SHISHA SYSTEM WITH A HEATING UNIT COMPRISING TWO ELECTRODES

Abstract

A shisha system comprising an aerosol-generating article (90) and a shisha device (50). The aerosol-generating article (90) comprises an aerosol-forming substrate (92). The shisha system further comprises a first electrode (15) and a second electrode (16). The shisha device (50) comprises a liquid cavity (54) configured to contain a volume of liquid, the liquid cavity (54) having a head space outlet (60); an article cavity (14) configured to receive an aerosol-forming substrate (92), the article cavity (14) being in fluid communication with the liquid cavity (54). The shisha device further comprises an oscillation circuit (10) configured for connection to the first electrode (15) and the second electrode (16). The oscillation circuit (10) is configured to supply a radio frequency (RF) alternating voltage to the first electrode (15) and the second electrode (16), the RF voltage between the first electrode (15) and the second electrode (16) generating an alternating radio frequency (RF) electromagnetic field between the first electrode (15) and the second electrode (16) for heating the aerosol-forming substrate (92) when the aerosol-generating article (90) is received in the article cavity (14).

Claims

1. A shisha system comprising: an aerosol-generating article comprising an aerosol-forming substrate; a first electrode and a second electrode; and a shisha device comprising: a liquid cavity configured to contain a volume of liquid, the liquid cavity having a head space outlet; an article cavity configured to receive the aerosol-forming article, the article cavity being in fluid communication with the liquid cavity; and an oscillation circuit configured for connection to the first electrode and the second electrode, wherein the oscillation circuit is configured to supply a radio frequency (RF) alternating voltage to the first electrode and the second electrode, the RF voltage between the first electrode and the second electrode generating an alternating radio frequency (RF) electromagnetic field between the first electrode and the second electrode for heating the aerosol-forming substrate when the aerosol-generating article is received in the article cavity.

2. A shisha system as claimed in claim 1, wherein the first electrode and the second electrode are arranged to contact the aerosol-generating article when the aerosol-generating article is received in the article cavity.

3. A shisha system as claimed in claim 1, wherein the second electrode is spaced apart from the first electrode to receive at least a portion of the aerosol-forming substrate between the first electrode and the second electrode.

4. A shisha system as claimed in claim 1, wherein the shisha device comprises the first electrode and the second electrode, and the first electrode and the second electrode are arranged in or around the article cavity.

5. A shisha system as claimed in claim 1, wherein: the aerosol-generating article comprises the first electrode and the second electrode, at least a portion of the aerosol-forming substrate being disposed between the first electrode and the second electrode; the shisha device comprises a first electrical contact for electrically connecting the first electrode to the oscillation circuit; and the shisha device comprises a second electrical contact for electrically connecting the second electrode to the oscillation circuit.

6. A shisha system as claimed in claim 1, wherein: the shisha device comprises one of the first electrode and the second electrode; the aerosol-generating article comprises the other one of the first electrode and the second electrode; and the shisha device further comprises an electrical contact for electrically connecting the other one of the first electrode and the second electrode to the oscillation circuit.

7. A shisha system as claimed in claim 1, wherein one or more slots are formed in at least one of the first electrode and the second electrode.

8. A shisha system as claimed in claim 1, wherein the first electrode and the second electrode are substantially planar, and wherein the second electrode is arranged substantially parallel to the first electrode.

9. A shisha system as claimed in claim 1, wherein the first electrode is a tubular electrode, and wherein the second electrode is arranged within the tubular first electrode.

10. A shisha device comprising: a liquid cavity configured to contain a volume of liquid, the liquid cavity having a head space outlet; an article cavity for receiving an aerosol-generating article, the article cavity being in fluid communication with the liquid cavity; a first electrode and a second electrode, the first electrode and the second electrode being arranged in or around the article cavity; and an oscillation circuit connected to the first electrode and the second electrode and configured to supply a radio frequency (RF) alternating voltage to the first electrode and the second electrode, the RF voltage between the first electrode and the second electrode generating an alternating radio frequency (RF) electromagnetic field between the first electrode and the second electrode for heating the aerosol-forming substrate when the aerosol-generating article is received in the cavity between the first electrode and the second electrode.

