Atomiser and method of using an atomiser

Abstract

The disclosure provides an atomiser arranged in use to atomise a fluid, the atomiser comprising a vessel for accommodating the fluid; a plate comprising a perforate region and a support region, wherein at least one perforation is provided in the perforate region, and wherein the perforate region has a lower thickness than that of the support region; and an actuator arranged in use to impart a pressure disturbance on the fluid, wherein the actuator is disposed at least in part in the vessel, and wherein the pressure disturbance ejects the fluid through the at least one perforation, thereby atomising the fluid. The disclosure provides an associated method of atomising a fluid.

Description

[0001] ATOMISER AND METHOD OF USING AN ATOMISER

[0002] TECHNICAL FIELD

[0003] The invention relates to an atomiser and, specifically, an ultrasonic mesh atomiser.

[0004] BACKGROUND TO THE INVENTION

[0005] Ultrasonic mesh atomisers use an actuator vibrating at an ultrasonic frequency to eject a fluid through perforations in a plate (‘mesh’), thereby forming a spray of fluid droplets and atomising the fluid.

[0006] In the state of the art, such atomisers typically consist of one of two standard approaches. The first approach involves an actuator applying a force or torque directly to a perforate plate to which it is physically connected, thereby causing the plate itself to vibrate and atomise the fluid. The second approach involves a similar arrangement to the first except that the actuator is disconnected from the plate and pressure oscillations are instead imparted on and transmitted through the fluid which, when passing through the perforations of the mesh, is then atomised.

[0007] The first approach can operate with only a limited range of plate materials due to the necessary requirements for high elastic modulus, large elastic strain and, in certain applications, other manufacturability constraints such as the requirement of the plate to be formed into curved or domed shapes. These constraints make it difficult to use, for example, ceramic, glass, or polymer materials in the manufacture of the plate. Even the commonly used metal and metal-alloy materials have been observed to crack and / or plastically deform in some circumstances.

[0008] Similarly, the perforate plates of the prior art approaches are limited by their inherent flexibility. An excessively low stiffness results in dissipation of the imparted pressure oscillations - either due to flexing of the nozzle plate or mechanical resonances - and poor atomisation performance. Likewise, if the plate bending stiffness is too low, the operating frequency falls well above the first resonant frequency of the fluid-loaded plate and the presence of standing waves with nodes and anti-nodes in the resulting vibration response results in dead spots where certain perforations, or groups thereof, do not eject atomised fluid reliably. These two issues are particularly difficult to overcome using polymer nozzles plates (where the elastic modulus is typically in the range 1-3GPa) but are also limiting for metal and ceramic nozzles plates (where the elastic modulus is typically in the range 70-300GPa) whenever a nozzle plate with a large active area is required. Mechanical resonances also lead to cracking or plastic deformation of the plate and associated reductions in performance. At worst, catastrophic failure may also occur. Coating applications (that is, where an atomiser is used to coat a substrate with a coating) often require an unduly large area of perforations in order to produce a continuous coating layer on a substrate. Likewise, material production applications (that is, where an atomiser is used in the production of another material) often also require a large perforate plate to make the process economical. These requirements are difficult or impossible to meet with the prior art approaches. In the art, the area of a perforate plate which comprises perforations is known as the active area.

[0009] Additionally, exotic plate materials and geometries are difficult to use in conjunction with the existing approaches in the state of the art. Certain profiles, dimensions and exit shapes of the perforations themselves (having benefits such as producing smaller droplets or ejecting fluids with complex rheology and / or low surface tension) must be fabricated with highly specialised processes, such as silicon MEMS processes.

[0010] The perforate plate often forms part of a consumable element, either to avoid cross-contamination (for example, of paint colours or fragrances), hygiene (for example, for drug nebulisers), or to allow for replacement of the nozzle plate, nozzles in which may block over time when in use in certain applications. In these applications, the cost of the commonly used laser-drilled steel or electroformed nickel nozzles may be prohibitive to manufacture. The behaviour of the atomisation process is also difficult to monitor and control with accuracy and precision using the above prior art approaches. Common difficulties include: flooding of the exterior of the perforate plate (for example, after a failed ejection event or bias pressure excursions in the ‘forward’ direction); ingestion of gas bubbles (again, due to ejection events or negative bias pressure excursions); blocking of perforations; and poor droplet uniformity (for example, due to sub-optimal drive conditions such as amplitude, frequency, waveform). It is difficult to monitor and control these processes at the required detail to prevent these particular difficulties from outside of the device due to obscuration by the spray plume.

