RU2778747C2 - Induction heating device for heating the aerosol-forming substrate - Google Patents

Abstract

FIELD: tobacco industry.

SUBSTANCE: group of inventions relates to the tobacco industry, namely to an induction heating device for heating an aerosol-forming substrate, an induction heating system for heating an aerosol-forming substrate, a kit for heating an aerosol-forming substrate and a method for using an induction heating system. An induction heating device for heating an aerosol-forming substrate contains a susceptor, a device housing, a DC power source having a DC supply voltage. The device additionally contains an electronic power supply circuit capable of operating at a frequency in the range from 1 to 30 MHz and containing an inverter for converting direct current to alternating current connected to a DC power source and including a Class E power amplifier containing a transistor switch, a transistor switch excitation circuit and an inductive-capacitive load circuit designed to operate at an ohmic load that is less than 2 ohms. The inductive-capacitive load circuit contains a shunt capacitor and a series circuit of a capacitor and an inductor having ohmic resistance. The device also contains a cavity located in the housing of the device and having an internal surface shaped to accommodate at least part of the aerosol-forming substrate. The cavity is arranged so that when a part of the aerosol-forming substrate is placed in this cavity, the inductor of the inductive-capacitive load circuit is inductively connected to the susceptor of the aerosol-forming substrate during use. The inductor is built into the device housing at the near end of the device housing to surround the cavity, which is also located at the near end of the device housing.

EFFECT: simplifying the design of the heater power supply circuit while providing fast heating.

15 cl, 6 dwg

Description

The present invention relates to an induction heating device for heating an aerosol-forming substrate, and more specifically, an induction heating device for heating an aerosol-forming substrate of a smoking article.

Conventional smoking articles known so far, such as cigarettes, deliver flavor and aroma to the user through a combustion process. A body of combustible material, primarily tobacco, is combusted and an adjacent portion of the material is pyrolyzed by heat applied drawn through the material, with typical combustion temperatures in excess of 800°C during puffs. During heating, inefficient oxidation of the combustible material occurs, and a variety of distillation and pyrolysis products are formed. As these products are drawn through the body of the smoking article towards the user's mouth, they cool and condense to form an aerosol or vapor that provides the user with the flavor and aroma associated with smoking.

Known alternatives to conventional smoking articles include those in which the combustible material itself does not directly deliver flavorants to the aerosol inhaled by the user. In these smoking articles, a combustible heating element, typically coal in nature, is burned to heat air as the latter is drawn over the heating element and through a zone containing heat activated elements that release a flavored aerosol.

Yet another alternative to conventional smoking articles is an aerosol-forming tobacco-containing solid substrate containing a magnetically permeable electrically conductive susceptor that is located in thermal proximity to the aerosol-forming tobacco-containing substrate. The susceptor of the tobacco-containing substrate is subjected to an alternating magnetic field generated by an induction source such that an alternating magnetic field is induced in the susceptor. This induced alternating magnetic field generates heat in the susceptor and at least a portion of the heat generated in the susceptor is transferred from the susceptor to an aerosol-forming substrate located in thermal proximity to the susceptor to form the aerosol and create the desired flavor.

US Pat. No. 5,613,505 discloses an induction heating device for heating an aerosol-forming substrate containing a susceptor. SUBSTANCE: induction heating device comprises a device housing, a DC power source having a DC supply voltage, and an electronic power supply circuit containing an inverter for converting DC into AC connected to the DC power source, and an inductive-capacitive load circuit. The induction heating device further comprises a cavity having an inner surface shaped to receive at least a portion of the aerosol-forming substrate. The cavity is located in such a way that when a part of the aerosol-forming substrate is placed in this cavity, the inductor of the inductive-capacitive load circuit is inductively connected to the susceptor of the aerosol-forming substrate. The inductor is embedded in the device body at the proximal end of the device body to surround a cavity which is also located at the proximal end of the device body.

However, there is still a need for an induction heating device for aerosol-forming substrates incorporating a susceptor, more specifically for solid aerosol-forming substrates incorporating a susceptor, such as solid aerosol-forming substrates in smoking articles, where the device should provide the ability to quickly and very efficiently generate the required heat in the susceptor, with the ability to subsequently transfer this heat to the aerosol-forming substrate to form an aerosol to enable the user to draw in this aerosol as needed. This induction heating device must be able to operate without the need to connect it to an external power source. In addition, this device must be small in size and convenient to use in order to be attractive to users. According to one aspect of the present invention, an induction heating device is provided for heating an aerosol-forming substrate containing a susceptor, in particular for heating a solid aerosol-forming substrate of a smoking article. The induction heating device according to the present invention comprises: - a body of the device - a DC power supply having a DC supply voltage - a power supply electronic circuit capable of operating at high frequency and containing an inverter for converting DC to AC connected to the power supply DC and includes a class E power amplifier containing a transistor switch and an inductive-capacitive load circuit configured to operate at a low-resistance load, while the inductive-capacitive load circuit contains a shunt capacitor and a series circuit of a capacitor and an inductor having an ohmic resistance , and - a cavity located in the body of the device, having an inner surface shaped to accommodate at least a part of the aerosol-forming substrate, and located in such a way that when placed in it part about of the aerosol-generating substrate, the inductor of the inductive-capacitive loading circuit is inductively coupled to the susceptor of the aerosol-generating substrate during use.

The aerosol-forming substrate is preferably a substrate capable of releasing volatile compounds that can form an aerosol. Volatile compounds are released as a result of heating the aerosol-forming substrate. The aerosol-forming substrate may be solid or liquid, or contain both solid and liquid components. Preferably, the aerosol-forming substrate is solid.

