Patent Publication Number: US-2018027882-A1

Title: Apparatus for generating an inhalable medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a National Phase entry of PCT Application No. PCT/EP2016/054232, filed Feb. 29, 2016, which claims priority from GB Patent Application No. 1503411.9, filed Feb. 27, 2015, and GB Patent Application No. 1517470.9, filed Oct. 2, 2015 each of which is hereby fully incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an apparatus and methods for generating an inhalable medium. 
     BACKGROUND 
     Smoking 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 articles that burn tobacco by creating products that release compounds without burning. 
     Examples of such products are heating devices which release compounds by heating, but not burning, the material. The material may be for example tobacco or other non-tobacco products, which may or may not contain nicotine. As another example, there are so-called e-cigarette devices. These devices typically contain a liquid which is heated to vaporize the liquid to produce an inhalable vapor or aerosol. The liquid may contain nicotine and/or flavorings and/or aerosol-generating substances, such as glycerol. The known e-cigarette devices typically do not contain or use tobacco. 
     SUMMARY 
     According to a first aspect of the present disclosure, there is provided an apparatus for generating an inhalable medium, the apparatus comprising: a liquid container for holding a liquid; a heater for volatilizing liquid held in the container; and a receiving portion for receiving a plurality of discrete material elements; the apparatus being arranged such that in use liquid volatized by the heater passes, in the form of at least one of a vapor and an aerosol, through one or more of the plurality of discrete material elements received by the receiving portion in use thereby to entrain one or more constituents of the one or more of the plurality of discrete material elements to produce the inhalable medium. 
     The container and the receiving portion may form an integral unit. 
     The receiving portion may be connectable to, and removable from, the liquid container. 
     The apparatus may be arranged such that the liquid volatized by the heater passes, in the form of at least one of a vapor and an aerosol, sequentially through each of the plurality of discrete material elements received by the receiving portion in use. 
     The apparatus may be arranged such that the liquid volatized by the heater passes, in the form of at least one of a vapor and an aerosol, simultaneously through each of the plurality of discrete material elements received by the receiving portion in use. 
     The apparatus may be arranged such that the liquid volatized by the heater flowing in the form of at least one of a vapor and an aerosol flows in a plurality of discrete streams, each stream for passing through a respective one of the plurality of discrete material elements received by the receiving portion in use. 
     The apparatus may be arranged to allow independent control of a flow of each discrete stream. 
     The independent control may comprise control to stop the flow of the vapor or aerosol through one or more of said plurality of discrete material elements whilst allowing the flow of the vapor or aerosol through one or more others of the plurality of discrete material elements. 
     The apparatus may comprise one or more retainers for retaining the plurality of material elements received by the receiving portion in use, wherein the one or more retainers are arranged so as to allow vapor or aerosol to pass there through. 
     The receiving portion may be arranged to allow user access to one or more of the plurality of discrete material elements received by the receiving portion in use. 
     The receiving portion may be arranged to allow one or more of: changing an order of one or more of the plurality of discrete material elements received by the receiving portion in use; adding one or more of the discrete material elements to the receiving portion; removing one or more of the discrete material elements from the receiving portion; and exchanging one or more of the plurality of discrete material elements received by the receiving portion in use for one or more other of the discrete material elements. 
     The receiving portion may have received therein a said plurality of discrete material elements. 
     The plurality of discrete material elements may be in an ordered arrangement. 
     Each of the plurality of discrete material elements may be the same. 
     One of the plurality of discrete material elements may have a property different to that of another of the plurality of discrete material elements. 
     Each one of the plurality of discrete material elements may have a property different to that of each other one of the plurality of discrete material elements. 
     The property may be one of aroma or flavor. 
     The plurality of discrete material elements may be stacked one on top of the other. 
     One or more of the plurality of discrete material elements may comprise material in solid form. 
     One or more of the plurality of discrete material elements may be a material in solid form, and the receiving portion may be a receptacle for receiving material in solid form. 
     A dimension of each of the plurality of discrete material elements relative to a dimension of the receptacle may be such that in use an ordered arrangement of the plurality of discrete material elements remains fixed. 
     The receptacle may comprise an inner portion and an outer portion, and the material in solid form may be annular in shape so as to be received between the inner portion and the outer portion. 
     Liquid volatized by the heater may pass, in the form of at least one of a vapor and an aerosol, from one of the inner portion and the outer portion, through the material in solid form, to the other one of the inner portion and the outer portion. 
     Each of the plurality of discrete material elements may be separated from one another by an impermeable membrane. 
     One or more of the discrete material elements may comprise: a material container for containing material; and material contained within the material container. 
     The material container may comprise a connector, and the receiving portion is for receiving the connector of the material container. 
     The material container may comprise a connector allowing connection of the material container to another such material container. 
     The material container may be annular in shape. 
     The material contained within the material container may be material in solid form. 
     The material in solid form may be or may comprise tobacco. 
     The material in solid form may be or may comprise a flavored solid material. 
     According to a second aspect of the present disclosure, there is provided a method of generating an inhalable medium using an apparatus comprising a container holding a liquid, a heater for volatizing the liquid, a plurality of discrete material elements, the method comprising: volatizing the liquid held in the container; and passing at least one of a vapor and an aerosol formed by the volatized liquid through one or more of said plurality of discrete material elements thereby to entrain one or more constituents of the one or more of said plurality of discrete material elements to produce the inhalable medium. 
     According to a third aspect of the present disclosure, there is provided a cartridge for use with an apparatus for generating an inhalable medium, the cartridge comprising: a container for holding a liquid; and a receiving portion for receiving a plurality of discrete material elements; the cartridge being arranged such that in use liquid exiting the container can flow, in the form of at least one of a vapor and an aerosol, through one or more of the plurality of discrete material elements received by the receiving portion in use, thereby to entrain one or more constituents of the one or more of the plurality of discrete material elements to produce the inhalable medium. 
     According to a fourth aspect of the present disclosure, there is provided a receptacle for receiving a plurality of discrete material elements, the receptacle being for use with an apparatus for generating an inhalable medium, the apparatus comprising a container for holding a liquid, the receptacle being arranged such that in use liquid exiting the container flowing in the form of at least one of a vapor and an aerosol can flow through one or more of the plurality of discrete material elements received by the receptacle in use, thereby to entrain one or more constituents of the one or more of the plurality of discrete material elements to produce the inhalable medium. 
     According to a fifth aspect of the present disclosure, there is provided a cap for use with an apparatus for generating an inhalable medium flowing in the form of one of a vapor and an aerosol, the cap comprising: a connecting portion for forming a seal between a mouthpiece of the apparatus and the cap; and a receiving portion for receiving material; the cap being arranged such that in use, the inhalable medium, flowing in the form of one of a vapor and an aerosol, can flow from the mouthpiece into the cap and through the material received by the receptacle, thereby to entrain one or more constituents of the material to produce the inhalable medium, into a mouth of a user. 
