Aerosol-generating system and method using dielectric heating

Abstract

To provide a system and method for generating an aerosol from an aerosol-forming substrate.SOLUTION: There is provided an aerosol-generating device for heating an aerosol-forming substrate to generate an aerosol, the aerosol-generating device comprising: a substrate cavity (28 / 49 / 58 / 78 / 88 / 108) configured to receive an aerosol-forming substrate; and an electromagnetic field generator (23 / 43 / 53 / 73 / 83 / 103) configured to generate a radio frequency (RF) electromagnetic field in the substrate cavity (28 / 49 / 58 / 78 / 88 / 108), the electromagnetic field generator (23 / 43 / 53 / 73 / 83 / 103) comprising a solid state RF transistor. The device can give rise to dielectric heating of the aerosol-forming substrate (36).SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to systems and methods for generating an aerosol from an aerosol-forming substrate. In particular, the present disclosure relates to systems and methods for heating an aerosol-forming substrate to generate an aerosol for inhalation by a user.

Background Art

[0002] Many different types of personal vaporizers and heat-not-burn products are available for generating an inhalable aerosol from an aerosol-forming substrate. Some of these systems heat a liquid composition, and others heat a solid tobacco mixture. Almost all available systems heat the aerosol-forming substrate by conduction of heat from a heating element to the aerosol-forming substrate. Most commonly, this is achieved by passing an electric current through an electrically resistive heating element to cause Joule heating of the heating element. Inductive heating systems have also been proposed, where Joule heating occurs as a result of eddy currents induced in a susceptor heating element.

[0003] One problem with these systems is that they cause non-uniform heating of the aerosol-forming substrate. The portion of the aerosol-forming substrate closest to the heating element is heated faster or to a higher temperature than the portion of the aerosol-forming substrate further from the heating element. To mitigate this problem, various designs have been used. Some designs use multiple heating elements to provide the ability to distribute heat or heat different portions of the substrate at different times. Other designs convey only a small portion of the aerosol-forming substrate to the heating element, such that only that small portion is vaporized before another portion of the aerosol-forming substrate is conveyed to the heating element.

[0004] It would be desirable to provide uniform heating of the aerosol-forming substrate in a manner that allows for greater design flexibility while being achievable in a compact, handheld system and enables heating control.

Summary of the Invention

[0005] The present disclosure provides an aerosol generating device for heating an aerosol-forming substrate to generate an aerosol, the aerosol generating device comprising: a substrate recess configured to receive the aerosol-forming substrate; and an electromagnetic field generating device configured to generate a radio frequency (RF) electromagnetic field in the substrate recess, the electromagnetic field generating device including a solid state RF transistor.

[0006] The device can cause dielectric heating of the aerosol-forming substrate. The dielectric heating can be uniform within a large amount of the aerosol-forming substrate without the generation of hot spots. The heating also does not require contact between a heating element and the aerosol-forming substrate. This means that there is no need to clean a heating element having an accumulation of aerosol residue thereon. The device allows for a significant degree of design flexibility with respect to the shape, volume and composition of the aerosol-forming substrate, and correspondingly the shape and volume of the substrate recess.

[0007] Using a solid state RF converter allows the device to be made compact. It is possible to manufacture a device that easily fits in one hand of a user. A conventional means for generating RF frequency radiation for heating, such as a household microwave oven, is a magnetron. Magnetrons are bulky and require very high voltages to operate, making them unsuitable for handheld devices. Furthermore, magnetrons have a relatively unstable frequency output and a relatively short lifespan. RF transistors provide consistent operation over a greater number of usage cycles and require a much lower operating voltage.

[0008] Advantageously, the solid state RF transistor is configured to generate and amplify an RF electromagnetic field. By using a single transistor to provide both generation and amplification of the RF electromagnetic field, it is possible to fabricate a compact device.

[0009] As used herein, radio frequency (RF) means a frequency between 3 Hz and 3 THz, including microwaves. The RF electromagnetic field preferably has a frequency of 500 MHz to 50 GHz, more preferably a frequency of 900 MHz to 30 GHz. The RF electromagnetic field may have a frequency of 900 MHz to 5 GHz. In one embodiment, the RF electromagnetic field has a frequency of about 2.4 GHz.

[0010] As used herein, the term "aerosol-forming substrate" relates to a substrate capable of releasing a volatile compound capable of forming an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. The aerosol-forming substrate is typically part of an aerosol-generating article.

[0011] As used herein, the term "aerosol-generating article" refers to an article comprising an aerosol-forming substrate capable of releasing a volatile compound capable of forming an aerosol. For example, the aerosol-generating article can be an article that generates an aerosol that can be directly inhaled by a user who sucks or smokes on a mouthpiece. The aerosol-generating article may be disposable. An article comprising an aerosol-forming substrate containing tobacco may be referred to as a tobacco stick.

[0012] As used herein, the term "aerosol-generating device" refers to a device that interacts with an aerosol-forming substrate to generate an aerosol. The aerosol-generating article is separated from and configured to be combined with an aerosol-generating device for heating the aerosol-generating article.

[0013] As used herein, the term "aerosol-generating system" refers to a combination of an aerosol-generating article and an aerosol-generating device. In an aerosol-generating system, the aerosol-generating article and the aerosol-generating device cooperate to generate an aerosol.

[0014] The substrate recess may comprise one or more outer walls formed from a material that does not pass RF electromagnetic fields. To allow the electromagnetic field to penetrate into the substrate recess, one or more slots may be formed in the one or more outer walls. It is desirable to contain the electromagnetic radiation generated by the electromagnetic field generating device within the substrate recess. This is to provide efficient heating and avoid radiation leakage. Such radiation leakage can damage other components of the system, including the electromagnetic field generating device itself. Also, it is desirable to minimize the user's exposure to RF radiation. The outer wall can include any suitable material that does not pass RF radiation, such as aluminum, stainless steel, silver, or gold. The outer wall may have a polished surface to improve the reflection of RF radiation within the recess.

