Apparatus for resonance circuit

Abstract

To provide a novel apparatus for use with an RLC resonance circuit for inductive heating of a susceptor of an aerosol generating device.SOLUTION: Disclosed are a method and an apparatus for use with an RLC resonance circuit for inductive heating of a susceptor of an aerosol generating device. The apparatus is arranged to determine a resonant frequency of the RLC resonance circuit; and determine, on the basis of the determined resonant frequency, a first frequency for the RLC resonance circuit for causing the susceptor to be inductively heated, the first frequency being above or below the determined resonant frequency. The apparatus may be arranged to control a drive frequency of the RLC resonance circuit to be at the determined first frequency in order to heat the susceptor. Also disclosed is an aerosol generating device including the apparatus.SELECTED DRAWING: Figure 3b

Description

[Technical Field]

[0001] The present invention relates to an apparatus for use with an RLC resonant circuit, and more particularly to an RLC resonant circuit for inductively heating a susceptor in an aerosol generating device. [Background technology]

[0002] Smoking articles, such as cigarettes and cigars, burn tobacco to produce tobacco smoke during use. Attempts have been made to provide alternatives to these smoking articles by creating products that release compounds without combustion. Examples of such products are so-called "heat-not-burn" products, or tobacco heating devices or products. These release compounds by heating, rather than burning, a material. The material may be, for example, tobacco or another non-tobacco product. The non-tobacco product may or may not contain nicotine. Summary of the Invention

[0003] According to a first aspect of the present invention, there is provided an apparatus for use with an RLC resonant circuit for inductively heating a susceptor of an aerosol generating device, the apparatus being configured to determine a resonant frequency of the RLC resonant circuit and, based on the determined resonant frequency, determine a first frequency for the RLC resonant circuit above or below the determined resonant frequency for inductively heating the susceptor.

[0004] The first frequency is for inductively heating the susceptor to a first degree at a given supply voltage, the first degree being less than a second degree, the second degree being the degree to which the susceptor is inductively heated at the given supply voltage when the RLC circuit is driven at the resonant frequency.

[0005] The apparatus may be configured to control a drive frequency of the RLC resonant circuit to be at the determined first frequency to heat the susceptor.

[0006] The apparatus may be configured to control the drive frequency to hold it at a first frequency for a first period of time.

[0007] The apparatus may be configured to control the drive frequency to be one of a plurality of first frequencies, each of which is different from the others.

[0008] The apparatus may be configured to control the drive frequency to step through a plurality of first frequencies in a sequence.

[0009] The apparatus may be configured to select the order from one of a number of predetermined orders.

[0010] The apparatus may be configured to control the drive frequency such that each of the plurality of first frequencies in the sequence is closer to the resonant frequency than the previous first frequency in the sequence, or to control the drive frequency such that each of the plurality of first frequencies in the sequence is further from the resonant frequency than the previous first frequency in the sequence.

[0011] The apparatus may be configured to control the drive frequency to hold it at one or more of the plurality of first frequencies for one or more respective periods of time.

[0012] The apparatus may be configured to measure an electrical characteristic of the RLC circuit as a function of drive frequency and to determine a resonant frequency of the RLC circuit based on the measurement.

[0013] The apparatus may be configured to determine the first frequency based on a measured electrical characteristic of the RLC circuit as a function of a drive frequency at which the RLC circuit is driven.

[0014] The electrical characteristic may be a voltage measured across an inductor in an RLC circuit, the inductor being for transferring energy to the susceptor.

[0015] The measurement of the electrical property may be a passive measurement.

[0016] The electrical characteristics can show the current induced in the sense coil, which is the one through which energy is transferred from the inductor of the RLC circuit, and the inductor is the one through which energy is transferred to the susceptor.

[0017] The electrical characteristics can show the current induced in the pickup coil, which is the source of energy transferred from the supply voltage element, which supplies voltage to the drive element, which drives the RLC circuit.

[0018] The apparatus may be configured to determine the resonant frequency of the RLC circuit and / or the first frequency substantially upon start-up of the aerosol generating device, and / or when a substantially new and / or replacement susceptor is attached to the aerosol generating device, and / or when a substantially new and / or replacement inductor is attached to the aerosol generating device.

[0019] The apparatus may be configured to determine a characteristic indicative of a bandwidth of a peak in the response of the RLC circuit corresponding to the resonant frequency, and to determine the first frequency based on the determined characteristic.

[0020] The apparatus may include a driving element configured to drive the RLC resonant circuit at one or more of a plurality of frequencies, and the apparatus is configured to control the driving element to drive the RLC resonant circuit at the determined first frequency.

[0021] The driving element may comprise an H-bridge driver.

[0022] The device may further comprise an RLC resonant circuit.

[0023] According to a second aspect of the present invention, there is provided an aerosol-generating apparatus configured to heat an aerosol-generating material and thereby generate an aerosol in use, the aerosol-generating apparatus comprising a susceptor configured to be inductively heated by an RLC resonant circuit, and an apparatus according to the first aspect.

[0024] The susceptor may include one or more of nickel and steel.

[0025] The susceptor may include a body having a nickel coating.

[0026] The thickness of the nickel coating may be substantially less than 5 μm, or may be substantially in the range of 2 μm to 3 μm.

[0027] The nickel coating may be electroplated onto the body.

[0028] The susceptor may be or comprise a sheet of mild steel.

[0029] The thickness of the mild steel sheet may range from substantially 10 μm to substantially 50 μm, or may be substantially 25 μm.

[0030] According to a third aspect of the present invention, there is provided a method for use with an RLC resonant circuit for inductively heating a susceptor of an aerosol generating device, the method comprising the steps of determining a resonant frequency of the RLC circuit and determining a first frequency for the RLC resonant circuit above or below the determined resonant frequency for inductively heating the susceptor.

[0031] The method can include controlling a drive frequency of the RLC resonant circuit to the determined first frequency to heat the susceptor.

[0032] According to a fourth aspect of the present invention there is provided a computer program which, when executed on a processing system, causes the processing system to carry out a method according to the third aspect.

[0033] Further features and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, with reference to the accompanying drawings. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a schematic diagram of an aerosol generating device according to an example. [Figure 2a] 1 is a schematic diagram of an RLC resonant circuit according to a first example; [Figure 2b] FIG. 10 is a schematic diagram of an RLC resonant circuit according to a second example. [Figure 2c] FIG. 10 is a schematic diagram of an RLC resonant circuit according to a third example. [Figure 3a] 1 is a schematic diagram of an example frequency response of an example RLC resonant circuit showing the resonant frequency; [Figure 3b] 1 is a schematic diagram of an example frequency response of an example RLC resonant circuit illustrating different drive frequencies. [Figure 3c] 4 is a schematic diagram of the temperature of a susceptor as a function of time, according to an example. [Figure 4] FIG. 1 is a flow diagram that schematically illustrates an exemplary method. DETAILED DESCRIPTION OF THE INVENTION

[0035] Induction heating is a process of heating a conductive object (or susceptor) by electromagnetic induction. An induction heater can include an electromagnet and a device for passing a varying current, such as an alternating current, through the electromagnet. The varying current in the electromagnet generates a varying magnetic field. The varying magnetic field penetrates a susceptor appropriately positioned relative to the electromagnet and generates eddy currents within the susceptor. The susceptor has an electrical resistance to the eddy currents, and therefore, the flow of eddy currents against this resistance heats the susceptor by Joule heating. If the susceptor comprises a ferromagnetic material such as iron, nickel, or cobalt, heat can also be generated by magnetic hysteresis losses in the susceptor, i.e., by the orientation of magnetic dipoles within the magnetic material changing as a result of aligning with the varying magnetic field.

