Patent Publication Number: US-2019191780-A1

Title: Apparatus for heating smokable material

Description:
PRIORITY CLAIM 
     The present application is a National Phase entry of PCT Application No. PCT/EP2017/065908, filed Jun. 27, 2017, which claims priority from Provisional Application No. 62/356,334, filed Jun. 29, 2016, each of which is hereby fully incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an apparatus for heating smokable material to volatilize at least one component of the smokable material, to heating elements for use with such an apparatus, to articles for use with such an apparatus, to systems comprising such an apparatus and such articles, and to methods of heating smokable material to volatilize at least one component of the smokable material. 
     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 by creating products that release compounds without combusting. Examples of such products are so-called “heat not burn” products or tobacco heating devices or products, which release compounds by heating, but not burning, material. The material may be, for example, tobacco or other non-tobacco products, which may or may not contain nicotine. 
     SUMMARY 
     A first aspect of the present disclosure provides a heating element for use with an apparatus for heating smokable material to volatilize at least one component of the smokable material, the heating element formed from heating material that is heatable by penetration with a varying magnetic field, wherein first and second portions of the heating element have different respective thermal masses. 
     In an exemplary embodiment, the thermal mass of the heating element varies with distance along the heating element. 
     In an exemplary embodiment, the thermal mass of the heating element varies over at least a majority of a length of the heating element. 
     In an exemplary embodiment, the thermal mass of the heating element reduces continuously with distance along the heating element. 
     In an exemplary embodiment, the thermal mass of the heating element reduces linearly with distance along the heating element. 
     In an exemplary embodiment, the first and second portions of the heating element have different respective thermal masses as a result of a density of the first portion of the heating element being different to a density of the second portion of the heating element. 
     In an exemplary embodiment, the first and second portions of the heating element have different respective thermal masses as a result of a thickness of the first portion of the heating element being different to a thickness of the second portion of the heating element. 
     In an exemplary embodiment, the first and second portions of the heating element have different respective thermal masses as a result of a material composition of the first portion of the heating element being different to a material composition of the second portion of the heating element. 
     In an exemplary embodiment, a material composition of the heating material of the first portion of the heating element is the same as a material composition of the heating material of the second portion of the heating element. 
     In an exemplary embodiment, a material composition of the heating material is homogenous throughout the heating element. 
     In an exemplary embodiment, a density of the first portion of the heating element is the same as a density of the second portion of the heating element. 
     In an exemplary embodiment, a density of the heating element is homogenous throughout the heating element. 
     In an exemplary embodiment, a cross-section of the first portion of the heating element is the same in both shape and dimensions as a cross-section of the second portion of the heating element. 
     In an exemplary embodiment, the heating material comprises one or more materials selected from the group consisting of: an electrically-conductive material, a magnetic material, and a magnetic electrically-conductive material. 
     In an exemplary embodiment, the heating material comprises a metal or a metal alloy. 
     In an exemplary embodiment, the heating material comprises one or more materials selected from the group consisting of: aluminum, gold, iron, nickel, cobalt, conductive carbon, graphite, plain-carbon steel, stainless steel, ferritic stainless steel, copper, and bronze. 
     A second aspect of the present disclosure provides an article for use with an apparatus for heating smokable material to volatilize at least one component of the smokable material, the article comprising a heating element formed from heating material that is heatable by penetration with a varying magnetic field, and smokable material in thermal contact in use with the heating element, wherein first and second portions of the heating element have different respective thermal masses. 
     In an exemplary embodiment, the smokable material is in surface contact with the heating element. 
     In an exemplary embodiment, the smokable material comprises tobacco and/or one or more humectants. 
     In an exemplary embodiment, the smokable material is non-liquid. 
     In an exemplary embodiment, the heating element of the article of the second aspect is the heating element of the first aspect. The heating element of the article of the second aspect may have any one or more of the features discussed above as being present in respective exemplary embodiments of the heating element of the first aspect. 
     A third aspect of the present disclosure provides an apparatus for heating smokable material to volatilize at least one component of the smokable material, the apparatus comprising: a magnetic field generator for generating a varying magnetic field; and a heating element formed from heating material that is heatable by penetration with the varying magnetic field, wherein first and second portions of the heating element have different respective thermal masses. 
     In an exemplary embodiment, the apparatus comprises a heating zone for receiving at least a portion of an article comprising smokable material, and the heating element projects into the heating zone. 
     In an exemplary embodiment, the apparatus comprises a heating zone for receiving at least a portion of an article comprising smokable material, and the heating element extends at least partially around the heating zone. 
     In an exemplary embodiment, the apparatus is for heating smokable material to volatilize at least one component of the smokable material without combusting the smokable material. 
     In an exemplary embodiment, the heating element of the apparatus of the third aspect is the heating element of the first aspect. The heating element of the apparatus of the third aspect may have any one or more of the features discussed above as being present in respective exemplary embodiments of the heating element of the first aspect. 
     A fourth aspect of the present disclosure provides a system for heating smokable material to volatilize at least one component of the smokable material, the system comprising: an article comprising smokable material; apparatus comprising a heating zone for receiving at least a portion of the article, and a magnetic field generator for generating a varying magnetic field to be used in heating the smokable material when the portion of the article is in the heating zone; and a heating element formed from heating material that is heatable by penetration with the varying magnetic field when the portion of the article is in the heating zone, wherein first and second portions of the heating element have different respective thermal masses. 
     In an exemplary embodiment, the apparatus of the system of the fourth aspect is the apparatus of the third aspect. The apparatus of the system of the fourth aspect may have any one or more of the features discussed above as being present in respective exemplary embodiments of the apparatus of the third aspect. 
     A fifth aspect of the present disclosure provides a method of heating smokable material to volatilize at least one component of the smokable material, the method comprising: providing a heating element formed from heating material that is heatable by penetration with a varying magnetic field, wherein first and second portions of the heating element have different respective thermal masses; providing smokable material in thermal contact with the heating element; and penetrating the heating material with a varying magnetic field so that the penetrating causes progressive heating of the heating element and thereby progressive heating of the smokable material. 
     In an exemplary embodiment, the heating element is the heating element of the first aspect. The heating element may have any one or more of the features discussed above as being present in respective exemplary embodiments of the heating element of the first aspect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  shows a schematic cross-sectional view of an example of a heating element for use with an apparatus for heating smokable material to volatilize at least one component of the smokable material. 
         FIG. 2  shows a schematic cross-sectional view of an example of another heating element for use with an apparatus for heating smokable material to volatilize at least one component of the smokable material. 
         FIG. 3  shows a schematic cross-sectional view of an example of an article for use with an apparatus for heating smokable material to volatilize at least one component of the smokable material. 
         FIG. 4  shows a schematic cross-sectional view of an example of another article for use with an apparatus for heating smokable material to volatilize at least one component of the smokable material. 
         FIG. 5  shows a schematic cross-sectional view of an example of an apparatus for heating the smokable material to volatilize at least one component of the smokable material. 
         FIG. 6  shows a schematic cross-sectional view of an example of another apparatus for heating the smokable material to volatilize at least one component of the smokable material. 
