WO2019138045A1

WO2019138045A1 - Aerosol-generating device comprising an elongate heating element

Info

Publication number: WO2019138045A1
Application number: PCT/EP2019/050647
Authority: WO
Inventors: Rui Nuno BATISTA; Chiara FASCIANI; Luca Rossi
Original assignee: Philip Morris Products S.A.
Priority date: 2018-01-12
Filing date: 2019-01-11
Publication date: 2019-07-18

Abstract

An aerosol-generating device (20) comprising: a cavity (22) for receiving at least part of an aerosol-forming substrate (102); a light source (38); an elongate heating element (30) extending into the cavity (22), and arranged to penetrate the aerosol-forming substrate (102) when the aerosol-forming substrate is received within the cavity (22); wherein said elongate heating element (30) comprises a light-transmitting core (32) and a heating surface (34) comprising a plurality of metallic nanoparticles; and wherein said light-transmitting core (32) is arranged to transmit light from the light source (38) to the plurality of metallic nanoparticles to generate heat by surface plasmon resonance.

Description

AEROSOL-GENERATING DEVICE COMPRISING AN ELONGATE HEATING ELEMENT

The present specification relates to an aerosol-generating device for heating an aerosol-forming substrate to generate an aerosol. Particularly, but not exclusively, the invention relates to an aerosol-generating device comprising an elongate heating element for such heating.

In a number of handheld aerosol-generating devices, an electrical heater is used for heating an aerosol-forming substrate to generate an aerosol. Typically, the aerosol-forming substrate is heated to temperatures of several hundred degrees centigrade for releasing one or more volatile compounds to form an aerosol. This may be accomplished by externally heating the aerosol-forming substrate using an external heater, such as a tubular heater, or by inserting a heater, such as a resistive heating element, to internally heat the aerosol-forming substrate.

Resistive heating elements for internally heating the aerosol-forming substrate may present a few drawbacks. For example, a resistive heating element generates heat by passing a current through the resistive heating element, which means that the entire area of the resistive heating element, including any portions of the resistive heating element not in contact with the aerosol-forming substrate, are also heated during use. This may lead to inefficiencies. In addition, the resistive heating element is typically wired to a power source and therefore it may be difficult to service or replace the resistive heating element. Indeed, servicing or replacing the resistive heating element may risk damaging electrical connections. Also, the resistive heating element may be exposed to the environment when not in use, which means that the device must be adapted, so that the device may be used in adverse weather conditions. Furthermore, a sufficiently high voltage drop is required across the resistive heating element in order to achieve a desired operating temperature. This may limit the choice of power sources that may be used.

Some internal resistive heating elements are provided in the shape of a substantially flat blade. Such blade shaped resistive heating elements must remain sufficiently thin so as to allow the blade to easily penetrate the aerosol-forming substrate. However, having such a thin profile means that the blade may be easily damaged during insertion into the substrate. Moreover, the substantially flat nature of the blade shaped resistive heating element limits the rate of heat transfer in a three-dimensional substrate, such as a cylindrical substrate.

It would be desirable to provide an aerosol-generating device that utilises a robust and efficient heating element which is insertable into an aerosol-forming substrate.

According to an aspect of the present invention there is provided an aerosol-generating device comprising: a cavity for receiving at least part of an aerosol-forming substrate; a light source; an elongate heating element extending into the cavity, and arranged to penetrate an aerosol-forming substrate when the aerosol-forming substrate is received within the cavity; wherein said elongate heating element comprises a light-transmitting core and a heating surface comprising a plurality of metallic nanoparticles; and wherein said light-transmitting core is arranged to transmit light from the light source to the plurality of metallic nanoparticles to generate heat by surface plasmon resonance.

As used herein, the term“surface plasmon resonance” refers to a collective resonant oscillation of free electrons of the metallic nanoparticles and thus polarization of charges at the surface of the metallic nanoparticles. The collective resonant oscillation of the free electrons and thus polarisation of charges is stimulated by light incident on the metallic nanoparticles from a light source. Energy from the oscillating free electrons may be dissipated by several mechanisms, including heat. Therefore, when the metallic nanoparticles are irradiated with a light source, the metallic nanoparticles generate heat by surface plasmon resonance.

As used herein, the term“metallic nanoparticles” refers to metallic particles having a maximum diameter of about 1 micrometre or less. Metallic nanoparticles that generate heat by surface plasmon resonance when excited by incident light may also be known as plasmonic nanoparticles.

As used herein, an‘aerosol-generating device’ relates to a device that may interact with an aerosol-forming substrate to generate an aerosol.

As used herein, the term‘aerosol-forming substrate’ relates to a substrate capable of releasing volatile compounds that may form an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. The aerosol-forming substrate may be part of an aerosol-forming article.

As used herein, the term‘aerosol generating system’ refers to a combination of an aerosol-generating device and one or more aerosol-forming articles for use with the device. An aerosol-generating system may include additional components, such as a charging unit for recharging an on-board electric power supply in an electrically operated or electric aerosol generating device.

Advantageously, the heating element of aerosol-generating devices according to the present invention comprises a plurality of metallic nanoparticles arranged to generate heat by surface plasmon resonance. Therefore, it is not necessary to electrically connect the heating element to a power supply. Advantageously, a heating element that is not electrically connected to a power supply may simplify manufacture of the aerosol-generating device. Advantageously, a heating element that is not electrically connected to a power supply may facilitate servicing of the heating element, replacement of the heating element, or both.

Advantageously, a heating element arranged to generate heat by surface plasmon resonance may provide more homogenous heating of an aerosol-forming substrate when compared to resistive and inductive heating systems. For example, the free electrons of the metallic nanoparticles are excited to the same extent regardless of an angle of incidence of incident light.

Advantageously, a heating element arranged to generate heat by surface plasmon resonance may provide more localised heating when compared to resistive and inductive heating systems. Advantageously, localised heating facilitates heating of discrete portions of an aerosol-forming substrate or a plurality of discrete aerosol-forming substrates. Advantageously, localised heating increases the efficiency of the aerosol-generating device by increasing or maximising the transfer of heat generated by the heating element to an aerosol forming substrate. Advantageously, localised heating may reduce or eliminate undesired heating of other components of the aerosol-generating device.

The heating element may be arranged to receive light from an external light source and generate heat by surface plasmon resonance. An external light source may comprise ambient light. Ambient light may comprise solar radiation. Ambient light may comprise at least one artificial light source external to the aerosol-generating device.

The aerosol-generating device may comprise a light source, wherein the heating element is arranged to receive light from the light source and generate heat by surface plasmon resonance.

The elongate heating element may provide an advantageous alternative to the blade shaped resistive heating elements that are adopted in aerosol-generating devices. The elongate heating element generates heat by exposing the plurality of nanoparticles at its heating surface to a light source. Heat generation may advantageously be limited to the heating surface comprising the metallic nanoparticles. Therefore the use of such plasmonic elongate heating element may have improved efficiencies over those experienced with bladed shaped resistive heaters.

Additionally, the elongate heating element may adapt a shape that is different to the conventional blade shaped heating element. For example the elongate heating element may be a pin shaped element, optionally with a thickened body. Departure from a planar external profile may improve the mechanical strength of the elongate heating element. The departure from a planar external profile may allow heat to be delivered to the aerosol-forming substrate in a more effective manner as compared to conventional substantially thin blade shaped elements.

The elongate heating element may form other three dimensional shapes and external profiles, such as a cone, a cylinder, a cuboid pin or a flat blade.