11. A shisha device comprising: a liquid cavity configured to contain a volume of liquid, the liquid cavity having a head space outlet; an article cavity for receiving an aerosol-generating article, the article cavity being in fluid communication with the liquid cavity; a first electrode arranged in or around the article cavity; an electrical contact arranged in or around the article cavity for electrical connection to a second electrode, when an aerosol-generating article comprising a second electrode is received in the article cavity; and an oscillation circuit connected to the first electrode and the electrical contact and configured to supply a radio frequency (RF) alternating voltage to the first electrode and the electrical contact.

12. A shisha device comprising: a liquid cavity configured to contain a volume of liquid, the liquid cavity having a head space outlet; an article cavity for receiving an aerosol-generating article, the article cavity being in fluid communication with the liquid cavity; a first electrical contact arranged in or around the article cavity, and arranged for electrical connection to a first electrode received in the article cavity; a second electrical contact arranged in or around the article cavity, and arranged for electrical connection to a second electrode received in the article cavity; and an oscillation circuit connected to the first electrical contact and the second electrical contact, and configured to supply a radio frequency (RF) alternating voltage to the first electrical contact and the second electrical contact.

13. An aerosol-generating article for an electrically heated shisha system, the aerosol-generating article comprising: a first electrode and a second electrode spaced apart from the first electrode to form a substrate cavity; and an aerosol-forming substrate disposed in the substrate cavity.

14. An aerosol-generating article as claimed in claim 13, wherein the first electrode and the second electrode are substantially planar, and the second electrode is arranged substantially parallel to the first electrode.

15. An aerosol-generating article as claimed in claim 13, wherein the first electrode is a tubular electrode and the second electrode is disposed within the first electrode.

16. An aerosol-generating article as claimed in claim 13, wherein one or more slots are formed in at least one of the first electrode and the second electrode.

Description

[0146] Embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0147] FIG. 1 is a schematic illustration of a dielectric heating system;

[0148] 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;

[0149] FIG. 3 is a schematic illustration of an embodiment of a shisha system having a dielectric heating system;

[0150] 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;

[0151] FIG. 5 is a schematic illustration of heating units of different embodiments of a shisha device according to embodiments of the disclosure;

[0152] 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;

[0153] 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;

[0154] 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

[0155] FIG. 9 is a schematic illustration of a heating unit of a shisha device and an aerosol-generating article configured for use with a shisha device according to an embodiment of the disclosure

[0156] FIG. 10 is a schematic illustration of an embodiment of a shisha system having the heating unit of FIG. 9.

[0157] 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 an oscillation circuit 10 including a radio frequency (RF) signal generator 11 and a phase shift network 12. The system further comprises a first electrode 15 connected to a first output of the phase shift network 12, and a second electrode 16 connected to a second output of the phase shift network 12. The second electrode 16 is spaced apart from the first electrode 15 to define an article cavity 14 between the first electrode 15 and the second electrode 16. The article cavity 14 is configured to receive an aerosol-generating article 18. An aerosol-generating article 18, which is to be heated, is placed in the article cavity 14 and subjected to radio frequency electromagnetic radiation between the first electrode 15 and the second electrode 16. Polar molecules within the aerosol-generating 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 aerosol-generating article 18. This kind of heating has the advantage that it is uniform throughout the aerosol-generating article 18 (provided that the polar molecules are uniformly distributed). It also has the advantage of reducing the likelihood of combustion of the substrate in contact with the first electrode and the second electrode compared to a conventional heating element that transfers heat to the substrate via conduction.

[0158] FIG. 2 illustrates a control scheme that may be used in any of the embodiments described in FIGS. 3 to 10. As previously described, the system comprises control circuitry for the oscillation circuit. In the example of FIG. 2, the oscillation circuit 10 comprises a RF signal generator 10 and a phase shift network 12 to split the signal from the RF signal generator 10 into two equal components, 180 degrees out of phase with each other.

