Aerosol-generating system comprising a mesh susceptor

Abstract

There is provided a cartridge for use in an aerosol-generating system, the aerosol-generating system including an aerosol-generating device, the cartridge configured to be used with the device, wherein the device includes a device housing, an inductor coil positioned on or within the housing, and a power supply connected to the inductor coil and configured to provide a high frequency oscillating current to the inductor coil, the cartridge including a cartridge housing containing an aerosol-forming substrate and a ferrite mesh susceptor element positioned to heat the aerosol-forming substrate.

Claims

1. A cartridge for rise in an aerosol-generating system, the aerosol-generating system comprising an aerosol-generating device, the cartridge configured to be used with the device, the aerosol-generating device comprising: a device housing; an inductor coil positioned on or within the housing; and a power supply connected to the inductor coil and configured to provide a high frequency oscillating current to the inductor coil; the cartridge comprising: a cartridge housing containing an aerosol-forming substrate and a mesh susceptor element positioned to heat the aerosol-forming substrate, and a capillary material within the cartridge housing, the capillary material holding the aerosol-forming substrate, wherein the aerosol-forming substrate is a liquid at room temperature and is configured to form a meniscus in interstices of the mesh susceptor element.

2. The cartridge according to claim 1, wherein the mesh susceptor element is a ferrite or ferrous mesh susceptor element.

3. The cartridge according to claim 1, wherein the mesh susceptor element has a mesh size of between 160 and 600 Mesh US.

4. The cartridge according to claim 1, wherein the mesh susceptor element comprises a plurality of filaments, each filament having a diameter between 8 μm and 100 μm.

5. The cartridge according to claim 1, wherein the mesh susceptor element has a relative permeability between 500 and 40000.

6. The cartridge according to claim 1, wherein the mesh susceptor element extends across an opening in cartridge housing.

7. The cartridge according to claim 1, wherein the mesh susceptor element is welded to the cartridge housing.

8. The cartridge according to claim 1, wherein the capillary material extends into interstices of the mesh susceptor element.

9. An aerosol-generating system, comprising an aerosol-generating device and a cartridge, the cartridge configured to be used with the device, the aerosol-generating device comprising: a device housing; an inductor coil positioned on or within the housing; and a power supply connected to the inductor coil and configured to provide a high frequency oscillating current to the inductor coil; the cartridge comprising: a cartridge housing containing an aerosol-forming substrate and a mesh susceptor element positioned to heat the aerosol-forming substrate, and a capillary material within the cartridge housing, the capillary material holding the aerosol-forming substrate, wherein the aerosol-forming substrate is a liquid at room temperature and is configured to form a meniscus in interstices of the mesh susceptor element.

10. The aerosol-generating system according to claim 9, wherein the inductor coil is a flat spiral inductor coil.

11. The aerosol-generating system according to claim 10, wherein the inductor coil has a diameter of less than 10 mm.

12. The aerosol-generating system according to claim 9, wherein the inductor coil is positioned adjacent to the susceptor element in use.

13. The aerosol-generating system according to claim 9, wherein an airflow channel is between the inductor coil and the susceptor element in use.

14. The aerosol-generating system according to claim 9, wherein the system 4is a handheld smoking system.

15. The cartridge according to claim 1, wherein the mesh susceptor element comprises a plurality of filaments, each filament having a diameter between 8 μm and 50 μm.

16. The cartridge according to claim 1. wherein the mesh susceptor element comprises a plurality of filaments, each filament having a diameter between 8 μm and 39 μm.

