Aerosol Generating Devices and Systems

Abstract

An aerosol generating device is disclosed. The device comprises a membrane having an aerosol-generation zone, the aerosol-generation zone including a plurality of nozzles, the plurality of nozzles being the only nozzles within the aerosol-generation zone; and an actuator coupled to the membrane, the actuator configured, in use, to excite the membrane to induce vibration of the membrane at one or more predetermined modal frequencies of the membrane to aerosolize a liquid aerosol-forming substrate passing through the plurality of nozzles, the plurality of nozzles being preferentially located adjacent to antinodes of the membrane that are excited at the one or more predetermined modal frequencies of the membrane. The membrane has a gradual change in thickness from a central region of the membrane to a periphery of the membrane.

Description

[Technical Field]

[0001] The present disclosure relates to an aerosol generating device and system for aerosolizing a liquid aerosol-forming substrate through the use of a vibratable perforated membrane. [Background technology]

[0002] Known vibrating nebulizers for aerosolizing liquid aerosol-forming substrates employ a membrane with a uniform distribution of nozzles. "Homogeneous" means that the nozzles are evenly distributed on the surface of the membrane, and all of the nozzles have the same profile and size. The membrane is connected to an actuator, which functions to induce vibration of the membrane. When the membrane contacts the liquid aerosol-forming substrate, the vibrating action of the membrane forces the liquid aerosol-forming substrate through the nozzles, forming aerosol droplets. However, these known vibrating nebulizers suffer from inconsistent aerosol quality across the area of the membrane.

[0003] There is a need to provide an improved means for aerosolizing a liquid aerosol-forming substrate using a vibrating perforated membrane. Summary of the Invention

[0004] According to one aspect of the present invention, a membrane having an aerosol-generation zone, the aerosol-generation zone including a plurality of nozzles, the plurality of nozzles being the only nozzles within the aerosol-generation zone; an actuator coupled to the membrane; an actuator configured, in use, to excite the membrane to induce vibration of the membrane at one or more predetermined modal frequencies of the membrane to aerosolize a liquid aerosol-forming substrate passing through the plurality of nozzles; An aerosol generating device is provided in which a plurality of nozzles are preferentially positioned adjacent antinodes corresponding to membranes excited at one or more predetermined modal frequencies of the membrane.

[0005] As used herein, the term "nozzle" refers to an opening, hole or aperture through a membrane that provides a passageway for the liquid aerosol-forming substrate to travel through the membrane.

[0006] As used herein, the term "antinode" refers to the position on the membrane where the magnitude of the membrane's displacement is greatest between adjacent nodal lines when the membrane is vibrating at its modal frequency.

[0007] The term "node" as used herein refers to a position on the membrane where the displacement of the membrane is always zero when the membrane is vibrating at its modal frequency. When a given vibration mode of the membrane is excited at the corresponding modal frequency, the nodes are defined along one or more lines, which are referred to as "nodal lines."

[0008] The term "modal frequency" as used herein refers to either the natural frequency or the resonant frequency of a membrane. Each vibration mode of a membrane has a different frequency and shape, referred to as the modal frequency and modal shape, respectively. The lowest (or first) modal frequency of a membrane is known as the fundamental frequency. The modal frequency of a membrane can be affected by its physical properties and any boundary conditions applied to the membrane. For example, the membrane's Young's modulus, Poisson's ratio, and mass density, as well as any constraints on the membrane, can independently affect the membrane's modal response in terms of both the modal frequency and modal shape associated with each given mode.

[0009] As used herein, the term "predetermined modal frequency" refers to the modal frequency of the membrane that the actuator is specifically designed to excite.

[0010] When this application refers to a first predetermined modal frequency and a second predetermined frequency, the terms "first" and "second" indicate that each frequency is associated with a different vibrational mode, and it is not necessary that the first predetermined modal frequency be the fundamental frequency of the membrane and the second predetermined modal frequency be a second overtone or harmonic of the membrane.

[0011] As used herein, the term "preferentially located" refers to more than 50% of the plurality of nozzles being located in close proximity to the antinodes corresponding to the membranes that are excited at one or more predetermined modal frequencies of the membranes.

[0012] As used herein, the term "proximal" refers to the nozzle being closer to the antinode than to the node, with the antinode and node corresponding to the membrane being excited at one or more predetermined modal frequencies of the membrane.

[0013] Preferentially locating nozzles adjacent to antinodes corresponding to membranes excited at one or more predetermined modal frequencies of the membrane helps maximize the energy and velocity imparted to individual aerosol droplets from membrane vibrations. Increasing the velocity imparted to individual aerosol droplets has the advantage of increasing the distance those droplets are ejected from the membrane nozzles. Preferentially locating nozzles adjacent to antinodes also provides increased uniformity of aerosol droplet formation across the aerosol-generation zone compared to aerosol droplet formation resulting from a membrane with a uniform nozzle distribution.

[0014] Preferably, the plurality of nozzles are non-homogeneously distributed across the aerosol-generation zone.

[0015] Different aerosol droplet formation regimes can be quantified by reference to various parameters, the value of which provides a measure of the quality of aerosol droplet formation. One example of such a parameter is the Weber number, We. For a membrane having an arrangement of nozzles within the aerosol-generation zone, where the nozzles are circular when the membrane is viewed in plan, all nozzles have the same diameter, the membrane is vibrated at a given frequency f, and a given liquid aerosol-forming substrate is in contact with the vibrating membrane to aerosolize the liquid aerosol-forming substrate through the nozzles, the Weber number can be expressed as:

number

[0016] A low Weber number (We) is associated with poor aerosol droplet formation. To further explain, the lower the Weber number, the greater the likelihood that individual aerosol droplets will break up into smaller droplets. In extreme cases, due to the low energy imparted to the liquid aerosol-forming substrate by the membrane's vibration, some droplets retreat and settle on the membrane's surface after passing through the nozzle in the membrane. The phenomenon of individual aerosol droplets breaking down into smaller droplets with the same collective volume but smaller surface area is called Rayleigh breakup or Rayleigh instability. Rayleigh breakup is highly undesirable and indicates poor aerosol droplet formation. In contrast, a high Weber number is associated with high-quality aerosol droplet formation, indicating increased energy and velocity imparted to the aerosol droplets. High-quality aerosol droplet formation can be indicated by the lack of Rayleigh breakup and the lack of aerosol droplets retreating and settling on the membrane's surface. In summary, droplet size, droplet mass, and droplet velocity are relevant parameters for quantifying the quality of aerosol droplet formation.

[0017] In use, the aerosol generating device preferably produces an aerosol droplet formation comprising droplets having diameters in the range of 0.1 μm to 5 μm.

[0018] In terms of the equation defining the Weber number, velocity v can be expressed as the characteristic velocity of the membrane when excited at frequency f. For a given location on the membrane, this characteristic velocity can be expressed as the displacement of the membrane at that location multiplied by frequency f. Therefore, it can be seen that locating the nozzle at the antinode, or as close to the antinode as possible, helps maximize the amount of energy and velocity imparted by the membrane to individual liquid aerosol-forming substrate droplets. This helps increase the Weber number of the resulting aerosol droplet formation and reduce the likelihood of Rayleigh breakup of the droplets. Additionally, locating multiple nozzles at the antinode, or as close to the antinode as possible, can increase the distance these droplets can be ejected from the membrane.

[0019] The nozzle is preferably circular in shape. The use of circular nozzles is preferred because it maximizes the area to perimeter ratio, thus reducing viscous drag forces and boundary layer buildup. However, the use of elliptical nozzles has also been found to provide acceptable performance in terms of resulting aerosol droplet formation.

[0020] The membrane may be formed from a polymeric material, thereby providing the advantage of reduced mass and inertia. However, the membrane may also be formed from any other material, such as a metallic material. The membrane may also be a composite of two or more different materials. Factors influencing the selection of the membrane material may include the specific liquid aerosol-forming substrate intended to be used in and aerosolized by the aerosol generating device. For example, it is highly desirable to select a membrane material that does not chemically react or decompose as a result of contact with the specific liquid aerosol-forming substrate. By way of example only, the membrane may be formed from palladium, stainless steel, copper-nickel alloy, polyimide, polyamide, silicon, or aluminum nitride.

