WO2019138053A1

WO2019138053A1 - An aerosol-generating device comprising a plasmonic heating element having a planar heating portion

Info

Publication number: WO2019138053A1
Application number: PCT/EP2019/050657
Authority: WO
Inventors: Rui Nuno BATISTA; Chiara FASCIANI
Original assignee: Philip Morris Products S.A.
Priority date: 2018-01-12
Filing date: 2019-01-11
Publication date: 2019-07-18

Abstract

There is provided an aerosol-generating device (10) for heating an aerosol-forming substrate (76), the aerosol-generating device (10) comprising a heating element (44) comprising a planar heating portion (52) arranged to heat an aerosol-forming substrate (76) when the aerosol- forming substrate (76) is received by the aerosol-generating device (10). The planar heating portion (52) comprises a plurality of metallic nanoparticles arranged to receive light from a light source (40) and generate heat by surface plasmon resonance.

Description

AN AEROSOL-GENERATING DEVICE COMPRISING A PLASMONIC HEATING ELEMENT

HAVING A PLANAR HEATING PORTION

The present invention relates to an aerosol-generating device comprising a heating element having a planar heating portion arranged to generate heat by surface plasmon resonance. The present invention also relates to an aerosol-generating system comprising the aerosol-generating device.

A number of electrically-operated aerosol-generating systems in which an aerosol- generating device having an electric heating element is used to heat an aerosol-forming substrate, such as a tobacco plug, have been proposed in the art. One aim of such aerosol-generating systems is to reduce known harmful or potentially harmful smoke constituents of the type produced by the combustion and pyrolytic degradation of tobacco in conventional cigarettes. The aerosol-forming substrate may be provided as part of an aerosol-generating article which is inserted into a chamber or cavity in the aerosol-generating device. In some known systems, to heat the aerosol-forming substrate to a temperature at which it is capable of releasing volatile components that can form an aerosol, a resistive heating element is inserted into or around the aerosol-forming substrate when the article is received in the aerosol-generating device.

Other known electrically operated aerosol-generating systems are configured to heat a liquid aerosol-forming substrate, such as a nicotine-containing liquid. Such systems typically comprise a wick arranged to transport liquid aerosol-forming substrate from a storage portion and a resistive heating element coiled around a portion of the wick.

A number of electrically-operated aerosol-generating systems comprising inductive heating systems have also been proposed.

However, heating systems in known aerosol-generating systems exhibit a number of disadvantages. For example, when using resistive heating elements, it may be difficult to achieve homogenous heating of an aerosol-forming substrate. Difficulty achieving accurate temperature control is another disadvantage commonly associated with resistive heating elements. The assembly process for resistive heating elements may also lead to resistive losses in the heating element circuit, for example at soldered connections between a resistive heating track and a power supply circuit.

Inductive heating systems also have their own disadvantages. For example, achieving efficient inductive heating of a susceptor element while minimising a power supply to an inductor coil requires positioning of the inductor coil as close to the susceptor element as possible. This may make it difficult to design an inductively heated aerosol-generating system that is efficient as well as practical to manufacture and use. Accordingly, it would be desirable to provide an aerosol-generating device comprising a heating arrangement that mitigates or overcomes at least some of these disadvantages with known devices.

According to a first aspect of the present invention there is provided an aerosol-generating device for heating an aerosol-forming substrate, the aerosol-generating device comprising a heating element comprising a planar heating portion arranged to heat an aerosol-forming substrate when the aerosol-forming substrate is received by the aerosol-generating device. The planar heating portion comprises a plurality of metallic nanoparticles arranged to receive light from a light source and 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. An aerosol-forming substrate may be part of an aerosol-generating article.

As used herein, the term “aerosol-generating system” refers to a combination of an aerosol-generating device and one or more aerosol-forming substrates or 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 of aerosol-generating devices according to the present invention includes a planar heating portion comprising the plurality of metallic nanoparticles.

Advantageously, a planar heating portion may increase or maximise a surface area of the heating portion. Advantageously, increasing or maximising a surface area of the heating portion may facilitate the transfer of heat from the heating portion to an aerosol-forming substrate.

Advantageously, a planar heating portion may facilitate use of the aerosol-generating device with a planar aerosol-forming substrate. Advantageously, a planar aerosol-forming substrate may increase or maximise a surface area of the aerosol-forming substrate. Advantageously, increasing or maximising the surface area of an aerosol-forming substrate may facilitate release of aerosol from the aerosol-forming substrate during use.

The planar heating portion 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 planar heating portion is arranged to receive light from the light source and generate heat by surface plasmon resonance.

Advantageously, providing the aerosol-generating device with a light source may allow the planar heating portion 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 planar heating portion. Advantageously, controlling the illumination of the planar heating portion controls the temperature to which the planar heating portion is heated by surface plasmon resonance.

The light source may be configured to emit at least one of ultraviolet light, infrared light and visible light. Preferably, the light source is configured to emit visible light. 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 planar heating portion by surface plasmon resonance, particularly when the plurality of metallic nanoparticles comprises at least one of gold, silver, platinum, and copper.

The light source may comprise at least one of a light emitting diode 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 planar heating portion. 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.

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 aerosol-generating device comprises a plurality of light sources, the electrical power supply may comprise a plurality of sources of electrical power arranged to supply electrical power to the plurality of light sources.

