, the aerosol generating device may further comprise a mouthpiece. 
     The inductively heatable susceptor may include a major surface which may be parallel with the major surfaces of the heating chamber. The major surface is easily penetrated by a larger proportion of the electromagnetic fields generated by the first and/or second planar coils thereby ensuring improved coupling of the generated electromagnetic fields with the inductively heatable susceptor and, hence, improved heating of the inductively heatable susceptor. 
     The heating chamber may include projections or grooves for supporting the aerosol generating article in the heating chamber and for providing said airflow path around a surface of the aerosol generating article between the air inlet and the air outlet. The airflow path ensures that vapour and/or aerosol generated during use of the aerosol generating system/device can flow easily through the heating chamber for delivery to the air outlet and to the user, for example through a mouthpiece which may be positioned at the air outlet. 
     The electromagnetic field generator may include at least three planar coils that surround the heating chamber. The planar coils may be activated sequentially. Each of the planar coils may be arranged to generate an electromagnetic field that penetrates the heating chamber in a different direction from the other planar coils. The major faces of the inductively heatable susceptor are penetrated by, and coupled with, the electromagnetic fields generated by the planar coils. With this arrangement, the efficiency of energy coupling can be improved even if the inductively heatable susceptor is randomly oriented. 
     The heating chamber may have a curved cross-sectional shape and the planar coils may lie on a curved plane surrounding the heating chamber. The major faces of the inductively heatable susceptor are penetrated by, and coupled with, the electromagnetic fields generated by the planar coils. This arrangement may be particularly suited to embodiments in which the aerosol generating article has a curved cross-sectional shape, e.g. circular or elliptical, and/or in which the inductively heatable susceptor is randomly oriented. 
     The aerosol generating device may include a power source and a may include a controller. 
     Electrical power may be supplied alternately to the first and second planar coils. The electromagnetic field generator may be configured to supply electrical power alternately to the first and second planar coils. For example, the controller may be configured to supply electrical power from the power source alternately to the first and second planar coils. The first and second planar coils may be connected by a center tap and electrical power may be supplied alternately to the first and second planar coils. This allows the first and second planar coils to be activated alternately (i.e. one at a time) to provide a desired heating effect. 
     The second planar coil may include a capacitor, electrical power may be supplied intermittently to the first planar coil and the first and second planar coils may be arranged to face each other. This arrangement constrains the electromagnetic fields generated by the first and second planar coils and reduces electromagnetic leakage. This in turn strengthens the current and electromagnetic fields generated during use of the system/device. 
     The second planar coil may include a capacitor and the aerosol generating device may include an electromagnetic shield positioned between the second planar coil and an outer cover. This arrangement further helps to reduce electromagnetic leakage. 
     The first and second planar coils may each include a first electrode and a second electrode. The first electrode may be connected to an outer end of the first and second planar coils and the second electrode may be connected to an inner end of the first and second planar coils. The first and second planar coils may be wound in the same direction from the first electrode to the second electrode, e.g. a clockwise direction or an anti-clockwise direction, about a winding axis perpendicular to a surface in which each coil lies and viewed from the same position outside the heating chamber. The first and second coils may be wound in opposite directions from the first electrode to the second electrode, e.g. a clockwise direction or an anti-clockwise direction, about a winding axis perpendicular to a surface in which each coil lies and viewed from the same position outside the heating chamber. 
     In a first arrangement, the electromagnetic field generator may be configured to supply electrical power to the first and second planar coils to cause current to flow in the first and second planar coils in opposite directions, and in particular in opposite directions between the first and second electrode of each planar coil. For example, the controller may be configured to supply electrical power from the power source to the first and second planar coils to cause current to flow in the first and second planar coils in opposite directions, and in particular in opposite directions between the first and second electrode of each planar coil. The opposite direction of the current flow within each planar coil may provide improved heating of the inductively heatable susceptor, by generating electromagnetic fields in the first and second planar coils in which the major direction of the electromagnetic field generated by the first planar coil at the axis of the first planar coil in the plane where the first planar coil lies is opposite to the major direction of the electromagnetic field generated by the second planar coil at the axis of the second planar coil in the plane where the second planar coil lies. The opposite direction of the current flow within each planar coil may also provide for increased heat generation within the inductively heatable susceptor when it is formed from a magnetic material, by increasing the magnetic losses within the inductively heatable susceptor. 
