THERMALLY ENHANCED AEROSOL-FORMING SUBSTRATE

Abstract

There is provided an aerosol-forming substrate for use in a heated aerosol-generating article, the aerosol-forming substrate comprising a co-laminated sheet comprising a layer of aerosol-forming material and a layer of carbon-based thermally conductive material.

Claims

1. An aerosol-forming substrate for use in a heated aerosol-generating article, the aerosol-forming substrate comprising a co-laminated sheet comprising a layer of aerosol-forming material and a layer of carbon-based thermally conductive material different to the aerosol-forming material, wherein: the layer of carbon-based thermally conductive material comprises a reconstituted carbon-based material, the reconstituted carbon-based material comprising an aerosol former and thermally conductive particles; and the thermally conductive particles each have a thermal conductivity of at least 1 Watt per metre Kelvin in at least one direction at 25 degrees Celsius.

2. An aerosol-forming substrate according to claim 1, wherein the layer of carbon-based thermally conductive material is in the form of a film or foil.

3. An aerosol-forming substrate according to claim 1, wherein the layer of carbon-based thermally conductive material comprises carbon fibres, graphite or graphene.

4. An aerosol-forming substrate according to claim 1, wherein the reconstituted carbon-based material comprises the aerosol former on a dry weight basis of between 7 and 60 wt %.

5. An aerosol-forming substrate according to claim 1, wherein the co-laminated sheet comprises or is in the form of a gathered sheet.

6. An aerosol-forming substrate according to claim 1, wherein some or all of the thermally conductive particles comprise one or more of graphite, expanded graphite, graphene, carbon nanotubes and charcoal.

7. An aerosol-forming substrate according to claim 1, wherein the reconstituted carbon-based material comprises one or both of fibres and a binder.

8. A rod for an aerosol-generating article, the rod comprising an aerosol-forming substrate as defined in claim 1.

9. A heated aerosol-generating article comprising a rod according to claim 8.

10. An aerosol-generating system comprising an aerosol-generating article according claim 9 and an electrically operated aerosol-generating device.

11. A method of forming an aerosol-forming substrate comprising: combining a layer of aerosol-forming material with a layer of carbon-based thermally conductive material different to the aerosol forming-material to form a co-laminated sheet, wherein: the layer of carbon-based thermally conductive material comprises a reconstituted carbon-based material, the reconstituted carbon-based material comprising an aerosol former and thermally conductive particles; and the thermally conductive particles each have a thermal conductivity of at least 1 Watt per metre Kelvin in at least one direction at 25 degrees Celsius.

12. A method of forming an aerosol-forming substrate according to claim 11, wherein the method further comprises the step of forming the layer of aerosol-forming material.

13. A method of forming an aerosol-forming substrate according to claim 12, wherein the step of combining the sheets comprises casting the layer of aerosol-forming material on top of the layer of carbon-based thermally conductive material.

14. A method of forming a rod comprising an aerosol-forming substrate, the method comprising the steps of: providing a co-laminated sheet comprising an aerosol-forming material and a carbon-based thermally conductive material different to the aerosol forming-material, wherein the layer of carbon-based thermally conductive material comprises a reconstituted carbon-based material, the reconstituted carbon-based material comprising an aerosol former and thermally conductive particles, the thermally conductive particles each having a thermal conductivity of at least 1 Watt per metre Kelvin in at least one direction at 25 degrees Celsius; gathering the co-laminated sheet transversely relative to its longitudinal axis; circumscribing the gathered co-laminated sheet with a wrapper to form a continuous rod; and severing the continuous rod into a plurality of discrete rods.

15. A method of forming an aerosol-generating article comprising assembling the aerosol-generating article from a plurality of components, the plurality of components including an aerosol-forming substrate according to claim 1.

Description

[0339] Specific embodiments will be further described, by way of example only, with reference to the accompanying drawings in which:

[0340] FIG. 1 shows a schematic cross-sectional view of a first embodiment of an aerosol-generating article;

[0341] FIG. 2 shows a schematic cross-section of a first apparatus for forming a rod according to a specific embodiment;

[0342] FIG. 3 shows a schematic cross-section of a first apparatus for forming a rod according to a specific embodiment;

[0343] FIG. 4 shows a schematic cross-sectional view of a first embodiment of an aerosol-generating system;

[0344] FIG. 5 shows a schematic cross-sectional view of a second embodiment of an aerosol-generating system; and

[0345] FIG. 6 shows a schematic cross-sectional view of a second embodiment of an aerosol-generating article.