     The connecting portion may be shaped so as to allow the connecting portion to form a seal between the cap and any one of a plurality of different shaped or dimensioned mouthpieces. 
     The seal may be an air tight seal. 
     The connecting portion may be arranged such that the cap is removably connectable to the mouthpiece. 
     The connecting portion may comprise a tapered recess. 
     The recess may be tapered such that a diameter of the recess decreases from an open end of the recess to a closed end of the recess. 
     The recess may be a frustroconical recess. 
     The connecting portion may be or may comprise rubber. 
     The cap may be shaped so as to allow the connecting portion to form a seal between the cap and a further such cap. 
     The receiving portion may have material received therein. 
     The material may be material in solid form. 
     The solid material may be or may comprise tobacco. 
     The solid material may be or may comprise a solid flavored material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages will become apparent from the following description of embodiments of the disclosure, given by way of example only, which is made with reference to the accompanying drawings, in which: 
         FIG. 1  shows a schematic cross section of an exemplary apparatus containing an exemplary cartridge. 
         FIG. 2  shows a schematic cross-section of an exemplary cartridge. 
         FIG. 3  shows a schematic cross-section of some exemplary containers. 
         FIG. 4  shows a schematic cross-section of some exemplary containers. 
         FIG. 5  shows a schematic cross-section of some exemplary containers. 
         FIG. 6  shows a schematic flow path through some exemplary containers. 
         FIG. 7  shows a schematic cross-section of an exemplary receptacle. 
         FIG. 8  shows a schematic cross-section of some exemplary containers. 
         FIG. 9  shows a schematic cross-section of an exemplary cap. 
         FIG. 10  shows schematic cross-sections of an exemplary cap connected to a variety of mouthpieces. 
         FIG. 11  shows a schematic cross-section of an exemplary cap. 
         FIG. 12  shows a schematic cross-section of an exemplary cap. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a schematic cross-section of an example of an apparatus  1  for generating an inhalable medium is illustrated. In broad outline, the apparatus  1  volatilizes a liquid to form a vapor or an aerosol which passes through a plurality of discrete solid material elements so as to produce an inhalable medium that contains one or more constituents derived from the material. 
     In this respect, first it may be noted that, in general, a vapor is a substance in the gas phase at a temperature lower than its critical temperature, which means that for example the vapor can be condensed to a liquid by increasing its pressure without reducing the temperature. On the other hand, in general, an aerosol is a colloid of fine solid particles or liquid droplets, in air or another gas. A “colloid” is a substance in which microscopically dispersed insoluble particles are suspended throughout another substance. 
     Returning to  FIG. 1 , the apparatus  1  comprises an outer body  102  which houses a cartridge  104  and a battery  106 , and a mouthpiece  110  on which a user can draw. The cartridge  104  is connected to, but removable from, the battery  106 . At least a portion of the outer body  102  may be removed so as to expose the cartridge  104 , and hence allow installation, removal and/or replacement of the cartridge  104 . The cartridge  104  has a liquid container  132  for containing liquid  118  and a receiving portion  150  comprising a receptacle  114  for receiving a plurality of discrete solid material elements  124 ,  126 ,  128  (also referred to herein as material elements). 
     As described in more detail below, the material elements  124 ,  126 ,  128  may be, for example, self-supporting disks  124 ,  126 ,  128  of solid material permeable to aerosol or vapor, or comprise solid material packaged in a self-supporting container (not shown) that itself is permeable to aerosol or vapor. The solid material (also referred to herein as material in solid form) may be for example tobacco, or other flavored materials that may be used to create a desired taste or aroma, or have other properties, such as nicotine content. In one example, each material element  124 ,  126 ,  128  may comprise a solid material with a flavor, aroma, or other properties that are the same as the solid material of the other ones of the plurality of material elements  124 ,  126 ,  128 . For example, each of the plurality of material elements  124 ,  126 ,  128  may be the same. In this example, by controlling the number of material elements  124 ,  126 ,  128  that the vapor or aerosol passes through, a user can control the amplitude of the flavor or other properties of the solid material imparted to the inhalable medium produced by apparatus  1 . In another example, each material element  124 ,  126 ,  128  may comprise a solid material with a flavor, aroma, or other properties that are different from the solid material of other ones of the plurality of material elements  124 ,  126 ,  128 . For example, one of the plurality of material elements  124 ,  126 ,  128  may have a property (e.g. aroma, flavor, etc.) different to that of another of the plurality of material elements  124 ,  126 ,  128 , and/or each one of the plurality of material elements  124 ,  126 ,  128  may have a property different to that of each other one of the plurality of material elements  124 ,  126 ,  128 . In this example, the material elements  124 ,  126 ,  128  may therefore be combined in different ways to allow a user to customize the properties (e.g. flavor) of the inhalable medium produced by the apparatus  1 . In other examples, any combination of material elements  124 ,  126 ,  128  may be used, for example to customize the amplitude of any one or any combination of flavors or other properties of the plurality of material elements  124 ,  126 ,  128 . 
     In the example of  FIG. 1 , the receptacle  114  is integral to the cartridge  104 . The receptacle  114  comprises a first retainer  122  and a second retainer  112  to retain the plurality of material elements  124 ,  126 ,  128  within the receptacle  114 . The plurality of material elements  124 ,  126 ,  128  may be received in receptacle  114  in an ordered arrangement. For example, the plurality of material elements  124 ,  126 ,  128  may be manually inserted into the receptacle  114  in an ordered positional arrangement. The dimensions of the material elements  124 ,  126 ,  128  relative to the receptacle  114  may be such that, once inserted, the ordered positional arrangement of the material elements  124 ,  126 ,  128  may remain fixed unless a manual reordering of one or more of the material elements  124 ,  126 ,  128  is performed. In the example of  FIG. 1 , the plurality of material elements  124 ,  126 ,  128  are stacked one on top of the other, i.e. a second material element  126  is stacked on top of a first material element  128 , and a third material element  124  is stacked on top of the second material element. Although in the example of  FIG. 1  there are three material elements  124 ,  126 ,  128 , it will be appreciated that in some examples there may only be two material elements, and in other examples there may be N material elements, where N is any positive integer greater than or equal to  2 . The first and second retainers  112 ,  122  are permeable so as to allow gas phase material, such as vapor or an aerosol, to pass through, but to prevent material in the solid phase, such as material elements  128 ,  126 ,  124 , from passing through. For example, the first and second retainers  112 ,  122  may comprise a mesh made from metal or plastic or ceramic or rubber or the like, or a permeable membrane, or simply a disc with holes running there through. The retainers  112 ,  122  may be integral to the receptacle  114 , and hence may be integral to the cartridge itself. 
     In this example, the cartridge  104  is arranged so that as the liquid  118  is volatilized so as to produce an aerosol of liquid droplets or sufficiently heated to produce a vapor, at least some and, in some embodiments, all or substantially all of the aerosol or vapor passes through each of the plurality of material elements  124 ,  126 ,  128  sequentially, for example so as to pick up flavor from each material element  124 ,  126 ,  128 . 