[0036] In induction heating, heat is generated inside the susceptor, which allows for rapid heating, as compared to, for example, conduction heating, and further, no physical contact is required between the induction heater and the susceptor, which allows for greater flexibility in design and application.

[0037] Electrical resonance occurs in an electric circuit at a particular resonant frequency when the imaginary parts of the impedances or admittances of the circuit elements cancel each other. One example of a circuit that exhibits electrical resonance is an RLC circuit with resistance (R) provided by a resistor, inductance (L) provided by an inductor, and capacitance (C) provided by a capacitor connected in series. Resonance occurs in an RLC circuit because the collapsing inductor's magnetic field generates a current in the inductor's winding that charges the capacitor, while the discharging capacitor supplies a current that creates a magnetic field in the inductor. When the circuit is driven at the resonant frequency, the series impedance of the inductor and capacitor is lowest and the circuit current is highest.

[0038] 1 schematically illustrates an exemplary aerosol-generating device 150 including an RLC resonant circuit 100 for inductively heating an aerosol-generating material 164 by a susceptor 116. In some examples, the susceptor 116 and the aerosol-generating material 164 form an integral unit that can be inserted into and / or removed from the aerosol-generating device 150, making it disposable. The aerosol-generating device 150 is portable. The aerosol-generating device 150 is configured to heat the aerosol-generating material 164 to generate an aerosol for inhalation by a user.

[0039] As used herein, the term "aerosol-generating material" includes materials that, upon heating, provide volatile components, typically in the form of a vapor or aerosol. Aerosol-generating materials may be non-tobacco-containing or tobacco-containing. Aerosol-generating materials may include, for example, one or more of tobacco itself, tobacco derivatives, expanded tobacco, reconstituted tobacco, tobacco extract, homogenized tobacco, or tobacco substitutes. Aerosol-generating materials may be in the form of ground tobacco, cut rag tobacco, extruded tobacco, reconstituted tobacco, reconstituted materials, liquids, gels, gelled sheets, powders, or chunks. Aerosol-generating materials may also include non-tobacco products. These non-tobacco products may or may not contain nicotine, depending on the product. Aerosol-generating materials may also include one or more humectants, such as glycerol or propylene glycol.

[0040] Returning to FIG. 1 , the aerosol-generating device 150 comprises an enclosure 151 that houses the RLC resonant circuit 100, a susceptor 116, an aerosol-generating material 164, a controller 114, and a battery 162. The battery is configured to provide power to the RLC resonant circuit 100. The controller 114 is configured to control the RLC resonant circuit 100, for example, by controlling the voltage provided to the RLC resonant circuit 100 from the battery 162 and the frequency f at which the RLC resonant circuit 100 is driven. The RLC resonant circuit 100 is configured to inductively heat the susceptor 116. The susceptor 116 is configured to heat the aerosol-generating material 364 in use to generate an aerosol. The enclosure 151 comprises a mouthpiece 160 that allows the generated aerosol to exit the device 150 in use.

[0041] In use, the user activates the controller 114, for example by means of a button (not shown) or a smoke detector (not shown) known per se, to activate, for example, the resonant frequency f of the RLC resonant circuit 100. r The RLC resonant circuit 100 can be driven by an inductively coupled rectifier 116. The resonant circuit 100 then inductively heats the susceptor 116, which in turn heats the aerosol-generating material 164, causing the aerosol to generate an aerosol. The aerosol is generated and enters air drawn into the device 150 through an air inlet (not shown), which is then carried to the mouthpiece 160, where it exits the device 150.

[0042] The controller 114 and the entire device 150 can be configured to heat the aerosol-generating material to a temperature range to volatilize at least one component of the aerosol-generating material without burning the aerosol-generating material. For example, the temperature range can be about 50°C to about 350°C, e.g., about 50°C to about 250°C, about 50°C to about 150°C, about 50°C to about 120°C, about 50°C to about 100°C, about 50°C to about 80°C, or about 60°C to about 70°C. In some examples, the temperature range is about 170°C to about 220°C. In some examples, the temperature range can be outside this range, or the upper limit of the temperature range can be greater than 300°C.

[0043] It may be desirable to control the rate at which the susceptor 116 is inductively heated, and therefore the rate at which the susceptor 116 heats the aerosol-generating material 164. For example, it may be useful to control the rate at which the susceptor 116 is heated and / or the extent to which the susceptor 116 is heated. For example, it may be useful to control the heating of the aerosol-generating material 164 (by the susceptor 116) according to a particular heating profile, for example, to change or enhance the characteristics of the generated aerosol, such as the nature, flavor, and / or temperature of the generated aerosol. As another example, it may be useful to control the heating of the aerosol-generating material 164 (by the susceptor 116) to different states, such as a "hold" state in which the aerosol-generating material is heated to a relatively low temperature below the temperature at which the aerosol-generating medium generates an aerosol, and a "heat" state in which the aerosol-generating material 164 is heated to a relatively high temperature at which the aerosol generates an aerosol. This control can help shorten the time that the aerosol-generating device 150 can generate an aerosol from a given activation signal. As a further example, it can be useful to control the heating of the aerosol-generating material 164 (by the susceptor 116) so that it does not exceed a certain range, e.g., to ensure that it does not heat above a certain temperature so as not to burn or carbonize. For example, it may be desirable for the temperature of the susceptor 116 not to exceed 400°C to ensure that the susceptor 116 does not burn or carbonize the aerosol-generating material 164. It will be appreciated that, for example, during heating of the susceptor 116, e.g., if the heating rate is high, there may be a difference between the temperature of the susceptor 116 and the temperature of the aerosol-generating material 164 overall. Thus, it will be appreciated that in some examples, the temperature of the susceptor 116 that one wishes to control, or that the susceptor 116 should not exceed, may be higher than, for example, the temperature to which one wishes to heat the aerosol-generating material 164 or the temperature that the aerosol-generating material 164 should not exceed.

[0044] One possible way to control the inductive heating of the susceptor 116 by the RLC resonant circuit 100 is to control the supply voltage applied to the circuit, which can control the current flowing through the circuit 100 and therefore the energy transferred to the susceptor 116 by the RLC resonant circuit 100, and therefore the degree to which the susceptor 116 heats up. However, adjusting the supply voltage increases costs, requires more space, and reduces efficiency due to losses in the voltage adjustment components.

[0045] According to examples of the present invention, an apparatus (e.g., controller 114) is configured to control the degree to which susceptor 116 is heated by controlling the drive frequency f of RLC resonant circuit 100. Broadly speaking, as described in more detail below, controller 114 may determine the resonant frequency f of RLC resonant circuit 100, e.g., by examining or, e.g., measuring, the resonant frequency of RLC resonant circuit 100. r The controller 114 is then configured to determine the determined resonant frequency f r The method is configured to determine a first frequency for inductively heating the susceptor based on the determined resonant frequency f r The controller 114 is then configured to control the drive frequency f of the RLC resonant circuit 100 to the determined first frequency to heat the susceptor 116. The first frequency is set to a value greater than or equal to the resonant frequency f of the RLC resonant circuit 100. r above or below (i.e., "off-resonance"), driving the RLC circuit 100 at a first frequency will result in a resonant frequency f r The current I through the circuit 100 is less than when it is driven at a resonant frequency f rThe susceptor 116 is inductively heated to a lesser extent than when driven at a first frequency. Thus, by controlling the drive frequency of the resonant circuit to be at the first frequency, the degree to which the susceptor 116 is heated can be controlled without having to control the voltage supplied to the circuit, thus resulting in a cheaper, more space-saving, and power-efficient apparatus 150.