[0011] Lastly, the use of particle-loaded and other multi-component fluids results in blocking of the perforations in the atomisers known in the state of the art. It is also known in the art that blocking and sedimentation in the perforations are reduced by providing a circulation of the fluid, and that favourable geometries for this effect include a smooth flow path. However, prior art atomisers do not have favourable geometries for circulation, as these typically include large steps at the edges of actuators which, in practice, results in unstable bias pressure across the perforate plate and / or stagnant regions where sediment accumulates.

[0012] According to the above technical needs presently encountered in the atomiser industry, the present invention aims to overcome these difficulties to provide a highly adaptable and manufacturable atomiser. In particular, the invention is directed to providing an improved nozzle plate with an increased robustness, a greater and more dense active area, and an extended lifetime. Further, the present invention aims to provide an atomiser that can be readily used with a wide range of plate materials and geometries and that has a means of monitoring and controlling the ejection of fluid droplets, making it compatible with more applications such as providing a smooth circulation of fluid.

[0013] Overall, the person skilled in the art will appreciate that the following technical solutions are intended, overall, to provide an improved ultrasonic atomiser that can be replaceable and adaptable with respect to different mechanical and chemical requirements and additional sub-assemblies for use in a wide range of fluid applications.

[0014] SUMMARY OF THE INVENTION

[0015] According to the invention, there is provided an atomiser arranged in use to atomise a fluid, the atomiser comprising: a vessel for accommodating the fluid; a plate comprising a perforate region and a support region, wherein at least one perforation is provided in the perforate region, and wherein the perforate region has a lower thickness than that of the support region; and an actuator arranged in use to impart a pressure disturbance on at least some of the fluid, wherein the actuator is disposed at least in part in the vessel, and wherein the pressure disturbance ejects at least some of the fluid through the at least one perforation, thereby atomising at least some of the fluid. Optionally, the actuator may be configured to be disposed at least in part within the to-be-atomised fluid.

[0016] It will be appreciated that the invention provides an atomiser which can be replaceable and with a design that is readily adapted to a number of different applications.

[0017] The atomiser may be an ultrasonic atomiser, and the actuator may be a piezoelectric axial mode actuator comprising a sonotrode. The sonotrode may be configured to be driven to vibrate in a substantially orthogonal direction to a plane of the plate whereby to impart a pressure disturbance on the fluid. The sonotrode may further comprise one or more embedded channels configured for heat exchange, that is, configured to permit heat exchange, whereby to permit control over a temperature of one or more of the sonotrode, the accommodated fluid, and / or the plate.

[0018] The atomiser may be an ultrasonic atomiser, and the actuator may be a piezoelectric bending mode actuator.

[0019] The actuator may be positioned or located separate from the plate, wherein the atomiser may be configured such that the fluid provides the separation therebetween. The plate may be replaceable and may be separable from the atomiser. The fluid vessel may also be replaceable and / or separable in the same way.

[0020] The atomiser may be arranged such that the part of the actuator disposed in the vessel is disposed at an oblique angle or perpendicular with respect to the plate.

[0021] The plate may at least in part be domed or curved, and may be domed or curved along a first in-plane axis and elongate longitudinally along a second in-plane axis, in which case, the actuator may also be elongate longitudinally along the second in-plane axis.

[0022] The atomiser and preferably the plate thereof may be made from or otherwise comprise a polymer, ceramic, or glass material.

[0023] The plate may have a thickness between 1mm and 2mm and an unsupported span between 5mm and 10mm.

[0024] The plate may further comprise a sensor or actuator for detecting an obstruction in the at least one perforation.