[0015] However, it is necessary for the radiation to be allowed to enter the substrate recess. By providing one or more slots through which the electromagnetic field can pass, the electromagnetic field can enter the substrate recess. At least one of the one or more slots may have an L-shape, S-shape, T-shape, or I-shape.

[0016] The substrate recess may include a wall that passes RF electromagnetic fields. The aerosol-forming substrate may be enclosed within a horn or container formed from a material that does not pass RF electromagnetic fields, and one or more slots may be formed in the horn or container to allow the penetration of the electromagnetic field.

[0017] The substrate recess may include a blind recess having an open end and a closed end. The substrate recess may be configured to receive an aerosol-forming article that includes an aerosol-forming substrate through the open end. The substrate recess may be configured to hold the aerosol-forming substrate within the substrate recess.

[0018] The device may comprise a closure or a mouthpiece for covering the open end of the substrate recess during use. The closure or the mouthpiece may include a radiation shield configured to reflect RF electromagnetic radiation. As another method, or additionally, the aerosol-forming article may include a radiation shield configured to reflect RF electromagnetic radiation. One or more radiation shields may be fluid-permeable such that the generated aerosol can pass through it. For example, the radiation shield may include a metal mesh.

[0019] The device may comprise an air inlet and an air outlet. An air flow path may be defined between the air inlet and the air outlet. The air flow path may pass through or bypass the substrate recess. In embodiments where the air flow path passes through the substrate recess or through the generated RF electromagnetic field, the air flow path may include a labyrinthine portion beyond one or more radiation shielding elements to prevent the escape of RF radiation through the air inlet or the air outlet. As another method, or additionally, one of the one or more fluid-permeable radiation shielding elements may be provided in the air flow path.

[0020] The device may include a device housing. The device may comprise a radiation containment recess within the housing, the radiation containment recess surrounding or adjacent to the substrate recess. The radiation containment recess may be provided to allow an RF electromagnetic field to enter the substrate recess through one or more slots or entry points. RF radiation may propagate freely within the radiation containment recess. The radiation containment recess may include a waveguide. The radiation containment recess may have an outer wall that does not allow RF electromagnetic radiation to pass through.

[0021] The aerosol generating device may further comprise a resonance cavity between the substrate cavity and the electromagnetic field generating device. As used herein, the term "resonance cavity" is a structure capable of confining electromagnetic waves of a given frequency. In this case, the selected frequency of the electromagnetic wave corresponds to the RF region of the spectrum. To confine the electromagnetic wave, the resonance cavity is made of a reflective material (e.g., metal) for that frequency. The structure can be hollow or filled with a dielectric material. The goal of the resonance cavity is to enable the electromagnetic wave to bounce back and forth inside to enhance the formation of standing waves and minimize power loss.

[0022] The resonance cavity can be designed to match the impedance of the electromagnetic field generating device and the load (in this case, the aerosol-forming substrate in the substrate cavity) in order to amplify the RF electromagnetic field at the resonance frequency, optimize the absorption of energy by the load, and minimize the reflection of radiation from the load. This improves the heating efficiency and minimizes the radiation leakage from the system. The resonance cavity may be positioned between the electromagnetic field generating device and the substrate cavity.

[0023] The aerosol generating device may further comprise one or more antennas connected to the electromagnetic field generating device and configured to direct the RF electromagnetic field. The one or more antennas may be at least partially positioned within the substrate cavity. In use, the one or more antennas may be at least partially positioned within the substrate cavity together with the aerosol-forming substrate. In use, the one or more antennas may be configured to pierce a container holding the aerosol-forming substrate. The one or more antennas may pass through slots in the outer wall of the substrate cavity. The one or more antennas may be at least partially positioned within the radiation confinement cavity. The one or more antennas may be positioned within the resonance cavity.

[0024] Providing an antenna to direct the radiation generated by the electromagnetic field generating device can improve the efficiency of the device. The one or more antennas may include conductive pins.

[0025] By using an RF transistor to generate an RF electromagnetic field, it is possible to use a closed-loop control scheme. The apparatus may include a sensor in or adjacent to the substrate recess that provides a signal indicative of the temperature in the substrate recess, and a controller connected to receive the signal from the sensor and connected to control the electromagnetic field generating device in accordance with the signal from the sensor.

[0026] The sensor may include a temperature sensor that directly measures temperature. As another method, or additionally, the sensor may comprise one or more sampling antennas configured to detect perturbations of the electromagnetic field in the substrate recess indicative of the temperature in the substrate recess. The dielectric properties of the aerosol-forming substrate vary depending on temperature. The frequency and / or amplitude of the electromagnetic field, or both the frequency and amplitude, may be adjusted by the controller based on the signal from the sensor to control the heating provided by the apparatus. In particular, overheating may be detected, insufficient heating may be detected, and the frequency and amplitude of the electromagnetic field may be adjusted accordingly. Malfunctions may be detected. It may also be possible to detect the presence of inappropriate materials in the substrate recess. If an inappropriate material is detected, the apparatus can be automatically turned off. Similarly, if the signal from the sensor suggests that the aerosol-forming substrate is not present in the substrate recess, the apparatus can be automatically turned off. This type of control is not possible when using a magnetron to generate RF radiation.

[0027] It may be desirable to maintain the temperature within the substrate recess within a predetermined temperature range. It may be desirable to maintain the temperature of the aerosol-forming substrate below the temperature of the combustion products of the aerosol-forming substrate.