[0021] The different membrane profiles have correspondingly different modal frequencies and shapes. Advantageously, the membrane has a circular profile. A circularly profiled membrane has been found to be beneficial when the aerosol generating device is used in a smoking system in the form of an elongated cylindrical smoking article. Furthermore, the use of a circularly profiled membrane also reflects the corresponding circular shape often associated with common liquid delivery mechanisms, such as wicks or tubes.

[0022] The liquid aerosol-forming substrate may comprise nicotine. The nicotine-containing liquid aerosol-forming substrate may be a nicotine salt matrix. The liquid aerosol-forming substrate may comprise a plant-derived material. The liquid aerosol-forming substrate may comprise tobacco. The liquid aerosol-forming substrate may comprise a homogenized tobacco material. The liquid aerosol-forming substrate may comprise a non-tobacco-containing material. The liquid aerosol-forming substrate may comprise a homogenized plant-derived material.

[0023] The liquid aerosol-forming substrate may contain at least one aerosol former. The aerosol former is any suitable known compound or mixture of compounds that facilitates the formation of a dense and stable aerosol upon use. Suitable aerosol formers are well known in the art and include, but are not limited to, polyhydric alcohols (such as triethylene glycol, 1,3-butanediol, and glycerin), esters of polyhydric alcohols (such as glycerol monoacetate, diacetate, or triacetate), and aliphatic esters of monocarboxylic, dicarboxylic, or polycarboxylic acids (such as dimethyl dodecanedioate and dimethyl tetradecanedioate). The aerosol former may be a polyhydric alcohol or a mixture thereof (such as triethylene glycol, 1,3-butanediol, and glycerin). The liquid aerosol-forming substrate may contain other additives and ingredients (such as flavoring agents).

[0024] The liquid aerosol-forming substrate may comprise water.

[0025] The liquid aerosol-forming substrate may comprise nicotine and at least one aerosol former. The aerosol former may comprise glycerin. The aerosol former may comprise propylene glycol. The aerosol former may comprise both glycerin and propylene glycol. The liquid aerosol-forming substrate may have a nicotine concentration of about 2% to about 10%.

[0026] The actuator may advantageously include one or more piezoelectric actuators. Piezoelectric actuators refer to piezoelectric actuators. Piezoelectric actuators are preferred because they provide an energy-efficient, lightweight means of inducing membrane vibration and have a high energy conversion efficiency from electricity to acoustic / mechanical power. Furthermore, piezoelectric actuators are available in a wide variety of materials and shapes. For piezoelectric actuators, inputting an electrical drive signal to the piezoelectric actuator can result in a mechanical output in the form of a vibration signal. The piezoelectric actuator may be coupled to the membrane so that the vibration signal is transmitted to the membrane. Tuning and adjusting the electrical drive signal input to the piezoelectric actuator can result in a corresponding change in the output vibration signal, thereby enabling the actuator to activate different vibration modes of the membrane. Other types of actuators or transducers may also be employed. For example, magnetostrictive transducers may be used, but they require more input power compared to piezoelectric actuators, and in addition, they have a more limited operating frequency range and require a magnetic field. As a further example, electrostrictive transducers may be used, but they require a higher drive current and are much more sensitive to temperature changes than piezoelectric actuators, thereby affecting performance. Piezoelectric transducers may also be used, which are bipolar but suffer from similar limitations as magnetostrictive transducers. Combining different types of actuators or transducers, for example in a layered structure or in parallel, is possible, but this may increase the complexity of the aerosol generating device design.

[0027] Optimal energy transfer from the film to individual aerosol droplets occurs when all of the nozzles are precisely located at the antinode. However, if the majority of the nozzles are spatially distributed within a short distance on either side of the antinode, aerosol droplet formation of acceptable quality (e.g., no visible Rayleigh breakup or little or no change in droplet size and velocity) can result.

[0028] Preferably, at least 60% of the nozzles are located within a region extending on either side of the antinode where the magnitude of the membrane displacement is at least 60% of the magnitude of the membrane displacement at the antinode for one or more corresponding predetermined modal frequencies. All of the nozzles may be located within this region. In other embodiments, at least 70%, at least 80%, or at least 90%, or all of the nozzles are located within a region extending on either side of the antinode where the magnitude of the membrane displacement is at least 60%, at least 70%, or at least 80% of the magnitude of the membrane displacement at the antinode for one or more corresponding predetermined modal frequencies. The greater the proportion of the nozzles located adjacent to the antinode, and the closer the proportion of nozzles to the antinode, the higher the quality of the resulting aerosol droplet formation produced by the aerosol generating device. As discussed above, improved quality may be indicated by a reduced tendency for Rayleigh breakup or a reduced variation in the size and velocity of the aerosol droplets.

[0029] Advantageously, less than 5% of the plurality of nozzles are located within a region extending on either side of a node where the magnitude of the membrane displacement is 20% or less of the magnitude of the membrane displacement at an antinode for one or more corresponding predetermined modal frequencies. At a node, zero or minimal energy can be transferred to any liquid aerosol-forming substrate in contact with the membrane. Therefore, avoiding or minimizing the presence of nozzles at nodes helps reduce the likelihood of aerosol droplets receding and settling on the membrane surface. It will be appreciated, therefore, that avoiding or minimizing the presence of nozzles at nodes helps reduce waste of liquid aerosol-forming substrates during use of the device. Advantageously, the membrane does not have nozzles within a region extending on either side of a node where the magnitude of the membrane displacement is 10% or less of the magnitude of the membrane displacement at an antinode for one or more corresponding predetermined modal frequencies. Having a membrane without nozzles in this region on either side of the node avoids the presence of nozzles in these portions of the membrane, which may impart minimal energy to the liquid aerosol-forming substrate, thus reducing Rayleigh decomposition and the likelihood of aerosol droplets receding and settling on the membrane surface.

[0030] The one or more predetermined modal frequencies are advantageously in the frequency range of about 50 kHz to about 300 kHz. This range has been found to be suitable for aerosol generation. A frequency that is too low may reduce the volumetric throughput of the liquid through the membrane nozzle and, in addition, may adversely affect the fluid dynamics and droplet breakup mechanism. A frequency that is too high may jeopardize acoustic absorption of energy in the liquid, potentially leading to undesirable heating effects.

[0031] To modify the aerosol properties, frequency tuning is i) varying the frequency on either side of a resonant mode, such as on either side of one of one or more predetermined modal frequencies; and ii) changing from one resonant mode to a different resonant mode, such as by changing from one predetermined modal frequency to a different predetermined modal frequency.

[0032] To reduce the complexity of the actuator configuration, it may be desirable to limit the number of predetermined modal frequencies that the actuator is configured to excite. Advantageously, the actuator is configured to excite the membrane at a single modal frequency of the membrane, thereby simplifying the complexity of the actuator design. However, the actuator is preferably configured to excite the membrane at two or more modal frequencies. The ability to excite the membrane at two or more modal frequencies allows for variation in the aerosol droplet formation process. When the aerosol generating device is used to aerosolize a given liquid aerosol-forming substrate, the use of different modal frequencies results in correspondingly different aerosol droplet formation, which may differ in one or more of velocity, droplet size, and droplet formation density. When the actuator is configured to induce membrane vibration at two or more modal frequencies of the membrane, the actuator may be configured to automatically switch between different vibration modes. Alternatively or additionally, switching may be achieved by manual intervention of a user who interacts with the actuator to switch the actuator between different vibration modes. As a non-limiting example, the actuator may comprise or be coupled to a dial, button, toggle, or any equivalent feature that a user may engage with their finger to switch the actuator between different vibration modes.

[0033] The one or more predetermined frequencies may include multiple modal frequencies, such as a lowest first modal frequency, a second modal frequency higher than the first modal frequency, a third modal frequency higher than the second modal frequency, etc. Limiting the number of distinct modal frequencies that the actuator is configured to excite in the membrane provides a balance between i) the ability to generate different aerosol droplet formations during use of the aerosol generating device and ii) reducing the complexity and weight of the actuator and device.

