The present invention relates to a heater for heating an aerosol-forming substrate. Preferably but not exclusively, the present invention relates to an electrical heater for heating an aerosol-forming substrate and to a heater for an electrically heated aerosol-generating system. The invention finds particular application as an internal heater for an electrically heated smoking system for heating an aerosol-forming substrate having a cavity.

EP-A-0 358 020 discloses a smoking article comprising a cigarette with a resistance heating element for heating tobacco material in the cigarette. The cigarette has an electrical connection plug for connection to a reusable, hand held controller. The hand held controller includes a battery and a current control circuit which controls the supply of power to the resistance heating element in the cigarette. One disadvantage with such a proposed smoking article is that the heating element is not in direct contact with the tobacco material, and so the resistance heating element only indirectly heats the tobacco material via air which is drawn over the heater and in turn over the tobacco material. This can lead to inefficient heating of the tobacco material because of the indirect heating process. This may also mean that the article can get hotter than is desirable because of the indirect heating process.

According to a first aspect of the invention, there is provided a heater for heating an aerosol-forming substrate, the heater comprising a plurality of elongate heating elements arranged in an elongate array having a support end with a first dimension, a heating end with a second dimension and a middle portion with a third dimension, the array arranged to heat the substrate to form an aerosol, wherein the third dimension is greater than the first dimension and greater than the second dimension.

A heater according to embodiments of the invention has the advantage that the heating elements can provide efficient heating of the substrate due to the contact with the substrate. The heating end may be inserted into a cavity of the aerosol-forming substrate while the support end opposite the heating end may remain outside (or near the outside) of the aerosol-forming substrate. The middle portion is between the support end and the heating end and may contact the aerosol-forming substrate. Because the middle portion of the array has the greatest dimension (which may be its diameter if the array has a circular or near-circular cross section), the elongate array can be easily inserted into the cavity of the aerosol-forming substrate at the heating end, whilst still providing good contact with the inside of the substrate. The heater is advantageous because the good contact with the substrate provides optimal heating of the substrate. Since the heating process is efficient, the temperature and power needed may be reduced.

In addition, the heater according to embodiments of the invention has the advantage that any condensate that forms on the outside of the heating elements will be removed by contact with the inside of the substrate. The heater may additionally have the advantage that the temperature of the heating elements is high enough to allow for any condensate that is not removed by contact with the substrate to evaporate during the heating process. The elongate array also provides a robust arrangement for the heater, which reduces the likelihood that the heating elements will break.

The heater may be used in an electrically heated aerosol-generating system. Preferably, the heater is an internal heater. However, the heater may also be an external heater.

Preferably, the plurality of elongate heating elements is arranged in a substantially tubular array. That is to say, the array may be substantially tubular in shape. At least one of the first dimension, the second dimension and the third dimension may be a diameter of the array. Preferably the first dimension is the diameter of the tubular array at the support end. Preferably the second dimension is the diameter of the tubular array at the heating end. Preferably the third dimension is the diameter of the array in the middle portion. The diameter of the array may be measured through and substantially perpendicular to the longitudinal axis of symmetry of the array. Alternatively, the heating elements are arranged in a substantially conical array. That is to say, the array may be substantially conical in shape.

Preferably, the second dimension at the heating end is smaller than the first dimension at the support end. In one preferred arrangement, the heating end is in the form of a point. This facilitates easy insertion of the heating elements into a cavity of the aerosol-forming substrate. Preferably, the heating elements are curved between the support end, the middle portion and the heating end. In one preferred arrangement, the heating elements are curved towards one another to form a point at the heating end. In that case, the elongate array is preferably nose-cone shaped, and each heating element preferably has a curved, elliptical shape.

The substantially elongate array preferably has a circular cross section. However, this need not be the case and a rectangular, oval or other shaped cross section is also possible. In that case, the dimension of each of the support end, heating end and middle portion may comprise a measurement substantially perpendicular to the longitudinal axis of the array. The measurement may include the span of the array, the breadth of the array or the width of the array. Preferably, the dimension of each of the support end, heating end and middle portion comprises the largest measurement substantially perpendicular to the longitudinal axis of the array which would be the limiting measurement if inserting the elongate array into an aerosol-forming substrate.

In one embodiment, the elongate array of heating elements extends from a collar at the support end. The collar may be substantially circular in cross section. However, the collar may also take a variety of other forms, for example, square, rectangular, oval or octagonal. In one embodiment, the collar comprises a ring. In another embodiment, the collar comprises an annular disc. The collar may be electrically conductive. Alternatively, the collar may be electrically insulating.

Preferably, the plurality of heating elements are electrically connected to each other at the heating end. Preferably, the plurality of heating elements are mechanically connected to each other at the heating end. The plurality of heating elements may be both electrically and mechanically connected to each other at the heating end.

In one embodiment, the dimension of the middle portion of the array is larger than an inside dimension of a cavity of the aerosol-forming substrate, such that, when the plurality of heating elements are inserted into the cavity of the aerosol-forming substrate, the heating elements are pressed towards each other so as to exert a force on the substrate. The dimension of the middle portion is preferably the diameter of the middle portion. The inside dimension of the cavity is preferably the inside diameter of the cavity. When the heating elements are pressed towards each other, they are preferably pressed towards the central axis of symmetry of the heater, that is to say, towards the longitudinal axis of symmetry of the elongate array. Preferably, the force exerted on the substrate is exerted in a direction away from the central axis of symmetry of the heater, that is to say, away from the longitudinal axis of symmetry of the elongate array. This arrangement further optimises the contact with the substrate, which increases efficiency of the heating process.