[0028] The ability to control the amount of heat provided by the device based on the feedback signal also allows for the use of different aerosol-forming substrates. It may be desirable to heat different aerosol-forming substrates to different temperatures. Thus, by providing a mechanism for temperature control, it becomes possible to achieve optimal conditions for different aerosol-forming substrates or different designs of aerosol-forming articles.

[0029] The aerosol-generating device may further comprise a liquid reservoir and a liquid pump configured to deliver liquid from the liquid reservoir to the substrate recess. The liquid in the liquid reservoir may contain water. The liquid in the liquid reservoir may also contain polar molecules that are susceptible to the effects of dielectric heating. For efficient dielectric heating, it is beneficial for the aerosol-forming substrate to contain molecules that absorb RF radiation in the frequency range generated by the electromagnetic field generator. It may be advantageous to add additional liquid to the aerosol-forming substrate immediately before or during heating.

[0030] The liquid pump may be connected to a control circuit. The control circuit may also be connected to the electromagnetic field generator. The control circuit may be able to coordinate the operation of the liquid pump and the electromagnetic field generator.

[0031] The liquid pump may include a stepper motor, a syringe pump, and a peristaltic pump combined with an osmotic pump or a piezoelectric pump.

[0032] The solid-state RF transistor may be, for example, an LDMOS transistor, a GaAs FET, a SiC MESFET, or a GaN HFET.

[0033] The aerosol-generating device may comprise a smoking detector configured to detect when the user smokes the aerosol-generating system. As used herein, the term "smoking" is used to refer to the user inhaling the aerosol-generating system to receive the aerosol.

[0034] The aerosol generating device is preferably portable. The aerosol generating device may have a size comparable to that of a conventional cigarette or roll-up tobacco. The aerosol generating device may have an overall length of about 30 millimeters to about 150 millimeters. The aerosol generating device may have an outer diameter of about 5 millimeters to about 30 millimeters. The base recess may have a diameter of 2 millimeters to 20 millimeters. The base recess may have a length of 2 millimeters to 20 millimeters. The aerosol generating device may be a personal vaporizer, an e-cigarette, or a heat-not-burn device.

[0035] The device may comprise a control circuit. The control circuit may be configured to control the power supply from the power source to the electromagnetic field generating device. The control circuit may include a microprocessor, a programmable microprocessor, a microcontroller, or an application-specific integrated circuit chip (ASIC) or other electronic circuit capable of providing control. The control circuit may further comprise additional electronic components. For example, in some embodiments, the control circuit may comprise any of a sensor, a switch, a display element. The control circuit may include an RF power sensor. The control circuit may include a power amplifier. The power source may be a DC power source. The power source may include at least one battery. The at least one battery may include a rechargeable lithium-ion battery. Alternatively, the power source may be another form of charge storage device such as a capacitor.

[0036] The power source may provide power of 0.5 watt to 30 watts. The impedance of the electromagnetic field generating device may be less than 100 ohms, preferably between 50 and 75 ohms.

[0037] In use, the aerosol-forming substrate is received in the base recess. An aerosol generating system is provided that includes the aerosol generating device described above and an aerosol-forming substrate received in the base recess.

[0038] The aerosol-forming substrate may contain a solid. The aerosol-forming substrate may contain a liquid. The aerosol-forming substrate may contain a gel. The aerosol-forming substrate may contain any combination of two or more of a solid, a liquid, and a gel.

[0039] The aerosol-forming substrate may contain nicotine, a nicotine derivative, or a nicotine analog. The aerosol-forming substrate may contain one or more nicotine salts. The one or more nicotine salts may be selected from the list consisting of nicotine citrate, nicotine lactate, nicotine pyruvate, nicotine bitartrate, nicotine pectinate, nicotine alginate, and nicotine salicylate.

[0040] The aerosol-forming substrate may contain an aerosol former. As used herein, "aerosol former" is any suitable known compound or mixture of compounds that promotes the formation of a high-density and stable aerosol during use and is substantially thermally degradation-resistant at the use temperature of the aerosol-generating article. 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, glycerin; esters of polyhydric alcohols such as glycerol monoacetate, diacetate, or triacetate; and aliphatic esters of monocarboxylic acids, dicarboxylic acids, or polycarboxylic acids such as dimethyl dodecanedioate, dimethyl tetradecanedioate. Preferred aerosol formers are polyhydric alcohols or mixtures thereof such as triethylene glycol, 1,3-butanediol, and glycerin.

[0041] The aerosol-forming substrate may further comprise a flavorant. The flavorant may comprise volatile flavor components. The flavorant may comprise menthol. As used herein, the term "menthol" refers to the compound 2-isopropyl-5-methylcyclohexanol in any of its isomers. The flavorant may provide a flavor selected from the group consisting of menthol, lemon, vanilla, orange, wintergreen, cherry, and cinnamon. The flavorant may also include volatile tobacco flavor compounds that are released from the substrate upon heating.

[0042] The aerosol-forming substrate may further comprise tobacco or a tobacco-containing material. For example, the aerosol-forming substrate may comprise any of tobacco leaves, fragments of tobacco stems, reconstituted tobacco, homogenized tobacco, extruded tobacco, tobacco slurries, cast leaf tobacco, and expanded tobacco. Optionally, the aerosol-forming substrate may comprise an inert material, such as glass or ceramic, or tobacco powder compressed with another suitable inert material.

[0043] When the aerosol-forming substrate comprises a liquid or a gel, in some embodiments, the aerosol-generating article may comprise an absorbent carrier. The aerosol-forming substrate may be coated on or impregnated within the absorbent carrier. For example, the nicotine compound and the aerosol-forming agent may be mixed with water as a solution. The solution may further comprise a flavorant in some embodiments. Such a solution may then be absorbed by or coated on the surface of the absorbent carrier. The absorbent carrier may be a sheet or tablet of a cellulose-based material on which the nicotine compound and the aerosol-forming agent can be coated or absorbed. The absorbent carrier may be a metal, polymer, or vegetable foam having liquid-retaining and capillary properties, on which a liquid or gel aerosol-forming substrate is coated or absorbed.