[0034] Preferably, the one or more predetermined modal frequencies include a first predetermined modal frequency of the membrane and a second predetermined modal frequency of the membrane, and the plurality of nozzles are preferentially located within a first and second intersection region of the aerosol-generation zone, such that for the first intersection region, an antinode corresponding to the first predetermined modal frequency of the membrane is proximate to a node corresponding to the second predetermined modal frequency of the membrane, and for the second intersection region, an antinode corresponding to the second predetermined modal frequency of the membrane is proximate to a node corresponding to the first predetermined modal frequency of the membrane. In the context of this preferred embodiment, the term "preferentially located" refers to 50% or less of the plurality of nozzles being located within the first and second intersection regions. Furthermore, in the context of this preferred embodiment, the term "proximate" refers to the antinode corresponding to the first predetermined modal frequency of the membrane being closer to the node corresponding to the second predetermined modal frequency than the antinode corresponding to the second predetermined modal frequency (and vice versa). As described above, an advantage of preferentially locating the nozzles in the first and second intersection regions is that by exciting the membrane at a first predetermined modal frequency, a majority of the aerosol droplets may be generated by the nozzles in the first intersection region. Then, by switching to exciting the membrane at a second predetermined modal frequency, a majority of the aerosol droplets will instead be generated by the nozzles in the second intersection region. It may be desirable to increase the proportion of the nozzles located within the first and second intersection regions.

[0035] Advantageously, all of the nozzles in the aerosol-generation zone are located within the first and second intersection regions. In such an advantageous embodiment, exciting the membrane at a first predetermined modal frequency results in aerosol droplets being generated exclusively by the nozzles in the first intersection region, and switching to exciting the membrane at a second predetermined modal frequency results in aerosol droplets being generated exclusively by the nozzles in the second intersection region instead. The features described in this paragraph provide the possibility of generating different aerosol droplet formations from different portions of the membrane at different corresponding modal frequencies.

[0036] For the first intersection region, the node corresponding to the second predetermined modal frequency may be located within a first zone extending on either side of the antinode corresponding to the first predetermined modal frequency, where the magnitude of the membrane displacement is at least 60%, at least 70%, or at least 80% of the magnitude of the membrane displacement at the antinode for the first predetermined modal frequency. Additionally or alternatively, for the second intersection region, the node corresponding to the first predetermined modal frequency may be located within a second zone extending on either side of the antinode corresponding to the second predetermined modal frequency, where the magnitude of the membrane displacement is at least 60%, at least 70%, or at least 80% of the magnitude of the membrane displacement at the antinode for the second predetermined modal frequency. This relative spacing of the antinode for the first predetermined modal frequency from the node for the second predetermined modal frequency (and vice versa) provides the advantage of increased uniformity in aerosol droplet formation (and its characteristics) emanating from the holes in each intersection region.

[0037] The nozzles of the first intersection region are advantageously different in either or both shape and size from the nozzles of the second intersection region, which provides additional customization of the aerosol droplet formation (and its characteristics) produced by the first and second intersection regions.

[0038] The modal frequency of a membrane and the corresponding displacement response of the membrane may depend on the physical properties of the membrane and the loads and boundary constraints acting on the membrane. For example, the Young's modulus, Poisson's ratio, and mass density of the membrane may each individually affect the modal response of the membrane, such as changing one or both of the modal frequency and modal shape associated with a given vibration mode. To further explain, increasing the mass density of the membrane may result in a decrease in the modal frequency of a given vibration mode of the membrane, assuming all other parameters remain unchanged. Providing a membrane with homogeneous material properties throughout the membrane may allow for easier membrane fabrication. However, it is advantageous for membranes to be formed with non-homogeneous material properties. Such non-homogeneous material properties may allow for tuning of the modal shape, modal frequency, and thereby aerosol droplet formation.

[0039] The device is preferably configured to selectively apply and release constraints on the membrane to adjust the membrane's response to one or more predetermined modal frequencies. Changing the boundary constraints acting on the membrane when the membrane is excited at a predetermined frequency can also have the effect of changing the membrane's displacement response to that frequency. A change in the membrane's displacement response to a given frequency can result in a change in the position of the antinode. The device is preferably configured to selectively apply and release constraints along one or more portions of the membrane's periphery. As an example, the constraints may be clamping constraints. The aerosol generation device may also include an electromechanical switch, where the constraints are selectively applied to and released from the membrane by operation of the electromechanical switch. The use of an electromechanical switch provides a simple yet effective means of changing the constraints acting on the membrane to adjust the membrane's response when excited at a predetermined frequency. The electromechanical switch advantageously acts to selectively apply and release the constraints proximate the membrane's periphery.

[0040] By way of non-limiting example, the membrane may be secured in place around its periphery through the use of a segmented clamp having individual clamp segments extending around the periphery, the device being configured to selectively release and apply one or more of the clamp segments. The segmented clamp may conveniently be included as part of the actuator of the aerosol generating device.

[0041] The actuator is preferably configured to selectively excite different portions of the membrane. By way of non-limiting example, the actuator may include multiple actuator segments, each coupled to a different portion of the membrane. Each of the multiple actuator segments is a physically separate element distinct from one another, and by way of example only, each individual and separate element may be provided with its own set of electrodes to provide actuation thereto. To provide additional customization of the vibration modes excited within the membrane, each of the actuator segments may be actuated independently of the other segments. Independently actuable actuator segments may allow for the phase of motion of one or more segments to be varied relative to the other segments, thereby providing the ability to excite vibration modes within the membrane with complex displacement responses. Advantageously, the multiple actuator segments are coupled to the membrane proximate the periphery of the membrane.

[0042] The actuator may be configured to apply a modulated drive signal to the membrane to excite the membrane. By way of example, the spectrum of the modulated signal may include frequency components at the membrane's natural frequency and at harmonic frequencies of the membrane. In one embodiment, the actuator may be configured to excite a vibration mode having a 100 kHz to 200 kHz sinusoidal carrier with a 1 kHz to 20 kHz AM sinusoidal modulation.

[0043] The modal frequency of the membrane and the corresponding displacement response of the membrane may also vary depending on the physical dimensions of the membrane. The thickness of the membrane may vary gradually when traversing from the central region of the membrane to the outer periphery of the membrane. Preferably, the membrane gradually decreases in thickness from the central region of the membrane to the outer periphery of the membrane. For example, in the case of a circular or elliptical membrane clamped around its periphery, the gradual decrease in thickness of the membrane as one moves away from the center of the membrane may reduce the variation in displacement at the antinodes across the diameter of the membrane when the membrane is excited at one of the higher harmonic frequencies. Alternatively, the membrane may gradually increase in thickness from the central region of the membrane to the outer periphery of the membrane.

[0044] According to a further aspect of the present invention, An aerosol generating system comprising the aerosol generating device described above, The system is An aerosol delivery system is provided, further comprising a liquid supply operable to supply a liquid aerosol-forming substrate to the membrane.

[0045] Conveniently, the aerosol delivery system further comprises a replaceable cartridge, the cartridge containing a reservoir of liquid aerosol-forming substrate. The cartridge may additionally contain a liquid supply.

[0046] The liquid supply may include a tube for transporting the liquid aerosol-forming substrate from the reservoir of the liquid aerosol-forming substrate to the membrane. The liquid supply may further include a supply nozzle through which the liquid aerosol-forming substrate can be discharged adjacent to the surface of the membrane. The liquid supply conveniently takes the form of a tube extending between the reservoir end and the membrane end, the tube terminating in a supply nozzle at the membrane end. The liquid supply may include one or more wicking materials. The use of a wicking material in the liquid supply allows for more gradual and controlled passage of the liquid aerosol-forming substrate through the membrane.

[0047] The liquid supply may be static relative to the membrane, thereby simplifying the design of the aerosol-generation device. However, the liquid supply is preferably configured to traverse along the aerosol-generation zone of the membrane during excitation of the membrane by the actuator to supply liquid aerosol-forming substrate to nozzles proximate antinodes corresponding to membranes excited at one or more predetermined modal frequencies. The use of such a traversable liquid supply can help reduce the weight of the device by enabling the use of a liquid supply having a smaller surface area footprint than a static liquid supply capable of covering the same surface area of the aerosol-generation zone.

