Aerosol generator with transducer feedback control

Abstract

An aerosol generating device is provided. The aerosol generating device may include a piezoelectric transducer (10). The aerosol generating device may include a driving circuit (12) connected to the piezoelectric transducer and configured to apply an oscillating current to the transducer. The aerosol generating device may include a control circuit (14) connected to the driving circuit and configured to monitor the resonant behavior of the piezoelectric transducer, wherein the control circuit is configured to control the operation of the driving circuit based on the resonant behavior of the piezoelectric transducer.

Description

Technology Field

[0001] The present disclosure relates to an aerosol generating device using a liquid aerosol forming substrate. In particular, the present disclosure relates to an aerosol generating device using a vibration transducer to move or spray the liquid aerosol forming substrate. Background Technology

[0002] One example of an aerosol generator is an electronic cigarette. Typically, in electronic cigarettes, a liquid aerosol-forming substrate is heated to generate vapor, thereby generating an aerosol. However, an alternative design has been proposed that uses a vibrating transducer to generate aerosol-forming droplets from a liquid aerosol generator.

[0003] Vibration transducers can also be used as the basis for small liquid pumps. Small liquid pumps can be used in aerosol generating devices, such as electronic cigarettes, to transfer liquid aerosol-forming materials from a reservoir to atomizing elements, such as heaters or vibration transducers.

[0004] To generate aerosols or move liquids within a device, it is desirable to optimize the efficiency of any vibration transducer used in the aerosol generator as much as possible. This is particularly important in handheld aerosol generators, such as electronic cigarettes, which are typically battery-powered and, preferably, need to be as small as possible but generate a significant volume of aerosol when required by the user. The problem to be solved

[0005] In addition, it would be desirable to be able to quickly and simply detect any changing operating conditions that affect the output and efficiency of the aerosol generator. means of solving the problem

[0006] According to an embodiment of the present invention, an aerosol generating device is provided. The aerosol generating device may include a transducer. The transducer may be a piezoelectric transducer. The aerosol generating device may include a driving circuit connected to the transducer and configured to apply an oscillating current to the transducer. The aerosol generating device may include a control circuit connected to the driving circuit and configured to monitor the resonant behavior of the transducer, wherein the control circuit is configured to control the operation of the driving circuit based on the resonant behavior of the transducer.

[0007] As used herein, "resonant behavior" refers to any measurable aspect of the response of a piezoelectric transducer to an oscillating input signal. For example, resonant behavior may be a resonant frequency or resonant frequencies, or a change in the resonant frequency or resonant frequencies, a maximum amplitude of the response or a minimum amplitude of the response, a maximum or minimum input impedance, a phase response or a change in the phase response.

[0008] The resonant behavior of a transducer can be expressed by one or more measurable parameters, such as input impedance or one or more frequencies of the maximum amplitude response.

[0009] A piezoelectric transducer may be part of a transducer assembly. The transducer assembly may be configured to interact with a liquid aerosol forming substrate within the device. The transducer assembly may be configured to generate an aerosol from the liquid aerosol forming substrate. The transducer assembly may be configured to move the liquid aerosol forming substrate.

[0010] In some embodiments, the transducer assembly comprises a perforated membrane or mesh. The transducer may be configured to drive the perforated membrane or mesh with vibrations at one or more frequencies. The vibration of the perforated membrane or mesh may force a liquid aerosol-forming substrate through the perforated membrane or mesh, which may result in the formation of an aerosol comprising droplets of the liquid aerosol-forming substrate.

[0011] In some embodiments, the transducer assembly comprises a membrane or surface configured to contact a liquid aerosol forming substrate. The transducer may be configured to drive the membrane or surface by vibration at one or more frequencies. Vibration of the membrane or surface may force liquid through an adjacent mesh or perforated membrane, which may result in the formation of an aerosol comprising droplets of the liquid aerosol forming substrate.

[0012] In some embodiments, the transducer assembly comprises a spray surface configured to contact a liquid aerosol-forming substrate, and an electrode on the transducer configured to generate a surface acoustic wave (SAW) on the spray surface. The SAW generates a droplet of the liquid aerosol-forming substrate that forms an aerosol.

[0013] In some embodiments, the transducer assembly forms part of a liquid pump. The transducer may include a membrane or surface configured to contact a liquid aerosol-forming substrate. The transducer may be configured to drive the membrane or surface to vibrate at one or more frequencies. The vibration of the membrane or surface may force liquid through an adjacent liquid valve.

[0014] In all of these embodiments, it is advantageous to be able to control the operating frequency of the transducer or the operating power of the transducer (or both the operating frequency and the operating power of the transducer) in response to changes in the resonant behavior of the transducer. In particular, controlling the operating frequency can be beneficial for improving the efficiency of the system. Controlling the operating frequency can maximize the generation of aerosols.

[0015] The control circuit may be configured to control the operation of the driving circuit at the time the device is first activated. The control circuit may be configured to control the operation of the driving circuit periodically or intermittently during the operation of the device.

[0016] There are several reasons why the resonant behavior of a piezoelectric transducer may change during the operation of the device. One parameter that can affect the resonant behavior of the transducer is temperature. The resonant frequency of the transducer assembly can vary with temperature as the material of the transducer assembly expands or contracts, which leads to changes in dimensions and residual stress within the transducer assembly. Changes in ambient temperature can cause temperature variations in the transducer assembly. Temperature variations in the transducer assembly can also occur due to heating of the transducer assembly as a result of energy dissipation within the device during operation. Typically, the transducer assembly will preheat during the operation of the device. Heating of the transducer assembly can lead to a decrease in the transducer's resonant frequency.

[0017] Other changes in ambient conditions can affect the resonant behavior of the transducer. For example, changes in atmospheric pressure or humidity can affect the resonant behavior of the transducer.