In embodiments in which the aerosol-generating device comprises a plurality of light sources, the controller may be configured to selectively supply electrical power to at least some of the plurality of light sources. The controller may be configured to selectively vary a supply of electrical power to at least some of 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 electrical power supply may comprise a DC power supply. The electrical power supply may comprise at least one 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 planar heating portion 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 planar heating portion. 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 planar heating portion 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.

The aerosol-generating device may comprise one or more optical elements to facilitate the transmission of light from a light source to the planar heating portion. The one or more optical elements may include at least one of an aperture, a window, a lens, a reflector, and an optical fibre.

Advantageously, at least one of an aperture and a window may facilitate the transmission of light from an external light source to the planar heating portion. The aerosol-generating device may comprise a housing, wherein at least one of an aperture and a window is positioned on the housing.

Advantageously, at least one of a lens, a reflector and an optical fibre may concentrate or focus light emitted from a light source onto the planar heating portion. Advantageously, concentrating or focussing light onto the planar heating portion may increase the temperature to which the planar heating portion is heated by surface plasmon resonance.

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.

In embodiments in which the aerosol-generating device comprises a light source, 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.

Preferably, the heating element is arranged so that the planar heating portion contacts an aerosol-forming substrate or an aerosol-generating article comprising an aerosol-forming substrate when the aerosol-forming substrate or the aerosol-generating article is received by the aerosol-generating device. Advantageously, arranging the planar heating portion to contact an aerosol-forming substrate or an aerosol-generating article may increase or maximise a rate of heat transfer from the planar heating portion to an aerosol-forming substrate.

The aerosol-generating device may comprise a device cavity for receiving an aerosol- forming substrate or an aerosol-generating article comprising an aerosol-forming substrate. Preferably, the heating element is arranged so that the planar heating portion contacts an aerosol- forming substrate or an aerosol-generating article when the aerosol-forming substrate or the aerosol-generating article is received within the device cavity. At least part of the planar heating portion may at least partially define the device cavity.

The device cavity may comprise an open end through which an aerosol-forming substrate may be inserted into the device cavity along a first direction. Preferably, the planar heating portion of the heating element is substantially parallel with the first direction.

The aerosol-generating device may comprise a housing. Preferably, the heating element is at least partially disposed within the housing. In embodiments in which the aerosol-generating device comprises a device cavity, the housing may at least partially define the device cavity.

The planar heating portion may comprise a first surface and a second surface opposite the first surface, wherein the heating element is arranged so that the first surface of the planar heating portion contacts an aerosol-forming substrate or an aerosol-generating article comprising an aerosol-forming substrate when the aerosol-forming substrate or the aerosol-generating articles is received by the aerosol-generating device. The second surface of the planar heating portion is arranged to receive light from a light source. Advantageously, arranging a second surface of the planar heating portion to receive light from a light source may prevent an aerosol- forming substrate or an aerosol-generating article obscuring the planar heating portion from a light source when the aerosol-forming substrate or the aerosol-generating article contacts a first surface of the planar heating portion.

The second surface of the planar heating portion may comprise a plurality of surface features defining a three-dimensional shape. The second surface may comprise at least one of a plurality of protrusions and a plurality of depressions. The second surface may have an undulating shape.

Advantageously, a second surface comprising a plurality of surface features may increase the surface area of the second surface. Advantageously, increasing the surface area of the second surface may increase heating of the plurality of metallic nanoparticles by surface plasmon resonance when light is incident on the second surface.

The heating element may be formed from the plurality of metallic nanoparticles.

The heating element may comprise a substrate layer and a coating layer positioned on at least a portion of the substrate layer, the coating layer comprising 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 comprise a first surface and a second surface opposite the first surface. The first surface of the substrate layer may form the first surface of the planar heating portion. The coating layer may be positioned on the second surface of the substrate layer. The coating layer may form at least part of the second surface of the planar heating portion. At least part of the second surface of the substrate layer may form at least part of the second surface of the planar heating portion.

The heating element may comprise one or more additional layers. The heating element may comprise a thermally conductive layer positioned on at least a portion of the substrate layer. Advantageously, a thermally conductive layer may facilitate the transfer of heat from the heating element to an aerosol-forming substrate received by the aerosol-generating article. In embodiments in which the coating layer is positioned on the second surface of the substrate layer, preferably the thermally conductive layer is positioned on the first surface of the substrate layer. The thermally conductive layer may comprise any suitable thermally conductive material. The thermally conductive layer may comprise at least one metal. 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.

At least a part of the planar heating portion may be porous. Advantageously, a porous part of the planar heating portion may allow airflow through the heating element.

At least a part of the planar heating portion may be formed from a porous material. At least a part of the planar heating portion may be formed from a woven material, wherein a plurality of pores are formed between threads of the woven material.

At least a part of the planar heating portion may be provided with a porosity. For example, a plurality of pores may be formed in at least a part of the planar heating portion. A plurality of pores may be formed using any suitable process. A plurality of pores may be formed using at least one of laser perforation and electron discharge machining.

In embodiments in which the heating element comprises a substrate layer and a coating layer, preferably at least a part of the substrate layer is porous.

The aerosol-generating device may comprise an airflow inlet, an airflow outlet, and an airflow path extending between the airflow inlet and the airflow outlet. Preferably, the aerosol- generating device is arranged so that, during use, an aerosol generated by heating an aerosol- forming substrate with the planar heating portion is received within the airflow path. In embodiments in which the aerosol-generating device comprises a housing, the housing may define at least one of the airflow inlet, the airflow outlet, and at least part of the airflow path. In embodiments in which the aerosol-generating device comprises a light source, at least part of the airflow path may be positioned between the light source and the planar heating portion of the heating element. Advantageously, positioning at least part of the airflow path between the light source and the planar heating portion may reduce or minimise heating of the light source by the planar heating portion.