The plurality of heating elements may comprise two heating elements. If the elongate array comprises two heating elements, each heating element may be positioned away from its adjacent heating element by an angle of approximately 180°, when viewed along the longitudinal axis of the heater. That is to say, the two heating elements may be substantially opposite one another. In that case, the dimension of each of the support end, the heating end and the middle portion may comprise the distance between the two heating elements measured substantially perpendicular to the longitudinal axis. Alternatively, the plurality of heating elements may comprise three heating elements. If the elongate array comprises three heating elements, each heating element may be positioned away from its adjacent heating element by an angle of approximately 120°, when viewed along the longitudinal axis of the heater. In that case, the dimension of each of the support end, the heating end and the middle portion may comprise the distance between two of the three heating elements or another dimension measured substantially perpendicular to the longitudinal axis. Alternatively, the plurality of heating elements may comprise four heating elements. If the elongate array comprises four heating elements, each heating element may be positioned away from its adjacent heating element by an angle of approximately 90°, when viewed along the longitudinal axis of the heater. In that case, the dimension of each of the support end, the heating end and the middle portion may comprise the distance between two of the heating elements measured substantially perpendicular to the longitudinal axis, preferably two of the heating elements which are opposite one another. The plurality of heating elements may comprise five, six, seven or eight heating elements. If the elongate array comprises eight heating elements, each heating element may be positioned away from its adjacent heating element by an angle of approximately 45° when viewed along the longitudinal axis of the heater. For any number of heating elements, the dimension of each of the support end, the heating end and the middle portion may comprise the distance between the two substantially opposite heating elements, measured substantially perpendicular to the longitudinal axis of the array.

Each of the plurality of elongate heating elements preferably comprises an electrically resistive material. Suitable electrically resistive materials include but are not limited to: semiconductors such as doped ceramics, electrically conductive ceramics (such as, for example, molybdenum disilicide), carbon, graphite, metals, metal alloys and composite materials made of a ceramic material and a metallic material. Such composite materials may comprise doped or undoped ceramics. Examples of suitable doped ceramics include doped silicon carbides. Examples of suitable metals include titanium, zirconium, tantalum and metals from the platinum group. Examples of suitable metal alloys include stainless steel, nickel-, cobalt-, chromium-, aluminium- titanium- zirconium-, hafnium-, niobium-, molybdenum-, tantalum-, tungsten-, tin-, gallium-, manganese- and iron-containing alloys, and super-alloys based on nickel, iron, cobalt, stainless steel, Timetal® and iron-manganese-aluminium based alloys. In composite materials, the electrically resistive material may optionally be embedded in, encapsulated or coated with an insulating material or vice-versa, depending on the kinetics of energy transfer and the external physicochemical properties required. Timetal ® is a registered trade mark of Titanium Metals Corporation, 1999 Broadway Suite 4300, Denver Colorado.

Alternatively, each of the plurality of elongate heating elements may comprise an infra-red heating element, a photonic source, or an inductive heating element.

Preferably, each of the plurality of elongate heating elements takes the form of an elongate blade.

In one embodiment, the plurality of heating elements is formed by flat stamping the heating elements from a single sheet of suitable material. The collar may also be formed by flat stamping from a sheet of suitable material. The collar may be substantially circular in shape. In one embodiment, the stamped heating elements may form a spider or star shape. In that case, the heating elements are then bent towards the collar to form the substantially elongate array. In an alternative embodiment, the stamped heating elements may form a comb shape. In that case, the linking element joining the teeth of the comb is then curved into a ring to form the substantially elongate array of heating elements. In another embodiment, the collar and the plurality of heating elements are formed separately and the heating elements are then connected to the linking element, for example, by welding. The support end of the heating elements may be held in place by the collar by welding, gluing or otherwise attaching them to the collar.

The heater may further comprise at least one external heating element for heating the outside of the aerosol-forming substrate. The external heating element or elements may comprise heating blades designed to surround the substrate. The external heating element or elements may comprise a tube designed to surround the substrate. The external heating element or elements may comprise a disk (end) heater. If a collar is provided at the support end, it is possible for the collar to include the external heating element. Suitable materials for the external heating element or elements are the same as those set out above for the heating elements.

In one embodiment, the heater further comprises an electrically conductive pin located substantially in the centre of the elongate array of heating elements. The pin may connect all the heating elements to a first voltage. Each heating element may also be connectable to a second voltage, via a switch, such that when the switch is on, the respective heating element is energised. Alternatively, all the heating elements may be connectable to a second voltage, via a single switch, such that when the switch is on, all the heating elements are energised. In those embodiments, preferably a collar at the support end is electrically conductive and is connected to the second voltage and to the support end of the heating elements.

Preferably, the electrically conductive pin is electrically connected to all the heating elements at the heating end, the pin preferably connecting all the heating elements to a first voltage. In that embodiment, the pin is preferably connected to a first voltage and is connected to all the heating elements at the heating end. The collar is preferably connected to a second voltage and is connectable to all the heating elements at the support end.