[0346] FIG. 1 shows a schematic cross-sectional view of a first embodiment of an aerosol-generating article 10. The aerosol-generating article 10 comprises a rod 12 of aerosol-forming substrate and a downstream section 14 at a location downstream of the rod 12 of aerosol-forming substrate. Further, the aerosol-generating article 10 comprises an upstream section 16 at a location upstream of the rod 12 of aerosol-forming substrate. Thus, the aerosol-generating article 10 extends from an upstream or distal end 18 to a downstream or proximal or mouth end 20.

[0347] The aerosol-generating article has an overall length of about 45 millimetres.

[0348] The downstream section 14 comprises a support element 22 located immediately downstream of the rod 12 of aerosol-forming substrate, the support element 22 being in longitudinal alignment with the rod 12. In the embodiment of FIG. 1, the upstream end of the support element 22 abuts the downstream end of the rod 12 of aerosol-generating substrate. In addition, the downstream section 14 comprises an aerosol-cooling element 24 located immediately downstream of the support element 22, the aerosol-cooling element 24 being in longitudinal alignment with the rod 12 and the support element 22. In the embodiment of FIG. 1, the upstream end of the aerosol-cooling element 24 abuts the downstream end of the support element 22.

[0349] As will become apparent from the following description, the support element 22 and the aerosol-cooling element 24 together define an intermediate hollow section 50 of the aerosol-generating article 10. As a whole, the intermediate hollow section 50 does not substantially contribute to the overall RTD of the aerosol-generating article. An RTD of the intermediate hollow section 26 as a whole is substantially 0 millimetres H.sub.2O.

[0350] The support element 22 comprises a first hollow tubular segment 26. The first hollow tubular segment 26 is provided in the form of a hollow cylindrical tube made of cellulose acetate. The first hollow tubular segment 26 defines an internal cavity 28 that extends all the way from an upstream end 30 of the first hollow tubular segment to a downstream end 32 of the first hollow tubular segment 20. The internal cavity 28 is substantially empty, and so substantially unrestricted airflow is enabled along the internal cavity 28. The first hollow tubular segment 26and, as a consequence, the support element 22does not substantially contribute to the overall RTD of the aerosol-generating article 10. In more detail, the RTD of the first hollow tubular segment 26 (which is essentially the RTD of the support element 22) is substantially 0 millimetres H.sub.2O.

[0351] The first hollow tubular segment 26 has a length of about 8 millimetres, an external diameter of about 7.25 millimetres, and an internal diameter (D.sub.FTS) of about 1.9 millimetres. Thus, a thickness of a peripheral wall of the first hollow tubular segment 26 is about 2.67 millimetres.

[0352] The aerosol-cooling element 24 comprises a second hollow tubular segment 34. The second hollow tubular segment 34 is provided in the form of a hollow cylindrical tube made of cellulose acetate. The second hollow tubular segment 34 defines an internal cavity 36 that extends all the way from an upstream end 38 of the second hollow tubular segment to a downstream end 40 of the second hollow tubular segment 34. The internal cavity 36 is substantially empty, and so substantially unrestricted airflow is enabled along the internal cavity 36. The second hollow tubular segment 28and, as a consequence, the aerosol-cooling element 24does not substantially contribute to the overall RTD of the aerosol-generating article 10. In more detail, the RTD of the second hollow tubular segment 34 (which is essentially the RTD of the aerosol-cooling element 24) is substantially 0 millimetres H.sub.2O.

[0353] The second hollow tubular segment 34 has a length of about 8 millimetres, an external diameter of about 7.25 millimetres, and an internal diameter (D.sub.STS) of about 3.25 millimetres. Thus, a thickness of a peripheral wall of the second hollow tubular segment 34 is about 2 millimetres. Thus, a ratio between the internal diameter (D.sub.FTS) of the first hollow tubular segment 26 and the internal diameter (D.sub.STS) of the second hollow tubular segment 34 is about 0.75.