At least a part of the planar heating portion may be disposed within the at least one airflow path. In embodiments in which at least part of the planar heating portion is porous, preferably at least part of the airflow path extends through the porous planar heating portion. Advantageously, arranging at least part of the airflow path to extend through the porous planar heating portion facilitates heat transfer from the planar heating portion to airflow through the aerosol-generating device during use.

In embodiments in which the aerosol-generating device comprises a device cavity for receiving an aerosol-forming substrate, the device cavity may form at least part of the at least one airflow passage.

In embodiments in which the device cavity comprises an open end through which an aerosol-forming substrate may be inserted into the device cavity, the open end may form at least one of the airflow inlet and the airflow outlet.

The airflow inlet may be positioned on a first side of the device cavity and the airflow outlet may be positioned on a second side of the device cavity, wherein the second side is opposite the first side. Advantageously, positioning the airflow inlet and the airflow outlet on opposite sides of the device cavity may facilitate airflow across or through the device cavity. Advantageously, airflow across or through the device cavity may facilitate the delivery of aerosol from an aerosol- forming substrate received within the cavity to a user.

Preferably, the airflow inlet is offset from the airflow outlet. Advantageously, offsetting the airflow inlet from the airflow outlet may facilitate airflow along at least a portion of the device cavity. Advantageously, airflow along at least a portion of the device cavity may increase or maximise the contact time between airflow through the device cavity and an aerosol-forming substrate received within the device cavity.

In embodiments in which the device cavity is arranged for insertion of an aerosol-forming substrate into the device cavity along a first direction, the first direction may extend between a first end of the device cavity and a second end of the device cavity. The airflow inlet may be positioned at the first end of the device cavity. The airflow outlet may be positioned at the second end of the device cavity. Advantageously, positioning the airflow inlet and the airflow outlet at opposite ends of the device cavity may increase or maximise the length of the airflow path extending along the cavity.

The aerosol-generating device may comprise an airflow sensor arranged to sense airflow through the aerosol-generating device. During use, airflow through the device may be indicative of a user drawing on the aerosol-generating device. In embodiments in which the aerosol- generating device comprises at least one light source, the aerosol-generating device may be arranged to supply electrical power to the at least one light source when the airflow sensor senses airflow through the aerosol-generating device. Advantageously, supplying electrical power to at least one light source when the airflow sensor senses airflow through the device may heat the planar heating portion only when a user is drawing on the aerosol-generating device. Advantageously, heating the planar heating portion only when a user is drawing on the aerosol- generating device may generate aerosol from an aerosol-forming substrate only when needed.

The 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 heating element comprises a substrate layer and a coating layer, the electrically resistive portion may comprise at least one of the substrate layer and the coating layer. 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 heating element comprises a thermally conductive layer, the electrically resistive portion may comprise the thermally conductive layer.

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 heating element may comprise at least one support portion extending from the planar heating portion, wherein the at least one support portion is non-parallel with the planar heating portion.

Advantageously, at least one support portion extending from the planar heating portion may facilitate mounting of the heating element. In embodiments in which the aerosol-generating device comprises a housing, the at least one support portion may facilitate mounting of the heating element to the housing.

Advantageously, providing at least one support portion that is non-parallel with the planar heating portion may facilitate positioning of the planar heating portion with respect to an aerosol- forming substrate received by the aerosol-generating device. In embodiments in which the aerosol-generating device comprises a device cavity, the at least one support portion may facilitate positioning of the planar heating portion within the device cavity.

At least part of the at least one support portion may be porous. At least part of the at least one support portion may be non-porous.

The at least one support portion may be formed separately from the planar heating portion and attached to the planar heating portion. The at least one support portion may be formed integrally with the planar heating portion. In embodiments in which the heating element comprises a substrate layer, the substrate layer may form the planar heating portion and the at least one support portion.

Preferably, the at least one support portion comprises a resilient material. Advantageously, at least one support portion comprising a resilient material may facilitate movement of the planar heating portion to accommodate an aerosol-forming substrate received by the aerosol-generating device. Advantageously, at least one support portion comprising a resilient material may bias the planar heating portion towards an aerosol-forming substrate received by the aerosol-generating device.

The at least one support portion may comprise a first end and a second end, wherein the at least one support portion depends at its first end from the planar heating portion. The at least one support portion may comprise an attachment portion at its second end. In embodiments in which the aerosol-generating device comprises a housing, preferably the attachment portion is attached to the housing. The attachment portion may be attached to the housing by any suitable means. The attachment portion may be attached to the housing using an adhesive. The attachment portion may be attached to the housing by an interference fit. The attachment portion may be received within a recess formed by the housing.

The at least one support portion may comprise a first support portion extending from a first end of the planar heating portion and a second support portion extending from a second end of the planar heating portion. At least part of the first support portion may be porous. The first support portion may be non-porous. At least part of the second support portion may be porous. The second support portion may be non-porous.

In embodiments in which the heating element comprises an electrically resistive portion, the first and second support portions may each comprise an electrically conductive material arranged to conduct a supply of electrical power to the electrically resistive portion. In embodiments in which the aerosol-generating device comprises a power supply, preferably the power supply is arranged to supply electrical power to the electrically resistive portion by the first and second support portions.

