Patent Publication Number: US-2022232896-A1

Title: Aerosol provision device

Description:
PRIORITY CLAIM 
     The present application is a National Phase entry of PCT Application No. PCT/EP2020/065886, filed Jun. 8, 2020, which claims priority from GB Patent Application No. 1908194.2, filed Jun. 7, 2019, each of which is hereby fully incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an aerosol provision device, a method of generating an aerosol using the aerosol provision device, and an aerosol-generating system comprising the aerosol provision device. 
     BACKGROUND 
     Articles such as cigarettes, cigars and the like burn tobacco during use to create tobacco smoke. Attempts have been made to provide alternatives to these types of articles, which burn tobacco, by creating products that release compounds without burning. Apparatus is known that heats smokable material to volatilize at least one component of the smokable material, typically to form an aerosol which can be inhaled, without burning or combusting the smokable material. Such apparatus is sometimes described as a “heat-not-burn” apparatus or a “tobacco heating product” (THP) or “tobacco heating device” or similar. Various different arrangements for volatilizing at least one component of the smokable material are known. 
     The material may be, for example, tobacco or other non-tobacco products or a combination, such as a blended mix, which may or may not contain nicotine. 
     SUMMARY 
     According to a first aspect of the present disclosure, there is provided an aerosol provision device for generating aerosol from aerosol-generating material, the device comprising: a heating chamber for receiving the aerosol-generating material; at least one heating unit for heating the aerosol-generating material during a session of use; and an aperture, which fluidically connects the heating chamber with the exterior of the aerosol provision device; wherein the aperture is non-circular and has a smallest dimension, as measured through the centroid of the aperture, of less than or equal to 0.65 mm. 
     According to a second aspect of the present disclosure, there is provided an aerosol provision device for generating aerosol from aerosol-generating material, the device comprising: a heating chamber for receiving the aerosol-generating material; at least one heating unit for heating the aerosol-generating material during a session of use; and an aperture, which fluidically connects the heating chamber with the exterior of the aerosol provision device; wherein the aperture has a perimeter of less than or equal to 3.40 mm. 
     According to a third aspect of the present disclosure, there is provided an aerosol provision device for generating aerosol from aerosol-generating material, the device comprising: a housing; a heating chamber, located within the housing, for receiving the aerosol-generating material; at least one inductive heating unit for heating the aerosol-generating material during a session of use; and an aperture, which fluidically connects the heating chamber with the exterior of the aerosol provision device; wherein the aperture has an area of less than or equal to 0.65 mm 2 . 
     According to a fourth aspect of the present disclosure, there is provided an aerosol provision device for generating aerosol from aerosol-generating material, the device comprising: a housing; a heating chamber, located within the housing, for receiving the aerosol generating material; at least one inductive heating unit for heating the aerosol-generating material during a session of use; and a plurality of apertures, the or each fluidically connecting the heating chamber with the exterior of the aerosol provision device; wherein the plurality of apertures has a total combined area of less than 4.00 mm 2 . 
     Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a front view of an example of an aerosol provision device. 
         FIG. 2  shows an enlarged cross-sectional view of a heating assembly within an aerosol provision device. 
         FIG. 3  shows a plan view of a door of the aerosol provision device of  FIG. 1 . 
         FIG. 4  shows a front view of the aerosol provision device of  FIG. 1  with an outer cover removed. 
         FIG. 5  shows a cross-sectional view of the aerosol provision device of  FIG. 1 . 
         FIG. 6  shows an exploded view of the aerosol provision device of  FIG. 4 . 
         FIG. 7A  shows a cross-sectional view of a heating assembly within an aerosol provision device. 
         FIG. 7B  shows a close-up view of a portion of the heating assembly of  FIG. 7A . 
     
    
    
     DETAILED DESCRIPTION 
     To facilitate formation of an aerosol in use, aerosol-generating material for aerosol-provision devices (e.g. tobacco heating products) usually contains more water and/or aerosol-generating agent than the smokeable material within combustible smoking articles. This higher water and/or aerosol-generating agent content can increase the risk of condensate collecting within the aerosol-provision device during use, particularly in locations away from the heating unit(s). 