Description

(1) Embodiments of a system in accordance with the disclosure will now be described in detail, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic illustration of a first embodiment of an aerosol-generating system, using a flat spiral inductor coil;

(3) FIG. 2 shows the cartridge of FIG. 1;

(4) FIG. 3 shows the inductor coil of FIG. 1;

(5) FIG. 4 shows an alternative susceptor element for the cartridge of FIG. 2;

(6) FIG. 5 is a schematic illustration of a second embodiment, using a flat spiral inductor coil;

(7) FIG. 6 is a schematic illustration of a third embodiment;

(8) FIG. 7 is a schematic illustration of a fourth embodiment, using flat spiral inductor coils;

(9) FIG. 8 shows the cartridge of FIG. 7;

(10) FIG. 9 shows the inductor coil of FIG. 7;

(11) FIG. 10 is a schematic illustration of a fifth embodiment;

(12) FIG. 11 shows the cartridge of FIG. 10;

(13) FIG. 12 shows the coil of FIG. 10;

(14) FIG. 13 is a schematic illustration of a sixth embodiment;

(15) FIG. 14 is a schematic illustration of a seventh embodiment;

(16) FIG. 15A is a first example of a driving circuit for generating the high frequency signal for an inductor coil; and

(17) FIG. 15B is a second example of a driving circuit for generating the high frequency signal for an inductor coil.

(18) The embodiments shown in the figures all rely on inductive heating. Inductive heating works by placing an electrically conductive article to be heated in a time varying magnetic field. Eddy currents are induced in the conductive article. If the conductive article is electrically isolated the eddy currents are dissipated by Joule heating of the conductive article. In an aerosol-generating system that operates by heating an aerosol-forming substrate, the aerosol-forming substrate is typically not itself sufficiently electrically conductive to be inductively heated in this way. So in the embodiments shown in the figures a susceptor element is used as the conductive article that is heated and the aerosol-forming substrate is then heated by the susceptor element by thermal conduction, convention and/or radiation. Because a ferromagnetic susceptor element is used, heat is also generated by hysteresis losses as the magnetic domains are switched within the susceptor element.

(19) The embodiments described each use an inductor coil to generate a time varying magnetic field. The inductor coil is designed so that it does not undergo significant Joule heating. In contrast the susceptor element is designed so that there is significant Joule heating of the susceptor.

(20) FIG. 1 is a schematic illustration of an aerosol-generating system in accordance with a first embodiment. The system comprises device 100 and a cartridge 200. The device comprises main housing 101 containing a lithium iron phosphate battery 102 and control electronics 104. The main housing 101 also defines a cavity 112 into which the cartridge 200 is received. The device also includes a mouthpiece portion 120 including an outlet 124. The mouthpiece portion is connected to the main housing 101 by a hinged connection in this example but any kind of connection may be used, such as a snap fitting or a screw fitting. Air inlets 122 are defined between the mouthpiece portion 12o and the main body 101 when the mouthpiece portion is in a closed position, as shown in FIG. 1.

(21) Within the mouthpiece portion is a flat spiral inductor coil 110. The coil 110 is formed by stamping or cutting a spiral coil from a sheet of copper. The coil 110 is more clearly illustrated in FIG. 3. The coil 110 is positioned between the air inlets 122 and the air outlet 124 so that air drawn through the inlets 122 to the outlet 124 passes through the coil.

(22) The cartridge 200 comprises a cartridge housing 204 holding a capillary material and filled with liquid aerosol-forming substrate. The cartridge housing 204 is fluid impermeable but has an open end covered by a permeable susceptor element 210. The cartridge 200 is more clearly illustrated in FIG. 2. The susceptor element in this embodiment comprises a ferrite mesh, comprising a ferrite steel. The aerosol-forming substrate can form a meniscus in the interstices of the mesh.

(23) When the cartridge 200 is engaged with the device and is received in the cavity 112, the susceptor element 210 is positioned adjacent the flat spiral coil 110. The cartridge 200 may include keying features to ensure that it cannot be inserted into the device upside-down.