[0018] Changes in the material in contact with the transducer assembly can alter the resonance behavior of the transducer. In particular, changes in the load on the transducer can alter the resonance behavior of the transducer. For example, changes in the volume of the liquid aerosol-forming substrate in contact with the transducer assembly can alter the load on the transducer. Changes in the composition of the liquid aerosol-forming substrate in contact with the transducer assembly can alter the load on the transducer.

[0019] The resonance behavior of the transducer may change as a result of the aging of one or more components of the transducer assembly.

[0020] Therefore, it can be seen that changes in the resonance behavior of the transducer assembly may be rapid or involve longer-term drift. It is beneficial for the device to be able to respond to both rapid changes and long-term drift.

[0021] The control circuit can be configured to control the operation of the driving circuit so that the oscillation current has a frequency equal to the resonant frequency of the piezoelectric transducer. Operation at the resonant frequency allows the maximum amount of power to be delivered to the transducer. Operation at the resonant frequency can result in the maximum amplitude and maximum vibration velocity of the vibration. This can be beneficial for generating aerosols with desirable characteristics.

[0022] The control circuit can be configured to control the operation of the driving circuit so that the oscillation current has a frequency offset from the transducer's resonant frequency. This can be advantageous in some situations. For example, when the transducer's impedance at its resonant frequency does not match the driving circuit's output impedance, a small frequency offset is useful for operating the system at the impedance matching point where maximum power is delivered to the transducer. This frequency may be somewhere between the resonant frequency and the anti-resonant frequency. In this region, the impedance varies significantly with frequency, enabling precise adjustment.

[0023] The control circuit may be configured to monitor the resonant behavior of the transducer at multiple resonant frequencies of the transducer corresponding to different vibration modes. The transducer may be driven at multiple different frequencies to generate aerosol droplets having different characteristics.

[0024] The control circuit can be configured to monitor the resonant behavior of the piezoelectric transducer by measuring the power delivered to the transducer or the input impedance of the transducer. At the resonant frequency, the delivered power is maximized and the input impedance is minimized.

[0025] The control circuit can be configured to monitor the resonant behavior of the piezoelectric transducer by determining the non-crossing point or the inflection point of the output signal from the transducer. The non-crossing point or the inflection point can be used to determine the operating frequency.

[0026] The control circuit may include a Phase Locked Loop (PLL). The PLL may include a phase comparator and can determine the phase shift from the response from the transducer. The use of a PLL can be advantageous because it does not require a microprocessor. This can be a low-cost and high-reliability solution.

[0027] In some embodiments, the driving and control circuits are:

[0028] a) Apply a current having a driving frequency to the transducer;

[0029] b) During periodically spaced time slots, apply a current having a second frequency that is higher or lower than the driving frequency;

[0030] c) determine whether the power delivered to the transducer increases at the second frequency compared to the first frequency;

[0031] d) If the delivered power is increased at the second frequency, use the second frequency as the driving frequency, or maintain the existing driving frequency;

[0032] e) is configured to repeat steps a) through d).

[0033] The driving circuit can use a second frequency higher than the driving frequency in an alternate time slot and a second frequency lower than the driving frequency in an alternate time slot.

[0034] This process results in a device that automatically tracks the resonant frequency of the transducer.

[0035] The second frequency can be higher or lower than the driving frequency by a predetermined amount.

[0036] Another option for detecting changes in resonant frequency involves the use of dedicated MEMS sensors. For example, a low-inertia MEMS cantilever can be positioned in contact with a vibrating element of the transducer assembly so that the cantilever is synchronized with the oscillation of the transducer assembly and provides a corresponding electrical signal. Another option is to use real-time impedance measurements by monitoring the voltage and current of the transducer. In this case, the series and parallel modes of the transducer can be specified individually. The transducer behavior can be described in terms of an electrical equivalent circuit consisting of a series capacitance (C1), inductance (L1), and resistance (R1) for the mechanical component, and a parallel capacitance (C0) and resistance (R0) for the transducer electrical component. Depending on the frequency, this circuit can operate in a state where the series branch (C1, L1, R1) resonates on its own (series resonant mode) or where this LCR-series resonates in parallel with C0 (parallel resonant mode). The series resonance frequency is close to the transducer's resonance frequency, and the parallel resonance frequency is close to the transducer's anti-resonance frequency. Series mode resonance provides low impedance and results in higher current and lower voltage for the same power. This provides a large mechanical displacement amplitude. Parallel mode resonance provides high impedance and results in lower current and higher voltage for the same power. Mechanical losses are lower. In this case, a tuning series inductance can be added, and the electro-acoustic energy transfer efficiency can be higher at anti-resonance.

[0037] The device may include means for adjusting the resonant frequency of the transducer. For example, a membrane coupled to a piezoelectric transducer may be pre-stressed by the application of a DC bias voltage, which will alter its resonant behavior. As the components of the device age, it may be advantageous to adjust the device's resonant response to match specific desired frequencies or frequencies associated with the aerosol-forming substrate.

[0038] The control circuit may include a microprocessor. The control circuit may include a field programmable gate array (FPGA). The driving circuit and the control circuit may be integrated into a single circuit.

[0039] The control circuit can be configured to control the carrier frequency, duty cycle, power, modulation frequency, or amplitude of the oscillation current from the driving circuit.

[0040] As described, the resonant behavior of the transducer may be affected by the amount of liquid in contact with a part of the transducer assembly. The control circuit may be configured to detect a decrease in the amount of liquid in contact with the transducer assembly based on a change in the resonant behavior of the transducer. This may be based on a sudden change in the resonant frequency greater than a critical amount. The control circuit may be configured to stop the operation of the driving circuit in response to detecting a significant decrease in the liquid delivered to the transducer assembly. The control circuit may be configured to stop or change the operation of the driving circuit based on any malfunction of the device determined based on the resonant behavior of the transducer.