     In a first example of the first arrangement, the first and second planar coils may be wound in opposite directions from the first electrode to the second electrode about a winding axis perpendicular to a surface in which each coil lies and viewed from the same position outside the heating chamber and the first electrodes of the first and second planar coils may be connected by a center tap. The second electrodes of the first and second planar coils may be connected to one or more switching devices, e.g. field-effect transistors (FETs), such as a metal-oxide-semiconductor field-effect transistors (MOSFETs). The first planar coil may be wound in a clockwise direction from the first electrode to the second electrode about a winding axis perpendicular to a surface in which the coil lies and viewed from a position outside the heating chamber and the second planar coil may be wound in an anti-clockwise direction from the first electrode to the second electrode about the same winding axis and viewed from the same position outside the heating chamber. In this example, current flows in the first planar coil from the first electrode to the second electrode (i.e. in a clockwise direction) and in the second planar coil from the first electrode to the second electrode (i.e. in an anti-clockwise direction). 
     In a second example of the first arrangement, the first and second planar coils may be wound in opposite directions from the first electrode to the second electrode about a winding axis perpendicular to a surface in which each coil lies and viewed from the same position outside the heating chamber and the second electrodes of the first and second planar coils may be connected by a center tap. The first electrodes of the first and second planar coils may be connected to one or more switching devices, e.g. field-effect transistors (FETs), such as metal-oxide-semiconductor field-effect transistors (MOSFETs). The first planar coil may be wound in a clockwise direction from the first electrode to the second electrode about a winding axis perpendicular to a surface in which the coil lies and viewed from a position outside the heating chamber and the second planar coil may be wound in an anti-clockwise direction from the first electrode to the second electrode about the same winding axis and viewed from the same position outside the heating chamber. In this example, current flows in the first planar coil from the second electrode to the first electrode (i.e. in an anti-clockwise direction) and in the second planar coil from the second electrode to the first electrode (i.e. in a clockwise direction). 
     In a third example of the first arrangement, the first and second planar coils may be wound in the same direction from the first electrode to the second electrode about a winding axis perpendicular to a surface in which each coil lies and viewed from the same position outside the heating chamber and the first electrode of the first planar coil and the second electrode of the second planar coil may be connected by a center tap. The second electrode of the first planar coil and the first electrode of the second planar coil may be connected to one or more switching devices, e.g. field-effect transistors (FETs), such as metal-oxide-semiconductor field-effect transistors (MOSFETs). The first planar coil may be wound in a clockwise direction from the first electrode to the second electrode about a winding axis perpendicular to a surface in which the coil lies and viewed from a position outside the heating chamber and the second planar coil may be wound in a clockwise direction from the first electrode to the second electrode about the same winding axis and viewed from the same position outside the heating chamber. In this example, current flows in the first planar coil from the first electrode to the second electrode (i.e. in a clockwise direction) and in the second planar coil from the second electrode to the first electrode (i.e. in an anti-clockwise direction). 
     In a second arrangement, the electromagnetic field generator may be configured to supply electrical power to the first and second planar coils to cause current to flow in the first and second planar coils in the same direction, and in particular in the same direction between the first and second electrode of each planar coil. For example, the controller may be configured to supply electrical power from the power source to the first and second planar coils to cause current to flow in the first and second planar coils in the same direction, and in particular in the same direction between the first and second electrode of each planar coil. 