     The inventors consider that this problem may be greater in devices with enclosed heating chambers. In some such devices, the heating chamber may be fluidically connected, in parallel, with the exterior of the device by several apertures, which may, for example, regulate the flow of air into the device. 
     Having studied the results of tests of devices having such apertures, the inventors consider that the apertures may be a significant contributing factor to the collection of condensate within the device. Furthermore, the inventors foresee a risk that any condensate that does accumulate within the device may leak out through the apertures, with such leakage inconveniencing the user of the device. 
     However, the inventors have determined that suitably configured apertures may reduce the risk of such leakage of condensate from the device. 
     In this regard, reference is directed to  FIG. 1 , which is a front view of an example of an aerosol provision device  100  for generating aerosol from an aerosol-generating medium/material. In broad outline, the device  100  may be used to heat a replaceable article  110  comprising the aerosol-generating medium, to generate an aerosol or other inhalable medium which is inhaled by a user of the device  100 . 
     The device  100  comprises a housing  102  (in the form of an outer cover) which surrounds and houses various components of the device  100 . The device  100  has an opening  104  in one end, through which the article  110  may be inserted for heating by a heating assembly. In use, the article  110  may be fully or partially inserted into the heating assembly where it may be heated by one or more components of the heater assembly. 
       FIG. 2  depicts a cross-sectional view of the heating assembly and neighboring components within the device  100  of  FIG. 1 . As shown, the device  100  includes a heating chamber  101  for receiving the aerosol-generating material  110   a . The device  100  additionally includes a number of apertures  141 . As is apparent, the apertures  141  fluidically connect, in parallel, the heating chamber  101  with the exterior of the device  100 . 
     Apertures  141  may provide suitable impedance to the flow of air into the device, so as to regulate the flow of air through the device  100 . However, such impedance may equally increase the risk that condensate collects within the device  100 , for example in inlet conduit  103 . Additionally, as mentioned above, there is a risk that such accumulated condensate leaks from the device, inconveniencing the user. Nonetheless, by configuration of the device  100 , in accordance with any of the aspects of this disclosure, the risk of condensate leaking from the device  100  may be substantially reduced. 
     As also shown in  FIG. 2 , the device  100  includes two heating units  161 ,  162  for heating the aerosol-generating material  110   a . Although the illustrated example includes two heating units  161 ,  162 , it should be understood that this is by no means essential and the device  100  could include only one heating unit, or could include three or more heating units, as appropriate. 
     The inventors have studied the results of tests of devices of similar construction to the device  100  of  FIGS. 1 and 2 . Based on these test results, the inventors foresee a particular risk that condensate collects within the device  100 . A possible contributing factor is that, in many cases, for condensate-forming substances to exit the device  100  would involve them travelling in the opposite direction to the flow of air through the apertures  141  and into the device  100  during use. An additional contributing factor is that the apertures  141 , which fluidically connect the inlet conduit  103  with the exterior of the device, offer resistance or impedance to the flow of air into the device, so as to regulate the flow of air through the device  100 ; however, such resistance/impedance hinders the exit of condensate-forming substances from the inlet conduit  103 , through the apertures  141 . 
     Moreover, as noted above, where condensate does accumulate within the device, there is a risk that it leaks out of the device, inconveniencing the user. 
     Nonetheless, by studying the test results, the inventors believe that they have determined suitable approaches for configuring the apertures  141  to reduce the risk of condensate leaking from the device  100 . 
     According to a first approach, the apertures  141  of the device  100  may be configured so as to be non-circular and to each have a smallest dimension (as measured through the centroid of the aperture in question) of less than or equal to 0.65 mm. Testing indicates that devices with such apertures are effective at preventing the leakage of condensate. 
     Without wishing to be bound by the theory, it is hypothesized that the fluidic resistance forces that inhibit condensate from passing through a given aperture may, in at least some cases, be related to the smallest dimension of the aperture, for example because this smallest dimension is indicative of capillary forces. A device having non-circular apertures with a smallest dimension of less than or equal to 0.65 mm may therefore, potentially as a result of such capillary forces, provide a suitable level of impedance to retain condensate within the device. On the other hand, the aperture&#39;s other dimensions may be selected so as to provide a suitable area for the aperture, for example so as to achieve a desired level of impedance to air flow. 