(24) In use, a user puffs on the mouthpiece portion 120 to draw air though the air inlets 122 into the mouthpiece portion 120 and out of the outlet 124 into the user's mouth. The device includes a puff sensor 106 in the form of a microphone, as part of the control electronics 104. A small air flow is drawn through sensor inlet 121 past the microphone 106 and up into the mouthpiece portion 120 when a user puffs on the mouthpiece portion. When a puff is detected, the control electronics provide a high frequency oscillating current to the coil 110. This generates an oscillating magnetic field as shown in dotted lines in FIG. 1. An LED 108 is also activated to indicate that the device is activated. The oscillating magnetic field passes through the susceptor element, inducing eddy currents in the susceptor element. The susceptor element heats up as a result of Joule heating and as a result of hysteresis losses, reaching a temperature sufficient to vapourise the aerosol-forming substrate close to the susceptor element. The vapourised aerosol-forming substrate is entrained in the air flowing from the air inlets to the air outlet and cools to form an aerosol within the mouthpiece portion before entering the user's mouth. The control electronics supplies the oscillating current to the coil for a predetermined duration, in this example five seconds, after detection of a puff and then switches the current off until a new puff is detected.

(25) It can be seen that the cartridge has a simple and robust design, which can be inexpensively manufactured as compared to the cartomisers available on the market. In this embodiment, the cartridge has a circular cylindrical shape and the susceptor element spans a circular open end of the cartridge housing. However other configurations are possible. FIG. 4 is an end view of an alternative cartridge design in which the susceptor element is a strip of steel mesh 220 that spans a rectangular opening in the cartridge housing 204.

(26) FIG. 5 illustrates a second embodiment. Only the front end of the system is shown in FIG. 5 as the same battery and control electronics as shown in FIG. 1 can be used, including the puff detection mechanism. In FIG. 5 a flat spiral coil 136 is positioned in the main body 101 of the device at the opposite end of the cavity to the mouthpiece portion 120 but the system operates in essentially the same manner. Spacers 134 ensure that there is an air flow space between the coil 136 and the susceptor element 210. Vapourised aerosol-forming substrate is entrained in air flowing past the susceptor from the inlet 132 to the outlet 124, In the embodiment shown in FIG. 5, some air can flow from the inlet 132 to the outlet 124 without passing the susceptor element. This direct air flow mixes with the vapour in the mouthpiece portion speeding cooling and ensuring optimal droplet size in the aerosol.

(27) In the embodiment shown in FIG. 5 the cartridge is the same size and shape as the cartridge of FIG. 1 and has the same housing and susceptor element. However, the capillary material within the cartridge of FIG. 5 is different to that of FIG. 1. There are two separate capillary materials 202, 206 in the cartridge of FIG. 5. A disc of a first capillary material 206 is provided to contact the susceptor element 210 in use. A larger body of a second capillary material 202 is provided on an opposite side of the first capillary material 206 to the susceptor element. Both the first capillary material and the second capillary material retain liquid aerosol-forming substrate. The first capillary material 206, which contacts the susceptor element, has a higher thermal decomposition temperature (at least 160° C. or higher such as approximately 250° C.) than the second capillary material 202. The first capillary material 206 effectively acts as a spacer separating the heater susceptor element, which gets very hot in use, from the second capillary material 202 so that the second capillary material is not exposed to temperatures above its thermal decomposition temperature. The thermal gradient across the first capillary material is such that the second capillary material is exposed to temperatures below its thermal decomposition temperature. The second capillary material 202 may be chosen to have superior wicking performance to the first capillary material 206, may retain more liquid per unit volume than the first capillary material and may be less expensive than the first capillary material. In this example the first capillary material is a heat resistant element, such as a fibreglass or fibreglass containing element and the second capillary material is a polymer such as high density polyethylene (HDPE), or polyethylene terephthalate (PET).

(28) FIG. 6 illustrates a third embodiment. Only the front end of the system is shown in FIG. 6 as the same battery and control electronics as shown in FIG. 1 can be used, including the puff detection mechanism. The third embodiment is similar to the second embodiment except that a helical coil is used, surrounding the cartridge. In FIG. 6 a helical coil 138 is positioned in the main body 101 of the device at the opposite end of the cavity to the mouthpiece portion 120, around the susceptor when the cartridge is in a use position. The system operates in essentially the same manner as in the second embodiment. Spacers 134 ensure that there is an air flow space between the device and the susceptor element 210. Vapourised aerosol-forming substrate is entrained in air flowing past the susceptor from the inlet 137 to the outlet 124 through air flow channel 135. As in the embodiment shown in FIG. 5, some air can flow from the inlet 137 to the outlet 124 without passing the susceptor element.

