AEROSOL-GENERATING DEVICE COMPRISING AN INDUCTIVE HEATING ARRANGEMENT COMPRISING FIRST AND SECOND LC CIRCUITS HAVING DIFFERENT RESONANCE FREQUENCIES

Abstract

An aerosol-generating device is provided, including: a device cavity having proximal and distal ends, the proximal end of the cavity to receive an aerosol-generating article; an inductive heating arrangement to heat the substrate and including: a susceptor arrangement heatable by penetration with a varying magnetic field to heat the substrate, a first LC circuit having a first resonance frequency and including a first inductor coil towards the proximal end and a first capacitor, and a second LC circuit having a second resonance frequency different from the first resonance frequency and including a second inductor coil towards the distal end and a second capacitor, and having a different number of turns than the first coil; and a controller to initiate heating of the substrate by driving a first varying current in the first coil and subsequently driving a second varying current in the second coil.

Claims

1.-23. (canceled)

24. An aerosol-generating device, comprising: a device cavity having a proximal end and a distal end opposite the proximal end, wherein the proximal end of the device cavity is substantially open and configured to receive an aerosol-generating article; an inductive heating arrangement configured to heat the aerosol-forming substrate, the inductive heating arrangement comprising: a susceptor arrangement that is heatable by penetration with a varying magnetic field to heat the aerosol-forming substrate, a first LC circuit comprising a first inductor coil arranged towards the proximal end of the device cavity and a first capacitor, wherein the first LC circuit has a first resonance frequency, and a second LC circuit comprising a second inductor coil arranged towards the distal end of the device cavity and a second capacitor, wherein the second LC circuit has a second resonance frequency different from the first resonance frequency of the first LC circuit, and wherein the second inductor coil has a different number of turns that that of the first inductor coil; and a controller configured to initiate heating of the aerosol-forming substrate by driving a first varying current in the first inductor coil and subsequently driving a second varying current in the second inductor coil.

25. The aerosol-generating device according to claim 24, wherein the controller is further configured to: drive the first LC circuit with a first AC current for generating a first alternating magnetic field for heating a first portion of the susceptor arrangement, drive the second LC circuit with a second AC current for generating a second alternating magnetic field for heating a second portion of the susceptor arrangement, supply the first AC current with a frequency corresponding to the first resonance frequency of the first LC circuit, and to supply the second AC current with a frequency corresponding to the second resonance frequency of the second LC circuit.

26. The aerosol-generating device according to claim 25, wherein the controller is further configured to: supply the first AC current to the first LC circuit during a first phase to increase the temperature of the first portion of the susceptor arrangement from an initial temperature to a first operating temperature, and supply the first AC current with a frequency corresponding to the first resonance frequency of the first LC circuit during the first phase.

27. The aerosol-generating device according to claim 26, wherein the controller is further configured to: supply the first AC current to the first LC circuit during a second phase to decrease the temperature of the first portion of the susceptor arrangement from the first operating temperature to a second operating temperature, and supply the first AC current with a frequency different from the first resonance frequency of the first LC circuit during the second phase.

28. The aerosol-generating device according to claim 26, wherein the controller is further configured to: supply the second AC current to the second LC circuit during the first phase to increase the temperature of the second portion of the susceptor arrangement from an initial temperature to a third operating temperature, lower than the first operating temperature, and supply the second AC current with a frequency different from the second resonance frequency of the second LC circuit during the first phase.

29. The aerosol-generating device according to claim 28, wherein the controller is further configured to: supply the second AC current to the second LC circuit during the second phase to increase the temperature of the second portion of the susceptor arrangement from the third operating temperature to a fourth operating temperature, higher than the second operating temperature, and supply the second AC current with a frequency corresponding to the second resonance frequency of the second LC circuit during the second phase.

30. The aerosol-generating device according to claim 28, further comprising a power supply configured to provide power to the inductive heating arrangement.

31. The aerosol-generating device according to claim 24, wherein the controller comprises a microcontroller.

32. The aerosol-generating device according to claim 31, wherein the microcontroller is configured to utilize the clock frequency of the microcontroller as the alternating frequency of the first AC current or of the second AC current.

33. The aerosol-generating device according to claim 24, wherein the controller further comprises an oscillator configured to generate one or both of the alternating frequency of the first AC current and of the second AC current.

34. The aerosol-generating device according to claim 24, wherein the second coil is wound in a different direction that that of the first coil.

35. The aerosol-generating device according to claim 24, wherein the second coil has a different length than that of the first coil.

36. An aerosol-generating system, comprising: an aerosol-generating device according to claim 24, and an aerosol-generating article comprising an aerosol-forming substrate.

Description

[0170] Embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0171] FIG. 1 shows a schematic illustration of a susceptor arrangement according to an embodiment of this disclosure arranged between a pair of inductor coils;

[0172] FIG. 2 shows a schematic illustration of a susceptor arrangement according to an embodiment of this disclosure arranged between a pair of inductor coils;

[0173] FIG. 3 shows an exploded perspective view of a susceptor arrangement according to an embodiment of this disclosure;

[0174] FIG. 4 shows a perspective view of the susceptor arrangement of FIG. 3;

[0175] FIG. 5 shows a cross-sectional view of an aerosol-generating system according to an embodiment of this disclosure, the aerosol-generating system comprising an aerosol-generating article, and an aerosol-generating device having an inductive heating arrangement;

[0176] FIG. 6 a cross-sectional view of the proximal end of the aerosol-generating device of FIG. 5;

[0177] FIG. 7 shows a cross-sectional view of the aerosol-generating system of FIG. 5, with the aerosol-generating article received in the aerosol-generating device;

[0178] FIG. 8 shows a schematic illustration of a susceptor arrangement according to an embodiment of this disclosure arranged between a pair of inductor coils;

[0179] FIG. 9 shows a cross-sectional view of an aerosol-generating system according to another embodiment of this disclosure, the aerosol-generating system comprising an aerosol-generating article, and an aerosol-generating device having an inductive heating arrangement;

[0180] FIG. 10 shows a graph of temperature over time for the susceptor arrangement of FIG. 8;

[0181] FIG. 11 shows an illustrative circuit of an inductive heating arrangement;

[0182] FIG. 12 shows an illustrative circuit for controlling the inductive heating arrangement; and

[0183] FIG. 13 shows an illustration of pulse width modulated signals for driving the inductive heating arrangement.

