WO2023144381A1

WO2023144381A1 - Heating apparatus for an aerosol generating device

Info

Publication number: WO2023144381A1
Application number: PCT/EP2023/052174
Authority: WO
Inventors: Kevin Schumacher; Sandro FEUERSTEIN; Eduardo Jose GARCIA GARCIA
Original assignee: Jt International Sa
Priority date: 2022-01-31
Filing date: 2023-01-30
Publication date: 2023-08-03

Abstract

A heating apparatus (100) for an aerosol generating device is disclosed and comprises a vacuum insulator (102) having a main longitudinal axis and comprising an inner wall (104) and an outer wall (106) between which a vacuum (108) is enclosed; a cavity (110) in which an aerosol forming substance can be received, positioned radially inwardly of the inner wall; a heater (112) provided inside the vacuum insulator in thermal contact with the inner wall of the vacuum insulator, configured to heat an aerosol forming substance received in the cavity by thermal conduction to generate an aerosol; and one or more wires (132) configured to connect the heater to a power source, wherein the one or more wires extend through at least one hole in the outer wall of the vacuum insulator, and wherein the one or more wires are circumferentially surrounded by an insulator (130). The insulator comprises glass and the one or more wires are made from a material that has thermal expansion characteristics that substantially match the thermal expansion characteristics of the insulator.

Description

HEATING APPARATUS FOR AN AEROSOL GENERATING DEVICE

FIELD OF INVENTION

The invention relates to heating apparatuses for aerosol generating devices. Specifically, the invention relates to a heating apparatus with a vacuum insulator.

BACKGROUND TO THE INVENTION

One type of heating apparatus for aerosol generating devices uses a vacuum insulator and a heater provided in thermal contact with an inner wall of the vacuum insulator. The vacuum insulator typically comprises a central cavity, positioned adjacent the inner wall, in which an aerosol generating substance can be received. The heater can heat the aerosol generating substance in the cavity in order to generate an aerosol that can be inhaled. The vacuum insulator can thermally insulate outer surfaces of the aerosol generating device from the heater so that it can be held comfortably by a user.

One problem to overcome when producing this type of heating apparatus is how to provide electrical power from a power source outside the vacuum insulator to a heater while maintaining an effective vacuum. It is an object of the invention to address this problem.

SUMMARY OF INVENTION

According to an aspect of the invention, there is provided a heating apparatus for an aerosol generating device, comprising: a vacuum insulator having a main longitudinal axis and comprising an inner wall and an outer wall between which a vacuum is enclosed; a cavity in which an aerosol forming substance can be received, positioned radially inwardly of the inner wall; a heater provided inside the vacuum insulator in thermal contact with the inner wall of the vacuum insulator, configured to heat an aerosol forming substance received in the cavity by thermal conduction to generate an aerosol; and one or more wires configured to connect the heater to a power source, wherein the one or more wires extend through at least one hole in the outer wall of the vacuum insulator, and wherein the one or more wires are circumferentially surrounded by an insulator; wherein the insulator comprises glass and the one or more wires are made from a material that has thermal expansion characteristics that substantially match the thermal expansion characteristics of the insulator.

In this way, an effective vacuum can be maintained while allowing electrical connection between the heater and a power source. This can be achieved by threading the one or more wires through the one or more holes in the outer wall and providing the insulator between the wires and the vacuum insulator. The present invention provides a way in which the wires can be positioned through holes in the outer wall without compromising the vacuum.

Preferably, the insulator is a thermal insulator and an electrical insulator. Thermal insulation is advantageous because it prevents heat conducting along the wires and thereby heating up the walls of the vacuum insulator. Electrical insulation is advantageous because it allows the vacuum insulator to be made of a material that conducts electricity, such as a metal, without causing a short circuit between the two terminals of the power source.

The heater is preferably a track heater that is printed or coated on the vacuum insulator. The heater is preferably provided on an outer surface of the inner wall.

The outer wall may have a circumferential portion and a bottom portion. A surface normal vector on the outer wall may extend radially on the circumferential portion and axially on the bottom portion. The at least one hole may extend through the circumferential portion or through the bottom portion. In some embodiments, a first hole may extend through the circumferential portion and a second hole may extend through the bottom portion.

Preferably, the heating apparatus comprises a first wire that extends through a first hole in the outer wall and a second wire that extends through a second hole in the outer wall. In this way, separate respective holes can be provided for the first and second wires. It has been found that this can provide effective electrical isolation between the wires. This can also allow the wires to be spaced apart from one another for connection to different points of the heater.