[0025] The at least one perforation provided in the perforate region may be a nozzle protruding outwardly from the plate. Preferably, at least one perforation provided in the perforate region comprises a nozzle configured to protrude outwardly from the plate in a direction in which fluid may be ejected.

[0026] The perforate region may have a thickness between 0.025mm and 0.5mm and preferably between 0.1 mm and 0.3mm, and wherein the perforate region has an unsupported span between 0.5mm and 4mm and preferably between 1mm and 2mm.

[0027] The perforate region may comprise a (gas) flow manifold and / or channel arranged in use for accommodating fluid cross-flow. Preferably, the perforate region may comprise such a channel arranged in use for accommodating a flow channel fluid (typically a gas), the channel being configured to permit cross-flow of the flow channel fluid with respect to the at least one perforation.

[0028] The atomiser may further comprise a meniscus pinning component. The plate may further comprises an upper electrode and a lower electrode, wherein the upper electrode and the lower electrode are arranged in use to detect a change in conductance or capacitance.

[0029] The atomiser may be arranged such that the actuator is configured at least in part to transmit light through the actuator and may be arranged such that the actuator is arranged in use to function substantially as a microscope. The actuator may also comprise an optical access path configured such that an inward surface of the plate is viewable through the actuator in use. Optionally, the optical access path may be configured to be provided by a hollow core of the actuator. Optionally, the plate may be configured to be at least in part optically transparent.

[0030] The atomiser may be arranged such that the actuator is further configured to transmit acoustic and preferably ultrasonic energy having frequencies between 20kHz and 120kHz or configured to transmit acoustic and preferably ultrasonic energy having frequencies between 1 M Hz and 10OM Hz. The actuator may further comprise a focusing element arranged in use to focus the acoustic and preferably ultrasonic energy. Preferably, the actuator may comprise an acoustic focussing element whereby the actuator is configured to transmit acoustic and preferably ultrasonic energy having frequencies between 20kHz and 120kHz. Optionally, the acoustic focussing element may be configured to be provided by a convex portion of the part of the actuator disposed in the vessel.

[0031] The atomiser may be configured so that the plate is curved with a radius of curvature of less than 15mm and preferably between 5mm and 10mm.

[0032] The atomiser may further comprise one or more fluid reservoirs comprising a flexible outer surface, the one or more fluid reservoirs being configured to feed fluid to be ejected to the at least one perforation. The atomiser may be configured to pump and / or mix the accommodated fluid.

[0033] The atomiser and preferably the plate thereof may further comprise one or more flow channels embedded therein, the one or more flow channels being configured to guide the accommodated fluid across the at least one perforation, wherein the one or more flow channels is configured to be coupled with the actuator whereby to couple acoustic energy from the actuator to the fluid to be ejected.

[0034] The atomiser may further comprise a fluidic cartridge comprising a rear wall arranged in use to accommodate the fluid and transmit acoustic energy from an actuator.

[0035] According to the invention, there is further provided a method using or employing an atomiser for atomising a fluid, the atomiser comprising a plate comprising a perforate region and a support region, wherein at least one perforation is provided in the perforate region, and wherein the perforate region has a lower thickness than that of the support region, and the method comprising: accommodating the fluid in a vessel; and imparting, by an actuator disposed at least in part in the vessel, a pressure disturbance on the fluid, wherein the pressure disturbance ejects at least some of the fluid through the at least one perforation and thereby atomises the at least some of the fluid.

[0036] Before exemplary embodiments of the invention are described in detail, concepts, and language relevant throughout this application are first described without reference to specific embodiments.

[0037] In embodiments of the invention, an atomiser may be understood to mean a device suitable for generating fluid droplets and, preferably, for generating fluid droplets in a spray. The atomiser may alternatively be known as an ‘aeroliser’, ‘nebuliser’, or ‘droplet generator’.

[0038] In embodiments of the invention, a plate may be understood to mean a continuous element having a thickness substantially lower than its in-plane dimensions. The plate may alternatively be known as a nozzle plate or membrane. Regions of the plate include a perforate region, alternatively known as a nozzle-bearing region or the like, and a support region, alternatively known as a reinforcement shoulder or the like.