     In a first example of the second arrangement, the first and second planar coils may be wound in the same direction from the first electrode to the second electrode about a winding axis perpendicular to a surface in which each coil lies and viewed from the same position outside the heating chamber and the first electrodes of the first and second planar coils may be connected by a center tap. The second electrodes of the first and second planar coils may be connected to one or more switching devices, e.g. field-effect transistors (FETs), such as metal-oxide-semiconductor field-effect transistors (MOSFETs). The first planar coil may be wound in a clockwise direction from the first electrode to the second electrode about a winding axis perpendicular to a surface in which the coil lies and viewed from a position outside the heating chamber and the second planar coil may be wound in a clockwise direction from the first electrode to the second electrode about the same winding axis and viewed from the same position outside the heating chamber. In this example, current flows in the first planar coil from the first electrode to the second electrode (i.e. in a clockwise direction) and in the second planar coil from the first electrode to the second electrode (i.e. in a clockwise direction). 
     In a second example of the second arrangement, the first and second planar coils may be wound in the same direction from the first electrode to the second electrode about a winding axis perpendicular to a surface in which each coil lies and viewed from the same position outside the heating chamber and the second electrodes of the first and second planar coils may be connected by a center tap. The first electrodes of the first and second planar coils may be connected to one or more switching devices, e.g. field-effect transistors (FETs), such as metal-oxide-semiconductor field-effect transistors (MOSFETs). The first planar coil may be wound in a clockwise direction from the first electrode to the second electrode about a winding axis perpendicular to a surface in which the coil lies and viewed from a position outside the heating chamber and the second planar coil may be wound in a clockwise direction from the first electrode to the second electrode about the same winding axis and viewed from the same position outside the heating chamber. In this example, current flows in the first planar coil from the second electrode to the first electrode (i.e. in an anti-clockwise direction) and in the second planar coil from the second electrode to the first electrode (i.e. in an anti-clockwise direction). 
     In a third example of the second arrangement, the first and second planar coils may be wound in opposite directions from the first electrode to the second electrode about a winding axis perpendicular to a surface in which each coil lies and viewed from the same position outside the heating chamber and the first electrode of the first planar coil and the second electrode of the second planar coil may be connected by a center tap. The second electrode of the first planar coil and the first electrode of the second planar coil may be connected to one or more switching devices, e.g. field-effect transistors (FETs), such as metal-oxide-semiconductor field-effect transistors (MOSFETs). The first planar coil may be wound in a clockwise direction from the first electrode to the second electrode about a winding axis perpendicular to a surface in which the coil lies and viewed from a position outside the heating chamber and the second planar coil may be wound in an anti-clockwise direction from the first electrode to the second electrode about the same winding axis and viewed from the same position outside the heating chamber. In this example, current flows in the first planar coil from the first electrode to the second electrode (i.e. in a clockwise direction) and in the second planar coil from the second electrode to the first electrode (i.e. in a clockwise direction). 
     The planar coils 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 power source and the controller may be configured to operate at a high frequency. 
     The power source and controller 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. 
     The planar coils may comprise a Litz wire or a Litz cable. It will, however, be understood that other materials may be used to manufacture the planar coils. 
     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 generates heat due to eddy currents and/or magnetic hysteresis losses resulting in a conversion of energy from electromagnetic to heat. 
     The aerosol generating material may be 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 material may comprise plant derived material and in particular, may comprise tobacco. 
     The foam material may comprise a plurality of fine particles (e.g. tobacco particles) and can also comprise a volume of water and/or a moisture additive, such as a humectant. The foam material may be porous, and may allow a flow of air and/or vapour through the foam material. 
     The aerosol generating material 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 material may comprise an aerosol-former content of between approximately 5% and approximately 50% on a dry weight basis. In some embodiments, the aerosol generating material 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 material may release volatile compounds. The volatile compounds may include nicotine or flavour compounds such as tobacco flavouring. 