     In this example, the liquid container  132  is provided generally centrally of the cartridge  104 . The liquid container  132  in the example shown is frustoconical in shape, but may have a different shape, such as conical, cylindrical, etc. The liquid container  132  is surrounded by an outer shell  134  which defines an annular channel  116  around the outside of the length of the liquid container  132  and which extends from one end of the liquid container  132  to the other. The liquid container  132  may be formed of rigid, watertight and airtight materials, such as metal, suitable plastics, etc. 
     The cartridge  104  is provided with a heater  130  and a wick  120  in (thermal) contact with the heater  130 . In this example, the heater  130  and the wick  120  are provided as a single unit. In this case, where the cartridge  104  includes a heater  130 , such a cartridge is often referred to as a “cartomizer.” The orientation of the heater  130  is shown schematically and, for example, the heater  130  may be a coil having its longitudinal axis perpendicular to the longitudinal axis of the cartridge  104  rather than parallel as shown in  FIG. 1 . The wick  120  is in contact with the liquid  118 . This may be achieved by, for example, the wick  120  being inserted through a through hole (not shown) in an end wall  136  of the liquid container  132 . Alternatively or additionally, the end wall  136  may be a porous member which allows liquid to pass through from the liquid container  132 , and the wick  120  may be in contact with the porous end wall  136 . The end wall  136  may be for example in the form of a porous ceramic disk. A porous end wall  136  of this type helps to regulate the flow of liquid onto the wick  120 . The wick  120  is generally absorbent and acts to draw in liquid  118  from the liquid container  132  by capillary action. The wick  120  can be non-woven and may be for example a cotton or wool material or the like, or a synthetic material, including for example polyester, nylon, viscose, polypropylene or the like, or a ceramic material. 
     In this example, the cartridge  104  is connected to the battery  106  to enable the heater  130  to be powered. When the heater  130  is powered (which may be instigated for example by the user operating a button of the apparatus  1  or by a puff detector of the overall apparatus, as is known per se), liquid  118  drawn in from the liquid container  132  by the wick  120  is heated by the heater  130  to volatilize or vaporize the liquid. As the user draws on the mouthpiece  110 , air is drawn through an air inlet (not shown). The liquid  118  is volatized or vaporized by the heater  130  into air from the air inlet (not shown) thereby to produce one of a vapor and an aerosol. The vapor or aerosol passes into the annular channel  116  around the outside of the length of the liquid container  132  as shown by arrows A. The vapor or aerosol is drawn towards the first retainer  122  of the receptacle  114 , and sequentially through the plurality of material elements  124 ,  126 ,  128 , as shown by arrow B. The vapor or aerosol picks up flavor (and/or other constituents) from each of the material elements  124 ,  126 ,  128 . In the case that the solid material of any one of the material elements  124 ,  126 ,  128  contains or includes nicotine, the vapor or aerosol may also contain nicotine entrained from that solid material. The vapor or aerosol can then exit through the second retainer  124  of the cartridge  104  and out through the mouthpiece  110  (as shown by arrow B). A one way valve (not shown) may be provided at or near either one of the first or second retainers  122 ,  124 , or at or near the mouthpiece  110  so that the vapor or aerosol can only exit the cartridge  104  and cannot back-flow to the heater  130  or the electronics (not shown) of the apparatus  1 . 
     The material elements  124 ,  126 ,  128  may be removable from the receptacle  114 . For example, the second retainer  112  may be removable so as to allow access to the material elements  124 ,  126 ,  128 . As another example, a portion of the cartridge  104  itself, for example a door or hatch like portion (not shown), may be removable so as to allow access to one or more of the material elements  124 ,  126 ,  128 . In such a way, a user may add, remove, or exchange one or more material elements  124 ,  126 ,  128  in the receptacle  114 . The material elements  124 ,  126 ,  128  may be manually inserted in the receptacle  114  in an ordered positional arrangement. A user may change the order of two or more of the plurality of material elements  124 ,  126 ,  128 . Optionally, the first retainer  112  (i.e. the upper retainer as drawn in  FIG. 1 ) may be omitted such that the plurality of material elements  124 ,  126 ,  128  are held in the receptacle  114  by only the second retainer  122  (i.e. the lower retainer as drawn in  FIG. 1 ) and, for example, gravity. Alternatively, the mouthpiece  110  or other component of the outer body  102  of apparatus  1  may be arranged so as to prevent the plurality of material elements  124 ,  126 ,  128  from falling out of receptacle when assembled, but allow the user access to the material elements  124 ,  126 ,  128  when the mouthpiece of portion of the outer body is removed. This allows a user easy access to the plurality of material elements. In other examples, the material elements  124 ,  126 ,  128  may not be removable from the receptacle  114 , and the cartridge  104  is disposable. 
     In the above example described with reference to  FIG. 1 , the receptacle  114  was integral to the cartridge  104 . However, this need not necessarily be the case. In other examples, the receptacle  114  is connectable to, and removable from, the cartridge  104 . 
       FIG. 2  illustrates a schematic cross section of an example cartridge  204  that may be used, for example, with apparatus  1  shown in  FIG. 1 , for example, in place of the cartridge  104  of  FIG. 1 . In the cartridge  204  shown in  FIG. 2 , a receptacle  214  is connectable to, and removable from, a receiving portion  250  of the cartridge  204 . For brevity, features in  FIG. 2  that do not differ from those features already described with reference to  FIG. 1  will not be described in detail again. 
     Referring now to the example of  FIG. 2 , a cartridge  204  comprises a receiving portion  250  which allows a receptacle  214  to be removably connected to the cartridge  204 . In this example, the receiving portion  250  is at an end of the cartridge opposite to the end comprising the heater. In this example, the receptacle  214  is annular in shape, and has received therein a plurality of material elements  224 ,  226 ,  228 . The plurality of material elements  224 ,  226 ,  228  are stacked one on top of the other, i.e. a second material element  226  is stacked on top of a first material element  228 , and a third material element  224  is stacked on top of the second material element  226 . The receptacle  214  comprises first retainer  222  and second retainer  212  for retaining the material elements  224 ,  226 ,  228  within the receptacle. The retainers  222 ,  212  allow vapor and aerosol to pass through them, but do not allow the material elements  224 ,  226 ,  228  to pass through them. In this example, the receptacle  214  is placed in, and removably connected to, the receiving portion  250  of the cartridge  204 . For example, the receiving portion  250  may comprise a thread (not shown) allowing a reciprocal thread (not shown) of the receptacle  114  to engage therewith. In other examples, a push fit or a snap fit or the like may be used between the receiving portion  250  and the receptacle  214 . 
     One or both of the retainers  222 ,  212  may be removable from the receptacle  214  so as to allow access to one or more of the plurality of material elements  224 ,  226 ,  228 , and hence to allow a user to add, remove, exchange one or more, or change the order of, of the material elements  224 ,  226 ,  228 , in the receptacle. In other examples, the retainers  222 ,  212  are not removable, and the receptacle  214  is disposable. The user may replace the entire receptacle  214 . 