Preferably the plurality of heating elements is connectable between a first voltage and a second voltage. In that embodiment, the support end of at least one of the heating elements may be connectable to one of the first and second voltages.

In one embodiment, all the heating elements are connectable to one of the first and second voltages at the support end and all the heating elements are connectable to the other of the first and second voltages at the heating end. That is to say, when connected, current flows between the first voltage at the support end, through each heating element, to the second voltage at the heating end.

In an alternative embodiment, the support end of at least one of the heating elements is connectable to one of the first and second voltages and the support end of at least one other of the heating elements is connectable to the other of the first and second voltages. That is to say, when connected, current flows between the first voltage at the support end of some of the heating elements, through those heating elements to the heating end, through the other heating elements from the heating end to the second voltage at the support end.

In either embodiment, the heater may include a switch for each heating element, each switch allowing electrical current to flow through the respective heating element. In that case, each heating element is under individual control. In that case, each heating element can be individually energised. Control of the switches will dictate which of the heating elements is energised. This is advantageous as it may allow different portions of the aerosol-forming substrate to be selectively heated.

Alternatively, the heater may include a switch, the switch allowing electrical current to flow through all the heating elements. In that case, preferably, the switch for all the heating elements is under one common control. In that case, the switch is either on or off, such that either all the heating elements are energised or none of the heating elements are energised. The switch may alternatively allow electrical current to flow through some but not all the heating elements.

In one preferred arrangement, the heater includes an electrically conductive pin which is electrically connected to a first voltage and is electrically connected to all of the heating elements at the heating end. At the support end, the heating elements are connectable to a second voltage, via a single switch.

In another preferred arrangement, the heater includes an electrically conductive pin which is electrically connected to a first voltage and is electrically connected to all of the heating elements at the heating end. At the support end, the heating elements are each connectable to a second voltage, via a respective switch.

In another preferred arrangement, some of the heating elements are connected to a first voltage at the support end. This may be via a single switch or via an individual switch for each heating element. Other of the heating elements are connected to a second voltage at the support end. Again, this may be via a single switch or via an individual switch for each heating element. The heating elements are connected to each other at the heating end.

According to a second aspect of the invention, there is provided an electrically heated aerosol generating system for receiving an aerosol-forming substrate, the system comprising a heater according to the first aspect of the invention.

According to the second aspect of the invention, there is also provided an electrically heated aerosol generating system for receiving an aerosol-forming substrate, the system comprising: a heater for heating the aerosol-forming substrate, the heater comprising a plurality of elongate heating elements arranged in an elongate array having a support end with a first dimension, a heating end with a second dimension and a middle portion with a third dimension, the array arranged to heat the substrate to form an aerosol, wherein the third dimension is greater than the first dimension and greater than the second dimension.

Preferably the electrically heated aerosol generating system is an electrically heated smoking system. In a preferred embodiment, a first voltage is connectable to at least one of the plurality of heating elements; and a second voltage is connectable to at least one other of the plurality of heating elements. Features described in relation to one aspect of the invention may also be applicable to the other aspect of the invention.

In a preferred embodiment, the aerosol-forming substrate comprises a tubular substrate having a cavity for receiving the plurality of heating elements. Alternatively, the aerosol-forming substrate may comprise a substantially conical substrate having a cavity for receiving the plurality of heating elements. In other embodiments, the aerosol-forming substrate may have any other suitable shape which allows insertion of the heating elements. The term "cavity" is used to mean a space within the aerosol-forming substrate into which the heater may be inserted.

The aerosol-forming substrate preferably comprises a tobacco-containing material containing volatile tobacco flavour compounds which are released from the substrate upon heating. The aerosol-forming substrate may comprise a non-tobacco material. The aerosol-forming substrate may comprise tobacco-containing material and non-tobacco containing material. Preferably, the aerosol-forming substrate further comprises an aerosol former. Examples of suitable aerosol formers are glycerine and propylene glycol.

The aerosol-forming substrate is preferably a solid substrate. The solid substrate may comprise, for example, one or more of: powder, granules, pellets, shreds, spaghettis, strips or sheets containing one or more of: herb leaf, tobacco leaf, fragments of tobacco ribs, reconstituted tobacco, extruded tobacco such as homogenised tobacco and expanded tobacco. The solid substrate may be in loose form, or may be provided in a suitable container or cartridge. Optionally, the solid substrate may contain additional tobacco or non-tobacco volatile flavour compounds, to be released upon heating of the substrate.

Optionally, the solid substrate may be provided on or embedded in a thermally stable carrier. In a preferred embodiment, the carrier is a tubular carrier having a thin layer of the solid substrate deposited on its inner surface, or on its outer surface, or on both its inner and outer surfaces. Such a tubular carrier may be formed of, for example, a paper, or paper like material, a non-woven carbon fibre mat, a low mass open mesh metallic screen, or a perforated metallic foil or any other thermally stable polymer matrix. Alternatively, the carrier may take the form of powder, granules, pellets, shreds, spaghettis, strips or sheets.

The solid substrate may be deposited on the surface of the carrier in the form of, for example, a sheet, foam, gel or slurry. The solid substrate may be deposited on the entire surface of the carrier, or alternatively, may be deposited in a pattern in order to provide a non-uniform flavour delivery during use.