[0184] FIG. 1 shows a schematic illustration of a susceptor arrangement 10 according to an embodiment of this disclosure. The susceptor arrangement 10 is an elongate, tubular element, having a circular transverse cross-section. The susceptor arrangement 10 comprises a first susceptor 12, a second susceptor 14, and a separation 15 between the first susceptor 12 and the second susceptor 14. The first susceptor 12 and the second susceptor 14 are each elongate, tubular elements having a circular transverse cross-section. The first susceptor 12 and the second susceptor 14 are coaxially aligned, end-to-end, along a longitudinal axis A-A.

[0185] The susceptor arrangement 10 comprises a cylindrical cavity 20, open at both ends, defined by an inner surfaces of the first susceptor 12 and the second susceptor 14. The cavity 20 is configured to receive a portion of a cylindrical aerosol-generating article (not shown), comprising an aerosol-forming substrate, such that an outer surface of the aerosol-generating article may be heated by the first susceptor and the second susceptor, thereby heating the aerosol-forming substrate.

[0186] The cavity 20 comprises three portions, a first portion 22 at a first end, defined by an inner surface of the tubular first susceptor 12, a second portion 24 at a second end, opposite the first end, defined by an inner surface of the tubular second susceptor 14, and an intermediate portion 26, bounded by the separation 15 between the first susceptor 12 and the second susceptor 14. The first susceptor 12 is arranged to heat a first portion of an aerosol-generating article received in the first portion 22 of the cavity 20, and the second susceptor 14 is arranged to heat a second portion of an aerosol-generating article received in the second portion 24 of the cavity 20.

[0187] A first inductor coil 32 is disposed around the first susceptor 12, and extends substantially the length of the first susceptor 12. As such, the first susceptor 12 is circumscribed by the first inductor coil 32 substantially along its length. When a varying electric current, preferably an AC current, is supplied to the first inductor coil 32, the first inductor coil 32 generates a varying magnetic field that is concentrated in the first portion 22 of the cavity 20. Such a varying magnetic field generated by the first inductor coil 32 induces eddy currents in the first susceptor 12, causing the first susceptor 12 to be heated.

[0188] A second inductor coil 34 is disposed around the second susceptor 14, and extends substantially the length of the second susceptor 14. As such, the second susceptor 14 is circumscribed by the second inductor coil 34 substantially along its length. When a varying electric current, preferably an AC current, is supplied to the second inductor coil 34, the second inductor coil 34 generates a varying magnetic field that is concentrated in the second portion 24 of the cavity 20. Such a varying magnetic field generated by the second inductor coil 34 induces eddy currents in the second susceptor 14, causing the second susceptor 14 to be heated.

[0189] The separation 15 between the first susceptor 12 and the second susceptor 14 provides a space between the first susceptor 12 and the second susceptor 14 that is not heated by induction when exposed to a varying magnetic field generated by either the first inductor coil 32 or the second inductor coil 34. Furthermore, the separation 15 thermally insulates the second susceptor 14 from the first susceptor 12, such that there is a reduced rate of heat transfer between the first susceptor 12 and the second susceptor 14, compared to a susceptor arrangement in which the first susceptor and the second susceptor are arranged adjacent each other, in direct thermal contact. As a result, providing the separation 15 between the first susceptor 12 and the second susceptor 14 enables selective heating of the first portion 22 of the cavity 20 by the first susceptor 12 with minimal heating of the second portion 24 of the cavity 20, and enables selective heating of the second portion 24 of the cavity 20 by the second susceptor 14 with minimal heating of the first portion 22 of the cavity 20.

[0190] The first susceptor 12 and the second susceptor 14 may be heated simultaneously by simultaneously supplying a varying electric current, preferably an AC current, to the first inductor coil 32 and the second inductor coil 34. Alternatively, the first susceptor 12 and the second susceptor 14 may be heated independently or alternately by supplying a varying electric current, preferably an AC current, to the first inductor coil 32 without supplying a current to the second inductor coil 34, and by subsequently supplying a varying electric current, preferably an AC current, to the second inductor coil 34 without supplying a current to the first inductor coil 32. It is also envisaged that a varying electric current, preferably an AC current, may be supplied to the first inductor coil 32 and the second inductor coil 34 in a sequence.

[0191] FIG. 2 shows a schematic illustration of a susceptor arrangement according to another embodiment of this disclosure. The susceptor arrangement shown in FIG. 2 is substantially identical to the susceptor arrangement shown in FIG. 1, and like reference numerals are used to describe like features.

[0192] The susceptor arrangement 10 of FIG. 2 is an elongate, tubular element, having a circular transverse cross-section. The susceptor arrangement 10 comprises a first susceptor 12, a second susceptor 14. The difference between the susceptor arrangement 10 of FIG. 1 and the susceptor arrangement 10 of FIG. 2 is that the susceptor arrangement 10 of FIG. 2 comprises an intermediate element 16 disposed between the first susceptor 12 and the second susceptor 14. In the embodiment of FIG. 2, there is still a separation between the first susceptor 12 and the second susceptor 14, however, the separation is filled by the intermediate element 16. In this embodiment, the intermediate element 16 is secured to an end of the first susceptor 12 and is also secured to an end of the second susceptor 14. Securing the intermediate element 16 to an end of the first susceptor 12, and securing the intermediate element 16 to an end of the second susceptor 14, indirectly connects the first susceptor 12 to the second susceptor 14. Advantageously, indirectly securing the first susceptor 12 to the second susceptor 14 enables the susceptor arrangement to form a unitary structure.