[0039] In embodiments of the invention, an actuator may be understood to mean any vibrating element suitable for use at the desired vibration frequency. Preferably, the actuator is an ultrasonic actuator, that is, it is suitable for use at vibration frequencies above the frequency of soundwaves. However, the invention is not limited thereto and alternatively the actuator may be a mechanical or acoustic actuator. In any case, the tip of the mechanical, acoustic, or ultrasonic actuator is typically referred to as a sonotrode or a sonotrode horn.

[0040] In embodiments of the invention, a fluid may be understood to mean any liquid suitable for spray atomisation, that is, the formation into droplets as a spray. The fluid to be sprayed may alternatively be known as a ‘spray medium’. However, the invention is not limited thereto, and the fluid may alternatively be any liquid, complex particle-laden slurry, other colloid, shear-thinning fluid exhibiting gel-like behaviour at low shear, a fluid medium containing biological cells, or any other fluid which may be formed into droplets by the methods disclosed herein. In embodiments of the invention, a vessel may be any means for containing or at least accommodating the fluid to be sprayed.

[0041] BRIEF DESCRIPTION OF THE FIGURES

[0042] The invention will now be described by way of examples and with reference to the accompanying Figures in which:

[0043] Figures 1 (a) to 1 (d) illustrate embodiments of the invention.

[0044] Figure 2 illustrates embodiments of the invention referred to hereon as ‘complex nozzle geometries’.

[0045] Figure 3 illustrates a further embodiment of the invention.

[0046] Figure 4 illustrates a further embodiment of the invention.

[0047] Figure 5 illustrates a further embodiment of the invention. Figure 6 illustrates embodiments of the invention referred to hereon as ‘mixing sonotrode designs’.

[0048] Figure 7 illustrates a further embodiment of the invention.

[0049] Figures 8(a) to 8(d) illustrate further embodiments of the invention.

[0050] DETAILED DESCRIPTION

[0051] Referring to Figure 1 (a), there is provided an exemplary atomiser according to a first embodiment of the invention.

[0052] In this example a sonotrode (105) is provided and has its tip disposed in the medium to be sprayed, the fluid (106), and is configured to move in a direction (109) which is substantially orthogonal to a plate (101). The fluid (106) is accommodated in a vessel (not labelled). The plate (101) comprises one or more perforate regions (102), which each contain one or more nozzles (104). Support regions (103) separate the perforate regions (102) and serve to stiffen and strengthen the plate (101) against pressure-induced deformation.

[0053] The perforate regions (102) are thinner than the support regions (103) so as to allow the manufacture of nozzles (104) with low hydraulic resistance and high nozzle density. Since nozzle production methods (such as laser drilling, etching, electroforming and micro-moulding) typically have manufacturing limitations (such as a significant taper angle and / or aspect ratio limitation) it is also advantageous to provide these thinned perforate regions (102) for the purpose of manufacturability.

[0054] In operation, the sonotrode (105) imparts a pressure transient (or pressure oscillation) in the fluid (106) which causes the fluid (106) to be ejected through the nozzles (104) in droplets, slugs, or jets (107) into a second medium, which is typically gaseous and will be referred to as the gas (108). The actuator (115) comprises piezoelectric rings (111) clamped between the sonotrode (105) and a rear nut (112) and are mounted on a central bolt (113). The piezoelectric rings (111) have their positive poles marked with a plus sign (+) and these face a live electrode, which is driven by an electronic drive circuit (114). This configuration of the actuator (115), sometimes known as an axial mode or ‘Langevin-type’ actuator, has the benefits of robustness and high power output. However, other ultrasonic actuation methods are also known to those skilled in the art and may be applied as part of this invention.

[0055] In operation, the sonotrode (105) is driven to vibrate at one of its resonant frequencies, typically between 20kHz and 120kHz, in order to produce a stream of droplets (107) from each nozzle (104). However, the invention is not limited thereto and the sonotrode (105) may alternatively be driven in short bursts to produce intermittent droplet streams or in a drop-on-demand mode to produce one drop from each nozzle (104) for each drive pulse.