Alternatively, the carrier may be a non-woven fabric or fibre bundle into which tobacco components have been incorporated. The non-woven fabric or fibre bundle may comprise, for example, carbon fibres, natural cellulose fibres, or cellulose derivative fibres.

Further, as known to those skilled in the art, an aerosol is a suspension of solid particles or liquid droplets in a gas, such as air. The aerosol may be a suspension of solid particles and liquid droplets in a gas, such as air. Air is a mixture of approximately 78% Nitrogen and 21 % Oxygen by volume. Carbon Dioxide and other trace gases make up the remaining 1%.

During operation, the substrate may be completely contained within the electrically heated aerosol generating system. In that case, a user may puff on a mouthpiece of the electrically heated aerosol generating system. Alternatively, during operation, the substrate may be partially contained within the electrically heated aerosol generating system. In that case, the substrate may form part of a separate article and the user may puff directly on the separate article. Preferably, the substrate forms part of a separate smoking article and the user may puff directly on the smoking article.

The smoking article may have a total length between approximately 30 mm and 100 mm. The smoking article may have an external diameter between approximately 5 mm and approximately 13 mm. The smoking article may comprise a filter plug. The filter plug may be located at the downstream end of the smoking article. The filter plug may be a cellulose acetate filter plug. The filter plug is preferably approximately 7 mm in length, but can have a length of between approximately 5 mm to approximately 10 mm.

Preferably, the smoking article is a cigarette. In a preferred embodiment, the smoking article has a total length between 40 mm and 50 mm. Preferably, the smoking article has a total length of approximately 45 mm. It is also preferable for the smoking article to have an external diameter of approximately 7.2 mm. Preferably, the aerosol-forming substrate comprises tobacco. Further, the aerosol-forming substrate may have a length of approximately 10 mm. However it is most preferable for the aerosol-forming substrate to have a length of approximately 12 mm.

Further, the diameter of the aerosol-forming substrate may also be between approximately 5 mm and approximately 12 mm.

The smoking article may comprise an outer paper wrapper.

Further, the smoking article may comprise a separation between aerosol-forming substrate and the filter plug. The separation may be approximately 18 mm, but can be in the range of approximately 5 mm to approximately 25 mm.

Preferably, the electrical energy is supplied to one or more of the heating elements until the heating element(s) reach a temperature of between approximately 200°C and 440 °C. Any suitable temperature sensor and control circuitry may be used in order to control heating of the heating element to reach the temperature of between approximately 200°C and 440 °C. This is in contrast to conventional cigarettes in which the combustion of tobacco and cigarette wrapper may reach 800 °C.

The system may further comprise a sensor to detect air flow indicative of a user taking a puff. In that embodiment, preferably, the sensor is connected such that the system is arranged to energise at least one of the heating elements when the sensor senses a user taking a puff. The sensor may be an electro-mechanical device. Alternatively, the sensor may be any of: a mechanical device, an optical device, an opto-mechanical device and a micro electro mechanical systems (MEMS) based sensor. In that embodiment, preferably, the sensor is connected to a power supply and the system is arranged to activate the heating elements, or some of the heating elements, when the sensor senses a user taking a puff. In an alternative embodiment, the system further comprises a manually operable switch, for a user to initiate a puff.

Preferably, the system further comprises a housing for receiving the aerosol-forming substrate and designed to be grasped by a user. The housing preferably houses the heater, a voltage source and any other components required for the system.

Preferably, the electrically heated smoking system further comprises a power supply for supplying power to the heating elements. The power supply for providing the first and second voltages may be any suitable power supply, for example a Direct Current (DC) voltage source. In one embodiment, the power supply is a Lithium-ion battery. Alternatively, the power supply may be a Nickel-metal hydride battery or a Nickel cadmium battery, or Lithium Iron Phosphate, or Lithium Manganese battery. The power supply may comprise a power cell contained in the electrically heated smoking system. Alternatively, the power supply may comprise circuitry, for example including a capacitor, which is chargeable by an external charging portion and an interface for connection to an external power source.

Preferably, the electrically heated smoking system further comprises electronic circuitry arranged to be connected to the power supply and the heating elements. In some embodiments, preferably the electronic circuitry provides for the heating elements to be independently controllable. The electronic circuitry may be programmable.

Features described in relation to one aspect of the invention may also be applicable to another aspect of the invention.

The invention will be further described, by way of example only, with reference to the accompanying drawings, in which:

• Figure 1 shows a plurality of heating elements of a first embodiment of a heater, during construction;
• Figure 2 shows a collar portion of the first embodiment of a heater, during construction;
• Figure 3 shows the heater of Figures 1 and 2, in constructed form;
• Figure 4 is an electrical circuit diagram showing the electrical connections of the heater of Figure 3 with common heating element control;
• Figure 5 is an electrical circuit diagram showing the electrical connections of the heater of Figure 3 with individual heating element control;
• Figure 6 shows a schematic section through a smoking article for use with embodiments of the invention, the smoking article including a tubular mat of aerosol-forming substrate;
• Figure 7 shows the heater of Figure 3 inserted into a tubular mat of tobacco;
• Figure 8 shows a heater similar to that of Figure 3 ready for use with a tubular mat of tobacco in a smoking article;
• Figures 9 and 10 show alternative methods of construction of the heater of Figure 3;
• Figure 11 shows a second embodiment of a heater according to the invention;
• Figure 12 is an electrical circuit diagram showing the electrical connections of the heater of Figure 11; and
• Figure 13 shows a heater similar to that of Figure 11 ready for use with a tubular mat of tobacco in a smoking article.