     According to a third aspect of the present disclosure, there is provided a plate-shaped aerosol generating article comprising aerosol generating material and an inductively heatable susceptor positioned in the aerosol generating material. 
     The plate-shaped aerosol generating article is particularly suitable for use with embodiments of the aerosol generating system/device defined above. In preferred embodiments, the aerosol generating material comprises a foam material or one or more aerosol generating sheets. 
     The inductively heatable susceptor may comprise a substantially planar susceptor element formed as an endless loop which lies in a flat plane. That is, the susceptor element may be formed as an endless loop in a direction that is parallel to the surface in which the susceptor element lies. The inductively heatable susceptor could advantageously comprise a plurality of said planar susceptor elements each formed as an endless loop. The plurality of planar susceptor elements could be distributed throughout the aerosol generating material, for example in the same plane. 
     The surface in which the or each susceptor element lies may be parallel to major surfaces of the aerosol generating article. Manufacture of the aerosol generating article is thereby facilitated. 
     In one embodiment, the or each loop may be polygonal, for example rectangular or square. In another embodiment, the or each loop may be curved and may, for example, comprise a loop with an oval or circular form. 
     The inductively heatable susceptor may comprise a plurality of strips of susceptor material. Each strip typically has two parallel major faces and two end faces. The strips may be arranged so that their major faces are substantially parallel to major surfaces of the aerosol generating article. The strips may be aligned with each other within the aerosol generating material such that the normal to a major face of each sheet or strip is directed in substantially the same direction. The strips may be spaced apart in the same plane between major edges of the aerosol generating article and/or may be arranged in multiple planes between major surfaces of the aerosol generating article. The use of susceptor strips may provide efficient heating and/or facilitate manufacture of the aerosol generating article. 
     The inductively heatable susceptor may comprise a particulate susceptor material. The use of particulate susceptor material may provide efficient heating and/or facilitate manufacture of the aerosol generating article. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic side view of a first example of an aerosol generating system; 
         FIG. 2  is a cross-sectional view along the line A-A in  FIG. 1 ; 
         FIGS. 3 to 8  are diagrammatic cross-sectional views of various examples of plate-shaped aerosol generating articles for use with the first example of the aerosol generating system illustrated in  FIGS. 1 and 2 , in which  FIGS. 3 b  to 8 b    are cross-sectional views respectively along the line A-A of  FIGS. 3 a  to 8 a    and  FIGS. 3 a  to 8 a    are also cross-sectional views of each plate-shaped aerosol generating article; 
         FIG. 9  is a diagrammatic side view of a second example of an aerosol generating system; 
         FIGS. 10 to 12  are cross-sectional views along the line A-A in  FIG. 9  of alternative configurations of the second example of the aerosol generating system; 
         FIGS. 13 a  to 13 d    are diagrammatic views of a first electrical arrangement of first and second planar coils, in which  FIG. 13 a    is a cross-sectional view along the line A-A in  FIG. 13 b   ,  FIG. 13 b    is a view in the direction of arrow B in  FIG. 13 a   , and  FIG. 13 c    and  FIG. 13 d    are perspective and side views respectively with an aerosol generating article positioned between first and second planar coils; and 
         FIGS. 14 a  to 14 d    are diagrammatic views of a second electrical arrangement of first and second planar coils, in which  FIG. 14 a    is a cross-sectional view along the line A-A in  FIG. 14 b   ,  FIG. 14 b    is a view in the direction of arrow B in  FIG. 14 a   , and  FIG. 14 c    and  FIG. 14 d    are perspective and side views respectively with an aerosol generating article positioned between first and second planar coils. 