Optionally, the aerosol-generating device may comprise a plurality of elongate heating elements. Each of the plurality of elongate heating elements may be of the same dimensions. Alternatively, at least one of the plurality of elongate heating elements may comprise different dimensions relative to the other elongate heating elements. Each of the elongate heating elements may be of a same shape. Alternatively, at least one of the plurality of elongate heating elements may be of a different shape relative to the other elongate heating elements. The plurality of elongate heating elements may share the same light source. Alternatively, each of the elongate heating elements may be provided with a discrete light source. Each of the elongate heating elements may share a plurality of light sources. The provision of multiple elongate heating elements may provide a substantial increase in the available surface area of the heating surface in the device. The provision of multiple elongate heating elements may enable multiple heating surfaces to be evenly distributed within the device. This may lead to an aerosol-forming substrate being more homogeneously heated when the aerosol-forming substrate is received in the device. A heating temperature for each of the plurality of elongate heating elements may be individually controllable to provide a more customizable heating profiles provided by the device.

The light source of the aerosol-generating device may not require a relatively large voltage drop to effect surface plasmon resonance. For example, the light source of the aerosol-generating device may comprise one or more light emitting diodes (LEDs). This may allow for a safer and more cost effective power source to be used to power the device. Moreover, it is not necessary to provide a physical connection between the elongate heating element and the light source. Therefore the use of the elongate heating element may advantageously reduce the likelihood of damage to the heating element during service and maintenance. Indeed, because a physical connection between the elongate heating element and the light source need not be provided, the elongate heating element may easily be repaired or replaced. The elongate heating element may also mean that the device is less vulnerable to an external environment because the use of the elongate heating element may eliminate a need for exposed electrical components.

The device may comprise an opening, through which an aerosol-forming substrate may be inserted to be at least partly received in the cavity. In some embodiments the elongate heating element is disposed on a base of the cavity, and extends into the cavity towards the opening. The elongate heating element may extend into the cavity towards the opening along a longitudinal axis of the cavity. In some embodiments, the elongate heating element is arranged to penetrate the aerosol-forming substrate as the aerosol-forming substrate is inserted into the cavity. In some embodiments, the elongate heating element may be provided on a cap for closing the opening of the cavity. In such embodiments, the elongate heating element may be arranged to penetrate an aerosol-forming substrate after the aerosol-forming substrate has been placed in the cavity, for example, by placing the cap over the opening to insert the elongate heating element into the aerosol-forming substrate. Other arrangements may also be adopted. For example the elongate heating element may extend from a sidewall of the cavity and be arranged penetrate an aerosol-forming substrate, which has been inserted through a side in the cavity.

The light transmitting need not necessarily comprise an integral light source. The phrase“light transmitting” as used herein may generally refer to the core being arranged to guide or to convey light from the light source, for example in a manner similar to an optic fibre. The light transmitting core therefore functions as a light conduit for transmitting light emitted from the light source to the heating surface. The light transmitting core may comprise a solid material, which may be optically transparent or semi-transparent. The light transmitting core may comprise a hollow void.

The elongate heating element may be arranged to heat the aerosol-forming substrate continuously during operation of the device. “Continuously” in this context means that heating is not dependent on air flow through the device; power may be delivered to the light source even when there is no airflow through the device. In some embodiments, the device may include means to detect air flow, and the elongate heating element may be arranged to heat the aerosol-forming substrate when the detected air flow level exceeds a threshold level. The threshold level may be indicative of a user drawing on the device.

As used herein, the term‘aerosol-forming substrate’ relates to a substrate capable of releasing volatile compounds that may form an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate.

The aerosol-forming substrate may be part of an aerosol-forming article. The aerosol forming substrate may have any suitable configuration, and may include any of the features described in more detail below.

The elongate heating element may comprise a base having at least one of a lens and a reflecting surface. The lens may refract the light as emitted by the light source, through the light transmitting core, to the heating surface. The refracted light may either be focused or dispersed by the lens to control how much light is transmitted to the heating surface or to portions of the heating surface. This may not only allow for control of the amount of light received by the heating surface, but may also allow for control of the degree of localised surface plasmon resonance at different portions of the heating surface. The reflecting surface reflects light from the light source to the heating surface, either directly or through the lens. The light as emitted by the light source may be consecutively reflected through a series of reflecting surfaces. The light source may be spaced apart from the light transmitting core in the aerosol-generating device.

The light-transmitting core may comprise a transparent material, such as at least one of glass, quartz, a thermosetting plastic, and a fluid. The light-transmitting core may comprise a void. In some embodiments, a void may be provided in one of the above materials such that the light-transmitting core comprises a shell having a hollow core. Preferably the light- transmitting core comprises glass. Glass is a relatively cheap material and has good optical properties, such as optical transparency. Furthermore, glass may advantageously withstand elevated temperatures, and thus may be located close to the heating surface without a significant risk of the glass becoming degraded or damaged by heat from the heating surface.

The light-transmitting core may comprise a filter for filtering certain light emitted from the light source, such as light having wavelength above or below a threshold value or within a range of threshold values. The filter may be a coloured filter. For example the light-transmitting core may be doped with a dye for absorbing light having certain wavelengths of light, such as certain wavelengths of light in the visible light spectrum.

The light source of the aerosol-generating device may comprise at least one of a light emitting diode (LED) and a laser. Advantageously, light emitting diodes and lasers may have a compact size suited to use in an aerosol-generating device. In embodiments in which the light source comprises at least one laser, the at least one laser may comprise at least one of a solid state laser and a semiconductor laser.

The light source may comprise a plurality of light sources. The light sources may be the same type of light source. At least some of the light sources may be different types of light source. The plurality of light sources may comprise any combination of the types of light source described herein. Advantageously, a plurality of light sources may facilitate customisation of a heating profile generated by the aerosol-generating device during use.

At least one of the light sources may be a primary light source and at least one of the light sources may be a backup light source. The aerosol-generating device may be configured to emit light from one or more backup light sources only when one or more of the primary light sources is inoperative.

At least one of the light sources may be arranged to irradiate only a portion of the plurality of metallic nanoparticles. Each of the plurality of light sources may be arranged to irradiate a different portion of the plurality of metallic nanoparticles.

The aerosol-generating device may be configured so that the plurality of light sources irradiate different portions of the plurality of metallic nanoparticles at the same time. Advantageously, irradiating different portions of the plurality of metallic nanoparticles at the same time may facilitate homogenous heating of the heating element. Advantageously, irradiating different portions of the plurality of metallic nanoparticles at the same time may facilitate simultaneous heating of a plurality of discrete aerosol-forming substrates.

The aerosol-generating device may be configured so that the plurality of light sources irradiate different portions of the plurality of metallic nanoparticles at different times. Advantageously, irradiating different portions of the plurality of metallic nanoparticles at different times may facilitate heating of different portions of an aerosol-forming substrate at different times. Advantageously, irradiating different portions of the plurality of metallic nanoparticles at different times may facilitate heating of a plurality of discrete aerosol-forming substrates at different times.