[0044] There can be aerosol generating articles of different categories, each providing a different user experience. For example, different categories can include articles having different recipes or compositions of the aerosol forming substrate, different concentrations of nicotine or other components, and different amounts or thicknesses of the aerosol forming substrate. Aerosol generating articles belonging to the same category can have the same shape, size, or color to make that distinguishable to the user or the aerosol generating system or device. The aerosol generating system or device can be configured to receive only aerosol generating articles of a particular category, for example, by having a recess or space shaped and sized to receive only a particular type of aerosol generating article. The recess or space may be keyed to receive only aerosol generating articles of complementary shape.

[0045] The aerosol forming substrate can include liquid-filled capsules. The aerosol forming substrate can include gel-filled capsules. The liquid-filled capsules or gel-filled capsules can be configured to rupture when the liquid or gel is heated by an RF electromagnetic field in the substrate recess. The liquid-filled capsules or gel-filled capsules may include one or more valves. The one or more valves can be configured to open when the liquid or gel is heated by an RF electromagnetic field in the substrate recess due to an increase in pressure within the capsule. The one or more valves can be configured to open when the user draws air through the aerosol generating system.

[0046] There is provided an aerosol generating article including an aerosol forming substrate, a mouthpiece through which a user can draw the generated aerosol or vapor, and a fluid-permeable radio frequency electromagnetic radiation shield positioned between the aerosol forming substrate and the mouthpiece.

[0047] An aerosol-generating article may be used with an aerosol-generating device as described above. The aerosol-generating article may be received in or partially received in a substrate recess. The aerosol-forming substrate may be as described above. The fluid-permeable radio-frequency electromagnetic radiation shield may be a metal mesh.

[0048] Preferably, the article is configured such that generated aerosol or vapor must pass through a fluid-permeable radio-frequency electromagnetic radiation shield in order to reach the mouthpiece. The fluid-permeable radio-frequency electromagnetic radiation shield may be positioned adjacent to or attached to the mouthpiece.

[0049] The aerosol-generating article may comprise a filter in the mouthpiece. The aerosol-generating article may include a cooling element. The aerosol-generating article may include a spacer.

[0050] A method for generating an aerosol from an aerosol-forming substrate is provided, the method comprising placing the aerosol-forming substrate within a substrate recess of an aerosol-generating device, and generating a radio-frequency (RF) electromagnetic field in the substrate recess using a solid-state RF transistor.

[0051] The aerosol-forming substrate may be an aerosol-forming substrate as described above. The aerosol-generating device may be as described above.

[0052] The radio-frequency (RF) electromagnetic field preferably has a frequency of 500 MHz to 50 GHz, and may more preferably have a frequency of 900 MHz to 30 GHz in some cases. The RF electromagnetic field may have a frequency of 900 MHz to 5 MHz. In one embodiment, the RF electromagnetic field has a frequency of about 2.4 GHz. Generally, the heating efficiency is higher at higher frequencies. Therefore, the use of frequencies in the microwave portion of the RF spectrum is desirable.

[0053] The method may further include sensing parameters within the substrate recess and adjusting a radio frequency (RF) electromagnetic field based on the sensed parameters. The parameter may be temperature. The parameter may be electromagnetic field strength. The parameter may be the frequency of the electromagnetic field. The method may include adjusting a radio frequency (RF) electromagnetic field based on a combination of the sensed parameters.

[0054] The method may further include injecting a liquid into an aerosol-forming substrate within the substrate recess.

[0055] Also, of course, specific combinations of the various features described above may be implemented, supplied, or used independently.

[0056] Here, embodiments of the present disclosure will be described by way of illustration only with reference to the accompanying drawings.

Brief Description of the Drawings

[0057]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

[0058] Figure 1 is a schematic diagram of a heating system using radio frequency electromagnetic radiation, sometimes referred to as dielectric heating. The system includes a radio frequency signal generator 10, a power amplifier 12 connected to the signal generator to amplify the radio frequency signal, and an antenna 16 positioned inside a heating recess 14, with the antenna connected to the output of the power amplifier 12. The output of the amplifier is fed back to the signal generator to provide closed-loop control. The object 18 to be heated is placed in the recess 14 and receives radio frequency electromagnetic radiation. Polar molecules within the object 18 align with the oscillating electromagnetic field and are agitated by the electromagnetic field as they vibrate, which causes the temperature of the object 18 to rise. This type of heating has the advantage of being uniform throughout the object (if the polar molecules are uniformly distributed). It also has the advantage of being a non-contact form of heating that does not require heat conduction or convection from a high-temperature heating element. The embodiments described with reference to Figures 2 - 13 use the basic heating principle illustrated in Figure 1.

[0059] In addition, the described embodiments use solid-state radio frequency (RF) transistors to perform both the signal generation function and the power amplification function illustrated in Figure 1. However, it would be possible to implement the described embodiments using an RF transistor for signal generation and separate electronic component(s) to provide power amplification.

[0060] Figure 2 is a schematic diagram of a heat-not-burn aerosol generation system. System 21 includes an aerosol generating article 22 received within a housing 26 of an aerosol generator. The aerosol generator includes a power source 25 such as a lithium-ion battery, a control circuit 24, an RF electromagnetic field generator 23 including a solid-state RF transistor, and a substrate recess 28 in which the aerosol generating article 22 is received. The RF electromagnetic field generator 23 is provided with power from the battery 25 under the control of the control circuit 24 and generates radio frequency electromagnetic radiation within the substrate recess 28. Surrounding the substrate recess 28 and positioned between the RF electromagnetic field generator and the substrate recess is a radiation containment recess 27, and the electromagnetic radiation generated by the RF electromagnetic field generator moves through it before reaching the substrate recess 28.