The at least one support portion may be substantially continuous about a periphery of the planar heating portion. In other words, the at least one support portion may comprise a support skirt. The support skirt may be non-porous. At least part of the support skirt may be porous.

The heating element may be a first heating element and the planar heating portion may be a first planar heating portion. The aerosol-generating device may further comprise a second heating element comprising a second planar heating portion arranged to heat an aerosol-forming substrate when the aerosol-forming substrate is received by the aerosol-generating device. The second planar heating portion comprises a second plurality of metallic nanoparticles arranged to receive light from a light source and generate heat by surface plasmon resonance. Preferably, the aerosol-generating device is configured so that, when an aerosol-forming substrate is received by the aerosol-generating device, the aerosol-forming substrate is received between the first planar heating portion of the first heating element and the second planar heating portion of the second heating element.

The second heating element may comprise any of the optional or preferred features described herein with respect to the first heating element.

The first heating element may comprise a first support skirt and the second heating element may comprise a second support skirt.

Both the first support skirt and the second support skirt may be non-porous. Non-porous first and second supports skirts may be advantageous in embodiments in which the aerosol- generating device comprises a device cavity, an airflow inlet positioned on a first side of the device cavity and the airflow outlet positioned on a second side of the device cavity. Advantageously, non-porous first and second support skirts may direct airflow from the airflow inlet, through the first planar heating portion, across the device cavity and through the second planar heating portion, to the airflow outlet. At least part of the first support skirt may porous and the second support skirt may be non- porous. A first support skirt that is at least partially porous and a non-porous support skirt may be advantageous in embodiments in which the aerosol-generating device comprises a device cavity comprising an open end forming at least one of the airflow inlet and the airflow outlet. Advantageously, during use, airflow entering the aerosol-generating device through the open end of the device cavity may flow through the first support skirt, through the first planar heating portion, across the device cavity and through the second planar heating portion, to the airflow outlet.

According to a second aspect of the present invention there is provided an aerosol- generating system comprising an aerosol-generating device according to the first aspect of the present invention, in accordance with any of the embodiments described herein. The aerosol- generating system also comprises an aerosol-generating article comprising at least one aerosol- forming substrate, wherein the aerosol-generating device is configured to receive at least a portion of the aerosol-generating article.

In embodiments in which the aerosol-generating device comprises a device cavity, preferably the device cavity is arranged to receive at least a portion of the aerosol-generating article.

Preferably, a portion of the aerosol-generating article comprising the at least one aerosol- forming substrate may be substantially planar. Advantageously, a substantially planar portion of the aerosol-generating article comprising the at least one aerosol-forming substrate may facilitate heat transfer from the planar heating portion of the heating element to the at least one aerosol- forming substrate. A substantially planar portion of the aerosol-generating contact may be particularly preferred in embodiments in which the aerosol-generating device is arranged so that the planar heating portion contacts the aerosol-generating article during use.

The entire aerosol-generating article may be substantially planar.

The aerosol-generating article may be substantially flat. As used herein, the term “substantially flat” refers to a component having a thickness to width ratio of at least 1 :2. Preferably, the thickness to width ratio is less than about 1 :20 to minimise the risk of bending or breaking the aerosol-generating article.

The aerosol-generating article may comprise a single aerosol-forming substrate.

The aerosol-generating article may comprise a plurality of aerosol-forming substrates. The plurality of aerosol-forming substrates may be the same. At least some of the aerosol-forming substrates may be different from each other.

The aerosol-generating device may be arranged to simultaneously heat the plurality of aerosol-forming substrates. The aerosol-generating device may be arranged to heat the plurality of aerosol-forming substrates to the same temperature.

In embodiments in which the aerosol-generating device comprises at least one of a plurality of light sources and a plurality of discrete areas of metallic nanoparticles, the aerosol- generating device may be arranged to heat at least some of the plurality of aerosol-forming substrates at different times.

In embodiments in which the aerosol-generating device comprises at least one of a plurality of light sources and a plurality of discrete areas of metallic nanoparticles, the aerosol- generating device may be arranged to heat at least some of the plurality of aerosol-forming substrates to different temperatures.

The aerosol-generating device may be arranged to heat only some of the plurality of aerosol-forming substrates. The aerosol-generating device may be arranged to that, during use, some of the plurality of aerosol-forming substrates are not heated by the heating element.

The aerosol-generating article may comprise a base layer. The at least one aerosol- forming substrate may be positioned on the base layer. The base layer may define at least one substrate cavity, wherein the at least one aerosol-forming substrate is positioned within the at least one substrate cavity. In embodiments in which the aerosol-generating article comprises a plurality of aerosol-forming substrates, preferably the base layer defines a plurality of substrate cavities. Preferably, each substrate cavity contains a single aerosol-forming substrate.

The at least one substrate cavity may have an open end and a closed end. Preferably, the aerosol-generating article comprises a cover layer overlying the base layer and overlying the open end of the at least one substrate cavity. Preferably, the at least one aerosol-forming substrate is positioned between the closed end of the at least one cavity and the cover layer. Preferably, at least a portion of the cover layer is porous.

The at least one substrate cavity may a first end and a second end, wherein both the first and second ends are open. Preferably, the aerosol-generating article comprises a first cover layer overlying a first side of the base layer and overlying the first open end of the at least one substrate cavity. Preferably, the aerosol-generating article comprises a second cover layer overlying a second side of the base layer and overlying the second open end of the at least one substrate cavity. Preferably, the at least one aerosol-forming substrate is positioned in the at least one substrate cavity and positioned between the first cover layer and the second cover layer. Preferably, at least a portion of the first cover layer is porous. Preferably, at least a portion of the second cover layer is porous.