[0354] The aerosol-generating article 10 comprises a ventilation zone 60 provided at a location along the second hollow tubular segment 34. In more detail, the ventilation zone is provided at about 2 millimetres from the upstream end of the second hollow tubular segment 34. In this embodiment, the ventilation zone 60 comprises a circumferential row of perforations through a paper wrapper 70 and a ventilation level of the aerosol-generating article 10 is about 25 percent.

[0355] In the embodiment of FIG. 1, the downstream section 14 further comprises a mouthpiece element 42 at a location downstream of the intermediate hollow section 50. In more detail, the mouthpiece element 42 is positioned immediately downstream of the aerosol-cooling element 24. As shown in the drawing of FIG. 1, an upstream end of the mouthpiece element 42 abuts the downstream end 40 of the aerosol-cooling element 24.

[0356] The mouthpiece element 42 is provided in the form of a cylindrical plug of low-density cellulose acetate.

[0357] The mouthpiece element 42 has a length of about 12 millimetres and an external diameter of about 7.25 millimetres. The RTD of the mouthpiece element 42 is about 12 millimetres H.sub.2O. The ratio of the length of the mouthpiece element 42 to the length of the intermediate hollow section 50 is approximately 0.6.

[0358] The rod 12 of aerosol-forming substrate has an external diameter of about 7.25 millimetres and a length of about 12 millimetres.

[0359] The upstream section 16 comprises an upstream element 46 located immediately upstream of the rod 12 of aerosol-forming substrate, the upstream element 46 being in longitudinal alignment with the rod 12. In the embodiment of FIG. 1, the downstream end of the upstream element 46 abuts the upstream end of the rod 12 of aerosol-forming substrate. The upstream element 46 is provided in the form of a cylindrical plug of cellulose acetate. The upstream element 46 has a length of about 5 millimetres. The RTD of the upstream element 46 is about 30 millimetres H.sub.2O.

[0360] The upstream element 46, rod 12 of aerosol-forming substrate, support element 22, aerosol-cooling element 24, and mouthpiece element 42 are circumscribed by the paper wrapper 70.

[0361] The rod 12 of aerosol-forming substrate comprises a gathered co-laminated sheet comprising a layer of aerosol-forming material 13 and a layer of carbon-based thermally conductive material 15. The layer of aerosol-forming material 13 is in intimate contact with the layer of carbon-based thermally conductive material with one layer being stacked on top of the other layer. As will be described below, the sheet is gathered so as to form a plurality of substantially parallel ridges or corrugations. As such, the cross-section of the sheet shown in FIG. 1 appears to have a plurality of layers of aerosol-forming material 13 sandwiched between layers of carbon-based thermally conductive material 15 resulting from the corrugated co-laminated structure of the rod of aerosol-forming substrate 12.

[0362] The aerosol-forming material 13 comprises a reconstituted sheet comprising tobacco material and glycerine.

[0363] The layer of carbon-based thermally conductive material 15 is a foil made of graphite, expanded graphite or both graphite and expanded graphite.

[0364] The cardboard tube 34 has a length of 16 mm and provides a free space within the article 10 within which volatile components generated by heating of the aerosol-forming substrate can cool and form an aerosol.

[0365] The mouthpiece element 42 is provided in the form of a cylindrical plug of low-density cellulose acetate. The mouthpiece element 42 has a length of about 12 millimetres and an external diameter of about 7.2 mm. The RTD of the mouthpiece element 42 is about 12 millimetres H.sub.2O.

[0366] It should be clear that the configuration of the aerosol-generating article 10 of FIG. 1 is intended to serve as an example only. The thermally enhanced aerosol-forming substrate could, for example, be employed in an aerosol generating article that is longer, for example 80 mm long, and thinner, for example 4.5 mm in diameter.

[0367] FIG. 2 shows an apparatus for forming the rod 12 of aerosol-forming substrate. The apparatus generally comprises: supply means for providing a continuous co-laminated sheet of homogenised tobacco and aluminium foil; crimping means for crimping the continuous co-laminated sheet; rod forming means for gathering the continuous crimped co-laminated sheet and circumscribing the gathered material with a wrapper to form a continuous rod; and cutting means for severing the continuous rod into a plurality of discrete rods. The apparatus also comprises transport means for transporting the continuous co-laminated sheet of material downstream through the apparatus from the supply means to the rod forming means via the crimping means.