     Based on experimental results, the inventors consider that, in many cases, a smallest dimension of less than or equal to 0.625 mm may be sufficient to cause a significant reduction in the risk of leakage of condensate. Nonetheless, in some cases, the apertures may be configured with a smallest dimension of less than or equal to 0.60 mm. 
     According to a second approach, the apertures  141  of the device  100  may be configured so as to have a perimeter of less than or equal to 3.40 mm. Testing indicates that devices with such apertures are effective at preventing the leakage of condensate. Again, without wishing to be bound by the theory, it is hypothesized that, in many cases, the frictional forces experienced by liquid passing through a given aperture may be related to the perimeter of the aperture. Accordingly, apertures with relatively small perimeters may be effective at preventing the leakage of condensate. 
     Based on experimental results, the inventors consider that, in many cases, a perimeter of less than or equal to 3.40 mm may be sufficient to cause a significant reduction in the risk of leakage of condensate. Nonetheless, in some cases, the apertures may be configured with a perimeter of less than or equal to 3.25 mm, in other cases less than or equal to 3.00 mm. 
     According to a third approach, the apertures  141  of the device may be configured so as to have an area of less than or equal to 0.65 mm 2 . Testing indicates that devices with such apertures are effective at preventing the leakage of condensate. Again, without wishing to be bound by the theory, it is hypothesized that the ability of liquid to pass through a given aperture may be inversely related to the area of that aperture because, where a given pressure is present within a liquid (e.g. as a result of gravity), and that pressure is applied over a smaller area, a smaller total force is imparted on the fluid. Accordingly, apertures with relatively small areas may be effective at preventing the leakage of condensate. 
     Based on experimental results, the inventors consider that, in many cases, an area of less than or equal to 0.65 mm 2  may be sufficient to cause a significant reduction in the risk of leakage of condensate. Nonetheless, in some cases, the apertures may be configured with an area of less than or equal to 0.60 mm 2 , in other cases less than or equal to 0.55 mm 2 . It will be appreciated that combinations of the above approaches may be employed when configuring a given aperture. For example, apertures might be configured so as to each have a smallest dimension of less than or equal to 0.65 mm and/or a perimeter of less than or equal to 3.40 mm and/or an area of less than or equal to 0.65 mm 2 . 
     Returning now to  FIG. 2 , it may be noted that, in the particular example device shown, the heating units  161 ,  162  are inductive heating units. Inductive heating units may provide rapid heating of aerosol-generating material. However, the inventors consider such rapid heating may be a risk factor for the accumulation of condensate, for example because inductive heating units may generate condensate-forming substances at a greater rate than they can be carried away through apertures  141 . 
     In the particular example device  100  shown in  FIG. 2 , each inductive heating unit  161 ,  162  comprises a respective coil  124 ,  126  and a respective heating element  134 ,  136 . In the particular example shown, the electrically-conductive heating elements  134 ,  136  of the two heating units  161 ,  162  correspond to respective sections of a single metal tube  132 . However, in other examples, each heating element may be a separate and distinct structure. 
     In general, the coil of an inductive heating unit may, for example, be configured to cause heating of one or more electrically-conductive heating elements, for instance so that heat energy is conductible from such electrically-conductive heating elements to aerosol-generating material to thereby cause heating of the aerosol-generating material. An inductive heating unit may be configured to cause the coil to generate a varying magnetic field for penetrating the at least one heating element, to thereby cause induction heating of the at least one heating element. In the device  100  shown in  FIG. 2 , the coil  124 ,  126  of each inductive heating unit  161 ,  162  causes heating of its corresponding electrically-conductive heating element  134 ,  136 . Each heating element  134 ,  136  then conducts heat to the aerosol-generating material  110   a.    
     As will be appreciated, heating units other than induction heating units might be employed in other examples. For instance, the device might include one or more resistive heating units. As an example, a resistive heating unit could be substituted for each of inductive heating units  161 ,  162 . A resistive heating unit may comprise (or consist essentially of) one or more resistive heating elements. By “resistive heating element”, it is meant that on application of a voltage to the element, current flows within the element, with electrical resistance in the element transducing electrical energy into thermal energy which heats the aerosol-generating substrate. A resistive heating element may, for example, be in the form of a resistive wire, mesh, coil and/or a plurality of wires. The heat source may be a thin-film heater. 