     
    
    
     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  FIGS. 1 and 2 , there is shown diagrammatically a first embodiment of an aerosol generating system  1 . The aerosol generating system  1  comprises an aerosol generating device  10  and an aerosol generating article  24 . 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  comprises a heating chamber  22  having air inlets  22   a  and an air outlet  22   b . The heating chamber  22  is positioned at the proximal end  12  of the aerosol generating device  10  and is arranged to receive a plate-shaped aerosol generating article  24  including an aerosol generating material  26  and an inductively heatable susceptor  28 . The aerosol generating article  24  is a disposable article  24  which may, for example, contain tobacco as the aerosol generating material  26 . The heating chamber  22  is rectangular when viewed in cross-section as best seen in  FIG. 2  so that it can receive the plate-shaped aerosol generating article  24 . The heating chamber  22  has major surfaces  21  and side surfaces  23 . 
     The aerosol generating device  10  includes a plurality of air inlets  30  to deliver air to the air inlets  22   a  of the heating chamber  22 . The aerosol generating device  10  also comprises a mouthpiece  32  which is removably mountable on the device body  16  at the proximal end  12  and through which a user may inhale an aerosol generated during use of the device  10 . The mouthpiece  32  includes air outlets  34  which allow aerosol generated during use of the device  10  to flow from the heating chamber  22  via the air outlet  22   b  of the heating chamber  22  and into the mouth of a user. 
     The heating chamber  22  includes an opening  36 , accessible by removal of the mouthpiece  32 , through which a user can insert an aerosol generating article  24  into, and remove an aerosol generating article  24  from, the heating chamber  22  in a direction which is parallel with a longitudinal axis of the heating chamber  22 . In the illustrated embodiment, the opening  36  of the heating chamber  22  also serves as the air outlet  22   b  of the heating chamber  22 . The heating chamber  22  includes a plurality of projections  38  which extend from the major surfaces  21  and the side surfaces  23 . The projections  38  support an aerosol generating article  24  in the heating chamber  22  and create a space between the aerosol generating article  24  and the major surfaces  21  and side surfaces  23 , thereby providing an air flow path  25  around a surface of the aerosol generating article  24  between the air inlet  22   a  and the air outlet  22   b  of the heating chamber  22 . 
     The aerosol generating device  10  comprises an electromagnetic field generator  40  including a first planar coil  42  and a second planar coil  44 . In the embodiment illustrated in  FIGS. 1 and 2 , the first and second planar coils  42 ,  44  are flat coils positioned on opposite sides of the heating chamber  22  and outwardly of the major surfaces  21 . The first and second planar coils  42 ,  44  are arranged to generate electromagnetic fields that penetrate the heating chamber  22  in different directions, thus allowing improved coupling of the electromagnetic fields with the inductively heatable susceptor  28 . The inductively heatable susceptor  28  includes major surfaces  29   a ,  29   b  which are parallel with the major surfaces  21  of the heating chamber  22  and, hence, with the first and second planar coils  42 ,  44 , thereby ensuring that the major surfaces  29   a ,  29   b  are easily penetrated by, and coupled with, the electromagnetic fields generated by the first and second planar coils  42 ,  44 . 
     The first and second planar coils  42 ,  44  can be energised by the power source  18  and controller  20 . The controller  20  may include, 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 first and second planar coils  42 ,  44 . When the first and second planar coils  42 ,  44  are energised by the alternating high-frequency current, alternating and time-varying electromagnetic fields are produced that penetrate the heating chamber  22  in different directions. The electromagnetic fields couple with the inductively heatable susceptor  28  and generate eddy currents and/or hysteresis losses in the inductively heatable susceptor  28  causing it to heat up. The heat is then transferred from the inductively heatable susceptor  28  to the aerosol generating material  26 , for example by conduction, radiation and convection. 
     The heat transferred from the inductively heatable susceptor  28  to the aerosol generating material  26  causes it to heat up and thereby produce a vapour or aerosol. The aerosolisation of the aerosol generating material  26  is facilitated by the addition of air from the surrounding environment through the air inlets  30 ,  22   a  which flows through the heating chamber  22  along the airflow path  25  around the outer surface of the aerosol generating article  24 . The aerosol generated by heating the aerosol generating material  26  then exits the heating chamber  22 , through the air outlets  22   b ,  34 , and is inhaled by a user of the device  10  through the mouthpiece  32 . It will be understood that the flow of air through the heating chamber  22 , i.e. from the air inlets  30 ,  22   a  through the heating chamber  22  and out of the air outlets  22   b ,  34 , can be aided by negative pressure created by a user drawing air from the outlet side of the device  10  using the mouthpiece  32 . 