[0368] As shown in FIG. 2, the supply means for providing a continuous co-laminated sheet comprises a continuous co-laminated sheet comprising a layer of aerosol-forming material and a layer of thermally conductive material, the continuous co-laminated sheet being mounted on a bobbin 4. The crimping means comprises a pair of rotatable crimping rollers 6. In use, the continuous co-laminated sheet 2 is drawn from the first bobbin 4 and transported downstream to the pair of crimping rollers 6 by the transport means via a series of guide and tensioning rollers. As the continuous co-laminated sheet 2 is fed between the pair of crimping rollers 6, the crimping rollers engage and crimp the sheet 2 to form a continuous crimped co-laminated sheet 8 having a plurality of spaced-apart ridges or corrugations substantially parallel to the longitudinal axis of the sheet through the apparatus.

[0369] The continuous crimped sheet 8 is transported downstream from the pair of crimping rollers 6 towards the rod forming means and fed through a converging funnel or horn 31. The converging funnel 31 gathers the continuous co-laminated sheet 8 transversely relative to its longitudinal axes. The sheet of material 8 assumes a substantially cylindrical configuration as it passes through the converging funnel 31.

[0370] Upon exiting the converging funnel 31, the gathered co-laminated sheet is wrapped in a continuous sheet of wrapping material 37. The continuous sheet of wrapping material is fed from a bobbin 35 and enveloped around the gathered continuous crimped sheet of homogenised tobacco material by an endless belt conveyor or garniture. As shown in FIG. 1, the rod forming means comprises an adhesive application means 17 that applies adhesive to one of the longitudinal edges of the continuous sheet of wrapping material, so that when the opposed longitudinal edges of the continuous sheet of wrapping material are brought into contact they adhere to one other to form a continuous rod.

[0371] The rod forming means further comprises a drying means 19 downstream of the adhesive application means 17, which in use dries the adhesive applied to the seam of the continuous rod as the continuous rod is transported downstream from the rod forming means to the cutting means.

[0372] The cutting means comprises a rotary cutter 21 that severs the continuous rod into a plurality of discrete rods of unit rod length or multiple unit rod length.

[0373] FIG. 3 shows an alternative apparatus for forming the rod 12 of aerosol-forming substrate. The apparatus of FIG. 3 is similar to the apparatus of FIG. 2 and like features are numbered accordingly. The difference between the apparatus of FIG. 2 and FIG. 3 is that the apparatus of FIG. 3 comprises separate bobbins for a continuous sheet of aerosol-forming material and a continuous sheet of thermally conductive material rather than a single bobbin 43 comprising a co-laminated sheet of aerosol-forming substrate.

[0374] In the apparatus of FIG. 3, a continuous sheet of aerosol-forming material is mounted on a primary bobbin 23 and a continuous sheet of carbon-based thermally conductive material is mounted on a secondary bobbin 33. In use, the continuous sheet of aerosol-forming material is drawn from the primary bobbin 23 and transported downstream to the pair of crimping rollers 6 by the transport mechanism via a series of guide and tensioning rollers. The continuous sheet carbon-based thermally conductive material is similarly drawn from the secondary bobbin 33 and transported downstream to the pair of crimping rollers 6 by the transport mechanism. Prior to passing through the crimping rollers 6, the continuous sheet of carbon-based thermally conductive material is brought into intimate contact with the aerosol-forming material such that the carbon-based thermally conductive material overlies the aerosol-forming material. This forms a continuous co-laminated sheet comprising a layer of carbon-based thermally conductive material and a layer of aerosol-forming material which passes through the crimping rollers 6. The continuous co-laminated sheet then proceeds through the apparatus of FIG. 3 in the same way as described in relation to FIG. 2.

[0375] In other embodiments, the bobbin of aerosol-forming material may be swapped with the bobbin of carbon-based thermally conductive material such that the aerosol-forming material overlies the carbon-based thermally conductive material prior to passing through the crimping rollers.