[0193] The intermediate element 16 comprises a thermally insulative material. The thermally insulative material is also electrically insulative. In this embodiment, the intermediate element 16 is formed from a polymeric material, such as PEEK. As such, the intermediate element 16 between the first susceptor 12 and the second susceptor 14 provides a space between the first susceptor 12 and the second susceptor 14 that is not heated by induction when exposed to a varying magnetic field generated by either the first inductor coil 32 or the second inductor coil 34. Furthermore, the intermediate element 16 thermally insulates the second susceptor 14 from the first susceptor 12, such that there is a reduced rate of heat transfer between the first susceptor 12 and the second susceptor 14, compared to a susceptor arrangement in which the first susceptor and the second susceptor are arranged adjacent each other, in direct thermal contact. The intermediate element 16 may also further reduce the rate of heat transfer between the first susceptor 12 and the second susceptor 14 compared to the separation 15 of the susceptor arrangement 10 of FIG. 1. As a result, providing the intermediate element 16 between the first susceptor 12 and the second susceptor 14 enables selective heating of the first portion 22 of the cavity 20 by the first susceptor 12 with minimal heating of the second portion 24 of the cavity 20, and enables selective heating of the second portion 24 of the cavity 20 by the second susceptor 14 with minimal heating of the first portion 22 of the cavity 20.

[0194] FIGS. 3 to 7 show schematic illustrations of an aerosol-generating system according to an embodiment of the present disclosure. The aerosol-generating system comprises an aerosol-generating device 100 and an aerosol-generating article 200. The aerosol-generating device 100 comprises an inductive heating arrangement 110 according to the present disclosure. The inductive heating arrangement 110 comprises a susceptor arrangement 120 according to the present disclosure.

[0195] FIGS. 3 and 4 show schematic illustrations of the susceptor arrangement 120. The susceptor arrangement 120 comprises: a first susceptor 122, a second susceptor 124, a third susceptor 126, a first intermediate element 128 and a second intermediate element 130. The first intermediate element 128 is disposed between the first susceptor 122 and the second susceptor 124. The second intermediate element 130 is disposed between the second susceptor 124 and the third susceptor 126.

[0196] In this embodiment, each of the first susceptor 122, the second susceptor 124 and the third susceptor 126 are identical. Each susceptor 122, 124, 126 is an elongate tubular susceptor, defining an inner cavity. Each susceptor, and its corresponding inner cavity, are substantially cylindrical, having a circular transverse cross-section that is constant along the length of the susceptor. The inner cavity of the first susceptor 122 defines a first region 134. The inner cavity of the second susceptor 124 defines a second region 136. The inner cavity of the third susceptor defines a third region 138.

[0197] Similarly, the first intermediate element 128 and the second intermediate element 130 are identical. The intermediate elements 128, 130 are tubular, defining an inner cavity. Each intermediate element 128, 130 is substantially cylindrical, having a circular transverse cross-section that is constant along the length of the intermediate element. The outer diameter of the intermediate elements 128, 130 is identical to the outer diameter of the susceptors 122, 124, 126, such that the outer surface of the intermediate elements 128, 130 may be aligned flush with the outer surface of the susceptors 122, 124, 126. The inner diameter of the intermediate elements 128, 130 is also identical to the inner diameter of the susceptors 122, 124, 126, such that the inner surface of the intermediate elements 128, 138 may be aligned flush with the inner surface of the susceptors 122, 124, 126.

[0198] The first susceptor 122, the first intermediate element 128, the second susceptor 124, the second intermediate element 130 and the third susceptor 126 are arranged end-to-end, and coaxially aligned on an axis B-B. In this arrangement, the susceptors 122, 124, 126 and the intermediate elements 128, 130 form a tubular, elongate, cylindrical structure. This structure forms the susceptor arrangement 120 in accordance with an embodiment of the present disclosure.

[0199] The elongate tubular susceptor arrangement 120 comprises an inner cavity 140. The susceptor arrangement cavity 140 is defined by the inner cavities of the susceptors 122, 124, 126 and the inner cavities of the intermediate elements 128, 130. The susceptor arrangement cavity 140 is configured to receive an aerosol-generating segment of the aerosol-generating article 200, as described in more detail below.

[0200] The intermediate elements 128, 130 are formed from an electrically insulative and thermally insulative material. As such, the susceptors 122, 124, 126 are substantially electrically and thermally insulated from each other. The material of the intermediate elements 128, 130 is also substantially impermeable to gas. In this embodiment, the tubular susceptor arrangement 120 is substantially impermeable to gas from an outer surface to an inner surface defining the susceptor arrangement cavity 140.

[0201] FIGS. 5, 6 and 7 show schematic cross-sections of the aerosol-generating device 100 and the aerosol-generating article 200.

[0202] The aerosol-generating device 100 comprises a substantially cylindrical device housing 102, with a shape and size similar to a conventional cigar. The device housing 102 defines a device cavity 104 at a proximal end. The device cavity 104 is substantially cylindrical, open at a proximal end, and substantially closed at a distal end, opposite the proximal end. The device cavity 104 is configured to receive the aerosol-generating segment 210 of the aerosol-generating article 200. Accordingly, the length and diameter of the device cavity 104 are substantially similar to the length and diameter of the aerosol-generating segment 210 of the aerosol-generating article 200.

[0203] The aerosol-generating device 100 further comprises a power supply 106, in the form of a rechargeable nickel-cadmium battery, a controller 108 in the form of a printed circuit board including a microprocessor, an electrical connector 109, and the inductive heating arrangement 110. The power supply 106, controller 108 and inductive heating arrangement 110 are all housed within the device housing 102. The inductive heating arrangement 110 of the aerosol-generating device 100 is arranged at the proximal end of the device 100, and is generally disposed around the device cavity 104. The electrical connector 109 is arranged at a distal end of the device housing 109, opposite the device cavity 104.

[0204] The controller 108 is configured to control the supply of power from the power supply 106 to the inductive heating arrangement 110. The controller 108 further comprises a DC/AC inverter, including a Class-D power amplifier, and is configured to supply a varying current, preferably an AC current, to the inductive heating arrangement 110. Additionally, or alternatively, the DC/AC inverter may comprise at least one of a Class-C and a Class-E power amplifier. The controller 108 is also configured to control recharging of the power supply 106 from the electrical connector 109. In addition, the controller 108 comprises a puff sensor (not shown) configured to sense when a user is drawing on an aerosol-generating article received in the device cavity 104.

[0205] The inductive heating arrangement 110 comprises three inductive heating units, including a first inductive heating unit 112, a second inductive heating unit 114 and a third inductive heating unit 116. The first inductive heating unit 112, second inductive heating unit 114 and third inductive heating unit 116 are substantially identical.

[0206] The first inductive heating unit 112 comprises a cylindrical, tubular first inductor coil 150, a cylindrical, tubular first flux concentrator 152 disposed about the first inductor coil 150 and a cylindrical, tubular first inductor unit housing 154 disposed about the first flux concentrator 152.