[0048] The plurality of nozzles may advantageously include a first plurality of nozzles and a second plurality of nozzles located in respective first and second regions of the aerosol-generation zone. The liquid supply may include a first liquid supply and a second liquid supply, the first liquid supply operable to supply a first liquid aerosol-forming substrate to the first region, and the second liquid supply operable to supply a second liquid to the second region, the first liquid aerosol-forming substrate and the second liquid aerosol-forming substrate being different from each other. In use, the actuator is operable to excite the membrane at one or more predetermined modal frequencies to aerosolize the first and second liquid aerosol-forming substrates passing through the respective first and second plurality of nozzles. This embodiment has the advantage of enabling different liquid aerosol-forming substrates to be aerosolized from different regions of the membrane. The first and second liquid aerosol-forming substrates may differ from each other in any of their physical and chemical properties, for example, in one or more of their mass density, viscosity, and surface tension. The first and second regions of the aerosol-generation zone may be selected to have different vibrational characteristics when excited at a given modal frequency. The selection of the first and second regions may be influenced by the physical properties of the respective first and second liquid aerosol-forming substrates, for example, so that aerosolized droplets of the first liquid aerosol-forming substrate from the first region are similar or identical to aerosolized droplets of the second liquid aerosol-forming substrate from the second region in one or more of droplet velocity, droplet size, and Weber number.

[0049] The membrane may be elliptical or circular in plan view, with the first and second regions concentrically disposed relative to one another. Furthermore, the first and second liquid supplies may be concentrically disposed to supply the first and second liquid aerosol-forming substrates to the corresponding first and second regions, respectively. Providing concentrically disposed first and second liquid supplies and a circular or elliptical membrane in plan view takes advantage of the fact that vibration modes for such circular or elliptical membranes will include displacement patterns in which antinodes and nodes are disposed in concentric zones.

[0050] Alternatively, the first and second liquid supplies may comprise respective first and second linear channels arranged to supply the first and second liquid aerosol-forming substrates to respective first and second regions of the aerosol-generation zone. Furthermore, the first and second linear channels are conveniently formed as part of a unitary body, the body being positioned above the aerosol-generation zone to ensure that the first and second linear channels are adjacent to the corresponding first and second regions. The use of liquid supplies in the form of linear channels as described in this paragraph is particularly suitable for use with membranes that are rectangular or square in plan view, since the antinodes for different vibration modes of the membrane are also likely to follow linear paths.

[0051] Advantageously, both the first and second plurality of nozzles are preferentially located proximate antinode positions corresponding to a common predetermined modal frequency of the membrane, and the actuator is configured to excite the membrane to induce a vibration response of the membrane at the common predetermined modal frequency. The first and second liquid supplies may be configured to simultaneously supply first and second liquid aerosol-forming substrates to the first and second regions, respectively. The first and second plurality of nozzles may be configured with one or both of a size and a shape such that, when the membrane is excited at the common predetermined modal frequency, the Weber number of the first liquid aerosol-forming substrate passing through the first plurality of nozzles is within 10% of the value of the Weber number of the second liquid aerosol-forming substrate passing through the second plurality of nozzles.

[0052] In a further non-limiting embodiment, the first plurality of nozzles may be preferentially located adjacent to antinodes corresponding to membranes excited at a first predetermined modal frequency of the membrane, and the second plurality of nozzles may be preferentially located adjacent to antinodes corresponding to membranes excited at a second predetermined modal frequency of the membrane, the first liquid aerosol-forming substrate supply configured to supply the first liquid aerosol-forming substrate to the first region in synchronization with an actuator that excites the membrane at the first predetermined modal frequency, and the second liquid aerosol-forming substrate supply configured to supply the second liquid aerosol-forming substrate to the second region in synchronization with an actuator that excites the membrane at the second predetermined modal frequency. The aerosol delivery system is preferably in the form of a consumer device for delivering non-thermally generated aerosol. Advantageously, the aerosol delivery system is a smoking system for non-thermally generating inhalable aerosol. For example, during use of the aerosol delivery system, aerosol droplets generated by vibration of the membrane of the aerosol generating device form inhalable aerosol. The smoking system may be in the form of an elongated smoking article. The smoking system may include an elongated housing containing the aerosol generator and the liquid supply, the elongated housing having a distal end and a mouth end, with a mouthpiece provided at the mouth end. The elongated housing is conveniently cylindrical. The aerosol generator and the liquid supply are preferably disposed within the elongated housing such that aerosolized droplets expelled from the membrane subsequently flow through the mouthpiece and exit the housing. The elongated housing is preferably sized and shaped to be held between the thumb and fingers of a user of the smoking system. The smoking system may further include a power source and electronic control circuitry, the electronic control circuitry configured to control operation of the actuator, and the power source configured to provide power to the electronic control circuitry and the actuator of the aerosol generator. The electronic control circuitry and the power source are preferably contained within the elongated housing. The power source is preferably rechargeable, for example, the power source may include a lithium-ion battery.If the power source is rechargeable, the electronic control circuitry may also be configured to control charging of the power source. Because heat is not used to generate the aerosol, the risk of generating harmful compounds is reduced, as these are typically associated with chemical reactions that occur at high temperatures. Furthermore, the membrane of the aerosol generator responds to changes induced by the actuator, allowing for the aerosol characteristics to be modified over the duration of a single puff (typically 2-3 seconds in duration). This can be achieved by modifying the actuator's electrical drive signal within the duration of the puff, thereby allowing the aerosol generation to rapidly adapt to the user's needs. The aerosol delivery system can be described as a "puff-on-demand" system.

[0053] In various embodiments of the aerosol delivery system, different liquids may be individually supplied to the membrane. For example, a first liquid containing nicotine or other stimulant and a second liquid containing a flavor may each be individually supplied to the membrane. These different liquids may be supplied to different regions of the membrane, each region responding to a different vibration mode activated by the actuator. Such an aerosol delivery system may result in droplets ejected from different regions of the membrane having different chemical compositions. For example, if nicotine is present in the first liquid and the flavor is present in the second liquid, delivery of these two different liquids to different regions of the membrane may be such that nicotine is present in smaller aerosol droplets and the flavor is present in larger aerosol droplets to provide improved user satisfaction. Alternatively, the presence of nicotine in relatively large aerosol droplets may have the disadvantage of risking irritation to the user's throat. The supply of liquids may be synchronized with the actuator's drive signal. As an example, a micropump or valve may operate to deliver one liquid when the actuator is activated in one mode, and alternatively, a different liquid may be delivered by operating a different micropump or switching the state of a valve when the actuator is activated in another mode. A user may have the option to tune or select their own personalized puff profile, which may take the form of a given electrical drive signal signature to the actuator to provide preferred aerosol characteristics.

[0054] The smoking system is preferably for non-thermal generation of aerosol, but optionally the smoking system comprises a heater element configured to apply heat to the liquid aerosol-forming substrate either before or after aerosolization of the substrate, i.e., upstream or downstream of the membrane. The smoking system preferably comprises a replaceable cartridge positioned within the elongated housing and containing a reservoir of liquid aerosol-forming substrate. Optionally, the cartridge additionally comprises a liquid supply.

[0055] The present invention is defined in the claims. However, the following non-limiting examples are provided in a non-exhaustive manner. Any one or more features of these examples may be combined with any one or more features of any other example, embodiment, or aspect described herein.