     Various examples of plate-shaped aerosol generating articles  24  for use with the aerosol generating device  10  are illustrated in  FIGS. 3 to 8  and will now be described in further detail. 
     In  FIGS. 3 a  and 3 b   , the aerosol generating article  24  includes an inductively heatable susceptor  28  in the form of a substantially planar susceptor element  46  positioned in the aerosol generating material  26 . The susceptor element  46  is formed as an endless rectangular loop. As will be apparent from  FIG. 3 b   , the surface in which the susceptor element  46  lies is substantially parallel to major surfaces  24   a ,  24   b  of the aerosol generating article  24 . Thus, the major surfaces  29   a ,  29   b  of the inductively heatable susceptor  28  are substantially parallel to the major surfaces  24   a ,  24   b  of the aerosol generating article  24 . 
     In  FIGS. 4 a  and 4 b   , the aerosol generating article  24  includes an inductively heatable susceptor  28  in the form of a substantially plate-shaped susceptor element  46  positioned in the aerosol generating material  26 . The major surfaces  29   a ,  29   b  of the inductively heatable susceptor  28  are substantially parallel to the major surfaces  24   a ,  24   b  of the aerosol generating article  24 . 
     In  FIGS. 5 a  and 5 b   , the aerosol generating article  24  includes an inductively heatable susceptor  28  in the form of a substantially planar susceptor element  46  positioned in the aerosol generating material  26 . The susceptor element  46  is formed as an endless elliptical (e.g. oval) loop. As will be apparent from  FIG. 5 b   , the surface in which the susceptor element  46  lies is substantially parallel to major surfaces  24   a ,  24   b  of the aerosol generating article  24 . Thus, the major surfaces  29   a ,  29   b  of the inductively heatable susceptor  28  are substantially parallel to the major surfaces  24   a ,  24   b  of the aerosol generating article  24 . 
     In  FIGS. 6 a  and 6 b   , the aerosol generating article  24  includes an inductively heatable susceptor  28  in the form of a plurality of substantially planar susceptor elements  46  positioned in the aerosol generating material  26 . Each susceptor element  46  is formed as an endless circular loop. As will be apparent from  FIG. 6 b   , the surface in which the susceptor elements  46  lie is substantially parallel to major surfaces  24   a ,  24   b  of the aerosol generating article  24 . Thus, the major surfaces  29   a ,  29   b  of the inductively heatable susceptor  28  are substantially parallel to the major surfaces  24   a ,  24   b  of the aerosol generating article  24 . 
     In  FIGS. 7 a  and 7 b   , the aerosol generating article  24  includes an inductively heatable susceptor  28  in the form of a plurality of strips  48  of susceptor material positioned in the aerosol generating material  26 . Each strip  48  has two substantially parallel major faces  48   a  and two end faces  48   b . The strips  48  are aligned with each other within the aerosol generating material  26  and are arranged so that their major faces  48   a  are substantially parallel to major surfaces  24   a ,  24   b  of the aerosol generating article  24 . The strips  48  are distributed throughout the aerosol generating material  26 , and in particular are spaced apart in substantially the same plane between major edges  24   c ,  24   d  of the aerosol generating article  24  (best seen in  FIG. 7 a   ) and arranged in multiple planes between major surfaces  24   a ,  24   b  of the aerosol generating article (best seen in  FIG. 7 b   ). 