Figures 1 to 5, 7 and 8 show a first embodiment of the heater of the invention. Referring particularly to Figures 1, 2 and 3, heater 101 comprises an electrically conductive pin in the form of common pin 103, annular collar 105 and a plurality of heating elements 107. The assembled heater 101 has a collar end A, a heating end B and a middle portion C. Figure 1 shows the heating elements 107 before final assembly, after being formed by flat stamping from a sheet of suitable material. Figure 2 shows the collar portion including annular collar 105 and common pin 103, before final assembly. The annular collar 105 may be an electrically insulating material which acts as a support to hold the position of the heating elements in the shape shown in Figure 3. The annular collar 105 may also hold the common pin 103 in a substantially central position on the collar. In embodiments which have common control of the heating elements (described below in relation to Figure 4), the collar may be electrically conductive so that when the heating elements are joined to the collar, an electrical connection is made between the heating elements and collar.

The common pin 103 is formed separately from the heating elements 107 and collar 105. In this embodiment, after flat stamping, the heating elements 107 are bent inwards relative to heating end B. The common pin 103 is inserted in the central aperture of the annular collar 105 but there may be no direct electrical connection between the common pin 103 and the collar 105. At the collar end A, the heating elements 107 are connected to the outer portion of the annular collar 105. At the heating end B, the heating elements 107 are electrically and physically connected to the common pin 103. This assembly forms the substantially elongate array structure shown in Figure 3.

Referring particularly to Figure 3, which is a side view of the assembled heater, the heating elements 107 of the assembled heater form a substantially elongate array having a circular cross-section collar end A, a pointed heating end B and a circular cross-section middle portion C. The diameter of the middle portion C is marked f in Figure 3. The heater may be referred to as an internal heater. The particular curved shape of the heating elements 107 will be discussed further below. As shown in Figure 3, the common pin 103 is connected to a first voltage, shown as V+, and the collar 105 is connected to a second voltage, shown as V-. For clarity, only four of the eight heating elements 107 are shown in Figure 3.

Preferably, when not in use, the diameter f of the heater in the middle portion C, that is to say approximately the distance between opposite heating elements in the middle portion, is between approximately 5 mm and 13 mm. When the heater is not compressed, the diameter f of the middle portion C may be larger than the diameter of the collar end A by approximately 0.5 mm or 1 mm. Preferably, the separation of the heating elements at the middle portion C, that is to say the distance between adjacent heating elements, when the heater is not compressed may be between 1 mm and 4 mm. More preferably, the separation of the heating elements at the middle portion C, when the heater is not compressed, may be between 1.25 mm and 3.25 mm.

In one embodiment, each of the heating elements at the collar end A are electrically connected to each other, and then to a single switch. This is shown in the circuit diagram in Figure 4 and is referred to as common control. Referring to Figure 4, the common pin 103 is connected to a first voltage V+. The heating elements 107 are connected to the first voltage and are connected in parallel to each provide a voltage drop to a lower voltage. The heating elements are connected to each other at the lower voltage and then to a single switch 109. The switch 109 is, in turn, electrically connected to a second voltage V- at collar 105. In this arrangement, a single switch 109 controls whether electrical current passes through all of the heating elements 107. The switch 109 shown in Figure 4 is a mechanical switch, but may alternatively be a transistor, such as a field effect transistor (FET), a bipolar transistor, MOSFET or another type of switch.

During operation, when the switch 109 is closed, electrical current flows, as indicated by the dashed lines in Figure 3 and the arrows in Figure 4. All the heating elements 107 heat up by virtue of the Joule heating effect. Of course, the current flow may be in the opposite direction. In that case, the common pin 103 which runs through the centre of the heater is connected to a voltage V-, and the collar ends of the heating elements are connected to a voltage V+. That is to say, it is sufficient for there to be a potential difference between the collar end of the common pin and the collar end of the heating elements for electrical current to flow. As already mentioned, this mode of operation, in which a single switch controls the current flow through all the heating elements 107 is referred to as common control.

In another embodiment, individual control of each of the heating elements 107 is possible. The circuit diagram for this embodiment is shown in Figure 5 and is referred to as individual control. Referring to Figure 5, the common pin 103 is connected to a first voltage V+, as in Figure 4. The common pin 103 is electrically and mechanically connected to all of the heating elements at the heating end B of the heater. Thus, the heating elements 107 are connected to the first voltage. The heating elements 107 are connected in parallel to each provide a voltage drop to a lower voltage. At the lower voltage, each of the heating elements 107 is connected to a non-conducting collar portion by welding or gluing or otherwise attaching them in a separate stage in the manufacturing process. The non-conducting collar may be stamped of sheet insulating material as previously described. At the collar end A each heating element 107 is connected via switch 109 to the second voltage, shown as V- at collar 105. The switches 109 shown in Figure 5 are mechanical switches, but may also be transistors, such as field effect transistors (FET's), bipolar transistors, MOSFET's or another type of switch.

