SHISHA DEVICE WITH DIELECTRIC HEATER

Abstract

A shisha device for heating an aerosol-forming substrate to generate an aerosol is provided, the shisha device including: a liquid cavity containing a volume of liquid through which aerosol generated by the shisha device is drawn before inhalation by a user, the liquid cavity having a head space outlet; an article cavity to receive the aerosol-forming substrate, the article cavity being in fluid communication with the liquid cavity; and an electromagnetic field generator to generate a radio frequency (RF) electromagnetic field in the article cavity, the electromagnetic field generator including a magnetron or a solid state RF transistor. A shisha system is also provided, including the shisha device and the aerosol-generating article. An aerosol-generating article for the shisha system is also provided.

Claims

1.-15. (canceled)

16. A shisha device for heating an aerosol-forming substrate to generate an aerosol, the shisha device comprising: a liquid cavity containing a volume of liquid through which aerosol generated by the shisha device is drawn before inhalation by a user, the liquid cavity having a head space outlet; an article cavity configured to receive the aerosol-forming substrate, the article cavity being in fluid communication with the liquid cavity; and an electromagnetic field generator configured to generate a radio frequency (RF) electromagnetic field in the article cavity, the electromagnetic field generator comprising a magnetron or a solid state RF transistor.

17. The shisha device according to claim 16, wherein the electromagnetic field generator comprises the solid state RF transistor, and wherein the solid state RF transistor is configured to generate and to amplify the RF electromagnetic field.

18. The shisha device according to claim 16, wherein the article cavity comprises one or more external walls formed from a material opaque to the RF electromagnetic field, and wherein one or more slots are formed in the one or more external walls.

19. The shisha device according to claim 16, wherein the article cavity comprises an open end configured to receive an aerosol-forming article comprising the aerosol-forming substrate, and a substantially closed end.

20. The shisha device according to claim 16, further comprising an antenna connected to the electromagnetic field generator and being configured to direct the RF electromagnetic field.

21. The shisha device according to claim 20, wherein the antenna is positioned at least partially in the article cavity.

22. The shisha device according to claim 16, further comprising a resonating cavity between the article cavity and the electromagnetic field generator.

23. The shisha device according to claim 16, further comprising a sensor in or adjacent to the article cavity, the sensor providing a signal indicative of a temperature in the article cavity, and a controller connected to receive the signal from the sensor and connected to control the electromagnetic field generator in dependence on the signal from the sensor.

24. A shisha system, comprising: a shisha device according to claim 16; and an aerosol-generating article comprising an aerosol-forming substrate.

25. The shisha system according to claim 24, wherein the aerosol-forming substrate comprises tobacco.

26. The shisha system according to claim 24, wherein the aerosol-generating article comprises one or more external surfaces formed from a material opaque to the RF electromagnetic field.

27. The shisha system according to claim 26, wherein one or more slots are formed in the one or more external surfaces formed from the material opaque to the RF electromagnetic field.

28. The shisha system according to claim 26, wherein the material opaque to the RF electromagnetic field forms a coating on the one or more external surfaces.

29. An aerosol-generating article for a shisha system, the aerosol-generating article comprising: an aerosol-forming substrate; and one or more external surfaces formed from a material opaque to an RF electromagnetic field, wherein the material opaque to the RF electromagnetic field is fluid-permeable.

30. The aerosol-generating article according to claim 29, wherein the material opaque to the RF electromagnetic field is a metal mesh.

Description

[0129] Embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0130] FIG. 1 is a schematic illustration of a dielectric heating system;

[0131] FIG. 2 is a schematic illustration of a closed-loop control system for a shisha system having a dielectric heating system according to embodiments of the disclosure;

[0132] FIG. 3 is a schematic illustration of an embodiment of a shisha system having a dielectric heating system;

[0133] FIG. 4 is a schematic illustration of a heating unit of a shisha device and an aerosol-generating article configured for use with the shisha device according to an embodiment of the disclosure;

[0134] FIG. 5 is a schematic illustration of heating units of different embodiments of a shisha device according to embodiments of the disclosure;

[0135] FIG. 6 is a schematic illustration of a heating unit of a shisha device and an aerosol-generating article configured for use with the shisha device according to an embodiment of the disclosure;

[0136] FIG. 7 is a schematic illustration of a heating unit of a shisha device and an aerosol-generating article configured for use with the shisha device according to an embodiment of the disclosure;

[0137] FIG. 8 is a schematic illustration of a heating unit of a shisha device and an aerosol-generating article configured for use with the shisha device according to an embodiment of the disclosure; and

[0138] FIG. 9 is a schematic illustration of an embodiment of a shisha system having a dielectric heating system.