[0159] A first output of the oscillation circuit 10 is passed to a first electrode 15. A second output 16 of the oscillation circuit 10 is passed to a second electrode 16. The first electrode 15 and the second electrode 16 are positioned on opposite sides of an article cavity 14, spaced apart such that the first electrode 15 and second electrode 16 are not in electrical contact and such that an aerosol-generating article 18 can be positioned in the space between the first electrode 15 and the second electrode 16. An aerosol-generating article 18 is positioned in the article cavity 14, in the space between the first electrode 15 and the second electrode 16.

[0160] In more detail, the phase shift network 12 comprises a transformer having a primary winding 21, a first secondary winding 22 and a second secondary winding 23. The primary winding 21 is connected at one end to an output of the RF signal generator 11 and at the other end to ground. One end of the first secondary winding 22 is connected to the first electrode 15 and one end of the second secondary winding 23 is connected to the second electrode 16. The other ends of the first secondary winding 22 and the second secondary winding 23 are connected together, and a centre tap between the first secondary winding 22 and the second secondary winding 23 is connected to ground. When power is supplied to the oscillation circuit 10, at any instant the voltages at the first electrode 15 and the second electrode 16 are substantially equal but opposite in polarity (i.e. 180 degrees out of phase with each other).

[0161] The control circuitry comprises a microcontroller 26 that can control both the frequency and the power output of the RF signal generator 11. 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 RF signal 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 RF signal generator 11.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] The embodiments described with reference to FIGS. 3 to 10 use the basic heating and control principles illustrated in FIGS. 1 and 2.

[0166] FIG. 3 is a schematic illustration of a shisha system according to an embodiment of this disclosure.

[0167] 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.

[0168] The shisha device 50 further comprises a heating unit 70 comprising an oscillator circuit 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.

[0169] 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.

[0170] 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.

[0171] 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. In this embodiment, the external housing 71 is formed from a material that is opaque to RF electromagnetic radiation, such as aluminium. However, it will be appreciated that the housing 71 does not need to be formed from a material that is opaque to RF electromagnetic radiation, but rather in some embodiments may be formed from a material that is substantially transparent to RF electromagnetic radiation, such as a ceramic material or a plastic material.

[0172] A closure 75 is moveable over the open end of the external housing 71 of the heating unit 70 to substantially close the open end. In this position, the external housing 71 and the closure 75 define a heating unit cavity. 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. 4a, and a closed position, as shown in FIG. 4b. 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 heating unit cavity, and for removal of the aerosol-generating article 90 from the heating unit cavity. When the closure 75 is in the closed position, the heating unit cavity is surrounded by material that is opaque to a RF electromagnetic field, such that a RF electromagnetic field is unable to propagate from the heating unit cavity.

[0173] A side wall of the external housing 71 comprises an air inlet (shown in FIG. 4b), for enabling ingress of ambient air into the heating unit cavity.

[0174] The heating unit 70 is arranged above the vessel 52 of the shisha device 50 on the airflow conduit 72. The airflow conduit 72 extends into the heating unit cavity and 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.

[0175] An article cavity 14 is defined within the heating unit cavity, for receiving the aerosol-generating article 90. The article cavity 14 is defined by a first electrode 15, a second electrode 16, opposite the first electrode 15, and a side wall 76 extending between the first electrode 15 and the second electrode 16. 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 first electrode 15 and the second electrode 16 are substantially identical planar electrodes with a substantially circular shape. The first electrode 15 is secured to an inner surface of the closure 15, such that the first electrode 15 moves with the closure 75, and the second electrode 16 and side wall 76 are supported in the heating unit cavity by the airflow conduit 72. The second electrode 16 forms a base of the article cavity 14, the side wall 76 forms a side wall of the article cavity 14, and the first electrode 15 forms a top wall of the article cavity 14 when the closure 75 is in the closed position. The side wall 76 is formed from an electrically insulative material, in this embodiment a ceramic material, such as PEEK. Accordingly, the side wall 76 ensures that the first electrode 15 and the second electrode 16 do not come into electrical contact with each other.