     In this example, briefly, liquid  218  drawn in from a liquid container  232  by a wick  220  is heated by a heater  230  to volatilize or vaporize the liquid. As the user draws on a mouthpiece (not shown in  FIG. 2 ), air is drawn through an air inlet (not shown) and the liquid  218  is volatized or vaporized by the heater  230  into the air to produce one of a vapor and an aerosol. The vapor or aerosol passes into an annular channel  216  around the outside of the length of the liquid container  232  as shown by arrows A in  FIG. 2 . The vapor or aerosol is drawn towards and through the receiving portion  250 , through the first retainer  222  of the receptacle  214 , and sequentially through the plurality of material elements  224 ,  226 ,  228 , as shown by arrow B in  FIG. 2 . The vapor or aerosol picks up flavor (and/or other constituents) from each of the material elements  224 ,  226 ,  228 . The vapor or aerosol then exits through the second retainer  224  of the cartridge  104  (as shown by arrow B) for inhalation by the user. 
     In the above examples described with reference to  FIGS. 1 and 2 , the plurality of material elements  124 ,  126 ,  128 , etc., were received in a common receptacle  114 ,  214 , and were held in place by one or more retainers  122 ,  112 . However, this need not necessarily be the case. In other examples, each of the plurality of material elements  124 ,  126 ,  128  etc. are removably connectable to a receiving portion  250 , etc., of a cartridge  104  etc., and to each other. 
       FIGS. 3 and 4  illustrate a schematic cross section of an example plurality of material elements  324 ,  326 ,  328  that are removably connectable to a receiving portion  350  of a cartridge  304 . The cartridge  304  may, for example, be used in apparatus  1 , for example, instead of the cartridge  104  shown in  FIG. 1 . For brevity, features that do not differ from those already described with reference to  FIGS. 1 and 2  are not shown in  FIGS. 3 and 4  and will not be described again. 
     Referring to  FIGS. 3 and 4 , a cartridge  304  comprises a receiving portion  350  for receiving one of a plurality of material elements  324 ,  326 ,  328 . In this example, each of the material elements  324 ,  326 ,  328  comprises a self-supporting container  344 ,  346 ,  348  (respectively) that contains a solid material  364 ,  366 ,  368  (respectively). As best seen in  FIG. 4 , with reference to material element  326 , each container  346  comprises a first retainer  374  and a second retainer  372  for retaining the solid material  366  in the container  346 . The first and second retainers  374 ,  372  allow vapor or aerosol to flow there through, but do not allow solid material  366  to pass there through. Each material element  326  comprises a connector  378  for connecting the material element  326  to another material element. The connector  378  additionally allows each material element  326  to be connected to the receiving portion  350  of the cartridge  304 . The connectors  378  allow for the plurality of material elements  324 ,  326 ,  328  to be received in the receiving portion  350  in an ordered arrangement. The connectors  378  may be such that, once connected, the ordered position arrangement of the plurality of material elements  324 ,  326 ,  328  may remain fixed unless a manual reordering of one or more of the material elements  124 ,  126 ,  128  is performed. In the example shown in  FIG. 4 , each material element  326  comprises a male connection portion  378  and a corresponding female connection portion  376  on the opposite side of the material element to the male connection portion  378  to allow the material elements to be stacked. The receiving portion  350  may also comprise such a connecting portion  378 ,  376  to allow a material element  324 ,  326 ,  328  to be connected thereto. The connecting portions  378  and  376  may be any suitable connecting portions, for example reciprocal threads, reciprocal elements of a push fit or a snap fit or the like. 
     In this example, a male connecting portion  378  of a first material element  328  is inserted into a female connecting portion  376  of the receiving portion  350  of the cartridge  304  so as to connect (i.e. fluidically and mechanically connect) the first material element  328  to the receiving portion  350  and hence the cartridge  304 . The male connecting portion  378  of a second material element  326  is then inserted into the female connecting portion  376  of the first material element  328  so as to connect (i.e. fluidically and mechanically connect) the second material element  326  to the first material element  328 , and hence, via receiving portion  350 , to the cartridge  304 . Similarly, material element  324  may be connected to material element  326 . Similarly to as described above, when a user draws on a mouthpiece (not shown) therefore, vapor or an aerosol flows sequentially through each of the solid materials  364 ,  366 ,  368  contained in material elements  324 ,  326 ,  328  (respectively). Since the plurality of material elements  324 ,  326 ,  328  can be interchangeably stacked, a user can easily customize the flavor and/or other properties of the inhalable medium emanating therefrom. 
     In the above examples described above with reference to  FIGS. 1-4 , the vapor or aerosol flowed sequentially through the plurality of material elements  124 ,  126 ,  128  etc. However, this need not necessarily be the case. In other examples, the aerosol or vapor drawn from a cartridge  104  etc. flows through each material element  124 ,  126 ,  128 , etc., simultaneously. 
       FIG. 5  illustrates a schematic cross section of an example plurality of material elements  524 ,  526 ,  528  in which the aerosol or vapor drawn from a cartridge  504  flows through each material element simultaneously. The cartridge  504  may, for example, be used in apparatus  1  shown in  FIG. 1 , for example, in place of the cartridge  104  shown in  FIG. 1 . For brevity, features that do not differ from those features already described with reference to  FIGS. 1-4  are not shown in  FIG. 5  and will not be described again. 
     Referring to  FIG. 5 , a plurality of material elements  524 ,  526 ,  528  are connected together and are received in and connected to a receiving portion  550  of a cartridge  504 . Each of the material elements  524 ,  526 ,  528  are basically the same, except that they contain different solid materials (e.g. solid materials with different properties such as aroma, flavor etc.), although of course it will be appreciated that this need not necessarily be the case and instead, for example, two or more of the material elements  524 ,  526 ,  528  may contain the same solid material (e.g. solid materials with the same or similar properties such as aroma, flavor, etc.). For brevity, only the characteristics of material element  526  will be described. Material element  526  comprises a self-supporting container  546  that contains solid material  566  in a central cavity  592 . The container  546  also comprises an outer cavity  594  that surrounds the central cavity  592 . For example, the outer cavity  594  may be annular. The outer cavity  594  is divided into two portions  596 ,  598  such that vapor or aerosol in a first portion  596  of the outer cavity  594  must flow through the central cavity  594 , and hence solid material  566 , in order to reach the second portion  598  of the annular cavity  594 . 
     The material elements  524 ,  526 ,  528  are arranged such that vapor or aerosol in the first portion  596  of a first material element  528  may flow into the first portion  596  of a second material element  526  to which the first material element  528  is connected, but not the second portion  598  of the second material element  528 . Similarly, the material elements  524 ,  526 ,  528  are arranged such that vapor or aerosol in the second portion  598  of a first material element  528  may flow into the second portion  598  of a second material element  526  to which the first material element  528  is connected, but not the first portion  596  of the second material element  528 . 