The aerosol-generating article may comprise at least one sealing layer. Preferably, the at least one sealing layer is removable from the aerosol-generating article. Preferably, the at least one sealing layer is non-porous. In embodiments in which the aerosol-generating article comprises a cover layer, preferably the at least one sealing layer overlies the cover layer. In embodiments in which the aerosol-generating article comprises first and second cover layers, preferably the at least one sealing layer comprises a first sealing layer overlying the first cover layer and a second sealing layer overlying the second cover layer.

The at least one aerosol-forming substrate may comprise nicotine. The at least one aerosol-forming substrate may comprise at least one aerosol-former. As used herein, the term ‘aerosol former’ is used to describe any suitable known compound or mixture of compounds that, in use, facilitates formation of an aerosol. Suitable aerosol-formers include, but are not limited to: polyhydric alcohols, such as propylene glycol, triethylene glycol, 1 ,3-butanediol and glycerine; esters of polyhydric alcohols, such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. Preferred aerosol formers are polyhydric alcohols or mixtures thereof, such as propylene glycol, triethylene glycol, 1 ,3-butanediol and, most preferred, glycerine.

The least one aerosol-forming substrate may comprise at least one flavourant. The at least one flavourant may comprise menthol.

The at least one aerosol-forming substrate may comprise a solid aerosol-forming substrate. The solid aerosol-forming substrate may comprise tobacco. The solid aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavour compounds which are released from the substrate upon heating.

The solid aerosol-forming substrate may comprise a non-tobacco material. The solid aerosol-forming substrate may comprise tobacco-containing material and non-tobacco containing material.

The solid aerosol-forming substrate may include at least one aerosol-former. Suitable aerosol-formers include, but are not limited to: polyhydric alcohols, such as propylene glycol, triethylene glycol, 1 ,3-butanediol and glycerine; esters of polyhydric alcohols, such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. Preferred aerosol formers are polyhydric alcohols or mixtures thereof, such as propylene glycol, triethylene glycol, 1 ,3-butanediol and, most preferred, glycerine.

The solid aerosol-forming substrate may comprise a single aerosol former. Alternatively, the solid aerosol-forming substrate may comprise a combination of two or more aerosol formers.

The solid aerosol-forming substrate may have an aerosol former content of greater than 5 percent on a dry weight basis.

The solid aerosol-forming substrate may have an aerosol former content of between approximately 5 percent and approximately 30 percent on a dry weight basis.

The solid aerosol-forming substrate may have an aerosol former content of approximately 20 percent on a dry weight basis.

The at least one aerosol-forming substrate may comprise a liquid aerosol-forming substrate.

The liquid aerosol-forming substrate may comprise water. The liquid aerosol-forming substrate may comprise an aerosol-former. Suitable aerosol- formers are well known in the art and include, but are not limited to: polyhydric alcohols, such as triethylene glycol, 1 ,3-butanediol and glycerine; esters of polyhydric alcohols, such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. Preferred aerosol formers are polyhydric alcohols or mixtures thereof, such as triethylene glycol, 1 ,3-butanediol and, most preferred, glycerine or polyethylene glycol.

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.

The at least one aerosol-forming substrate may comprise at least a first aerosol-forming substrate and a second aerosol-forming substrate.

The first aerosol-forming substrate may comprise a nicotine source and the second aerosol-forming substrate may comprise an acid source. During use, the heating element may heat the nicotine source and the acid source to generate a nicotine-containing vapour and an acid vapour. The nicotine vapour and the acid vapour react with each other in the gas phase to generate an aerosol comprising nicotine salt particles.

The nicotine source may comprise nicotine, nicotine base or a nicotine salt.

The nicotine source may comprise a first carrier material impregnated with between about 1 milligram and about 50 milligrams of nicotine. The nicotine source may comprise a first carrier material impregnated with between about 1 milligram and about 40 milligrams of nicotine. Preferably, the nicotine source comprises a first carrier material impregnated with between about 3 milligrams and about 30 milligrams of nicotine. More preferably, the nicotine source comprises a first carrier material impregnated with between about 6 milligrams and about 20 milligrams of nicotine. Most preferably, the nicotine source comprises a first carrier material impregnated with between about 8 milligrams and about 18 milligrams of nicotine.

In embodiments in which the first carrier material is impregnated with nicotine base or a nicotine salt, the amounts of nicotine recited herein are the amount of nicotine base or amount of ionised nicotine, respectively.

The first carrier material may be impregnated with liquid nicotine or a solution of nicotine in an aqueous or non-aqueous solvent.

The first carrier material may be impregnated with natural nicotine or synthetic nicotine.

The acid source may comprise an organic acid or an inorganic acid.

Preferably, the acid source comprises an organic acid, more preferably a carboxylic acid, most preferably an alpha-keto or 2-oxo acid or lactic acid. Preferably, the acid source comprises an acid selected from the group consisting of 3- methyl-2-oxopentanoic acid, pyruvic acid, 2-oxopentanoic acid, 4-methyl-2-oxopentanoic acid, 3- methyl-2-oxobutanoic acid, 2-oxooctanoic acid, lactic acid and combinations thereof. Preferably, the acid source comprises pyruvic acid or lactic acid. More preferably, the acid source comprises lactic acid.

Preferably, the acid source comprises a second carrier material impregnated with acid.

The first carrier material and the second carrier material may be the same or different.