[0176] The side wall 76 of the article cavity 14 is gas permeable, having slots formed therein to enable air to flow through the article cavity 14, from one side to the other, as shown in FIG. 4b. Accordingly, the heating unit 70 is configured such that air may be drawn into the heating unit cavity through the air inlet, through the article cavity 14 through the slots in the side wall 76 of the article cavity 14, and from the heating unit cavity into the airflow conduit 72, through the opening 73. The heating unit 70 further comprises an oscillation circuit 10. The oscillation circuit 10 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 oscillation circuit 10. 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.

[0177] The first electrode 15 is electrically connected to the oscillation circuit 10 by a flexible circuit. The second electrode 16 is also electrically connected to the oscillation circuit 10.

[0178] 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 wrapper 94, formed from a gas permeable, electrically insulating material, such as tipping paper. The aerosol-generating article 90 has a substantially cylindrical shape, similar to a hockey puck, which is complimentary to the shape of the article cavity 14 of the shisha device 50.

[0179] As shown in FIG. 4b, when the aerosol-generating article 90 is received in the article cavity 14 of the heating unit 70, a circular base of the aerosol-generating article 90 contacts the second electrode 16 of the article cavity 14, and the sides of the aerosol-generating article 90 contact the side wall 76 of the article cavity 14. When the closure 75 is arranged in the closed position, the circular top of the aerosol-generating article 90 contacts the first electrode 15 of the article cavity 14. In this arrangement, the first electrode 15, second electrode 16 and aerosol-generating article 90 form a capacitor, with the aerosol-forming substrate 90 defining the dielectric material between the first electrode 15 and the second electrode 16.

[0180] When a user draws on the mouthpiece 64 of the shisha device 50, air is drawn into the shisha device 50 through the air inlet of the external housing 71. An airflow path through the aerosol-generating article 90 and heating unit 70 is shown by the arrows in FIG. 4b. Air is drawn into the heating unit cavity through the air inlet of the external housing 71, and from the heating unit cavity into the aerosol-generating article 90 through the side wall 76 of the article cavity 14. Air is drawn through the aerosol-forming substrate 92 and back into the heating unit cavity through an opposite portion of the side wall 76 of the article cavity 14, and from the heating unit cavity into the airflow conduit 72 through the opening 73 in the external housing 71 of the heating unit 70.

[0181] In use, power is supplied to the oscillation circuit 10 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 oscillation circuit 10, the oscillation circuit generates two substantially equal, out of phase RF electromagnetic signals with a frequency of between 1 Hz and 300 MHz. One of the signals is supplied to the first electrode 15, and the other signal is supplied to the second electrode 16.

[0182] The RF electromagnetic signals supplied to the first electrode 15 and the second electrode 16 establish an alternating RF electromagnetic field in the article cavity 14, which 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.

[0183] 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 airflow through the aerosol-generating article 90 and are drawn out of the aerosol-generating article 90, through the heating unit 70 and into the airflow conduit 72 through the opening 73. From the airflow conduit 72, the volatile compounds are drawn through the shisha device 50 to and out of the mouthpiece 66 as described above.

[0184] FIG. 5 shows a heating unit 70 and aerosol-generating article 90 for a shisha device according to other embodiments of this disclosure. The heating unit 70 shown in FIG. 5 is substantially similar to the heating unit 70 shown in FIG. 4, and like reference numerals are used to represent like features. FIG. 5a 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. 5b shows the aerosol-generating article 90 received in the article cavity 14 of the heating unit 70.

[0185] The heating unit 70 shown in FIG. 5 differs from the heating unit 70 shown in FIG. 4 in that the heating unit 70 shown in FIG. 5 does not comprise the first electrode 15 and the second electrode 16. Instead, in this embodiment the aerosol-generating article 90 comprises the first electrode 15 and the second electrode 16, and the heating unit 70 comprises a first electrical contact 82 and a second electrical contact 84.