The aerosol-forming substrate may contain nicotine. The nicotine-containing aerosol-forming substrate may be a nicotine salt matrix. The aerosol-forming substrate may comprise a plant-based material. The aerosol-forming substrate may comprise tobacco, and preferably, the tobacco-containing material contains tobacco-flavored volatile compounds that are released from the aerosol-forming substrate upon heating.

The aerosol-forming substrate may comprise homogenized tobacco material. Homogenized tobacco material can be obtained by agglomerating tobacco particles. If present, the homogenized tobacco material may have an aerosol former content of at least 5% dry weight, and preferably more than 5% to 30% dry weight.

The aerosol-forming substrate may alternatively comprise a tobacco-free material. The aerosol-forming substrate may comprise a homogenized plant-based material.

The aerosol-forming substrate may comprise at least one aerosol former. The aerosol former may be any suitable known compound or mixture of compounds which, when used, produces a dense and stable aerosol and which is substantially resistant to thermal degradation at the operating temperature of the aerosol generating device. Suitable aerosolizers are well known in the art and include, but are not limited to: polyhydric alcohols such as triethylene glycol, 1,3-butanediol, and glycerol; 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. Particularly preferred aerosol formers are polyhydric alcohols or mixtures thereof, such as triethylene glycol, 1,3-butanediol, and most preferably glycerol. The aerosol-forming substrate may contain other additives and ingredients such as flavors. The aerosol-forming substrate preferably contains nicotine and at least one aerosol former. In a particularly preferred embodiment, the aerosol former is glycerin.

The DC power supply may typically comprise any suitable DC power source, including but not limited to a plug-in power supply, one or more disposable batteries, accumulators, or any other suitable DC power source capable of providing the required DC supply voltage. and the required DC power supply. In one embodiment, the DC supply voltage of the DC power supply is in the range of about 2.5 Volts to about 4.5 Volts, and the DC supply current is in the range of about 2.5 to about 5 Amps (corresponding to the supply power DC in the range of about 6.25 watts to about 22.5 watts). Preferably, the DC power supply comprises batteries. Such batteries are commonly available and have an acceptable total volume of about 1.2-3.5 cubic centimeters. Such batteries may have a substantially cylindrical or rectangular solid shape. In addition, the DC power supply may include a DC supply choke.

As a general rule, when the term "about" is used in conjunction with a specific value throughout this application, it should be understood that the value following the term "about" need not be exactly equal to the specific value for technical reasons. However, the term "about" when used in conjunction with a specific amount should always be understood to include and expressly express the specific amount following the term "about".

The electronic power supply circuit is configured to operate at a high frequency. For the purposes of this application, the term "high frequency" should be understood to mean a frequency in the range from about 1 Megahertz (MHz) to about 30 Megahertz (MHz) (including the range from 1 MHz to 30 MHz), more specifically from about 1 Megahertz ( MHz) up to about 10 Megahertz (MHz) (including the range from 1 MHz to 10 MHz), and more specifically from about 5 Megahertz (MHz) to about 7 Megahertz (MHz) (including the range from 5 MHz to 7 MHz).

The power supply electronic circuitry comprises a DC/AC inverter for converting DC to AC connected to a DC power supply. This DC-AC inverter includes a class E power amplifier containing a transistor switch, a transistor switch driving circuit, and an inductive-capacitive load circuit. Class E power amplifiers are well known and are described in detail, for example, in the article "Class-E RF Power Amplifiers" by Nathan O. Sokal, published in the bimonthly QEX magazine, issue 2 January/February 2001, pp. 9-20, American Radio Relay League (ARRL), Newington, CT, USA. Class E power amplifiers are advantageous for high frequency operation and yet have a simple circuit structure containing a minimum number of components (for example, only one transistor switch is needed, which is an advantage over class D power amplifiers containing two transistor switches, which must be controlled at a high frequency in such a way as to ensure that one of the two transistors is turned off while the other of these two transistors is on). In addition, Class E power amplifiers are known for their minimal power dissipation in the switching transistor during switching transients. Preferably, the class E power amplifier is a single-ended first-order class E power amplifier containing only one transistor switch.

The class E power amplifier transistor switch can be any type of transistor and can be a Bipolar Junction Transistor (BJT). More preferably, however, the transistor switch is in the form of a field effect transistor (FET), such as a metal-oxide-semiconductor field effect transistor (MOSFET) or a metal-oxide-semiconductor field effect transistor (MOSFET) or a metal-oxide-semiconductor field effect transistor (MOSFET). semiconductor (metal-semiconductor field effect transistor, MESFET).

The inductive-capacitive load circuit of the class E power amplifier of the induction heating device according to the present invention is configured to operate with a low-resistance load. The term "low resistance load" should be understood to mean a resistive load that is less than about 2 ohms. The inductive-capacitive load circuit contains a shunt capacitor and a series circuit of a capacitor and an ohmic inductor. This ohmic resistance of the inductor is usually a few tenths of an ohm. When used, the ohmic resistance of the susceptor is added to the ohmic resistance of the inductor and must exceed the ohmic resistance of the inductor, since the electrical power supplied must be converted into heat in the susceptor to the maximum extent possible in order to increase the efficiency of the power amplifier and ensure that the maximum possible amount of heat can be transferred from the susceptor to the rest of the an aerosol-forming substrate for efficient aerosol generation.