Alternatively, the outer wall may comprise a hole through which both of the first wire and the second wire are positioned. In this case, the first wire and the second wire may be embedded in a shared sheet or piece of the insulator that circumferentially surrounds each wire. In this case, the first wire and the second wire can be spaced apart to avoid a short circuit between the terminals of a power source.

The insulator comprises glass. In one example, the insulator comprises borosilicate glass. In other embodiments, the insulator could comprise other suitable insulating glass materials.

The one or more wires are made from a material that has thermal expansion characteristics that substantially match the thermal expansion characteristics of the insulator. This can provide a tight and stable sealing of the vacuum chamber because the integrity of the mechanical joint is preserved over a wide temperature range. Each wire can be joined with the glass insulator in an oven to provide a very strong connection that is maintained even when the wire is heated by conduction due to its connection to the heater.

Preferably, the one or more wires comprise Kovar, which is a group of ferrous alloys. In one example a nickel-cobalt ferrous alloy can be used. These materials provide substantially the same thermal expansion properties as glass over a wide range of temperatures that extend from room temperature to at least the normal temperature of operation of the heater.

Preferably, the insulator comprises borosilicate glass and the one or more wires comprise Kovar. This combination provides a particularly effective seal for the vacuum across the operating temperatures of the heating apparatus.

Preferably, the heating apparatus comprises a sensor positioned within the vacuum insulator and a sensor wire that is connected to the sensor and extends through a further hole in the vacuum insulator, wherein the sensor wire is circumferentially surrounded by an insulator. This can allow sensors to be provided in the vacuum chamber, principally to monitor the operation and function of the heater, without compromising the integrity of the vacuum. This is preferably achieved using a Kovar sensor wire that is wrapped with a glass insulator. Any kind of sensor may be used such as a temperature sensor or a pressure sensor. In some embodiments, a plurality of sensors may be provided.

Preferably, the further hole extends through the outer wall of the vacuum insulator. The further hole may be provided on a circumferential portion or on a bottom portion of the outer wall.

Alternatively, the further hole extends between the inner wall and the outer wall of the vacuum insulator.

In some embodiments, the sensor wire may be provided at a different region of the vacuum insulator, or on a different face of the outer wall, compared to the one or more wires for the heater.

Preferably, the heater is a resistive heater. The heater may comprise an electrically resistive track that is printed or coated onto the inner wall. The resistive track could be provided on particular sections of the inner wall, or the resistive track could be coated or printed onto the inner wall to cover a substantially full amount of the inner wall. The resistive track may follow a serpentine or sinuous path on the inner wall from a first end to a second end of the track. In other examples, the heater could comprise one or more resistive heating plates or elements provided on the inner wall. The heating plates or elements could also be provided as a sinuous or serpentine resistive track.

Preferably, the heater comprises an exposed external surface having a material susceptible to an oxidation reaction in the presence of oxygen. Many heaters comprise materials that oxidise in the presence of oxygen, which can adversely affect the performance of the heater unless an anti-oxidation coating is provided. Allowing the heater to have an exposed external surface without an antioxidation coating in this way takes advantage of the heater being provided within the vacuum to make the heater less costly, have a lower mass, and/or easier to produce.

Preferably, the inner wall has a thickness of about 0.1 mm or less. In this way, the inner wall has a thickness corresponding to a threshold of significantly improved thermal efficiency of the vacuum insulator. The outer wall may have a thickness of about 0.25 mm.

Preferably, the one or more wires each extend through a different respective hole in the outer wall and each hole contains a corresponding insulator surrounding a corresponding wire. More preferably, each respective hole is sized mainly to accommodate the corresponding wire to minimise the amount of insulator in contact with the outer wall. In this way, each hole can be sized to minimise the circumference or perimeter of the outer wall in contact with the insulator, which better retains the vacuum within the vacuum insulator. The skilled person would appreciate that “sized mainly to accommodate a single wire” means each hole is made a small as possible to retain a single insulated wire while still enabling practical assembly of the insulator around each wire. Thus, in some examples, each hole may have a diameter that is about 1.5, 2, or 3 times the diameter of its corresponding wire. The insulator in each hole may surround the corresponding wire with a thickness roughly equal to the thickness of the corresponding wire, i.e., having a thickness of about 0.5 to 2 times that of the wire.