     In  FIGS. 8 a  and 8 b   , the inductively heatable susceptor  28  comprises a particulate susceptor material which is distributed throughout the aerosol generating material  26 , between the major edges  24   c ,  24   d  of the aerosol generating article  24  (best seen in  FIG. 8 a   ) and between the major surfaces  24   a ,  24   b  of the aerosol generating article  24  (best seen in  FIG. 8 b   ). 
     Referring now to  FIGS. 9 to 12 , there is shown diagrammatically a second embodiment of an aerosol generating system  2 . The aerosol generating system  2  comprises an aerosol generating device  50  which is similar to the aerosol generating device  10  described above and in which corresponding elements are identified using the same reference numerals. 
     The heating chamber  22  has a curved cross-sectional shape and in the illustrated embodiment has a circular cross-section which is adapted to receive a cylindrical or rod-shaped aerosol generating article  52  having a corresponding circular cross-section. The aerosol generating article  52  includes a body  54  of aerosol generating material  26 , a hollow tubular member  56  positioned downstream of the body  54  of aerosol generating material  26  and a filter  58 , for example comprising cellulose acetate fibres, positioned downstream of the tubular member  56 . The body  54  of aerosol generating material  26 , the tubular member  56  and the filter  58  are wrapped by a sheet of material, for example a paper wrapper  60 , to maintain the positional relationship between component parts of the aerosol generating article  52 . 
     The aerosol generating article  52  includes an inductively heatable susceptor (not shown) positioned in the aerosol generating material  26 . The inductively heatable susceptor may extend along the longitudinal axis or longitudinal direction of the aerosol generating article  52 , for example from a first end to a second end, and may comprise a sheet or strip. The inductively heatable susceptor could comprise a tubular susceptor or particulate susceptor material distributed throughout the aerosol generating material  26 . 
     The aerosol generating article  52  is positioned in the heating chamber  22  by inserting the body  54  of aerosol generating material  26  into the heating chamber  22  via the opening  36 . The heating chamber  22  and aerosol generating article  52  are dimensioned so that the filter  58  projects from the heating chamber  22  at the proximal end  12  of the aerosol generating device  50 . 
     In a first configuration shown in  FIG. 10 , the aerosol generating device  50  includes an electromagnetic field generator  40  as described above with reference to  FIGS. 1 and 2 . Thus, the electromagnetic field generator  40  includes first and second planar coils  42 ,  44  positioned on opposite sides of the heating chamber  22  which are arranged to generate electromagnetic fields that penetrate the heating chamber  22  in different directions. 
     In a second configuration shown in  FIG. 11 , the aerosol generating device  50  includes an electromagnetic field generator  40  similar to that described above with reference to  FIGS. 1 and 2  but comprising four planar coils  41 ,  42 ,  43 ,  44  positioned around the heating chamber  22 . In this configuration, each of the planar coils  41 ,  42 ,  43 ,  44  is arranged to generate an electromagnetic field that penetrates the heating chamber  22  in different a direction from the other planar coils. In some embodiments, the planar coils  41 ,  42 ,  43 ,  44  may be activated sequentially by the controller  20 . The controller  20  may advantageously activate the planar coils in the sequence  41 : 43 : 42 : 44 , although it will be understood by one of ordinary skill in the art that any sequence may be adopted. 
     In a third configuration shown in  FIG. 12 , the aerosol generating device  50  includes an electromagnetic field generator  40  including first and second planar coils  62 ,  64  that lie on a curved plane which surrounds the heating chamber  22  and which follows the contour of the heating chamber  22 . The first and second planar coils  62 ,  64  are arranged to generate electromagnetic fields that penetrate the heating chamber  22  in different directions and may be formed by winding the coils in a flat Euclidean plane and thereafter bending the coils to lie on a curved plane. 