     Similarly, for a material element  528  adjacent and connected to the receiving portion  550  of the cartridge  504 , the material element  528  is arranged such that vapor or aerosol from the cartridge  504  may only flow into the first portion  596  of the outer cavity  594  of the material element  528 , but not the second portion  598 . Similarly, for a material element  524  that is the furthest of the plurality of material elements  524 ,  526 ,  528  from the receiving portion  550  of the cartridge  504 , vapor or aerosol may flow out of the second portion  598  of the outer cavity  594  for inhalation by a user, but not out of the first portion  596 . 
     As shown by the arrows in  FIG. 5 , according to the above described arrangement, vapor or aerosol may be drawn from the cartridge  504 , split into a plurality of individual streams that flow simultaneously through a respective material element  524 ,  526 ,  528 , before being recombined and exiting the material elements for inhalation by a user. 
     In some examples, the relative flow of the vapor or aerosol through each of the plurality of material elements  124 ,  126 ,  128 , etc., may be controlled.  FIG. 6  illustrates schematically a flow path  601  in which vapor or aerosol may be controlled to flow at different rates through each different material element  624 ,  626 ,  628 . The flow path  601  comprises a branch  603  upstream of the material elements  624 ,  626 ,  628  that splits the vapor or aerosol flow into a plurality of discrete streams  605 ,  607 ,  609  each associated with each material element  624 ,  626 ,  628  (respectively). Each discrete stream  605 ,  607 ,  609  has a regulator X, Y, Z (respectively) that can regulate the flow of vapor or aerosol into the respective material element  624 ,  626 ,  628 . The regulators X,Y,Z can be independently controlled. For example, each regulator X,Y,Z may be adjustable by the user mechanically, for example via an adjustment lever (not shown) accessible to the user. The regulators X,Y,Z may be adjustable electronically, for example, by a user pressing one or more buttons, or interacting with an user interface, located on the outside of the overall apparatus (not shown). Alternatively or additionally, the user may control the regulators X,Y, Z via controls or an interface external to the overall apparatus (not shown), for example via radio control signals, or Bluetooth or the like from a separate control device, such as a smartphone or the like. The regulators X,Y,Z may take the form of a valve. As another example, the regulators X,Y,Z may each comprise a plurality of overlapping perforated plates, wherein as the plates move relative to each other, the perforations in the plates align or misalign so as to allow an increased or decreased flow through the plates accordingly. Being able to regulate the flow of vapor or aerosol through each one of the material elements  624 ,  626 ,  628  independently allows a user to further customize the properties (e.g. flavor) of the inhalable medium produced by an apparatus  1 . 
     In some examples, independent control of the streams comprises control to stop the flow of the vapor or aerosol through one or more of the material elements  624 ,  626 ,  628  whilst allowing the flow of the vapor or aerosol through one or more others of the material elements  624 ,  626 ,  628 . For example, the user may control the regulators X,Y,Z such that vapor or aerosol only flows through, say, one of the material elements (say,  624 ) and not through the other material elements  626 ,  628  etc. In such a way, a user may control the apparatus  1  such that, even though a plurality of material elements  624 ,  626 ,  628  are available, the vapor or aerosol only passes through one material element (say  624 ) at a time. The user may control the apparatus  1  so as to select on each puff (i.e. inhalation) which of the plurality of the material elements  624 ,  626 ,  628  the vapor or aerosol is to pass through and so may vary their taste experience from puff to puff. 
     There may also be a bypass channel (not shown in the figures) that bypasses all of the plurality of material elements, and the user may control the apparatus such that the vapor or aerosol passes through the bypass channel, and hence does not pass through any of the plurality of material elements  624 ,  626 ,  628 . 
     In one example of flow regulation, referring again to  FIG. 5 , the flow from the first portion  596  of the outer cavity  594  of the material element  526  into the central cavity  592  of the material element  526  may be regulated. Alternatively or additionally, the flow from the central cavity  592  of the material element  526  to the second portion  598  of the outer cavity  594  of the material element  526  may be regulated. In one example, similar regulation may be applied to each of the material elements  524 ,  526 ,  528  to allow a user to control the flow of vapor or aerosol through each of the material elements  524 ,  526 ,  528 , independently. 
     Other configurations of flow of the vapor or aerosol from the cartridge  104  etc., through the plurality of material elements  124 ,  126 ,  128  etc., and out for inhalation by a user may also be used. For example, the vapor or aerosol may flow out radially from the centre of a material element  124 ,  126 ,  128  etc. to an extremity of the material element  124 ,  126 ,  128 , etc. In a similar example, the vapor or aerosol may flow in radially from an extremity of the material element  124 ,  126 ,  128 , etc., to the center of the material element  124 ,  126 ,  128 , etc. 
       FIG. 7  illustrates schematically a cross-section of an example receptacle  714  received in a receiving portion  750  of a cartridge  704  wherein the vapor flows radially through the material elements  724 ,  726 ,  728 . The cartridge  704  shown in  FIG. 7  may be used, for example, in apparatus  1  shown in  FIG. 1 , for example, instead of the cartridge  104  shown in  FIG. 1 . For brevity, features that do not differ from those features already described with reference to  FIGS. 1-5  are not shown in  FIG. 7  and will not be described again. 
     Referring to  FIG. 7 , the receptacle  714  comprises an outer portion  731  and an inner portion  733 . The outer portion  731  is annular in shape, and allows for a plurality of material elements  724 ,  726 ,  728  to be received therein. The inner portion  733  is cylindrical in shape, and is placed centrally of the outer portion  731 , i.e. coaxially with the outer portion  731 . In order to be placed in the receptacle  714  therefore, each of the plurality of material elements  724 ,  726 ,  728  are also annular in shape, such that the inner portion  733  of the receptacle  714  is passed through a central hole (not shown) in each of the plurality of material elements  724 ,  726 ,  728 . The plurality of material elements  724 ,  726 ,  728  may be received in the receptacle  714  in an ordered arrangement. For example, the plurality of material elements  724 ,  726 ,  728  may be manually inserted into the receptacle  714  in an ordered positional arrangement. The dimensions of the material elements  724 ,  726 ,  728  relative to the receptacle  714  may be such that, once inserted, the ordered positional arrangement of the material elements  724 ,  726 ,  728  may remain fixed unless a manual reordering of one or more of the material elements  124 ,  126 ,  128  is performed. The outer portion  731  of the receptacle  714  comprises a first cavity  794  within the body of the outer portion  731  itself. The first cavity  794  opens at one end of the outer portion  731  to allow vapor or aerosol to flow into (or out of) the cavity  794 . An inner wall  735  of the outer portion  731  is arranged so as to allow vapor or aerosol to pass there through, but to prevent solid material passing there through. For example the inner wall  735  may be perforated or the like. The inner portion  733  of the receptacle  714  comprises a second cavity  796  that is open at one end to allow vapor or aerosol to flow out of (or into) the second cavity  796 . An outer wall  737  of the inner portion  733  of the receptacle  714  is arranged so as to allow vapor or aerosol to pass there through but to prevent solid material passing there through. 