[0056] Example 1: 1. An aerosol generating device comprising: a membrane having an aerosol-generation zone, the aerosol-generation zone including a plurality of nozzles, the plurality of nozzles being the only nozzles in the aerosol-generation zone; and an actuator coupled to the membrane, the actuator configured, in use, to excite the membrane to induce vibration of the membrane at one or more predetermined modal frequencies of the membrane in order to aerosolize a liquid aerosol-forming substrate passing through the plurality of nozzles, the plurality of nozzles being preferentially located adjacent to antinodes of the membrane that are excited at the one or more predetermined modal frequencies of the membrane. Example 2: 2. The aerosol generation device of example 1, wherein the plurality of nozzles are non-homogeneously distributed across the aerosol-generation zone. Example 3: An aerosol generating device as described in either Example 1 or 2, wherein at least 60%, or at least 70%, or at least 80%, or at least 90% of the plurality of nozzles are located within a region extending on either side of the antinode, wherein the magnitude of the membrane displacement is at least 60%, or at least 70%, or at least 80% of the magnitude of the membrane displacement at the antinode for a corresponding one or more predetermined modal frequencies. Example 4: 4. The aerosol generation device of example 3, wherein all of the plurality of nozzles are located within a region extending on either side of the antinode. Example 5: An aerosol generating device as described in any of Examples 1 to 3, wherein less than 5% of the plurality of nozzles are located within a region extending on either side of a node where the magnitude of the membrane displacement is 20% or less of the magnitude of the membrane displacement at an antinode for a corresponding one or more predetermined modal frequencies. Example 6: An aerosol generating device as described in any of Examples 1 to 5, wherein the aerosol generation zone is a region extending on either side of a node and does not have a nozzle within the region where the magnitude of the membrane displacement is 10% or less of the magnitude of the membrane displacement at an antinode for one or more corresponding predetermined modal frequencies. Example 7: 7. The aerosol generating device according to any one of Examples 1 to 6, wherein the one or more predetermined frequencies include a plurality of modal frequencies. Example 8: 8. An aerosol generating device according to any one of claims 1 to 7, wherein the one or more predetermined modal frequencies include a first predetermined modal frequency of the membrane and a second predetermined modal frequency of the membrane, the plurality of nozzles being preferentially located within first and second intersection regions of the aerosol generation zone, and wherein, for the first intersection region, an antinode corresponding to the first predetermined modal frequency of the membrane is adjacent to a node corresponding to the second predetermined modal frequency of the membrane, and for the second intersection region, an antinode corresponding to the second predetermined modal frequency of the membrane is adjacent to a node corresponding to the first predetermined modal frequency of the membrane. Example 9: 9. The aerosol generating device of example 8, wherein all of the plurality of nozzles are located in the first and second intersection regions. Example 10: An aerosol generating device as described in either Example 8 or 9, wherein, for the first intersection region, the node corresponding to the second predetermined modal frequency is located within a first zone extending on either side of the antinode corresponding to the first predetermined modal frequency, wherein the magnitude of the membrane displacement is at least 60%, or at least 70%, or at least 80% of the magnitude of the membrane displacement at the antinode for the first predetermined modal frequency; and for the second intersection region, the node corresponding to the first predetermined modal frequency is located within a second zone extending on either side of the antinode corresponding to the second predetermined modal frequency, wherein the magnitude of the membrane displacement is at least 60%, or at least 70%, or at least 80% of the magnitude of the membrane displacement at the antinode for the second predetermined modal frequency. Example 11: An aerosol generating device described in any of Examples 1 to 10, wherein the device is configured to selectively apply and release constraints on the membrane to adjust the response of the membrane to one or more predetermined modal frequencies. Example 12: 12. The aerosol generating device of Example 11, wherein the device is configured to selectively apply and release a constraint along one or more portions of the periphery of the membrane. Example 13: 13. An aerosol generating device according to any of Examples 11 or 12, wherein the constraint is a clamp constraint. Example 14: 14. The aerosol generating device of any one of Examples 11 to 13, wherein the device further comprises an electromechanical switch, and wherein the constraint is selectively applied to and released from the membrane by operation of the electromechanical switch. Example 15: 15. The aerosol generating device of example 14, wherein the electromechanical switch is configured to selectively apply and release a constraint adjacent to the outer periphery of the membrane. Example 16: 16. The aerosol generation device according to any one of Examples 1 to 15, wherein the actuator is configured to selectively excite different parts of the membrane. Example 17: 17. The aerosol generating device of Example 16, wherein the actuator comprises multiple actuator segments, each connected to a different portion of the membrane. Example 18: 18. The aerosol generating device of Example 17, wherein the plurality of actuator segments are coupled to the membrane proximate the periphery of the membrane. Example 19: 19. The aerosol generation device according to any one of Examples 1 to 18, wherein the actuator is configured to apply a modulated drive signal to the membrane to excite the membrane. Example 20: 20. The aerosol generating device according to any one of Examples 1 to 19, wherein the membrane has a thickness that gradually decreases from a central region of the membrane towards the outer periphery of the membrane. Example 21: 21. An aerosol delivery system comprising the aerosol-generating device of any of Examples 1-20, and further comprising a liquid supply operable to supply a liquid aerosol-forming substrate to the membrane. Example 22: 22. The aerosol delivery system of Example 21, wherein the liquid supply is configured to traverse along the aerosol-generation zone of the membrane during excitation of the membrane by the actuator to supply a liquid aerosol-forming substrate to a nozzle proximate an antinode corresponding to the membrane being excited at one or more predetermined modal frequencies. Example 23: 23. The aerosol delivery system of either Example 21 or Example 22, wherein the plurality of nozzles comprises a first plurality of nozzles and a second plurality of nozzles located within respective first and second regions of the aerosol-generation zone, the liquid supply comprises a first liquid supply and a second liquid supply, the first liquid supply operable to supply a first liquid aerosol-forming substrate to the first region and the second liquid supply operable to supply a second liquid aerosol-forming substrate to the second region, the first liquid aerosol-forming substrate and the second liquid aerosol-forming substrate being different from each other, and the actuator is operable, in use, to excite the membrane at one or more predetermined modal frequencies to aerosolize the first and second liquid aerosol-forming substrates passing through the respective first and second plurality of nozzles. Example 24: 24. The aerosol delivery system of Example 23, wherein the membrane is elliptical or circular in plan view, the first and second regions are arranged concentrically relative to each other, and the first liquid supply and the second liquid supply are arranged concentrically relative to each other so as to supply respective first and second liquid aerosol-forming substrates to the corresponding first and second regions. Example 25: An aerosol delivery system as described in either Example 23 or 24, wherein both the first plurality of nozzles and the second plurality of nozzles are preferentially located in close proximity to antinode positions corresponding to a common predetermined modal frequency of the membrane, and the actuator is configured to excite the membrane to induce vibration of the membrane at the common predetermined modal frequency. Example 26: 26. The aerosol delivery system of Example 25, wherein the first liquid supply and the second liquid supply are configured to simultaneously supply the respective first and second liquid aerosol-forming substrates to the respective first and second regions. Example 27: 27. An aerosol delivery system according to any one of Examples 25 or 26, wherein the first and second plurality of holes are configured with one or both of a size and a shape such that, when the membrane is excited at a common predetermined modal frequency, the Weber number of the first liquid aerosol-forming substrate passing through the first plurality of holes is within 10% of the Weber number of the second liquid aerosol-forming substrate passing through the second plurality of holes. Example 28: 25. The aerosol delivery system of any one of Examples 23 or 24, wherein the first plurality of holes are preferentially located adjacent to antinodes corresponding to membranes excited at a first predetermined modal frequency of the membrane, and the second plurality of holes are preferentially located adjacent to antinodes corresponding to membranes excited at a second predetermined modal frequency of the membrane, the first liquid supply is configured to supply the first liquid aerosol-forming substrate in synchronization with the actuator that excites the membrane at the first predetermined modal frequency, and the second liquid supply is configured to supply the second liquid aerosol-forming substrate in synchronization with the actuator that excites the membrane at the second predetermined modal frequency. Example 29: The aerosol delivery system of any of Examples 21 to 28, wherein the aerosol delivery system is a smoking system for generating an inhalable aerosol. Example 30: 29. The aerosol delivery system of claim 29, wherein the aerosol delivery system comprises an elongated housing that houses an aerosol generator and a liquid supply, the elongated housing having a distal end and an oral end, and a mouthpiece provided at the oral end. Example 31: The aerosol delivery system of Example 30, further comprising a power source and an electronic control circuit, wherein the electronic control circuit is configured to control the operation of the actuator, and the power source is configured to provide power to the electronic control circuit and the actuator, wherein the electronic control circuit and the power source are contained within the elongated housing. [Brief explanation of the drawings]

[0057] The embodiments will now be further described with reference to the figures.