     Referring to  FIGS. 13 a  to 13 d   , there is shown a first electrical arrangement of first and second planar coils  42 ,  44  for use in the aerosol generating devices  10 ,  50  described above. The first planar coil  42  is illustrated in  FIGS. 13 a  and 13 b    and includes a first electrode  66   a  and a second electrode  68   a . The first planar coil  42  is wound in a clockwise direction as viewed in  FIG. 13 a    from the first electrode  66   a  to the second electrode  68   a . As best seen in  FIGS. 13 c  and 13 d   , the second planar coil  44  has a similar structure to the first planar coil  42  and includes first and second electrodes  66   b ,  68   b , but is wound in an anti-clockwise direction from the first electrode  66   b  to the second electrode  68   b , in other words in an opposite direction to the first planar coil  42 . The first and second planar coils  42 ,  44  are connected by a center tap  70 , and more particularly the first electrodes  66   a ,  66   b , are connected by the center tap  70  as shown in  FIGS. 13 c  and 13 d   . With this electrical arrangement, the controller  20  can be configured to activate the first and second planar coils  42 ,  44  alternately (i.e. one at a time), for example by switching MOSFETs connected to each second electrode  68   a ,  68   b . This causes current to flow in the first and second planar coils  42 ,  44  in opposite directions as indicted by the arrows in  FIG. 13 c   , and more particularly causes current to flow in a clockwise direction in the first planar coil  42  as viewed in  FIG. 13 c    from the first electrode  66   a  to the second electrode  68   a , and in an anti-clockwise direction in the second planar coil  44  as viewed in  FIG. 13 c    from the first electrode  66   b  to the second electrode  68   b . This provides a desired heating effect when an aerosol generating article  24  is positioned between the first and second planar coils  42 ,  44  as shown in  FIGS. 13 c  and 13 d   , for example in the heating chamber  22  of the aerosol generating device  10  described above. 
     Referring to  FIGS. 14 a  to 14 d   , there is shown a second electrical arrangement of first and second planar coils  42 ,  44  for use in the aerosol generating devices  10 ,  50  described above. The first planar coil  42 , illustrated in  FIGS. 14 c  and 14 d   , is as described above with reference to  FIGS. 13 a  to 13 d    and comprises first and second electrodes  66   a ,  68   a . The second planar coil  44  is similar to the first planar coil  42  shown in  FIGS. 14 c  and 14 d    but includes a capacitor  72  positioned between first and second electrodes  66   b ,  68   b . In this second electrical arrangement, the first planar coil  42  is an ‘active’ coil and the second planar coil  44  is a ‘passive’ coil. 
     In more detail, in operation the first planar coil  42  (‘active’ coil) is activated by the controller  20  by supplying electrical power from the power source  18  to the first and second electrodes  66 ,  68 . This generates an electromagnetic field that penetrates the heating chamber  22  in a first direction and inductively heats an inductively heatable susceptor  28  of an aerosol generating article  24  positioned between the first and second planar coils  42 ,  44  as shown in  FIGS. 14 c  and 14 d   , for example in the heating chamber  22  of the aerosol generating device  10  described above. During the period of activation of the first planar coil  42 , the capacitor  72  of the second planar coil  44  (‘passive’ coil) is charged. 
     The first planar coil  42  is then deactivated by the controller  20  and the capacitor  72  of the second planar coil  44  is discharged, thereby causing the second planar coil  44  to generate an electromagnetic field that penetrates the heating chamber  22  in a different direction to the electromagnetic field generated by the first planar coil  42 . The electromagnetic field generated by the second planar coil  44  inductively heats the inductively heatable susceptor  28  of the aerosol generating article  24  positioned between the first and second planar coils  42 ,  44  as shown in  FIGS. 14 c    and  14   d.    
     The first and second planar coils  42 ,  44  are activated repeatedly in the manner described above such that the capacitor  72  of the second planar coil  44  (‘passive’ coil) charges and discharges in counter-phase with the first planar coil  42  (‘active’ coil). 
     It will be understood by one of ordinary skill in the art that the electrical arrangements described above with reference to  FIGS. 13 and 14  are provided by way of example only and that other suitable electrical arrangements could be adopted. 
     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”.