         FIG. 7  shows a schematic cross-sectional view of an example of a system comprising the apparatus of  FIG. 5  and an article comprising smokable material. 
         FIG. 8  shows a schematic cross-sectional view of an example of another system comprising the apparatus of  FIG. 6  and an article comprising smokable material. 
         FIG. 9  shows a flow diagram showing an example of a method of heating smokable material to volatilize at least one component of the smokable material. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, the term “smokable material” includes materials that provide volatilized components upon heating, typically in the form of vapor or an aerosol. “Smokable material” may be a non-tobacco-containing material or a tobacco-containing material. “Smokable material” may, for example, include one or more of tobacco per se, tobacco derivatives, expanded tobacco, reconstituted tobacco, tobacco extract, homogenized tobacco or tobacco substitutes. The smokable material can be in the form of ground tobacco, cut rag tobacco, extruded tobacco, reconstituted tobacco, reconstituted smokable material, liquid, gel, gelled sheet, powder, or agglomerates, or the like. “Smokable material” also may include other, non-tobacco, products, which, depending on the product, may or may not contain nicotine. “Smokable material” may comprise one or more humectants, such as glycerol or propylene glycol. 
     As used herein, the term “heating material” or “heater material” refers to material that is heatable by penetration with a varying magnetic field. 
     Induction heating is a process in which an electrically-conductive object is heated by penetrating the object with a varying magnetic field. The process is described by Faraday&#39;s law of induction and Ohm&#39;s law. An induction heater may comprise an electromagnet and a device for passing a varying electrical current, such as an alternating current, through the electromagnet. When the electromagnet and the object to be heated are suitably relatively positioned so that the resultant varying magnetic field produced by the electromagnet penetrates the object, one or more eddy currents are generated inside the object. The object has a resistance to the flow of electrical currents. Therefore, when such eddy currents are generated in the object, their flow against the electrical resistance of the object causes the object to be heated. This process is called Joule, ohmic, or resistive heating. An object that is capable of being inductively heated is known as a susceptor. 
     It has been found that, when the susceptor is in the form of a closed circuit, magnetic coupling between the susceptor and the electromagnet in use is enhanced, which results in greater or improved Joule heating. 
     Magnetic hysteresis heating is a process in which an object made of a magnetic material is heated by penetrating the object with a varying magnetic field. A magnetic material can be considered to comprise many atomic-scale magnets, or magnetic dipoles. When a magnetic field penetrates such material, the magnetic dipoles align with the magnetic field. Therefore, when a varying magnetic field, such as an alternating magnetic field, for example as produced by an electromagnet, penetrates the magnetic material, the orientation of the magnetic dipoles changes with the varying applied magnetic field. Such magnetic dipole reorientation causes heat to be generated in the magnetic material. 
     When an object is both electrically-conductive and magnetic, penetrating the object with a varying magnetic field can cause both Joule heating and magnetic hysteresis heating in the object. Moreover, the use of magnetic material can strengthen the magnetic field, which can intensify the Joule heating. 
     In each of the above processes, as heat is generated inside the object itself, rather than by an external heat source by heat conduction, a rapid temperature rise in the object and more uniform heat distribution can be achieved, particularly through selection of suitable object material and geometry, and suitable varying magnetic field magnitude and orientation relative to the object. Moreover, as induction heating and magnetic hysteresis heating do not require a physical connection to be provided between the source of the varying magnetic field and the object, design freedom and control over the heating profile may be greater, and cost may be lower. 
     Referring to  FIG. 1  there is shown a schematic perspective view of an example of a heating element according to an embodiment of the disclosure. The heating element  10  is for use with an apparatus for heating smokable material to volatilize at least one component of the smokable material. 
     The heating element  10  is formed from heating material that is heatable by penetration with a varying magnetic field. Examples of such materials are discussed below. 
     The heating element  10  of this embodiment is elongate with a length that extends from a first end of the heating element  10  to an opposite second end of the heating element  10 . Moreover, the heating element  10  has a cross-section perpendicular to the length, wherein the cross-section has a width and a depth. In this embodiment, the length is greater than the width, and the width is greater than the depth. 
     In this embodiment, the heating element  10  has a rectangular cross-section perpendicular to its length. The depth or thickness of the heating element  10  is relatively small as compared to the other dimensions of the heating element  10 . Therefore, a greater proportion of the heating element  10  may be heatable by a given varying magnetic field, as compared to a heating element  10  having a depth or thickness that is relatively large as compared to the other dimensions of the heating element  10 . Thus, a more efficient use of material is achieved. In turn, costs are reduced. However, in other embodiments, the heating element  10  may have a cross-section that is a shape other than rectangular, such as circular, elliptical, annular, star-shaped, polygonal, square, triangular, X-shaped, or T-shaped. In this embodiment, a cross-section of the first portion  10   a  of the heating element  10  is the same in both shape and dimensions as a cross-section of the second portion  10   b  of the heating element  10 . Moreover, in this embodiment, the cross-section of the heating element  10  is constant in both shape and dimensions along the length of the heating element  10 . Furthermore, in this embodiment, the heating element  10  is planar, or substantially planar. The heating element  10  of this embodiment can be considered a flat strip. However, in other embodiments, this may not be the case. For example, in some embodiments, the heating element may be non-planar, such as twisted, corrugated, having at least one curved major surface. In some embodiments, the heating element may be hollow or perforated. 
     The thermal mass of a body is proportional to the mass (weight) of the body multiplied by its heat capacity (the ability of the body to store thermal energy). Different portions of a body can have different thermal masses only if the weight or densities are different, and/or if their heat capacities are different. 
     First and second portions  10   a ,  10   b  of the heating element  10  have different respective thermal masses. This enables the first and second portions  10   a ,  10   b  of the heating element  10  to heat at different respective rates, when the first and second portions  10   a ,  10   b  of the heating element  10  are penetrated with a varying magnetic field. That is, the first portion  10   a  of the heating element  10  is heatable at a first rate when penetrated with a varying magnetic field, and the second portion  10   b  of the heating element  10  is heatable at a second rate when penetrated with the varying magnetic field, and the first rate differs from the second rate. This means that the heating element  10  is progressively heatable by penetration with a given varying magnetic field, and so the heating element  10  is usable to progressively heat its surroundings. 
     In this embodiment, the first and second portions  10   a ,  10   b  of the heating element  10  have different respective thermal masses as a result of a density of the first portion  10   a  of the heating element  10  being different to a density of the second portion  10   b  of the heating element  10 . In this embodiment, the first portion  10   a  of the heating element  10  has a greater density, and therefore a greater thermal mass, than the second portion  10   b  of the heating element  10 . For example, the first portion  10   a  of the heating element  10  may be made from a first material, and the second portion  10   b  of the heating element  10  may be made from a second material that is different from the first material and less dense than the first material. Alternatively or additionally, the first and second portions  10   a ,  10   b  of the heating element  10  may contain respective different levels or amounts of a non-permeable additive. The second portion  10   b  of the heating element  10  is therefore heatable by penetration with a given varying magnetic field at a greater rate than the first portion  10   a  of the heating element  10 . 