[0058] [Figure 1] FIG. 1 shows a schematic diagram of an aerosol delivery system in the form of a smoking article for generating an inhalable aerosol. [Figure 2] FIG. 2 shows a perspective view of an aerosol generating device according to one embodiment. [Figure 3] FIG. 3 shows a plan view of the membrane of the aerosol generating device of FIG. [Figure 4] Figure 4 shows a graph of displacement versus radial distance for a circular membrane clamped around the periphery of the membrane in response to activation of vibration mode (0, 3) within the membrane. The graph also includes an indication of the position of the nozzle within the membrane. [Figure 5a] Figure 5 a is a plan view of a circular membrane clamped around its periphery in response to vibration mode (0, 2) being activated in the membrane, with overlaid contour lines showing the displacement of different parts of the membrane. [Figure 5b] Figure 5b is a top view of a circular membrane clamped around its periphery in response to vibration mode (1, 2) being activated in the membrane, with overlaid contour lines showing the displacement of different parts of the membrane. [Figure 5c] Figure 5c is a top view of a circular membrane clamped around its periphery in response to vibration mode (3, 1) being activated in the membrane, with overlaid contour lines showing the displacement of different parts of the membrane. [Figure 6a] Figure 6a shows a plan view of a square membrane simply supported around its periphery in response to vibration mode (1, 2) being activated in the membrane, with overlaid contour lines showing the displacement of different parts of the membrane. [Figure 6b] Figure 6b is a plan view of a square membrane simply supported around its periphery in response to vibration mode (3, 3) being activated in the membrane, with overlaid contour lines showing the displacement of different parts of the membrane. [Figure 7]Figure 7 shows a graph of displacement versus radial distance for a circular membrane clamped around its periphery in response to two distinct vibration modes (0,3) and (4,1) being activated within the membrane. The graph also includes an indication of the position of the nozzle within the membrane. [Figure 8a] Figures 8a and 8b show side elevational views of one embodiment of an aerosol generation device configured to selectively apply and release a constraint to a membrane, with Figure 8a showing the constraint being applied to the membrane and Figure 8b showing the constraint being released from the membrane. [Figure 8b] Same as above. [Figure 9] FIG. 9 shows a side elevation view of one embodiment of an aerosol generating device in which the thickness of the membrane gradually decreases when traversing from the central region of the membrane towards the periphery of the membrane. [Figure 10] FIG. 10 shows a side elevation view of one embodiment of an aerosol generating device in which the thickness of the membrane increases gradually as one traverses from the central region of the membrane towards the periphery of the membrane. [Figure 11] FIG. 11 shows a perspective view of a first embodiment of a liquid supply assembly. [Figure 12] FIG. 12 shows a perspective view of a second embodiment of a liquid supply assembly. [Figure 13] FIG. 13 shows a perspective view of a third embodiment of a liquid supply assembly. DETAILED DESCRIPTION OF THE INVENTION

[0059] FIG. 1 is a schematic diagram of an aerosol delivery system 100. For the embodiment shown in FIG. 1, the aerosol delivery system 100 is a smoking system for generating an inhalable aerosol 101. The system 100 has an elongated housing 102. The elongated housing 102 houses a power source 103, an electronic control circuitry 104, a cartridge 105, a liquid supply assembly 106, and an aerosol generation device 107. The power source 103 is coupled to and provides power to the electronic control circuitry 104 and the aerosol generation device 107. The electronic control circuitry 104 is configured to control the operation of the aerosol generation device 107. In an alternative embodiment in which the power source 103 is a rechargeable battery, the electronic control circuitry 104 is also configured to control the charging of the rechargeable battery. The elongated housing 102 has a distal end 108 and an oral end 109. A mouthpiece 110 is provided at the oral end 109 of the housing 102. The cartridge 105 contains a reservoir of liquid-forming substrate (not shown). Although not shown in Figure 1, the cartridge 105 is replaceable, and the elongated housing 102 is adapted to allow for removal and replacement of the cartridge. An exemplary embodiment of an aerosol generating device 107 suitable for use in the aerosol delivery system 100 illustrated in Figure 1 is described in the following paragraphs.

[0060] FIG. 2 illustrates one embodiment of an aerosol generating device 107. The device 107 includes a membrane 20 and an actuator 40 coupled to the membrane. For the embodiment illustrated in FIG. 2, the membrane 20 has a circular shape when viewed in plan. The actuator 40 is segmented around its periphery and includes four individual segments 41, 42, 43, and 44. Each segment 41, 42, 43, and 44 has an upper half and a lower half that act on the upper and lower surfaces of the corresponding segment of the membrane 20, respectively. Each of the actuator segments 41, 42, 43, and 44 thereby acts to constrain the corresponding segment of the membrane 20. Each of the actuator segments 41, 42, 43, and 44 is designed to be driven independently of the other segments. During operation of the actuator 40, the segments 41, 42, 43, and 44 may be driven in phase with each other or in any desired phase relationship. In an alternative embodiment not illustrated, the actuator 40 may be continuous and not segmented.

[0061] FIG. 3 shows a plan view of the membrane 20 of the aerosol-generation device 107, i.e., as viewed in the direction of arrow A in FIG. 2. The membrane 20 is circular when viewed in plan. For convenience, the actuator 40 has been omitted from FIG. 3. The membrane 20 has an aerosol-generation zone 21 (the periphery of which is represented by a dashed line in FIG. 3). The aerosol-generation zone 21 is provided with a plurality of nozzles 22. The nozzles 22 are in the form of holes extending through the thickness of the membrane 20. For the embodiment shown in FIG. 3, the plurality of nozzles 22 are located exclusively within two annular regions 23, 24. An annular gap 25 exists between the periphery 26 of the membrane 20 and the periphery of the aerosol-generation zone 21. The annular gap 25 provides space to allow segments of the actuator 40 (see, e.g., FIG. 2) to be coupled to the membrane 20.

[0062] The actuator 40 is configured to excite the membrane 20 to induce vibration of the membrane at one or more predetermined modal frequencies of the membrane. In various embodiments, the actuator 40 may be configured to excite the membrane 20 to induce vibration of the membrane at multiple distinct modal frequencies of the membrane. However, for ease of understanding, the displacement of the membrane 20 in response to the actuator 40 exciting a single vibration mode of the membrane will first be described with reference to FIG. 4. Each vibration mode of the membrane 20 has a corresponding modal frequency.

[0063] 4 shows a graph of the displacement of the circular membrane 20 versus the radial distance r from the center 27 of the membrane 20 (see FIG. 3) for vibration mode (0, 3) of the membrane, where the entire periphery 26 of the membrane is clamped by the actuator 40. The radial distance r in FIG. 4 is expressed as a percentage of the radius R of the aerosol-generation zone 21. For mode (0, 3), the number 0 indicates that no circumferential vibration mode is activated in the membrane 20, and the number 3 indicates that the third harmonic vibration mode is activated in the radial direction (relative to the center 27 of the membrane).

[0064] As shown in FIG. 4, when mode (0,3) is activated in the membrane 20, antinodes exist in three regions of the membrane. The displacement shown in FIG. 4 is annular for mode (0,3) about the center 27 of the membrane 20, with three defined antinode regions 201, 202, and 203 corresponding to the locations of the antinodes. The magnitude of the antinode displacement is greatest at the center 27 of the membrane 20 (i.e., in antinode region 201) and progressively decreases with increasing radial distance from the center of the membrane toward the outer periphery 26 of the membrane (i.e., see antinode regions 202 and 203). The decrease in the magnitude of the antinode displacement with increasing radial distance r is due to the outer periphery 26 of the membrane 20 being clamped by the actuator 40 (see FIG. 2). FIG. 4 includes gray bands indicating the widths of the annular regions 23 and 24 in which the multiple nozzles 22 are provided. The annular regions 23, 24 are localized around (i.e., adjacent to) the corresponding antinodes (see antinode regions 202, 203 in FIG. 4). The wavelength λ of the waveform associated with this vibrational mode (0, 3) is shown in FIG.

[0065] When a liquid aerosol-forming substrate is supplied to the membrane 20 while the actuator 40 activates mode (0, 3) of the membrane, aerosol droplets can be generated by nozzles 22 located within the annular regions 23, 24. These annular regions 23, 24, and thereby the plurality of nozzles 22, can be localized around the antinodes (i.e., antinode regions 202, 203) for vibration mode (0, 3), maximizing the energy and velocity imparted to the aerosol droplets by the membrane 20. Such an arrangement of nozzles 22 localized around the antinodes 202, 203 can also increase the Weber number and the distance over which the membrane 20 can eject aerosol droplets. Alternatively or additionally, if the actuator 40 is configured to excite different vibration modes in the membrane, the plurality of nozzles 22 can be preferentially located in proximity to the antinodes corresponding to the different vibration modes.