     In the example illustrated in  FIG. 7 , as shown by the arrows in the figure, vapor or aerosol flows from the cartridge  704  into the first cavity of the outer portion  731  of the receptacle  714 . The vapor or aerosol then flows through the inner wall  735  of the outer portion  731  of the receptacle, inwardly, radially, and simultaneously through the plurality of material elements  724 ,  726 ,  728 , through the outer wall  737  of the inner portion  733  of the receptacle  714 , and into the second cavity  796  of the inner portion  722 . The vapor or aerosol then exits the second cavity  796  of the inner portion  722  for inhalation by a user. 
     Although in the example illustrated in  FIG. 7 , the vapor flows inwardly through the material elements  724 ,  726 ,  728  from the outer portion  731  to the inner portion  733  of the receptacle  714 , in other examples the receptacle  714  may be arranged such that the vapor or aerosol flows outwardly through the material elements  724 ,  726 ,  728  for inhalation by a user. 
     Each material element  724 ,  726 ,  728  may be separated by an impermeable membrane (not shown), i.e. a membrane impermeable to gas, vapor, aerosol, solid, liquid, or the like. This impermeable membrane (not shown) may, for example, take the form of a thin annular disc (not shown) or the like placed over the inner portion  733  of the receptacle  714 , and separating each material element  724 ,  726 ,  728  from another of the plurality of material elements  724 ,  726 ,  728 . For example, in the example of  FIG. 7 , a second material element  726  is stacked on top of a first material element  728 , and a third material element  724  is stacked on top of the second material element  726 . In this example, there may be an impermeable membrane (not shown) placed between the first material element  728  and the second material element  726 , and another impermeable membrane between the third material element  724  and the second material element  726 . The impermeable membrane prevents mixing of the material elements  724 ,  726 ,  728  with one another. The impermeable membrane (not shown) may be, for example, made from any suitably impermeable material, for example, plastic, rubber or the like. 
     In the example illustrated in  FIG. 7 , the annular material elements  724 ,  726 ,  728  are received in a receptacle  714 . However, in other examples, the material elements may comprise annular self-supporting containers for containing solid material, each of which can be received in (and removably connected to) the receiving portion of the cartridge, and removably connectable to each other. 
       FIG. 8  illustrates a schematic cross section of an example plurality of annular material elements  824 ,  826 ,  828  comprising respective annular containers  844 ,  846 ,  848  for containing respective solid material  864 ,  866 ,  868 . In the example of  FIG. 8 , aerosol or vapor drawn from a cartridge  804  flows, in separate streams, radially through each material element  824 ,  826 ,  828 . The cartridge  804  may be, for example, used in apparatus  1  shown in  FIG. 1 , for example, in place of the cartridge  104  shown in  FIG. 1 . For brevity, features that do not differ from those features already described with reference to  FIGS. 1-7  are not shown in  FIG. 8  and will not be described again. 
     Referring to  FIG. 8 , the annular containers  844 ,  846 ,  848  are connected together and are received in and connected to a receiving portion  850  of the cartridge  804 . Each of the containers  844 ,  846 ,  848  are basically the same, except that (in this example) they contain different solid materials, although of course it will be appreciated that this need not be the case and instead, for example, two or more of the containers  844 ,  846 ,  848  may contain the same solid or contain solid materials with the same or similar properties (e.g. flavor, aroma, etc.). Each container  844 ,  846 ,  848 , for example container  846 , comprises an inner annular cavity  892  for containing solid material, and an outer annular cavity  894  surrounding the inner annular cavity  892 . The inner annular cavity  892  itself surrounds an inner cylindrical cavity  896 . The outer annular cavity  894  and the inner annular cavity  892  are separated by a permeable retainer that allows vapor or aerosol, but not solid material, to pass there through. Similarly, the inner annular cavity  892  and the inner cylindrical cavity  896  are separated by a permeable retainer that allows vapor or aerosol, but not solid material, to pass there through. In the example illustrated in  FIG. 8 , the containers  844 ,  846 ,  848  are connected so as to be stacked one on top of the other. When the annular containers  844 ,  846 ,  848  are connected together, the inner cylindrical cavity  896  of each annular container  844 ,  846 ,  848  combine to form a central cylindrical cavity  840  along their longitudinal axis along which vapor or aerosol can flow. Also, when the annular containers  844 ,  846 ,  848  are connected together, the outer annular cavity  894  of each annular container  844 ,  846 ,  848  connect together so that vapor or aerosol can flow there between. However, when the annular containers  844 ,  846 ,  848  are connected together, the inner annular cavity  896  of each container  844 ,  846 ,  848  do not connect together, and are separated by an impermeable membrane that does not allow vapor or aerosol or solid material to pass there through. 
     As shown by the arrows in the figure, according to the above described arrangement, vapor or aerosol flows from the cartridge  804  into the outer annular cavity  894  of each of the containers  844 ,  846 ,  848 . For each of the containers  844 ,  846 ,  848 , an individual stream of the vapor or aerosol flows radially inwardly from the outer annular cavity  894 , through the inner annular cavity  892  (and hence the solid material contained therein), to the inner cylindrical cavity  896 . The separate vapor or aerosol streams from each of containers  844 ,  846 ,  848  combine in the central cylindrical cavity  840  and then exit the central cylindrical cavity for inhalation by a user. 
     Although in the example illustrated in  FIG. 8 , the vapor flows radially inwardly from the outer annular cavity  894 , through the inner annular cavity  892  (and hence the solid material contained therein), to the inner cylindrical cavity  896 , in other examples the containers  844 ,  846 ,  848  and/or the receiving portion  850  and/or the cartridge  804  may be arranged such that the vapor or aerosol flows radially outwardly from the inner cylindrical cavity  896 , through the inner annular cavity  892  (and hence the solid material contained therein), to the outer annular cavity  894  and then on for inhalation by a user. In this example, it will be appreciated that the outer annular cavity  894  may be omitted, and the vapor or aerosol may simply flow out the inner annular cavity  892  for inhalation by the user. 
     Although the examples above referred to use of the plurality of material elements  124 ,  126 ,  128 , etc., with a cartridge  104  etc., it will be readily appreciated that there are many configurations of so called e-cigarettes (some of which not having cartridges as such, but rather, for example, refillable chambers integral to the apparatus  1 ) and that the above examples may also be applied to these other configurations. Indeed, the flow of a vapor or aerosol through a plurality of material elements  124 ,  126 ,  128 , etc., as described above may be independent of the configuration of the source of that vapor or aerosol. 
       FIG. 9  shows a schematic cross section of an exemplary cap  20  placed over a mouthpiece  22  of an apparatus for generating an inhalable medium such as. The apparatus may be, for example, an e-cigarette similar to or the same as apparatus  1  described above, or indeed any e-cigarette. 