[0046] 2a, there is shown an exemplary RLC resonant circuit 100 for inductively heating a susceptor 116. The resonant circuit 100 comprises a resistor 104, a capacitor 106, and an inductor 108 connected in series. The resonant circuit 100 has a resistance R, an inductance L, and a capacitance C.

[0047] The inductance L of the circuit 100 is provided by an inductor 108 configured to inductively heat the susceptor 116. The inductive heating of the susceptor 116 is due to an alternating magnetic field generated by the inductor 108, which, as described above, causes Joule heating and / or magnetic hysteresis losses within the susceptor 116. A portion of the inductance L of the circuit 100 may be due to the magnetic permeability of the susceptor 116. The varying magnetic field generated by the inductor 108 is generated by an alternating current flowing through the inductor 108. The alternating current flowing through the inductor 108 is the alternating current flowing through the RLC resonant circuit 100. The inductor 108 may be, for example, in the form of a coiled wire, e.g., a copper coil. The inductor 108 may, for example, comprise a Litz wire, e.g., a wire formed by twisting together several individually insulated wires. Litz wire, as known per se, may be particularly useful when using a driving frequency f in the MHz range, since it can reduce power losses due to the skin effect. At these relatively high frequencies, a low value of inductance is required. In another example, the inductor 108 may be a coiled track on, for example, a printed circuit board. Using a coiled track on a printed circuit board may be useful because it provides a rigid, free-standing track, has a cross-section that eliminates any requirement for Litz wire (which can be expensive), and can be mass-produced at low cost and with high reproducibility. While one inductor 108 is shown, it will be readily appreciated that there may be one or more inductors configured to inductively heat one or more susceptors 116.

[0048] The capacitance C of the circuit 100 is provided by a capacitor 106. The capacitor 106 may be, for example, a class 1 ceramic capacitor, such as a COG capacitor. The capacitance C may also include stray capacitance of the circuit 100. However, this is small or negligible compared to the capacitance C provided by the capacitor 106.

[0049] The resistance R of circuit 100 is given by resistor 104, the resistance of the tracks or wires connecting the components of resonant circuit 100, the resistance of inductor 108, and the resistance to current flow through resonant circuit 100 offered by susceptor 116 configured for energy transfer with inductor 108. It will be appreciated that it is not necessary for circuit 100 to include resistor 104, and that the resistance R of circuit 100 can be given by the resistance of the connecting tracks or wires, inductor 108, and susceptor 116.

[0050] The circuit 100 is driven by an H-bridge driver 102. The H-bridge driver 102 is a driving element for providing an AC current to the resonant circuit 100. The H-bridge driver 102 is connected to a DC voltage supply V SUPP 110 and connected to ground GND 112. DC voltage supply V SUPP 110 may for example come from a battery 162. The H-bridge 102 may be an integrated circuit or may comprise discrete switching components (not shown), which may be of the semiconductor or mechanical type. The H-bridge driver 102 may for example be a high efficiency bridge rectifier. As is known per se, the H-bridge driver 102 reverses (and then reverses) the voltage across the circuit to provide a DC supply V SUPP An AC current can be applied to the circuit 100 from 110. This can be useful because the RLC resonant circuit can be powered by a DC battery and the frequency of the AC current can be controlled.

[0051] The H-bridge driver 104 is connected to a controller 114. The controller 114 controls the H-bridge 102 or its components (not shown) to provide an AC current I to the RLC resonant circuit 100 at a given drive frequency f. For example, the drive frequency f may be in the MHz range, e.g., in the range of 0.5 MHz to 4 MHz, e.g., in the range of 2 MHz to 3 MHz. It will be appreciated that other frequencies f or frequency ranges may be used, depending, for example, on the particular resonant circuit 100 (and / or its components), controller 114, susceptor 116, and / or drive element 102 used. For example, the resonant frequency f of the RLC resonant circuit 100 may be r It will be appreciated that f depends on the inductance L and capacitance C of the circuit 100, which in turn depends on the inductor 108, capacitor 106, and susceptor 116. The range of drive frequencies f may vary depending, for example, on the resonant frequency f of the particular RLC resonant circuit 100 and / or susceptor 116 used. r It will be appreciated that the resonant circuit 100 and / or drive frequency or range of drive frequencies f used may also be selected based on other factors for a given susceptor 116. For example, to improve the transfer of energy from the inductor 108 to the susceptor 116, it may be useful to have the skin depth (i.e., the depth from the surface of the susceptor 116 at which the AC magnetic field from the inductor 108 is absorbed) shallower than the thickness of the susceptor 116 material, e.g., 1 / 3 to 1 / 2. The skin depth varies for different susceptor 116 materials and structures and decreases as the drive frequency f increases. Thus, in some instances, it may be advantageous to use a relatively high drive frequency f. On the other hand, it may be advantageous to use a lower drive frequency f, e.g., to reduce the proportion of power supplied to the resonant circuit 100 and / or drive element 102 that is lost as heat in the electronic device. Thus, in some instances, a compromise between these factors may be chosen as appropriate and / or desired.

[0052] As described above, the controller 114 controls the resonant frequency f of the RLC resonant circuit 100. r Then, the determined resonant frequency fr is configured to determine a first frequency f at which the RLC resonant circuit 100 is controlled to be driven based on

[0053] Figure 3a shows a schematic representation of the frequency response 300 of the resonant circuit 100. In the example of Figure 3a, the frequency response 300 of the resonant circuit 100 is illustrated by a schematic plot of the current I flowing through the circuit 100 as a function of the drive frequency f at which the circuit is driven by the H-bridge driver 104.

[0054] The resonant circuit 100 of FIG. 2a has a resonant frequency f where the series impedance Z of the inductor 108 and capacitor 106 is lowest and therefore the circuit current I is highest. r Therefore, as shown in FIG. 3a, the H-bridge driver 104 has a resonant frequency f r When the circuit 100 is driven with a rectifier, the AC current I in the circuit 100, and therefore the AC current I in the inductor 108, is a maximum of I max Therefore, the oscillating magnetic field generated by the inductor 106 is at a maximum, and therefore the induction heating of the susceptor 116 by the inductor 106 is at a maximum. r When driving the circuit 100 at a frequency f above or below (for a given supply voltage V SUPP 110), the AC current I in circuit 100, and therefore the AC current I in inductor 108, is less than maximum, and therefore the oscillating magnetic field generated by inductor 106 is less than maximum, and therefore the inductor 106 causes less than maximum inductive heating of susceptor 116. Thus, as can be seen in FIG. 3a, the frequency response 300 of resonant circuit 100 is r and therefore has a peak centered at the resonant frequency f r It becomes gradually smaller at frequencies above and below .