The susceptor is a conductor capable of inductive heating. "Thermal proximity" means that the susceptor is positioned relative to the rest of the aerosol-forming substrate such that sufficient heat is transferred from the susceptor to the rest of the aerosol-forming substrate to form an aerosol.

Since the susceptor is not only magnetically permeable, but also electrically conductive (it is a conductor as mentioned above), a current known as eddy current is induced in the susceptor and this current flows in the susceptor according to Ohm's law. The susceptor must have a low electrical resistivity ρ to increase the Joule heat dissipation. In addition, it is necessary to take into account the frequency of the alternating eddy current due to the skin effect (more than 98% of the electric current flows within the layer, the depth of which from the outer surface of the conductor is equal to four times the depth δ of the surface layer). With this in mind, the ohmic resistance R _S of the susceptor is calculated from the equation

_Rs =

where

f denotes the frequency of the alternating eddy current

μ ₀ denotes the magnetic permeability of free space

μ _r denotes the relative magnetic permeability

susceptor material, and

ρ denotes the electrical resistivity of the material

susceptor.

The power loss P _e due to eddy current is calculated by the formula

P _e \u003d I ² ⋅R _S

where

I denotes the magnitude (rms value) of the eddy current, and

R _S denotes the electrical resistance of the susceptor (see

above)

From this equation for calculating P _e and from calculating R _S it clearly follows that in the case of a material having a known relative magnetic permeability μ _r and a given electrical resistivity ρ, the power loss P _e due to eddy current (due to conversion to heat) , increase with increasing frequency and current (rms value). On the other hand, the frequency of the alternating eddy current (and, accordingly, the alternating magnetic field that induces an eddy current in the susceptor) cannot increase arbitrarily, since the depth δ of the surface layer decreases as the frequency of the eddy current (or the alternating magnetic field that induces an eddy current in susceptor) so that above a certain cutoff frequency, eddy currents can no longer be generated in the susceptor because the depth of the surface layer is too shallow to allow eddy currents to be generated. Increasing the magnitude of the current (rms value) requires an alternating magnetic field having a high magnetic flux density, and therefore requires bulky sources of induction (inductors).

In addition, heat is generated in the susceptor by a heating mechanism associated with hysteresis. The power loss due to hysteresis is calculated from the equation

P _H = V ⋅ W _H ⋅ f

where

V stands for susceptor volume

W _H denotes the work required to magnetize the susceptor

along the closed hysteresis loop in the B-H diagram, and

f denotes the frequency of the alternating magnetic field.

The work W _H required to magnetize the susceptor along a closed hysteresis loop can also be expressed as

W _H =

The maximum possible value of work W _H depends on the properties of the susceptor material (remanent magnetic induction B _R at saturation, coercivity H _C ), and the actual value of work W _H depends on the actual magnetization hysteresis loop in the B-H diagram induced in the susceptor by an alternating magnetic field, and this actual magnetization hysteresis loop in the B-H diagram depends on the magnitude of the magnetic excitation.

There is a third heat generation mechanism (power loss) in the susceptor. This heat generating mechanism is due to dynamic losses of magnetic domains in the magnetically permeable material of the susceptor when the susceptor is subjected to an external alternating magnetic field, and these dynamic losses usually also increase with increasing frequency of the alternating magnetic field.

In order to be able to generate heat in the susceptor according to the mechanisms described above (mainly through eddy current losses and hysteresis losses), a cavity is located in the body of the device. The cavity has an inner surface shaped to accommodate at least a portion of the aerosol-forming substrate. This cavity is positioned such that, when a portion of the aerosol-forming substrate is placed therein, the inductor of the inductive-capacitive load circuit is inductively coupled to the susceptor of the aerosol-forming substrate in use. This means that the class E power amplifier's inductor-capacitive load circuit is used to heat the susceptor by magnetic induction. This eliminates the need for additional components such as matching circuits to match the output impedance of the Class E power amplifier to the load, and thus further minimizes the size of the power supply electronics.

In general, the induction heating device according to the present invention is a small, easy to handle, efficient, clean and reliable heating device due to non-contact heating of the substrate. In the case of susceptors producing the above low-resistance loads, as described above, and yet having an ohmic resistance significantly higher than the ohmic resistance of an inductor-capacitive load circuit, it is possible to achieve susceptor temperatures in the range of 350-400 degrees Celsius in as little as five seconds or for a period of time that is even less than five seconds, and at the same time the temperature of the inductor remains low (due to the fact that the bulk of the power is converted into heat in the susceptor).

As already noted, in accordance with one aspect of the induction heating device according to the present invention, this device is configured to heat the aerosol-forming substrate of the smoking article. Specifically, this includes applying power to the susceptor within the aerosol-forming substrate such that the aerosol-forming substrate is heated to an average temperature of 200-240 degrees Celsius. Even more preferably, the device is configured to heat the tobacco-containing solid aerosol-forming substrate of the smoking article.

According to another aspect of the induction heating device according to the present invention, the total volume of the power supply electronic circuit is not more than 2 cm ³ . Thus, it is possible to accommodate the batteries, the power supply electronics and the cavity in the device body having a small overall size, which provides convenience and ease of handling.

In accordance with yet another aspect of the induction heating device of the present invention, the inductor of the inductive-capacitive load circuit comprises a cylindrical, helical-wound induction coil having an elongated shape and having an internal volume in the range of from about 0.15 cm ³ to about 1.10 cm ³ . For example, the inner diameter of the cylindrical helical induction coil may be from about 5 mm to about 10 mm, and preferably may be about 7 mm, and the length of the cylindrical helical induction coil may be from about 8 mm to about 14 mm. The diameter or thickness of the coil wire may be from about 0.5 mm to about 1 mm, depending on whether a coil wire with a round cross section or a coil wire with a flat rectangular cross section is used. The helically wound induction coil is located on or near the inner surface of the cavity. A helical-wound cylindrical induction coil positioned on or near the interior surface of the cavity allows for further minimization of device dimensions.