[0186] The first electrical contact 82 is secured to an inner surface of the closure 75, in a similar position to the first electrical contact 15 of the embodiment of FIG. 4. The second electrical contact 84 is secured to a base 78 supported in the external housing 71 in a position similar to the second electrode 16 of the embodiment of FIG. 4. In this embodiments, the article cavity is merely defined by the base 78, and does not comprise a side wall. The first electrical contact 82 and the second electrical contact 84 are substantially identical, and comprise circular sheets of metal with a diameter that is significantly smaller than the diameter of the aerosol-generating article 90. The first electrical contact and the second electrical contact are electrically connected to the oscillation circuit 10.

[0187] In this embodiment, the aerosol-generating article 90 has a substantially similar cylindrical form to the aerosol-generating article 90 of the embodiment of FIG. 4. However, in this embodiment, the aerosol-forming substrate 92 is not wrapped in a wrapper, but rather is contained within a container. Circular bottom and top walls of the container are formed from an electrically conductive material, typically metal. The circular top wall forms the first electrode 15, and the circular bottom wall forms the second electrode 16. A side wall 98 extends between the periphery of the bottom wall and the periphery of the top wall, and is formed from an electrically insulative material, such as a plastics material, which ensures that the bottom and top walls do not come into electrical contact. A plurality of slots are provided in the side wall 98, to enable air to flow into and out of the aerosol-generating article 90.

[0188] As shown in FIG. 5b, when the aerosol-generating article 90 is received in the article cavity 14, and the closure 75 is rotated into the closed position, the first electrical contact 82 contacts the first electrode 15 and electrically connects the first electrode 15 to the oscillation circuit 10, and the second electrical contact 82 contacts the second electrode 15 and electrically connects the second electrode 15 to the oscillation circuit 10.

[0189] Also as shown in FIG. 4b, in use ambient air is drawn into the heating unit 70 through an air inlet, and into the aerosol-generating article 90 through the slots in the side wall 98. Air is drawn out of the aerosol-generating article 90 through the slots in the side wall 98 and into the airflow conduit 72, where the air passes into the vessel of the shisha device.

[0190] 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.

[0191] The heating unit 70 shown in FIG. 6 differs from the heating unit 70 shown in FIG. 4 in that the first electrode 15 comprises an elongate, cylindrical electrode, and the second electrode 16 comprises an elongate, tubular electrode that circumscribes the first electrode 15.

[0192] The article cavity 14 is defined between the first electrode 15, the second electrode 16, and a base 78, forming an elongate annular cavity that is open at one end and substantially closed at the opposite end. The base 78 is formed from an electrically insulating material, such as PEEK, and comprises a plurality of slots to enable air to flow out of the article cavity 14. The base 78 is supported above a flared end of the airflow conduit 72, such that air flowing out of the article cavity 14 flows into the airflow conduit 72, as shown in FIG. 5b. In some embodiments, the flared end of the airflow conduit 72 is an integral part of the airflow conduit 72, however, in this embodiment, the flared end of the airflow conduit 72 is an integral part of the heating unit 70, and is removable from the airflow conduit with the heating unit 70.

[0193] The heating unit 70 shown in FIG. 6 also differs from the heating unit 70 shown in FIG. 4 in that the external housing 71 does not comprises a closure, but rather the article cavity 14 comprises a closure 80, which is hingedly mounted to the second electrode 16. The closure 80 is movable between an open position, as shown in FIG. 6a, to enable the aerosol-generating article to be inserted in the article cavity 14, and a closed position, as shown in FIG. 6b, for closing the open end of the article cavity 14. The closure 80 is similar to the base 78, in that it is formed from an electrically insulative material, such as PEEK, and comprises a plurality of slots to enable air to enter the article cavity 14 when the closure 80 is in the closed position. The closure 80 further comprises an electrical contact 82, centrally positioned on the closure, for contact with the first electrode 15 when the closure 80 is in the closed position, electrically connecting the first electrode 15 to the oscillation circuit 10. The electrical contact 82 is electrically connected to the oscillation circuit via a flexible circuit. The outer surface of the second electrode 16 is also electrically connected to the oscillation circuit 10.