     As is also apparent from  FIG. 2 , the particular device  100  shown additionally includes an inlet conduit  103 , which fluidically connects the heating chamber  101  with the exterior of the device  100 . During use, air may be drawn into the device  100 , through the apertures  141 , before flowing along inlet conduit  103  and later into heating chamber  101 . Thus, the apertures  141  fluidically connect, in parallel, the inlet conduit  103  (as well as heating chamber  101 ) with the exterior of the device  100 . 
     It may additionally be noted that, in the specific example shown in  FIG. 2 , the distal end of the inlet conduit  103  is adjacent the apertures  141  and thus each aperture  141  opens, on one side, to the distal end of the inlet conduit  103 , and, at an opposite side, to the exterior of the device  100 . 
     Reference is now directed to  FIG. 3  which is a plan view of the part of the device  100  in which apertures  141  are formed; that part of the device is a door but it could be any other component. 
     In the particular example shown, the device  100  includes six apertures  141 . However, any suitable number of apertures could be included as a plurality of apertures; for instance, some embodiments might have as few as four apertures, whereas other embodiments might have as many as eight or ten apertures  141 . Alternatively, a single aperture could be provided. 
     As illustrated in  FIG. 3 , the apertures  141  may be distributed circumferentially about a longitudinal axis  1035  of the inlet conduit  103 . More particularly, the apertures  141  are arranged in a ring-shaped array. In the example shown, the center of the ring-shaped array is defined by an axis  1035  of the inlet conduit  103 , optionally a longitudinal axis of the inlet conduit  103 . 
     As is apparent from  FIG. 3 , in the particular example shown  3 , the apertures  141  are spaced substantially equidistantly. This may, for example, ensure a smooth and stable flow of air into the device  100 . However, this is by no means essential and in other embodiments groups of the apertures  141  could be clustered together. 
     As is also apparent from  FIG. 3 , each aperture  141  has a largest dimension  143 , as measured through the centroid of the aperture, that is directed generally circumferentially (i.e. it lies in a direction that is closer to a circumferential direction than to a radial direction, as defined relative to the longitudinal axis  1035  of the inlet conduit  103 ). Such an arrangement may, for example, tend to cause in-flowing air to adopt a helical flow pattern, which may, in some cases, lead to a smooth and stable flow of air into the device  100 . The largest dimension  143  may be less than or equal to 1.20 mm, as measured through the centroid of the aperture. 
     It may further be noted that each of the apertures  141  is shaped as a regular polygon. However, in other embodiments the apertures  141  could be shaped as irregular polygons. 
     Furthermore, while each aperture  141  in the device of may have substantially the same shape, this is by no means essential and in other embodiments two or more groups of apertures could be provided, where all the apertures in a group have substantially the same shape. Where there is only one aperture, it could be shaped as described above. 
     Reference is next directed to  FIGS. 4-7B , which illustrate various features of the construction and operation of the devices of  FIGS. 1-3 . 
     Turning first to  FIG. 4 , as shown, the device  100  may comprise a first end member  106  which comprises a lid  108  which is moveable relative to the first end member  106  to close the opening  104  when no article  110  is in place. In  FIG. 1 , the lid  108  is shown in an open configuration, however the lid  108  may move into a closed configuration. For example, a user may cause the lid  108  to slide in the direction of arrow “A”. 
     The device  100  may also include a user-operable control element  112 , such as a button or switch, which operates the device  100  when pressed. For example, a user may turn on the device  100  by operating the switch  112 . 
     The device  100  may also comprise an electrical component, such as a socket/port  114 , which can receive a cable to charge a battery of the device  100 . For example, the socket  114  may be a charging port, such as a USB charging port. 
       FIG. 4  depicts the device  100  of  FIG. 1  with the outer cover  102  removed and without an article  110  present. The device  100  defines a longitudinal axis  180 . 
     As shown in  FIG. 4 , the first end member  106  is arranged at one end of the device  100  and a second end member  116  is arranged at an opposite end of the device  100 . The first and second end members  106 ,  116  together at least partially define end surfaces of the device  100 . For example, the bottom surface of the second end member  116  at least partially defines a bottom surface of the device  100 . Edges of the outer cover  102  may also define a portion of the end surfaces. In this example, the lid  108  also defines a portion of a top surface of the device  100 . 