[0207] The second inductive heating unit 114 comprises a cylindrical, tubular second inductor coil 160, a cylindrical, tubular second flux concentrator 162 disposed about the second inductor coil 160 and a cylindrical, tubular second inductor unit housing 164 disposed about the second flux concentrator 162.

[0208] The third inductive heating unit 116 comprises a cylindrical, tubular third inductor coil 170, a cylindrical, tubular third flux concentrator 172 disposed about the third inductor coil 170 and a cylindrical, tubular third inductor unit housing 174 disposed about the third flux concentrator 172.

[0209] Accordingly, each inductive heating unit 112, 114, 116 forms a substantially tubular unit with a circular transverse cross-section. In each inductive heating unit 112, 114, 116, the flux concentrator extends over the proximal and distal ends of the inductor coil, such that the inductor coil is arranged within an annular cavity of the flux concentrator. Similarly, each inductive heating unit housing extends over the proximal and distal ends of the flux concentrator, such that the flux concentrator and inductor coil are arranged within an annular cavity of the inductive heating unit housing. This arrangement enables the flux concentrator to concentrate the magnetic field generated by the inductor coil in the inner cavity of the inductor coil. This arrangement also enables the inductor unit housing to retain the flux concentrator and inductor coil within the inductor unit housing.

[0210] The inductive heating arrangement 110 further comprises the susceptor arrangement 120. The susceptor arrangement 120 is disposed about the inner surface of the device cavity 104. In this embodiment, the device housing 102 defines an inner surface of the device cavity 104. However, it is envisaged that in some embodiments the inner surface of the device cavity is defined by the inner surface of the susceptor arrangement 120.

[0211] The inductive heating units 112, 114, 116 are disposed about the susceptor arrangement 120, such that the susceptor arrangement 120 and the inductive heating units 112, 114, 116 are concentrically arranged about the device cavity 104. The first inductive heating unit 112 is disposed about the first susceptor 122, at a distal end of the device cavity 104. The second inductive heating unit 114 is disposed about the second susceptor 124, at a central portion of the device cavity 104. The third inductive heating unit 116 is disposed about the third susceptor 126, at a proximal end of the device cavity 104. It is envisaged that in some embodiments the flux concentrators may also extend into the intermediate elements of the susceptor arrangement, in order to further distort the magnetic fields generated by the inductor coils towards the susceptors.

[0212] The first inductor coil 150 is connected to the controller 108 and the power supply 106, and the controller 108 is configured to supply a varying electric current, preferably an AC current, to the first inductor coil 150. When a varying electric current, preferably an AC current, is supplied to the first inductor coil 150, the first inductor coil 150 generates a varying magnetic field, which heats the first susceptor 122 by induction.

[0213] The second inductor coil 160 is connected to the controller 108 and the power supply 106, and the controller 108 is configured to supply a varying electric current, preferably an AC current, to the second inductor coil 160. When a varying electric current, preferably an AC current, is supplied to the second inductor coil 160, the second inductor coil 160 generates a varying magnetic field, which heats the second susceptor 124 by induction.

[0214] The first inductor coil 170 is connected to the controller 108 and the power supply 106, and the controller 108 is configured to supply a varying electric current, preferably an AC current, to the third inductor coil 170. When a varying electric current, preferably an AC current, is supplied to the third inductor coil 170, the third inductor coil 170 generates a varying magnetic field, which heats the third susceptor 126 by induction.

[0215] The device housing 102 also defines an air inlet 180 in close proximity to the distal end of the device cavity 106. The air inlet 180 is configured to enable ambient air to be drawn into the device housing 102. An airflow pathway 181 is defined through the device, between the air inlet 180 and an air outlet in the distal end of the device cavity 104, to enable air to be drawn from the air inlet 180 into the device cavity 104.

[0216] The aerosol-generating article 200 is generally in the form of a cylindrical rod, having a diameter similar to the inner diameter of the device cavity 104. The aerosol-generating article 200 comprises a cylindrical cellulose acetate filter plug 204 and a cylindrical aerosol-generating segment 210 wrapped together by an outer wrapper 220 of cigarette paper.

[0217] The filter plug 204 is arranged at a proximal end of the aerosol-generating article 200, and forms the mouthpiece of the aerosol-generating system on which a user draws to receive aerosol generated by the system.

[0218] The aerosol-generating segment 210 is arranged at a distal end of the aerosol-generating article 200, and has a length substantially equal to the length of the device cavity 104. The aerosol-generating segment 210 comprises a plurality of aerosol-forming substrates, including: a first aerosol-forming substrate 212 at a distal end of the aerosol-generating article 200, a second aerosol-forming substrate 214 adjacent the first aerosol-forming substrate 212, and a third aerosol-forming substrate 216 at a proximal end of the aerosol-generating segment 210, adjacent the second aerosol-forming substrate 216. It will be appreciated that in some embodiments two or more of the aerosol-forming substrates may be formed from the same materials. However, in this embodiment each of the aerosol-forming substrates 212, 214, 216 is different. The first aerosol-forming substrate 212 comprises a gathered and crimped sheet of homogenised tobacco material, without additional flavourings. The second aerosol-forming substrate 214 comprises a gathered and crimped sheet of homogenised tobacco material including a flavouring in the form of menthol. The third aerosol-forming substrate comprises a flavouring in the form of menthol, and does not comprise tobacco material or any other source of nicotine. Each of the aerosol-forming substrates 212, 214, 216 also comprises further components, such as one or more aerosol formers and water, such that heating the aerosol-forming substrate generates an aerosol with desirable organoleptic properties.

[0219] The proximal end of the first aerosol-forming substrate 212 is exposed, as it is not covered by the outer wrapper 220. In this embodiment, air is able to be drawn into the aerosol-generating segment 210 via the proximal end of the first aerosol-forming substrate 212, at the proximal end of the article 200.

[0220] In this embodiment, the first aerosol-forming substrate 212, the second aerosol-forming substrate 214 and the third aerosol-forming substrate 216 are arranged end-to-end. However, it is envisaged that in other embodiments, a separation may be provided between the first aerosol-forming substrate and the second aerosol-forming substrate, and a separation may be provided between the second aerosol-forming substrate and the third aerosol-forming substrate.