[0056] Additionally, the position of the meniscus between the fluid (106) and the gas (108) is controlled by a bias pressure, which may be understood to be the quasi-static pressure difference between the fluid (106) and the gas (108), that is, the pressure difference when the sonotrode (105) is not in operation. In practice, this is typically a few tens of millibars in the forward (that is, higher pressure in the fluid) or reverse (that is, higher pressure in the gas) direction, so that the meniscus position is maintained by surface tension in combination with this bias pressure.

[0057] Figure 1 (b) illustrates an alternative view of the first embodiment, including one or more nozzles (104, wherein only one is labelled for clarity) located within perforate regions (102) of a plate (101). The sonotrode (105) is separated from the plate (101) by the fluid (106) and, in operation, is driven to vibrate in a direction (109) substantially orthogonal to the plane of the plate (101).

[0058] Droplets (107) produced typically have a diameter of 1-3 times the nozzle diameter. It has been found that useful nozzle diameters for the production of evaporating or inhalable droplets are commonly in the range 1-10pm and useful nozzle diameters for the production of droplets for coating applications are commonly in the range 10-100pm. Several other drug delivery and medical applications, such as eye drops and nasal drug delivery can also utilise nozzles in the range 10-100pm. Overall, nozzle diameters from 0.5pm to 200pm have been utilised with this droplet generation approach.

[0059] When the length of the nozzle (104) is a significant multiple of the diameter of the nozzle (104), the viscous flow resistance becomes significant. Whilst some tapering of the nozzle (104) can be used to mitigate this, when the inlet size of the nozzle (104) becomes too large, the maximum nozzle density of the perforate region (102) becomes lower. It has been found that it is beneficial to provide a perforate region (102) which is not more than 800pm in thickness, and more preferably between 25pm and 500pm, and has a thickness which is between 1 and 20 times the nozzle diameter.

[0060] Figure 1(c) illustrates a nozzle plate (101) with perforate regions (102) in order to help define thickness and span of the various regions. In operation, the nozzle plate is clamped, bonded of otherwise attached to a comparatively rigid body around a clamping perimeter (116).

[0061] The perforate region (102) will have an unsupported span, Dp, which may be understood to be the distance between support regions (103). Dpwould be the diameter of the perforate region, if circular. The situation is more complex for other shapes of perforate region, but Dpwould generally be the short side of a rectangular region, provided high order mechanical resonances along the long axis of the rectangle can be avoided. The perforate region (102) has a thickness, Hp. The maximum unsupported span Dpis limited by the stress, deflection, and mechanical resonances which the perforate region (102) experiences, particularly in response to pressure oscillations imparted on the fluid (106) generated by the sonotrode (105). The thickness of the support regions (103) is labelled Ht. We define the total span of the nozzle plate (101), Dt, to be the distance between clamping or mounting points (116) at opposite edges of the nozzle plate (i.e. diameter for a circular plate or short side for a rectangular plate). Htand Dtare preferably also selected such as to avoid excessive mechanical stress, deflection, and resonances. The practical limits on the thicknesses will depend on the plate (101) material or materials. In practice, a perforate region (102) thickness of 100-300pm and unsupported span of 1-2mm is found to be acceptable for polymer plates (for example, PET or polyimide plates). A support region (103) thickness of 1-2mm and total span of 5-10mm is also found to be acceptable for polymer plates. In both cases, the relationship of span (Dpor Dt) to thickness (Hpor Ht) is guided by D2 / H < 50mm and more preferably D2 / H ~ 10mm, although there may be other constraints too. Other materials such as ceramics, glass and metals tend to have a higher stiffness than polymers, so can often accommodate relatively thinner membranes (H) or larger spans (D) (typically D2 / H < 150mm and more preferably D2 / H ~ 50mm). Some ceramics have failure modes initiated by micro-cracking, and the design rules for polymers are also appropriate for such materials, due to their lower strength in operation. Considering a wider range of materials, a perforate region (102) with a thickness in the range 30-300pm and span of 1 -5mm is appropriate, along with a support region (103) with a thickness of 0.3-3mm and span of 4-40mm.