     The cap  20  comprises a connecting portion  28  for connecting to the mouthpiece  22  and a receiving portion  30  for receiving solid material  24 . The connecting portion  28  is shaped so as to allow the connecting portion  28  to form a seal, for example, an air tight seal, between the cap  20  and any one of a plurality of mouthpieces  22 . The connecting portion  28  allows the cap  20  to be connected to a mouthpiece  22  such that the cap  20  does not become detached from the mouthpiece  22  for example when a user draws on the cap  20  in use to inhale an inhalable medium, but does become detached from the mouthpiece  22  for example when a user intentionally pulls the cap  20  away from the mouthpiece  22  so as to remove it. In this example, the cap  20  is frustroconical in shape. The connecting portion  28  of the cap  20  comprises a frustroconical recess  26  for receiving the mouthpiece  22  therein and forming a seal between the cap  20  and the mouthpiece  22 , for example an airtight seal. The connecting portion  28  may be made, for example, from rubber, or plastic, or any material suitable for forming an airtight seal between the connecting portion  28  and the mouthpiece  22 . The connecting portion  28  is such so as to allow the cap  20  to be removable from the mouthpiece  22 . 
     The receiving portion  30  may have received therein a solid material, such as tobacco, or any material that may impart flavor or other constituents to vapor or aerosol passing there through. The receiving portion may be integral to the cap  20 , and the solid material  24  therein may not be accessible or replaceable by a user. The cap  20  may therefore be disposable. Alternatively, the receiving portion  30  may be arranged so as to allow a user access to the solid material  24 , and hence allow a user to add, remove, or exchange the solid material  24  received therein. The cap  20  may therefore be reusable. The receiving portion  30  is arranged so as to allow vapor or aerosol emanating from the mouthpiece  22  to pass from the recess  26 , through the solid material  32 , and out of a first end  32  of the cap  20  for inhalation by a user (as illustrated by the arrow in  FIG. 9 ). For example, the receiving portion may comprise a container with perforated walls (not shown) that allow vapor or aerosol to pass there through, but not allow the solid material  24  to pass there through. The receiving portion may have received therein a plurality of discrete solid material elements (not shown), such as self-supporting portions of solid material, or solid material contained in a container arranged so as to allow vapor or aerosol to pass there through, but not to allow the solid material to pass there through. 
     Different caps  20  that each contain a different solid material or plurality of solid material elements (and hence each imparting different flavors or other properties, such as nicotine content, to the vapor or aerosol passing there through) may be available, hence allowing a user to easily customize their experience. Multiple caps  20  may be placed one on top of the other (not shown), each forming an airtight seal with adjacent caps, so as to allow the flavor or other constituent properties imparted by the caps to the vapor or aerosol passing there through to be easily combined. 
     The frustroconical recess  26  of the connecting portion  28  of the cap  20  allows the cap  20  to be connected universally to any one of a variety of different shapes of mouthpiece  22  or a variety of mouthpieces of the same general shape but of different sizes.  FIG. 10  illustrates schematically how an exemplary cap  20  with a frustroconical recess  26  may be connected so as to form a seal, for example an air tight seal, with a mouthpiece  34  that itself is conical or frustroconical in shape, with a mouthpiece  36  that is cylindrical in shape, and with a mouthpiece  38  with a bulbous end  40 . Essentially the decreasing diameter of the frustroconical recess  26  from the opening of the recess  26  towards the receiving portion  30  allows the cap  20  to be lowered (pushed) onto a mouthpiece  38  until the diameter of the mouthpiece matches the diameter of the recess  26 , hence allowing a seal, for example an air tight seal, to be formed. 
     It will be appreciated that the recess  26  need not necessarily be frustroconical in shape, and may be instead any tapered recess in which the diameter of the recess  26  decreases from the opening of the recess  26  towards the receiving portion  30  of the cap  20 , for example, a cone, a dome, a pyramid, a frustro-pyramid, or the like. 
     Moreover, it will be appreciated that the cap  20  need not be frustroconical in shape.  FIGS. 11 and 12  illustrate schematically cross sections of alternative caps  50 ,  60  that comprise a tapered recess (in this example a frustroconical recess), but are not in themselves frustroconical in shape. 
     Referring to  FIG. 11 , the cap  50  comprises connecting portion  56  and receiving portion  501 . The receiving portion  501  is cylindrical in shape, and the connecting portion  56  is frustroconical in shape. The connecting portion  56  comprises a frustroconical recess  56  allowing the cap  50  to be placed on a mouthpiece (not shown) so as to form an airtight seal between the connecting portion  58  and the mouthpiece (not shown). 
     Referring to  FIG. 12 , the cap  60  comprises connecting portion  66  and receiving portion  601 . The receiving portion  601  is cylindrical in shape, and the connecting portion  66  is cylindrical in shape. The connecting portion  66  comprises a frustroconical recess  56  allowing the cap  60  to be placed on a mouthpiece (not shown) so as to form an airtight seal between the connecting portion  68  and the mouthpiece (not shown). 
     A number of other variations and alternatives to the examples described above are possible. 
     For example, in some cases it may be possible for the plurality of solid material elements to be located, exclusively or additionally, in the mouthpiece of the apparatus (battery section, etc.) with which the cartridge described above is used. 
     As another example, the plurality of material elements may be selectively omitted from the receptacle, for example at the option of the user. This provides the user with more flexibility. 
     It is described above that the channel  116 ,  216 , etc., is annular and completely surrounds the liquid container  132 ,  232 , etc. In other examples, the channel is not annular and does not surround the liquid container  132 ,  232 , etc. For example, there may be a single, substantially tubular channel or groove extending from the liquid container  132 ,  232 , etc. As another example, there may be plural channels or grooves extending from the liquid container  132 ,  232 , etc., one or more of which may be substantially tubular. Where there are plural channels, it is possible for the channels to lead to a separate one or more of the plurality of material elements. 
     In some of the examples above, the liquid container and the plurality of material elements or receptacle are arranged substantially in-line, along a longitudinal axis of the apparatus or cartridge. In other examples, the liquid container and the material elements or receptacle are arranged so as to at least partially overlap in the longitudinal direction of the apparatus or cartridge; in such examples, the liquid container and the material elements or receptacle may still be arranged generally in-line along the longitudinal axis of the apparatus or cartridge, or may be arranged side by side, or with one partially or completely inside the other. In yet other examples, the liquid container and the material elements or receptacle are arranged concentrically (either with the liquid container inside the material elements or receptacle or vice versa), and may be arranged to be entirely off-set with respect to each other along the longitudinal axis of the apparatus or cartridge, or overlapping, or one completely within the other. 