[0055] As described above, the controller 114 controls the resonant frequency f of the circuit 100. r is configured to determine

[0056] In one example, the controller 114 may select the resonant frequency f from, for example, a memory (not shown). r By examining r For example, the resonant frequency f of the circuit 100 is determined. r can be calculated, measured, or otherwise determined in advance and pre-stored in a memory (not shown), for example, during manufacture of device 150. In another example, the resonant frequency f r may be communicated to the controller 114, for example, from a user input (not shown), or, for example, from another device or input. The resonant frequency f of the circuit 100 from which the circuit is controlled r As such, the use of a pre-stored resonant frequency allows for simple control of the circuit 100. Even if the pre-stored resonant frequency is not exactly the same as the actual resonant frequency of the circuit 100, useful control based on the pre-stored resonant frequency 100 is possible.

[0057] The resonant frequency f of circuit 100 (series RLC circuit) r depends on the capacitance C and inductance L of the circuit 100 and is given by:

[0058]

number

[0059] In some examples, to determine the resonant frequency of the circuit 100, the controller 114 is configured to measure the frequency response 300 of the RLC resonant circuit 100. For example, the controller can be configured to measure the electrical characteristics of the RLC circuit 100 as a function of the drive frequency f at which the RLC circuit is driven. The controller 114 may include a clock generator (not shown) to determine the absolute frequency at which the RLC circuit 100 is driven. The controller 114 can be configured to control the H-bridge 104 to scan a range of drive frequencies f over a period of time. The electrical characteristics of the RLC circuit 100 can be measured during the drive frequency scan, and thus the frequency response 300 of the RLC circuit 100 as a function of the drive frequency f can be determined.

[0060] This electrical property measurement may be a passive measurement, ie, a measurement that does not involve any direct electrical contact with the resonant circuit 100 .

[0061] For example, referring again to the example shown in FIG. 2a, the electrical characteristic can indicate a current induced in sense coil 120a by inductor 108 of RLC circuit 100. As shown in FIG. 2a, sense coil 120a is positioned to receive energy transfer from inductor 108 and is configured to detect current I flowing through circuit 100. Sense coil 120a can be, for example, a coil of wire or a track on a printed circuit board. For example, if inductor 108 is a track on a printed circuit board, sense coil 120a can be a track on the printed circuit board and can be positioned above or below inductor 108, for example, in a plane parallel to the plane of inductor 108. In another example, in an example with two or more inductors 108, sense coil 120a can be positioned between the inductors 108 to receive energy transfer from both of the inductors. For example, if the inductors 108 are tracks on a printed circuit board and lie in parallel planes, then the sense coil 120a can be a track on the printed circuit board midway between the two inductors and in a plane parallel to the inductors 108. In either case, an alternating current I flowing through the circuit 100, and therefore the inductors 108, causes the inductors 108 to generate an alternating magnetic field. The alternating magnetic field induces a current in the sense coil 120a. The induced current in the sense coil 120a generates a voltage V across the sense coil 120a. IND The voltage V across the sense coil 120a is generated. IND can be measured and is proportional to the current I flowing through the RLC circuit 100. The voltage V across the sense coil 120a IND can be recorded as a function of the drive frequency f at which the H-bridge driver 104 is driving the resonant circuit 100, and thus the determined frequency response 300 of the circuit 100 can be recorded. For example, the controller 114 may record the voltage V across the sense coil 120a as a function of the frequency f at which the H-bridge driver 104 is controlling the H-bridge driver 104 to drive the AC current in the resonant circuit 100. IND The controller can then analyze the frequency response 300 to identify the resonant frequency f at the center of the peak.r , and therefore the resonant frequency of the circuit 100 can be determined.

[0062] 2b shows another example of passive measurement of the electrical characteristics of the RLC circuit 100. FIG. 2b is the same as FIG. 2a except that the sense coil 120a of FIG. 2a has been replaced with a pickup coil 120b. As shown in FIG. 2b, the pickup coil 120b is positioned to intercept a portion of the magnetic field generated by the DC supply voltage wire or track 110 when the DC current flowing through the DC supply voltage wire or track 110 changes due to a change in the power demand of the RLC circuit. The magnetic field generated by the change in current flowing in the DC supply voltage wire or track 110 induces a current in the pickup coil 120b, which in turn generates a voltage V across the pickup coil 120b. IND For example, in an ideal case, the current flowing in the DC supply voltage wires or tracks 110 should be direct current only, but in reality, the current flowing in the DC supply voltage wires or tracks 110 may be modulated to some extent by the H-bridge driver 104, for example, due to switching imperfections in the H-bridge driver 104. These current modulations therefore induce currents in the pickup coil, which in turn induce a voltage V across the pickup coil 120b. IND It is detected by

[0063] The voltage V across the pickup coil 120b IND can be measured and recorded as a function of the drive frequency f at which the H-bridge driver 104 drives the resonant circuit 100, and thus the determined frequency response 300 of the circuit 100. For example, the controller 114 may measure and record the voltage V across the pickup coil 120a as a function of the frequency f at which the H-bridge driver 104 drives the AC current in the resonant circuit 100. IND The controller can then analyze the frequency response 300 to identify the resonant frequency f at the center of the peak. r , and therefore the resonant frequency of the circuit 100 can be determined.

[0064] It should be noted that in some instances it may be desirable to reduce or eliminate modulation components of the current in the DC supply voltage wires or tracks 110 that may be caused by imperfections in the H-bridge driver 104. This may be accomplished, for example, by implementing a bypass capacitor (not shown) across the H-bridge driver 104. In this case, it will be appreciated that the electrical characteristics of the RLC circuit 100 used to determine the frequency response 300 of the circuit 100 may be measured by means other than the pickup coil 120b.

[0065] 2c shows an example of an active measurement of the electrical characteristics of an RLC circuit, where the sense coil 120a of FIG. L 2a, except that the resonant circuit 100 is replaced by an element 120c, e.g., a passive differential circuit 120c, configured to measure the voltage V across the inductor 108 as the current I in the resonant circuit 100 changes. L The voltage V across the inductor 108 changes. L can be measured and recorded as a function of the drive frequency f at which the H-bridge driver 104 drives the resonant circuit 100, and thus the determined frequency response 300 of the circuit 100. For example, the controller 114 may control the H-bridge driver 104 to measure the voltage V across the inductor 108 as a function of the frequency f at which the H-bridge driver 104 drives the AC current in the resonant circuit 100. L The controller 114 can then analyze the frequency response 300 to identify the resonant frequency f at the center of the peak. r , and therefore the resonant frequency of the circuit 100 can be determined.

[0066] In each of the examples shown in FIGS. 2a-2c, or elsewhere, the controller 114 analyzes the frequency response 300 to identify the resonant frequency f at the center of the peak. rFor example, the controller 114 can determine the resonant frequency f from the frequency response using known data analysis techniques. For example, the controller can determine the resonant frequency f directly from the frequency response data. r For example, the controller 114 may estimate the frequency f at which the maximum response is recorded as the resonant frequency f r Alternatively, the frequencies f at which the two largest responses are recorded can be determined and the average of these two frequencies f can be calculated as the resonant frequency f r As yet another example, the controller 114 may fit a function indicating the current I (or another response, such as impedance) as a function of frequency f for the RLC circuit to the frequency response data and determine the resonant frequency f from the fitted function. r can be estimated or calculated.

[0067] Based on the measurement of the frequency response of the RLC circuit 100, the resonant frequency f r Determining π ...