[0062] Advantageously, portions of the plate (101) may be curved or domed to increase mechanical stiffness.

[0063] Figure 1 (d) illustrates an example of the first embodiment, the example including one or more nozzles (104, wherein only one is labelled for clarity) located within perforate regions (102) of a plate (101). The sonotrode (105) is configured to be separated from the plate (101) by the fluid (106) and, in operation, is configured to be driven to vibrate in a direction (109) substantially orthogonal to the plane of the plate (101 ). In applications, it is often advantageous to control the temperature of one or more of the fluid (106), sonotrode (105), and nozzle plate (101). Exemplary fluids such as paints and other coating materials may need to be kept at a particular temperature in order to control their viscosity thereby ensuring efficient ejection via the nozzles of the device herein disclosed is possible. In other exemplary fluids (e.g. liquid metal alloys), solidification and / or evaporation rates may need to be managed by precise temperature control. Other chemical and biological formulations (e.g. pharmaceutical compounds and emulsions) need to avoid damage by overheating when undergoing vaporisation. The temperature of piezoelectric materials in the sonotrode actuator also needs to be kept below a certain threshold (e.g. well below the Curie temperature) to avoid thermal depoling.

[0064] This example of the first embodiment includes one or more internal channels (also referred to as coolant channels) in the sonotrode (127) and / or in the nozzle plate (128). In operation, a heat transfer fluid (typically a fluid that is or comprises a coolant, such as water or mineral oil) is circulated through the internal channels (127, 128) embedded in the sonotrode and / or plate in order to, for example, help maintain the desired operating temperature of the fluid (106) and other parts. Where the one or more internal channels (127) are comprised in the sonotrode (105), said channels may be arranged within a body of the sonotrode (105) and may be fed with a coolant. Where the one or more internal channels (128) are comprised in the nozzle plate (101), the inlet (129a) and outlet (129b) ports of said channels may be arranged on a surface of the plate (101) such as an inwardly facing surface or a surface (as illustrated), such that they may be fed with a coolant via a gasket or tube fitting (illustrated as coolant inlet (130a) and outlet (130b) tubes in this embodiment). In this way, the embedded channels are configured to permit a heat exchange process whereby temperature control of the fluid, plate, and / or vessel etc. may be achieved.

[0065] For applications where only heating is required, the coolant channels (127, 128) may be replaced by embedded resistive heating elements. In such examples, one or more resistive heating elements are comprised, arranged, or embedded within a body of the sonotrode (105) and / or on an inwardly facing surface of the plate (101).

[0066] Referring to Figure 2, there is provided exemplary embodiments of the invention comprising complex nozzle geometries, which cannot be readily appropriated in prior art atomisers. Collectively, the designs in Figure 2 may be referred to as complex nozzle geometries. Figure 2a illustrates a perforate region (212) of the plate (101) with protruding nozzles (214). The protruding nozzles (214) have a sharp tip, that is, a small radius of curvature. This helps to pin the meniscus (213) of the fluid (106) in at the nozzle exit and reduces the occurrence of flooding of the exterior (gas-facing side) of the plate (101). This enables the ejection of fluids (106) with low surface tension or with other rheological properties which make droplet ejection unreliable with a flat plate.

[0067] In operation, a droplet (216) forms atthe tip ofthe nozzle (214) and may be ejected without surface tension making it favourable to wet the outside of the nozzle (214). Protruding nozzles (214) may be fabricated by any of the known methods of producing hollow microneedles, including, but not limited to, laser machining, electroforming, micro-moulding, and silicon micro-fabrication. Support regions (not shown in the illustration) such as collars or grids of bars or continuous supports between perforate regions may be formed as part of the fabrication process or subsequently added by an additional electroforming step, wafer bonding (fusion, anodic, eutectic bonding etc.), lamination, thermal bonding, adhesive bonding, or by another process.