In accordance with yet another aspect of the induction heating device of the present invention, the device body is substantially cylindrical with a cavity located at the proximal end of the device body and a DC power source located at the distal end of the device body. The power supply electronic circuit is located between the DC power supply and the cavity. This allows all components of the induction heating device to be compactly and aesthetically pleasing in a small and easy to handle body of the device.

As noted above, in accordance with another aspect of the induction heating device of the present invention, the DC power supply comprises a DC battery. This allows the batteries to be recharged, preferably by being connected to the mains via a charger containing an AC/DC converter.

In accordance with yet another aspect of the induction heating device of the present invention, the power supply electronic circuitry further comprises a microcontroller that is programmed to interrupt the inverter's AC generation to convert DC to AC if the temperature of the aerosol-forming substrate's susceptor has exceeded the Curie temperature of that susceptor during time of use, and which is programmed to resume generating alternating current if the susceptor temperature drops below that Curie temperature again. This feature can be used to control the temperature of the susceptor using a microcontroller.

In case the susceptor is made of a single material, the Curie temperature must correspond to the maximum temperature that the susceptor must have (in other words, the Curie temperature is identical to the maximum temperature to which the susceptor must be heated, or deviates from this maximum temperature by about 1-3% ). If the temperature of the susceptor exceeds the Curie temperature of said single material, the ferromagnetic properties of the susceptor disappear and the susceptor becomes only paramagnetic.

In case the susceptor is made from more than one material, the materials of the susceptor can be optimized in additional aspects. For example, materials may be selected such that the first material of the susceptor may have a Curie temperature in excess of the maximum temperature to which the susceptor is to be heated. On the one hand, the first material of the susceptor may in this case be optimized, for example, in terms of maximum heat generation and its transfer to the rest of the aerosol-forming substrate to ensure efficient heating of the susceptor, however, the susceptor may additionally contain a second material having a Curie temperature corresponding to the maximum temperature to which the susceptor must be heated, and the moment the susceptor reaches this Curie temperature, the magnetic properties of the susceptor as a whole change. This change can be detected and alerted to the microcontroller, which then interrupts AC power generation until the temperature drops below the Curie temperature again, after which AC power generation can be resumed.

According to another aspect of the induction heating device according to the present invention, the class E power amplifier has an output impedance, and the power supply electronics further comprise a matching circuit for matching the output impedance of the class E power amplifier to a low resistance load. This measure can be useful to further increase the power loss in the low-resistance load, resulting in increased heat generation in the low-resistance load. For example, the matching circuit may contain a small matching transformer.

Yet another aspect of the present invention relates to an induction heating system comprising an induction heating device according to any of the embodiments described above and an aerosol-forming substrate containing a susceptor. At least a portion of the aerosol-generating substrate is placed in the cavity of the induction heating device such that the inductor of the inductive-capacitive load circuit of the inverter for converting DC to AC current of the induction heating device is inductively coupled to the susceptor of the aerosol-generating substrate during use.

In accordance with one aspect of the induction heating system of the present invention, the aerosol-forming substrate may be the aerosol-forming substrate of a smoking article. In particular, the aerosol-forming substrate may be a tobacco-containing solid aerosol-forming substrate that can be used in smoking articles (eg, such as cigarettes).

Another aspect of the present invention relates to a kit containing an induction heating device corresponding to any of the above embodiments, and an aerosol-forming substrate containing a susceptor. The induction heating device and the aerosol-forming substrate are configured to accommodate, during use, at least a portion of the aerosol-forming substrate in a cavity of the induction heating device, such that the inductor of the inductive-capacitive load circuit of the inverter for converting DC to AC current of the induction heating device is inductively coupled. with a susceptor of an aerosol-forming substrate. Although typically the aerosol-forming substrate and the induction heating device are separate, they can also be made as a kit. Or, alternatively, the starter kit may comprise an induction heating device and a plurality of aerosol-forming substrates, wherein in addition only aerosol-forming substrates are provided, so that after a consumer has purchased the induction heating device in the starter kit and consumed the aerosol-forming substrates contained in this starter kit, the user will only need additional aerosol-forming substrates. As before, according to one aspect of the kit according to the present invention, the aerosol-forming substrate may be an aerosol-forming substrate of a smoking article, and in particular, this aerosol-forming substrate of a smoking article may be a tobacco-containing solid aerosol-forming substrate.

Another aspect of the present invention relates to a method for using an induction heating system. The method comprises the steps of: - providing a DC power supply having a DC supply voltage - providing a power supply electronic circuit configured to operate at high frequency and comprising an inverter for converting DC to AC, including a power amplifier class E, containing a transistor switch, a transistor switch excitation circuit and an inductive-capacitive load circuit configured to operate at a low ohmic load, while the inductive-capacitive load circuit contains a shunt capacitor and a series circuit of a capacitor and an inductor having an ohmic resistance, - provide a cavity configured to receive at least a part of the aerosol-forming substrate and located in such a way that when a part of the aerosol-forming substrate is placed in this cavity, the inductor of the inductive-capacitive load circuit induct visibly coupled to the susceptor of the aerosol-forming substrate, and - providing an aerosol-forming substrate containing the susceptor, and inserting at least a portion of the aerosol-forming substrate into the cavity such that the inductor of the inductive-capacitive load circuit is inductively coupled to the susceptor of the aerosol-forming substrate.