The light-transmitting core is arranged to transmit light from the light source of the aerosol-generating device to the plurality of metallic nanoparticles. The light-transmitting core may also be arranged to transmit ambient light to the plurality of metallic nanoparticles from a light source external to the aerosol-generating device. The light source external to the aerosol generating device is referred to herein as“the ambient light source”. The ambient light may comprise solar radiation. The ambient light source may comprise at least one artificial light source external to the aerosol-generating device. The light transmitting core may receive ambient light from the ambient light source directly, or it may receiving the ambient light via one or more additional light transmitting elements in the device. Ambient light may be received into the aerosol-generating device via one or more windows or openings on the external surface of the aerosol-generating device. The ambient light source may function to supplement the light source of the aerosol-generating device. This may be advantageous when seeking to pre-heat the aerosol-forming substrate to an elevated temperature prior to operating the internal light source of the device. This may also advantageously reduce the amount of power required by the light source of the aerosol-generating device. The aerosol-generating device may comprise an ambient light controlling means for controlling the amount of ambient light that light transmitting core may receive from the ambient light source. The ambient light controlling means may comprise an automatic controlling means such as an automatic shutter. The ambient light controlling means may comprise a manual controlling means, such as a releasable cap for covering one or more windows or openings in the device.

The light source may comprise a light source arranged to emit light in the visible light range of the electromagnetic spectrum. The light source may comprise a light source arranged to emit light beyond the visible light range of the electromagnetic spectrum, such as at least one of an ultraviolet light source and an infrared light source. This may advantageously excite a broader range of nanoparticles, such as nanoparticles of varying sizes or compositions.

Advantageously, providing the aerosol-generating device with a light source may allow the heating element to generate heat without receiving light from an external light source. Advantageously, providing the aerosol-generating device with a light source may provide improved control of the illumination of the heating element. Advantageously, controlling the illumination of the heating element controls the temperature to which the heating element is heated by surface plasmon resonance. Advantageously, a light source configured to emit visible light may be inexpensive, convenient to use, or both.

Preferably, the light source is configured to emit light comprising at least one wavelength between 380 nanometres and 700 nanometres.

Preferably, the light source is configured for a peak emission wavelength of between about 495 nanometres and about 580 nanometres. As used herein, “peak emission wavelength” refers to the wavelength at which a light source exhibits maximum intensity. Advantageously, a peak emission wavelength of between about 495 nanometres and about 580 nanometres may provide maximum heating of the heating element by surface plasmon resonance, particularly when the plurality of metallic nanoparticles comprises at least one of gold, silver, platinum, and copper.

Using a laser as the light source, may enable the emission of light within a relatively narrow range of wavelengths. The narrow range of wavelengths may be a range of wavelengths matched to the size and composition of the nanoparticles, as will later be described. This may advantageously improve efficiency, most, if not all light outputted by the light source may be absorbed by the metallic nanoparticles to generate heat by surface plasmon resonance. In some embodiments, the light source comprises a light emitting diode (LED). Such a light source may be advantageously powered by a relatively low power input, and be relatively energy efficient. Additionally, such a light source may be relatively robust and simple in construction in comparison to other light sources.

The amount of light emitted by the light source, such as a number of photons emitted per second, may be varied by controlling an amplitude, or a frequency, or a combination of amplitude and frequency of the emitted light. The amount of light emitted by the light source, such as number of photons emitted per second may be varied by emitting light pulses.

The plurality of metallic nanoparticles may comprises at least one of gold, silver, platinum, copper, palladium, aluminium, chromium, titanium, rhodium, and ruthenium. The plurality of metallic nanoparticles may comprise at least one metal in elemental form. The plurality of metallic nanoparticles may comprise at least one metal in a metallic compound. The metallic compound may comprise at least one metal nitride.

Preferably, the plurality of metallic nanoparticles comprises at least one of gold, silver, platinum, and copper. Advantageously, gold, silver, platinum, and copper nanoparticles may exhibit strong surface plasmon resonance when irradiated with visible light.

The plurality of metallic nanoparticles may comprise a single metal. The plurality of metallic nanoparticles may comprise a mixture of different metals. The plurality of metallic nanoparticles may comprise a plurality of first nanoparticles comprising a first metal and a plurality of second nanoparticles comprising a second metal.

At least some of the plurality of metallic nanoparticles may each comprise a mixture of two or more metals. At least some of the plurality of metallic nanoparticles may comprise a metal alloy. At least some of the plurality of metallic nanoparticles may each comprise a core shell configuration, wherein the core comprises a first metal and the shell comprises a second metal.

Preferably the plurality of metallic nanoparticles comprises a number average maximum diameter that is less than or equal to the peak emission wavelength of the light source.

The plurality of metallic nanoparticles may comprise a number average maximum diameter of less than about 700 nanometres, preferably less than about 600 nanometres, preferably less than about 500 nanometres, preferably less than about 400 nanometres, preferably less than about 300 nanometres, preferably less than about 200 nanometres, preferably less than about 150 nanometres, preferably less than about 100 nanometres.

The elongate heating element may comprise a substrate layer and a coating layer positioned on at least a portion of the substrate layer, wherein the coating layer comprises the plurality of metallic nanoparticles. Advantageously, the substrate layer may be formed from a material selected for desired mechanical properties. Advantageously, the coating layer may be formed to optimise the surface plasmon resonance of the plurality of metallic nanoparticles when the coating layer is exposed to light from a light source.

The substrate layer may be formed from any suitable material. The substrate layer may comprise a metal. The substrate layer may comprise a polymeric material. The substrate layer may comprise a ceramic.

The substrate layer may be electrically conductive. The substrate layer may be electrically insulating.

The coating layer may be provided on the substrate layer using any suitable process. The coating layer may be formed by depositing the plurality of metallic nanoparticles on the substrate layer using a physical vapour deposition process.

The coating layer may be a substantially continuous layer.

The coating layer may comprise a plurality of discrete areas of metallic nanoparticles, wherein the plurality of discrete areas are spaced apart from each other on the substrate layer. Advantageously, a plurality of discrete areas of metallic nanoparticles may facilitate heating of a plurality of discrete portions of an aerosol-forming substrate. Advantageously, a plurality of discrete areas of metallic nanoparticles may facilitate heating of a plurality of discrete aerosol forming substrates.

The aerosol-generating device may comprise a light source arranged to irradiate a plurality of the discrete areas of metallic nanoparticles. The aerosol-generating device may comprise a plurality of light sources arranged to irradiate the plurality of discrete areas of metallic nanoparticles. Each of the plurality of light sources may be arranged to irradiate only one of the discrete areas of metallic nanoparticles.

The surface of the elongate heating element may comprise a non-stick coating, or friction reducing coating. Where a coating layer comprising at least some of the plurality of metallic nanoparticles is provided, the non-stick or friction reducing coating is preferably provided over at least a portion of the coating layer comprising metallic nanoparticles. The use of a non-stick coating may reduce friction between the heating surface and a corresponding contact surface of the aerosol-forming substrate. This may help the aerosol forming substrate to be more easily removed from the heating surface. This may also help to reduce the amount of residue that may be left behind at the heating surface after the aerosol forming substrate has been removed. The non-stick coating may be any suitable friction reducing coating, such as a polytetrafluoroethylene (PTFE) coating. Optionally, the surface of the elongate heating element may comprise a friction reducing surface profile, such as a profile comprising dimples.

The device may comprise an annular heating element extending along at least a portion of a sidewall of the cavity, the annular heating element and the elongate heating element defining an annular space there-between. In use, an aerosol-forming substrate may be disposed in the annular space so that it may be heated by one or both of the annular heating element and the elongate heating element. The provision of the combination of the annular heating element and the elongate heating element advantageously allows both internal and external heating of the aerosol-forming substrate, either simultaneously, independently, or in a sequential manner. The combined use of an elongate heating element and an annular heating element may provide a more efficient heating system because the combination of internal and external heating may promote homogeneous heating of the aerosol-forming substrate.