[0139] FIG. 1 is a schematic illustration of a system for heating using radio frequency (RF) electromagnetic radiation, sometimes referred to as dielectric heating. The system comprises a radio frequency signal generator 10, a power amplifier 12 connected to the signal generator to amplify the radio frequency signal, and antennas 16 positioned inside an article cavity 14, the antennas 16 being connected to an output of the power amplifier 12. The output of the power amplifier 12 is fed back to the signal generator 10 to provide closed-loop control. An article 18, which is to be heated, is placed in the article cavity 14 and subjected to radio frequency electromagnetic radiation. Polar molecules within the article 18 align with the oscillating electromagnetic field and so are agitated by the electromagnetic field as it oscillates. This causes an increase in temperature of the article 18. This kind of heating has the advantage that it is uniform throughout the article (provided that the polar molecules are uniformly distributed). It also has the advantage of being a non-contact form of heating, which does not require conduction or convection of heat from high temperature heating element.

[0140] FIG. 2 illustrates a control scheme that may be used in any of the embodiments described in FIGS. 3 to 9. As previously described, the system comprises control circuitry for the electromagnetic field generator. In the example of FIG. 2, the electromagnetic field generator 11 comprises a solid state RF LDMOS transistor that performs the function of both a RF signal generator 10 and a power amplifier 12 to amplify the generated RF electromagnetic signal. The output of the RF solid state transistor is passed to a radiating antenna 16 positioned to radiate an aerosol-forming substrate 20 positioned within an aerosol-generating article 18 that is received in an article cavity 14.

[0141] The control circuitry comprises a microcontroller 26 that can control both the frequency and the power output of the RF solid state transistor. One or more sensors provide input to the microcontroller 26. The microcontroller 26 adjusts the frequency or the power output, or both the frequency and the power output, of the electromagnetic field generator 11 based on the sensor inputs. In the example shown in FIG. 2, there is a temperature sensor 28 positioned to sense the temperature within the article cavity 14. A sampling antenna 30 may be provided in the article cavity 14 as an alternative, or in addition, to the temperature sensor 28. The sampling antenna 30 is configured as a receiver and can detect perturbation of the electromagnetic field in the article cavity 14, which is an indication of the efficiency of the energy absorption by the aerosol-forming substrate 20. A RF power sensor 32 is also provided to detect the power output from the electromagnetic field generator 11.

[0142] The microcontroller 26 receives signals from the RF power sensor 32, the temperature sensor 28 and the sampling antenna 30. The signals can be used to determine at least one of: whether the temperature is too low, whether the temperature is too high, if there is a fault, and if there is no substrate, or a substrate with inappropriate dielectric properties, in the article cavity 14.

[0143] Based on the determination made by the microcontroller 26, the frequency and power of the electromagnetic filed generated by the RF solid state transistor is adjusted or the electromagnetic filed is switched off. Typically, it is desirable to provide for a stable and consistent volume of aerosol, which means maintaining the aerosol-forming substrate within a particular temperature range. However, the desired target temperature may vary with time as the composition of the aerosol-forming substrate changes and the temperature of the surrounding system changes. Also, the dielectric properties of the aerosol-forming substrate change with temperature and so the electromagnetic field may need to be adjusted as temperature increases or decreases.

[0144] It should be clear that features described in relation one embodiment may be applied to other embodiments. The embodiments described provide the advantages of uniform, contactless heating of an aerosol-forming substrate in a manner that can be controlled to provide for particular, desirable aerosol properties. In comparison to conventional microwave heating using a magnetron, the use of a solid state RF transistor also allows for better control of frequency and power and longer operational lifetime.

[0145] The embodiments described with reference to FIGS. 3 to 8 use the basic heating and control principles illustrated in FIGS. 1 and 2. In addition, the embodiments described with reference to FIGS. 3 to 8 use a solid state radiofrequency (RF) transistor to perform both the signal generation and power amplification functions illustrated in FIG. 1. However, it would be possible to implement the embodiments described using a RF transistor for the signal generation and a separate electronic component or components to provide for the power amplification. It would also be possible to implement the embodiments described using conventional microwave heating systems, such as systems using a magnetron.

[0146] FIG. 3 is a schematic illustration of a shisha system according to an embodiment of this disclosure.

[0147] The shisha device 50 comprises a vessel 52 defining a liquid cavity 54. The vessel 52 is configured to retain a volume of liquid in the liquid cavity 54, and is formed from a rigid, optically transparent material, such as glass. In this embodiment, the vessel 52 has a substantially frustoconical shape, and is supported in use at its wide end on a flat, horizontal surface, such as a table or shelf. The liquid cavity 54 is divided into two sections, a liquid section 56 for receiving a volume of liquid, and a headspace 58 above the liquid section 58. A liquid fill level 60 is positioned at the boundary between the liquid section 56 and the headspace 58, the liquid fill level 60 being demarcated on the vessel 52 by a dashed line marked on an outer surface of the vessel 52. A headspace outlet 62 is provided on a side wall of the vessel 52, above the liquid fill level 60. The headspace outlet 62 enables fluid to be drawn out of the liquid cavity 54 from the headspace 58. A mouthpiece 64 is connected to the headspace outlet 62 by a flexible hose 66. A user may draw on the mouthpiece 64 to draw fluid out of the headspace 58 for inhalation.