[0061] The substrate recess is generally a cylindrical blind recess having an open end and a closed end and a sidewall extending between the open end and the closed end. The aerosol generating article is inserted into the substrate recess through its open end. Both the substrate recess 28 and the radiation containment recess 27 have an outer wall formed from a suitable metallic material such as aluminum that does not pass RF radiation. This causes the electromagnetic field to concentrate within the substrate recess and prevents leakage of radiation from the device. To allow radiation to pass from the radiation containment recess into the substrate recess, slots 29 are formed in the outer wall of the substrate recess 28. In the example shown in Figure 2, one slot is formed in the wall at the closed end of the substrate recess and two further slots are formed in the sidewall of the substrate recess.

[0062] The aerosol generating article 22 of this embodiment has the appearance and feel of a cigarette. It comprises a mouthpiece end through which a user can smoke and draw aerosol from the aerosol generation system. On the opposite side of the mouthpiece end, the aerosol generating article holds an aerosol forming substrate. In this embodiment, the aerosol forming substrate includes a reconstituted tobacco together with an aerosol former such as glycerol and water. The mouthpiece may be provided with a filter.

[0063] The aerosol generating device is designed to be a portable handheld device that can be easily held by the user with one hand. The housing 26 may be formed of a suitable plastic material such as polyetheretherketone (PEEK). An air inlet (not shown) may be provided in the housing to allow air to be drawn into the device through the substrate recess 28 and out through the mouthpiece of the aerosol generating article.

[0064] During operation, after the aerosol generating article is placed in the substrate recess, the device is activated. RF radiation from the electromagnetic field generating device is then directed into the substrate recess, causing dielectric heating of the aerosol forming substrate. In this example, the frequency of the electromagnetic field is between 900 MHz and 2.4 GHz. As will be described in detail, the temperature inside the substrate recess can be adjusted using a feedback control mechanism. The temperature inside the substrate recess can be sensed, or another parameter indicating the temperature inside the substrate recess can be sensed, in order to provide a feedback signal to the control circuit 24. The control circuit then adjusts the frequency or amplitude of the electromagnetic field, or both the frequency and amplitude, to maintain the temperature inside the substrate recess within a desired temperature range.

[0065] As described above, the walls of the substrate recess and the radiation containment recess are made of a material that does not allow RF radiation to pass through. For example, aluminum, stainless steel, silver, and gold can be used. The walls of the substrate recess are preferably surfaces that have been polished to improve the reflection of RF radiation. Also, it is desirable to minimize the escape of RF radiation through the mouthpiece end of the aerosol generating article. For this purpose, as shown in FIG. 3, a radiation shielding element may be included within the aerosol generating article.

[0066] The aerosol generating article 22 shown in FIG. 3 includes an aerosol generating substrate portion 36, which may be a plug of a reconstituted tobacco that is curled, together with an aerosol former and water. The aerosol generating article may also include a support element 35, which may be a hollow acetate tube, and a ventilation portion 34 including laser perforations 33 in an outer wrapper to allow air ingress to cool the generated vapor aerosol, and a mouthpiece filter 31. A metal mesh radiation shielding element 32 is provided between the mouthpiece filter 31 and the cooling portion 34. The radiation shielding element reflects any RF radiation (depicted by arrows in FIG. 3) that escapes from the substrate recess in the direction of the mouthpiece. The provision of the radiation shielding element minimizes the leakage of radiation towards the mouthpiece and thus towards the user of the device. For the generated aerosol to pass to the user's mouth, it is necessary for the radiation shielding element to be fluid permeable.

[0067] FIG. 4 shows another embodiment of an aerosol generating system similar to the embodiment illustrated in FIG. 2. However, in the embodiment of FIG. 4, the substrate recess has a wall that passes through an RF electromagnetic field. For example, the wall of the substrate recess 49 may include, for example, Teflon®, high purity quartz, or polytetrafluoroethylene. These materials can withstand high temperatures and provide a smooth and easily cleanable surface. Similar to the embodiment of FIG. 2, the system includes an aerosol generating article 22 received within a housing 46 of an aerosol generating device. The aerosol generating device includes a power source 45, such as a lithium ion battery, a control circuit 44, an RF electromagnetic field generating device 43 including a solid state RF transistor, and a substrate recess 49 in which the aerosol generating article 22 is received. The RF electromagnetic field generating device 43 is powered from the battery 45 under the control of the control circuit 44 to generate RF electromagnetic radiation within the substrate recess 49.

[0068] Figure 5 shows a further embodiment of the present invention in which the provision of an antenna or waveguide 59 improves the delivery of the electromagnetic field to the substrate recess. The components of the system of the embodiment of Figure 5 are otherwise the same as those described with reference to Figure 2. The system includes an aerosol generating article 22 received within a housing 56 of an aerosol generating device. The aerosol generating device includes a power source 55, a control circuit 54, an RF electromagnetic field generating device 53 including a solid state RF transistor, and a substrate recess 58 in which the aerosol generating article 22 is received. Surrounding the substrate recess 58 and positioned between the RF electromagnetic field generating device and the substrate recess is a radiation containment recess 57, and the electromagnetic radiation generated by the RF electromagnetic field generating device moves through it before reaching the substrate recess 58.