[0041] A piezoelectric transducer may include a single-crystal material. A piezoelectric transducer may include quartz. A piezoelectric transducer may include a ceramic. The ceramic may include barium titanate (BaTiO3). The ceramic may include lead zirconate titanate (PZT). The ceramic may include doping materials such as Ni, Bi, La, Nd, or Nb ions. A piezoelectric transducer may have polarity. A piezoelectric transducer may not have polarity. A piezoelectric transducer may include both a polarized piezoelectric material and a non-polarized piezoelectric material.

[0042] The driving circuit may be configured to apply an oscillating current having a frequency of about 20 kHz to about 1500 kHz, or about 50 kHz to about 1000 kHz, or about 100 kHz to about 500 kHz. This can provide a desired aerosol output rate and a desired droplet size.

[0043] The aerosol generator may be configured to generate an aerosol for user inhalation. The aerosol generator may be an electrically operated smoking device.

[0044] The aerosol generating device may include a liquid reservoir containing a liquid aerosol forming substrate. When in use, a piezoelectric transducer may come into contact with the liquid from the liquid reservoir.

[0045] The aerosol generating device may include a liquid aerosol forming material reservoir containing a liquid storage portion. The liquid storage portion may form part of a cartridge that is detachable from the rest of the device. The liquid storage portion of the aerosol generating system may include a housing that is substantially cylindrical, with an opening at one end of the cylinder. The housing of the liquid storage portion may have a substantially circular cross-section. The housing may be a rigid housing. As used herein, the term 'rigid housing' is used to mean a self-supporting housing. The rigid housing of the liquid storage portion may provide mechanical support for a heating means.

[0046] The liquid storage unit may further include a carrier material within a housing for holding an aerosol-forming substrate.

[0047] The liquid aerosol-forming substrate may be adsorbed onto a carrier or support or otherwise loaded. The carrier material may be made of any suitable absorbent plug or absorbent, for example, foamed metal or plastic material, polypropylene, tylene, nylon fiber, or ceramic. The liquid aerosol-forming substrate may be retained within the carrier material prior to use of the aerosol generation system. The liquid aerosol-forming substrate may be released into the carrier material during use. The liquid aerosol-forming substrate may be released into the carrier material immediately before use.

[0048] In one embodiment, a liquid aerosol forming substrate is contained within a capillary material. The capillary material is a material that actively transfers liquid from one end of the material to the other. The capillary material may be advantageously oriented within a housing to transfer the liquid aerosol forming substrate to a transducer assembly. The capillary material may have a fibrous structure. The capillary material may have a sponge structure. The capillary material may include a capillary bundle. The capillary material may include a plurality of fibers. The capillary material may include a plurality of threads. The capillary material may include a microbore tube. The capillary material may include a combination of fibers, threads, and microbore tubes. Fibers, threads, and microbore tubes may generally be aligned to transfer liquid to a vibrating element. The capillary material may include a sponge-type material. The capillary material may include a foam-type material. The structure of the capillary material can form multiple small bores or tubes through which liquid can be transported by capillary action.

[0049] The capillary material may include any suitable material or combination of materials. Examples of suitable materials include sponge or foam materials, ceramic or graphite-based materials in the form of fibers or calcined powders, foamed metal or plastic materials, fibrous materials composed of, for example, spun or extruded fibers, such as cellulose acetate, polyester, or combined polyolefin, polyethylene, tylene or polypropylene fibers, nylon fibers, or ceramics. The capillary material may have any suitable capillary action and porosity to be used with different liquid properties. The liquid aerosol-forming substrate has properties including, but not limited to, viscosity, surface tension, density, thermal conductivity, boiling point, and atomic pressure, which enable the liquid to be transported through the capillary material by capillary action. The capillary material may be configured to transport the aerosol-forming substrate to a transducer assembly.

[0050] The carrier material can come into contact with the transducer assembly. The liquid aerosol forming substrate can be transported from the liquid storage portion to the transducer assembly by capillary action.

[0051] Alternatively or additionally, the device may include a pump. The liquid aerosol-forming material may be transferred from the reservoir to the transducer assembly by the pump.

[0052] The aerosol generating device may include a liquid aerosol forming substrate within the housing of a liquid storage portion. The liquid aerosol forming substrate is a substrate capable of releasing volatile compounds capable of forming an aerosol. Volatile compounds may be released by moving the liquid aerosol forming substrate through a passage of a vibrating element.

[0053] The liquid aerosol forming substrate may contain nicotine. The nicotine-containing liquid aerosol forming substrate may be a nicotine salt matrix. The liquid aerosol forming substrate may contain a plant-based material. The liquid aerosol forming substrate may contain tobacco. The liquid aerosol forming substrate may contain a tobacco-containing material containing a volatile tobacco flavor compound that is released from the aerosol forming substrate upon heating. The liquid aerosol forming substrate may contain a homogenized tobacco material. The liquid aerosol forming substrate may contain a non-tobacco-containing material. The liquid aerosol forming substrate may contain a homogenized plant-based material.

[0054] The liquid aerosol forming substrate may comprise at least one aerosol forming agent. The aerosol forming agent is any suitable known compound or mixture of compounds that facilitates the formation of a dense and stable aerosol upon use and substantially resists thermal decomposition at the operating temperature of the system. Suitable aerosol forming agents are well known in the art and include, but are not limited to, polyhydric alcohols such as triethylene glycol, 1,3-butanediol, and glycerin; 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. The aerosol forming agent may be a polyhydric alcohol such as triethylene glycol, 1,3-butanediol, and glycerin, or a mixture thereof. The liquid aerosol forming substrate may comprise other additives and components such as flavoring agents.

[0055] The aerosol-forming substrate may include nicotine and at least one aerosol-forming agent. The aerosol-forming agent may be glycerin. The aerosol-forming agent may be propylene glycol. The aerosol-forming agent may include both glycerin and propylene glycol. The aerosol-forming substrate may have a nicotine concentration of about 2% to about 10%.