[0148] The shisha device 50 further comprises a heating unit 70 comprising an electromagnetic field generator in accordance with the present disclosure. Examples of different heating units will be discussed in more detail below with reference to FIGS. 4, 5, 6, 7 and 8. The heating unit 70 is arranged above the vessel 52 by an airflow conduit 72. In this embodiment, the heating unit 70 is supported above the vessel 52 by the airflow conduit 72, however, it will be appreciated that in other embodiments the heating unit 70 may be supported above the vessel 52 by a housing of the shisha device or another suitable support. The airflow conduit 72 extends from the heating unit 70 into the liquid cavity 54 of the vessel 52. The airflow conduit 72 extends through the headspace 58, and below the liquid fill level 60 into the liquid section 58. The airflow conduit 72 comprises an outlet 74 in the liquid section 56 of the liquid cavity 54, below the liquid fill level 60. This arrangement enables air to be drawn from the heating unit 70 to the mouthpiece 64. Air may be drawn from an environment external to the device 50, into the heating unit 70, through the heating unit 70, though the airflow conduit 72 into the volume of liquid in the liquid section 56 of the liquid cavity 54, out of the volume of liquid into the headspace 58, and out of the vessel from the headspace 58 at the headspace outlet 62, through the hose 66 and to the mouthpiece 64.

[0149] In use, a user may draw on the mouthpiece 64 of the shisha device 50 to receive aerosol from the shisha device 50. In more detail, an aerosol-generating article comprising an aerosol-forming substrate can be positioned in an article cavity within the heating unit 70 of the shisha device 50. The heating unit 70 may be operated to heat the aerosol-forming substrate within the aerosol-generating article and release volatile compounds from the heated aerosol-forming substrate. When a user draws on the mouthpiece 64 of the shisha device 50, the pressure within the shisha device 50 is lowered, which draws the released volatile compounds from the aerosol-forming substrate out of the heating unit 70 and into the airflow conduit 72. The volatile compounds are drawn out of the airflow conduit 72 at the outlet 74, into the volume of liquid in the liquid section 56 of the liquid cavity 54. The volatile compounds cool in the volume of liquid and are released into the headspace 58 above the liquid fill level 60. The volatile compounds in the headspace 58 condense to form an aerosol that is drawn out of the headspace at the headspace outlet 62 and to the mouthpiece 64 for inhalation by the user.

[0150] FIG. 4 shows schematic illustrations of a heating unit 70 of the shisha device 50 of FIG. 3 in combination with an aerosol-generating article 90, forming a shisha system according to an embodiment of this disclosure. FIG. 4a shows the heating unit 70 and the aerosol-generating article 90 before insertion of the aerosol-generating article 90 into an article cavity 14 of the heating unit 70. FIG. 4b shows the aerosol-generating article 90 received in the article cavity 14 of the heating unit 70.

[0151] As shown in FIG. 4a, the heating unit 70 comprises an external housing 71. The external housing 71 forms a cylindrical tube that is open at one end for insertion of the aerosol-generating article 90, and is substantially closed at the opposite end. The external housing 71 is formed from a material that is opaque to RF electromagnetic radiation, such as aluminium.

[0152] An article cavity 14 is defined within the external housing 71 by a base 78 and a side wall 76, extending between the periphery of the base 78 and the open end of the external housing 71. The article cavity 14 is configured to receive the aerosol-generating article 90, and has a shape and size that is complementary to the aerosol-generating article 90. The diameter of the base 78 of the article cavity 14 is less than the diameter of the open end of the external housing 71, such that the side wall 76 is inclined relative to the cylindrical side wall of the external housing 71. Accordingly, the article cavity 14 has a substantially frustoconical shape that is open at its wide end to receive the aerosol-generating article 90. The side wall 76 and base 78 of the article cavity 14 are formed from a material that is opaque to RF electromagnetic radiation, such as aluminium. However, the base 78 of the article cavity 14 comprises a plurality of slots 79 configured to enable a RF electromagnetic field to propagate into the article cavity 14 via the base 78.

[0153] A resonating cavity 80 is located below the base 78 of the article cavity 14. In this embodiment, the resonating cavity 80 is defined between the base 78 of the article cavity 14, the substantially closed end of the external housing 71, and an interior wall 82. The interior wall 82 extends between the periphery of the base 78 of the article cavity 14 and the substantially closed end of the external housing 71. In this embodiment, the interior wall 82 is formed of a material opaque to RF electromagnetic radiation, such as aluminium.