     In this embodiment, the first and second portions  10   a ,  10   b  of the heating element  10  are at opposite ends of the heating element  10 . However, in other embodiments, one of the first and second portions  10   a ,  10   b  of the heating element  10  may be located between two of the other of the first and second portions  10   a ,  10   b  of the heating element  10 . That is, in some embodiments, the heating element  10  may have a relatively denser portion between two relatively less dense portions, or may have a relatively less dense portion between two relatively denser portions. 
     In this embodiment, the thermal mass of the heating element  10  varies with distance along the length of the heating element  10 . This is as a result of the density of the heating element  10  correspondingly varying with distance along the length of the heating element  10 . Accordingly, during use, the heating element  10  heats progressively along its length. In other embodiments, the thermal mass of the heating element may vary with distance along a path other than a length of the heating element. For example, the thermal mass may vary with distance in a direction of the width or thickness of the heating element. 
     The thermal mass of the heating element  10  of  FIG. 1  varies over the full length of the heating element  10 , as a result of the density of the heating element  10  correspondingly varying over the full length of the heating element  10 . In other embodiments, the thermal mass may vary over only a majority of the length of the heating element, or over only a portion of the length of the heating element. Again, this may be due to appropriate selection of changes in the density of the heating element along its length. The skilled person would readily be able to determine a distance over which they wish the thermal mass to vary, to provide a desired progressive heating profile in use. They would also be able to select an appropriate profile for how the density of the heating element varies along its length to provide that desired progressive heating profile. 
     In this embodiment, the thermal mass reduces continuously with distance along the length of the heating element  10  from the first portion  10   a  of the heating element  10  to the second portion  10   b  of the heating element  10 . More specifically, in this embodiment, the thermal mass reduces linearly, or substantially linearly, with distance along the length. This is due to the density of the heating element  10  reducing linearly, or substantially linearly, with distance along the length of the heating element  10 . Accordingly, in use the heating element  10  is progressively heatable at a constant, or substantially constant, rate along its length. However, in other embodiments, the thermal mass may vary other than continuously with distance along the length of the heating element  10  from the first portion  10   a  of the heating element  10  to the second portion  10   b  of the heating element  10 . For example, the variation may be stepwise, or continuous over at least one section and stepwise over at least one other section. The skilled person would readily be able to determine a manner in which they wish the thermal mass to vary, to provide a desired progressive heating profile in use. They would also be able to select an appropriate profile for how the density of the heating element varies along its length to provide that desired progressive heating profile. 
     The heating element  10  of  FIG. 1  may be incorporated into an apparatus for heating smokable material to volatilize at least one component of the smokable material, or may be incorporated into an article comprising smokable material and for use with such an apparatus. An example of such an article is discussed below with reference to  FIG. 3 . 
     Referring to  FIG. 2  there is shown a schematic cross-sectional view of an example of another heating element according to an embodiment of the disclosure. The heating element  20  is for use with an apparatus for heating smokable material to volatilize at least one component of the smokable material. 
     The heating element  20  is again formed from heating material that is heatable by penetration with a varying magnetic field, and again has first and second portions  20   a ,  20   b  that have different respective thermal masses. In this embodiment, however, the material composition of the heating material, including the density of the heating material, of the first portion  20   a  of the heating element  20  is the same as the material composition of the heating material of the second portion  20   b  of the heating element  20 . In fact, in this embodiment, the material composition of the heating material, including the density of the heating material, is homogenous throughout the heating element  20 . The first and second portions  20   a ,  20   b  of the heating element  20  have different respective thermal masses as a result of a thickness of the first portion  20   a  of the heating element  20  being different to a thickness of the second portion  20   b  of the heating element  20 . 
     More specifically, the heating element  20  of this embodiment is elongate with a length that extends from a first end of the heating element  20  to an opposite second end of the heating element  20 . The heating element  20  has a cross-section perpendicular to the length, wherein the cross-section has a width and a depth. The depth is the thickness of the heating element  20 . In this embodiment, the length is greater than the width, and the width is greater than the depth. Moreover, in this embodiment the width is constant along the length of the heating element  20 , but the depth is different at different respective points along the length. 
     In this embodiment, the heating element  10  has a rectangular cross-section perpendicular to its length. However, in other embodiments, the heating element  10  may have a cross-section that is a shape other than rectangular, such as one of the alternative shapes discussed above with reference to the embodiment of  FIG. 1 . 
     The heating element  20  of this embodiment has planar, or substantially planar, major surfaces. However, in other embodiments, this may not be the case. For example, in some embodiments, the heating element may be twisted, corrugated, or have at least one curved major surface. In some embodiments, the heating element may be hollow or perforated. 
     In this embodiment, the first and second portions  20   a ,  20   b  of the heating element  20  are at opposite ends of the heating element  20 . However, in other embodiments, one of the first and second portions  20   a ,  20   b  of the heating element  20  may be located between two of the other of the first and second portions  20   a ,  20   b  of the heating element  20 . That is, in some embodiments, the heating element  20  may have a relatively thick portion between two relatively thin portions, or may have a relatively thin portion between two relatively thick portions. 
     In this embodiment, the first portion  20   a  of the heating element  20  has a greater thickness, and therefore a greater thermal mass, than the second portion  20   b  of the heating element  20 . The second portion  20   b  of the heating element  20  is therefore heatable by penetration with a given varying magnetic field at a greater rate than the first portion  20   a  of the heating element  20 . 
     In this embodiment, the thermal mass of the heating element  20  varies with distance along the length of the heating element  20 . This is as a result of the thickness of the heating element  20  correspondingly varying with distance along the length of the heating element  20 . Accordingly, during use, the heating element  20  heats progressively along its length. In other embodiments, the thermal mass of the heating element may vary with distance along a path other than a length of the heating element. For example, the thermal mass may vary with distance in a direction of the width of the heating element. 
     The thermal mass of the heating element  20  of  FIG. 2  varies over the full length of the heating element  20 , as a result of the thickness of the heating element  20  correspondingly varying over the full length of the heating element  20 . In other embodiments, the thermal mass may vary over only a majority of the length of the heating element, or over only a portion of the length of the heating element. Again, this may be due to appropriate selection of changes in the thickness of the heating element along its length. The skilled person would readily be able to determine a distance over which they wish the thermal mass to vary, to provide a desired progressive heating profile in use. They would also be able to select an appropriate profile for how the thickness of the heating element varies along its length to provide that desired progressive heating profile. 
     In this embodiment, the thermal mass reduces continuously with distance along the length of the heating element  20  from the first portion  20   a  of the heating element  20  to the second portion  20   b  of the heating element  20 . More specifically, in this embodiment, the thermal mass reduces linearly, or substantially linearly, with distance along the length. This is due to the thickness of the heating element  20  reducing linearly, or substantially linearly, with distance along the length of the heating element  20 . In other words, the heating element  20  is linearly tapered. Accordingly, in use the heating element  20  is progressively heatable at a constant, or substantially constant, rate along its length. However, in other embodiments, the thermal mass may vary other than continuously with distance along the length of the heating element  20  from the first portion  20   a  of the heating element  20  to the second portion  20   b  of the heating element  20 . For example, the variation may be stepwise, or continuous over at least one section of the heating element  20  and stepwise over at least one other section of the heating element  20 . The skilled person would readily be able to determine a manner in which they wish the thermal mass to vary, to provide a desired progressive heating profile in use. They would also be able to select an appropriate profile for how the thickness of the heating element varies along its length to provide that desired progressive heating profile. 