[0221] As shown in FIG. 7, when the aerosol-generating segment 210 of the aerosol-generating article 200 is received in the device cavity 104, the length of the first aerosol-forming substrate 212 is such that the first aerosol-forming substrate 212 extends from the distal end of the device cavity 104, through the first region 134 of the first susceptor 122, and to the first intermediate member 128. The length of the second aerosol-forming substrate 214 is such that the second aerosol-forming substrate 214 extends from the first intermediate member 128, through the second region 136 of the second susceptor 124, and to the second intermediate member 130. The length of the third aerosol-forming substrate 216 is such that the third aerosol-forming substrate 216 extends from the second intermediate member 130 to the proximal end of the device cavity 104.

[0222] In use, when an aerosol-generating article 200 is received in the device cavity 104, a user may draw on the proximal end of the aerosol-generating article 200 to inhale aerosol generated by the aerosol-generating system. When a user draws on the proximal end of the aerosol-generating article 200, air is drawn into the device housing 102 at the air inlet 180, and is drawn along the airflow pathway 181, into the device cavity 104. The air is drawn into the aerosol-generating article 200 at the proximal end of the first aerosol-forming substrate 212 through the outlet in the distal end of the device cavity 104.

[0223] In this embodiment, the controller 108 of the aerosol-generating device 100 is configured to supply power to the inductor coils of the inductive heating arrangement 110 in a predetermined sequence. The predetermined sequence comprises supplying a varying electric current, preferably an AC current, to the first inductor coil 150 during a first draw from the user, subsequently supplying a varying electric current, preferably an AC current, to the second inductor coil 160 during a second draw from the user, after the first draw has finished, and subsequently supplying a varying electric current, preferably an AC current, to the third inductor coil 170 during a third draw from the user, after the second draw has finished. On the fourth draw, the sequence starts again at the first inductor coil 150. This sequence results in heating of the first aerosol-forming substrate 212 on a first puff, heating of the second aerosol-forming substrate 214 on a second puff, and heating of the third aerosol-forming substrate 216 on a third puff. Since the aerosol forming substrates 212, 214, 216 of the article 100 are all different, this sequence results in a different experience for a user on each puff on the aerosol-generating system.

[0224] It will be appreciated that the controller 108 may be configured to supply power to the inductor coils in a different sequence, or simultaneously, depending on the desired delivery of aerosol to the user. In some embodiments, the aerosol-generating device may be controllable by the user to change the sequence.

[0225] FIG. 8 shows a schematic illustration of a susceptor arrangement 310 according to an embodiment of this disclosure. The susceptor arrangement 310 is an elongate, tubular element, having a circular transverse cross-section. The susceptor arrangement 310 comprises a single elongate susceptor, having a first portion 312 and a second portion 314. The first portion 312 and the second portion 314 are each elongate, tubular elements having a circular transverse cross-section. The first portion 312 and the second portion 314 are coaxially aligned, end-to-end, along a longitudinal axis A-A.

[0226] The susceptor arrangement 310 comprises a cylindrical cavity 320, open at both ends, defined by an inner surfaces of the first portion 312 and the second portion 314. The cavity 320 is configured to receive a portion of a cylindrical aerosol-generating article (not shown), comprising an aerosol-forming substrate, such that an outer surface of the aerosol-generating article may be heated by the first susceptor and the second susceptor, thereby heating the aerosol-forming substrate.

[0227] The cavity 320 is configured to receive a portion of an aerosol-generating article comprising an aerosol-forming substrate.

[0228] The cavity 320 comprises two portions, a first portion 322 at a first end, defined by an inner surface of the first portion 312 of the susceptor arrangement 310, and a second portion 324 at a second end, opposite the first end, defined by an inner surface of the second portion 314 of the susceptor arrangement 310. The first portion 312 of the susceptor arrangement 310 is arranged to heat a first portion of an aerosol-generating article received in the first portion 322 of the cavity 320, and the second portion 314 of the susceptor arrangement 310 is arranged to heat a second portion of an aerosol-generating article received in the second portion 324 of the cavity 320.

[0229] A first inductor coil 332 is disposed around the first portion 312 of the susceptor arrangement 310, and extends substantially the length of the first portion 312 of the susceptor arrangement 310. As such, the first portion 312 of the susceptor arrangement 310 is circumscribed by the first inductor coil 332 substantially along its length. When a varying electric current, preferably an AC current, is supplied to the first inductor coil 332, the first inductor coil 332 generates a varying magnetic field that is concentrated in the first portion 322 of the cavity 320. Such a varying magnetic field generated by the first inductor coil 332 induces eddy currents in the first portion 312 of the susceptor arrangement 310, causing the first portion 312 of the susceptor arrangement 310 to be heated.

[0230] A second inductor coil 334 is disposed around the second portion 314 of the susceptor arrangement 310, and extends substantially the length of the second portion 314 of the susceptor arrangement 310. As such, the second portion 314 of the susceptor arrangement 310 is circumscribed by the second inductor coil 334 of the susceptor arrangement 310 substantially along its length. When a varying electric current, preferably an AC current, is supplied to the second inductor coil 334, the second inductor coil 334 generates a varying magnetic field that is concentrated in the second portion 324 of the cavity 320. Such a varying magnetic field generated by the second inductor coil 334 induces eddy currents in the second portion 314 of the susceptor arrangement 310, causing the second susceptor 314 to be heated.

[0231] The first portion 312 of the susceptor arrangement 310 and the second portion 314 of the susceptor arrangement 310 may be heated simultaneously by simultaneously supplying a varying electric current, preferably an AC current, to the first inductor coil 332 and the second inductor coil 334. Alternatively, the first portion 312 of the susceptor arrangement 310 and the second portion 314 of the susceptor arrangement 310 may be heated independently or alternately by supplying a varying electric current, preferably an AC current, to the first inductor coil 332 without supplying a current to the second inductor coil 334, and by subsequently supplying a varying electric current, preferably an AC current, to the second inductor coil 334 without supplying a current to the first inductor coil 332. It is also envisaged that a varying electric current, preferably an AC current, may be supplied to the first inductor coil 332 and the second inductor coil 334 in a sequence.