(29) In the embodiment shown in FIG. 6 the cartridge is the same size and shape as the cartridge of FIG. 1 and has the same housing and susceptor element. However, as in the second embodiment, shown in FIG. 5, the cartridge is inserted so that the susceptor is in the base of the cavity in the device, closest to the battery.

(30) FIG. 7 illustrates a fourth embodiment. Only the front end of the system is shown in FIG. 7 as the same battery and control electronics as shown in FIG. 1 can be used, including the puff detection mechanism. In FIG. 7 the cartridge 240 is cuboid and is formed with two strips of the susceptor element 242 on opposite side faces of the cartridge. The cartridge is shown alone in FIG. 8. The device comprises two flat spiral coils 142 positioned on opposite sides of the cavity so that the susceptor element strips 242 are adjacent the coils 142 when the cartridge is received in the cavity. The coils 142 are rectangular to correspond to the shape of the susceptor strips, as shown in FIG. 9. Airflow passages are provided between the coils 142 and susceptor strips 242 so that air from inlets 144 flows past the susceptor strips towards the outlet 124 when a user puffs on the mouthpiece portion 120.

(31) As in the embodiment of FIG. 1, the cartridge contains a capillary material and a liquid aerosol-forming substrate. The capillary material is arranged to convey the liquid substrate to the susceptor element strips 242.

(32) FIG. 10 is a schematic illustration of a fifth embodiment. Only the front end of the system is shown in FIG. 10 as the same battery and control electronics as shown in FIG. 1 can be used, including the puff detection mechanism.

(33) In FIG. 10 the cartridge 250 is cylidrical and is formed with a band shaped susceptor element 252 extending around a central portion of the cartridge. The band shaped susceptor element covers an opening formed in the rigid cartridge housing The cartridge is shown alone in FIG. 11. The device comprises a helical coil 152 positioned around the cavity so that the susceptor element 252 is within the coil 152 when the cartridge is received in the cavity. The coil 152 is shown alone in FIG. 12. Airflow passages are provided between the coil 152 and susceptor 252 so that air from inlets 154 flows past the susceptor strips towards the outlet 124 when a user puffs on the mouthpiece portion 120.

(34) In use, a user puffs on the mouthpiece portion 120 to draw air though the air inlets 154 past the susceptor element 262, into the mouthpiece portion 120 and out of the outlet 124 into the user's mouth. When a puff is detected, the control electronics provide a high frequency oscillating current to the coil 152. This generates an oscillating magnetic field. The oscillating magnetic field passes through the susceptor element, inducing eddy currents in the susceptor element. The susceptor element heats up as a result of Joule heating and hysteresis losses, reaching a temperature sufficient to vapourise the aerosol-forming substrate close to the susceptor element. The vapourised aerosol-forming substrate passes through the susceptor element and is entrained in the air flowing from the air inlets to the air outlet and cools to form an aerosol within the passageway and mouthpiece portion before entering the user's mouth.

(35) FIG. 13 illustrates a sixth embodiment. Only the front end of the system is shown in FIG. 13 as the same battery and control electronics as shown in FIG. 1 can be used, including the puff detection mechanism. The device of FIG. 13 has a similar construction to the device of FIG. 7, with flat spiral coils positioned in a sidewall of the housing surrounding the cavity in which the cartridge is received. But the cartridge has a different construction. The cartridge 260 of FIG. 13 has a hollow cylindrical shape similar to that of the cartridge shown in FIG. 10. The cartridge contains a capillary material and is filled with liquid aerosol-forming substrate. An interior surface of the cartridge 260, i.e. a surface surrounding the internal passageway 166, comprises a fluid permeable susceptor element, in this example a ferrite mesh. The ferrite mesh may line the entire interior surface of the cartridge or only a portion of the interior surface of the cartridge.