     The heating element  20  of  FIG. 2  may be incorporated into an apparatus for heating smokable material to volatilize at least one component of the smokable material, or may be incorporated into an article comprising smokable material and for use with such apparatus. An example of such an article is discussed below with reference to  FIG. 4 , and an example of such an apparatus is discussed below with reference to  FIG. 5 . 
     It is to be noted that a tapered, or only partially tapered, heating element need not necessarily have a varying thermal mass along its length. For example, the density or material composition of such a heating element may also vary to offset the tapering, so that the thermal mass is constant along the length of the heating element. However, in some embodiments of the disclosure, the heating element is tapered and the material composition of the heating material, including the density of the heating material, is homogenous throughout the heating element, so that first and second portions of the heating element have different respective thermal masses. 
     In another embodiment, the first and second portions of the heating element may have different respective thermal masses as a result of a material composition of the first portion of the heating element being different to a material composition of the second portion of the heating element. For example, the first and second portions of the heating element may be made from different materials. For instance, one of the first and second portions of the heating element may be made from soft iron and the other from a stainless steel. Other materials that could be joined include steel, aluminum and iron. The first and second portions of the heating element may for example be joined by welding, brazing, thermal epoxy, a mechanical fastening, or the like. In some embodiments, the densities of the first and second portions of the heating element may differ through utilization of varying foamed material or a varying mesh material. 
     Referring to  FIGS. 3 and 4  there are shown respective schematic cross-sectional views of examples of articles according to respective embodiments of the disclosure. Each of the articles  1 ,  2  is for use with apparatus for heating smokable material to volatilize at least one component of the smokable material. 
     The article  1  of  FIG. 3  comprises the heating element  10  of  FIG. 1 , smokable material  60  in thermal contact with the heating element  10 , and a cover  70  around the smokable material  60 . The article  2  of  FIG. 4  comprises the heating element  20  of  FIG. 2 , smokable material  60  in thermal contact with the heating element  20 , and a cover  70  around the smokable material  60 . Any of the herein-described possible variations to the heating element  10  of  FIG. 1  may be made to the heating element  10  of the article  1  of  FIG. 3  to form separate respective embodiments of articles. Similarly, any of the herein-described possible variations to the heating element  20  of  FIG. 2  may be made to the heating element  20  of the article  2  of  FIG. 4  to form separate respective embodiments of articles. 
     In each of the articles  1 ,  2 , the cover  70  encircles the smokable material  60 . The cover  70  helps to protect the smokable material  60  from damage during transport and use of the article  1 ,  2 . During use, the cover  70  may also help to direct the flow of air into and through the smokable material  60 , and may help to direct the flow of vapor or aerosol through and out of the smokable material  60 . 
     In each of these embodiments, the cover  70  comprises a wrapper  72  that is wrapped around the smokable material  60  so that free ends of the wrapper  72  overlap each other. The wrapper  72  thus forms all of, or a majority of, a circumferential outer surface of the article  1 ,  2 . The wrapper  72  may be formed from paper, reconstituted smokable material, such as reconstituted tobacco, or the like. The cover  70  of each of these embodiments also comprises an adhesive (not shown) that adheres the overlapped free ends of the wrapper  72  to each other. The adhesive may comprise one or more of, for example, gum Arabic, natural or synthetic resins, starches, and varnish. The adhesive helps prevent the overlapped free ends of the wrapper  72  from separating. In other embodiments, the adhesive may be omitted. 
     The cover  70  of each of these embodiments defines an outer surface of the article  1 ,  2  and may contact the apparatus in use. In each of these embodiments, the article  1 ,  2  is elongate and cylindrical with a substantially circular cross-section, and has proportions approximating those of a cigarette. However, in other embodiments, the article  1 ,  2  may have a cross-section other than circular and/or not be elongate and/or not be cylindrical. 
     In the embodiments of  FIGS. 3 and 4 , the smokable material  60  is in the form of a tube. The tube has a substantially circular cross-section. The smokable material  60  extends from one end of the article  1 ,  2  to an opposite end of the article  1 ,  2 . Thus, in use, air may be drawn into the smokable material  60  at one end of the article  1 ,  2 , the air may pass through the smokable material  60  and pick up volatilized components released from the smokable material  60 , and then the volatilized components, typically in the form of vapor or an aerosol, may be drawn out of the smokable material  60  at the opposite end of the article  1 ,  2 . In each of these embodiments in which the article  1 ,  2  is elongate, these ends of the article  1 ,  2  between which the smokable material  60  extends are opposite longitudinal ends of the article  1 ,  2 . However, in other embodiments, the ends may be any two ends or sides of the article, such as any two opposite ends or sides of the article. 
     As noted above, in each of the articles  1 ,  2  of  FIGS. 3 and 4 , the heating element  10 ,  20  is in thermal contact with the smokable material  60 . Therefore, the heating material is heatable in use to heat the smokable material  60 . More specifically, in each of these embodiments, the smokable material  60  is in surface contact with the heating element  10 ,  20 . This is achieved by adhering the smokable material  60  to the heating element  10 ,  20 . However, in other embodiments, the fixing may be by other than adhesion. In some embodiments the smokable material  60  may not be fixed to the heating element  10 ,  20  as such. 
     In each of the embodiments of  FIGS. 3 and 4 , the heating element  10 ,  20  extends from one end of the smokable material  60  to an opposite end of the smokable material  60 . This can help to provide more complete heating of the smokable material  60  in use. However, in other embodiments, the heating element  10 ,  20  may not extend to either of the opposite ends of the smokable material  60 , or may extend to only one of the ends of the smokable material  60  and be spaced from the other of the ends of the smokable material  60 . 
     Moreover, in each of the embodiments of  FIGS. 3 and 4 , the heating element  10 ,  20  extends from one end of the article  1 ,  2  to an opposite end of the article  1 ,  2 . This can aid manufacturing of the article  1 ,  2 . However, in other embodiments, the heating element  10 ,  20  may not extend to either of the opposite ends of the article  1 ,  2 , or may extend to only one of the ends of the article  1 ,  2  and be spaced from the other of the ends of the article  1 ,  2 . 
     The heating element  10 ,  20  of each of the embodiments of  FIGS. 3 and 4  extends along a longitudinal axis that is substantially aligned with a longitudinal axis of the article  1 ,  2 . This can aid manufacturing of the article  1 ,  2 . In these embodiments, the aligned axes are coincident. In a variation to these embodiments, the aligned axes may be parallel to each other. However, in other embodiments, the axes may be oblique to each other. 
     In each of these embodiments, the heating element  10 ,  20  is encircled by the smokable material  60 . That is, the smokable material  60  extends around the heating element  10 ,  20 . In embodiments in which the heating element  10 ,  20  does not extend to either of the opposite ends of the smokable material  60 , the smokable material  60  may extend around the heating element  10 ,  20  and also cover the ends of the heating element  10 ,  20 , so that the heating element  10 ,  20  is surrounded by the smokable material  60 . 