[0232] Temperature sensors, in the form of thermocouples, are also provided on outer surfaces of the susceptor arrangement 310. A first thermocouple 342 is provided on an outer surface of the first portion 312 of the susceptor arrangement 310 to sense the temperature of the first portion 312 of the susceptor arrangement 310. A second thermocouple 344 is provided on an outer surface of the second portion 314 of the susceptor arrangement 310 to sense the temperature of the second portion 314 of the susceptor arrangement 310.

[0233] FIG. 9 shows a cross-sectional view of an aerosol-generating system 600 according to another embodiment of the present disclosure. The aerosol-generating system 600 comprises an aerosol-generating device 602 comprising the susceptor arrangement 310, the first inductor coil 332 and the second inductor coil 334 of FIG. 8. The aerosol-generating device 602 is similar to the aerosol-generating device 100 of FIG. 5 and like reference numerals are used to designate like parts.

[0234] The aerosol-generating system 600 also comprises an aerosol-generating article 700. The aerosol-generating article 700 comprises an aerosol-forming substrate 702 in the form of a cylindrical rod and comprising tobacco strands made from homogenised tobacco and an aerosol former. The cylindrical rod of aerosol-forming substrate 702 has a length substantially equal to the length of the device cavity 104. The aerosol-generating article 700 also comprises a tubular cooling segment 704, a filter segment 706, and a mouth end segment 708. The aerosol-forming substrate 702, the tubular cooling segment 704, the filter segment 706 and the mouth end segment 708 are held together by an outer wrapper 710.

[0235] In one example, the aerosol-forming substrate 702 is between 34 millimetres and 50 millimetres in length, more preferably, the aerosol-forming substrate 702 is between 38 millimetres and 46 millimetres in length, more preferably still, the aerosol-forming substrate 702 is 42 millimetres in length.

[0236] In one example, the total length of the article 700 is between 71 millimetres and 95 millimetres, more preferably, the total length of the article 700 is between 79 millimetres and 87 millimetres, more preferably still, the total length of the article 700 is 83 millimetres.

[0237] In one example, the cooling segment 704 is an annular tube and defines an air gap within the cooling segment 704. The air gap provides a chamber for heated volatilised components generated from the aerosol-forming substrate 702 to flow. The cooling segment 704 is hollow to provide a chamber for aerosol accumulation yet rigid enough to withstand axial compressive forces and bending moments that might arise during manufacture and whilst the article 700 is in use during insertion into the aerosol-generating device 602. In one example, the thickness of the wall of the cooling segment 704 is approximately 0.29 millimetres.

[0238] The cooling segment 704 provides a physical displacement between the aerosol-forming substrate 702 and the filter segment 706. The physical displacement provided by the cooling segment 704 provides a thermal gradient across the length of the cooling segment 704 during use. In one example the cooling segment 704 is configured to provide a temperature differential of at least 40 degrees Celsius between a heated volatilised component entering a distal end of the cooling segment 704 and a heated volatilised component exiting a proximal end of the cooling segment 704. In one example the cooling segment 704 is configured to provide a temperature differential of at least 60 degrees Celsius between a heated volatilised component entering a distal end of the cooling segment 704 and a heated volatilised component exiting a proximal end of the cooling segment 704. This temperature differential across the length of the cooling element 704 protects the temperature sensitive filter segment 706 from the high temperatures of the aerosol formed from the aerosol-forming substrate 702.

[0239] In one example, the length of the cooling segment 704 is at least 15 millimetres. In one example, the length of the cooling segment 704 is between 20 millimetres and 30 millimetres, more particularly 23 millimetres to 27 millimetres, more particularly 25 millimetres to 27 millimetres and more particularly 25 millimetres.

[0240] The cooling segment 704 is made of paper. In one example, the cooling segment 704 is manufactured from a spirally wound paper tube which provides a hollow internal chamber yet maintains mechanical rigidity. Spirally wound paper tubes are able to meet the tight dimensional accuracy requirements of high-speed manufacturing processes with respect to tube length, outer diameter, roundness and straightness. In another example, the cooling segment 704 is a recess created from stiff plug wrap or tipping paper. The stiff plug wrap or tipping paper is manufactured to have a rigidity that is sufficient to withstand the axial compressive forces and bending moments that might arise during manufacture and whilst the article 700 is in use during insertion into the aerosol-generating device 602.

[0241] For each of the examples of the cooling segment 704, the dimensional accuracy of the cooling segment is sufficient to meet the dimensional accuracy requirements of high-speed manufacturing process.

[0242] The filter segment 706 may be formed of any filter material sufficient to remove one or more volatilised compounds from heated volatilised components from the aerosol-forming substrate 702. In one example, the filter segment 706 is made of a mono-acetate material, such as cellulose acetate. The filter segment 706 provides cooling and irritation-reduction from the heated volatilised components without depleting the quantity of the heated volatilised components to an unsatisfactory level for a user.

[0243] The density of the cellulose acetate tow material of the filter segment 706 controls the pressure drop across the filter segment 706, which in turn controls the draw resistance of the article 700. Therefore the selection of the material of the filter segment 706 is important in controlling the resistance to draw of the article 700. In addition, the filter segment performs a filtration function in the article 700.

[0244] The presence of the filter segment 706 provides an insulating effect by providing further cooling to the heated volatilised components that exit the cooling segment 704. This further cooling effect reduces the contact temperature of the user's lips on the surface of the filter segment 706.

[0245] One or more flavours may be added to the filter segment 706 in the form of either direct injection of flavoured liquids into the filter segment 706 or by embedding or arranging one or more flavoured breakable capsules or other flavour carriers within the cellulose acetate tow of the filter segment 706. In one example, the filter segment 706 is between 6 millimetres to 10 millimetres in length, more preferably 8 millimetres.

[0246] The mouth end segment 708 is an annular tube and defines an air gap within the mouth end segment 708. The air gap provides a chamber for heated volatilised components that flow from the filter segment 706. The mouth end segment 708 is hollow to provide a chamber for aerosol accumulation yet rigid enough to withstand axial compressive forces and bending moments that might arise during manufacture and whilst the article is in use during insertion into the aerosol-generating device 602. In one example, the thickness of the wall of the mouth end segment 708 is approximately 0.29 millimetres.

[0247] In one example, the length of the mouth end segment 708 is between 6 millimetres to 10 millimetres and more preferably 8 millimetres.