[0068] In some examples, the susceptor 116 may be replaceable. For example, the susceptor 116 may be disposable, e.g., integrated with the aerosol-generating material 164 arranged to be heated. Thus, when the susceptor 116 is replaced, the determination of the resonant frequency by measurement may take into account differences between different susceptors 116 and / or differences in the placement of the susceptor 116 relative to the inductor 108. Furthermore, the inductor 108, or indeed any component of the resonant circuit 100, may be replaceable, e.g., after a certain amount of use or damage. Thus, when the inductor 108 is replaced, the determination of the resonant frequency may take into account differences between different inductors 108 and / or differences in the placement of the inductor 108 relative to the susceptor 116.

[0069] Therefore, the controller can be configured to determine the resonant frequency of the RLC circuit 100 substantially at the time of start-up of the aerosol generating device 150, and / or when a substantially new and / or replacement susceptor 116 is installed in the aerosol generating device 150, and / or when a substantially new and / or replacement inductor 108 is installed in the aerosol generating device 150.

[0070] As described above, the controller 114 is configured to determine, based on the determined resonant frequency, a first frequency f above or below (i.e., off-resonance with) the determined resonant frequency for inductively heating the susceptor 116.

[0071] FIG. 3b shows a schematic diagram of the frequency response 300 of the RLC resonant circuit 100, according to one example, where certain points (black circles) indicate the frequency response at different drive frequencies f A , f B , f C , f' A3b, the frequency response 300 of the resonant circuit 100 is shown by a schematic plot of the current I flowing through the circuit 100 as a function of the drive frequency f at which the circuit 100 is driven. The response 300 may correspond to, for example, the current I (or alternatively, another electrical characteristic) of the circuit 100, as measured by, for example, the controller 114, as a function of the drive frequency f at which the circuit 100 is driven. As shown in FIG. 3b and as described above, the response 300 may correspond to, for example, the current I (or alternatively, another electrical characteristic) of the circuit 100, as measured by, for example, the controller 114, as a function of the drive frequency f at which the circuit 100 is driven. r When the resonant circuit 100 has a resonant frequency f r When driven with , for a given supply voltage, the current I through resonant circuit 100 is up to I max The resonant circuit has a resonant frequency of f r an upper (e.g., higher) frequency f' A When driven with A is the maximum I max Similarly, if a resonant circuit has a resonant frequency f r A lower (e.g., lower) frequency f A , f B , f C When driven with A , I B , I C is the maximum I max For a given supply voltage, the circuit has a resonant frequency f r compared to when driven at the first frequency f A , f B , f C , f' A , the current I through the resonant circuit is less, so less energy is transferred from the inductor 108 of the resonant circuit 110 to the susceptor 116, and therefore, for a given supply voltage, the circuit operates at a resonant frequency f r The degree to which the susceptor 116 is inductively heated is less than the degree to which the susceptor 116 is inductively heated when driven at the first frequency f A , f B , f C, f' A By controlling the resonant circuit 100 to be driven by one of the following, the controller can control the degree to which the susceptor 116 is heated.

[0072] As will be appreciated, the frequency at which the resonant circuit 100 is controlled to be driven is the resonant frequency f r The further away (above or below) the susceptor 116 is from the first frequency f A , f B , f C , f' A In each of these steps, energy is transferred from the inductor 108 of the circuit 100 to the susceptor 116, causing the susceptor 116 to be inductively heated.

[0073] In some examples, the controller 114 may adjust the predetermined amount to the determined resonant frequency f r Add to or determine the resonant frequency f r or by subtracting a predetermined number from the resonant frequency f r or multiply by a predetermined number to find the resonant frequency f r or by any other operation, the first frequency f A , f B , f C , f' A and control the resonant circuit 100 to be driven at the first frequency f A , f B , f C , f' A so that the susceptor 116 is still inductively heated when driven at the first frequency f A , f B , f C , f' AThe predetermined amount or number or other operation can be set so that the susceptor 116 is at a resonance frequency that is not so far off resonance that it does not substantially heat the susceptor 116. The predetermined amount or number or operation can be determined or calculated in advance, e.g., during manufacturing, and can be stored, e.g., in a memory (not shown) accessible by the controller 114. For example, the response 300 of the circuit 100 can be measured in advance, and the response 300 can be calculated by measuring the response of the circuit 100 to different currents I A , I B , I C , i.e., a first frequency f corresponding to different degrees of induction heating of the susceptor 116. A , f B , f C , f' A is determined and stored in a memory (not shown) accessible by the controller 114. The controller then determines the appropriate operation, and thus the first frequency f, to control the degree to which the susceptor 116 is inductively heated. A , f B , f C , f' A You can select:

[0074] In another example, as described above, the controller 114 can determine the response 300 of the resonant circuit 100 as a function of the drive frequency f, for example, by measuring and recording the electrical characteristics of the circuit 100 as a function of the drive frequency f at which the circuit 100 is driven. As described above, this can be done, for example, upon start-up of the device 150 or upon replacement of a component of the circuit 100. Alternatively, or in addition, this can be done while the device is in operation. The controller 114 can then determine the resonant frequency f by analyzing the measured response 300, for example, using techniques such as those described above. r for the first frequency f A , f B , f C , f' A The controller 114 can then determine an appropriate first frequency f to control the degree to which the susceptor 116 is inductively heated. A , f B , f C , f' ASimilar to the above, determining the first frequency based on the measured response of the resonant circuit 100 allows for more accurate and robust control to changes in the apparatus 150, such as replacement of components of the resonant circuit 100 or their relative placement, as well as changes in the response 300 itself due to, for example, different temperatures or other conditions of the susceptor 116, the resonant circuit 100, or the apparatus 150.

[0075] In some examples, the controller 114 may determine a characteristic indicative of a bandwidth of a peak in the response 300 and adjust the first frequency f based on the determined characteristic. A , f B , f C , f' A For example, the controller may determine a first frequency f based on the bandwidth B of the peak in the response 300. A , f B , f C , f' A As shown in Figure 3a, the bandwidth B of the peak can be determined as

number

number

[0076] In other examples, as discussed above, it will be appreciated that the controller 114 can determine a characteristic indicative of the bandwidth B from analyzing the response 300 of the circuit 100, for example, from measuring the electrical characteristics of the circuit 100 as a function of the drive frequency f at which the circuit 100 is driven.

[0077] The determined first frequency f at which the circuit 100 is controlled to be driven. A , f B , f C , f' A is the resonant frequency f r above or below (i.e., off-resonance), and therefore for a given supply voltage, the resonant frequency f r The susceptor 116 is inductively heated to a lesser extent by the resonant circuit 100 than when driven by the resonant circuit 100. Thus, control of the degree to which the susceptor 116 is inductively heated is achieved.

[0078] As noted above, it may be useful to control the rate at which the susceptor 116 heats up and / or the extent to which the susceptor 116 heats up. To accomplish this, the controller 114 may adjust the drive frequency f of the resonant circuit 100 to a first frequency f A , f B , f C , f' A For example, the frequency f may be controlled to be one or more of the first frequencies f A , f B , f C , f'A are each determined by the controller 114, and then a plurality of first frequencies f are selected according to the desired degree to which the susceptor 116 (and therefore the aerosol-generating material 164) is heated. A , f B , f C , f' A An appropriate one of these is selected.