According to a further aspect of the invention, there is provided an aerosol generating device configured to generate an aerosol for inhalation by a user, comprising the heating apparatus as described above.

BREIF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are now described, by way of example, with reference to the drawings, in which:

Figure 1 shows a schematic perspective view of a heating apparatus according to an embodiment of the invention; Figure 2 shows a cross-sectional schematic view of a portion of a heating apparatus according to an embodiment of the invention;

Figure 3A shows a perspective view of a portion of a heating apparatus according to an embodiment of the invention;

Figure 3B shows a perspective view of a portion of a heating apparatus according to an embodiment of the invention; and

Figure 3C shows a perspective view of a portion of a heating apparatus according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 shows a schematic perspective view of a heating apparatus for an aerosol generating device according to an embodiment of the invention. Figure 2 shows a cross-sectional schematic view of a portion of the heating apparatus shown in Figure 1.

With reference to Figures 1 and 2, a heating apparatus 100 is provided and comprises a vacuum insulator 102 comprising an inner wall 104 and an outer wall 106, spaced radially apart from one another so that a vacuum 108 is enclosed between them. The heating apparatus 100 comprises a cavity 110 that is provided adjacent the inner wall 104 and is configured to receive a consumable comprising a tobacco rod and a filter held together by a tipping wrapper. The consumable can be inserted into the cavity 110 by a user via an opening 111 to the cavity 110 to be held in place by friction with the inner wall 104.

A heater 112 is provided within the vacuum 108 and on an outer surface of the inner wall 104. The heater 112 is configured to be heated when an electrical current passes through it and to pass this heat on to the inner wall 104 by conduction. Heat is then transferred through the inner wall 104 by conduction so that the inner surface of the inner wall 104 heats the consumable and the air inside the cavity 110. The heater 112 can be powered by a battery or any other power source provided on an aerosol generating device.

The outer wall 106 comprises a circumferential portion 106a having a surface normal vector extending radially into the cavity 110 and a bottom portion 106b having a surface normal vector parallel to a main longitudinal axis of the vacuum insulator 102. A first heater wire 114 and a second heater wire 116 are each inserted through respective holes in the bottom portion 106b and are configured to electrically connect the heater 112 to a power source and control electronics provided on an aerosol generating device. A first connection lead 118 is provided to electrically connect a first end 120 of the heater 112 to the first heater wire 114. A second connection lead 122 is provided to electrically connect the second heater wire 116 to a second end 124 of the heater 112. The first and second connection leads 118, 122 may be welded to the heater 112 or to the inner wall 104.

A temperature sensor (not shown) is provided within the vacuum insulator 102. A first sensor wire 126 and a second sensor wire 128 are also provided through respective holes in the bottom portion 106b. The first sensor wire 126 and the second sensor wire 128 are configured to electrically connect the temperature sensor to a power source and control electronics provided on an aerosol generating device. The first sensor wire 126 and the second sensor wire 128 may also be attached to additional respective connections leads (not shown) configured to electrically connect each sensor wire to the temperature sensor.

The first and second heater wires 114, 116 and the first and second sensor wires 126, 128 may be referred to collectively as the “wires” 132. As shown in Figures 1 and 2, each of the wires 132 are provided through a respective hole in the bottom portion 106b. Each of the wires 132 are joined to the bottom portion 106b by one of a plurality of airtight seals 130 that prevents the intrusion of air into the interior of the vacuum insulator 102. Each of the seals 130 comprises an insulator that circumferentially surrounds one of the wires 132. The vacuum insulator 102 is hollow and encloses a vacuum 108 between its curved inner wall 104 and its curved outer wall 106. The vacuum insulator 102 has a substantially cylindrical shape that enables the vacuum insulator 102 to surround the consumable fully. The vacuum insulator 102 provides thermal insulation so that the heater 112 can heat an aerosol generating substrate effectively while not heating other portions of the aerosol generating device, especially portions of the aerosol generating device that are held by a user. The vacuum insulator 102 is elongate along its main longitudinal axis, as shown in Figure 1 . This enables it to receive a consumable in the form of an elongate rod comprising tobacco. The vacuum insulator 102 has an approximately elliptical or circular cross-sectional shape when viewed along one of its ends, parallel to its longitudinal axis. However, in other embodiments the vacuum insulator 102 may have other types of cross sectional shape, for example shapes that are approximately square or polygonal.