[0376] In one embodiment, the aerosol-forming material described above is formed by a casting process comprising the following steps: [0377] pre-mixing finely shredded tobacco material, a binder, guar gum, with an aerosol-former, glycerine, to form a pre-mixture; [0378] mixing the pre-mixture with water to form a slurry; [0379] homogenising the slurry using a high-shear mixer; [0380] casting the slurry onto a conveyor belt; and [0381] controlling a thickness of the slurry and drying the slurry to form a large sheet of aerosol-forming material.

[0382] The above process may be used to produce a continuous sheet of aerosol-forming material for the bobbin 23 of the apparatus of FIG. 3.

[0383] In another embodiment, the aerosol-forming material described above is formed by a casting process comprising the following steps: [0384] pre-mixing finely shredded tobacco material, a binder, guar gum, with an aerosol-former, glycerine, to form a pre-mixture; [0385] mixing the pre-mixture with water to form a slurry; [0386] homogenising the slurry using a high-shear mixer; [0387] casting the slurry onto a continuous sheet of carbon-based thermally conductive material; and [0388] controlling a thickness of the slurry and drying the slurry to form a large sheet of aerosol-forming material.

[0389] The above process may be used to produce a continuous co-laminated sheet comprising a layer of aerosol-forming material. The above process may be used to produce a continuous sheet of aerosol-forming material for the bobbin 4 of the apparatus of FIG. 2.

[0390] In one embodiment, the carbon-based thermally conductive material is a commercially available foil or film.

[0391] Suitable carbon-based thermally conductive materials are available from NeoGraf solutions LLC, 11709 Madison Avenue, Lakewood, Ohio, United States 44107. In particular, the range of eGraf SpreaderShield (registered trademark) Heat Spreaders are suitable carbon-based thermally conductive materials. NeoGraf solutions provide low density Heat Spreaders in the form of a film or foil and having an in-plane conductivity of between 300 and 1600 W/(mK), a thickness as low as 17 micrometres and a tensile strength of greater than 7 Megapascals.

[0392] Another example of suitable carbon-based thermally conductive materials are the range of EYGS182307 PGS graphite sheets of Panasonic Industry available from RS Components (https://uk.rs-online.com/web/).

[0393] In another embodiment, the carbon-based thermally conductive material is a reconstituted carbon-based material.

[0394] In one embodiment, the method comprises forming the reconstituted carbon-based material. A slurry is formed using a lab disperser capable of mixing viscous liquids, dispersing powders through liquids, and removing gas from a mixture (for example by applying a vacuum or other suitably low pressure). In this embodiment, a commercially available lab disperser from PC Laborsystem was used.

[0395] To form the slurry, a first mixture is formed by adding to the lap disperser around 7.11 grams of the aerosol former, then around 157.5 grams of water, then around 1.57 grams of the fibres. Then, these first ingredients are mixed at 25 degrees Celsius for 5 minutes at 600-700 rpm to ensure a homogeneous mixture and to hydrate the fibers. Then, a second mixture is formed by manually mixing around 32.95 grams of the thermally conductive particles and around 0.92 grams of the binder. This mixing of the second mixture avoids the formation of lumps in the lab dispersion. Then, the second mixture is added to the first mixture to form a combined mixture. Then, the combined mixture is mixed at 5000 rpm for 4 minutes at 25 degrees Celsius and a first reduced pressure of around 200 mbar. The reduced pressure may help to ensure that the thermally conductive particles are homogeneously dispersed in the mixture and that there is little trapped air and few lumps in the combined mixture. Then, the combined mixture is mixed at 5000 rpm for 20 second minutes at 25 degrees Celsius and a second reduced pressure of around 100 mbar. This second reduced pressure may help to remove any remaining air bubbles. This forms a slurry for casting.

[0396] The slurry is then casted and dried using a suitable apparatus. In this embodiment, a commercially available Labcoater Mathis apparatus is used. This apparatus includes a stainless steel, flat support, and a coma blade for adjusting a thickness of slurry cast onto the flat support.

[0397] The slurry is cast onto the flat support and a gap between the coma blade and the flat support is set at 0.6 millimetres. This ensures that a thickness of the slurry is no more than 0.6 millimetres at any given point.