Preferably, the first carrier material and the second carrier material have a density of between about 0.1 grams/cubic centimetre and about 0.3 grams/cubic centimetre.

Preferably, the first carrier material and the second carrier material have a porosity of between about 15 percent and about 55 percent.

The first carrier material and the second carrier material may comprise one or more of glass, cellulose, ceramic, stainless steel, aluminium, polyethylene (PE), polypropylene, polyethylene terephthalate (PET), poly(cyclohexanedimethylene terephthalate) (PCT), polybutylene terephthalate (PBT), polytetrafluoroethylene (PTFE), expanded polytetrafluoroethylene (ePTFE), and BAREX^®.

The first carrier material acts as a reservoir for the nicotine. Preferably, the first carrier material is chemically inert with respect to nicotine.

The second carrier material acts as a reservoir for the acid. Preferably, the second carrier material is chemically inert with respect to the acid.

Preferably, the acid source is a lactic acid source comprising a second carrier material impregnated with between about 2 milligrams and about 60 milligrams of lactic acid.

Preferably, the lactic acid source comprises a second carrier material impregnated with between about 5 milligrams and about 50 milligrams of lactic acid. More preferably, the lactic acid source comprises a second carrier material impregnated with between about 8 milligrams and about 40 milligrams of lactic acid. Most preferably, the lactic acid source comprises a second carrier material impregnated with between about 10 milligrams and about 30 milligrams of lactic acid.

According to a third aspect of the present invention there is provided a heating element for an aerosol-generating device, the heating element comprising a planar heating portion for heating an aerosol-forming substrate, wherein the planar heating portion comprises a plurality of metallic nanoparticles arranged to receive light from a light source and generate heat by surface plasmon resonance. The heating element may comprise any of the optional or preferred features according to the first aspect of the present invention, in accordance with any of the embodiments described herein.

The invention will now be further described, by way of example only, with reference to the accompanying drawings in which: Figures 1 and 2 show a perspective view of an aerosol-generating device according to an embodiment of the present invention;

Figure 3 shows a cross-sectional view of the aerosol-generating section and the mouthpiece of the aerosol-generating device of Figures 1 and 2;

Figure 4 shows an enlarged cross-sectional view of the device cavity of the aerosol- generating section of Figure 3;

Figure 5 shows a perspective view of the first heating element of the aerosol-generating section of Figure 4;

Figure 6 shows a cross-sectional view of part of the planar heating portion of the heating element of Figure 5;

Figure 7 shows a cross-sectional view showing an alternative configuration of the aerosol- generating section of the aerosol-generating device of Figures 1 and 2;

Figure 8 shows an exploded perspective view of an aerosol-generating article for use with the aerosol-generating device of Figures 1 and 2;

Figure 9 shows a plan view of the aerosol-generating article of Figure 8; and

Figure 10 shows a plan view of an alternative aerosol-generating article.

Figures 1 and 2 show a perspective view of an aerosol-generating device 10 according to an embodiment of the present invention. The aerosol-generating device 10 comprises a power supply section 12, an aerosol-generating section 14 and a mouthpiece 16.

The power supply section 12 comprises a power supply for supplying electrical power to components of the aerosol-generating section 14. The aerosol-generating section 14 comprises a connector 18 for receiving the power supply section 12, the connector 18 including an electrical connector 20 for transferring electrical power from the power supply section 12 to the aerosol- generating section 14.

The aerosol-generating section 14 comprises a push-button 22 to allow a user to switch the aerosol-generating device 10 on and off, and an electronic display 24 for providing visual feedback to a user. The aerosol-generating device 10 also comprises a housing 25 defining a device cavity 26 in the aerosol-generating section 14, the device cavity 26 for receiving an aerosol-generating article 28. During use, an aerosol-generating article 28 is received within the device cavity 26 so that the aerosol-generating device 10 and the aerosol-generating article 28 together form an aerosol-generating system.

Figure 3 shows a cross-sectional view of the aerosol-generating section 14 and the mouthpiece 16. The aerosol-generating section 14 further comprises a controller 29 arranged to supply electrical power from the power supply section 12 to components within the aerosol- generating section 14. The aerosol-generating section 14 also includes two airflow inlets 30 and an airflow outlet 32 in fluid communication with each other via the device cavity 26. During use, aerosol generated within the device cavity 26 is entrained within airflow through the device cavity 26 and exits the device cavity 26 through the airflow outlet 32. An airflow passage 34 in the aerosol-generating section 14 transfers airflow from the airflow outlet 32 to mixing chambers 36 within the mouthpiece 16. Airflow from the mixing chambers 36 exits the mouthpiece 16 via a mouthpiece outlet 38 for delivery to a user.

Figure 4 shows an enlarged cross-section view of the device cavity 26. Positioned within the device cavity 26 is a first light source 40, a second light source 42, a first heating element 44 and a second heating element 46. When an aerosol-generating article 28 is received within a slot 47 within the device cavity 26, the aerosol-generating article 28 is positioned between the first and second heating elements 44, 46. The first and second light sources 40, 42 each comprise a light emitting diode 48 and a diffuser 50 overlying a surface of the light emitting diode 48.

Figure 5 shows a perspective view of the first heating element 44. Although only the first heating element 44 is described in detail, it will be appreciated that the second heating element 46 is identical to the first heating element 44 in the embodiment shown in Figure 4.

The first heating element 44 comprises a planar heating portion 52 and a support portion 54 in the form of a support skirt extending about a periphery of the planar heating portion 52. The support portion 54 comprises an attachment portion 56 that is received within the housing 25 of the aerosol-generating device 10 to mount the first heating element 44 within the device cavity 25.