     In each of the illustrated embodiments, the heating element  10 ,  20  is impermeable to air or volatilized material, and is substantially free from discontinuities. The heating element  10 ,  20  may thus be relatively easy to manufacture. However, in variations to these embodiments, the heating element  10 ,  20  may be permeable to air and/or permeable to volatilized material created when the smokable material  60  is heated. Such a permeable nature of the heating element  10 ,  20  may help air passing through the article  1 ,  2  to pick up the volatilized material created when the smokable material  60  is heated. 
     As noted above, in some embodiments the heating element  10 ,  20  may be non-planar. For example, the heating element  10 ,  20  may follow a wavelike or wavy path, be twisted, be corrugated, be helical, have a spiral shape, comprise a plate or strip or ribbon having protrusions thereon and/or indentations therein, comprise a mesh, comprise expanded metal, or have a non-uniform non-planar shape. Such non-planar shapes may help air passing through the article  1 ,  2  to pick up the volatilized material created when the smokable material  60  is heated. Non-planar shapes can provide a tortuous path for air to follow, creating turbulence in the air and causing better heat transfer from the heating element  10 ,  20  to the smokable material  60 . The non-planar shapes can also increase the surface area of the heating element  10 ,  20  per unit length of the heating element  10 ,  20 . This can result in greater or improved Joule heating of the heating element  10 ,  20 , and thus greater or improved heating of the smokable material  60 . 
     Referring to  FIG. 5  there is shown a schematic perspective view of an example of an apparatus according to an embodiment of the disclosure. The apparatus  100  is for heating smokable material to volatilize at least one component of the smokable material. The apparatus  100  comprises a magnetic field generator  112  for generating a varying magnetic field in use, and a heating element  20  formed from heating material that is heatable by penetration with the varying magnetic field. First and second portions  20   a ,  20   b  of the heating element  20  have different respective thermal masses. 
     More specifically, the apparatus  100  of this embodiment comprises a body  110  and a mouthpiece  120 . The mouthpiece  120  may be made of any suitable material, such as a plastics material, cardboard, cellulose acetate, paper, metal, glass, ceramic, or rubber. The mouthpiece  120  defines a channel  122  therethrough. The mouthpiece  120  is locatable relative to the body  110  so as to cover an opening into the heating zone  111 . When the mouthpiece  120  is so located relative to the body  110 , the channel  122  of the mouthpiece  120  is in fluid communication with the heating zone  111 . In use, the channel  122  acts as a passageway for permitting volatilized material to pass from smokable material of an article inserted in the heating zone  111  to an exterior of the apparatus  100 . In this embodiment, the mouthpiece  120  of the apparatus  100  is releasably engageable with the body  110  so as to connect the mouthpiece  120  to the body  110 . In other embodiments, the mouthpiece  120  and the body  110  may be permanently connected, such as through a hinge or flexible member. In some embodiments, such as embodiments in which the article itself comprises a mouthpiece, the mouthpiece  120  of the apparatus  100  may be omitted. 
     The apparatus  100  may define an air inlet that fluidly connects the heating zone  111  with the exterior of the apparatus  100 . Such an air inlet may be defined by the body  110  of the apparatus  100  and/or by the mouthpiece  120  of the apparatus  100 . A user may be able to inhale the volatilized component(s) of the smokable material by drawing the volatilized component(s) through the channel  122  of the mouthpiece  120 . As the volatilized component(s) are removed from the article, air may be drawn into the heating zone  111  via the air inlet of the apparatus  100 . 
     In this embodiment, the body  110  comprises the heating zone  111 . In this embodiment, the heating zone  111  comprises a recess  111  for receiving at least a portion of the article. In other embodiments, the heating zone  111  may be other than a recess, such as a shelf, a surface, or a projection, and may require mechanical mating with the article in order to co-operate with, or receive, the article. In this embodiment, the heating zone  111  is elongate, and is sized and shaped to accommodate the whole article. In other embodiments, the heating zone  111  may be dimensioned to receive only a portion of the article. 
     In this embodiment, the magnetic field generator  112  comprises an electrical power source  113 , a coil  114 , a device  116  for passing a varying electrical current, such as an alternating current, through the coil  114 , a controller  117 , and a user interface  118  for user-operation of the controller  117 . 
     The electrical power source  113  of this embodiment is a rechargeable battery. In other embodiments, the electrical power source  113  may be other than a rechargeable battery, such as a non-rechargeable battery, a capacitor, a battery-capacitor hybrid, or a connection to a mains electricity supply. 
     The coil  114  may take any suitable form. In this embodiment, the coil  114  is a helical coil of electrically-conductive material, such as copper. In some embodiments, the magnetic field generator  112  may comprise a magnetically permeable core around which the coil  114  is wound. Such a magnetically permeable core concentrates the magnetic flux produced by the coil  114  in use and makes a more powerful magnetic field. The magnetically permeable core may be made of iron, for example. In some embodiments, the magnetically permeable core may extend only partially along the length of the coil  114 , so as to concentrate the magnetic flux only in certain regions. In some embodiments, the coil may be a flat coil. That is, the coil may be a two-dimensional spiral. 
     It will be understood from consideration of  FIG. 5  that in this embodiment the heating element  20  projects into the heating zone  111 . The heating element  20  has a length from a first end at which the heating element  20  is mounted to the rest of the body  110  to a free second end. The free end is arranged relative to the heating zone  111  so as to enter the article as the article is inserted into the heating zone  111 . The tapered shape of the heating element  20  may facilitate this entry. 
     When the article is located in the heating zone  111 , the heating element  20  is in thermal contact with the smokable material of the article. In some embodiments, when the article is located in the heating zone  111 , the heating element  20  is in surface contact with the smokable material of the article. Thus, heat may be conducted directly from the heating element  20  to the smokable material. In other embodiments, the heating element  20  may be kept out of surface contact with the smokable material. For example, in some embodiments, the article and/or apparatus  100  may comprise a thermally-conductive barrier that is free from heating material and that spaces the heating element  20  from the smokable material of the article in use. In some embodiments, the thermally-conductive barrier may be a coating on the heating element  20 . The provision of such a barrier may be advantageous to help to dissipate heat to alleviate hot spots in the heating element  20 , or to aid cleaning of the heating element  20 . 
     The heating element  20  of the apparatus  10  is the same as the heating element  20  of  FIG. 2 . The first and second portions  20   a ,  20   b  of the heating element  20  of  FIG. 5  correspond respectively to the first and second portions  20   a ,  20   b  of the heating element  20  of  FIG. 2 . Therefore, in the interest of conciseness, features common to the two heating elements  20  will not be described again in detail. Any of the herein-described possible variations to the heating element  20  of  FIG. 2  may be made to the heating element  20  of the apparatus  100  of  FIG. 5  to form separate respective embodiments of the apparatus. 