The elongate heating element may comprise an electrically resistive portion arranged to receive a supply of electrical power. During use, a supply of electrical power to the electrically resistive portion may resistively heat the electrically resistive portion. Advantageously, the electrically resistive portion may provide a source of heat in addition to heat generated by surface plasmon resonance of the plurality of metallic nanoparticles.

The plurality of metallic nanoparticles may form the electrically resistive portion.

In embodiments in which the elongate heating element comprises a substrate layer and a coating layer, at least one of the substrate layer and the coating layer may form the electrically resistive portion. The substrate layer may comprise an electrically resistive material. The electrically resistive material may comprise at least one of an electrically resistive metal and an electrically resistive ceramic. The substrate layer may be formed from the electrically resistive material. The substrate layer may comprise a woven material, wherein a plurality of threads of the electrically resistive material form at least part of the woven material.

In embodiments in which the aerosol-generating device comprises an electrical power supply and a controller, preferably the controller is arranged to provide a supply of electrical power from the electrical power supply to the electrically resistive portion.

The aerosol-generating device may be arranged to generate heat using the electrically resistive portion in addition to generating heat by surface plasmon resonance of the plurality of metallic nanoparticles. The aerosol-generating device may be arranged to generate heat using the electrically resistive portion as an alternative to generating heat by surface plasmon resonance of the plurality of metallic nanoparticles.

The aerosol-generating device may be arranged to generate heat using the electrically resistive portion as a backup to generating heat by surface plasmon resonance of the plurality of metallic nanoparticles. For example, the aerosol-generating device may be arranged to generate heat using the electrically resistive portion in the event that heating of the plurality of metallic nanoparticles by surface plasmon resonance is insufficient.

The aerosol-generating device may be arranged to generate heat using the electrically resistive portion at the start of a heating cycle. In other words, the electrically resistive portion may be used to generate heat to raise the temperature of the heating element to an initial operating temperature. The aerosol-generating device may be arranged to reduce or terminate a supply of electrical power to the electrically resistive portion when the temperature of the heating element reaches an initial operating temperature.

The annular heating element may operate to supplement plasmonic heating of the elongate heating element. The annular heating element may operate as a backup heating element, such as in case of a failure involving the elongate heating element or the light source.

The annular heating element may comprise a resistive heating element. That is the annular heating element may comprise an electrically resistive portion arranged to receive a supply of electrical power. During use, a supply of electrical power to the electrically resistive portion may resistively heat the electrically resistive portion. Advantageously, the electrically resistive portion may provide a source of heat in addition to or as an alternative to heat generated by surface plasmon resonance of the plurality of metallic nanoparticles. Resistive heating elements may advantageously be cheap and simple in construction. Thus the use of an annular heating element as a supplementary heating element or a backup heating element may be economical. 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 comprising 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, platinum, gold and silver. Examples of suitable metal alloys include stainless steel, nickel-, cobalt-, chromium-, aluminium- titanium- zirconium-, hafnium-, niobium-, molybdenum-, tantalum-, tungsten-, tin-, gallium-, manganese-, gold- 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.

The annular heating element may comprise an inductive coil which generates an eddy current within the cavity, so as to heat a ferrous susceptor. The wall of the cavity may comprise the susceptor. The susceptor may be a discrete piece or pieces of ferrous metal embedded in the aerosol-forming substrate. Similar to plasmonic heating, inductive heating generates localised heat at the susceptor, therefore reducing waste heat.

The annular heating element may comprise a plurality of metallic nanoparticles arranged to receive light from a light source of the aerosol-generating device and generate heat by surface plasmon resonance. The light source for the annular heating element may comprise the same light source as that used for the elongate heating element, where light emitted by said light source is transmitted through a suitable light guiding conduit to each of the annular heating element and elongate heating element. The light source for the annular heating element may alternatively comprise a different light source to the light source used for the elongate heating element. In this case, the different light source may operate simultaneously or independently to the light source used for the elongate heating element.

The elongate heating element and the annular heating element may be independently controllable. For example, the two heating elements may operate independently to achieve different temperatures or to apply heating at different moments in time. The elongate heating element and the annular heating element may be arranged to provide different heating profiles.

The annular heating element may comprise a mount slidable with respect to the elongate heating element. The mount may be formed integrally with the annular heating element, or alternatively the annular heating element may be mounted or attached onto the mount. The mount may be slidable between an operating position where the elongate heating element is inserted into the aerosol-forming substrate, and a discharge position where the mount is arranged to discharge the aerosol-forming substrate from the elongate heating element. The slidable mount may therefore be used as an ejector mechanism. This arrangement advantageously allows the user to remove or replace an expired aerosol-forming substrate without having to directly touch or grip the aerosol-forming substrate.

Plasmonic heating elements do not require an electrical connection between the power source and the plasmonic heating element. Therefore the use of a plasmonic annular heating element advantageously enables an additional annular heating element to be provided on the slidable mount without affecting the reliability of the annular heating element.

According to a second aspect of the present invention, there is provided an aerosol generating device comprising: a cavity for receiving at least part of an aerosol-forming substrate; a light source; and an annular heating element extending along at least a portion of a sidewall of the cavity, and arranged to surround at least a part of an aerosol-forming substrate when the aerosol-forming substrate is received within the cavity; wherein said annular heating element comprises a heating surface comprising a plurality of metallic nanoparticles arranged to receive light from the light source to generate heat by surface plasmon resonance.

The plasmonic annular heat element may extend along at least a portion of the length of the cavity, and preferably along the entire length of the cavity. This may allow the plasmonic annular heating element to form a heating jacket around an aerosol-forming substrate, when the substrate is inserted into the cavity, and thereby supply heat to the aerosol-forming substrate. Preferably, the plasmonic annular heating element is arranged to contact an outer surface of the aerosol-forming substrate when the aerosol-forming substrate is received within the cavity.

Preferably, the light source for the annular heating element is spaced apart from the annular heating element to define an air flow passage therebetween. This may advantageously allow incoming air to flow between the light source and the annular heating element as the incoming air travels towards the cavity, and any aerosol-forming substrate contained therein. This is advantageous because it helps the air to be heated before it reaches the aerosol-forming substrate. This is also particularly advantageous because the air may also cool the light source or portions of the device other than the annular heating element and the aerosol-forming substrate. This may help to reduce any thermal damage to such portions of the device not intended to be heated by the annular heating element. Put another way, this portion of the airflow passage may be used to pre-heat air before it reaches the aerosol-forming substrate, and cool portions of the device which do not require heating.

According to a third aspect of the present invention, there is provided an aerosol generating system comprising the aerosol-generating device as described in the first aspect or the second aspect of the present invention, and an aerosol-generating article comprising an aerosol-forming substrate. The aerosol-forming substrate may comprise one or more of any of the features described above or below in respect of the other aspects of the present invention.

According to a fourth aspect of the present invention, there is provided an aerosol generating article comprising a first aerosol-forming substrate and a second aerosol-forming substrate extending around the first aerosol-forming substrate in a coaxial arrangement. Such arrangement advantageously allows two different aerosol-forming substrates to be independently heated by an elongate heating element and, where provided, an annular heating element as described in other aspects of the present invention. In some embodiments, the first aerosol-forming substrate may comprise a liquid aerosol-forming substrate arranged to be heated by the elongate heating element, whilst the second aerosol-forming substrate may comprise a solid aerosol-forming substrate, such as a tobacco plug, arranged to be heated by an annular heating element. In some embodiments, the first aerosol-forming substrate may comprise a solid aerosol-forming substrate, whilst the second aerosol-forming substrate may comprise a liquid aerosol forming substrate. In some embodiments, the first and second aerosol-forming substrates may both comprise liquids. In some embodiments, the first and second aerosol-forming substrates may both comprise solids. As used hereinabove, the terms “liquid” and“solid” refer to a state of the aerosol-forming substrate at room temperature or 25°C.