[0079] As noted above, it may be useful to control the heating of the aerosol-generating material 164 (by the susceptor 116) according to a particular heating profile, for example, to alter or enhance the characteristics of the generated aerosol, such as the nature, flavor, and / or temperature of the generated aerosol. To accomplish this, the controller 114 may control the drive frequency f of the resonant circuit 100 to sequentially step through a plurality of first frequencies according to a sequence. For example, this sequence may correspond to a heating sequence, where the degree to which the susceptor 116 is inductively heated increases in that sequence. For example, the controller 114 may control the drive frequency f at which the resonant circuit 100 is driven so that each first frequency in the sequence is closer to the resonant frequency than the previous first frequency in the sequence. For example, with reference to FIG. 3b, the sequence may include a first frequency f C followed by the first frequency f B , followed by the first frequency f A In this case, f A is f B than the resonant frequency f r Close to f B is f C than the resonant frequency f r Therefore, in this case, the current I flowing through the resonant circuit 100 is close to I C , followed by I B , followed by I A In this case, I C I B Smaller, I B I AAs a result, the degree to which the susceptor 116 is inductively heated increases as a function of time. This can be useful for controlling and therefore adjusting the temporal heating profile of the aerosol-generating material 164, and therefore, for example, adjusting aerosol delivery. Thus, the apparatus 150 is more flexible. For example, the sequence can correspond to a heating sequence, where the degree to which the susceptor 116 is inductively heated increases in that sequence. As another example, the controller 114 can control the drive frequency f at which the resonant circuit 100 is driven such that each first frequency in the sequence is further away from the resonant frequency than the previous first frequency in the sequence. For example, referring to FIG. 3b, the sequence can include a first frequency f A followed by the first frequency f B , followed by the first frequency f C Therefore, the current I flowing through the resonant circuit 100 is I A , followed by I B , followed by I C In this case, I C I B Smaller, I B I A As a result, the degree to which the susceptor 116 is inductively heated decreases as a function of time. This can be useful, for example, to reduce the temperature of the susceptor 116 or the aerosol-generating medium 164 in a more controlled manner. It will be appreciated that although the above sequence has each frequency in the sequence closer to (or further from) the resonant frequency than the last frequency, this is not necessarily the case and other sequences, including any sequence of multiple first frequencies, may be followed as desired.

[0080] In some examples, the controller 114 may select a plurality of first frequencies f from a plurality of predetermined sequences stored, for example, in a memory (not shown) accessible by the controller 114. A , f B , f C , f' AThe controller 114 can select one of the multiple sequences. This sequence can be, for example, the heating sequence or the cooling sequence described above, or any other predetermined sequence. The controller 114 can determine which of the multiple sequences to select based on, for example, a user input such as a heating or cooling mode selection, the type of susceptor 116 or aerosol-generating medium 164 being used (identified, for example, by a user input or from another identification means), an operational input from the overall apparatus 150 such as the temperature of the susceptor 116 or aerosol-generating medium 164, etc. This can be useful for controlling, and therefore adjusting, the temporal heating profile of the aerosol-generating material 164 according to the user's wishes or the operating environment, allowing for a more flexible apparatus 150.

[0081] In some examples, the controller 114 may set the drive frequency f to a first frequency f for a first period of time. A , f B , f C , f' A In some examples, the controller 114 may control the first frequency f to be held at a frequency of one or more first frequencies f A , f B , f C , f' A This allows for more control and flexibility in the heating profile of the susceptor 116 and aerosol-generating material 164.

[0082] As a particular example, it may be useful to control the heating of the aerosol-generating material 164 (by the susceptor 116) to different states or modes, such as a "hold" state in which the aerosol-generating material 164 is heated to a relatively low "hold" or "preheat" degree for a period of time, and a "heat" state in which the aerosol-generating material 164 is heated to a relatively high degree for a period of time. As explained below, controlling such states may help shorten the time it takes for the aerosol-generating device 150 to be able to generate a substantial amount of aerosol from a given activation signal.

[0083] A particular example is shown diagrammatically in Figure 3b, which, according to one example, shows a plot of the temperature T of the susceptor 116 (or aerosol-generating material 164) as a function of time t. Before time t1, the device 150 may be in an "off" state, i.e., no current is flowing through the resonant circuit 100. Therefore, the temperature of the susceptor 116 is lower than the ambient temperature T G , for example, 21° C. At time t1, device 150 switches to the “on” state, for example, by a user switching device 150 on. Controller 114 controls a first frequency f B The controller 114 controls the circuit 100 so that the power supply 114 is driven by the period P 12 During this time, the driving frequency f is set to the first frequency f B Hold for period P 12 can be of variable duration, lasting until further input is received by the controller 114 at time t2, as follows: B The AC current I B flows through circuit 100, and thus inductor 108, thereby inductively heating susceptor 116. As susceptor 116 is inductively heated, its temperature (and therefore the temperature of aerosol-generating material 164) increases over a period P 12 In this example, the susceptor 116 (and the aerosol-generating material 164) is heated to a steady-state temperature T B period P 12 It is heated to temperature T B is the ambient temperature T G The temperature may be higher, but lower than the temperature at which the aerosol-generating material 164 generates a substantial amount of aerosol. For example, the temperature T Bmay be 100°C. Thus, device 150 is in a "preheat" or "hold" state or mode, in which aerosol-generating material 164 is heated but substantially no aerosol is generated, or a substantial amount of aerosol is not generated. At time t2, controller 114 receives an input, such as an activation signal. The activation signal may originate from a user pressing a button (not shown) on device 150, or from a smoke detector (not shown), known per se. Upon receiving the activation signal, controller 114 adjusts the resonant frequency f r The controller 114 can control the circuit 100 to be driven with a period P 23 During this time, the driving frequency f is set to the resonant frequency f r Hold for period P 23 may be of variable duration, lasting until further input is received by the controller 114 at time t3, for example, when the user is no longer pressing a button (not shown) or the smoke detector (not shown) is no longer activated, or until the maximum heating period has elapsed. r The AC current I MAX flows through circuit 100 and inductor 108, and thus susceptor 116 is inductively heated to its maximum extent for a given voltage. When susceptor 116 is inductively heated to its maximum extent, its temperature (and the temperature of aerosol-generating material 164) increases over a period P 23 In this example, the susceptor 116 (and aerosol-generating material 164) is heated to a steady-state temperature T MAX period P 23 It is heated to temperature T MAX is the "preheat" temperature T B The higher temperature may be substantially at or above the temperature at which the aerosol-generating material 164 generates a substantial amount of aerosol. MAXmay be, for example, 300°C (although, of course, it may be a different temperature depending on the material 164, the susceptor 116, the overall configuration of the apparatus 105, and / or other requirements and / or conditions). Thus, the apparatus 150 is in a "heating" state or mode, in which the aerosol-generating material 164 reaches a temperature at which an aerosol is substantially generated, or a substantial amount of aerosol is generated. Because the aerosol-generating material 164 is already preheated, the time it takes from an activation signal to the apparatus 150 to the generation of a substantial amount of aerosol is therefore shorter than if the "preheat" or "hold" state were not applied. Thus, the apparatus 150 responds faster.