[0056] The aerosol-forming substrate may have a dynamic viscosity (μ) of about 0.4 mPa.S (0.4 mPl, 0.4 cP) to about 1000 mPa.S (1000 mPl, 1000 cP), or about 1 mPa.S to about 100 mPa.S, or about 1.5 mPa.S to about 10 mPa.S at a temperature of 20°C.

[0057] The aerosol generator may include a power supply. The power supply may be a battery. The battery may be a lithium-based battery, for example, a lithium-cobalt, lithium-iron-phosphate, lithium titanate, or lithium-polymer battery. The battery may be a nickel-hydrogen alloy battery or a nickel-cadmium battery. The power supply may be another form of charge storage device, such as a capacitor. The power supply may require recharging and may be configured for a number of charge and discharge cycles. The power supply may have a capacity to store enough energy to experience one or more puffs; for example, the power supply may have a capacity sufficient to continuously generate aerosols for a period of about 6 minutes, corresponding to the usual time taken to smoke a conventional cigarette, or for a period of several times 6 minutes. In another embodiment, the power supply may have a sufficient capacity to allow a predetermined number of puffings, or a predetermined number of discrete activations of the heating means and the actuator.

[0058] The aerosol generating device may be portable. The aerosol generating device may have a size similar to a conventional cigar or cigarette. The aerosol generating system may have a total length of about 30 mm to about 150 mm. The aerosol generating device may have an outer diameter of about 5 mm to about 30 mm.

[0059] The aerosol generating device may include a housing. The housing may be elongated. The housing may include any suitable material or combination of materials. Examples of suitable materials include metals, alloys, plastics, or composite materials comprising one or more of these materials, or thermoplastic resins suitable for food or pharmaceutical applications, such as polypropylene, polyetheretherketone (PEEK), and polyethylene. The material may be lightweight and non-brittle.

[0060] The housing may include a cavity for accommodating a power supply. The housing may include a mouthpiece. The mouthpiece may include at least one air inlet and at least one air outlet. The mouthpiece may include more than one air inlet.

[0061] The action of the transducer assembly on the liquid aerosol forming substrate may heat the aerosol forming substrate. This may be desirable when it is desirable to deliver a heated aerosol to a user. Alternatively or additionally, the device may include a heater. The heater may heat the liquid aerosol forming substrate before reaching the transducer assembly, at the transducer assembly, or after the aerosol is formed.

[0062] According to another aspect of the present invention, a method for operating an aerosol generating device is provided. The device may include a piezoelectric transducer. The device may include a driving circuit connected to the piezoelectric transducer. The device may include a control circuit connected to the driving circuit and configured to monitor parameters of the piezoelectric transducer. The method may include the step of applying an oscillating current to the transducer using the driving circuit. The method may further include the step of monitoring the resonant behavior of the piezoelectric transducer using the control circuit. The method may further include the step of controlling the operation of the driving circuit based on the monitored resonant behavior of the piezoelectric transducer.

[0063] A piezoelectric transducer may be part of a transducer assembly. The transducer assembly may be located within a liquid pump. The transducer assembly may include a membrane or surface configured to contact a liquid aerosol-forming substrate. The piezoelectric transducer may be configured to drive the membrane or surface by vibration. The vibration of the membrane or surface may force liquid through an adjacent liquid valve within the liquid pump.

[0064] The above method may include the step of stopping the operation of the driving circuit based on the monitored resonant behavior of the piezoelectric transducer. The method may include the step of controlling the carrier frequency, duty cycle, power, modulation frequency, or amplitude of the oscillation current from the driving circuit.

[0065] The step of monitoring resonance behavior may include the step of periodically applying an oscillation current at different frequencies and the step of determining the resonance behavior of the transducer at different frequencies. The method may include the step of applying an oscillation current including a plurality of sinusoidal frequencies.

[0066] The present invention can provide the advantage of efficient operation throughout operation, regardless of changes in the load on the transducer and changes in ambient or device conditions. The present invention can also provide means for detecting malfunctions and abnormal operating conditions, such as a reduced supply of a liquid aerosol-forming substrate.

[0067] The present invention is defined in the claims. However, a non-limiting, non-comprehensive list of examples is provided below. Any one or more features of these examples may be combined with any one or more features of other examples, embodiments, or modes described herein.

[0068] Example Ex1: An aerosol generating device comprising: a piezoelectric transducer; a driving circuit connected to the piezoelectric transducer and configured to apply an oscillating current to the transducer; and a control circuit connected to the driving circuit and configured to monitor the resonant behavior of the piezoelectric transducer and configured to control the operation of the driving circuit based on the resonant behavior of the piezoelectric transducer.

[0069] Example Ex2: An aerosol generating device in which, in Example Ex1, the control circuit controls the operation of the driving circuit so that the oscillation current has the same frequency as the resonance frequency of the piezoelectric transducer.

[0070] Example Ex3: An aerosol generating device in which, in Example Ex1, the control circuit is configured to control the operation of the driving circuit so that the oscillation current has a frequency offset from the resonant frequency of the piezoelectric transducer.

[0071] Example Ex4: An aerosol generating device in any one of the above-described embodiments, wherein the control circuit is configured to monitor the resonance behavior of a piezoelectric transducer at a plurality of resonance frequencies of the piezoelectric transducer corresponding to different vibration modes.

[0072] Example Ex5: An aerosol generating device in any one of the above-described embodiments, wherein the control circuit is configured to monitor the resonance behavior of the piezoelectric transducer by measuring the power delivered to the piezoelectric transducer or the impedance of the piezoelectric transducer.

[0073] Example Ex6: An aerosol generating device in any one of the above-described examples, wherein the driving circuit and the control circuit include a phase-locked loop (PLL).

[0074] Example Ex7: An aerosol generating device in any one of the above-described examples, wherein the piezoelectric transducer is an aerosol generating element configured to generate an aerosol from a liquid aerosol forming substrate.