Preferably, the substrates are held in a fixed position with respect to one another. More specifically, preferably the first aerosol-forming substrate is secured to the second aerosol- forming substrate such that the substrates are held in a fixed position relative to each other. The substrates may therefore not be movable independent of one another. The substrates may be secured to one another by an affixing member, such a wrapper having one or more adhesive surfaces. The first aerosol-forming substrate may have a central cavity extending along a longitudinal axis of the aerosol-generating article.

According to a fifth aspect of the present invention, there is provided an aerosol generating article comprising a first aerosol-forming substrate having a central cavity, bore or channel, extending along a longitudinal axis of the aerosol-generating article. The central cavity, bore or channel, may correspond to a shape of an elongate heating element, as described above. This advantageously allow the elongate heating element to penetrate the aerosol-forming substrate with ease. The central cavity, bore or channel may comprise dimensions slightly smaller than dimensions of the elongate heating element. Advantageously, this allows the elongate heating element to be received within the central cavity, bore or channel in an interference fit. As the aerosol-forming substrate is depleted, the dimensions of the central cavity, bore or channel may expand. This advantageously allows the aerosol forming substrate to be easily removed after use. The aerosol-generating article of the fourth aspect of the present invention may have any of the features of the aerosol-generating article of the fifth aspect of the present invention, and vice versa.

The aerosol-forming article may have a total length between approximately 30 mm and approximately 100 mm. The aerosol-forming article may have an external diameter between approximately 5 mm and approximately 12 mm. The aerosol-forming article may comprise a filter plug. The filter plug may be located at a downstream end of the aerosol-forming article. The filter plug comprise a cellulose acetate filter plug. The filter plug is approximately 7 mm in length in some embodiments. In some embodiments, the filter plug may have a length of between approximately 5 mm to approximately 10 mm.

In some embodiments, the aerosol-forming article has a total length of approximately 45 mm. The aerosol-forming article may have an external diameter of approximately 7.2 mm. The aerosol-forming substrate may have a length of approximately 10 mm. Alternatively, the aerosol-forming substrate may have a length of approximately 12 mm. The diameter of the aerosol-forming substrate may be between approximately 5 mm and approximately 12 mm. The aerosol-forming article may comprise an outer paper wrapper. The aerosol-forming article may comprise a separation between the aerosol-forming substrate and the filter plug. The separation may be approximately 18 mm. The separation may be in the range of approximately 5 mm to approximately 25 mm.

The aerosol-forming substrate may be a solid aerosol-forming substrate. Alternatively, the aerosol-forming substrate may comprise both solid and liquid components. The aerosol forming substrate may comprise a tobacco-containing material comprising volatile tobacco flavour compounds which are released from the substrate upon heating. Alternatively, the aerosol-forming substrate may comprise a non-tobacco material. The aerosol-forming substrate may further comprise an aerosol former that facilitates the formation of a dense and stable aerosol. Examples of suitable aerosol formers are glycerine and propylene glycol.

If the aerosol-forming substrate is a solid aerosol-forming substrate, the solid aerosol forming 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, homogenised tobacco, extruded tobacco, cast leaf tobacco and expanded tobacco. The solid aerosol-forming substrate may be in loose form, or may be provided in a suitable container or cartridge. Optionally, the solid aerosol forming substrate may comprise additional tobacco or non-tobacco volatile flavour compounds, to be released upon heating of the substrate. The solid aerosol-forming substrate may also contain capsules that, for example, include the additional tobacco or non-tobacco volatile flavour compounds and such capsules may melt during heating of the solid aerosol-forming substrate.

As used herein, homogenised tobacco refers to material formed by agglomerating particulate tobacco. Homogenised tobacco may be in the form of a sheet. Homogenised tobacco material may have an aerosol-former content of greater than 5% on a dry weight basis. Homogenised tobacco material may alternatively have an aerosol former content of between 5% and 30% by weight on a dry weight basis. Sheets of homogenised tobacco material may be formed by agglomerating particulate tobacco obtained by grinding or otherwise comminuting one or both of tobacco leaf lamina and tobacco leaf stems. Alternatively, or in addition, sheets of homogenised tobacco material may comprise one or more of tobacco dust, tobacco fines and other particulate tobacco by-products formed during, for example, the treating, handling and shipping of tobacco. Sheets of homogenised tobacco material may comprise one or more intrinsic binders, that is tobacco endogenous binders, one or more extrinsic binders, that is tobacco exogenous binders, or a combination thereof to help agglomerate the particulate tobacco; alternatively, or in addition, sheets of homogenised tobacco material may comprise other additives including, but not limited to, tobacco and nontobacco fibres, aerosol-formers, humectants, plasticisers, flavourants, fillers, aqueous and non-aqueous solvents and combinations thereof.

Optionally, the solid aerosol-forming substrate may be provided on or embedded in a thermally stable carrier. The carrier may take the form of powder, granules, pellets, shreds, spaghettis, strips or sheets. Alternatively, the carrier may be 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.

The solid aerosol-forming substrate may be deposited on the surface of the carrier in the form of, for example, a sheet, foam, gel or slurry. The solid aerosol-forming 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.

Although reference is made to solid aerosol-forming substrates above, it will be clear to one of ordinary skill in the art that other forms of aerosol-forming substrate may be used with other embodiments. For example, the aerosol-forming substrate may be a liquid aerosolforming substrate. If a liquid aerosol-forming substrate is provided, the aerosol-generating device preferably comprises means for retaining the liquid. For example, the liquid aerosolforming substrate may be retained in a container. Alternatively or in addition, the liquid aerosolforming substrate may be absorbed into a porous carrier material. The porous carrier material may be made from any suitable absorbent plug or body, for example, a foamed metal or plastics material, polypropylene, terylene, nylon fibres or ceramic. The liquid aerosol-forming substrate may be retained in the porous carrier material prior to use of the aerosol-generating device or alternatively, the liquid aerosol-forming substrate material may be released into the porous carrier material during, or immediately prior to use. For example, the liquid aerosolforming substrate may be provided in a capsule. The shell of the capsule preferably melts upon heating and releases the liquid aerosol-forming substrate into the porous carrier material. The capsule may optionally contain a solid in combination with the liquid.

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. The liquid aerosol-forming substrate may comprise at least one of nicotine or a tobacco product. Additionally, or alternatively, the liquid aerosol-forming substrate may comprise another target compound for delivery to a user. In embodiments in which the liquid aerosol forming substrate comprises nicotine, the nicotine may be included in the liquid aerosol forming substrate with an aerosol-former.

Preferably, the aerosol-generating device comprises an electrical power supply and a controller configured to supply electrical power from the electrical power supply to the light source. In embodiments in which the aerosol-generating device comprises a plurality of light sources, the electrical power supply may comprise a single source of electrical power arranged to supply electrical power to the plurality of light sources.

In embodiments in which the plurality of light sources are configured to irradiate different portions of the plurality of metallic nanoparticles to heat a plurality of discrete aerosol forming substrates, the controller may selectively supply electrical power to at least some of the plurality of light sources to selectively heat at least some of the plurality of discrete aerosol- forming substrates. The controller may selectively vary a supply of electrical power to at least some of the plurality of light sources to vary a ratio of heating of at least some of the plurality of discrete aerosol-forming substrates.