[0154] It will be appreciated that in other embodiments, the position of the interior wall 82 may be altered in order to change the size and shape of the resonating cavity 80. It may be necessary to alter the position of the interior wall 82 to enable an electromagnetic field of a particular frequency to resonate within the resonating cavity 80.

[0155] Preferably, the base 78 and side wall 76 of the article cavity 14, and the interior wall 82 and external housing 71 have polished surfaces to improve reflection of RF radiation.

[0156] The heating unit 70 further comprises an electromagnetic field generator 11. The electromagnetic field generator 11 comprises a solid state RF LDMOS transistor that performs the function of both a RF signal generator and a power amplifier to amplify the generated RF electromagnetic signal. The output of the RF solid state transistor is coupled to a wave guide 15. The wave guide 15 extends into the resonating cavity 80 through the substantially closed end of the external housing 71. The wave guide 15 is coupled to an antenna 16, which is positioned within the resonating cavity 80 and configured to radiate the RF electromagnetic field generated by the RF solid state transistor into the resonating cavity 80.

[0157] The electromagnetic field generator 11 is connected to a power supply (not shown) and control circuitry (not shown) of the shisha device, the control circuitry being configured to control the supply of power from the power supply to the electromagnetic field generator 11. In this embodiment, the power supply is a rechargeable lithium ion battery, and the shisha device 50 comprises a power connector that enables the shisha device 50 to be connected to a mains power supply for recharging the power supply. Providing the shisha device 50 with a power supply, such as a battery, enables the shisha device 50 to be portable and used outdoors or in locations in which a mains power supply is not available.

[0158] The heating unit 70 is arranged above the vessel 52 of the shisha device 50 by the airflow conduit 72. The airflow conduit 72 is fixedly attached to the substantially closed end of the external housing 71 of the heating unit 70. It will be appreciated that in other embodiments, the heating unit 70 may be removably attached to the airflow conduit 72, such that the heating unit 70 may be removed for cleaning or replacement if necessary. An opening 73 is provided in the substantially closed end of the external housing 71 to fluidly connect the resonating cavity 80 to the airflow conduit 72. A radiation shielding element (not shown), in the form of a metal mesh, is provided over the opening 73 of the external housing 71 to substantially prevent egress of a RF electromagnetic field from within the resonating cavity 80 into the airflow conduit 72, without substantially affecting fluid flow between the resonating cavity 80 and the airflow conduit 72.

[0159] Accordingly, the heating unit 70 is configured such that air may be drawn from the article cavity 14 into the resonating cavity 80, through the slots 79 in the base 78, and from the resonating cavity 80 into the airflow conduit 72, through the opening 73 and the radiation shielding element.

[0160] The aerosol-generating article 90 comprises an aerosol-forming substrate 92. In this embodiment, the aerosol-forming substrate 92 is a shisha substrate, comprising molasses and tobacco. The aerosol-forming substrate 92 is encased within a container. The container has a substantially frustoconical shape, complementary to that of the article cavity 14. The container comprises a bottom wall 94, a top wall 96 and a side wall 98 extending between the bottom wall 94 and the top wall 96. The bottom wall 94 and side wall 98 of the container are formed from a material that is fluid permeable, and substantially transparent to a RF electromagnetic field, such as a perforated cardboard or plastic material. This enables air to be drawn into or out of the aerosol-generating article though the bottom wall 94 and the side wall 98 and enables ingress of a RF electromagnetic field into the aerosol-generating article through the bottom wall 94 and side wall 98. The top wall 96 comprises a material that is opaque to a RF electromagnetic field, such as a metal mesh. This enables air to be drawn into the aerosol-generating article through the top wall 96, and prevents egress of a RF electromagnetic field from the aerosol-generating article through the top wall 96.

[0161] As shown in FIG. 4b, when the aerosol-generating article 90 is received in the article cavity 14 of the heating unit 70, the bottom wall 94 of the aerosol-generating article 90 contacts the bottom wall 78 of the article cavity 14, and the side wall 98 of the aerosol-generating article 90 contacts the side wall 76 of the article cavity 14. The top wall 96, formed from a material opaque to the RF electromagnetic field, aligns with and contacts side wall 76 of the article cavity 14, which is also formed from a material opaque to the RF electromagnetic field. In this position, the aerosol-forming substrate 92 is surrounded by material opaque to the RF electromagnetic field, at the top wall 96 of the aerosol-generating article 90, and the side wall 76 and base 78 of the article cavity 14. The slots 79 in the base 78 of the article cavity 14 are the only entry and exit point for the RF electromagnetic field into and out of the aerosol-forming substrate 92.