[0084] In the above example, upon receiving the activation signal, the controller 114 adjusts the resonant frequency f r In other examples, the controller 114 may control the resonant circuit 100 to be driven at a first frequency f in a “preheat” mode or state. B than the resonant frequency f r The first frequency f is close to A , f C The resonant circuit 100 may be controlled so as to be driven by

[0085] In some examples, the susceptor 116 may include nickel. For example, the susceptor 116 may comprise a body or substrate with a thin nickel coating. For example, the body may be a sheet of mild steel approximately 25 μm thick. In other examples, the sheet may be made of a different material, such as aluminum, plastic, stainless steel, or other non-magnetic material, and / or may have a different thickness, such as 10 μm to 50 μm. The body may be coated or electroplated with nickel. The nickel may have a thickness less than 5 μm, for example, 2 μm to 3 μm. The coating or electroplating may be of another material. A relatively small thickness for the susceptor 116 may help reduce the time required to heat the susceptor 116 during use. Having the susceptor 116 in sheet form may increase the efficiency of thermal coupling from the susceptor 116 to the aerosol-generating material 164. The susceptor 116 may be integrated into a consumable product that includes the aerosol-generating material 164. Thin sheets of susceptor 116 material can be particularly useful for this purpose. The susceptor 116 may be disposable. Such a susceptor 116 can be cost-effective. In one example, a nickel-coated or plated susceptor 116 can be heated to a temperature in the range of about 200° C. to about 300° C., which may be the operating range of the aerosol generating device 150.

[0086] In some examples, the susceptor 116 may be or include steel. The susceptor 116 may be a sheet of mild steel having a thickness of about 10 μm to about 50 μm, e.g., about 25 μm. Making the susceptor 116 only slightly, relatively thin, may help reduce the time required to heat the susceptor during use. The susceptor 116 may be integrated into the apparatus 105, as opposed to being integrated with the aerosol-generating material 164, which may be disposable. Nevertheless, the susceptor 116 may be removable from the apparatus 115 after use, for example, to allow replacement of the susceptor 116 after degradation due to thermal and oxidative stress during use. Thus, the susceptor 116 may be “semi-permanent,” in which case it is replaced infrequently. A mild steel sheet or foil or a nickel-coated steel sheet or foil as the susceptor 116 may be particularly suitable for this purpose because it is durable and therefore can withstand damage, for example, with many uses and / or many contacts with the aerosol-generating material 164. Having the susceptor 116 in sheet form can allow for more efficient thermal coupling from the susceptor 116 to the aerosol-generating material 164.

[0087] Curie temperature of iron, T C The Curie temperature of mild steel is 770°C. C The Curie temperature of cobalt, T C In one example, the mild steel susceptor 116 can be heated to a temperature in the range of about 200°C to about 300°C, which may be the operating range of the aerosol generating device 150. The Curie temperature T C A susceptor 116 having a temperature coefficient of 0.1 V may be useful in this case because the change to the response 300 of the circuit 100 may be relatively small over the operating temperature range of the susceptor 116. For example, the change in saturation magnetization of a susceptor material such as mild steel at 250° C. may be relatively small, e.g., less than 10% relative to its value at ambient temperature, and therefore the resulting change in inductance L, and hence resonant frequency f, of the circuit 100 at different temperatures in the exemplary operating range may be small.r The change in the resonant frequency f can be relatively small, which allows the resonant frequency f to be determined based on a predetermined value. r can be more accurate and therefore more easily controlled.

[0088] 4 is a flow diagram that schematically illustrates a method 400 for controlling an RLC resonant circuit 100 for inductively heating a susceptor 116 of an aerosol-generating device 150. In step 402, the method 400 determines the resonant frequency f of the RLC circuit 100, for example, by looking it up from memory or by measuring it. r In step 404, the method 400 determines the determined resonant frequency f for inductively heating the susceptor 116. r A first frequency f above or below A , f B , f C , f' A For example, this determination may involve determining a pre-stored quantity relative to the resonant frequency f r Add to, or resonant frequency f r This can be done by subtracting from or based on a measurement of the frequency response of the circuit 100. In step 406, the method 400 uses the determined first frequency f to heat the susceptor 116. A , f B , f C , f' A For example, the controller 114 may send a control signal to the H-bridge driver 114 to drive the RLC resonant circuit 100 at the first frequency f A , f B , f C , f' A The RLC circuit 100 can be driven by

[0089] The controller 114 may include a processor and memory (not shown). The memory may store instructions executable by the processor. For example, the memory may store instructions that, when executed by the processor, cause the processor to perform the method 400 described above and / or perform any one or combination of functions from the examples described above. The instructions may be stored in any suitable storage medium, for example, a non-transitory storage medium.

[0090] While some of the above examples have referenced the frequency response 300 of the RLC resonant circuit 100 in terms of the current I flowing through the RLC resonant circuit 100 as a function of the frequency f at which the circuit is driven, it will be appreciated that this is not necessary and that in other examples, the frequency response 300 of the RLC circuit 100 may be any measurement that can relate to the current I flowing through the RLC resonant circuit as a function of the frequency f at which the circuit is driven. For example, the frequency response 300 may be the response of the impedance of the circuit to frequency f, or, as noted above, the voltage measured across an inductor as a function of the frequency f at which the circuit is driven, or the voltage or current resulting from the induction of current in a pickup coil due to changes in current flowing in a supply voltage line or track, or the voltage or current resulting from the induction of current in a sense coil by the inductor 108 of the RLC resonant circuit, or a signal from a non-inductive field sensor such as a non-inductive pickup coil or Hall Effect device. In each case, the frequency characteristics of the peaks in the frequency response 300 can be determined.

[0091] In some of the above examples, reference has been made to the bandwidth B of the peak of response 300, but it will be appreciated that any other measure of the width of the peak of response 300 may instead be used. For example, the full width or half width of any given response amplitude peak, or a percentage of the maximum response amplitude, may be used. In other examples, the so-called "Q" or "quality" factor or value of resonant circuit 100 may be determined as Q=f r / B determines the bandwidth B and the resonant frequency f r, which can be determined and / or measured to obtain the bandwidth B and / or resonant frequency f in a similar manner as described in the example above with the appropriate coefficients applied. r It will also be appreciated that the resonant frequency f of the circuit 100 may be used instead of the Q factor f of the circuit 100. Thus, in some examples, the Q factor of the circuit 100 may be measured or determined, and the resonant frequency f of the circuit 100 may then be calculated based on the determined Q factor. r , the bandwidth B of circuit 100, and / or the first frequency at which circuit 100 is driven can be determined.

[0092] While the above examples have referred to peaks associated with maxima, it will be readily appreciated that this is not necessarily the case and that, depending on the determined frequency response 300 and how it is measured, the peaks can be associated with minima. For example, at resonance, the impedance of the RLC circuit 100 is at a minimum, and thus, for example, if the impedance as a function of drive frequency f is used as the frequency response 300, the peaks of the RLC circuit's frequency response 300 will be associated with minima.

[0093] While in some of the above examples the controller 114 is described as being configured to measure the frequency response 300 of the RLC resonant circuit 100, it will be appreciated that in other examples, for example, the controller 114 can determine the resonant frequency or first frequency by analyzing frequency response data communicated by a separate measurement or control system (not shown), or can determine the resonant frequency or first frequency directly as communicated by a separate control or measurement system. The controller 114 can then control the frequency at which the RLC circuit 100 is driven to the so-determined first frequency.