During operation, when one or more of the switches 109 are closed, current passes through the respective resistive heating elements 107 as a result of the voltage drop between the common pin first voltage V+ and the second voltage V-. As shown by the arrows in Figure 5, electrical current flows from V+ to V-. As the current flows, the temperature of the heating elements 107 whose corresponding switch has been closed increases, thereby heating the aerosol-forming substrate. Of course, as in Figure 4, the current flow may be in the opposite direction. As discussed further below, the temperature of common pin 103 increases, but preferably significantly less than the temperature of the heating elements 107.

The heating elements 107 and are formed from an electrically resistive sheet material, for example Nickel Chromium, Iron Aluminide, a tungsten alloy or any other electrically resistive, high performance metal alloy. The common pin is typically formed from an electrically conducting material such as copper. The common pin does not substantially contribute to the heating of the substrate. It typically has a resistance of about 5% to 10% of the overall resistance of the heating elements. Preferably, the common pin is of a size such that it does not become a heat sink and dissipate heat from the heating elements. The collar 105 may be formed from an electrically conducting material such as copper. Alternatively, the collar may be formed from an electrically insulating material, such as plastics or ceramics. In this case, after the heating elements at the support end have been mechanically connected to the collar by gluing, welding or otherwise attaching them, an electrical connection is made between each of the heating elements at the support end and the switch, to control the flow of current in the heating elements.

The switches 109 in Figures 4 and 5 may be formed in a number of ways. Firstly, a wire can be soldered to one end, marked V-, of the electrically conductive collar as well as a soldering a second wire to the common pin marked V+ in Figure 3. In this embodiment, the collar and the plurality of heating elements are electrically joined to one another.

A switch 109 may be provided on a separate printed circuit board away from the heating element. The switch is preferably a metal-oxide-semiconductor field-effect transistor (MOSFET), and the wires are electrically connected to a power supply via the switch.

Alternatively, after flat stamping of the heating element as previously described, a separate printed circuit board approximately in the shape of the collar 105 may be manufactured including the switches such as MOSFETS and the electrical circuitry of Figure 4. Suitable electrical connections are then made between the collar mounted printed circuit board and the heating elements and common pin to form the electrical circuit of Figure 4.

In Figures 1, 3, 4 and 5, eight heating elements 107 are shown. However, any suitable number of heating elements is possible. For example, there may be between 5 and 15 heating elements. More preferably, there may be 10, 11 or 12 heating elements. Also, external heating elements may be provided in addition to the heating elements 107. This will be described further in relation to Figures 8 and 13.

Figure 6 shows a smoking article 601 for use with an electrically heated smoking system according to embodiments of the invention. The smoking article 601 has an elongate cylindrical shape and comprises an aerosol-forming substrate 115, and a filter plug 611, arranged sequentially and in coaxial alignment. The components 115 and 611 are overwrapped with an outer paper wrapper 615. The aerosol-forming substrate 115 is substantially tubular. The length I of the tube may be substantially parallel to the length of the smoking article. Further, the length I of the tube may be substantially parallel to the direction of airflow (not shown) in the electrically heated smoking system when a user puffs on the smoking article. The circumference of the tube may be substantially perpendicular to the length, and the inner diameter of the tube is d.

Figure 7 shows the heater of Figure 3 inserted into a tubular mat of tobacco 115, like that in Figure 6. In the heater of Figure 3, the heating elements form a substantially bullet-shaped array which narrows to a tip at the heating end B. In Figure 3, the diameter of the array at the middle portion C, marked f in Figure 3, is greater than the diameter of the array at the tip (heating end B) and at the support end A.

Referring to Figure 7, common pin 103, which runs through the centre of the heater and is connected to the first voltage V+, provides a common connection for each of the heating elements 107. At heating end B, the common pin 103 is electrically and physically connected to each heating element 107. Each heating element is a resistor, which heats up when current passes through, thereby heating the substrate. Figure 7 shows the heater inserted into the tubular mat when the internal diameter d of the tubular mat is smaller than the diameter f of the heater at middle portion C, shown in Figure 3. The act of inserting the heater in the mat causes the heating elements 107 to be forced inwards towards the common pin 103. In order to facilitate this movement, the heating elements are deformed as shown in Figure 7. This movement of the heating elements is referred to as mechanical articulation. This brings more of the heating element into contact with the tubular mat than would be the case if the diameter of the heater f at middle portion C in Figure 3 were the same as or smaller than the internal diameter of the tubular mat d, shown in Figures 6 and 7. In addition, it ensures good contact between the heating element and the tubular mat.

When the heating element is inserted in the tubular mat, the shape of the heating element changes from a substantially bullet shape, with a diameter at the middle portion C which is larger than the diameter at either of the two ends A, B, to a substantially tubular shape in which the sides of the heater are substantially parallel to the tubular mat. Further, when the heater is substantially tubular in shape, the diameter of the heater is substantially constant along the length of the heater. Further, the shape of the tip of the heater B is also transformed from a pointed shape, as shown in Figure 3, to a more rounded shape, as shown in Figure 7.