[0162] When a user draws on the mouthpiece 64 of the shisha device 50, air is drawn into the shisha device 50 through the top wall 96 of the aerosol-generating article 90. An air flow path through the aerosol-generating article 90 and heating unit 70 is shown by the arrows in FIG. 4b. Air is drawn into the aerosol-generating article 90 through the top wall 96 of the aerosol-generating article 90, through the aerosol-forming substrate 92 and into the resonating cavity 80 of the heating unit 70 through the bottom wall 94 of the aerosol-generating article 90 and the slots 79 in the bottom wall 78 of the article cavity 14. From the resonating cavity 80, air is drawn into the airflow conduit 72 through the opening 73 in the external housing 71 of the heating unit 70.

[0163] In use, power is supplied to the electromagnetic field generator 11 from the power supply when a user activates the shisha device 50. In this embodiment, the shisha device is activated by a user pressing an activation button (not shown) provided on an external surface of the heating unit 70. It will be appreciated that in other embodiments, the shisha device may be activated in another manner, such as on detection of a user drawing on the mouthpiece 64 by a puff sensor provided on the mouthpiece 64. When power is supplied to the electromagnetic field generator 11, the electromagnetic field generator 11 generates and amplifies a RF electromagnetic field with a frequency of between 900 MHz and 2.4 GHz. The RF electromagnetic field is directed along the wave guide 15 and into the resonating cavity 80 by the antenna 16. From the resonating cavity 80, the RF electromagnetic field propagates into the aerosol-forming substrate 92 of the aerosol-generating article 90 via the slots 79 in the bottom wall 78 of the article cavity 14 and the bottom wall 94 of the aerosol-generating article 90. The top wall 96 of the aerosol-generating article 90 prevents egress of the RF electromagnetic field from the aerosol-generating article 90. The RF electromagnetic field dielectrically heats the aerosol-forming substrate 90, which releases volatile compounds. As described above, the temperature in the article cavity 14 can be regulated using a feedback control mechanism. The temperature inside the article cavity 14 can be sensed, or another parameter indicative of the temperature inside the substrate cavity can be sensed, to provide a feedback signal to the control circuitry of the shisha device 50. The control circuitry is configured to adjust the frequency or amplitude, or both the frequency and the amplitude, of the RF electromagnetic field in order to maintain the temperature inside the article cavity 14 within a desired temperature range.

[0164] When a user draws on the mouthpiece 64 of the shisha device 50, the volatile compounds released from the heated aerosol-forming substrate 90 are entrained in the air flow through the aerosol-generating article 90 and are drawn out of the aerosol-generating article 90, through the resonating cavity 80 and into the airflow conduit 72. From the airflow conduit, the volatile compounds are drawn through the shisha device 50 to and out of the mouthpiece 66 as described above.

[0165] FIG. 5 shows heating units 70 for a shisha device according to other embodiments of this disclosure. The heating units 70 shown in FIG. 5 are substantially similar to the heating unit 70 shown in FIG. 4, and like reference numerals are used to represent like features.

[0166] The heating unit 70 shown in FIG. 5a differs from the heating unit 70 shown in FIG. 4 in that the base 78 of the article cavity 14 does not comprise slots 79, and so the RF electromagnetic radiation is unable to propagate from the resonating cavity 80 into the article cavity 14 through the base 78 of the article cavity 14. In the embodiment of FIG. 5a, slots 83 are provided in the interior wall 82, and slots 77 are provided in the side wall 76 of the article cavity 14. Accordingly, the RF electromagnetic field is able to enter the article cavity 14 through the side wall 76 of the article cavity 14, via the slots 83 in the interior wall 82. This arrangement changes the size and shape of the resonating cavity 80 compared to the resonating cavity 80 of the embodiment of FIG. 4. Changing the size and shape of the resonating cavity 80 may be necessary when using a RF electromagnetic field of different frequencies, in order to ensure that the RF electromagnetic field resonates within the resonating cavity 80.

[0167] The heating unit 70 shown in FIG. 5b differs from the heating unit 70 shown in FIG. 4 in that, in addition to the base 78 of the article cavity 14 comprising slots 79, the interior wall 82 also comprises slots 83 and the side wall 76 of the article cavity 14 comprises slots 77, such that the RF electromagnetic field may enter the article cavity 14 through both the base 78 and the side wall 76 of the article cavity 14. This arrangement provides a further alternative size and shape for the resonating cavity 80, which may provide a suitable resonating cavity for a RF electromagnetic field of an alternative frequency.

[0168] FIG. 6 shows a heating unit 70 for a shisha device and an aerosol-generating article 90, forming a shisha system according to another embodiment of this disclosure. The heating unit 70 and aerosol-generating article 90 shown in FIG. 6 are substantially similar to the heating unit 70 and aerosol-generating article 90 shown in FIG. 4, and like reference numerals are used to represent like features. FIG. 6a shows the heating unit 70 and the aerosol-generating article 90 before insertion of the aerosol-generating article 90 into an article cavity 14 of the heating unit 70. FIG. 6b shows the aerosol-generating article 90 received in the article cavity 14 of the heating unit 70.