(36) In use, a user puffs on the mouthpiece portion 120 to draw air though the air inlets 164 through the central passageway of the cartridge, past the susceptor element 262, into the mouthpiece portion 120 and out of the outlet 124 into the user's mouth. When a puff is detected, the control electronics provide a high frequency oscillating current to the coils 162. This generates an oscillating magnetic field. The oscillating magnetic field passes through the susceptor element, inducing eddy currents in the susceptor element. The susceptor element heats up as a result of Joule heating and hysteresis losses, reaching a temperature sufficient to vapourise the aerosol-forming substrate close to the susceptor element. The vapourised aerosol-forming substrate passes through the susceptor element and is entrained in the air flowing from the air inlets to the air outlet and cools to form an aerosol within the passageway and mouthpiece portion before entering the user's mouth.

(37) FIG. 14 illustrates as seventh embodiment. Only the front end of the system is shown in FIG. 14 as the same battery and control electronics as shown in FIG. 1 can be used, including the puff detection mechanism. The cartridge 270 shown in FIG. 14 is identical to that shown in FIG. 13. However the device of FIG. 14 has a different configuration that includes an inductor coil 172 on a support blade 176 that extends into the central passageway of the cartridge to generate an oscillating magnetic field close to the susceptor element 272.

(38) All of the described embodiments may be driven by the essentially the same electronic circuitry 104. FIG. 15A illustrates a first example of a circuit used to provide a high frequency oscillating current to the inductor coil, using a Class-E power amplifier. As can be seen from FIG. 15A, the circuit includes a Class-E power amplifier including a transistor switch 1100 comprising a Field Effect Transistor (FET) 1110, for example a Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET), a transistor switch supply circuit indicated by the arrow 1120 for supplying the switching signal (gate-source voltage) to the FET 1110, and an LC load network 1130 comprising a shunt capacitor C1 and a series connection of a capacitor C2 and inductor coil L2. The DC power source, which comprises the battery 101, includes a choke L1, and supplies a DC supply voltage. Also shown in FIG. 16A is the ohmic resistance R representing the total ohmic load 1140, which is the sum of the ohmic resistance R.sub.Coil of the inductor coil, marked as L2, and the ohmic resistance R.sub.Load of the susceptor element.

(39) Due to the very low number of components the volume of the power supply electronics can be kept extremely small. This extremely small volume of the power supply electronics is possible due to the inductor L2 of the LC load network 1130 being directly used as the inductor for the inductive coupling to the susceptor element, and this small volume allows the overall dimensions of the entire inductive heating device to be kept small.

(40) While the general operating principle of the Class-E power amplifier is known and described in detail in the already mentioned article “Class-E RF Power Amplifiers”, Nathan O. Sokal, published in the bimonthly magazine QEX, edition January/February 2001, pages 9-20, of the American Radio Relay League (ARRL), Newington, Conn., U.S.A., some general principles will be explained in the following.

(41) Let us assume that the transistor switch supply circuit 1120 supplies a switching voltage (gate-source voltage of the FET) having a rectangular profile to FET 1110. As long as FET 1321 is conducting (in an “on”-state), it essentially constitutes a short circuit (low resistance) and the entire current flows through choke L1 and FET 1110. When FET 1110 is non-conducting (in an “off”-state), the entire current flows into the LC load network, since FET 1110 essentially represents an open circuit (high resistance). Switching the transistor between these two states inverts the supplied DC voltage and DC current into an AC voltage and AC current.

(42) For efficiently heating the susceptor element, as much as possible of the supplied DC power is to be transferred in the form of AC power to inductor L2 and subsequently to the susceptor element which is inductively coupled to inductor L2. The power dissipated in the susceptor element (eddy current losses, hysteresis losses) generates heat in the susceptor element, as described further above. In other words, power dissipation in FET 1110 must be minimized while maximizing power dissipation in the susceptor element.