Figure 6 shows a cross-sectional view through part of the planar heating portion 52. The planar heating portion 52 comprises a substrate layer 58, a thermally conductive layer 60 positioned on a first surface of the substrate layer 58 and a coating layer 62 positioned on a second surface of the substrate layer 58. The coating layer 62 comprises a plurality of metallic nanoparticles. The first heating element 44 is arranged so that the coating layer 62 faces the first light source 40. During use, the metallic nanoparticles of the coating layer 62 receive light from the first light source 40 and generate heat by surface plasmon resonance. The thermally conductive layer 60 facilitates the transfer of heat generated by the coating layer 62 to the aerosol- generating article 28 received within the device cavity 26. It will be appreciated that the structure and function of the second heating element 46 and the second light source 42 are the same as the described structure and function of the first heating element 44 and the first light source 40.

The planar heating portion 52 also comprises a plurality of pores 64 that allow air to flow through the planar heating portion 52. Therefore as shown in Figures 3 and 4, during use, airflow enters the aerosol-generating device 10 through the airflow inlets 30, flows through the planar heating portion 52 of the first heating element 44, through the aerosol-generating article 28, through the planar heating portion of the second heating element 46, and out of the device cavity 26 through the airflow outlet 32. Aerosol generated by heating the aerosol-generating article 28 with the first and second heating elements 44, 46 is entrained in the airflow as it flows through the aerosol-generating article 28. In the embodiment shown in Figure 4 the support portions 54 of the first and second heating elements 44, 46 are non-porous to direct airflow through the planar heating portions 52.

Figure 7 shows an alternative arrangement of the aerosol-generating section 12 of the aerosol-generating device 10. The alternative arrangement shown in Figure 7 is similar to the arrangement shown in Figure 4 and like reference numerals are used to designate like parts.

The alternative arrangement shown in Figure 7 differs in the lack of dedicated airflow inlets to the device cavity 26. Instead, an open end 66 of the device cavity 26 through which an aerosol- generating article 28 may be inserted into the device cavity 26 functions as an airflow inlet. As a result of the different positioning of the airflow inlet, the first heating element 44 comprises a support portion 154 that is porous. The porous support portion 154 allows airflow entering the device cavity 26 to flow into the space between the first light source 40 and the first heating element 44 so that the airflow may flow through the planar heating portions 52 of the first and second heating elements 44, 46 and the aerosol-generating article 28 in the same manner as described with reference to Figure 4.

Figures 8 and 9 show an aerosol-generating article 70 for use with the aerosol-generating device 10. The aerosol-generating article 70 comprises a base layer 72 defining a substrate cavity 74 extending through the base layer 72. An aerosol-forming substrate 76 comprising tobacco is positioned within the substrate cavity 74. A first porous cover layer 78 overlies a first side of the base layer 72 and a second porous cover layer 80 overlies a second side of the base layer 72. The first and second porous cover layers 78, 80 are secured to the base layer 72 so that the aerosol-forming substrate 76 is positioned between the first and second porous cover layers 78, 80 and retained within the substrate cavity 74. During use of the aerosol-generating article 70 with the aerosol-generating device 10, the first and second heating elements 44, 46 heat the aerosol-forming substrate 76 to generate an aerosol. Airflow from the planar heating portion 52 of the first heating element 44 to the planar heating portion of the second heating element 46 flows through the first and second porous cover layers 78, 80 and through the aerosol- forming substrate 76 to entrain the generated aerosol within the airflow.

Figure 10 shows an alternative aerosol-generating article 170 for use with the aerosol- generating device 10. The alternative aerosol-generating article 170 is similar to the aerosol- generating article 70 and like reference numerals designate like parts.

The aerosol-generating article 170 comprises a base layer 72 defining a plurality of substrate cavities 74. A first aerosol-forming substrate 176 comprises a flavourant is positioned within a first substrate cavity 74. A second aerosol-forming substrate 177 comprising a nicotine- containing liquid provided on a carrier material is positioned within a second substrate cavity 74. A third aerosol-forming substrate 179 comprising an aerosol former is positioned within a third substrate cavity 74. During use, aerosol generated by the first, second and third aerosol-forming substrates 176, 177, 179 is entrained within airflow flowing through the aerosol-generating article 170. The different aerosols are mixed together within the airflow outlet 32, the airflow passage 34 and the mixing chambers 36 for delivery to a user as a combined aerosol.

Advantageously, generating heat by surface plasmon resonance may provide more localised heating when compared to other methods of generating heat, such as resistive heating. Therefore, advantageously, the aerosol-generating device 10 may be adapted to allow localised and selective heating of the first, second and third aerosol-forming substrates 176, 177, 179. For example, the aerosol-generating device may be adapted so that at least one of the first light source 40 and the second light source 42 comprises an array of LEDs. One or more first LEDs of the array of LEDs may correspond to a first area of the planar heating portion 52 corresponding to the first aerosol-forming substrate 176. One or more second LEDs of the array of LEDs may correspond to a second area of the planar heating portion 52 corresponding to the second aerosol-forming substrate 177. One or more third LEDs of the array of LEDs may correspond to a third area of the planar heating portion 52 corresponding to the third aerosol-forming substrate 179. The controller 29 may be configured to selectively supply power to first LEDs, the second LEDs, the third LEDs, and combinations thereof, in response to a user input received from a user input device, such as the push-button 22. Using the push-button 22, a user may vary the ratio of aerosolised first, second and third aerosol-forming substrates 176, 177, 179. In response to the user input, the controller 29 may vary a total light output for each of the first, second and third LEDs to provide the required heating of the first, second and third aerosol-forming substrates 176, 177, 179 that generates the desired aerosol ratio. Advantageously, since heating by surface plasmon resonance is fast when compared to other heating mechanisms, such as resistive heating, the aerosol-generating device 10 may modify the generated aerosol in real-time in response to user inputs.