     The end of the device closest to the opening  104  may be known as the proximal end (or mouth end) of the device  100  because, in use, it is closest to the mouth of the user. In use, a user inserts an article  110  into the opening  104 , operates the user control  112  to begin heating the aerosol-generating material and draws on the aerosol generated in the device. This causes the aerosol to flow through the device  100  along a flow path towards the proximal end of the device  100 . 
     The other end of the device furthest away from the opening  104  may be known as the distal end of the device  100  because, in use, it is the end furthest away from the mouth of the user. As a user draws on the aerosol generated in the device, the aerosol flows away from the distal end of the device  100 . 
     The device  100  may further comprise a power source  118 . The power source  118  may be, for example, a battery, such as a rechargeable battery or a non-rechargeable battery. Examples of suitable batteries include, for example, a lithium battery (such as a lithium-ion battery), a nickel battery (such as a nickel-cadmium battery), and an alkaline battery. The battery is electrically coupled to the heating assembly to supply electrical power when required and under control of a controller (not shown) to heat the aerosol-generating material. In this example, the battery is connected to a central support  120  which holds the battery  118  in place. 
     The device may further comprise at least one electronics module  122 . The electronics module  122  may comprise, for example, a printed circuit board (PCB). The PCB  122  may support at least one controller, such as a processor, and memory. The PCB  122  may also comprise one or more electrical tracks to electrically connect together various electronic components of the device  100 . For example, the battery terminals may be electrically connected to the PCB  122  so that power can be distributed throughout the device  100 . The socket  114  may also be electrically coupled to the battery via the electrical tracks. 
     As noted above, in the example device  100 , the heating assembly is an inductive heating assembly and comprises various components to heat the aerosol-generating material  110   a  via an inductive heating process. Induction heating is a process of heating an electrically conducting object (such as a susceptor) by electromagnetic induction. An induction heating assembly may comprise an inductive element, for example, one or more inductor coils, and a device for passing a varying electric current, such as an alternating electric current, through the inductive element. The varying electric current in the inductive element produces a varying magnetic field. The varying magnetic field penetrates a susceptor suitably positioned with respect to the inductive element, and generates eddy currents inside the susceptor. The susceptor has electrical resistance to the eddy currents, and hence the flow of the eddy currents against this resistance causes the susceptor to be heated by Joule heating. In cases where the susceptor comprises ferromagnetic material such as iron, nickel or cobalt, heat may also be generated by magnetic hysteresis losses in the susceptor, i.e. by the varying orientation of magnetic dipoles in the magnetic material as a result of their alignment with the varying magnetic field. In inductive heating, as compared to heating by conduction for example, heat is generated inside the susceptor, allowing for rapid heating. Further, there need not be any physical contact between the inductive heater and the susceptor, allowing for enhanced freedom in construction and application. 
     The induction heating assembly of the example device  100  comprises a susceptor arrangement  132  (herein referred to as “a susceptor”), a first inductor coil  124  and a second inductor coil  126 . The first and second inductor coils  124 ,  126  are made from an electrically conducting material. In this example, the first and second inductor coils  124 ,  126  are made from Litz wire/cable which is wound in a helical fashion to provide helical inductor coils  124 ,  126 . Litz wire comprises a plurality of individual wires which are individually insulated and are twisted together to form a single wire. Litz wires are designed to reduce the skin effect losses in a conductor. In the example device  100 , the first and second inductor coils  124 ,  126  are made from copper Litz wire which has a rectangular cross section. In other examples the Litz wire can have other shape cross sections, such as circular. 
     The first inductor coil  124  is configured to generate a first varying magnetic field for heating a first section  134  of the susceptor  132  and the second inductor coil  126  is configured to generate a second varying magnetic field for heating a second section  136  of the susceptor  132 . Thus, as discussed above with reference to  FIG. 2 , first inductor coil  124  and first section  134  of susceptor  132  may be considered part of a first heating unit  161 , in which first section  134  of susceptor  132  acts as a heating element, generating heat that is transferred to the aerosol-generating material. By contrast, second inductor coil  126  and second section  136  of susceptor  132  may be considered part of a second heating unit  162 , in which second section  136  of susceptor  132  acts as a heating element, generating heat that is transferred to the aerosol-generating material. 