[0398] The slurry is then dried with hot air between 120 and 140 degrees Celsius for between 2 and 5 minutes. After this drying, a sheet of the aerosol-forming substrate is formed. This sheet has a thickness of around 159 microns, a grammage of around 125.7 grams per metre squared, and a density of around 0.79 kilograms per metre cubed.

[0399] FIG. 4 shows a schematic cross-sectional view of a first embodiment of an aerosol-generating system 100. The system 100 comprises an aerosol-generating device 102 and the aerosol-generating article 10 of FIG. 1.

[0400] The aerosol-generating device 102 comprises a battery 104, a controller 106, a heating blade 108 coupled to the battery, and a puff-detection mechanism (not shown). The controller 106 is coupled to the battery 104, the heating blade 108 and the puff-detection mechanism.

[0401] The aerosol-generating device 102 further comprises a housing 110 defining a substantially cylindrical cavity for receiving a portion of the article 10. The heating blade 108 is positioned centrally within the cavity and extends longitudinally from a base of the cavity.

[0402] In this embodiment, the heating blade 108 comprises a substrate and an electrically resistive track located on the substrate. The battery 104 is coupled to the heating blade 108 so as to be able to pass a current through the electrically resistive track and heat the electrically resistive track and heating blade 108 to an operational temperature.

[0403] In use, a user inserts the article 10 into the cavity, causing the heating blade 108 to penetrate the upstream element 46 and rod 12 of aerosol-forming substrate of the article 10. FIG. 4 shows the article 10 inserted into the cavity of the device 102.

[0404] Then, the user puffs on the downstream end of the article 10. This causes air to flow through an air inlet (not shown) of the device 102, then through the article 10, from the upstream end 18 to the downstream end 20, and into the mouth of the user.

[0405] The user puffing on the article 10 causes air to flow through the air inlet of the device. The puff-detection mechanism detects that the air flow rate through the air inlet has increased to greater than a non-zero threshold flow rate. The puff-detection mechanism sends a signal to the controller 106 accordingly. The controller 106 then controls the battery 104 so as to pass a current through the electrically resistive track and heat up the heating blade 108. This heats up the rod 12 of aerosol-forming substrate, which is in contact with the heating blade 108.

[0406] The layer of thermally conductive material has a significantly higher thermal conductivity than the surrounding aerosol-forming material. As such, the layer of thermally conductive material may conduct heat energy throughout the bulk of the aerosol-forming material. This may result in a greater proportion of the aerosol-forming substrate reaching a sufficiently high temperature to release volatile compounds, and thus a higher usage efficiency of the aerosol-forming substrate.

[0407] Heating of the aerosol-forming substrate causes the aerosol-forming substrate to release volatile compounds. These compounds are entrained by the air flowing from the upstream end 18 of the article 10 towards the downstream end 20 of the article 10. The compounds cool and condense to form an aerosol as they pass through the internal cavities 28, 36 of the support element 22 and the aerosol-cooling element 24. The aerosol then passes through the mouthpiece element 42, which may filter out unwanted particles entrained in the air flow, and into the mouth of the user.

[0408] When the user stops inhaling on the article 10, the air flow rate through the air inlet of the device decreases to less than the non-zero threshold flow rate. This is detected by the puff-detection mechanism. The puff-detection mechanism sends a signal to the controller 106 accordingly. The controller 106 then controls the battery 104 so as to reduce the current being passed through the electrically resistive track to zero.

[0409] After a number of puffs on the article 10, the user may choose to replace the article 10 with a fresh article.

[0410] FIG. 5 shows a schematic cross-sectional view of a second embodiment of an aerosol-generating system 200. The system 200 comprises an aerosol-generating device 202 and the aerosol-generating article 11 of FIG. 1.

[0411] The aerosol-generating device 202 comprises a battery 204, a controller 206, an inductor coil 208, and a puff-detection mechanism (not shown). The controller 206 is coupled to the battery 204, the inductor coil 208 and the puff-detection mechanism.

[0412] The aerosol-generating device 202 further comprises a housing 210 defining a substantially cylindrical cavity for receiving a portion of the article 11. The inductor coil 208 spirals around the cavity.

[0413] The battery 204 is coupled to the inductor coil 208 so as to be able to pass an alternating current through the inductor coil 208.