The vacuum insulator 102 comprises an opening 111 for receiving the consumable at one longitudinal end and is closed at the opposite end. Thus, when viewed perpendicularly to its longitudinal axis as shown in Figures 1 and 2, the vacuum insulator 102 has a cross-section that is cup-shaped. In other embodiments, the vacuum insulator 102 may be open at both longitudinal ends such that it has a tube-shaped cross-section when viewed perpendicularly to its longitudinal axis. In such cases, the outer wall 106 may comprise only or mainly a circumferential portion 106a and each of the wires 132 may be provided through a respective hole in the circumferential portion 106a while being surrounded by a respective seal 130. In the embodiment of Figures 1 and 2, the inner wall 104 and the outer wall 106 are joined or welded together at the same end of the vacuum insulator 102 at which the opening 111 can be found. The bottom portion 106b and the circumferential portion 106a are also joined or welded at a join 134 shown in Figure 2.

The opening 111 and the inner wall 104 have a cross-section that is the same across the full longitudinal extent of the inner wall 104. In other embodiments, the opening 111 may be flared outwardly to enable a user to insert the consumable into the cavity 110 more easily.

The outer wall 106 comprises stainless steel. In other embodiments, the outer wall 106 could comprise other suitable materials, such as other metals, alloys, or plastics. The circumferential portion 106a of the outer wall 106 comprises a single curved face that is substantially or wholly cylindrical. The outer wall 106 could have other shapes in accordance with alternatively shaped vacuum insulators.

The inner wall 104 may have a thickness of about 0.1 millimetres (mm) or less. Having a relatively low thickness reduces the thermal mass of the vacuum insulator 102, and increases the rate of heat conduction through the inner wall 104 to the cavity 110 and the consumable. In particular, less heat is conducted away from the cavity 110 by the outer face of the inner wall 104. The threshold of 0.1 mm or less has been found to be significant in terms of improving the energy efficiency of the heating apparatus 100 by these mechanisms. In particular, an inner wall thickness of 0.1 mm has been found to have significantly improved thermal efficiency compared to an inner wall thickness of 0.25 mm.

The outer wall 106 may have a thickness of about 0.25 mm, which may be preferable to a thickness of 0.1 mm to give the vacuum insulator 102 increased mechanical sturdiness and thermal insulation properties.

The cavity 110 is substantially cylindrical and is positioned immediately adjacent the inner wall 104. Preferably, the side of the inner wall 104 facing the cavity 110, i.e. , the “inner surface” of the inner wall 104, is substantially or completely free of additional components so that the consumable can be in direct contact with the inner face when it is received in the cavity 110. This can maximise the efficiency of heat transfer from the inner wall 104 to the consumable. Further, the lack of additional components keeps the thermal mass of the heating apparatus low, which can improve the amount of time required to heat the tobacco to aerosol generating temperatures. In the embodiment of Figures 1 and 2, the heater 112 is a resistance heater configured to generate heat when applied with an electric current. The heater 112 comprises a winding resistive heating track that extends from a first end 120 of the heater 112 to a second end 124. The track follows a sinuous path along the length of the inner wall 104, as shown in Figure 1 . The first end 120 and the second end 124 of the heater 112 are connected to the first and second connection leads 118, 122, respectively. The first heater wire 114 is configured to be in electrical connection with a first terminal of a battery on an aerosol generating device, and the second heater wire 116 is configured to be in connection with the opposite terminal of the battery. Thus, during operation of the heating apparatus 100, the battery can be used to provide an electric current through the heating track. The electrical resistance of the heater 112 then causes the heater 112 to generate heat in response to the current flowing through the heater 112 via the first heater wire 114 and the second heater wire 116.

The heater 112 is printed or coated onto the outer face of the inner wall 104. In other embodiments, the heater 112 can comprise a heating element or plate provided on and attached to the inner wall 104. Thus, the heater 112 may provide “trace heating” to the cavity 110. The heater 112 may have a sinuous shape on the surface of the inner wall 104 so that a substantially full length of the inner wall 104 receives heating, as shown in Figure 1. In other embodiments, the heater 112 may cover a substantially full circumference and/or area of the inner wall 104.

The heater 112 may comprise a material susceptible to an oxidation reaction in the presence of oxygen, and also may be provided without an anti-oxidation coating. Exposing the heater 112 to the vacuum 108 in this way takes advantage of the lack of oxygen in the vacuum insulator 102 to make the heater 112 cheaper and/or easier to manufacture.