(43) The power dissipation in FET 1110 during one period of the AC voltage/current is the product of the transistor voltage and current at each point in time during that period of the alternating voltage/current, integrated over that period, and averaged over that period. Since the FET 1110 must sustain high voltage during a part of that period and conduct high current during a part of that period, it must be avoided that high voltage and high current exist at the same time, since this would lead to substantial power dissipation in FET 1110. In the “on-”state of FET 1110, the transistor voltage is nearly zero when high current is flowing through the FET. In the “off-”state of FET 1110, the transistor voltage is high but the current through FET 1110 is nearly zero.

(44) The switching transitions unavoidably also extend over some fractions of the period. Nevertheless, a high voltage-current product representing a high power loss in FET 1110 can be avoided by the following additional measures. Firstly, the rise of the transistor voltage is delayed until after the current through the transistor has reduced to zero. Secondly, the transistor voltage returns to zero before the current through the transistor begins to rise. This is achieved by load network 1130 comprising shunt capacitor C1 and the series connection of capacitor C2 and inductor L2, this load network being the network between FET 1110 and the load 1140. Thirdly, the transistor voltage at turn-on time is practically zero (for a bipolar-junction transistor “BJT” it is the saturation offset voltage V.sub.o). The turning-on transistor does not discharge the charged shunt capacitor C1, thus avoiding dissipating the shunt capacitor's stored energy. Fourthly, the slope of the transistor voltage is zero at turn-on time. Then, the current injected into the turning-on transistor by the load network rises smoothly from zero at a controlled moderate rate resulting in low power dissipation while the transistor conductance is building up from zero during the turn-on transition. As a result, the transistor voltage and current are never high simultaneously. The voltage and current switching transitions are time-displaced from each other. The values for L1, C1 and C2 can be chosen to maximize the efficient dissipation of power in the susceptor element.

(45) Although a Class-E power amplifier is preferred for most systems in accordance with the disclosure, it is also possible to use other circuit architectures. FIG. 15B illustrates a second example of a circuit used to provide a high frequency oscillating current to the inductor coil, using a Class-D power amplifier. The circuit of FIG. 15B comprises the battery 101 connected to two transistors 1210, 1212. Two switching elements 1220, 1222 are provided for switching two transistors 1210, 1212 on and off. The switches are controlled at high frequency in a manner so as to make sure that one of the two transistors 1210, 1212 has been switched off at the time the other of the two transistors is switched on. The inductor coil is again indicated by L2 and the combined ohmic resistance of the coil and the susceptor element indicated by R. the values of C1 and C2 can be chosen to maximize the efficient dissipation of power in the susceptor element.

(46) The susceptor element can be made of a material or of a combination of materials having a Curie temperature which is close to the desired temperature to which the susceptor element should be heated. Once the temperature of the susceptor element exceeds this Curie temperature, the material changes its ferromagnetic properties to paramagnetic properties. Accordingly, the energy dissipation in the susceptor element is significantly reduced since the hysteresis losses of the material having paramagnetic properties are much lower than those of the material having the ferromagnetic properties. This reduced power dissipation in the susceptor element can be detected and, for example, the generation of AC power by the DC/AC inverter may then be interrupted until the susceptor element has cooled down below the Curie temperature again and has regained its ferromagnetic properties. Generation of AC power by the DC/AC inverter may then be resumed again.

(47) Other cartridge designs incorporating a susceptor element in accordance with this disclosure can now be conceived by one of ordinary skill in the art. For example, the cartridge may include a mouthpiece portion and may have any desired shape. Furthermore, a coil and susceptor arrangement in accordance with the disclosure may be used in systems of other types to those already described, such as humidifiers, air fresheners, and other aerosol-generating systems.

(48) The exemplary embodiments described above illustrate but are not limiting. In view of the above discussed exemplary embodiments, other embodiments consistent with the above exemplary embodiments will now be apparent to one of ordinary skill in the art.