[0075] Example Ex8: An aerosol generating device in Example Ex7, wherein the piezoelectric transducer comprises a perforated plate.

[0076] Example Ex9: An aerosol generating device in any one of Examples Ex1 to Ex6, wherein the piezoelectric transducer is part of a liquid pump.

[0077] Example Ex10: An aerosol generating device comprising, in any one of the above-described examples, a liquid reservoir containing a liquid aerosol forming substrate, wherein, in use, the piezoelectric transducer comes into contact with the liquid from the liquid reservoir.

[0078] Example Ex11: An aerosol generating device in Example Ex10, wherein the liquid comprises a mixture of different compounds.

[0079] Example Ex12: An aerosol generating device in Example Ex10 or Ex11, wherein the control circuit is configured to detect a decrease in the amount of liquid in contact with the piezoelectric transducer based on a change in the resonance behavior of the piezoelectric transducer.

[0080] Example Ex13: An aerosol generating device in any one of the above-described examples, wherein the aerosol generating device is an electronic cigarette.

[0081] Example Ex14: An aerosol generating device in any one of the above-described examples, wherein the oscillating current comprises a first frequency modulated with at least one other frequency.

[0082] Example Ex15: A method for operating an aerosol generating device, wherein the device comprises a piezoelectric transducer, a driving circuit connected to the piezoelectric transducer, and a control circuit connected to the driving circuit configured to monitor parameters of the piezoelectric transducer, and the method comprises:

[0083] A step of applying an oscillation current to the transducer using the above driving circuit;

[0084] A step of monitoring the resonance behavior of the piezoelectric transducer using the above control circuit; and

[0085] A method comprising the step of controlling the operation of the driving circuit based on the monitored resonant behavior of the piezoelectric transducer. Brief explanation of the drawing

[0086] Now, an example will be further explained with reference to the drawing. FIG. 1 illustrates a feedback control system according to the present invention; FIG. 2 is a schematic diagram of an aerosol generating device according to the present invention; FIG. 3 illustrates a transducer assembly for use in the system of FIG. 2; FIG. 4 is a schematic diagram illustrating the change in the response of a transducer over time; FIG. 5 illustrates an example of a driving and control circuit implementing feedback control; FIG. 6 is a schematic diagram of an aerosol generating device including a piezoelectric pump according to the present invention. Specific details for implementing the invention

[0087] FIG. 1 is a schematic diagram of a feedback control loop according to the present invention. The feedback loop includes a transducer (12), a driving circuit (14), and a control circuit (14). In this embodiment, the transducer is a piezoelectric transducer. The transducer is coupled to a membrane for generating an aerosol from a liquid supply unit and vibrates it. The transducer (12) is driven at a specific driving frequency by the driving circuit (12). The driving circuit (12) supplies an oscillating current to the transducer, causing the transducer to expand and contract. This ultimately causes the membrane to vibrate.

[0088] A transducer has one or more resonant frequencies. The resonant frequency depends on several factors, including the load on the transducer. The load on the transducer depends on the characteristics of the membrane and any load on the membrane. The resonant frequency also depends, for example, on temperature.

[0089] To ensure that the transducer is driven to a resonant frequency by the driving circuit, the control circuit (14) completes a feedback loop. The control circuit receives feedback parameters, such as phase shift or oscillation amplitude, from the transducer. The value of the feedback parameter depends on how close the driving frequency is to the transducer's resonant frequency. The driving circuit (12) adjusts the driving frequency of the oscillation current applied to the transducer (10), and the effect of such change in the driving frequency on the feedback parameter is monitored by the control circuit. Subsequently, the control circuit transmits a control signal to the driving circuit, and the driving circuit adjusts the frequency of the applied oscillation current based on the control signal to achieve a specific effect. In many cases, it is desirable to drive the transducer as close as possible to the resonant frequency. However, in some situations, it may be desirable to drive the transducer at a specific offset from the resonant frequency or at a frequency between the resonant frequency and the anti-resonant frequency. The control circuit may include a filter, a microcontroller, or any analog or digital means for processing the feedback parameter to generate a control signal.

[0090] FIG. 2 is a schematic diagram of a first embodiment of an aerosol generating device according to the present invention, comprising the feedback control exemplified in FIG. 1. FIG. 2 is essentially schematic. Specifically, the dimensions of the illustrated components are not necessarily proportional, either individually or relative to one another. The aerosol generating device comprises a reusable device portion (100) that works in conjunction with a cartridge (200), which is preferably disposable. In FIG. 2, the device is an electrically operated smoking system.

[0091] The device portion (100) comprises a main body having a housing (101). The housing (101) is substantially circularly cylindrical in shape and has a longitudinal length of about 100 mm and an outer diameter of about 20 mm, which is similar to a conventional cigar. In the device, an electric power supply unit in the form of a battery (102) and an electronic control circuit (104) are provided. The electric control circuit (104) includes a driving circuit and a control circuit for a transducer, as described with reference to FIG. 1. The main body housing (101) also defines a cavity (112) in which a cartridge (200) is received.

[0092] A cartridge (200) (pictured in schematic form in FIG. 2) comprises a rigid housing that defines a liquid storage portion (201). The liquid storage portion (201) holds a liquid aerosol forming substrate (not shown). The housing of the cartridge (200) is fluid impermeable but has an open end (not shown) that can be covered by a removable lid (not shown) when the cartridge is removed from the device (100). The lid can be removed from the cartridge (200) before the cartridge is inserted into the device. The cartridge (200) includes a key coupling feature (not shown) to prevent the cartridge (200) from being inserted into the device upside down.