In this embodiment, each of the wires 132 comprise Kovar, which is a group of ferrous alloys configured to exhibit particular thermal expansion properties to match the properties of glass, such as borosilicate glass. In one example, Kovar may have thermal expansion properties of about 5 x 10'⁶ /K between 30 and 200 °C, and about 10 x 10’⁶ /K at 800 °C. Borosilicate glass may have a thermal expansion coefficient of 3 x 1O^-6 /K at 20 °C. Borosilicate glass is particularly preferred because Kovar can be configured to have thermal expansion properties matching borosilicate glass. This allows the borosilicate glass to form a tight seal around Kovar wires across a large temperature range.

Each of the seals 130 comprise insulators that circumferentially surround one of the respective wires 132. Each seal 130 is embedded in a respective hole in the bottom portion 106b and each of the wires 132 are positioned through a respective hole. In this embodiment, the seals 130 comprise glass, which enables the Kovar wires 132 and the seals 130 to form an airtight joint over a wide range of temperatures. Having substantially matching thermal expansion properties is important because heat from the heater 112, which typically operates at temperatures over 100°C, can reach the bottom portion 106b by conduction through the inner wall 104 and the circumferential portion 106a. Thus, this particular selection of materials for the wires 132 and the seals 130 provides a particularly effective mechanical joint over a wide range of operating temperatures, thereby helping to preserve the integrity of the vacuum. Additionally, the glass electrically insulates the bottom portion 106b from the wires 132, thereby avoiding the need for a separate insulation layer to prevent electrical conduction from the wires 132 to the outer wall 106.

During manufacturing of the heating apparatus 100, the seals 130 may be preformed into an annular shape inside holes in the bottom portion 106b before the insertion of the wires 132 through the seals 130. Subsequently, the seals 130 and the wires 132 may be joined or welded together using an oven to create a strong permanent join after cooling. This may provide a convenient method of manufacturing the heating apparatus 100.

In other embodiments, the wires 132 and the seals 130 may comprise other conducting and insulating materials, respectively. In particular, the wires 132 and the seals 130 may comprise materials selected to have substantially matching thermal expansion properties over typical operating temperatures of the heating apparatus 100.

In the embodiment of Figures 1 and 2, the wires 132 are provided through holes in the bottom portion 106b of the outer wall 106. However, in other embodiments, the wires 132 and seals 130 may be provided elsewhere on the outer wall 106, for example through holes on the circumferential portion 106a or at different positions on the bottom portion 106b.

The temperature sensor (not shown) may be provided within the vacuum insulator 102 on the inner face of the outer wall 106 or the outer face of the inner wall 104. The temperature sensor can be configured to detect the temperature of the heater 112 or of the cavity 110 and transmit the detected temperature to a controller provided on an aerosol generating device incorporating the heating apparatus 100. The temperature sensor may transmit the detected temperatures via one or more additional connection leads (not shown) attached to one or both of the first sensor wire 126 or the second sensor wire 128. In one example, the temperature sensor may comprise a thermistor. In other embodiments, the temperature sensor could be provided alongside, or be replaced with, other types of sensors, such as a pressure sensor.

As described above, the heating apparatus 100 can be used with or provided in an aerosol generating device. The aerosol generating device would typically comprise a battery or other power source for powering the heater 112, a button or other input mechanism to enable a user to initiate the heater 112, and a controller to control the electronic components of the device, such as the heater 112. The heating apparatus 100 may be provided within a housing of the aerosol generating device, wherein the housing comprises an opening aligned with the opening 111 of the heating apparatus 100. The aerosol generating device may be configured as an electronic smoking device.

The heating apparatus 100 is configured to be used with a consumable comprising tobacco and a filter, which may be held together by a tipping wrapper. The consumable may be a cylindrical rod; however, other shapes of consumable designed to be received within the cavity 110 could also be used. Other forms of aerosol forming substance may be used alternatively or addition to tobacco.

Now, an example use of the heating apparatus 100, as used within an aerosol generating device, will now be described with reference to Figures 1 and 2.

In use, a user can insert the consumable through the opening 111 into the cavity 110. When the user is ready to initiate vaporisation, the user may press a button provided on the aerosol generating device, after which the controller may allow a current to flow from the battery to the heater 112 via the first heater wire 114 and the second heater wire 116. The heater 112 generates heat, due to its electrical resistance, that is transmitted to the inner wall 104 by conduction and radiation.