     The liquid can be a liquid that is volatilizable at reasonable temperatures, such as in the range of 100-300° C. or more particularly around 150-250° C., as that helps to keep down the power consumption of the apparatus with which the cartridge is used. Suitable materials include those conventionally used in e-cigarette devices, including for example propylene glycol and glycerol (also known as glycerine). Also as described in relation to the examples above, the solid material is a material that may be used to impart a flavor (or other constituent) to the aerosol or vapor produced from the liquid as the aerosol or vapor passes through the material. For example, the material may comprise constituents that impart cooling sensations, heating sensations, nutraceutical benefits, stimulating benefits or produce or induce any other sensation or benefit in the user. The material may for example consist of or comprise tobacco. As the aerosol or vapor passes through and over the tobacco material, the aerosol or vapor entrains organic and other compounds or constituents from the tobacco material that lend tobacco its organoleptic properties, thus imparting the flavor to the aerosol or vapor as it passes to the mouthpiece. Materials other than tobacco may be used to impart different flavors to the aerosol or vapor stream. For example, materials other than tobacco may be blended with tobacco, or blends of other materials such as, for example, vanilla pods, star anise, mint leaves, other herbs, and the like. Flavorants may be included in the material or in the liquid or both. 
     In any of the examples described above, an apparatus controller may control operation of the apparatus as a whole. The controller for example may cause the heater to be powered as and when required and switch off the heater when heating is not required. Operation of the heater may be controlled so that the liquid and/or material is heated to an optimum temperature. Particular considerations include ensuring that the solid material does not burn, ensuring that adequate vaporization of the liquid is achieved, ensuring that the vaporized liquid or aerosol is at an appropriate temperature to liberate compounds from the solid material, and ensuring that the vapor or aerosol that reaches the user is at a comfortable and safe temperature. A puff detector, a device which is known per se, may be provided to signal to the controller when the heating elements need to be energized. The apparatus may also have one or more filters for filtering the vapor or aerosol before it reaches the user, cooling arrangements for cooling the vapor or aerosol before it reaches the user, insulation internally of the apparatus to protect the user from the heat generated inside the housing, etc. 
     Heating of the material may encourage release of the constituents of the solid material into the vapor or aerosol passing there through. In use, the material may be heated by the vapor or aerosol that passes through the solid material. Alternatively or additionally, the solid material may be heated using a dedicated heater, for example an electro-resistive heater or an induction heater separate to the heater that heats the liquid. The use of an induction heater allows the material to be heated quickly, such that, for example, the solid material can be heated to a sufficient temperature to encourage release of constituents thereof within the duration of a draw of the user. The dedicated heater may, for example, surround the solid material or the receptacle/container in which it is received. For example, particularly in the case that the solid material is tobacco, the tobacco, or at least the surface of the tobacco, can be heated to a temperature of between around 190° C. to 210° C., such as around 200° C., so as to ensure that an adequate or appropriate amount of the compounds are released from the tobacco. The heating of the material may comprise pre-heating. In the case of pre-heating, the material, particularly in the case of tobacco, may be pre-heated to a temperature in the range of around 100 to 150° C. It will be appreciated however that other temperatures may be used. For example, the solid material, or at least the tobacco in contact with the heater, may be heated to a temperature above 210° C., such as up to around 230° C. or 240° C. or so and even as high as 290° C. or so. The amount of tobacco present may be for example in the range 50 to 300 mg or so. A most suitable value for the amount of tobacco may be for example in the range 50 to 150 mg, with 130 mg being a value that is currently found to be particularly suitable in some applications. In a typical example, the amount of tobacco that is heated per operation of the apparatus (i.e. per puff) may be in the corresponding range of around 8 to 50 mg. The function of dedicated heater may be independently controllable by the user from other functions of the overall apparatus, for example to allow the user to control whether or not, or to what extent, the material is pre-heated or heated by the dedicated heater. 
     In use, the liquid may be heated to a temperature of between around 100-300° C. or more particularly around 150° C. to 250° C. Suitable materials  14 , etc., include materials that provide volatilized components upon heating, typically in the form of an aerosol. Suitable solid materials include any tobacco-containing material and may, for example, include one or more of tobacco per se, different varieties of tobacco, tobacco derivatives, pelletized tobacco, extruded tobacco, expanded tobacco, reconstituted tobacco, ground tobacco, tobacco extract, homogenized tobacco or tobacco substitutes. In the case of tobacco, the solid material may be in the form of a rod of tobacco, a pod or plug of tobacco, loose tobacco, agglomerates, etc., and may be in relatively dry form or in relatively moist form for example. The tobacco may have been modified, for example chemically modified, for example had its pH modified so as to promote the release of selected constituents of the tobacco such as nicotine. Suitable solid materials may include other, non-tobacco, products, which, depending on the product, may or may not contain nicotine. In some examples, the receptacle or container for the solid material is transparent, so that the user can see the contents (i.e. the solid material) in use, which is appealing to some users. The tobacco rod may be formed using a transparent material as a wrapping material, again so that the user can see the tobacco. A particularly suitable material is NatureFlex™, a biodegradable film made from renewable raw materials by Innovia Films Limited. 
     As used herein, the terms “flavor” and “flavorant” refer to materials which, where local regulations permit, may be used to create a desired taste or aroma in a product for adult consumers. They may include extracts (e.g., licorice, hydrangea, Japanese white bark magnolia leaf, chamomile, fenugreek, clove, menthol, Japanese mint, aniseed, cinnamon, herb, wintergreen, cherry, berry, peach, apple, Drambuie, bourbon, scotch, whiskey, spearmint, peppermint, lavender, cardamom, celery, cascarilla, nutmeg, sandalwood, bergamot, geranium, honey essence, rose oil, vanilla, lemon oil, orange oil, cassia, caraway, cognac, jasmine, ylang-ylang, sage, fennel, piment, ginger, anise, coriander, coffee, or a mint oil from any species of the genus Mentha), flavor enhancers, bitterness receptor site blockers, sensorial receptor site activators or stimulators, sugars and/or sugar substitutes (e.g., sucralose, acesulfame potassium, aspartame, saccharine, cyclamates, lactose, sucrose, glucose, fructose, sorbitol, or mannitol), and other additives such as charcoal, chlorophyll, minerals, botanicals, or breath freshening agents. They may be imitation, synthetic or natural ingredients or blends thereof. They may be in any suitable form, for example, oil, liquid, or powder. For example, a liquid, oil, or other such fluid flavorant may be impregnated in a porous solid material so as to impart flavor and/or other properties to that porous solid material. As such, the liquid or oil is a constituent of the solid material in which it is impregnated. 
     Each discrete material element may have, for example, a volume in the range of 100 mm 3  to 1200 mm 3 , such as in the range of 150 mm 3  to 800 mm 3  or 200 mm 3  to 800 mm 3 , and more particularly in the range 150 mm 3  to 500 mm 3 . 
     Each discrete material element may have, for example, a mass in the range of 20 mg to 600 mg, such as in the range of 40 mg to 300 mg and more particularly in the range 60 mg to 200 mg. 
     Although in the above examples, the material was described as being a solid material or material in solid form, this need not necessarily be the case. In other examples, the material may be a fluid, such as a liquid. 
     The above embodiments are to be understood as illustrative examples of the invention. 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.