[0194] In this embodiment, the aerosol-generating article 90 has an elongate, tubular shape that is complementary to the shape of the article cavity 14. In particular, the aerosol-forming substrate 92 comprises an inner passage 97 that is complementary in size and shape to the first electrode 15. When the aerosol-generating article 90 is received in the article cavity 14, the inner surface of the inner passage 97 of the aerosol-generating article 90 contacts the outer surface of the first electrode 15, and the outer surface of the aerosol-generating article 90 contacts the inner surface of the second electrode 16.

[0195] FIG. 7 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. 7 are substantially similar to the heating unit 70 and aerosol-generating article 90 shown in FIG. 6, 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.

[0196] The heating unit 70 shown in FIG. 7 differs from the heating unit 70 shown in FIG. 6 in that the heating unit 70 of FIG. 7 does not comprise the second electrode 16, but rather comprises a tubular side wall 76, formed from an electrically insulating material, such as PEEK, with an electrical contact 84 arranged at an inner surface of the side wall 76. The electrical contact 84 is a substantially point contact, electrically connected to the oscillation circuit 10.

[0197] The heating unit 70 shown in FIG. 7 differs from the heating unit 70 shown in FIG. 6 in that the heating unit 70 of FIG. 7 does not comprise a closure.

[0198] The aerosol-generating article 90 shown in FIG. 7 differs from the aerosol-generating article 90 shown in FIG. 6 in that the aerosol-generating article 90 of FIG. 7 comprises the second electrode 16, in the form of an electrically conductive wrapper circumscribing the cylindrical outer surface of the aerosol-forming substrate 92. In addition, the aerosol-generating article 90 of FIG. 7 does not comprise an inner passage. As such, the first electrode 15 is configured to penetrate the aerosol-forming substrate 92 when the aerosol-generating article 90 is received in the article cavity 14.

[0199] When the aerosol-generating article 90 is received in the article cavity 14, the second electrode 16 contacts the electrical contact 84 on the inner surface of the cylindrical side wall 76, and electrically connects the second electrode 16 to the oscillation circuit 10.

[0200] FIG. 8 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. 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. 8a 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. 8b shows the aerosol-generating article 90 received in the article cavity 14 of the heating unit 70.

[0201] The heating unit 70 shown in FIG. 8 differs from the heating unit 70 shown in FIG. 7 in that the heating unit 70 of FIG. 8 does not comprise the first electrode 15 or the second electrode 16, but rather comprises a first electrical contact 82 and a second electrical contact 84. The first electrical contact 82 is arranged centrally at the base 78, and is substantially similar to the electrical contact 82 on the closure 80 of the embodiment of FIG. 6. The second electrical contact 84 is a ring contact circumscribing the inner surface of the side wall 76.

[0202] The aerosol-generating article 90 shown in FIG. 8 differs from the aerosol-generating article 90 shown in FIG. 7 in that the aerosol-generating article 90 of FIG. 7 comprises the first electrode 15 and the second electrode 16. The first electrode 15 comprises an elongate, cylindrical electrode, extending centrally through the aerosol-forming substrate 92. The second electrode 16 comprises an electrically conductive wrapper circumscribing the cylindrical outer surface of the aerosol-forming substrate 92.

[0203] When the aerosol-generating article 90 is received in the article cavity 14, an end of the first electrode 15 of the aerosol-generating article 90 contacts the first electrical contact 82 at the base 78 of the article cavity 14, electrically connecting the first electrode 15 to the oscillation circuit 10, and the second electrode 16 of the aerosol-generating article contacts the second electrical contact 84 on the inner surface of the cylindrical side wall 76, electrically connecting the second electrode 16 to the oscillation circuit 10.