While the heater 112 is operating, the vacuum 108 within the vacuum insulator 102 inhibits the escape of heat from the cavity 110. In this way, the cavity 110, the heater 112, and the vacuum insulator 102 form a highly efficient heating oven in which the tobacco within the consumable can be heated to a desired aerosol generating temperature. The controller may be configured to instruct the heater 112 to heat the tobacco to temperatures below the combustion temperature of tobacco. It may take several seconds for the cavity 110 to reach aerosol generating temperatures.

As the tobacco is heated, an aerosol is produced inside the cavity 110. The user can then inhale the aerosol by drawing air from the cavity 110 via the filter. This may draw air into the cavity 110 through a periphery of the opening 111 so that the user can continuously inhale aerosol from the cavity 110.

At the same time, while the heater 112 is operating, heat reaches the seals 130 and the wires 132 by radiation and by conduction through the walls of the vacuum insulator 102. The wires 132 and the seals 130 comprise Kovar and glass, respectively, which enables the wires 132 and the seals 130 to expand thermally at substantially the same rate as their temperature increases. This provides a secure and airtight mechanical joint even while the heater 112 is turned on and the heating apparatus 100 reaches peak operating temperatures.

In the embodiment of Figures 1 and 2, the heat from the heater 112 that is transmitted to the wires 132 and seals 130 by conduction through the vacuum insulator 102 has to travel upwards towards the join between the inner and outer walls 104, 106 at the opening 111. Subsequently, the heat then has to travel down the circumferential portion 106a before reaching the bottom portion 106b and heating up the wires 132 and seals 130. Thus, for this embodiment, the bottom portion 106b substantially corresponds to a maximum “conduction path length” for heat from the heater 112 travelling via the vacuum insulator 102. While heat is travelling by conduction, some heat is re-transmitted by radiation to the internal wall 104 or is lost from the vacuum insulator 102. Accordingly, less heat reaches regions further, in terms of a minimum conduction path length, from the heater 112. These further regions generally correspond to the coldest region of the vacuum insulator 102 during use. The coldest region will in general depend on the particular shape of the vacuum insulator and the location of the heater.

Thus, positioning the wires 132 and the seals 130 at the bottom portion 106b can increase the efficiency of the heating apparatus 100 by minimising the amount of heat that is lost from the cavity 110 by conduction through the walls of the vacuum insulator 102.

Figures 3A to 3C show perspective views of a portion of a heating apparatus according to various embodiments of the invention. Figure 3A shows a perspective view of the bottom portion 106b of the vacuum insulator 102 of Figures 1 and 2.

Figure 3B shows an alternative bottom portion 206b that may be used within the heating apparatus 100 as described above alternatively to the bottom portion 106b. The bottom portion 206b comprises a plurality of wires 232, including two heater wires and two or more sensor wires. Each of the wires 232 are provided through a respective hole in the bottom potion 206b and sealed by one of a plurality of seals 230. The bottom portion 206b may enable an additional number of sensors or other electronic components to be provided in the vacuum insulator 102.

The wires 232 and seals 232 may be configured in the same manner as any of the embodiments of the wires 132 and seals 130 as described above. In particular, the wires 232 and the seals 230 may comprise Kovar and glass, respectively, or, alternatively, may comprise other suitable conductors and insulators as described above.

Figure 3C shows an alternative bottom portion 306b that may be used within the heating apparatus 100 as described above alternatively to the bottom portion 106b. The bottom portion 306b comprises a plurality of wires 332, including a central paired heating wire comprising two individual heater wires for connection with either end of the heater 112. The wires 332 also comprise four thinner wires provided for connection with two sensors provided in the vacuum insulator 102. The bottom portion 306b comprises a ring of stainless steel (or any other suitable material) and an insulating sheet 330 comprising glass provided internally to the ring to form a substantially circular end of the outer wall 106. Each of the wires 332 are provided through a respective hole in the insulating sheet 330 and joined to the insulating sheet 330 in an airtight manner. Thus, the insulating sheet 330 circumferentially surrounds each of the wires 332. The wires 332 are spaced apart to prevent short circuits between any of the wires 332. The insulation properties of the seal 330 prevents unwanted electrical connection between each of the wires 332.

The wires 332 and the insulating sheet 330 may otherwise be configured in the same manner as embodiments of the wires 132 and seals 130 as described above. In particular, the wires 332 and the insulating sheet 330 may comprise Kovar and glass, respectively, or alternatively may comprise other suitable conductors and insulators.