[0414] In use, a user inserts the article 11 into the cavity. FIG. 5 shows the article 11 inserted into the cavity of the device 202.

[0415] Then, the user puffs on the downstream end of the article 11. This causes air to flow through an air inlet (not shown) of the device 202, then through the article 11, from the upstream end 18 to the downstream end 20, and into the mouth of the user.

[0416] The user puffing on the article 11 causes air to flow through the air inlet of the device. The puff-detection mechanism detects that the air flow rate through the air inlet has increased to greater than a non-zero threshold flow rate. The puff-detection mechanism sends a signal to the controller 206 accordingly. The controller 206 then controls the battery 204 so as to pass an alternating current through the inductor coil 208. This causes the inductor coil 208 to generate a fluctuating electromagnetic field. The rod 13 of combined aerosol-forming substrate is located within this fluctuating electromagnetic field. The materials of the thermally conductive material 15, graphite and expanded graphite, are susceptor materials. Thus, the fluctuating electromagnetic field causes eddy currents in the thermally conductive material 15 (which is also electrically conductive). This causes the thermally conductive material 15 to heat up, thereby also heating nearby aerosol-forming material.

[0417] Heating of the aerosol-forming material cause the aerosol-forming material to release volatile compounds. These compounds are entrained by the air flowing from the upstream end 18 of the article 11 towards the downstream end 20 of the article 11. The compounds cool and condense to form an aerosol as they pass through the internal cavities 28, 36 of the support element and the aerosol-cooling element. The aerosol then passes through the mouthpiece element 42, which may filter out unwanted particles entrained in the air flow, and into the mouth of the user.

[0418] When the user stops inhaling on the article 11, the air flow rate through the air inlet of the device decreases to less than the non-zero threshold flow rate. This is detected by the puff-detection mechanism. The puff-detection mechanism sends a signal to the controller 206 accordingly. The controller 206 then controls the battery 204 so as to reduce the current being passed through the electrically resistive track to zero.

[0419] After a number of puffs on the article 11, the user may choose to replace the article 11 with a fresh article.

[0420] FIG. 6 shows a schematic cross-sectional view of a second embodiment of an aerosol-generating article 510. This second embodiment is identical to the first embodiment of FIG. 1 except that the rod 12 of aerosol-forming substrate has been replaced by an alternative rod 512 of aerosol-forming substrate. Identical reference numerals have been used for identical components in the embodiments of FIGS. 1 and 6.

[0421] The rod 512 of aerosol-forming substrate of the second embodiment of FIG. 6 is identical to the rod 12 of aerosol-forming substrate of the first embodiment of FIG. 1 except that the rod 512 of aerosol-forming substrate of the second embodiment of FIG. 6 additionally includes an elongate susceptor element 580.

[0422] The susceptor element 580 is arranged substantially longitudinally within the rod 512 of aerosol-forming substrate so as to be approximately parallel with a longitudinal axis of the rod 512 of aerosol-forming substrate. As shown in the drawing of FIG. 6, the susceptor element 580 is positioned in a radially central position within the rod and extends along the longitudinal axis of the rod 12.

[0423] The susceptor element 580 extends all the way from an upstream end to a downstream end of the rod 512 of aerosol-forming substrate. As such, the susceptor element 580 has substantially the same length as the rod 512 of aerosol-forming substrate.

[0424] In the embodiment of FIG. 6, the susceptor element 580 is provided in the form of a strip of a ferromagnetic steel and has a length of about 12 millimetres, a thickness of about 60 micrometres, and a width of about 4 millimetres.

[0425] The aerosol-generating article 510 of FIG. 6 may be used with the aerosol-generating device 202 of FIG. 4 in the same way as the aerosol-generating article 11 of FIG. 2. Notably, the inclusion of the susceptor element 580 means that the article 510 may be inductively heated regardless of whether the thermally conductive material comprise a suitable susceptor material for inductive heating.

[0426] For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term about. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In this context, therefore, a number A is understood as A10% of A. Within this context, a number A may be considered to include numerical values that are within general standard error for the measurement of the property that the number A modifies. The number A, in some instances as used in the appended claims, may deviate by the percentages enumerated above provided that the amount by which A deviates does not materially affect the basic and novel characteristic(s) of the claimed invention. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.