[0093] The device portion (100) also includes a mouthpiece portion (120). In this example, the mouthpiece portion (120) is connected to the main body housing (101) by a hinged connection, but any type of connection such as a snap fit or a screw fit may be used. The mouthpiece portion (120) includes a plurality of air inlets (122), air outlets (124) and an aerosol forming chamber (125), and a sprayer (300) mounted therein (schematically illustrated in FIG. 2). As illustrated in FIG. 2, the air inlets (122) are limited between the mouthpiece portion (120) and the main body housing (101) of the device (100) when the mouthpiece portion is in a closed position. As illustrated by the arrow in FIG. 2, an airflow path (127) is formed from the air inlets (122) through the aerosol forming chamber (125) and the sprayer (300) to the air outlets (124).

[0094] As illustrated in FIG. 3, the atomizer (300) comprises a vibrating element (301) and a transducer (302) housed inside the atomizer housing (304). The atomizer housing (304) comprises a hollow cylindrical box, with an inlet opening (305) and an outlet opening (306) arranged coaxially on opposite sides of the housing (304). The housing (304) is detachably connected to the mouthpiece (120) of the device part (100) by a threaded connection (not shown). Male threads (not shown) are provided on the outer surface of the atomizer housing (304), and the male threads are complementary to female threads (not shown) on the inner surface of the mouthpiece (120). The atomizer (300) can be removed from the mouthpiece part (120) of the device part for disposal or cleaning.

[0095] The vibrating element (301) comprises an aluminum disc that is about 2 mm thick and about 15 mm in diameter and substantially circular.

[0096] A plurality of passages (303) extend from the inlet side (308) of the vibrating element to the opposite outlet side (309). The plurality of passages form a substantially circular array. The substantially circular array has a diameter of about 7 mm and is positioned substantially in the center of the element (301).

[0097] The passage (not shown) has a substantially circular cross-section and tapers from the inlet side (308) to the outlet side (309) of the vibrating element (301). The passage has a diameter of about 8 μm at the inlet side and a diameter of about 6 μm at the outlet side. The passage is generally formed by high-speed laser drilling. The plurality of passages consists of about 4,000 passages spaced evenly across the array.

[0098] The transducer (302) includes a piezoelectric transducer. The piezoelectric transducer is a substantially circular annular disc made of a piezoelectric material, generally lead zirconate titanate (PZT). The piezoelectric transducer has a thickness of about 2 mm, an outer diameter of about 17 mm, and an inner diameter of about 8 mm.

[0099] As illustrated in FIG. 3, the transducer (302) is in direct contact with the vibrating element (301) at the outlet side (309) of the vibrating element. The inner diameter of the piezoelectric transducer (302) surrounds the array of passages (303) of the vibrating element (301), and the open end of the passages at the outlet side is not covered by the piezoelectric transducer (302). In another embodiment (not shown), it is believed that the piezoelectric transducer (302) may be in direct contact with the vibrating element (301) at the inlet side (308).

[0100] The vibrating element (301) and the piezoelectric transducer (302) are supported within the atomizer housing (304) by a pair of elastomeric O-rings (311), which allow the vibrating element (301) and the piezoelectric transducer (302) to vibrate within the housing (304). The vibrating element (301) and the piezoelectric transducer (302) are held together by pressure from the opposing O-rings (311). However, in other embodiments (not shown), the vibrating element (301) and the piezoelectric transducer (302) may be joined by any suitable means, such as an adhesive layer.

[0101] The vibrating element (301) and the piezoelectric transducer (302) are placed within the sprayer housing (304) such that an array of passages (303) is coaxially aligned with the inlet and outlet openings (305, 306) of the housing (304).

[0102] One or more spring pins (310) extend through an opening (312) of the atomizer housing (304) to electrically connect the piezoelectric transducer (302) to the control circuit (104) and the battery (102) of the device (100). The one or more spring pins (310) are maintained in contact with the piezoelectric transducer (302) by pressure rather than mechanical connection so that good electrical contact is maintained while the piezoelectric transducer (302) vibrates.

[0103] During use, when the atomizer (300) is detachably connected to the mouthpiece portion (120) of the device portion (100) and the cartridge (200) is received in the cavity (112) of the device, an elongated capillary body (not shown in FIG. 2) extends from the liquid storage portion (201) of the cartridge (200) to the atomizer (300) to fluidly connect the cartridge (200) to the atomizer (300). As shown in FIG. 3, the elongated capillary body (204) extends into the atomizer housing (304) and contacts the inlet side (308) of the vibrating element (301) in an array of passages (303). A heating means is provided within the liquid storage portion in the form of a coil heater (205) surrounding the capillary body (204). Note that the coil heater is shown only schematically in FIG. 3. Although not shown in FIG. 2 or FIG. 3, the coil heater (205) is connected to the electrical circuit (104) and battery (102) of the device (100) through a connection (not shown) that can pass along the outside of the liquid storage portion (200).

[0104] During use, a liquid aerosol forming material (not shown) is transferred by capillary action from a liquid storage unit (201) to the other end of a capillary body (204) extending into the liquid storage unit (201), passing through a heater coil (205), and the other end of the capillary body (204) extending into a sprayer housing (304) and contacting a vibrating element (301) at the inlet side (308) in an array of passages (303).

[0105] When the user inhales from the air outlet (124) of the mouthpiece (120), ambient air is drawn in through the air inlet (122). In the embodiment of FIG. 2, a puffing detection device (106) in the form of a microphone is also provided as part of the control electronic device (104). A small amount of airflow is drawn through the sensor inlet (121) of the main body housing (101), past the microphone (106), and into the mouthpiece (120). When puffing is detected by the electric circuit (104), the electric circuit (104) activates the heater coil (205) and the piezoelectric transducer (302). The battery (102) supplies electrical energy to the coil heater (205) to heat the capillary body (204) surrounded by the coil heater.