Returning to the embodiment of Figure 3A, one additional advantage of this arrangement relates to the total circumference of the join between the bottom portion 106b and the seals 130. In this embodiment, each wire 132 and a corresponding seal 130 is provided through a dedicated hole in the bottom portion 106b. Using a dedicated hole for each wire 132 means the hole can have a lower diameter, which minimises the total perimeter of contact between the seal 130 and the bottom portion 106b. This contributes to more reliable retention of the enclosed vacuum 108 because the bottom portion 106b may not have thermal expansion characteristics matching that of the seals 130.

In contrast, the embodiment of Figure 3C, for example, uses a single insulating sheet 330 and a bottom portion 306b comprising a ring with an inner hole sized to accommodate several wires 332. Thus, in Figure 3C the circumference of the join or interface between the insulating sheet 330 and the bottom portion 306b is equal to the inner circumference of the ring making up the bottom portion 306b. This arrangement may have a larger circumference in contact between the insulating sheet 330 and the bottom portion 306b compared to the arrangement of Figure 3A and may be less effective at retaining the vacuum 108 compared to embodiments similar to Figure 3A.

In the example of Figure 3A having four wires 132, using dedicated holes for each wire 132 can significantly reduce the total circumference of interfacing portions between the seals 130 and bottom portion 106b by adjusting the size of each dedicated hole, compared to a similar arrangement of four wires using an insulating sheet.

The size of each hole may be made as small as possible without hindering construction of the vacuum insulator 102, i.e. , without making it overly difficult to assemble the seals 130 and wires 132 while maintaining a vacuum 108. Thus, each hole may be sized mainly, in other words as far as practically possible, to minimise the contact perimeter between the seals 130 and the bottom portion 106b.

These advantages apply equally to the arrangement of Figure 3B, which uses similarly dedicated holes for each wire 232. Dedicated holes used in this way may also be positioned elsewhere on the outer wall 106.

Claims

1 . A heating apparatus for an aerosol generating device, comprising: a vacuum insulator having a main longitudinal axis and comprising an inner wall and an outer wall between which a vacuum is enclosed; a cavity in which an aerosol forming substance can be received, positioned radially inwardly of the inner wall; a heater provided inside the vacuum insulator in thermal contact with the inner wall of the vacuum insulator, configured to heat an aerosol forming substance received in the cavity by thermal conduction to generate an aerosol; and one or more wires configured to connect the heater to a power source, wherein the one or more wires extend through at least one hole in the outer wall of the vacuum insulator, and wherein the one or more wires are circumferentially surrounded by an insulator; wherein the insulator comprises glass and the one or more wires are made from a material that has thermal expansion characteristics that substantially match the thermal expansion characteristics of the insulator.

2. The heating apparatus of claim 1 , comprising a first wire that extends through a first hole in the outer wall and a second wire that extends through a second hole in the outer wall.

3. The heating apparatus of claim 1 or claim 2, wherein the one or more wires comprise Kovar.

4. The heating apparatus of any of the preceding claims, further comprising a sensor positioned within the vacuum insulator and a sensor wire that is connected to the sensor and extends through a further hole in the vacuum insulator, and wherein the sensor wire is circumferentially surrounded by an insulator.

5. The heating apparatus of claim 4, wherein the further hole extends through the outer wall of the vacuum insulator.

6. The heating apparatus of claim 4, wherein the further hole extends between the inner wall and the outer wall of the vacuum insulator.

7. The heating apparatus of any of the preceding claims, wherein the heater is a resistive heater.

8. The heating apparatus of any of the preceding claims, wherein the heater comprises an exposed external surface having a material susceptible to an oxidation reaction in the presence of oxygen.

9. The heating apparatus of any of the preceding claims, wherein the inner wall has a thickness of about 0.1 mm or less.

10. The heating apparatus of any of the preceding claims, wherein the insulator comprises borosilicate glass.

11. The heating apparatus of any of the preceding claims, wherein the one or more wires each extend through a different respective hole in the outer wall and each hole contains a corresponding insulator surrounding a corresponding wire.

12. The heating apparatus of claim 11 , wherein each respective hole is sized mainly to accommodate the corresponding wire to minimise the amount of insulator in contact with the outer wall.

13. An aerosol generating device configured to generate an aerosol for inhalation by a user, comprising the heating apparatus of any of the preceding claims.