Figure 8 shows a heater, similar to that of Figure 3, ready for use with a tubular mat of tobacco in a smoking article. The heater is shown in cross section on the left hand side of Figure 8. The heater comprises the common pin 103, heating elements 107 and collar 105 as previously described, and additionally comprises a substantially tubular frame 113. The tubular frame may include one or more external heating elements on its inner surface, although this is not shown in Figure 8. The aerosol-forming substrate 115 is shown schematically on the right hand side of Figure 8. Preferably, the aerosol-forming substrate is a substantially tubular mat of tobacco. The heater is inserted into the tubular mat at the heating end B, such that the array of heating elements 107 is positioned inside the tubular mat, and the frame 113 is positioned outside the tubular mat. The internal diameter d of the tubular mat is preferably comparable to or slightly smaller than the diameter f of the middle portion C of the elongate array. Thus, when the elongate array is inserted into the tubular mat, there may be an outward force exerted on the tubular mat by the curved heating elements. This ensures a tight fit so that the array stays in position and good contact between the heating elements and the substrate, as described in relation to Figure 7. The external diameter e of the tubular mat is preferably comparable to or slightly smaller than the internal diameter g of the frame 113. This also ensures a tight fit. It also maximises heating efficiency if external heating elements are provided on the inner surface of frame 113.

Figures 9 and 10 show alternative methods for constructing the heater of an embodiment of the invention. In both Figures 9 and 10, before final assembly, the heater 201 comprises a linking element 206 and a plurality of heating elements 207.

In the embodiment shown in Figure 9, the heating elements 207 are formed by flat stamping from a single sheet of suitable material using an appropriately shaped stamp. The heating elements are stamped out to form a number of substantially parallel legs. All of the legs are electrically and mechanically joined to each other by a substantially straight linking element 206. The linking piece may be substantially perpendicular to the legs.

In the embodiment shown in Figure 10, the heating elements 207 are formed separately and each heating element 207 is then spot welded at weld 203 to the linking element 206.

In either Figure 9 or Figure 10, after forming, the linking element 206 is bent, as shown by the arrows in Figures 9 and 10, to form a ring. The ring has heating elements 207 extending at approximately a 90° angle from the linking element 206. The two ends of the linking element may be joined together by welding or gluing or using any other suitable joining method. When bent or shaped in this way, the linking element 206 is preferably substantially circular in shape. Then, the heating elements 207 are shaped into the shape shown in Figure 3, and mechanically attached to a collar 105 (like that shown in Figure 2) using welding, gluing or any other joining process. Once again, the collar may be electrically insulating in the case of individual heating element control, but may be electrically conductive in the case of common control of the heating elements. The collar also serves as a mechanical support for the heating elements 207. In addition, slots may be formed in the collar portion by laser cutting or using a saw and the heating elements may be inserted into the slots and fixed into place using glue, welding, screwing or bending of the heating elements. The switches 109 (not shown in Figures 9 and 10) may be formed as previously described. In Figures 9 and 10, the collar end is marked A, the heating end is marked B and the middle portion is marked C. The common pin may be attached to the heater as previously described with reference to Figures 1 to 3.

Figures 11, 12 and 13 show a second embodiment of the heater of the invention. Figure 11 shows a side view of the assembled heater and includes an electrical circuit diagram showing the electrical connections of the heater. Figure 12 is an electrical circuit diagram showing the electrical connections of the heater of Figure 11. Figure 13 shows a heater similar to that shown in Figure 11 ready for use with a tubular mat of tobacco in a smoking article. Unlike the embodiment of Figures 1 to 5, 7 and 8, there is no common pin; instead, an electrical multipath system is used. The heater of Figure 11 may be made using the method shown in Figures 1 and 2 or Figure 9 or Figure 10.

Figure 11 shows a side view of the assembled heater. For clarity, in Figure 11, only six of the heating elements 207 are shown. The heating elements 207 of the assembled heater form a substantially elongate array having a circular cross-section collar end A, a pointed heating end B and a circular cross-section middle portion C. The particular curved shape of the heating elements 207 will be discussed further below. As shown in Figures 11 and 12, some of the individual heating elements are connected at collar end A to a first voltage, shown as V+, and some are connected at collar end A to a second voltage, shown as V-. All the heating elements are electrically and mechanically connected to each other at the heating end B of the heater. Electrical circuitry, wires and switches are provided as previously described to form the circuitry shown in Figures 11 and 12. The dashed lines in Figure 11 show how the electrical current flows in the heating elements 207 when the appropriate switches are closed.

Referring to Figure 12, as previously described, some of the heating elements at the collar end A are connected to the first voltage V+ via switches 210, a switch 210 being provided for each heating element. A connection 205 to the first voltage V+ is provided within the circuitry of the heater. Others of the heating elements at the collar end A are connected to the second voltage V-via switches 209, a switch 209 being provided for each heating element. A connection 211 to the second voltage V- is provided within the circuitry of the heater. Each heating element 207 is a resistor which heats up when current passes through, thereby heating the substrate. In Figure 12, four heating elements are shown connectable to the first voltage and four heating elements are shown connectable to the second voltage. However, any allocation between the two voltages is possible, as long as least one heating element can be connected to the first voltage and at least one heating element can be connected to the second voltage. In Figure 11, the arrows show the direction of flow of the electrical current when the appropriate switches are closed. The switches 209, 210 in Figure 12 are shown as mechanical switches, but could easily be transistors, such as field effect transistors, FET, bipolar transistors, or another type of switch.