Advantageously, by varying the relative heating of at least some of a plurality of discrete aerosol-forming substrates, the aerosol-generating device may vary the composition of an aerosol delivered to a user.

Preferably, the aerosol-generating device comprises a user input device. The user input device may comprise at least one of a push-button, a scroll-wheel, a touch-button, a touch-screen, and a microphone. Advantageously, the user input device allows a user to control one or more aspects of the operation of the aerosol-generating device. In embodiments in which the aerosol-generating device comprises a light source, a controller and an electrical power supply, the user input device may allow a user to activate a supply of electrical power to the light source, to deactivate a supply of electrical power to the light source, or both.

In embodiments in which the controller is configured to selectively supply electrical power to at least some of a plurality of light sources, preferably the controller is configured to selectively supply electrical power to at least some of the plurality of light sources in response to a user input received by the user input device.

In embodiments in which the controller is configured to selectively vary a supply of electrical power to at least some of a plurality of light sources, preferably the controller is configured to selectively vary a supply of electrical power to at least some of the plurality of light sources in response to a user input received by the user input device.

The power supply may be any suitable power supply, for example a DC voltage source such as a battery. In one embodiment, the power supply is a Lithium-ion battery. Alternatively, the power supply may be a Nickel-metal hydride battery, a Nickel cadmium battery, or a Lithium based battery, for example a Lithium-Cobalt, a Lithium-Iron-Phosphate, Lithium Titanate or a Lithium-Polymer battery.

The at least one battery may include a rechargeable lithium ion battery. The electrical power supply may comprise another form of charge storage device such as a capacitor. The electrical power supply may require recharging. The electrical power supply may have a capacity that allows for the storage of enough energy for one or more uses of the aerosol generating device. For example, the electrical power supply may have sufficient capacity to allow for the continuous generation of aerosol for a period of around six minutes, corresponding to the typical time taken to smoke a conventional cigarette, or for a period that is a multiple of six minutes. In another example, the electrical power supply may have sufficient capacity to allow for a predetermined number of puffs or discrete activations.

The controller may be configured to commence a supply of electrical power from the electrical power supply to the light source at the start of a heating cycle. The controller may be configured to terminate a supply of electrical power from the electrical power supply to the light source at the end of a heating cycle.

The controller may be configured to provide a continuous supply of electrical power from the electrical power supply to the light source.

The controller may be configured to provide an intermittent supply of electrical power from the electrical power supply to the light source. The controller may be configured to provide a pulsed supply of electrical power from the electrical power supply to the light source.

Advantageously, a pulsed supply of electrical power to the light source may facilitate control of the total output from the light source during a time period. Advantageously, controlling a total output from the light source during a time period may facilitate control of a temperature to which the heating element is heated by surface plasmon resonance.

Advantageously, a pulsed supply of electrical power to the light source may increase thermal relaxation of free electrons excited by surface plasmon resonance compared to other relaxation processes, such as oxidative and reductive relaxation. Therefore, advantageously, a pulsed supply of electrical power to the light source may increase heating of the heating element. Preferably, the controller is configured to provide a pulsed supply of electrical power from the electrical power supply to the light source so that the time between consecutive pulses of light from the light source is equal to or less than about 1 picosecond. In other words, the time between the end of each pulse of light from the light source and the start of the next pulse of light from the light source is equal to or less than about 1 picosecond.

The controller may be configured to vary the supply of electrical power from the electrical power supply to the light source. In embodiments in which the controller is configured to provide a pulsed supply of electrical power to the light source, the controller may be configured to vary a duty cycle of the pulsed supply of electrical power. The controller may be configured to vary at least one of a pulse width and a period of the duty cycle.

The aerosol-generating device may comprise a temperature sensor. The temperature sensor may be arranged to sense a temperature of at least one of the heating element and an aerosol-forming substrate during use of the aerosol-generating device. The aerosol generating device may be configured to vary a supply of electrical power to the light source in response to a change in temperature sensed by the temperature sensor. In embodiments in which the aerosol-generating device comprises an electrical power supply and a controller, preferably the controller is configured to vary the supply of electrical power from the electrical power supply to the light source in response to a change in temperature sensed by the temperature sensor.

Features described in relation to one aspect may equally be applied to other aspects of the invention.

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

Figure 1 is a sectional view of an aerosol-generating system according to an embodiment of the present invention;

Figures 2a and 2b are respective sectional views of a plasmonic elongate heating element and a plasmonic annular heating element in the aerosol-generating system of Figure 1.

Figures 3a and 3b are respective sectional view and plan view of a heater assembly comprising the plasmonic elongate heating element and the plasmonic annular heating element of Figure 1 ;

Figures 4a and 4b are respective sectional views of the heater assembly of Figures 3a and 3b in an operating position and in a discharge position;

Figure 5 is a sectional view of an aerosol-generating system according to another embodiment of the present invention; and

Figure 6 is a sectional view of an aerosol-generating article according to yet another embodiment of the present invention.

Figure 1 shows an aerosol-generating system 10 comprising an aerosol-generating device 20 and an aerosol-forming article 100 for use with the aerosol-generating device 20. The aerosol-forming article 100 in this illustrated example comprises an aerosol-forming substrate 102 comprising a tobacco plug, a mouthpiece 106 and an intermediate portion 104 between the aerosol-forming substrate 102 and the mouthpiece 106. In use, a user puffs on the mouthpiece to receive a volume of aerosol generated at the aerosol-forming substrate 102 through the intermediate portion 104 and the mouthpiece 106. The intermediate portion 104 comprises an aerosol cooling element, such as a crimped polylactic acid sheet for cooling the generated aerosol.

The aerosol-generating device 20 comprises a housing 12 having a cavity 22 for receiving the aerosol-forming article 100 through an opening at a proximal end 11 of the housing. The device 20 comprises an elongate heating element 30 in the cavity 22. As the aerosol-forming article 100 is inserted into the cavity 22 through the opening, the elongate heating element penetrates the aerosol-forming substrate 102, for internally heating the aerosol-forming substrate 102. In the illustrated embodiment, an additional heating element 40 is provided along an interior wall of the cavity 22. The additional heating element 40 comprises an annular heating element for externally heating the aerosol-forming substrate 102. It will be appreciated that in other embodiments, the device 20 may be provided with only the elongate heating element 30, without an additional annular heating element 40. In other embodiments, the device 20 may be provided with only the annular heating element 40, without an additional elongate heating element 30. The illustrated embodiment provides an elongate heating element 30 and an annular heating element 40 that are capable of heating both the interior and the external surface of the aerosol-forming substrate 102 simultaneously, or in a sequential manner. In some other embodiments, only one of the elongate heating element 30 and the annular heating element 40 is provided.

The elongate heating element 30 and the annular heating element 40 in the illustrated embodiment are plasmonic heating elements, which generate heat by surface plasmon resonance (SPR). More specifically, plasmonic heating elements comprise a heating surface comprising a plurality of metallic nanoparticles. Incident light absorbed by the metallic nanoparticles results in a collective oscillation of free electrons of the metallic nanoparticles and polarization of charges at the surface of the nanoparticles. In order for the electrons to relax to their initial state, the nanoparticles release the surplus of energy in form of heat. Generally, the nanoparticles as used in the heating elements 30, 40 have particle sizes that are equal to or less than the wavelength of the incident light. It will therefore be appreciated that metallic nanoparticles having any of a variety of diameters may be used, and a light source having an appropriate wavelength may be selected based on the given diameter. Similarly, a light source having any of a variety of wavelengths may be used and a diameter of metal nanoparticles may then be selected based on the given wavelength.