According to one aspect of the method of the present invention, the DC power supply is a battery, and the method further comprises charging the battery before inserting a portion of the aerosol-forming substrate into the cavity. This aspect is particularly advantageous because, in the case of using rechargeable batteries, the device can be used (after charging the batteries) without the need to be connected to the mains or to another external power source. When the state of charge of the battery is low, the battery provides an easy recharging capability, so there is no need to carry any disposable spare batteries. If the battery state of charge is low, the battery can be easily recharged and the device will be ready for use again. In addition, batteries are environmentally friendly as they are not disposable batteries that must be properly disposed of.

Additional advantageous aspects of the present invention will become apparent from the following description of embodiments, supplemented by drawings, where:

In FIG. 1 shows the general heating principle underlying the present invention,

In FIG. 2 is a block diagram of an embodiment of an induction heating device and system according to the present invention,

In FIG. 3 shows an embodiment of an induction heating device with the main components located in the body of the heating device,

In FIG. 4 shows an embodiment of the main components of the electronic power supply circuit in an induction heating device according to the present invention (without a matching circuit),

In FIG. 5 shows an embodiment of an inductor of an inductive-capacitive load circuit in the form of a cylindrical induction coil with a spiral winding, having an elongated shape,

In FIG. 6 shows a fragment of an inductive-capacitive load circuit, including the inductance and ohmic resistance of the coil, and in addition, the ohmic load resistance is shown.

In FIG. 1 schematically shows the general heating principle underlying the present invention. In FIG. 1 schematically shows a cylindrical helical wound induction coil L2, having an elongated shape and forming an internal volume in which the aerosol-forming substrate 20 of a smoking article 2 containing a susceptor 21 is partially or completely located. A smoking article 2 containing an aerosol-forming substrate 20 with a susceptor 21, shown schematically in an enlarged sectional view, shown alone on the right side of FIG. 1. As already mentioned, the aerosol-forming substrate 20 of the smoking article 2 may be, but is not limited to, a tobacco-containing solid substrate.

In addition, in FIG. 1, the magnetic field inside the internal volume of the induction coil L2 is schematically shown by several lines of force B _L of the magnetic field at one particular moment in time, since the magnetic field induced by the alternating current i _L2 flowing through the induction coil L2 is an alternating magnetic field that changes its polarity from AC frequency i _L2 , which may be in the range from about 1 MHz to about 30 MHz (including the range from 1 MHz to 30 MHz) and, in particular, may be in the range from about 1 MHz to about 10 MHz (including the range from 1 MHz to 10 MHz, and in particular may be less than 10 MHz) and, more specifically, the frequency may be in the range from about 5 MHz to about 7 MHz (including the range from 5 MHz to 7 MHz, and may be, for example, 5 MHz). The two main mechanisms responsible for the generation of heat in the susceptor 21 are the power losses P _e due to eddy currents (these eddy currents are shown as a closed circle) and the power losses P _h due to hysteresis (this hysteresis is shown as a closed hysteresis). curve) are also shown schematically in Fig. 1. A more detailed description of these mechanisms is presented above.

In FIG. 3 shows an embodiment of an induction heating device 1 according to the present invention. The induction heating device 1 includes a device body 10, which may be made of plastic, and a DC power supply 11 (see FIG. 2) containing a battery 110. The induction heating device 1 further includes a connection port 12 containing a pin 120 for connecting an induction heating device to the charging station or battery recharger 110. In addition, the induction heating device 1 includes a power supply electronic circuit 13 that is configured to operate at a desired frequency, such as 5 MHz as described above. The power supply electronic circuit 13 is electrically connected to the battery 110 via a suitable electrical connection 130. The power supply electronic circuit 13 includes additional components not shown in FIG. 3; in particular, it contains an inductive-capacitive load circuit (see Fig. 4), which, in turn, contains an inductor L2, which is indicated by dotted lines in Fig. 3. An inductor L2 is embedded in the device body 10 at the proximal end of the device body 10 and surrounds a cavity 14 which is also located at the proximal end of the device body 10. The inductor L2 may comprise a cylindrical helically wound induction coil having an elongated shape as shown in FIG. 5. The helically wound cylindrical induction coil L2 may have a radius r in the range of about 5 mm to about 10 mm, and in particular, the radius r may be about 7 mm. The length l of the helically wound cylindrical induction coil may range from about 8 mm to about 14 mm. Accordingly, its internal volume may range from about 0.15 cm ³ to about 1.10 cm ³ .

As shown in FIG. 3, a tobacco-containing solid aerosol-forming substrate 20 containing a susceptor 21 is placed in a cavity 14 at the proximal end of the device body 10 such that, during use, an inductor L2 (helical-wound cylindrical induction coil) is inductively coupled to the tobacco-containing solid aerosol-forming susceptor 21 of the substrate 20 of the smoking article 2. The filter portion 22 of the smoking article 2 may be positioned outside the cavity 14 of the induction heating device 1 so that during use, the user can draw aerosol through the filter portion 22. When the smoking article is removed from the cavity 14, easy cleaning is possible. cavity 14 because, with the exception of the open distal end through which the aerosol-forming substrate 20 of the smoking article 2 is inserted, the cavity is completely closed and surrounded by the inner walls of the device's plastic housing 10 forming cavity 14.