     In the example shown in  FIG. 4 , the first inductor coil  124  is adjacent to the second inductor coil  126  in a direction along the longitudinal axis  180  of the device  100  (that is, the first and second inductor coils  124 ,  126  to not overlap). The susceptor arrangement  132  may comprise a single susceptor, or two or more separate susceptors. Ends  130  of the first and second inductor coils  124 ,  126  can be connected to the PCB  122 . 
     It will be appreciated that the first and second inductor coils  124 ,  126 , in some examples, may have at least one characteristic different from each other. For example, the first inductor coil  124  may have at least one characteristic different from the second inductor coil  126 . More specifically, in one example, the first inductor coil  124  may have a different value of inductance than the second inductor coil  126 . In  FIG. 2 , the first and second inductor coils  124 ,  126  are of different lengths such that the first inductor coil  124  is wound over a smaller section of the susceptor  132  than the second inductor coil  126 . Thus, the first inductor coil  124  may comprise a different number of turns than the second inductor coil  126  (assuming that the spacing between individual turns is substantially the same). In yet another example, the first inductor coil  124  may be made from a different material to the second inductor coil  126 . In some examples, the first and second inductor coils  124 ,  126  may be substantially identical. 
     In this example, the first inductor coil  124  and the second inductor coil  126  are wound in opposite directions. This can be useful when the inductor coils are active at different times. For example, initially, the first inductor coil  124  may be operating to heat a first section/portion of the article  110 , and at a later time, the second inductor coil  126  may be operating to heat a second section/portion of the article  110 . Winding the coils in opposite directions helps reduce the current induced in the inactive coil when used in conjunction with a particular type of control circuit. In  FIG. 4 , the first inductor coil  124  is a right-hand helix and the second inductor coil  126  is a left-hand helix. However, in another embodiment, the inductor coils  124 ,  126  may be wound in the same direction, or the first inductor coil  124  may be a left-hand helix and the second inductor coil  126  may be a right-hand helix. 
     The susceptor  132  of this example is hollow and therefore defines a heating chamber  101  within which aerosol-generating material is received. For example, the article  110  can be inserted into the susceptor  132 . In this example the susceptor  120  is tubular, with a circular cross section. 
     The susceptor  132  may be made from one or more materials. Optionally, the susceptor  132  comprises carbon steel having a coating of Nickel or Cobalt. 
     In some examples, the susceptor  132  may comprise at least two materials capable of being heated at two different frequencies for selective aerosolization of the at least two materials. For example, a first section of the susceptor  132  (which is heated by the first inductor coil  124 ) may comprise a first material, and a second section of the susceptor  132  which is heated by the second inductor coil  126  may comprise a second, different material. In another example, the first section may comprise first and second materials, where the first and second materials can be heated differently based upon operation of the first inductor coil  124 . The first and second materials may be adjacent along an axis defined by the susceptor  132 , or may form different layers within the susceptor  132 . Similarly, the second section may comprise third and fourth materials, where the third and fourth materials can be heated differently based upon operation of the second inductor coil  126 . The third and fourth materials may be adjacent along an axis defined by the susceptor  132 , or may form different layers within the susceptor  132 . Third material may the same as the first material, and the fourth material may be the same as the second material, for example. Alternatively, each of the materials may be different. The susceptor may comprise carbon steel or aluminum for example. 
     The device  100  of  FIG. 4  further comprises an insulating member  128  which may be generally tubular and at least partially surround the susceptor  132 . The insulating member  128  may be constructed from any insulating material, such as plastic for example. In this particular example, the insulating member is constructed from polyether ether ketone (PEEK). The insulating member  128  may help insulate the various components of the device  100  from the heat generated in the susceptor  132 . 
     The insulating member  128  can also fully or partially support the first and second inductor coils  124 ,  126 . For example, as shown in  FIG. 4 , the first and second inductor coils  124 ,  126  are positioned around the insulating member  128  and are in contact with a radially outward surface of the insulating member  128 . In some examples the insulating member  128  does not abut the first and second inductor coils  124 ,  126 . For example, a small gap may be present between the outer surface of the insulating member  128  and the inner surface of the first and second inductor coils  124 ,  126 . 