The device 10 comprises an electrical energy supply 24 in the housing 12, for example a rechargeable lithium ion battery. The device 10 further comprises a controller communicable coupled to one or more light sources. In the illustrated embodiment, the light sources comprise Light Emitting Diodes (LED) 38, 48. The controller is also communicable coupled to the electrical energy supply 24 and a user interface 26. In this embodiment, the user interface 26 comprises a mechanical button. Upon activating the user interface 26, the controller controls the power supplied to the light source 38, 48 in order to independently heat the elongate heating element 30 and the annular heating element 40 to a required operating temperature. In some embodiments, the controller independently controls the power supplied to the light source 38, 48, to independently heat the elongate heating element 30 and the annular heating element 40 to provide respective heating profiles over a period of time in which the device is in use.

Figure 2a shows an example of the elongate heating element 30. To facilitate its insertion into the aerosol-forming substrate 102, the elongate heating element 30 is shaped as a pin. The elongate heating element 30 comprises a three dimensional body, which, in comparison to a conventional blade heating element, improves its mechanical strength and thus it is more robust for insertion into the aerosol-forming substrate 102. The three dimensional body not only fits snuggly in the aerosol-forming article 102 to hold it in place, but it also allows heat to dissipate homogeneously towards the aerosol-forming substrate 102 in all three dimensions. The elongate heating element 30 comprises a light transmitting core 32 and a heating surface 34. The heating surface 34 is provided at an external surface of the light transmitting core 32. As discussed above with respect to Figure 1 , the heating surface 34 comprises the plurality of metallic nanoparticles for effecting surface plasmon resonance.

The elongate heating element 30 comprises a lens 36 at its base for refracting and focusing light emitted by LED 38, through the light transmitting core 32 towards the heating surface 34. The light transmitting core 32 functions as a light conduit for transmitting light emitted by the LED 38 towards the heating surface 34 to raise the temperature of the heating surface to a temperature of between 200 and 350 degrees centigrade. In the illustrated embodiment, the light transmitting core 32 comprises glass. However, it will be appreciated that the light transmitting core 32 may comprise other optically transparent or translucent materials, such as quartz or a fluid. In some embodiments, the light transmitting core 32 comprises a hollow chamber or void. This reduces a weight of the aerosol-generating device.

Figure 2b shows an example of the annular heating element 40 as used in the aerosol generating device 20 of Figure 1. The annular heating element 40 is provided along a wall of the cavity 22 and is mounted on a mount 60. The annular heating element 40 comprises an outer annular heating tube 42a and an inner annular tube 42b with an annular gap defined in between. The annular gap forms an air flow passage 50 for providing an ambient air supply to the aerosol-forming substrate 102 as received in the cavity 22.

A heating surface 44 is defined at the internal surface of inner annular tube 42b, and comprises a plurality of metallic nanoparticles for generating heat by surface plasmon resonance. Both of the outer annular heating tube 42a and inner annular heating tube 42b comprise an optically transparent or translucent material, such that light emitted by the LED 48 is transmittable through the annular tubes 42a, 42b. Such arrangement allows the nanoparticles as on the heating surface 44 to absorb incident light from the light source to generate heat by surface plasmon resonance. The annular heating element 40 may operate simultaneously as the elongate heating element 30, or it may operate independently to the elongate heating element 30 depending the amount of heating required or a distribution of heating required.

In some other embodiments, alternative light sources may be used as the light source. For example the light source may comprise a laser diode. The laser diode permits maximum excitation of a particular type of nanoparticles. In some embodiments, the lens 36 of the elongate heating element 30 may be in connection with a light conduit (not shown) extending towards an environment external to the housing 12 of the device 20, to capture and transmit an external light, such as natural daylight or ambient light, towards the heating surface 34 of the elongate heating element 30. In such cases the external light as collected at the lens 36 is may be of a lower intensity in comparison to the artificial light source 38. Nevertheless the external light source may be used for preheating the aerosol-forming substrate 102 to an elevated temperature above an ambient temperature, thus the power consumption at the artificial light source 38 may accordingly be reduced.

In this example, the heating surfaces 34, 44 are coated with a layer of silver nanoparticles with a mean diameter of 10Onm, although nanoparticles of smaller sizes are also applicable. Alternatively other metal colloid or nanoparticles may be used, for example gold or platinum nanoparticles. A mixture of metallic nanoparticles may also be applied at the heating surface 34, 44 for providing plasmonic heating. As the quantity of nanoparticles is a critical factor governing a power output of the heating element 30, 40, it is preferable to provide as many nanoparticles as possible on a given heating surface. Therefore, in order to increase the nanoparticle density and thus to increase heat generated by surface plasmon resonance, the heating surface, in some embodiments, comprises a plurality of nanoparticle layers for building up a total number of available metallic nanoparticles.

Figure 3a is a cross-sectional view of a heater assembly comprising the elongate heating element 30 and the annular heating element 40 as shown in Figures 2a and 2b respectively. Figure 3b is a sectional view taken across the heater assembly along a dotted line in Figure 3a. In this example, the heating surface 34, 44 is arranged to contact, or at least be in close proximity to, the aerosol-forming substrate 102 during use. As used herein, the term“close proximity” refers to a separation of 3mm or less. In this way, each of the elongate heating element 30 and the annular heating element 40 are arranged to heat the aerosol forming substrate to generate aerosol.

As shown in Figure 3a, the annular air flow passage 50 extends between an air inlet 52 at the proximal end 11 of the cavity 22 and an air outlet 54 adjacent to an outlet conduit 56 defining a distal end of the cavity 22. The outlet conduit 56 comprises a porous wall 58 which abuts the aerosol-forming substrate 102 when the aerosol-forming substrate 102 is received in the cavity 22. In use, the user puffs on the mouthpiece 104 to draw in an air supply from the air inlet 52, through the air flow passage 50, through the air outlet 54 to the air conduit 56 and through the air conduit 56 towards the aerosol-forming substrate 102, as illustrated by an air flow path indicated by the arrows in Figure 3a. The outlet conduit 56 allows the air supply to be evenly distributed across a width of the aerosol-forming substrate 102 and thus minimises the formation of stagnated air pockets.

As the air passes through the annular air flow passage 50, it is first heated by the heating surface 44 before being drawn into the aerosol-forming substrate 102, resulting in a warmer air supply at the aerosol-forming substrate 102. Moreover, the flow of ambient air supply also cools down the LED 48 to protect it from overheating. A warmer air supply to the upstream sections of the aerosol-forming substrate 102 also prevents unwarranted vapor condensation in the cavity 22 and limits formation of oversized aerosol droplets.

In some embodiments, the heating surface 34 may comprise a plurality of discrete heating sections each having a different nanoparticle density or a different number of nanoparticle layers. This enables a variation in temperature rise across the different heating sections when all of the heating sections are exposed to a uniform light source. This is beneficial because it allows selective localised heating. For example, since the upstream heating sections, e.g. those closest to the air inlet, are more affected by the incoming cooling air supply, these heating sections may be coated with more nanoparticles in comparison to downstream heating sections proximal to the mouthpiece 106. In some cases, multiple heating sections also allows selective heating of aerosol-forming substrate, thus allowing different tobacco and flavoring compositions along the substrate to be heated to different temperatures.