In FIG. 2 shows a block diagram of an embodiment of an induction heating device 1 according to the present invention, with, however, some optional aspects or components, as will be described below. The induction heating device 1, together with the aerosol-forming substrate 20 containing the susceptor 21, is an embodiment of the induction heating system according to the present invention. The block diagram shown in FIG. 2 is an illustration given in consideration of the usage method. As can be seen, the induction heating device 1 comprises a DC power supply 11 (in FIG. 3 containing a battery 110), a microprocessor control module 131, an inverter 132 for converting DC to AC current, a matching circuit 133 for adapting to the load, and an inductor L2. The microprocessor control unit 131, the inverter 132 for converting DC to AC and the matching circuit 133, and the inductor L2 are parts of the power supply electronic circuit 13 (see Fig. 1). Two feedback channels 134 and 135 are provided to provide feedback signals indicative of the voltage and current through the inductor L2, which allows further power supply to be controlled. For example, if the temperature of the susceptor exceeds the desired temperature, an appropriate signal can be generated to interrupt further energization until the temperature of the susceptor falls below the desired temperature again, after which the energization can be resumed. Accordingly, it is possible to adjust the switching voltage frequency for optimal power transfer to the susceptor. Matching circuit 133 may be provided for optimal adaptation to the load, however, it is not required and is not included in the implementation described in more detail below.

In FIG. 4 shows some of the main components of the power supply electronic circuit 13, more specifically the inverter 132 for converting direct current to alternating current. As can be seen in FIG. 4, the DC-AC inverter includes a class E power amplifier including a transistor switch 1320 having a field-effect transistor (FET) 1321, such as a metal-oxide-semiconductor field-effect transistor (MOSFET), feeding the transistor switch circuit, indicated by an arrow 1322 for supplying a switching signal (gate-source voltage) to a field-effect transistor 1321, and an inductive-capacitive load circuit 1323 comprising a shunt capacitor C1 and a series circuit of a capacitor C2 and an inductor L2. In addition, the DC power supply 11 is shown including a choke L1 for supplying the DC supply voltage +V _CC . Also in FIG. 4 shows the ohmic resistance R representing the total ohmic load 1324, which is the sum of the ohmic resistance R _Coil of the inductor L2 and the ohmic resistance R _Load of the susceptor 21, as shown in FIG. 6.

Obviously, due to the very small number of components, it is possible to maintain an extremely small volume of the power supply electronics 13 . For example, the volume of the electronic power supply circuit may be no more than 2 cm ³ . This extremely small volume of the electronic power supply circuit is possible because the inductor L2 of the inductive-capacitive load circuit 1323 is directly used as an inductor for inductively coupling with the susceptor 21 of the aerosol-forming substrate 20, and this small volume makes it possible to keep the overall dimensions of the induction heating device small. 1 in general. If a separate inductor other than inductor L2 is used to inductively couple the susceptor 21, this automatically increases the volume of the power supply electronic circuit, and this volume also increases if a matching circuit 133 is included in the power supply electronic circuit.

Although the general principle of operation of a Class E power amplifier is known and detailed in the previously mentioned article "Class E RF Power Amplifiers", by Nathan O. Sokal, published in the bimonthly QEX January/February 2001 issue. , pp. 9-20, American Amateur Radio League (ARRL) publication, Newington, CT, USA, some general principles will be explained later.

Assume that the transistor switch supply circuit 1322 supplies a square-wave switching voltage (FET gate-source voltage) to the FET 1321. resistance) and all current flows through inductor L1 and FET 1321. circuit (with high resistance). Switching the transistor between these two states causes the supplied DC voltage and DC current to be inverted into AC voltage and AC current, respectively.

In order to effectively heat the susceptor 21, it is necessary to transfer as much DC power as possible in the form of AC power to the inductor L2 (helical-wound induction coil) and then to the susceptor 21 of the aerosol-forming substrate 20 inductively coupled to the inductor 2. Power, dissipated in the susceptor 21 (eddy current loss, hysteresis loss) generates heat in the susceptor 21 as detailed above. In other words, the power dissipation in the FET 1321 should be minimized while the power dissipation in the susceptor 21 should be maximized.

The power dissipation in the FET 1321 during one AC voltage/current cycle is the product of the voltage and current of the transistor at each point in time during the AC voltage/current cycle, integrated over that cycle and averaged over that cycle. Because the FET 1321 must maintain a high voltage for part of this period and conduct a high current for part of that period, the simultaneous presence of high voltage and high current must be avoided, as this will lead to significant power dissipation in the FET 1321. In the "on" state field effect transistor 1321, the voltage across the transistor is close to zero when a high electric current flows through the field effect transistor 1321. In the "off" state of the FET 1321, the voltage across the transistor is high, but the current through the FET 1321 is close to zero.

Switching transients are also inevitable, lasting for some part of the period. However, high voltage-current product, which is a large power loss in the FET 1321, can be eliminated with the following additional measures. First, they delay the increase in the voltage of the transistor until the current flowing through the transistor decreases to zero. Secondly, they ensure that the voltage of the transistor returns to zero before the increase in the current flowing through the transistor begins. This is achieved by a load circuit 1323 comprising shunt capacitor C1 and a series circuit of capacitor C2 and inductor L2, with the load circuit connected between FET 1321 and load 1324. zero (for a BJT, this is the saturation bias voltage V _o ). The turn-on transistor does not discharge the charged shunt capacitor C1, thereby preventing the energy stored in the shunt capacitor from dissipating. Fourth, ensure that the voltage slope of the transistor is zero during firing. Then, the electric current injected into the turn-on transistor by the load circuit is ramped up from zero at a controlled moderate rate, resulting in low power dissipation while the transistor conductance rises from zero during the turn-on transient. As a result, the voltage and current of the transistor will never be high at the same time. Transients during voltage and current switching are shifted in time relative to each other.