[0069] The antenna 59 extends from the electromagnetic field generating device 53 into the substrate recess 58 through a slot 51 formed in the base of the substrate recess. When the aerosol generating article is inserted into the substrate recess, the antenna pierces the aerosol forming substrate. The antenna 59 delivers RF electromagnetic radiation directly into the substrate recess. The antenna 59 may also serve to hold the aerosol generating article within the device. The antenna 59 may be a conductive pin. The RF electromagnetic field can also propagate freely within the radiation containment recess 57 and enter the substrate recess through the slot 51 in the side wall of the substrate recess.

[0070] Figure 6 shows a further embodiment that is substantially the same as the embodiment of Figure 5. The features of Figure 6 are the same as those of Figure 5 and are labeled with the same reference numerals. In the embodiment of Figure 6, the antenna 59 extends into the substrate recess, but in this case the antenna 59 does not penetrate the aerosol forming substrate. A stop surface 60 is provided within the substrate recess to prevent the aerosol generating article from being pushed down onto the antenna 59. This has the advantage that condensate or debris does not accumulate on the antenna. However, the antenna can still deliver the electromagnetic field directly into the substrate recess.

[0071] The heating efficiency and reduction of radiative leakage can also be improved by using a resonance cavity positioned between the RF electromagnetic field generating device and the substrate recess. A system including a resonance cavity is shown in FIG. 7.

[0072] The system of FIG. 7 includes an aerosol generating article 22 received within a housing 76 of an aerosol generating device. The aerosol generating device includes a power source 75, a control circuit 74, an RF electromagnetic field generating device 73 including a solid state RF transistor, and a substrate recess 78 in which the aerosol generating article 22 is received. Surrounding the substrate recess 78 is a radiation containment recess 77 through which electromagnetic radiation generated by the RF electromagnetic field generating device can pass.

[0073] Positioned between the electromagnetic field generating device and the substrate recess is a resonance cavity 65. An antenna 79 connected to the output of the electromagnetic field generating device 73 is positioned within the resonance cavity. The walls of the resonance cavity are configured to reflect RF radiation. The dimensions of the resonance cavity are matched to the operating frequency of the system such that resonance of the electromagnetic field occurs and the electromagnetic field is amplified at the resonance frequency. The use of the resonance cavity enables impedance matching between the source (in this case the electromagnetic field generating device 73) and the load (in this case the aerosol forming substrate). When the impedance of the load and the source match, no reflection of the electromagnetic field from the load back to the source occurs.

[0074] In one embodiment, the operating frequency is 2.4 GHz. The resonance cavity is generally cylindrical and has a length of 22.75 mm (extending in the direction between the electromagnetic field generating device and the substrate recess) and a diameter of 21.75 mm. The antenna has a length of 8.74 mm. The radiation containment recess has the same dimensions as the resonance cavity. The substrate recess within the radiation containment recess has a length of 13 mm and a diameter of 7 mm. The slots between the resonance cavity and the radiation containment recess, and between the radiation containment recess and the substrate recess, may be rectangular and may have dimensions of 1 mm×3 mm.

[0075] Dielectric heating is typically most efficient for molecules in the liquid phase that move more freely than those in the solid phase. Gels, especially those that liquefy upon heating, can also be effectively heated. For this reason, it is advantageous for the aerosol-forming substrate to have a certain amount of gel or liquid content. The liquid or gel content can also be beneficial for generating a high-density aerosol. In the examples described so far, the aerosol-forming substrate contains tobacco material. Only the reconstituted tobacco can be heated using dielectric heating. However, it may be advantageous to immerse or moisten the tobacco with liquid glycerin and water. The water and aerosol-forming agent can be provided in capsules within the tobacco in the liquid or gel phase at room temperature. When the liquid or gel in the capsule is heated by dielectric heating, it expands. The wall of the capsule may be configured to rupture as the liquid or gel expands, or may be configured to melt or disintegrate as the temperature rises. The capsule may be ruptured immediately before use by the application of mechanical pressure. Alternatively, or additionally, the tobacco material can be coated with a composition that is a gel at room temperature but liquefies as the temperature rises. In these methods, the aerosol-forming substrate can be stored for a long time without the liquid content drying out, and the liquid is only released during use.

[0076] A further option is to embed liquid capsules that do not rupture within the aerosol-forming substrate body. The liquid in the capsule is heated by RF radiation, and the heat is transferred by conduction from the capsule to the rest of the aerosol-forming substrate.

[0077] At least a portion of the gel or liquid may be selected to be heated by RF radiation but not significantly vaporized at the operating temperature. In this way, the gel or liquid imparts heat to the aerosol-forming substrate, but the liquid or gel content of the substrate, which can affect the heating efficiency, does not decrease during heating.

[0078] Another possibility is to inject or pump liquid into the substrate recess immediately before or during use. FIG. 8 is a schematic view of an embodiment of an aerosol generation system similar to the embodiment of FIG. 2, where the liquid from the liquid reservoir is pumped into the aerosol-forming substrate during heating of the substrate.

[0079] The system of FIG. 8 includes an aerosol-generating article 22 received within a housing 86 of an aerosol generator. The aerosol generator includes a power source 85, a control circuit 84, an RF electromagnetic field generator 83 including a solid-state RF transistor, and a substrate recess 88 in which the aerosol-generating article 22 is received. Surrounding the substrate recess 88 is a radiation containment recess 87 through which electromagnetic radiation generated by the RF electromagnetic field generator can pass. A slot 81 is provided within the substrate recess to allow radiation to pass from the radiation containment recess into the substrate recess.

[0080] The aerosol generator comprises a liquid reservoir containing a liquid aerosol former such as glycerol and water. A liquid conduit 95 leads from the liquid reservoir 94 to the substrate recess 88. A pump 94 is configured to pump liquid from the liquid reservoir to the substrate recess at a controlled rate. By pumping liquid into the substrate recess, the heating efficiency can be improved. A control module 92 is connected to the control circuit 84 of the electromagnetic field generator 83. The operation of the pump 94 can be coordinated with the operation of the electromagnetic field generator in response to the sensed temperature within the substrate recess. The pump may be, for example, a piezoelectric micropump.