In some embodiments, the LED 38, 48 each comprises a plurality of independently operable LEDs. For example, the plurality of LEDs may each emit light in a sequential manner, or at different intensity. This enables a variation in temperature rise across the heating surface. This is beneficial because it also allows selective localised heating.

To facilitate insertion and removal of the aerosol-forming substrate, a non-stick coating or a friction reducing coating, such as a PTFE coating, is provided over at least a portion of the layer of metallic nanoparticles. In such embodiments, the heating surface 34, 44 may be sandwiched between the light transmitting core and the non-stick coating. The non stick coating reduces friction between the heating surface 34, 44 and a corresponding contacting surface of the aerosol-forming substrate 102, thus reducing residue. In addition, the non-stick coating may also seal in the layer of nanoparticle. This prolongs the usable life of the heating element 30, 40.

In another embodiment, the elongate heating element 30 is movable relative to the annular heating element 40 in the longitudinal direction as shown in Figures 4a and 4b. In Figure 4a, the heater assembly comprising the elongate heating element 30 and the annular heating element 40 is positioned in an operating position as shown in Figure 1.

A lever 62, formed integrally with the mount 60, extends outwardly through a slit 14 in the housing 12. By moving the lever 62 along the slit 14, the mount 60 may be toggled away from the elongate heating element 30 to a discharge position as shown in Figure 4b. This allows the removal of an expired aerosol-forming substrate 102 from the elongate heating element 30 without the need for the user to grip onto any part of the aerosol-forming article 100. A length of the slit 14 limits travel of the mount 60 relative to the elongate heating element 30.

Figure 5 shows an aerosol-generating system 10b similar to that shown in Figure 1. In the embodiment illustrated in Figure 5, the aerosol-generating system 10b comprises an aerosol-generating device 20b and aerosol-forming article 100b. In this embodiment, the aerosol-forming article 100b does not comprise a mouthpiece and instead a mouthpiece 108 is releasably attached to the device 20b, for example, by an interference fit, by mating internal and external screw threads on the mouthpiece 108 and housing 12, respectively, by a screw attachment or by a clip attachment. It will be appreciated that a variety of means may be employed to releasably attach the mouthpiece 108 to the device 20b. The mouthpiece 108 encloses the cavity 22 and thus shields the aerosol-forming article 100b from an external environment. In use, the user puffs on the mouthpiece 108 to draw a stream of aerosol generated in the cavity 22 through the mouthpiece 108.

Figure 6 shows an aerosol-forming substrate 100c comprising a plurality of substrate sections 102a, 102b. Each of the plurality of substrate sections 102a, 102b comprises a different substrate. The substrates among the plurality of substrate sections 102a, 102b may each comprise an aerosol-forming substrate, such as a tobacco composition or flavorings. Such a consumable may be particularly suitable for use with a device 20, 20b as described above, because the combination of an elongate heating element 30 for providing internal heating and an annular heating element 40 for providing external heating means that the substrate sections 102a, 102b may each be heated to different temperatures, or at different times, or both. Indeed, the elongate and annular heating elements 30, 40 of the aerosol generating devices 20, 20b shown in Figures 1 and 5 are arranged to be independently controllable. Therefore different heating profiles may be used for each of the substrate sections 102a, 102b.

In the illustrated example as shown in Figure 6, the plurality of substrate sections comprises a porous outer substrate section 102a formed of compacted granules of tobacco compound and a liquid inner substrate section 102b having a retaining material impregnated with aerosol-forming liquid or aerosol-forming gel. The liquid inner substrate section 102b may alternatively comprise a volume of aerosol-forming gel contained within the outer substrate section 102a. For example, the porous outer substrate section 102a may form a receptacle for containing the aerosol-forming gel.

In some embodiments, such as those illustrated in Figures 1 , 5 and 6, the aerosol forming article 100, 100b, 100c comprises a hollow core 101. The hollow core 101 may comprise a slightly smaller diameter than a corresponding diameter of the elongate heating element 30. This may allow a snug fit to form between the aerosol-forming article 100c and the elongate heating element 30. In an alternative embodiment (not shown), the aerosol forming article may not comprise a hollow core. In use, the elongate heating element 30 perforates the aerosol-forming substrate to effect a snug fit.

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

Claims

1. An aerosol-generating device comprising:

a cavity for receiving at least part of an aerosol-forming substrate;

a light source;

an elongate heating element extending into the cavity, and arranged to penetrate an aerosol-forming substrate when the aerosol-forming substrate is received within the cavity;

wherein said elongate heating element comprises a light-transmitting core and a heating surface comprising a plurality of metallic nanoparticles; and

wherein said light-transmitting core is arranged to transmit light from the light source to the plurality of metallic nanoparticles to generate heat by surface plasmon resonance.

2. The aerosol-generating device of claim 1 , wherein the elongate heating element comprises a base having at least one of a lens and a reflecting surface.

3. The aerosol-generating device of claim 1 or claim 2, wherein the light-transmitting core comprises at least one of a glass, a quartz, a thermosetting plastic, a fluid and a void.

4. The aerosol-generating device of any preceding claim, wherein the light source comprises at least one of a natural light source, a light emitting diode and a laser.

5. The aerosol-generating device of any preceding claim, wherein each of the metallic nanoparticles comprises at least one of gold, silver, copper and platinum.

6. The aerosol-generating device of any preceding claim, wherein the heating surface of the elongate heating element comprises a coating layer on at least a portion of the light transmitting core, wherein the coating layer comprises the plurality of metallic nanoparticles.

7. The aerosol-generating device of claim 6, wherein the surface of the elongate heating element comprises a non-stick coating on at least a portion of the coating layer.

8. The aerosol-generating device of any preceding claim, wherein the device comprises an annular heating element extending along at least a portion of a sidewall of the cavity, the annular heating element and the elongate heating element defining an annular space there-between.

9. The aerosol-generating device of claim 8, wherein the annular heating element comprises a plurality of metallic nanoparticles arranged to receive light from the light source and generate heat by surface plasmon resonance.

10. The aerosol-generating device of claim 8 or claim 9, wherein the elongate heating element and the annular heating element are independently controllable.

11. The aerosol-generating device of any of claims 8 to 10, wherein the annular heating element comprises a mount slidable with respect to the elongate heating element.

12. An aerosol-generating device comprising:

a cavity for receiving at least part of an aerosol-forming substrate;

a light source; and

an annular heating element extending along at least a portion of a sidewall of the cavity, and arranged to surround at least a part of an aerosol-forming substrate when the aerosol-forming substrate is received within the cavity;

wherein said annular heating element comprises a heating surface comprising a plurality of metallic nanoparticles arranged to receive light from the light source to generate heat by surface plasmon resonance.

13. The aerosol-generating device of claim 12, wherein the light source is spaced apart from the annular heating element to define an air flow passage therebetween.

14. An aerosol-generating system comprising the aerosol-generating device of any of claims 1 to 13 and an aerosol-generating article comprising an aerosol-forming substrate.

15. An aerosol-generating article comprising a first aerosol-forming substrate and a second aerosol-forming substrate extending around the first aerosol-forming substrate in a coaxial arrangement, wherein the first aerosol-forming substrate is secured to the second aerosol-forming substrate such that the substrates are held in a fixed position relative to each other.

16. An aerosol-generating article according to claim 15, wherein the first aerosol-forming substrate has a central cavity extending along a longitudinal axis of the aerosol generating article.