To size the various components of the DC/AC inverter 132 shown in FIG. 4, the following equations must be taken into account, which are well known and are detailed in the aforementioned article "Class E RF Power Amplifiers" by Nathan O. Sokal, published in the QEX bimonthly January/February 2001 issue. , pp. 9-20, American Radio Amateur League (ARRL), Newington, CT, USA.

Let Q _L (the quality factor of an inductive-capacitive load circuit) be a value that in any case exceeds 1.7879, but is a value that can be chosen by the designer (see the above article); further, let P be the output power supplied to the resistance R and let f be the frequency. The various components are then calculated numerically from the following equations (where V _o is zero in the case of FETs and is the saturation bias voltage in the case of BJTs, see above):

L2=Q _L ⋅R/2πf

R=((V _{CC -} V _o ) ² /P)⋅ 0.576801 ⋅(1.0000086-0.414395/Q _L -

0.557501/Q _L ² +0.205967/Q _L ³ )

C1=(1/(34.2219⋅f⋅R))⋅(0.99866+0.91424/Q _L -1.03175/Q _L ² )+0.6/(2πf) ² ⋅(L1)

C2=(1/2πfR)⋅(1/Q _L -0.104823)⋅(1.00121+(1.01468/Q _L -1.7879))-(0.2/((2πf) ² ⋅L1 )))

This allows the susceptor, having an ohmic R=0.6 ohm, to rapidly heat up to deliver about 7W of power for 5-6 seconds, assuming a current of about 3.4A is available with a DC power supply, whose maximum output voltage is 2.8 V, the maximum output current is 3.4 A, frequency f=5 MHz (duty cycle=50%), inductance L2 is about 500 nH, ohmic resistance of inductor L2 is R _Coil =0 .1 ohm, inductance L1 is approximately 1 µH, capacitor C1 is 7 nF, and capacitor C2 is 2.2 nF. The effective resistance of R _Coil and R _Load is approximately 0.6 ohm. It is possible to obtain an efficiency (power dissipated in the susceptor 21/maximum power of the DC power supply 11) of about 83.5%, which is a very high efficiency.

As indicated above, the susceptor 21 may be made from a material or combination of materials having a Curie temperature close to the desired temperature to which the susceptor is to be heated. Once the temperature of the susceptor 21 has exceeded the specified Curie temperature, the ferromagnetic properties of the material change to paramagnetic properties. Accordingly, power dissipation in the susceptor 21 is greatly reduced because the hysteresis loss in a material having paramagnetic properties is much smaller than the hysteresis loss in a material having ferromagnetic properties. This reduced power dissipation in the susceptor 21 can be detected, whereupon, for example, the AC-to-DC inverter's AC generation can be interrupted until the susceptor 21 cools below the Curie temperature again and regains its ferromagnetic properties. Then, AC power generation by the DC-to-AC inverter can be restarted.

For use, the smoking article 2 is inserted into the cavity 14 (see FIG. 2) of the induction heating device 1 such that the aerosol-forming substrate 20 containing the susceptor 21 is inductively coupled to the inductor 2 (eg, a cylindrical helically wound coil). The susceptor 21 is then heated for a few seconds as described above, after which the consumer can begin to draw the aerosol through the filter 22 (of course, the smoking article need not include the filter 22).

The induction heating device and smoking articles may generally be sold individually or as a kit of parts. For example, a so-called "starter kit" may be sold containing an induction heating device as well as a plurality of smoking articles. The consumer, after he has purchased such a starter kit, in the future has the opportunity to purchase only smoking articles that can be used together with the induction heating device of this starter kit. The induction heating device is easy to clean and, in the case of using batteries as a DC power source, these batteries can be easily recharged using a suitable charger, which must be connected to the connection port 12 containing the pin 120 (or the induction heating device must be connected to an appropriate charger connection station).

Based on the described embodiments of the present invention, supplemented by drawings, it is obvious that numerous changes and modifications are possible without going beyond the general idea underlying the present invention. Therefore, it is intended that the scope of protection is not limited to particular embodiments and is defined by the appended claims.

Claims (24)