In the embodiment of Figures 11 and 12, the switches 209, 210 are preferably each controlled individually. This allows each heating element to be selectively energised. This provides a way to heat different portions of the aerosol-generating substrate. Further, this allows for different portions of the substrate to be heated sequentially. However, all switches 209 could be replaced by a single switch if desired. All switches 210 could be replaced by a single switch if desired.

In operation, when at least one switch 209 is closed and at least one switch 210 is closed, a connection is formed between the first and second voltages and current passes through the respective heating elements 207. The temperature of the heating elements 207 increases, thereby heating the aerosol-forming substrate. The particular heating elements to be energised are selected by switching the appropriate switches 209, 210. When no switches are connected, no voltage drop is provided, so that none of the heating elements 207 are energised.

The heating elements 207 are formed from one or more electrically resistive sheets of material, for example Nickel Chromium, Iron Aluminide, a tungsten alloy or any other electrically resistive, high performance metal alloy as already described. The collar may be formed from a separate electrically non-conductive material, as previously described.

In the embodiments shown in Figures 7, 8 9, 10, 11 and 12 eight heating elements 207 are shown. However, any suitable number of heating elements is possible. For example, there may be between 5 and 15 heating elements. More preferably, there may be 10, 11 or 12 heating elements. Also, external heating elements may be provided in addition to the heating elements 207.

Figure 13 shows a heater, similar to that of Figure 11, ready for use with a tubular mat of tobacco in a smoking article. For clarity, only six heating elements are shown. The heater is shown in cross section on the left hand side of Figure 13. The heater comprises heating elements 207 and collar 205 as previously described, and additionally comprises a substantially tubular frame 213. The tubular frame may include one or more external heating elements on its inner surface, although this is not shown in Figure 13. The aerosol-forming substrate 115 is shown schematically on the right hand side of Figure 13. Preferably, the aerosol-forming substrate is a substantially tubular mat of tobacco. The heater is inserted into the tubular mat at the heating end B, such that the array of heating elements 207 is positioned inside the tubular mat, and the frame 213 is positioned outside the tubular mat. The internal diameter d of the tubular mat is preferably comparable to or slightly smaller than the diameter f of the middle portion C of the elongate array. Thus, when the elongate array is inserted into the tubular mat, there may be an outward force exerted on the tubular mat by the curved heating elements. This ensures a tight fit so that the array stays in position and good contact between the heating elements and the substrate, as previously described. As previously described, this is known as mechanical articulation. The external diameter e of the tubular mat is preferably comparable to or slightly smaller than the internal diameter g of the frame 213. This also ensures a tight fit. It also maximises heating efficiency if external heating elements are provided on the inner surface of frame 213.

Note that many of the features of the embodiments described above are interchangeable.

In operation, the heating elements of the heaters typically reach a temperature less than 500°C. More preferably, the temperature reached is between approximately 300 °C and approximately 500°C. Even more preferably, the temperature reached is approximately 250 °C.

The heaters shown in the drawings may be internal heaters. The term "internal heater" refers to a heater in which the heating elements are arranged to be internal to or within the aerosol-forming substrate during use. In this way, any condensate that does form on the heating elements evaporates in the heating process, or is removed by contact with the substrate. In particular, this differs from an external heating element, in which the outer surface of each heating element may easily become dirty since it is never in contact with the substrate to remove any condensate. In the embodiments described which include a common pin 103, some self-heating of the common pin 103 is acceptable because the heat will prevent condensate from forming on the surface of the common pin and even on the inside surfaces of the heating elements.

Alternatively, the heater may be an external heater. The term "external heater" refers to a heater which at least partially surrounds the aerosol-forming substrate.

In addition, because the heater may be an internal heater, the heating process can be more efficient. Thus, less power may be required and the time between a user's puff and the aerosol being generated can be minimised. This is because the heating elements are internal to the aerosol-forming substrate during operation, so that most of the heat is used to heat the substrate and only a small amount of the heat is dissipated. In addition, unlike external heating elements, there is contact only with the substrate itself rather than, for example, an outer paper sleeve. This increases efficiency and also reduces the likelihood that undesirable flavours are released.

The heaters shown in the drawings are optimised when used with an aerosol-forming substrate having a substantially conical or tubular shape. For example, the substrate may comprise a conical or tubular shaped mat of tobacco material which defines a cavity for receiving the heating elements. Preferably, the heater and substrate are sized such that the heating elements need to be pressed inwards slightly in order to be inserted into the tubular or conical substrate. This results in an outward force being exerted by the heating elements on the inside wall of the substrate, which ensures good contact with the substrate. This may also assist in keeping the heating elements in place in the substrate. The tubular substrate may be formed in a rod of smoking material, such as in a cigarette.

In Figures 3, 7, 8, 11, and 13, the heating elements are shown with an elliptical shape, that is to say, bowed outward along their length. The heater has a first dimension at the support or collar end (marked A), a second dimension at the heating end (marked B) and a third dimension at the middle portion (marked C). (Because the heater in the drawings has a substantially circular cross-section, those dimensions are diameters.) This means that the largest diameter of the assembled heater is at the middle portion, around the centre of the heating elements. This ensures a good contact with the substrate. Also preferably, the diameter at heating end B is smaller than the diameter at support end A, which facilitates insertion of the assembled heater into a tubular substrate. Preferably, the heating elements have a stiffness that allows them to be inserted into the substrate and a flexibility that allows them to fill the cavity formed by the substrate and maintain contact with the substrate.