[0248] The mouth end segment 708 may be manufactured from a spirally wound paper tube which provides a hollow internal chamber yet maintains critical mechanical rigidity. Spirally wound paper tubes are able to meet the tight dimensional accuracy requirements of high-speed manufacturing processes with respect to tube length, outer diameter, roundness and straightness.

[0249] The mouth end segment 708 provides the function of preventing any liquid condensate that accumulates at the exit of the filter segment 706 from coming into direct contact with a user.

[0250] It should be appreciated that, in one example, the mouth end segment 708 and the cooling segment 704 may be formed of a single tube and the filter segment 706 is located within that tube separating the mouth end segment 708 and the cooling segment 704.

[0251] Ventilation holes 707 are located in the cooling segment 704 to aid with the cooling of the article 700. In one example, the ventilation holes 707 comprise one or more rows of holes, and preferably, each row of holes is arranged circumferentially around the article 700 in a cross-section that is substantially perpendicular to a longitudinal axis of the article 700.

[0252] In one example, there are between one to four rows of ventilation holes 707 to provide ventilation for the article 700. Each row of ventilation holes 707 may have between 12 to 36 ventilation holes 707. The ventilation holes 707 may, for example, be between 100 to 500 micrometres in diameter. In one example, an axial separation between rows of ventilation holes 707 is between 0.25 millimetres and 0.75 millimetres, more preferably, an axial separation between rows of ventilation holes 707 is 0.5 millimetres.

[0253] In one example, the ventilation holes 707 are of uniform size. In another example, the ventilation holes 707 vary in size. The ventilation holes 707 can be made using any suitable technique, for example, one or more of the following techniques: laser technology, mechanical perforation of the cooling segment 704 or pre-perforation of the cooling segment 704 before it is formed into the article 700. The ventilation holes 707 are positioned so as to provide effective cooling to the article 700.

[0254] In one example, the rows of ventilation holes 707 are located at least 11 millimetres from the proximal end of the article 700, more preferably the ventilation holes 707 are located between 17 millimetres and 20 millimetres from the proximal end of the article 700. The location of the ventilation holes 707 is positioned such that user does not block the ventilation holes 707 when the article 700 is in use.

[0255] Advantageously, providing the rows of ventilation holes 707 between 17 millimetres and 20 millimetres from the proximal end of the article 700 enables the ventilation holes 707 to be located outside of the aerosol-generating device 602 when the article 700 is fully inserted in the aerosol-generating device 602. By locating the ventilation holes 707 outside of the device 602, non-heated air is able to enter the article 700 through the ventilation holes 707 from outside the device 602 to aid with the cooling of the article 700.

[0256] FIG. 10 shows a graph of temperature 404 as a function of time 402 during one heating cycle for the first portion 312 of the susceptor arrangement 310, using readings from the first thermocouple 342, and the second portion of the susceptor arrangement 310, using readings from the second thermocouple 344. In FIG. 10, the temperature of the first portion 312 of the susceptor arrangement 310, from the first thermocouple 342, is shown by the solid line 406. In FIG. 10, the temperature of the second portion 314 of the susceptor arrangement 310, from the second thermocouple 344, is shown by the dashed line 408.

[0257] As shown in FIG. 10, when heating is started, the first portion 312 of the susceptor arrangement 310 is heated quickly during a first phase 410, and reaches an operating temperature after a first period 414 of about 60 seconds. The second portion 314 of the susceptor arrangement 310 is heated during the first phase 410, but at a much slower rate than the first portion 312. The temperature of the first portion 312 of the susceptor arrangement 310 is greater than the temperature of the second portion 314 of the susceptor arrangement 310 throughout the first phase 410. The second portion 314 of the susceptor arrangement 310 does not reach an operating temperature during the first phase 410. In this embodiment, the operating temperature refers to the desired temperature at which the most desirable aerosol is released from the aerosol-forming substrate.

[0258] Also as shown in FIG. 10, after a second period 416, of about 150 seconds from the start of heating, the first phase 410 ends, and a second phase 412 begins. In the second phase 412, the first portion 312 of the susceptor arrangement 312 is heated to a lower temperature, but still within about 50 degrees Celsius of the operating temperature. Also in the second phase 412, the second portion 314 of the susceptor arrangement 310 is heated quickly to the operating temperature, and reaches the operating temperature after a third period 418, of about 210 seconds from the start of heating.

[0259] In particular, FIG. 10 shows a desirable temperature profile for an aerosol-generating system, wherein the first portion 312 of the susceptor arrangement 310 is arranged to heat a proximal portion of an aerosol-forming substrate, and the second portion 314 of the susceptor arrangement 310 is arranged to heat a distal portion of an aerosol-forming substrate. The proximal portion of the aerosol-forming substrate is closer to a mouthpiece end of an aerosol-generating article comprising the aerosol-forming substrate. Such a temperature profile across the aerosol-forming substrate enables an aerosol with desired characteristics to be generated throughout an entire, extended, aerosol-generating time period. Heating a proximal portion of an aerosol-forming substrate before heating a distal portion of the substrate facilitates optimum delivery of the generated aerosol to a user. In particular, it is believed that this is because the hot aerosol from the heated proximal portion of the aerosol-forming substrate does not interact with the non-heated distal portion of the aerosol-forming substrate during the first phase, and as such, the hot aerosol from the proximal portion does not release volatile compounds from the distal portion.

[0260] Such a temperature profile can be achieved by driving varying currents, preferably AC currents, in the first inductor coil 312 and the second inductor coil 314 in a variety of ways. For example, in the first phase, a first varying current, preferably an AC current, can be driven in the first inductor coil 312 at a first duty cycle, and a second varying current, preferably an AC current, can be driven in the second inductor coil 314, the duty cycle of the second varying current being less than the duty cycle of the first varying current, such that the current driven in the first inductor coil 312 is greater than the current driven in the second inductor coil 314 during the first phase. It will be appreciated that in some embodiments, a varying current is not supplied to the second inductor coil 314 in the first phase 410. In the second phase, the opposite may apply, such that the duty cycle of the first varying current is lower than the duty cycle of the second varying current.