     In this embodiment, the coil  114  encircles the heating element  20  and the heating zone  111 . The coil  114  extends along a longitudinal axis that is substantially aligned with a longitudinal axis of the heating zone  111 . The aligned axes are coincident. In a variation to this embodiment, the aligned axes may be parallel to each other. However, in other embodiments, the axes may be oblique to each other. Moreover, the coil  114  extends along a longitudinal axis that is substantially coincident with a longitudinal axis of the heating element  20 . In other embodiments, the longitudinal axes of the coil  114  and the heating element  20  may be aligned with each other by being parallel to each other, or may be oblique to each other. 
     In this embodiment, the device  116  for passing a varying current through the coil  114  is electrically connected between the electrical power source  113  and the coil  114 . In this embodiment, the controller  117  also is electrically connected to the electrical power source  113 , and is communicatively connected to the device  116  to control the device  116 . More specifically, in this embodiment, the controller  117  is for controlling the device  116 , so as to control the supply of electrical power from the electrical power source  113  to the coil  114 . In this embodiment, the controller  117  comprises an integrated circuit (IC), such as an IC on a printed circuit board (PCB). In other embodiments, the controller  117  may take a different form. In some embodiments, the apparatus may have a single electrical or electronic component comprising the device  116  and the controller  117 . The controller  117  is operated in this embodiment by user-operation of the user interface  118 . In this embodiment, the user interface  118  is located at the exterior of the body  110 . The user interface  118  may comprise a push-button, a toggle switch, a dial, a touchscreen, or the like. In other embodiments, the user interface  118  may be remote and connected to the rest of the apparatus wirelessly, such as via Bluetooth. 
     In this embodiment, operation of the user interface  118  by a user causes the controller  117  to cause the device  116  to cause an alternating electrical current to pass through the coil  114 . This causes the coil  114  to generate an alternating magnetic field. The coil  114  and the heating element  20  of the apparatus  100  are suitably relatively positioned so that the varying magnetic field produced by the coil  114  penetrates the heating material of the heating element  20 . In this embodiment, the heating material of the heating element  20  is an electrically-conductive material, and so this penetration causes the generation of one or more eddy currents in the heating material. The flow of eddy currents in the heating material against the electrical resistance of the heating material causes the heating material to be heated by Joule heating. When the heating material is made of a magnetic material, the orientation of magnetic dipoles in the heating material changes with the changing applied magnetic field, which causes heat to be generated in the heating material. 
     As the second portion  20   b  of the heating element  20  has less thermal mass than the first portion  20   a  of the heating element  20 , the penetration of the heating element  20  with the varying magnetic field causes the second portion  20   b  of the heating element  20  to heat at a greater rate than the first portion  20   a  of the heating element  20 . Accordingly, when an article comprising smokable material is located in the heating zone  111  in use (as shown in  FIG. 7 , discussed below), a first portion of the article closest to the second portion  20   b  of the heating element  20  is heated first by heat emanating from the second portion  20   b  of the heating element  20 . This initiates volatilization of at least one component of the smokable material of that first portion of the article and formation of an aerosol therein. Over time, the temperature of the first portion  20   a  of the heating element  20  increases. This causes a second portion of the article closest to the first portion  20   a  of the heating element  20  to be heated by heat emanating from the first portion  20   a  of the heating element  20 . In turn, this initiates volatilization of at least one component of the smokable material of the second portion of the article and formation of an aerosol therein. 
     Accordingly, there is provided progressive heating of the article, and thus the smokable material of the article, over time. This helps to enable an aerosol to be formed and released relatively rapidly for inhalation by a user, yet provides time-dependent release, so that aerosol continues to be formed and released even after the smokable material of the first portion of the article has ceased generating aerosol. Such cessation of aerosol generation may occur as a result of the smokable material of the first portion of the article becoming exhausted of volatilizable components of the smokable material. 
     It will be noted that, in this embodiment, the second portion  20   b  of the heating element  20  is closer to the channel  122  of the mouthpiece  120  than the first portion  20   a  of the heating element  20 . Therefore, in use the first portion of the article to be heated to volatilize component(s) of the smokable material is also closer to the channel  122  of the mouthpiece  120  than the second portion of the article. However, in other embodiments the heating element  20  may instead be arranged relative to the channel  122  so that the second portion  20   b  of the heating element  20  is further from the channel  122  of the mouthpiece  120  than the first portion  20   a  of the heating element  20 . 
     In this embodiment, an impedance of the coil  114  of the magnetic field generator  112  is equal, or substantially equal, to an impedance of the heating element  20 . If the impedance of the heating element  20  were instead lower than the impedance of the coil  114 , then the voltage generated across the heating element  20  in use may be lower than the voltage that may be generated across the heating element  20  when the impedances are matched. Alternatively, if the impedance of the heating element  20  were instead higher than the impedance of the coil  114 , then the electrical current generated in the heating element  20  in use may be lower than the current that may be generated in the heating element  20  when the impedances are matched. Matching the impedances may help to balance the voltage and current to maximize the heating power generated at the heating element  20  in use. In some embodiments, the impedance of the device  116  may be equal, or substantially equal, to a combined impedance of the coil  114  and the heating element  20 . 
     The apparatus  100  of this embodiment comprises a temperature sensor  119  for sensing a temperature of the heating zone  111 . The temperature sensor  119  is communicatively connected to the controller  117 , so that the controller  117  is able to monitor the temperature of the heating zone  111 . On the basis of one or more signals received from the temperature sensor  119 , the controller  117  may cause the device  116  to adjust a characteristic of the varying or alternating electrical current passed through the coil  114  as necessary, in order to ensure that the temperature of the heating zone  111  remains within a predetermined temperature range. The characteristic may be, for example, amplitude or frequency or duty cycle. Within the predetermined temperature range, in use the smokable material within an article located in the heating zone  111  is heated sufficiently to volatilize at least one component of the smokable material without combusting the smokable material. Accordingly, the controller  117 , and the apparatus  100  as a whole, is arranged to heat the smokable material to volatilize the at least one component of the smokable material without combusting the smokable material. In some embodiments, the temperature range is about 50° C. to about 300° C., such as between about 50° C. and about 250° C., between about 50° C. and about 150° C., between about 50° C. and about 120° C., between about 50° C. and about 100° C., between about 50° C. and about 80° C., or between about 60° C. and about 70° C. In some embodiments, the temperature range is between about 170° C. and about 220° C. In other embodiments, the temperature range may be other than this range. In some embodiments, the upper limit of the temperature range could be greater than 300° C. In some embodiments, the temperature sensor  119  may be omitted. In some embodiments, the heating material may have a Curie point temperature selected on the basis of the maximum temperature to which it is desired to heat the heating material, so that further heating above that temperature by induction heating the heating material is hindered or prevented. 
     Referring to  FIG. 6  there is shown a schematic cross-sectional view of an example of another apparatus according to an embodiment of the disclosure. The apparatus  200  of  FIG. 6  is identical to the apparatus  100  of  FIG. 5  except for the form of the heating element, heating zone, and coil of the apparatus. Therefore, in the interest of conciseness, features common to the two embodiments will not be described again in detail. Any of the herein-described possible variations to the apparatus  100  of  FIG. 5  may be made to the apparatus  200  of  FIG. 6  to form separate respective embodiments of the apparatus. 