[0169] The heating unit 70 shown in FIG. 6 differs from the heating unit 70 shown in FIG. 4 in that the base 78 of the article cavity 14, the side wall 76 of the article cavity 14 and the interior wall 82 are all formed from a material that is substantially transparent to the RF electromagnetic field, such as a rigid plastic material, ceramic or clay. In this embodiment, each of the base 78 of the article cavity 14, the side wall 76 of the article cavity 14 and the interior wall 82 are each configured to be fluid permeable, such that air may be drawn through each of these walls. It will be appreciated that in other embodiments, the base 78 of the article cavity 14 may be fluid permeable and the side wall 76 of the article cavity 14 and the interior wall 82 may be substantially impermeable to fluid, or the side wall 76 of the article cavity 14 and the interior wall 82 may be fluid permeable and the base 78 of the cavity 14 may be substantially fluid impermeable.

[0170] The aerosol-generating article 90 shown in FIG. 6 differs from the aerosol-generating article 90 shown in FIG. 4 in that the bottom wall 94 and the side wall 80 of the aerosol-generating article are formed from a material that is opaque to the RF electromagnetic field. To allow the RF electromagnetic field to enter the aerosol-generating article 90, and heat the aerosol-forming substrate 92, a plurality of slots 95 are provided in the bottom wall 94 and the side wall 90. It will be appreciated that in some embodiments, only one slot will be provided, on one of the bottom wall and the top wall. It will also be appreciated that the size and shape of the one or more slots may vary depending on the geometry of the aerosol-generating article and the shisha device. In this embodiments, the slots 95 also make the bottom wall 95 and the side wall 98 fluid permeable, such that air may be drawn through the aerosol-generating article 90 and into the heating unit 70 of the shisha device 50.

[0171] An advantage of providing the bottom wall and side wall of the aerosol-generating article with the material opaque to the RF electromagnetic field is that the number, size, shape and arrangement of the slots in the bottom wall and side wall may be chosen depending on the aerosol-forming substrate encased within the aerosol-generating article. The number, size, shape and arrangement of the slots in the bottom wall and side wall may influence the RF electromagnetic field within the aerosol-generating article, thereby influencing the heating of the aerosol-forming substrate and the temperature to which the aerosol-forming substrate is heated.

[0172] FIG. 7 shows a heating unit 70 for a shisha device and an aerosol-generating article 90 according to another embodiment of this disclosure. The heating unit 70 and aerosol-generating article 90 shown in FIG. 7 are substantially similar to the heating unit 70 and aerosol-generating article shown in FIG. 4, and like reference numerals are used to represent like features.

[0173] The heating unit 70 shown in FIG. 7 comprises an external housing 71, forming a cylindrical tube that is open at one end and substantially closed at the opposite end. The external housing 71 is formed from a material that is opaque to RF electromagnetic radiation.

[0174] An article cavity 14 is defined within the external housing 71 and is sized and shaped to receive the aerosol-generating article 90. The heating unit is arranged above the vessel 52 of the shisha device 50 by the airflow conduit 72, which extends into the substantially closed end of the external housing 71 of the heating unit 70 to fluidly connect the article cavity 14 to the vessel 52 of the shisha device 50. A radiation shielding element (not shown), in the form of a metal mesh, is provided in the airflow conduit 72 to prevent egress of the RF electromagnetic field from the article cavity 14 through the airflow conduit 72.

[0175] The heating unit 70 shown in FIG. 7 differs from the heating unit 70 shown in FIG. 4 in that the heating unit 70 shown in FIG. 7 comprises a closure 75. The closure 75 is moveable over the open end of the external housing 71 of the heating unit 70 to substantially close the open end. The closure 75 comprises an external housing similar to the external housing 71 of the heating unit, formed from the same material opaque to the RF electromagnetic field and sized and shaped to align and engage with the external housing 71 to close the open end. The closure 75 is rotatably connected to the external housing 71 by a hinge, and is rotatable between an open position, as shown in FIG. 7a, and a closed position, as shown in FIG. 7b. When the closure 75 is in the open position, the open end of the external housing 71 is open for insertion of an aerosol-generating article 90 into the article cavity 14, and for removal of the aerosol-generating article 90 from the article cavity 14. When the closure 75 is in the closed position, the article cavity 14 is surrounded by material that is opaque to the RF electromagnetic field, such that the RF electromagnetic field is unable to propagate from the article cavity 14.