[0106] The battery (102) additionally supplies electrical energy to the piezoelectric transducer (302) under the control of the driving and control circuit, causing it to deform in the thickness direction by vibrating. The piezoelectric transducer (302) typically vibrates at about 150 kHz. The driving current supplied to the transducer has an initial frequency and waveform based on parameters stored in memory. During the fabrication of the device, the frequency response of the transducer assembly including the vibrating element (301) can be characterized, and the initial frequency and waveform can be set. The piezoelectric transducer (302) transmits vibration to the vibrating element (301), and the vibrating element also vibrates while deforming in the thickness direction. Additionally, the LED (108) is activated to indicate that the device is active. As described below, during operation, a feedback control loop is used to adjust the driving current supplied to the transducer in response to detected changes in resonant behavior.

[0107] The coil heater (205) heats the liquid aerosol forming substrate, which is delivered along the capillary body through the coil heater (205), to a predetermined temperature of about 45°C.

[0108] The vibration of the vibrating element deforms a plurality of passages (303), which draw heated liquid aerosol-forming material from the capillary body (204) through the plurality of passages (303) located on the inlet side (308) of the vibrating element (301), and discharge droplets of the sprayed aerosol-forming material through the passages located on the outlet side (309) of the vibrating element (301) to form an aerosol. At the same time, the sprayed heated liquid is replaced by additional liquid moving along the capillary body (204) by capillary action. (This is sometimes referred to as 'pumping action'.) The aerosol droplets discharged from the vibrating element (301) are mixed with and returned to the airflow (127) from the inlet (122) within the aerosol-forming chamber (125), and are returned toward the air outlet (124) of the mouthpiece (120) so that the user can inhale.

[0109] As previously mentioned, the resonant response of the transducer may change during operation. FIG. 4 is a schematic diagram of the detected parameters from the transducer illustrating the change in frequency over time. The time distance between successive crossings of the signal through zero is a measure of frequency and can be used to synchronize the driving signal with the operating frequency of the transducer, in this example, its resonant frequency. The signal may be, for example, a current measured by a sensing resistor in series with the transducer. In that case, the amplitude may have units of amperes relative to the current, or the amplitude may be normalized, for example, by a maximum value, in which case the unit of amplitude is 1. The time may have units of milliseconds or microseconds, for example, depending on the characteristic frequency operating range covered by the transducer.

[0110] A specific example of a possible implementation of such a feedback loop is illustrated in FIG. 5. In the embodiment of FIG. 3, a transducer (500) connected to a vibrating perforated plate is driven by a half-bridge (505) consisting of two power MOSFETs 510 and 515. An optional series inductor (520), for example, a 10 microhenry inductor, may be used between the half-bridge and the transducer to adjust the impedance. For example, a current sensing resistor (525) of 1 Ω may be placed at the bottom of the transducer (500). The voltage measured across the current sensing resistor is proportional to the current passing through the transducer. This voltage signal may be filtered by a filter and amplified by a gain stage (530). The filter and gain stage (530) may include, for example, a low-pass filter to block high-frequency harmonics, and a FET amplifier, for example, an AD823, to amplify the signal. The comparator (540) generates a feedback signal, which in this example generates a square wave signal as an appropriate input waveform for the gate driver (550). The gate driver (550) may be, for example, an IC of the LT1162 type and drives the half-bridge (505). As a change in frequency is detected and transmitted back to the driver, the transducer (500) will always be driven at its operating frequency, for example, its resonant frequency. The driving circuit and control circuit shown in FIG. 5 can be integrated into the control circuit (104) shown in FIG. 2.

[0111] FIG. 6 is an example of an aerosol generating device according to another embodiment of the present invention. FIG. 6 is essentially schematic. Specifically, the dimensions of the illustrated components are not necessarily proportional, either individually or relative to one another. The device of FIG. 6 generates an aerosol by heating a liquid aerosol-forming substrate using a heater. However, the device includes a pump using a piezoelectric transducer to transfer the liquid aerosol-forming substrate to the heater.

[0112] The device is a handheld, electric-operated smoking device (600) and includes a housing (610). Inside the housing (610) is an electric power supply in the form of a battery (612) and a control circuit (614). Additionally, inside the housing is a liquid reservoir (620) containing a liquid aerosol-forming material that is vaporized to form an aerosol for the user to inhale. A nebulizer assembly (630) is provided within the housing coupled to the liquid reservoir (620). The nebulizer assembly includes a vaporizer (634), which is an electric heater in this example, and a pump (632) positioned to pump liquid from the liquid reservoir (620) to the vaporizer (634). Both the pump (632) and the electric heater (634) are powered by the battery (612) under the control of the control circuit (614) as described below.

[0113] The housing (610) includes an air inlet (618) and an air outlet (616). The air outlet (616) is provided at the mouthpiece end of the housing. When in use, the user draws in air from the mouthpiece end of the housing. This draws air into the housing through the air inlet (618), passes through the vaporizer (634), and exits through the outlet (616) into the user's mouth. The air drawn in and passing through the vaporizer carries a droplet of vaporized aerosol-forming material. The vaporized aerosol-forming material moves through the device into the user's mouth, where it cools to form an aerosol.

[0114] The operation of the heater can be directly controlled by the user pressing a button on the housing (610). Alternatively, the system may include an airflow sensor, such as a microphone (615), that detects the airflow passing through the system, and the heater may be operated based on a signal from the airflow sensor. When the user draws air through the system (referred to herein as puffing), the air flows past the airflow sensor (615). If the airflow detected by the airflow sensor exceeds a threshold value, the control circuit may power the heater to operate the heater. The control circuit may power the heater for a predetermined time, or power the heater while the detected airflow exceeds the threshold value. The control circuit may include a temperature sensing means, such as a dedicated temperature sensor, or a temperature sensing means by monitoring the electric resistance of the heater. Subsequently, the control circuit may power the heater to raise the temperature of the heater to within a desired temperature range. The temperature should be sufficient to vaporize the aerosol-forming material, but not so high that there is a significant risk of combustion.