     As noted above, in the apparatus  100  of  FIG. 5 , the heating element  20  projects into the heating zone  111 . In contrast, the apparatus  200  of  FIG. 6  comprises a heating element  40  of heating material that extends around the heating zone  111 . Therefore, whereas in the embodiment of  FIG. 5  the heating zone  111  and any article therein in use is heated from the inside outwards, in the embodiment of  FIG. 6  the heating zone  111  and any article therein in use is heated from the outside inwards. 
     The heating element  40  is made from heating material that is heatable by penetration with a varying magnetic field. The heating element  40  is a tubular heating element  40  that encircles the heating zone  111 . However, in other embodiments, the heating element  40  may not be fully tubular. For example, in some embodiments, the heating element  40  may be tubular save for an axially-extending gap or slit formed in the heating element  40 . The heating element  40  has a substantially circular cross-section. However, in other embodiments, the heating element may have a cross-section other than circular, such as square, rectangular, polygonal or elliptical. The heating element  40  extends along a longitudinal axis that is substantially aligned with a longitudinal axis of the heating zone  111 . In this embodiment, the aligned axes are coincident. In a variation to this embodiment, the aligned axes may be parallel to each other. However, in other embodiments, the axes may be oblique to each other. 
     In this embodiment, the heating zone  111  is defined at least in part by the heating element  40 . That is, the heating element  40  at least partially delineates or delimits the heating zone  111 . The cross-section of the heating zone  111  perpendicular to the longitudinal axis of the heating zone  111  is constant along the length of the heating zone  111 , in this embodiment. However, in other embodiments, the cross-section may vary with distance along the length of the heating zone  111 . In this embodiment the cross-section of the heating zone  111  is circular, but in other embodiments the cross-section of the heating zone  111  may be other than circular, such as square, rectangular, polygonal or elliptical. 
     When an article comprising smokable material is located in the heating zone  111 , the heating element  40  is in thermal contact with the article. In some embodiments, when an article comprising smokable material is located in the heating zone  111 , the heating element  40  is in surface contact with the article. Thus, heat may be conducted directly from the heating element  40  to the article. In other embodiments, the heating element may be kept out of direct surface contact with the article. Examples of how this may be achieved, and benefits that may be attained by doing so, are as discussed above. 
     Similarly to the heating element  20  of the embodiment of  FIG. 5 , the heating element  40  of the embodiment of  FIG. 6  has a first portion  40   a  and a second portion  40   b , wherein the first and second portions  40   a ,  40   b  of the heating element  40  have different respective thermal masses. In this embodiment, the material composition of the heating material, including the density of the heating material, of the first portion  40   a  of the heating element  40  is the same as the material composition of the heating material of the second portion  40   b  of the heating element  40 . Moreover, in this embodiment, the material composition of the heating material, including the density of the heating material, is homogenous throughout the heating element  40 . The first and second portions  40   a ,  40   b  of the heating element  40  have different respective thermal masses as a result of a thickness of the first portion  40   a  of the heating element  40  being different to a thickness of the second portion  40   b  of the heating element  40 . 
     More specifically, and as will be appreciated from consideration of  FIG. 6 , the first portion  40   a  of the heating element  40  has a greater thickness, and therefore a greater thermal mass, than the second portion  40   b  of the heating element  40 . The second portion  40   b  of the heating element  40  is therefore heatable by penetration with a given varying magnetic field at a greater rate than the first portion  40   a  of the heating element  40 . Accordingly, during penetration on the heating element  40  with the varying magnetic field generated by the generator  112 , a similar progressive heating effect to that discussed above can be provided. That is, in use, when an article is located in the heating zone  111  (as shown in  FIG. 8 , discussed below), the second portion  40   b  of the heating element  40  is heated quickest so as to heat a first portion of the article, and the first portion  40   a  of the heating element  40  is heated more slowly to heat a second portion of the article. As also noted above, this helps to enable an aerosol to be formed and released relatively rapidly for inhalation by a user, yet provides time-dependent release, so that aerosol continues to be formed and released even after the smokable material of the first portion of the article has ceased generating aerosol. 
     In this embodiment, the first and second portions  40   a ,  40   b  of the heating element  40  are at opposite ends of the heating element  40 . However, in other embodiments, one of the first and second portions  40   a ,  40   b  of the heating element  40  may be located between two of the other of the first and second portions  40   a ,  40   b  of the heating element  40 . That is, in some embodiments, the heating element  40  may have a relatively thick portion between two relatively thin portions, or may have a relatively thin portion between two relatively thick portions. 
     As for the previous embodiment, the second portion  40   b  of the heating element  40  is closer to the channel  122  of the mouthpiece  120  than the first portion  40   a  of the heating element  40 . However, in other embodiments the heating element  40  may instead be arranged relative to the channel  122  so that the opposite is true. 
     The thermal mass of the heating element  40  of  FIG. 6  varies over the full length of the heating element  40 , as a result of the thickness of the heating element  40  correspondingly varying over the full length of the heating element  40 . In other embodiments, the thermal mass may vary over only a majority of the length of the heating element, or over only a portion of the length of the heating element. Again, this may be due to appropriate selection of changes in the thickness of the heating element  40  along its length. Furthermore, in this embodiment, the thermal mass reduces continuously with distance along the length of the heating element  40  from the first portion  40   a  of the heating element  40  to the second portion  40   b  of the heating element  40 . More specifically, in this embodiment, the thermal mass reduces linearly, or substantially linearly, with distance along the length. This is due to the thickness of the heating element  40  reducing linearly, or substantially linearly, with distance along the length of the heating element  40 . Accordingly, in use the heating element  40  is progressively heatable at a constant, or substantially constant, rate along its length. However, in other embodiments, the thermal mass may vary other than continuously with distance along the length of the heating element  40  from the first portion  40   a  to the second portion  40   b . For example, the variation may be stepwise, or continuous over at least one section of the heating element  40  and stepwise over at least one other section of the heating element  40 . 
     In this embodiment, as noted above, the cross-section of the heating zone  111  perpendicular to the longitudinal axis of the heating zone  111  is constant along the length of the heating zone  111 . Moreover, as also noted above, the thickness or diameter of the heating element  40  varies linearly with distance along the length of the heating element  40 . Therefore, the heating element  40  is conical or frustoconical. It will be noted that the coil  114  of this embodiment extends along an axis that is substantially coincident with the longitudinal axis of the heating zone  111 . The coil  114  has a diameter that varies with distance along the longitudinal axis of the heating zone  111  so that the coil is a conic helix. However, in other embodiments, the coil  114  may have a substantially constant diameter along its full length so that the coil  114  is a circular helix. 
     In a variation to this embodiment, the apparatus may comprise both the heating element  40  that extends at least partially around the heating zone  111 , and another heating element that protrudes into the heating zone  111 , similar to the heating element  20  of the embodiment of  FIG. 5 . Such an embodiment may help deliver heating of the heating zone  111  and any article therein in use from both the middle and the outside. 