For example, a user may use the push-button 22 to request an increased amount of flavourant in the delivered aerosol. In response, the controller 29 may increase a supply of power to the first LEDs to increase heating of the first area of the planar heating portion 52, which increases heating of the first aerosol-forming substrate 176.

In another example, a user may use the push-button 22 to request a decreased amount of flavourant and an increased amount of nicotine. In response, the controller 29 may decrease a supply of power to the first LEDs to decrease heating of the first area of the planar heating portion 52 and decrease heating of the first aerosol-forming substrate 176, and increase a supply of power to the second LEDs to increase heating of the second area of the planar heating portion 52 and increase heating of the second aerosol-forming substrate 177.

To simplify user interaction with the aerosol-generating device 10, the push-button 22 may be supplemented with or replaced by a different type of user input device, such as a touch-screen.

Claims

1. An aerosol-generating device for heating an aerosol-forming substrate, the aerosol- generating device comprising:

a heating element comprising a planar heating portion arranged to heat an aerosol-forming substrate when the aerosol-forming substrate is received by the aerosol-generating device, wherein the planar heating portion comprises a plurality of metallic nanoparticles arranged to receive light from a light source and generate heat by surface plasmon resonance.

2. An aerosol-generating device according to claim 1 , wherein the heating element is arranged so that the planar heating portion contacts an aerosol-forming substrate or an aerosol- generating article when the aerosol-forming substrate or the aerosol-generating article is received by the aerosol-generating device.

3. An aerosol-generating device according to claim 1 or 2, wherein the planar heating portion comprises a first surface and a second surface opposite the first surface, wherein the heating element is arranged so that the first surface of the planar heating portion contacts an aerosol- forming substrate or an aerosol-generating article when the aerosol-forming substrate or the aerosol-generating article is received by the aerosol-generating device, and wherein the second surface of the planar heating portion is arranged to receive light from a light source.

4. An aerosol-generating device according to any preceding claim, wherein at least the planar heating portion comprises a substrate layer and a coating layer positioned on at least a portion of the substrate layer, the coating layer comprising the plurality of metallic nanoparticles.

5. An aerosol-generating device according to any preceding claim, wherein at least a part of the planar heating portion is porous.

6. An aerosol-generating device according to claim 5, wherein the aerosol-generating device comprises an airflow inlet, an airflow outlet, and an airflow path extending between the airflow inlet and the airflow outlet, wherein at least part of the airflow path extends through the porous planar heating portion.

7. An aerosol-generating device according to claim 6, wherein the aerosol-generating device comprises a device cavity for receiving an aerosol-forming substrate, wherein the airflow inlet is positioned on a first side of the device cavity, wherein the airflow outlet is positioned on a second side of the device cavity, and wherein the second side is opposite the first side.

8. An aerosol-generating device according to any preceding claim, wherein the heating element comprises at least one support portion extending from the planar heating portion, wherein the at least one support portion is non-parallel with the planar heating portion.

9. An aerosol-generating device according to claim 8, wherein the at least one support portion comprises a resilient material.

10. An aerosol-generating device according to claim 8 or 9, wherein the at least one support portion comprises a first support portion extending from a first end of the planar heating portion and a second support portion extending from a second end of the planar heating portion.

1 1. An aerosol-generating device according to claim 10, wherein the first and second support portions each comprise an electrically conductive material arranged to conduct a supply of electrical power to the planar heating portion to resistively heat the planar heating portion.

12. An aerosol-generating device according to any preceding claim, further comprising a light source, wherein the planar heating portion is arranged to receive light from the light source and generate heat by surface plasmon resonance.

13. An aerosol-generating device according to any preceding claim, wherein the heating element is a first heating element and wherein the planar heating portion is a first planar heating portion, the aerosol-generating device further comprising:

a second heating element comprising a second planar heating portion arranged to heat an aerosol-forming substrate when the aerosol-forming substrate is received by the aerosol- generating device, wherein the second planar heating portion comprises a second plurality of metallic nanoparticles arranged to receive light from a light source and generate heat by surface plasmon resonance, and wherein the aerosol-generating device is configured so that, when an aerosol-forming substrate is received by the aerosol-generating device, the aerosol-forming substrate is received between the first planar heating portion of the first heating element and the second planar heating portion of the second heating element.

14. An aerosol-generating system comprising:

an aerosol-generating device according to any preceding claim; and

an aerosol-generating article comprising at least one aerosol-forming substrate, wherein the aerosol-generating device is configured to receive at least a portion of the aerosol-generating article.

15. An aerosol-generating system according to claim 14, wherein a portion of the aerosol- generating article comprising the at least one aerosol-forming substrate is substantially planar.

16. A heating element for an aerosol-generating device, the heating element comprising a planar heating portion for heating an aerosol-forming substrate, wherein at least a part of the planar heating portion is porous, and wherein the planar heating portion comprises a plurality of metallic nanoparticles arranged to receive light from a light source and generate heat by surface plasmon resonance.