[0176] In this embodiment, the closure 75 also comprises an electromagnetic field generator 11, in the form of a solid state RF LDMOS transistor, a wave guide 15 coupled to the output of the RF solid state transistor, a resonating cavity 80, and an antenna 16 coupled to the wave guide 16 and positioned in the resonating cavity 80. In this embodiment, the resonating cavity 80 comprises a substantially cylindrical body of dielectric material encased in a metallic outer container. The metallic outer container of the resonating cavity 80 comprises a pair of slots 79, which are provided to enable a RF electromagnetic field generated by the electromagnetic field generator 11 and directed into the resonating cavity 80 to propagate from the resonating cavity 80 into the article cavity 14 when the closure 75 is in the closed position. Control circuitry (not shown) and a battery (not shown) are also comprised in the closure 75 to provide a controlled supply of power to the electromagnetic field generator 11.

[0177] It will be appreciated that in some embodiments, the shisha device may comprise electrical components on the vessel 50 or on the mouthpiece 64 that require power from the battery, or control from the control circuitry. In these embodiments, a flexible circuit or wire may be provided from the control circuitry and battery in the enclosure 75, over the hinge to the components arranged at other locations on the shisha device 50.

[0178] In this embodiment, the closure 75 also comprises an air inlet (not shown), in the form of a fluid permeable region of material that is opaque to the RF electromagnetic field. The air inlet enables air to be drawn into the article cavity 14 when the closure 75 is in the closed position.

[0179] This embodiment has a particularly advantageous configuration in that is straightforward to manufacture, and comprises relatively few component parts. Furthermore, since the article cavity 14 is completely enclosed by material that is opaque to the RF electromagnetic field, the aerosol-generating article 90 is not required to have any external surfaces formed from a material opaque to the RF electromagnetic field. Since the aerosol-generating article 90 is typically a disposable component of the shisha system, this may reduce the cost of manufacture of the aerosol-generating article 90.

[0180] FIG. 8 shows a heating unit 70 for a shisha device 50 and an aerosol-generating article 90 according to another embodiment of this disclosure. The heating unit 70 and aerosol-generating article 90 shown in FIG. 8 are substantially similar to the heating unit 70 and aerosol-generating article 90 shown in FIG. 7, and like reference numerals are used to represent like features. FIG. 7a shows the heating unit 70 and the aerosol-generating article 90 before insertion of the aerosol-generating article 90 into an article cavity 14 of the heating unit 70. FIG. 7b shows the aerosol-generating article 90 received in the article cavity 14 of the heating unit 70.

[0181] The heating unit 70 shown in FIG. 8 differs from the heating unit 70 shown in FIG. 7 in that the heating unit 70 shown in FIG. 8 comprises the electromagnetic field generator 11, wave guide 15, antenna 60 and resonating cavity 80 in the external housing 71, rather than in the closure 75. In this embodiment, the closure 75 is merely a covering for closing the article cavity 14 to prevent egress of the RF electromagnetic field from the article cavity 14.

[0182] The resonating cavity 80 of the heating unit 70 shown in FIG. 8 comprises a substantially annular body of dielectric material encased in a metallic outer container. The resonating cavity 80 comprises a tapered inner passage that widens towards the open end of the external housing 71. In this embodiment, the inner passage of the resonating cavity 80 substantially defines the article cavity 14, being configured to receive the generally frustoconical aerosol-generating article 90. A plurality of slots 79 are provided in the metallic outer container of the resonating cavity 80, at the inner passage, to enable the RF electromagnetic field to propagate into the article cavity 14.

[0183] In this embodiment, the air flow path through the heating unit 70 is substantially longitudinal through the article cavity 14, in the direction of the airflow conduit 72, and the RF electromagnetic field propagates from the resonating cavity 80 into the article cavity 14 in a direction substantially transverse to the air flow. This arrangement ensures that the electromagnetic field generating apparatus is removed from the air flow pathway through the heating unit 70. This type of arrangement may make it easier to control the resistance to draw through the heating unit 70. This type of arrangement may also make management of the temperature of the electromagnetic field generating apparatus more straightforward, as the temperature of the electromagnetic field generating apparatus is less likely to fluctuate during use as a result of a user puffing on the device and drawing air over the electromagnetic field generating apparatus.

[0184] FIG. 9 shows a shisha system according to another embodiment of this disclosure. The shisha system is similar to the shisha system shown in FIG. 3, and like reference numerals are used to represent like features.

[0185] The shisha device 50 comprises a vessel 52 defining a liquid cavity 54, which is divided into two sections, a liquid section 56 comprising a volume of liquid, and a headspace 58 above the liquid section. In this embodiment, the vessel 52 is substantially cylindrical. A liquid fill level 60 is defined at the boundary between the liquid section 56 and the headspace 58, and is demarcated by a dashed line 60 on an external surface of the vessel 52. A headspace outlet 62 is provided on a side wall of the vessel 52, above the liquid fill level, and is configured to enable fluid to be drawn out of the liquid cavity at the headspace 58. A mouthpiece 64 is connected to the headspace outlet 62 by a flexible hose 66.