[0094] While in some of the above examples the controller 114 is described as being configured to determine the first frequency and control the frequency at which the resonant circuit is driven, it will be appreciated that this is not necessarily the case, and in other examples a device that is not necessarily the controller 114 or that does not necessarily include the controller 114 is configured to determine the first frequency and control the frequency at which the resonant circuit is driven. This device may be configured to determine the first frequency, for example, by the methods described above. This device may be configured to send a control signal, for example, to the H-bridge driver 102, to control the resonant circuit 100 to be driven at the first frequency so determined. It will be appreciated that this device or controller 114 is not necessarily an integral part of the aerosol generation device 150, but may be, for example, a separate device or controller 114 for use with the aerosol generation device 150. It will be appreciated further that the device or controller 114 need not necessarily be for controlling the resonant circuit and / or need not necessarily be configured to control the frequency at which the resonant circuit is driven; in other examples, the device or controller 114 may be configured to determine a first frequency but not itself control the resonant frequency. For example, upon determining the first frequency, the device or controller 114 can send this information, or information indicative of the determined first frequency, to a separate controller (not shown), or the separate controller (not shown) can obtain this information or an indication from the device or controller 114, and then, based on this information or indication, the separate controller (not shown) can control the frequency at which the resonant circuit is driven, e.g., control the frequency at which the resonant circuit is driven to the first frequency, e.g., control the H-bridge driver 102 to drive the resonant circuit at the first frequency.

[0095] In the above example, the device or controller 114 is described as being for use with an RLC resonant circuit for inductively heating a susceptor of an aerosol generating device, but this is not necessarily the case, and in other examples, the device or controller 114 may be for use with an RLC resonant circuit for inductively heating a susceptor of any device, for example, any inductive heating device.

[0096] Although in the above example the RLC resonant circuit 100 is described as being driven by the H-bridge driver 102, this is not necessarily the case and in other examples the RLC resonant circuit 100 may be driven by any suitable driving element for providing an alternating current to the resonant circuit 100, such as an oscillator.

[0097] The above examples should be understood as illustrative examples for the present invention. It should be understood that any feature described with respect to any one example can be used alone or in combination with other features described, or in combination with one or more features of any other of the examples, or in any combination with any other of the other examples. Furthermore, equivalents and modifications not described above may also be used without departing from the scope of the present invention, as defined in the appended claims. [Explanation of symbols]

[0098] 100...RLC resonant circuit, 114...controller (device), 116...susceptor, 150...aerosol generating device.

Claims

1. 1. An apparatus for use with an RLC resonant circuit for inductively heating a susceptor of an aerosol generating device, comprising: determining a resonant frequency of the RLC resonant circuit; determining a first frequency for the RLC resonant circuit above or below the determined resonant frequency for inductively heating the susceptor based on the determined resonant frequency; A device configured as follows.

2. 2. The apparatus of claim 1, wherein the first frequency is for inductively heating the susceptor to a first degree at a given supply voltage, the first degree being less than a second degree, the second degree being the degree to which the susceptor is inductively heated at the given supply voltage when the RLC circuit is driven at the resonant frequency.

3. 3. The apparatus of claim 1, configured to control a drive frequency of the RLC resonant circuit to be at the determined first frequency to heat the susceptor.

4. 4. The apparatus of claim 3, configured to control the drive frequency to hold it at the first frequency for a first period of time.

5. 5. Apparatus according to claim 3 or 4, configured to control the drive frequency to be one of a plurality of first frequencies, each of which is different from the others.

6. The apparatus of claim 5 , configured to control the drive frequency to step through the plurality of first frequencies according to a sequence.

7. The apparatus of claim 6 , configured to select the order from one of a plurality of predetermined orders.

8. controlling the drive frequency such that each of the plurality of first frequencies in the sequence is closer to the resonant frequency than the previous first frequency in the sequence; or 8. The apparatus of claim 6 or 7, configured to control the drive frequency such that each of the plurality of first frequencies in the sequence is farther from the resonant frequency than the previous first frequency in the sequence.

9. 9. An apparatus according to any one of claims 5 to 8, configured to control the drive frequency to hold it at one or more of the plurality of first frequencies for each of one or more periods.

10. measuring an electrical characteristic of the RLC circuit as a function of the drive frequency; An apparatus according to any preceding claim, configured to determine the resonant frequency of the RLC circuit based on the measurement.

11. 11. The apparatus of claim 10, configured to determine the first frequency based on the measured electrical characteristic of the RLC circuit as a function of the drive frequency at which the RLC circuit is driven.

12. 12. The apparatus of claim 10 or 11, wherein the electrical characteristic is a voltage measured across an inductor of the RLC circuit, the inductor being for transferring energy to the susceptor.

13. 12. The apparatus of claim 10 or 11, wherein the measurement of the electrical property is a passive measurement.

14. 14. The apparatus of claim 13, wherein the electrical characteristic is indicative of a current induced in a sense coil, the sense coil being for transferring energy from an inductor of the RLC circuit, and the inductor being for transferring energy to the susceptor.

15. 14. The apparatus of claim 13, wherein the electrical characteristic is indicative of a current induced in a pickup coil, the pickup coil being for transferring energy from a supply voltage element, the supply voltage element being for supplying a voltage to a drive element, and the drive element being for driving the RLC circuit.

16. 16. An apparatus according to any one of claims 1 to 15, configured to determine the resonant frequency of the RLC circuit and / or the first frequency substantially upon start-up of the aerosol generating device, and / or when a substantially new and / or replacement susceptor is attached to the aerosol generating device, and / or when a substantially new and / or replacement inductor is attached to the aerosol generating device.

17. determining a characteristic indicative of a bandwidth of a peak in the response of the RLC circuit corresponding to the resonant frequency; An apparatus according to any preceding claim, configured to determine the first frequency based on the determined characteristic.

18. a driving element configured to drive the RLC resonant circuit at one or more of a plurality of frequencies; Apparatus according to any preceding claim, configured to control the driving element to drive the RLC resonant circuit at the determined first frequency.

19. 20. The apparatus of claim 18, wherein the driving element comprises an H-bridge driver.

20. The apparatus of any one of claims 1 to 19, further comprising the RLC resonant circuit.

21. a susceptor configured to heat an aerosol-generating material and thereby generate an aerosol in use, the susceptor being configured to be inductively heated by an RLC resonant circuit; A device according to any one of claims 1 to 20; An aerosol generating device comprising:

22. 22. The aerosol generating device of claim 21, wherein the susceptor comprises one or more of nickel and steel.

23. 23. The aerosol generating device of claim 22, wherein the susceptor comprises a body having a nickel coating.

24. 24. An aerosol generating device according to claim 23, wherein the thickness of the nickel coating is substantially less than 5 μm, or substantially in the range of 2 μm to 3 μm.

25. 25. The aerosol generating device of claim 23 or 24, wherein the nickel coating is electroplated onto the body.

26. 26. An aerosol generating device according to any one of claims 22 to 25, wherein the susceptor is or comprises a sheet of mild steel.

27. 27. An aerosol generating device according to claim 26, wherein the sheet of mild steel has a thickness in the range of substantially 10 μm to substantially 50 μm, or substantially 25 μm.

28. 1. A method for use with an RLC resonant circuit for inductively heating a susceptor of an aerosol generating device, comprising: determining a resonant frequency of the RLC circuit; determining a first frequency for the RLC resonant circuit above or below the determined resonant frequency for inductively heating the susceptor; A method comprising:

29. 30. The method of claim 28, comprising controlling a drive frequency of the RLC resonant circuit to be at the determined first frequency to heat the susceptor.

30. 30. A computer program which, when executed on a processing system, causes said processing system to carry out the method of claim 28 or 29.

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