[0081] The slots provided to enable RF radiation to the aerosol-forming substrate may be in various positions. Figure 9 shows various possibilities for the position of the slots. Option a) includes a single slot at the closed end of the substrate recess. Option b) includes slots diametrically opposite on the side walls of the recess. Option c) includes both a slot at the closed end and slots diametrically opposite on the side walls of the recess. Option d) includes two slots at the closed end and a slot diametrically opposite on the side walls of the recess. Option e) includes only two slots at the closed end of the recess. Option f) includes two slots at the closed end and a single slot on the side walls of the recess. Option g) includes three slots at the closed end of the recess. Option h) includes three slots at the closed end of the recess and two diametrically opposite slots on the side walls of the recess. Option i) includes three slots at the closed end of the recess and two pairs of diametrically opposite slots on the side walls of the recess. These are only some exemplary configurations. Each slot can have a specific shape. For example, some or all of the slots can be I-shaped, L-shaped, S-shaped, or T-shaped. Some or all of the slots can be circular, or oval or rectangular.

[0082] In embodiments where the walls of the substrate recess allow RF radiation to pass through, in particular, the aerosol-generating article can have a wrapper or casing that does not allow RF radiation to pass through, and it is clear that slots or windows can be provided in the wrapper or casing in various configurations to allow RF radiation to penetrate the aerosol-forming substrate.

[0083] In the embodiments described so far, the aerosol-forming substrate is provided in an aerosol-generating article that a user smokes. Figure 10 illustrates an alternative embodiment in which the aerosol-generating article is positioned with an aerosol-generating device. The aerosol-generating system of Figure 10 includes a mouthpiece portion that is part of the device and that the user smokes, and a capsule 110 that contains an aerosol-forming substrate fully received within the device housing 106.

[0084] The system of FIG. 10 includes an aerosol - generating capsule 110 received within a housing 106 of an aerosol - generating device. The aerosol - generating device includes a power source 105, a control circuit 104, an RF electromagnetic - field generating device 103 including a solid - state RF transistor, and a substrate recess 108 in which the aerosol - generating capsule 110 is received. Positioned between the electromagnetic - field generating device 103 and the substrate recess is a resonance recess 107. An antenna 109 connected to the output of the electromagnetic - field generating device 103 is positioned within the resonance recess as described with reference to the embodiment of FIG. 7. The outer surface of the capsule generally does not pass RF radiation, but a window 112 that passes RF electromagnetic fields is provided to allow the radiation to penetrate the capsule. The capsule may be provided, for example, with a plastic coating that passes RF radiation.

[0085] The mouthpiece portion 101 is fixed to the housing 106 to cover the capsule. The mouthpiece can be attached to the device housing by a screw - in joint, snap - fit, hinge, or any other suitable method. The mouthpiece portion 101 includes a metal - mesh radiation shield 102 through which the generated aerosol can pass.

[0086] An air - flow inlet (not shown) is provided in the housing 106 to allow air to be drawn into the device, pass through the outlet of the capsule 110 (or through the capsule), and exit through the mouthpiece of the aerosol - generating device.

[0087] FIG. 11 shows another embodiment similar to the embodiment of FIG. 10, but with a waveguide provided instead of the resonance recess. Features identical to those of the embodiment of FIG. 10 are provided with the same reference numerals. The aerosol generating device includes a power source 105, a control circuit 104, an RF electromagnetic field generating device 103 including a solid-state RF transistor, and a substrate recess 108 in which an aerosol generating capsule 120 is received. In the embodiment of FIG. 11, RF radiation is induced from the electromagnetic field generating device 103 through a waveguide 124 to an antenna 126 positioned adjacent to a window in the side wall of the capsule 120. Again, the outer surface of the capsule generally does not pass RF radiation, but a window 122 that passes RF electromagnetic fields is provided, allowing the radiation to penetrate the capsule. The window 122, as will be described next, has the window through which the radiation enters the recess positioned on the opposite side of the capsule, allowing the RF electromagnetic field to be sampled by the sampling antenna.

[0088] In the embodiments shown in FIGS. 10 and 11, the capsule is filled with a gel or a liquid aerosol-forming substrate, but the same range of substrates may be used as described with reference to the previous embodiments. The gel may include a majority of glycerol along with nicotine and flavorants. The liquid may include a mixture of one or more aerosol-forming substances such as glycerol and propylene glycol, water, nicotine, and flavorants. In one example, the liquid in the capsule of FIG. 11 includes 39% (by weight) glycerol, 39% propylene glycol, 20% water, and 2% nicotine. In another example, the liquid includes 58% (by weight) glycerol, 20% propylene glycol, 20% water, and 2% nicotine.

[0089] Figure 12 is a schematic diagram of a possible mechanism that allows for the escape of aerosol from a gel or liquid-filled capsule for use in the embodiment of FIG. 10 or 11. The capsule of FIG. 12 includes a metal housing 130 that is refillable with a gel or liquid aerosol-forming substrate 132. A window is formed in the capsule housing to allow the entry of RF radiation so that the gel or liquid can be heated. A valve 134 is provided at the mouthpiece end of the capsule. When the user sucks on the mouthpiece of the system, the pressure drop within the mouthpiece pulls the valve open, allowing vapor and aerosol to escape from the capsule and be drawn into the user's mouth. Heating of the gel or liquid can also increase the pressure within the capsule, providing an additional opening force on the valve 134.