[0261] In FIG. 11, an inductive heating arrangement 501 is depicted. The inductive heating arrangement 501 comprises a first LC circuit 510. The first LC circuit 510 comprises a first inductor coil 512 and a first capacitor 514. The first inductor coil 512 has a first inductance. The first capacitor 514 has a first capacitance. The resonance frequency of the first LC circuit 510 is determined by the first inductance and the first capacitance.

[0262] FIG. 11 further shows a first transistor 516, such as a FET, connected to the first LC circuit 510. Furthermore, terminals 518 of a DC power supply are depicted in FIG. 11. The terminals 518 of the DC power supply are connected with the power supply, preferably a battery, of the device. The first LC circuit 510 is configured to inductively heat a first portion of a susceptor arrangement. The first portion of the susceptor arrangement may be arranged adjacent to the first inductor coil so that the first inductor coil may heat the first portion of the susceptor element by one or both of eddy currents and hysteresis.

[0263] The inductive heating arrangement 501 of FIG. 11 also comprises a second LC circuit 520 comprising a second inductor coil 522 a second capacitor 524. A second transistor 526 is associated with the second LC circuit 520.

[0264] The first transistor 516 is configured for controlling operation of the first LC circuit 510. The second transistor 526 is configured for controlling operation of the second LC circuit 520.

[0265] The components of the second LC circuit 520 may be similar to the components of the first LC circuit 510. In other words, the second inductor coil 522 may have a second inductance, the second capacitor 524 may have a second capacitance and the second transistor 526 may be an FET. The two LC circuits 510, 520 may be connected to the DC power supply in parallel.

[0266] FIG. 12 shows a controller 527 in addition to a power stage 528. The power stage 528 may comprise the first LC circuit 510 and the first transistor 516 as depicted in FIG. 11. The power stage 528 may alternatively all of the components depicted in FIG. 11. The controller 527 depicted in FIG. 12 may comprise an oscillator 530. The oscillator 530 may be connected to one or both of the first transistor 516 and the second transistor 526. A DC power supply 532 is also shown in FIG. 12. The DC power supply 532 may be utilized for powering the elements shown in FIG. 11. Additionally, the DC power supply 532 may be utilized to power the controller 527, preferably the oscillator 530.

[0267] The controller 527 may further comprise a pulse width modulation module 534. The pulse width modulation module 534 may be configured to modulate the signal used for driving the LC circuits 510, 520. The controller 527 may be configured to drive the LC circuits 510, 520. In other words, the controller 527 may be configured to supply an electric signal to the LC circuits 510, 520.

[0268] The pulse width modulation module 534 is optional. The controller 527 may be configured to drive the first LC circuit 510 with an AC current of a first frequency. The first frequency may correspond to the resonance frequency of the first LC circuit 510. The controller 527 may be configured to drive a second LC circuit 520 with an AC current of a second frequency. The second frequency may correspond to the resonance frequency of the second LC circuit 520.

[0269] The resonance frequency of the first LC circuit 510 is different from the resonance frequency of the second LC circuit 520. During the first phase, the controller 527 may be configured to supply an AC current to the first LC circuit 510 with a frequency corresponding to the resonance frequency of the first LC circuit 510. An AC current with the same frequency may be supplied to the second LC circuit 520. Due to the resonance frequency of the second LC circuit 520 being different from the resonance frequency of the first LC circuit 510, the second LC circuit 520 may only heat the second portion of the susceptor arrangement to a lower temperature than the first LC circuit 510 heating first portion of the susceptor arrangement. In the second phase, in which heating of the second portion of the susceptor arrangement is desired, the controller 527 may be configured to supply an AC current with a frequency corresponding to the resonance frequency of the second LC circuit 520, while this AC current will lead to a lower heating of the first portion of the susceptor arrangement by the first LC circuit 510.

[0270] FIG. 13 shows an embodiment in which the first LC circuit 510 is heated predominantly in the first phase, while the second LC circuit 520 is heated to a lower temperature during the first phase. This is reversed in the second phase, in which the first LC circuit 510 is heated to a lower temperature than the second LC circuit 520. To facilitate this, pulse width modulation is employed. In more detail, the top of FIG. 13 shows complementary duty cycles of a first alternating pulse width modulated signal (top left) and of a second alternating pulse width modulated signal (top right). The first alternating pulse width modulated signal will herein be denoted as first signal 536. The second alternating pulse width modulated signal will herein be denoted as second signal 538. The duty cycle refers to the percentage of on-time of the respective signal. As can be seen in FIG. 13, the first signal 536 has a high duty cycle of around 80%, while the second signal 538 has a low duty cycle of around 20%. The embodiment shown in FIG. 13 corresponds to the first phase, in which the first portion 541 of the susceptor arrangement 540 is predominantly heated, while the second portion 542 of the susceptor arrangement 540 is heated to a lower temperature. Below the signals shown in FIG. 13, the first inductor coil 512 and the second inductor coil 522 are depicted. Below the inductor coils 512, 522, the susceptor arrangement 540, comprising the first portion 541 and the second portion 542, is illustrated. Below the susceptor arrangement 540, an aerosol-generating article 542 comprising aerosol-forming substrate is shown. Below the aerosol-generating article 542, a diagram 544 is depicted showing heat over distance. The heat predominantly is high in the first portion 541 of the susceptor arrangement 540, while the heat is lower in the second portion 542 of the susceptor arrangement 540. During the second phase, the heating of the susceptor arrangement 540 will be different. During the second phase, the second LC circuit 520 will heat the second portion 542 of the susceptor arrangement 540 to a higher temperature and the temperature of the first portion 541 of the susceptor arrangement 540 will be lower than in the first phase. To facilitate this, pulse width modulation may be employed similar to the first phase. The duty cycle of the second signal 538 may be increased, while the duty cycle of the first signal 536 may be decreased. The degrees may be gradual from the first phase to the second phase. The duty cycle of the first signal 536 and the duty cycle of the second signal 538 may add up to 100%. Alternatively, the duty cycle of the first signal 536 and the duty cycle of the second signal 538 may add up to an amount lower than 100%. Exemplarily, in the first phase, the duty cycle of the first signal 536 may be above 50% such as 80% and the duty cycle of the second signal 538 may be close to 0% or 0%; and vice versa during the second phase.

[0271] It will be appreciated that the embodiments described above are specific examples only, and other embodiments are envisaged in accordance with this disclosure.