     In a specific example, the susceptor  132 , the insulating member  128 , and the first and second inductor coils  124 ,  126  are coaxial around a central longitudinal axis of the susceptor  132 . 
       FIG. 5  shows a cross-sectional view of device  100 . The outer cover  102  is present in this example. The rectangular cross-sectional shape of the first and second inductor coils  124 ,  126  is more clearly visible. 
     The device  100  further comprises inlet conduit support component  131  which, in the particular example illustrated, engages one end of the susceptor tube  132  to hold the susceptor tube  132  in place. The inlet conduit support component  131  is connected to the second end member  116 . 
     The device may also comprise a second printed circuit board  138  associated within the control element  112 . 
     The device  100  further comprises a second lid/cap  140  and a spring  142 , arranged towards the distal end of the device  100 . The spring  142  allows the second lid  140  to be opened, to provide access to the susceptor tube  132 . A user may open the second lid  140  to clean the susceptor tube  132  and/or the interior surface of inlet conduit  103 . 
     The device  100  further comprises an expansion chamber  144  which extends away from a proximal end of the susceptor  132  towards the opening  104  of the device. Located at least partially within the expansion chamber  144  is a retention clip  146  to abut and hold the article  110  when received within the device  100 . The expansion chamber  144  is connected to the end member  106 . 
       FIG. 6  is an exploded view of the device  100  of  FIG. 1 , with the outer cover  102  omitted. 
       FIG. 7A  depicts a cross-section of a portion of the device  100  of  FIG. 4 .  FIG. 7B  depicts a close-up of a region of  FIG. 7A .  FIGS. 7A and 7B  show the article  110  received within the susceptor  132 , where the article  110  is dimensioned so that the outer surface of the article  110  abuts the inner surface of the susceptor  132 . This ensures that the heating is most efficient. The article  110  of this example comprises aerosol-generating material  110   a . The aerosol-generating material  110   a  is positioned within the susceptor  132 . The article  110  may also comprise other components such as a filter, wrapping materials and/or a cooling structure. 
       FIG. 7B  shows that the outer surface of the susceptor  132  is spaced apart from the inner surface of the inductor coils  124 ,  126  by a distance  150 , measured in a direction perpendicular to a longitudinal axis  158  of the susceptor  132 . In one particular example, the distance  150  is about 3 mm to 4 mm, about 3-3.5 mm, or about 3.25 mm. 
       FIG. 7B  further shows that the outer surface of the insulating member  128  is spaced apart from the inner surface of the inductor coils  124 ,  126  by a distance  152 , measured in a direction perpendicular to a longitudinal axis  158  of the susceptor  132 . In one particular example, the distance  152  is about 0.05 mm. In another example, the distance  152  is substantially 0 mm, such that the inductor coils  124 ,  126  abut and touch the insulating member  128 . 
     In one example, the susceptor  132  has a wall thickness  154  of about 0.025 mm to 1 mm, or about 0.05 mm. 
     In one example, the susceptor  132  has a length of about 40 mm to 60 mm, about 40 mm to 45 mm, or about 44.5 mm. 
     In one example, the insulating member  128  has a wall thickness  156  of about 0.25 mm to 2 mm, 0.25 mm to 1 mm, or about 0.5 mm. 
     “Session of use” as used herein refers to a single period of use of the aerosol-provision device by a user. The session of use begins at the point at which power is first supplied to at least one heating unit present in the heating assembly. The device will be ready for use after a period of time has elapsed from the start of the session of use. The session of use ends at the point at which no power is supplied to any of the heating elements in the aerosol-provision device. The end of the session of use may coincide with the point at which the smoking article is depleted (the point at which the total particulate matter yield (mg) in each puff would be deemed unacceptably low by a user). The session will have a duration of a plurality of puffs. Said session may have a duration less than 7 minutes, or 6 minutes, or 5 minutes, or 4 minutes and 30 seconds, or 4 minutes, or 3 minutes and 30 seconds. In some embodiments, the session of use may have a duration of from 2 to 5 minutes, or from 3 to 4.5 minutes, or 3.5 to 4.5 minutes, or suitably 4 minutes. A session may be initiated by the user actuating a button or switch on the device, causing at least one heating element to begin rising in temperature. 
     The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.