[0204] FIGS. 9 and 10 show 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.

[0205] 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.

[0206] 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.

[0207] The heating unit 70 is removably attachable to the vessel 52 by a screw thread (not shown), and is shown separate from the vessel 52 in FIG. 9. The heating unit 70 is substantially similar to the heating unit shown in FIG. 6, and like reference numerals will be used to describe like features.

[0208] 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 one end, and open at the other end.

[0209] An article cavity 14 is defined within the external housing 71, between a tubular first electrode 15 and a cylindrical second electrode 16. The tubular first electrode 15 comprises a sheet electrode bent into a cylindrical form, which defines a cylindrical inner passage. The cylindrical second electrode 16 extends within the inner passage of the first electrode 15, and is aligned coaxially with the first electrode 15, such that the article cavity 14 is substantially annular. The diameter of the inner passage of the first electrode 15 is substantially the same as the diameter of the aerosol-generating article 90, such that the inner surface of the first electrode 15 contacts the outer surface of the aerosol-generating article 90 when the aerosol-generating article 90 is received in the article cavity 14. The second electrode 16 is configured to penetrate the aerosol-generating article 90 when the aerosol-generating article 90 is received in the article cavity 14. By penetrating the aerosol-generating article 90, the second electrode 16 contacts the aerosol-forming substrate 92 of the aerosol-generating article 90 when the aerosol-generating article 90 is received in the article cavity 14.

[0210] The article cavity 14 is open at the same end as the open end of the external housing 71, to enable the aerosol-generating article 90 to be inserted into the article cavity 14, and removed from the article cavity 14, at this end. The opposite end of the article cavity 14 is substantially closed to correctly locate the aerosol-generating article 90 in the article cavity 14.

[0211] An air inlet 85 is provided in the external housing 71, and an airflow passage extends between the air inlet 85 and the substantially closed end of the article cavity 14. The substantially closed end of the article cavity 14 comprises a plurality of slots that enable air to be drawn into the article cavity 14 from the airflow passage 86.

[0212] An oscillation circuit 10 is provided in the heating unit 70, beneath the article cavity 14 and airflow passage 86. The first electrode 15 and the second electrode 16 are electrically connected to the oscillation circuit 10, such that the oscillation circuit may provide an oscillating voltage to each of the first electrode 15 and the second electrode 16. An outer surface of the first electrode 15 is electrically connected to the oscillation circuit 10. A proximal end of the second electrode 16, extending beyond the substantially closed end of the article cavity 14, and through the airflow passage 86, is electrically connected to the oscillation circuit 10.

[0213] The oscillation circuit 10 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 oscillation circuit 10 to control the RF alternating voltage generated by the oscillation circuit 10.

[0214] As shown in FIG. 10, an airflow conduit 72 extends from the vessel 52 into the article cavity 14 and fluidly connects the article cavity 14 to the liquid section 56 of the vessel 52. The airflow conduit 72 extends to a position in the liquid section 56 below the liquid fill level 60. 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. The end of the airflow conduit 72 extending into the heating unit 70 flares outwardly to contact the periphery of the open end of the article cavity 14. The flared end of the airflow conduit 72 may be formed from an elastomeric material, such as silicon, such that the flared end of the airflow conduit 72 forms an airtight seal with the periphery of the open end of the article cavity 14.

[0215] In use, when a user draws on the mouthpiece 64, ambient air is drawn into the shisha device 50 through the air inlet 85 and the airflow passage 86 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 oscillation circuit 10, causing a first RF alternating voltage to be supplied to first electrode 15 and a second RF alternating voltage, 180 degrees out of phase with the first RF alternating voltage, to be supplied to the second electrode 16, heating heat the aerosol-forming substrate in the aerosol-generating article 90 in the article cavity 14. 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 into the airflow conduit 72, through the one-way valve, and 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.

[0216] 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 10. 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.