[0066] Figures 5a-c and 6a-b show the displacement response of different membrane geometries to different vibration modes.

[0067] Figures 5a-5c show plan views of a circular membrane 20 clamped around the membrane's perimeter 26 for different vibration modes. Each vibration mode may have its own corresponding modal frequency. For each of Figures 5a-5c, a graduated contour is overlaid on the membrane 20 to show the displacement response of different portions of the membrane to the particular vibration mode.

[0068] 5a shows the displacement of a clamped circular membrane 20 for vibration mode (0,2). For mode (0,2), the number 0 indicates that no circumferential vibration mode is activated in the membrane 20, and the number 2 indicates that a second, higher harmonic vibration mode is activated in the radial direction (relative to the membrane's center 27). The displacement response of the membrane 20 for this vibration mode has two defined antinode regions along a line extending radially outward from the membrane's center 27.

[0069] 5b shows the displacement of the clamped circular membrane 20 for vibration mode (1,2). For mode (1,2), the numeral 1 indicates that a fundamental circumferential vibration mode is activated in the membrane 20, and the numeral 2 indicates that a second, higher harmonic vibration mode is activated in the radial direction (relative to the membrane's center 27). The displacement response of the membrane 20 for this vibration mode has a single antinode region in the circumferential direction for each half of the membrane, and two antinode regions along a line extending radially outward from the membrane's center 27.

[0070] 5c shows the displacement response of the clamped circular membrane 20 for vibration mode (3,1). For mode (3,1), the numeral 3 indicates that a third harmonic vibration mode is activated in the membrane 20, and the numeral 1 indicates that the fundamental vibration mode is activated in the radial direction (relative to the membrane center 27). The displacement response of the membrane 11 for this vibration mode has three antinode regions circumferentially for each half of the membrane, and one antinode region along a line extending radially outward from the membrane center 27.

[0071] Figures 6a and 6b show plan views of a square membrane 20' simply supported around the membrane's perimeter 26' for different vibration modes. Each vibration mode may have its own corresponding modal frequency. For each of Figures 6a and 6b, a graduated contour is overlaid on the membrane 20 to show the displacement response of different portions of the membrane to a particular vibration mode.

[0072] 6a shows the displacement of a simply supported square membrane 20' for vibration mode (1,2). For mode (1,2), the numeral 1 indicates that a fundamental vibration mode is activated in membrane 20' in the y-direction, and the numeral 2 indicates that a second, higher harmonic vibration mode is activated in the x-direction. The displacement response of membrane 20' for this vibration mode has a single antinode region in the y-direction and two antinode regions in the x-direction.

[0073] Figure 6b shows the displacement of a simply supported rectangular membrane 20' for vibration mode (3,3). For mode (3,3), the number 3 indicates that a second harmonic vibration mode is activated in membrane 20' in both the x and y directions. The displacement response of membrane 20' for this vibration mode has three antinode regions in each of the x and y directions.

[0074] When the actuator 40 is configured to excite either of the vibration modes shown for the circular clamped membrane 20 of FIGS. 5a-5c or the square, simply supported membrane 20′ of FIGS. 6a and 6b, a displacement response contour plot provides an indication of where peak displacement magnitudes (i.e., peaks or troughs) are likely to occur within the membrane. Such plots can assist in preferentially positioning multiple nozzles 22 within the membrane 20 in proximity to those regions of the membrane that experience the highest displacement magnitudes (i.e., antinodes). As previously discussed, preferentially positioning nozzles near antinodes in this manner assists in maximizing the energy and velocity imparted to aerosol droplets during use of the aerosol generation device 107.

[0075] In an alternative embodiment of the aerosol generating device, the actuator 40 is configured to excite the membrane 20 of the aerosol generating device 107 at two distinct predetermined modal frequencies. Each distinct modal frequency is associated with a corresponding vibration mode. By way of example, FIG. 7 shows the vibration response of a clamped circular membrane 20 as the radial distance r from the membrane's center 27 increases for two distinct vibration modes of the membrane. The two vibration modes are modes (0, 3) and (4, 1), represented by solid and dashed lines in FIG. 7 . For mode (0, 3), the number 0 indicates that no circumferential vibration mode is activated in the membrane 20, and the number 3 indicates that a third, higher harmonic vibration mode is activated in the radial direction (relative to the membrane's center 27). For mode (4, 1), the number 4 indicates that a fourth circumferential vibration mode is activated in the membrane 20, and the number 1 indicates that a fundamental vibration mode is activated in the radial direction (relative to the membrane's center 27). In this alternative embodiment, the plurality of nozzles 22 are located in two distinct regions 231, 241 of the aerosol-generation zone 21. The first of these regions 231 defines a circle located at the center of the membrane 20, and the second of these regions 241 is in the form of an annular band. The first region 231 is a first intersection region where an antinode corresponding to vibration mode (0, 3) is located adjacent to a node corresponding to vibration mode (4, 1). The second region 241 is a second intersection region where an antinode corresponding to vibration mode (4, 1) is located adjacent to a node corresponding to vibration mode (0, 3). When the actuator 40 excites mode (0, 3) and a liquid aerosol-forming substrate is supplied to the membrane 20, aerosol droplets are primarily emitted from the nozzles 22 in the first intersection region 231. However, when the actuator 40 switches to excitation mode (4, 1), aerosol droplets are instead primarily emitted from the nozzles 22 in the second intersection region 241.

[0076] 8a and 8b show schematic diagrams of an embodiment in which an aerosol generation device 107 is configured to selectively apply and release a constraint on a membrane 20. For convenience, the location of multiple nozzles 22 within the membrane 20 of this embodiment is not shown in FIG. 8a or 8b. As shown in FIG. 8a, two opposite edges of the membrane 20 are both clamped. A clamp 41 is provided on the left edge of the membrane 20. The clamp 41 is fixed, meaning that the clamp 41 continues to clamp the left edge of the membrane 20 during operation of the actuator 40 of the aerosol generation device 107. A releasable clamp 42 is provided on the right edge of the membrane 20. The releasable clamp 42 is coupled to an electromechanical switch 43. As shown in Figures 8a and 8b (see arrow B), electromechanical switch 43 is operable to move upper half 42a of releasable clamp 42 relative to lower half 42b of the clamp to selectively apply and release upper half 42a from membrane 20, thereby applying and releasing the clamp on the membrane's right edge. When the membrane is excited by actuator 40 at a given modal frequency, releasing and reapplying the clamp on the edge of membrane 20 has the effect of changing the membrane's displacement response to that modal frequency. The change in the membrane's 20 displacement response in response to changes in the constraint applied to the membrane can be exploited by preferentially positioning multiple nozzles 22 adjacent to antinodes corresponding to the membrane's 20 displacement for each of the membrane's different constraint states.

[0077] Figures 9 and 10 show two different embodiments of an aerosol generating device 107 in which there is a gradual change in the thickness of the membrane 20 when traversing from the central region of the membrane towards the periphery of the membrane. The nozzle 22 is represented schematically in both Figures 9 and 10, and the actuator 40 is coupled to the upper and lower surfaces of the membrane in the region of the periphery of the membrane. Figure 9 shows an example in which the thickness of the membrane 20 gradually decreases when moving from the center of the membrane towards the periphery of the membrane. Figure 10 shows the reverse situation in which the thickness of the membrane 20 gradually increases when moving from the center of the membrane towards the periphery of the membrane. The thickness of the membrane 20 is indicated by the radial position r relative to the center of the membrane, and the thickness is represented by the symbol t r It is shown as follows.

[0078] The liquid aerosol-forming substrate may be supplied to the membrane 20 of the aerosol-generating device 107 in a variety of ways. Figures 11, 12 and 13 show examples of liquid supply assemblies 106, 106', 106'' for supplying one or more liquid aerosol-forming substrates to the membrane 20 of the aerosol-generating device 107. For convenience, the actuator 40 is not shown in any of Figures 11-13.