[0090] In all of the described embodiments, it is desirable to be able to regulate the temperature of the aerosol-forming substrate. The ability to adjust the frequency or amplitude of the electromagnetic field using feedback control is one of the advantages of using solid-state RF transistors.

[0091] Figure 13 shows a control scheme that can be used in any of the described embodiments. As described above, the system includes a control circuit for the electromagnetic field generator. In the example of FIG. 13, the electromagnetic field generator 11 includes a solid-state RF LDMOS transistor that performs both the functions of an RF signal generator 10 and a power amplifier 12, amplifying the generated RF electromagnetic signal. The output of the RF solid-state transistor 11 is passed to a radiation antenna 149 that is positioned to radiate an aerosol-forming substrate 152 located within an aerosol-generating article 150 received within a substrate recess 148.

[0092] The control circuit includes a microcontroller 140 that can control both the frequency and power output of the RF solid state transistor. One or more sensors provide inputs to the microcontroller. The microcontroller adjusts the frequency or power output, or both the frequency and power output, of the electromagnetic field generator based on the sensor inputs. In the embodiment shown in FIG. 13, there is a temperature sensor 142 positioned to sense the temperature within the substrate recess. A sampling antenna 144 may be provided within the recess as an alternative to, or in addition to, the temperature sensor. The sampling antenna is configured as a receiver and can detect perturbations in the electromagnetic field within the substrate recess, which is an indication of the efficiency of energy absorption by the aerosol-forming substrate. An RF power sensor 147 is also provided to detect the power output from the electromagnetic field generator.

[0093] The microcontroller 140 receives signals from the RF power sensor, the temperature sensor 142, and the sampling antenna 144. The signals can be used to determine whether the temperature in the substrate recess is too low, too high, if there are defects, and if there is no substrate or a substrate with inappropriate dielectric properties. A substrate with inappropriate substrate properties can be a substrate in which the liquid or gel content has been depleted by use and thus needs to be replaced.

[0094] Based on the determination made by the microcontroller 140, the frequency and power of the electromagnetic field generated by the RF solid state transistor 11 are adjusted or the electromagnetic field is turned off. Typically, it is desirable to provide a stable and consistent volume of aerosol, which means maintaining the aerosol-forming substrate within a specific temperature range. However, the desired target temperature can change over time as the composition of the aerosol-forming substrate changes and the temperature of the surrounding system changes. Also, since the dielectric properties of the aerosol-forming substrate change with temperature, it may be necessary to adjust the electromagnetic field as the temperature rises or falls.

[0095] The features described with respect to one embodiment are clearly applicable to other embodiments. The described embodiments provide the advantages of uniform non-contact heating of an aerosol-forming substrate in a manner that can be controlled to provide certain desirable aerosol characteristics. Compared to conventional microwave heating using magnetrons, the use of solid-state RF transistors provides a compact system that can be implemented as a handheld system. Also, the use of solid-state RF transistors allows for better control of frequency and power, as well as a longer operating life.

Claims

1. An aerosol generating device for heating an aerosol-forming substrate to generate an aerosol, comprising: a substrate recess configured to receive the aerosol-forming substrate; and an electromagnetic field generating device configured to generate a radio frequency (RF) electromagnetic field in the substrate recess, the electromagnetic field generating device including a solid-state RF transistor, the aerosol generating device comprising the electromagnetic field generating device.

2. The aerosol generating device according to claim 1, wherein the solid-state RF transistor is configured to generate and amplify the RF electromagnetic field.

3. The aerosol generating device according to claim 1, wherein the substrate recess comprises one or more outer walls formed of a material that does not allow the RF electromagnetic field to pass through, and one or more slots are formed in the one or more outer walls.

4. The aerosol generating device according to any one of claims 1 to 3, wherein the substrate recess includes a blind recess configured to receive an aerosol-forming article containing the aerosol-forming substrate.

5. The aerosol generating device according to any one of claims 1 to 4, further comprising a resonance recess between the substrate recess and the electromagnetic field generating device.

6. The aerosol generating device according to any one of claims 1 to 5, further comprising an antenna connected to the electromagnetic field generating device configured to direct the RF electromagnetic field.

7. The aerosol generating device according to claim 6, wherein the antenna is at least partially positioned in the substrate recess.

8. A sensor in or adjacent to the substrate recess, the sensor providing a signal indicative of a temperature in the substrate recess, and a controller connected to receive the signal from the sensor and configured to control the electromagnetic field generating device depending on the signal from the sensor, the aerosol generating device according to any one of claims 1 to 7.

9. The aerosol generating device according to any one of claims 1 to 8, further comprising a liquid storage unit and a liquid pump configured to deliver liquid from the storage unit to the substrate recess.

10. An aerosol generating system comprising the aerosol generating device according to any one of claims 1 to 9 and an aerosol-forming substrate received in the substrate recess.

11. The aerosol generation system according to claim 10, wherein the aerosol forming substrate contains tobacco.

12. The aerosol generation system according to claim 10 or 11, wherein the aerosol forming substrate includes a liquid-filled capsule or a gel-filled capsule.

13. The aerosol generation system according to claim 12, wherein the liquid-filled capsule or the gel-filled capsule is configured to rupture when the liquid or the gel is heated by the radio frequency (RF) electromagnetic field in the substrate recess.

14. A method for generating an aerosol from an aerosol forming substrate, comprising: placing the aerosol forming substrate in a substrate recess of an aerosol generating device; generating a radio frequency (RF) electromagnetic field in the substrate recess using a solid state RF transistor.

15. An aerosol generating article, comprising: an aerosol forming substrate; a mouthpiece through which a user can draw the generated aerosol or vapor; a fluid-permeable radio frequency electromagnetic radiation shield positioned between the aerosol forming substrate and the mouthpiece.

Images