1. An induction heating device (1) for heating an aerosol-forming substrate (20) containing a susceptor (21), said induction heating device (1) comprising: - body (10) of the device, - a DC power source (11) having a DC supply voltage (V _CC ), - an electronic power supply circuit (13) configured to operate at a frequency in the range from 1 to 30 MHz and containing an inverter (132) for converting direct current into alternating current, connected to a DC power source (11) and including an amplifier power class E, containing a transistor switch (1320), a transistor switch excitation circuit (1322), and an inductive-capacitive load circuit (1323) configured to operate with an ohmic load (1324) that is less than 2 ohms, while the inductive-capacitive load circuit (1323) contains a shunt capacitor (C1) and a series circuit of a capacitor (C2) and an inductor (L2) having an ohmic resistance (R _Coil ), and - a cavity (14) located in the body (10) of the device and having an inner surface shaped to accommodate at least a part of the aerosol-forming substrate (20), while the cavity (14) is located so that when placed in this cavity part of the aerosol-forming substrate (20) the inductor (L2) of the inductive-capacitive load circuit (1323) is inductively connected to the susceptor (21) of the aerosol-forming substrate (20) during use, wherein the inductor (L2) is embedded in the device body (10) at the proximal end of the device body (10) to surround a cavity (14) which is also located at the proximal end of the device body (10). 2. The induction heating device according to claim 1, which is configured to heat the tobacco-containing solid aerosol-forming substrate (20) of the smoking article (2). 3. An induction heating device according to any one of the preceding claims, wherein the total volume of the power supply electronic circuit (13) is equal to or less than 2 cm ³ . 4. An induction heating device according to any one of the preceding claims, wherein the inductor (L2) of the inductive-capacitive load circuit (1323) comprises a cylindrical helical wound induction coil having an elongated shape (r, l) and forming an internal volume ranging from 0, 15 to 1.10 cm ³ , and in which a cylindrical helical induction coil is located on or near the inner surface of the cavity (14). 5. An induction heating device according to any one of the preceding claims, wherein the device body (10) has a cylindrical shape with a cavity (14) located at the proximal end of the device body (10) and with a DC power source (11) located at the far end. end of the body (10) of the device, and in which the electronic circuit (13) power supply is located between the DC power source (11) and the cavity (14). 6. An induction heating device according to any one of the preceding claims, wherein the power supply electronic circuit (13) further comprises a microcontroller (131) that is programmed to interrupt the inverter's AC generation to convert DC to AC if the temperature of the susceptor (21) aerosol-forming substrate (20) has exceeded the Curie temperature of that susceptor (21) during use, and which is programmed to resume AC generation if the temperature of the susceptor (21) falls below that Curie temperature again. 7. An induction heating device according to any one of the preceding claims, wherein the class E power amplifier has an output impedance, wherein the power supply electronic circuit (13) further comprises a matching circuit (133) for matching said class E power amplifier output impedance to an ohmic load (1324) that is less than 2 ohms. 8. The induction heating device according to claim 6, wherein the power supply electronic circuit (13) further comprises two feedback channels (134, 135) to provide feedback signals indicative of voltage and current through the inductor (L2), which allows control further power supply. 9. An induction heating system for heating an aerosol-forming substrate, comprising an induction heating device (1) according to any one of the preceding claims and an aerosol-forming substrate (20) comprising a susceptor (21), wherein at least a portion of the aerosol-forming substrate (20) is placed in the cavity (14) of the induction heating device (1) so that during use, the inductor (L2) of the inductive-capacitive load circuit (1323) of the inverter (132) for converting direct current into alternating current of the induction heating device (1) is inductively connected to the susceptor (21) an aerosol-forming substrate (20). 10. A kit for heating an aerosol-forming substrate, comprising an induction heating device (1) according to any one of paragraphs. 1-8 and an aerosol-forming substrate (20) containing a susceptor (21), wherein the induction heating device (1) and the aerosol-forming substrate (20) are configured to accommodate, during use, at least a portion of the aerosol-forming substrate (20) in the cavity (14) of the induction heating device (1) so that the inductor (L2) of the inductive-capacitive load circuit (1323) of the inverter (132) for converting direct current into alternating current of the induction heating device (1) is inductively connected to the susceptor (21) aerosol-forming substrate (20). 11. The kit according to claim 10, wherein the aerosol-forming substrate (20) is the aerosol-forming substrate of a smoking article (2). 12. The kit according to claim 11, wherein the aerosol-forming substrate (20) of the smoking article (2) is a tobacco-containing solid aerosol-forming substrate. 13. A method for using an induction heating system, comprising the steps of: - providing a DC power source (11) having a DC supply voltage (V _CC ), - provide an electronic power supply circuit (13) capable of operating at a frequency in the range from 1 to 30 MHz and containing an inverter (132) for converting direct current into alternating current, connected to a DC power source (11) and including class E power amplifier comprising a transistor switch (1321), a transistor switch drive circuit (1322), and an inductive-capacitive load circuit (1323) configured to operate with an ohmic load (1324) that is less than 2 ohms, while inductive-capacitive the load circuit (1323) contains a shunt capacitor (C1) and a series circuit of a capacitor (C2) and an inductor (L2) having an ohmic resistance (R _Coil ), - provide a cavity (14) made with the ability to accommodate at least a part of the aerosol-forming substrate (20) and located so that when a part of the aerosol-forming substrate (20) is placed in this cavity, the inductor (L2) of the inductive-capacitive load circuit ( 1323) is inductively coupled to the susceptor (21) of the aerosol-forming substrate (20), wherein the inductor (L2) is embedded in the device body (10) at the proximal end of the device body (10) to surround a cavity (14) which is also located at the proximal end of the body (10) of the device, and - provide an aerosol-forming substrate (20) containing a susceptor (21), and insert at least a part of the aerosol-forming substrate (20) into the cavity (14) so that the inductor (L2) of the inductive-capacitive load circuit (1323) is inductively connected to a susceptor (21) of an aerosol-forming substrate (20). 14. The method of claim 13, wherein the DC power supply (11) is a battery, the method further comprising charging the battery before inserting a portion of the aerosol-forming substrate (20) into the cavity (14). 15. The method according to claim 13 or 14, wherein the power supply electronic circuit (13) further comprises a microcontroller (131) that is programmed to interrupt or resume AC generation by the inverter to convert DC to AC, whereby feedback signals are generated. links indicating the voltage and current through the inductor (L2), and if the temperature of the susceptor (21) exceeds the desired temperature, an appropriate signal is generated, interrupting further power supply until the temperature of the susceptor again falls below the desired temperature, after which power supply is restored.

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