[0186] The vessel 52 is arranged on a heating unit 70, which in this embodiment is a cylindrical unit with a diameter substantially equal to that of the vessel 52. Accordingly, when the vessel 52 and heating unit 70 are arranged together for use, the shisha device 50 forms a substantially cylindrical unit.

[0187] The heating unit 70 is substantially similar to the heating unit shown in FIG. 7, and like reference numerals will be used to describe like features.

[0188] The heating unit 70 comprises an external housing 71 formed from a material that is opaque to RF electromagnetic radiation. The external housing 71 forms a cylindrical tube that is substantially closed at both ends. A door (not shown) is formed in a side wall of the external housing 71 and coupled to the side wall by a hinge. The door is rotatable between an open position and a closed position to allow aerosol-generating articles to be inserted into the heating unit 70 and removed from the heating unit 70. The door is lockable in the closed position to ensure that the door is not opened when the shisha device 50 is in operation, and the door is formed from a metal mesh that is opaque to RF electromagnetic radiation but is fluid permeable, such that ambient air can be drawn into the heating unit 70.

[0189] An article cavity 14 is defined in the heating unit 70 for receiving an aerosol-generating article 90. In this embodiment, the article cavity 14 is substantially frustoconical, such that the article cavity 14 is configured to receive a substantially frustoconical aerosol-generating article 90. The article cavity 14 is arranged above a resonating cavity 80. In this embodiment, the resonating cavity 80 comprises a substantially cylindrical body of dielectric material encased in a metallic outer container. The metallic outer container of the resonating cavity 80 comprises a pair of slots 79, which are provided to enable a RF electromagnetic field to propagate from the resonating cavity 80 into the article cavity 14.

[0190] An electromagnetic field generator 11, in the form of a solid state RF LDMOS transistor, is provided below the resonating cavity 80. The output of the electromagnetic field generator 80 is coupled to a wave guide 15, in the form of a waveguide. The wave guide 15 is arranged to direct a RF electromagnetic field generated by the electromagnetic field generator 11 to an antenna 16, which is arranged in the resonating cavity 80. With this arrangement, a RF electromagnetic field generated by the electromagnetic field generator 11 is directed to the resonating cavity 80, and propagates out of the resonating cavity 80, through the slots 79, into the article cavity 14 for heating an aerosol-forming substrate arranged in the article cavity 14. The electromagnetic field generator 11 is connected to control circuitry (not shown) and a lithium ion battery (not shown), which are arranged and configured to control the supply of power to the electromagnetic field generator 11 to control the RF electromagnetic field generated by the electromagnetic field generator 11.

[0191] An airflow conduit 72 extends from the article cavity 14 into the vessel 52, to a position in the liquid section 56, below the liquid fill level 60. The airflow conduit 72 fluidly connects the article cavity to the liquid section 56 of the vessel 52. To prevent liquid from the liquid section 56 flowing into the article cavity 14 through the airflow conduit 72 under the influence of gravity, a one way valve (not shown) is arranged in the airflow conduit 72 at the opening 73 between the heating unit 70 and vessel 52. The one way valve does not permit fluid to flow from the vessel 52 into the heating unit 70, and also requires a minimum pressure to be reached before fluid is able to flow from the heating unit 70 to the vessel 52.

[0192] In use, when a user draws on the mouthpiece 64, ambient air is drawn into the shisha device 50 through the mesh door (not shown) and into the article cavity 14. A puff sensor (not shown), provided in the article cavity 14 and connected to the control circuitry and battery, senses that a user is drawing on the mouthpiece 64 as air flows into the article cavity 14. When the puff sensor detects a user drawing on the mouthpiece 64, the control circuitry supplies power from the battery to the electromagnetic field generator 11, causing a RF electromagnetic field to propagate into the article cavity 14 and heat the aerosol-forming substrate in the aerosol-generating article 90. Volatile compounds are released from the heated aerosol-forming substrate. The air being drawn into the article cavity 14 entrains the released volatile compounds, and the entrained volatile compounds are drawn through the airflow conduit 72, through the one-way valve, into the liquid section 56 of the vessel 52. The volatile compounds cool in the volume of liquid in the liquid section 56, and are released from the liquid into the headspace 58, where they condense to form an aerosol. The aerosol is drawn out of the headspace 58 through the headspace outlet 62, along the hose 66 and to the mouthpiece 64 for inhalation by the user.

[0193] It will be appreciated that the embodiments described above are exemplary embodiments only, and various other embodiments according with this disclosure are also envisaged. For example, it will be appreciated that the heating unit embodiments described above may be used with any suitable design of shisha device, such as the devices shown in FIGS. 3 and 9. For example, it will also be appreciated that vessels, aerosol-forming articles and any other features of shisha systems according to this disclosure may be any other shape and size, as desired. For example, the liquid within the liquid sections of the shisha devices is preferably water, but may be another suitable liquid.