[0079] FIG. 11 shows a liquid supply assembly 106 operable to supply a liquid aerosol-forming substrate to the membrane 20. The liquid supply assembly 106 has a movable stage 1061. A flexible tube 1062 extends between a reservoir of liquid aerosol-forming substrate (not shown) and a supply nozzle 1063. Arrow L indicates the passage of the liquid aerosol-forming substrate from the reservoir through the flexible tube 1062. Although not shown in FIG. 11 , an electric motor is coupled to the movable stage 1061. Operation of the motor causes the movable stage 1061 to traverse along the aerosol-generation zone 21 of the membrane 20 along a path P. During excitation of the membrane 20 by the actuator 40, the movable stage 1061 traverses across the membrane to supply the liquid aerosol-forming substrate through a supply nozzle 1063 adjacent to the antinode and nozzle 22 corresponding to a predetermined modal frequency. The liquid supply assembly 106 shown in FIG. 11 can be applied to any shape of membrane 20.

[0080] 12 shows an alternative liquid supply assembly 106′. The liquid supply assembly 106′ is shown in conjunction with a circular membrane 20. The liquid supply assembly 106′ has three concentrically arranged tubes 1064, 1065, and 1066. The radially innermost tube 1064 defines a first concentric liquid aerosol-forming substrate supply channel for supplying a first liquid aerosol-forming substrate to the membrane 20. The annular gap between the radially innermost tube 1064 and the intermediate tube 1065 defines a second concentric liquid aerosol-forming substrate supply channel for supplying a second liquid aerosol-forming substrate to the membrane 20. The annular gap between the intermediate tube 1065 and the radially outermost tube 1066 defines a third concentric liquid aerosol-forming substrate supply channel for supplying a third liquid aerosol-forming substrate to the membrane 20. Each of the concentrically arranged feed channels is supplied or filled with a respective liquid aerosol-forming substrate from a reservoir (not shown). The concentrically arranged first, second, and third liquid aerosol-forming substrate feed channels supply their respective liquid aerosol-forming substrate to corresponding annular regions of the membrane 20. In an alternative embodiment (not shown), a wicking material may be located in each of the concentrically arranged first, second, and third liquid aerosol-forming substrate feed channels, with the wicking material of each concentric feed channel being wetted with that channel's respective liquid aerosol-forming substrate. In a further alternative embodiment, the liquid feed assembly 106' may be used in conjunction with an elliptical membrane.

[0081] FIG. 13 shows a further alternative liquid supply assembly 106″. The liquid supply assembly 106″ is shown in conjunction with a square membrane 20′. The liquid supply assembly 106″ has three linear channels 1067, 1068, 1069 defined in a substrate 1070. Each of the linear channels 1067, 1068, 1069 is supplied with a respective liquid aerosol-forming substrate from a reservoir (not shown) by a respective liquid aerosol-forming substrate inlet 1071, 1072, 1073. The linear channels 1067, 1068, 1069 supply the respective liquid aerosol-forming substrate to a corresponding linear region of the membrane 20′. In an alternative embodiment (not shown), wicking material is located in each of the linear channels 1067, 1068, 1069, and the wicking material for each channel is wetted with that channel's respective liquid aerosol-forming substrate.

[0082] Although not shown in Figures 11-13, the liquid supply assemblies 106, 106', 106" include one or more micropumps for actively supplying the liquid aerosol-forming substrate to the membranes 20, 20'. The micropumps of the liquid supply assemblies 106, 106', 106" are coupled to and powered by a power source (e.g., see power source 103 shown in Figure 1, dashed line connected to the liquid supply assembly 106 in Figure 1).

[0083] For purposes of this specification and the appended claims, unless otherwise indicated, all numbers expressing amounts, quantities, percentages, and the like should be understood in all instances to be modified by the term "about." Also, all ranges include the disclosed maximum and minimum points, and any intermediate ranges therebetween, which may or may not be specifically recited herein. Accordingly, in this context, the number "A" is understood as "A" ± 10%. Within this context, the number "A" may be considered to include a numerical value that is within the typical standard error for the measurement of the property that the number "A" modifies. In some cases, as used in the appended claims, the number "A" may deviate by the percentages recited above, provided that the amount by which "A" deviates does not materially affect the basic and novel characteristics of the claimed invention. Also, all ranges include the disclosed maximum and minimum points, and any intermediate ranges therebetween, which may or may not be specifically recited herein.

Claims

1. a membrane having an aerosol-generation zone, the aerosol-generation zone including a plurality of nozzles, the plurality of nozzles being the only nozzles within the aerosol-generation zone; an actuator coupled to the membrane; the actuator is configured, in use, to excite the membrane to induce vibration of the membrane at one or more predetermined modal frequencies of the membrane to aerosolize a liquid aerosol-forming substrate passing through the plurality of nozzles; more than 50% of the plurality of nozzles are located closer to antinodes than to nodes of the membrane, the antinodes and nodes corresponding to membranes excited at the one or more predetermined modal frequencies of the membrane; An aerosol generating device, wherein the membrane has a thickness that gradually changes from the center of the membrane to the outer periphery of the membrane.

2. 2. The aerosol generating device of claim 1, wherein the plurality of nozzles are non-uniformly distributed across the aerosol-generation zone.

3. 3. The aerosol generating device of claim 1, wherein at least 60% of the plurality of nozzles are located within a region extending on either side of the antinode, wherein the magnitude of the membrane displacement is at least 60% of the magnitude of the membrane displacement at the antinode for a corresponding one or more predetermined modal frequencies.

4. 4. The aerosol generating device of claim 3, wherein all of the plurality of nozzles are located within the region extending on either side of the antinode.

5. the one or more predetermined modal frequencies include a first predetermined modal frequency of the membrane and a second predetermined modal frequency of the membrane, and the plurality of nozzles are preferentially located within first and second intersection regions of the aerosol-generation zone; for the first intersection region, an antinode corresponding to the first predetermined modal frequency of the membrane is adjacent to a node corresponding to the second predetermined modal frequency of the membrane; An aerosol generating device as described in any one of claims 1 to 4, wherein, for the second intersection region, an antinode corresponding to the second predetermined modal frequency of the membrane is adjacent to a node corresponding to the first predetermined modal frequency of the membrane.

6. 6. The aerosol generating device of claim 5, wherein all of the plurality of nozzles are located within the first and second intersection regions.

7. for the first intersection region, the node corresponding to the second predetermined modal frequency is located within a first zone extending on either side of the antinode corresponding to the first predetermined modal frequency, the magnitude of the membrane displacement being at least 60% of the magnitude of the membrane displacement at the antinode for the first predetermined modal frequency; 7. The aerosol generating device of claim 5, wherein for the second intersection region, the node corresponding to the first predetermined modal frequency is located within a second zone extending on either side of the antinode corresponding to the second predetermined modal frequency, and wherein the magnitude of the displacement of the membrane is at least 60% of the magnitude of the displacement of the membrane at the antinode for the second predetermined modal frequency.

8. An aerosol generating device as described in any one of claims 1 to 7, wherein the device is configured to selectively apply and release constraints on the membrane to adjust the response of the membrane to the one or more predetermined modal frequencies.

9. 9. The aerosol generating device of claim 8, wherein the device is configured to selectively apply and release the constraint along one or more portions of the outer periphery of the membrane.

10. 10. An aerosol generating device according to any one of claims 1 to 9, wherein the actuator is configured to selectively excite different parts of the membrane.

11. 11. The aerosol generating device of claim 10, wherein the actuator comprises a plurality of actuator segments, each actuator segment being connected to a different portion of the membrane.

12. 12. An aerosol generating device according to any one of claims 1 to 11, wherein the actuator is configured to apply a modulated drive signal to the membrane to excite the membrane.

13. 13. An aerosol generating device according to any one of claims 1 to 12, wherein the membrane has a thickness that gradually decreases from the centre of the membrane to the outer periphery of the membrane.

14. 13. An aerosol generating device according to any one of claims 1 to 12, wherein the membrane has a thickness that gradually increases from the centre of the membrane to the outer periphery of the membrane.

15. 1. An aerosol delivery system, comprising: The aerosol generating device according to any one of claims 1 to 14 is provided, The system comprises: The aerosol delivery system further comprising a liquid supply operable to supply a liquid aerosol-forming substrate to said membrane.

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