[0115] The liquid in this embodiment comprises a mixture of water, glycerol, propylene glycol, nicotine, and flavoring agents. The liquid is maintained within a liquid reservoir (620). The liquid reservoir may be provided as a cartridge that can be replaced when the liquid is consumed. To prevent leakage of the liquid, the liquid reservoir has a housing formed of a rigid plastic material and is liquid-tight for both the period before and during use. As used herein, "rigid" means that the housing is self-supporting. In this embodiment, the reservoir is formed by 3D printing using an acrylic photopolymer. The cartridge must be rigid and capable of withstanding significant loads during transport and storage. However, because the liquid reservoir housing is sealed and rigid, the liquid reservoir has a fixed internal volume. If the liquid is removed by a pump and the internal pressure of the liquid reservoir decreases, it may adversely affect the performance of pumping the liquid from the reservoir. To prevent a significant drop in pressure, the liquid reservoir has a balance air inlet valve (622). When the pressure difference between the inside and outside of the storage exceeds the critical pressure difference, the equilibrium valve (622) allows air to flow into the liquid storage.

[0116] The pump can operate in the same way as the heater. For example, the control circuit can supply power to the pump for the same duration as power is supplied to the heater. Alternatively, the control circuit can supply power to the pump for the period immediately following the operation of the heater.

[0117] The control circuit (614) includes a feedback loop as illustrated in FIG. 1 for controlling the pump (632). The pump (632) includes a piezoelectric transducer that drives a flexible diaphragm to vibrate. The vibration of the flexible diaphragm pushes the liquid aerosol-forming material out of the pump chamber through the outlet valve when the chamber volume decreases, and draws the liquid aerosol-forming material into the pump chamber through the inlet valve when the liquid aerosol-forming material increases the chamber volume. To maximize pumping efficiency, it is advantageous to operate the pump (632) at or close to the resonant frequency of the transducer. However, as previously mentioned, the resonant frequency of the transducer may be changed for a number of reasons.

[0118] Changes in the resonant frequency of the transducer due to temperature changes, other environmental changes, or aging can be monitored, and the driving signal can be modified accordingly using one of the aforementioned feedback mechanisms.

[0119] Changes in the resonance frequency of the transducer due to insufficient liquid being drawn into the pump chamber can be detected as sudden changes in resonance behavior, such as a change greater than a predetermined threshold between two measurement cycles. If a sudden change in resonance behavior is detected, the operation of the pump and heater may be stopped until a new liquid reservoir is placed in the device.

Claims

Claim 1 An aerosol generating device comprising: a piezoelectric transducer; a driving circuit connected to the piezoelectric transducer and configured to apply an oscillating current to the transducer; and a control circuit connected to the driving circuit and configured to monitor the resonant behavior of the piezoelectric transducer and configured to control the operation of the driving circuit based on the resonant behavior of the piezoelectric transducer, wherein the piezoelectric transducer forms part of a transducer assembly within a liquid pump, and the transducer assembly comprises a membrane or surface configured to contact a liquid aerosol forming substrate, and the transducer assembly is configured to drive the membrane or surface by vibration, and the vibration of the membrane or surface forces the liquid through an adjacent liquid valve within the liquid pump. Claim 2 An aerosol generating device according to claim 1, wherein the control circuit is configured to control the operation of the driving circuit so that the oscillation current has the same frequency as the resonance frequency of the piezoelectric transducer. Claim 3 An aerosol generating device according to claim 1, wherein the control circuit is configured to control the operation of the driving circuit so that the oscillation current has a frequency offset from the resonant frequency of the piezoelectric transducer. Claim 4 An aerosol generating device according to any one of claims 1 to 3, wherein the control circuit is configured to monitor the resonant behavior of the piezoelectric transducer at a plurality of resonant frequencies of the piezoelectric transducer corresponding to different vibration modes. Claim 5 An aerosol generating device according to any one of claims 1 to 3, wherein the control circuit is configured to monitor the resonance behavior of the piezoelectric transducer by measuring the power delivered to the piezoelectric transducer or the impedance of the piezoelectric transducer. Claim 6 An aerosol generating device according to any one of claims 1 to 3, wherein the driving circuit and the control circuit include a phase-locked loop (PLL). Claim 7 An aerosol generating device according to any one of claims 1 to 3, wherein the piezoelectric transducer is an aerosol generating element configured to generate an aerosol from a liquid aerosol forming substrate. Claim 8 In claim 7, the aerosol generating device wherein the piezoelectric transducer comprises a perforated plate. Claim 9 An aerosol generating device according to any one of claims 1 to 3, comprising a liquid reservoir containing a liquid aerosol forming substrate, wherein, in use, the piezoelectric transducer comes into contact with the liquid from the liquid reservoir. Claim 10 In claim 9, the above liquid comprises a mixture of different compounds, an aerosol generating device. Claim 11 An aerosol generating device according to claim 9, wherein the control circuit is configured to detect a decrease in the amount of liquid in contact with the piezoelectric transducer based on a change in the resonance behavior of the piezoelectric transducer. Claim 12 An aerosol generating device according to any one of paragraphs 1 to 3, wherein the aerosol generating device is an electronic cigarette. Claim 13 An aerosol generating device according to any one of claims 1 to 3, wherein the oscillating current comprises a first frequency modulated with at least one other frequency. Claim 14 A method for operating an aerosol generating device, wherein the device comprises: a transducer assembly within a liquid pump, wherein the transducer assembly comprises a piezoelectric transducer and a membrane or surface configured to contact a liquid aerosol forming substrate, wherein the piezoelectric transducer is configured to drive the membrane or surface by vibration, and the vibration of the membrane or surface forces a liquid through an adjacent liquid valve within the liquid pump; a driving circuit connected to the piezoelectric transducer; and a control circuit connected to the driving circuit and configured to monitor parameters of the piezoelectric transducer; and the method comprises the steps of: applying an oscillating current to the transducer using the driving circuit; monitoring the resonant behavior of the piezoelectric transducer using the control circuit; and controlling the operation of the driving circuit based on the monitored resonant behavior of the piezoelectric transducer.

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