     Referring to  FIGS. 7 and 8  there are shown schematic cross-sectional views of examples of systems according to respective embodiments of the disclosure. The system  1000  of  FIG. 7  comprises the apparatus  100  of  FIG. 5  and an article  3  comprising smokable material. The system  2000  of  FIG. 8  comprises the apparatus  200  of  FIG. 6  and an article  4  comprising smokable material. The heating zone  111  of each of the apparatuses  100 ,  200  is for receiving the article  3 ,  4  of the respective system  1000 ,  2000 . In each of these embodiments, the article  3 ,  4  is insertable into the heating zone  111  of the respective apparatus  100 ,  200  when the mouthpiece  120  is disengaged from the body  110  of the respective apparatus  100 ,  200 . In each system  1000 ,  2000 , operation of the magnetic field generator  112  generates a varying magnetic field that penetrates the heating element  20 ,  40  as discussed above, to cause progressive heating of the heating element  20 ,  40 . In turn, the progressive heating of the heating element  20 ,  40  causes progressive heating of the smokable material of the respective article  3 ,  4 , such as to volatilize at least one component of the smokable material without combusting the smokable material as also discussed above. 
     In the interest of conciseness, the apparatuses  100 ,  200  will not be described again in detail. Any of the herein-described possible variations to the apparatuses  100 ,  200  of  FIGS. 5 and 6  may be made to the apparatuses  100 ,  200  of the systems  1000 ,  2000  of  FIGS. 7 and 8  to form separate respective embodiments of systems. 
     Referring to  FIG. 9  there is shown a flow diagram showing an example of a method of heating smokable material to volatilize at least one component of the smokable material according to an embodiment of the disclosure. 
     The method  900  comprises providing  901  a heating element formed from heating material that is heatable by penetration with a varying magnetic field, wherein first and second portions of the heating element have different respective thermal masses. The heating element could, for example, be a heating element of apparatus for heating smokable material to volatilize at least one component of the smokable material, such as one of the heating elements  20 ,  40  discussed above with reference to  FIGS. 5 and 6 . Alternatively, the heating element could, for example, be a heating element of an article comprising the smokable material, such as one of the heating elements  10 ,  20  discussed above with reference to  FIGS. 3 and 4 . The thermal masses may differ as a result of the density or the thickness of the first and second portions of the heating element differing. 
     The method also comprises providing  902  smokable material in thermal contact with the heating element. The smokable material could be comprised in an article, such as that shown in  FIG. 3  or that shown in  FIG. 4 . The smokable material may be in thermal contact with the heating element as a result of the heating element also being part of the article, as is the case in  FIGS. 3 and 4 . Alternatively, the smokable material may be placed in thermal contact with the heating element as a result of inserting smokable material into the heating zone of an apparatus comprising the heating element, as is the case in  FIGS. 5 and 6 . 
     The method further comprises penetrating  903  the heating element with a varying magnetic field so that the penetrating causes progressive heating of the heating element and thereby progressive heating of the smokable material. Examples of such progressive heating are described above. The heating of the smokable material may be such as to volatilize at least one component of the smokable material without combusting the smokable material. 
     In each of the embodiments discussed above the heating material is steel. However, in other embodiments, the heating material may comprise one or more materials selected from the group consisting of: an electrically-conductive material, a magnetic material, and a magnetic electrically-conductive material. In some embodiments, the heating material may comprise a metal or a metal alloy. In some embodiments, the heating material may comprise one or more materials selected from the group consisting of: aluminum, gold, iron, nickel, cobalt, conductive carbon, graphite, plain-carbon steel, stainless steel, ferritic stainless steel, copper, and bronze. Other heating material(s) may be used in other embodiments. It has been found that, when magnetic electrically-conductive material is used as the heating material, magnetic coupling between the magnetic electrically-conductive material and an electromagnet of the apparatus in use may be enhanced. In addition to potentially enabling magnetic hysteresis heating, this can result in greater or improved Joule heating of the heating material, and thus greater or improved heating of the smokable material. 
     In each of the embodiments discussed above the heating element consists of, or consists essentially of, the heating material. However, in other embodiments, this may not be the case. 
     The heating material may have a skin depth, which is an exterior zone within which most of an induced electrical current and/or induced reorientation of magnetic dipoles occurs. By providing that the heating material has a relatively small thickness, a greater proportion of the heating material may be heatable by a given varying magnetic field, as compared to heating material having a depth or thickness that is relatively large as compared to the other dimensions of the heating material. Thus, a more efficient use of material is achieved and, in turn, costs are reduced. 
     In each of the above described embodiments, the smokable material comprises tobacco. However, in respective variations to each of these embodiments, the smokable material may consist of tobacco, may consist substantially entirely of tobacco, may comprise tobacco and smokable material other than tobacco, may comprise smokable material other than tobacco, or may be free from tobacco. In some embodiments, the smokable material may comprise a vapor or aerosol forming agent or a humectant, such as glycerol, propylene glycol, triacetin, or diethylene glycol. 
     In each of the above described embodiments, the smokable material is non-liquid smokable material, and the apparatus is for heating non-liquid smokable material to volatilize at least one component of the smokable material. In other embodiments, the opposite may be true. 
     In each of the above described embodiments, the article  1 ,  2 ,  3 ,  4  is a consumable article. Once all, or substantially all, of the volatilizable component(s) of the smokable material  60  in the article  1 ,  2 ,  3 ,  4  has/have been spent, the user may remove the article  1 ,  2 ,  3 ,  4  from the apparatus  100 ,  200  and dispose of the article  1 ,  2 ,  3 ,  4 . The user may subsequently re-use the apparatus  100 ,  200  with another of the articles  1 ,  2 ,  3 ,  4 . However, in other respective embodiments, the article may be non-consumable, and the apparatus and the article may be disposed of together once the volatilizable component(s) of the smokable material has/have been spent. 
     In some embodiments, the apparatus  100 ,  200  is sold, supplied or otherwise provided separately from the articles  1 ,  2 ,  3 ,  4  with which the apparatus  100 ,  200  is usable. However, in some embodiments, the apparatus  100 ,  200  and one or more of the articles  1 ,  2 ,  3 ,  4  may be provided together as a system, such as a kit or an assembly, possibly with additional components, such as cleaning utensils. 
     In order to address various issues and advance the art, the entirety of this disclosure shows by way of illustration and example various embodiments in which the claimed invention may be practiced and which provide for superior heating elements for use with an apparatus for heating smokable material to volatilize at least one component of the smokable material, superior articles comprising such heating elements and usable with such an apparatus, superior apparatus comprising such heating elements and for heating smokable material to volatilize at least one component of the smokable material, superior systems comprising such an apparatus, and superior methods of heating smokable material to volatilize at least one component of the smokable material. The advantages and features of the disclosure are of a representative sample of embodiments only, and are not exhaustive and/or exclusive. They are presented only to assist in understanding and teach the claimed and otherwise disclosed features. It is to be understood that advantages, embodiments, examples, functions, features, structures and/or other aspects of the disclosure are not to be considered limitations on the disclosure as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilized and modifications may be made without departing from the scope and/or spirit of the disclosure. Various embodiments may suitably comprise, consist of, or consist in essence of, various combinations of the disclosed elements, components, features, parts, steps, means, etc. The disclosure may include other inventions not presently claimed, but which may be claimed in future.