[0068] Figure 2b illustrates an alternative perforate region (222) with a gas flow manifold (229) configured to provide a flow (228) of the second medium, the gas (108). The gas flow manifold (229) is usefully configured to flow the gas (108) into a co-flow, a cross-flow, a pulsating flow, or a swirl flow to provide functions such as flow focussing, droplet drying, droplet cooling, droplet break-up, and / or change of droplet momentum. A co-flow configuration is illustrated, wherein a jet on the left (226a) is accelerated downwards to encourage separation from the nozzle (224) and enhance heat and mass transfer between the two fluids (106, 108) and a jet on the right (226b) is subject to flow focussing, which enables the production of droplets which are smaller than the nozzle diameter.

[0069] Figure 2c illustrates a perforate region (232) wherein the nozzle (234) has a floodable region (239a) atthe exit where, in operation, the fluid meniscus is pinned at a meniscus pinning feature (239b) at the perimeter of the floodable region (239a). The meniscus pinning feature (239b) may take the form of a step or ridge or change in surface wettability, for example, through localised hydrophobic or hydrophilic surface treatment. In operation, droplets (237) are ejected through the floodable region (239a), without disturbing the pinning of the meniscus.

[0070] Figure 2d illustrates a perforate region (242) wherein the plate (101) comprises additional sensing and / or actuation functionalities. In the illustrated example, the perforate region (242) comprises one or more upper electrodes (244), an insulating region (247), and one or more lower electrodes (245a, 245b). As illustrated, the lower electrode is segmented to allow individual nozzles (241a, 241 b) to be separately addressed, that is, lower electrode 245a is adjacent to nozzle 241a and electrode 245b is adjacent to nozzle 241b. The fluid (246) is present on the upper side and the gas (248) is on the lower side, separated by the fluid meniscus (243) which is typically located near the nozzle exit. The electrodes (244, 245a, 245b) are arranged so as to detect a change in electrical properties (conductance or capacitance) when an obstruction (249) with some electrical contrast from the fluid (246) is present.

[0071] In operation, this may be configured to run as a coulter-counter to detect when a cell passes through the nozzle (241a, 241 b) or when a bubble is present. The insulating region (247) may be a polymer or ceramic layer. The plate may be constructed using printed circuit board (PCB) technology to provide the required structure of layers. Advantageously, the electrodes may be electroplated after the nozzles (241a, 241 b) have been drilled (mechanically or by laser drilling), so that they overlap the edges of the nozzles (241a, 241 b) as illustrated and, in operation, form a good electrical contact with the fluid (246). Alternatively, the plate (101) may be manufactured by laser drilling a polymer or ceramic substrate, followed by adding electrodes (244, 245a, 245b) by vacuum evaporation at an oblique angle. Other methods of manufacturing this structure are also possible, as will be apparent to those skilled in the art.

[0072] In an alternative embodiment, the insulating region (247) may be a piezoelectric or an electro-strictive material, which would enable actuation of the nozzles (241a, 241 b) to modulate nozzle size, enhance cleaning / unblocking, or provide additional stimulus to enhance droplet ejection.

[0073] Referring to Figure 3, there is provided an exemplary atomiser according to a further embodiment of the invention, the atomiser comprising a sonotrode (317) with a transparent front face (314) and a Langevin-type piezoelectric transducer. However, the invention is not limited thereto and alternative transducer types, such as magneto-strictive and electromagnetic transducers, may also be used in any of the embodiments disclosed herein.

[0074] The transducer, having an axis of symmetry (315), comprises a hollow core which provides an optical access path (316). The transducer further comprises a bolt (313), a back-nut (312), piezoelectric rings (311), and sonotrode (317) surrounding the hollow core. The front face (i.e. the face closest to and face-to-face with the plate (301) comprises a (optically) transparent front face, window, or lens (314), which enables viewing of the fluid (306) contained between it and the plate (301). The plate (301) comprises support regions (303) and perforate regions (302) comprising nozzles (304). In operation, fluid droplets, jets, or slugs (307) are ejected into the gas (308).

[0075] It is desirable to monitor and control the ejection process in order to maximise process efficiency in various applications. There are several advantages of this embodiment. Failure to eject the fluid (306) is readily remedied by adjusting the drive parameters (which include bias pressure, drive amplitude, drive frequency and waveform). In combination with a transparent plate (301), flooding of the nozzles (304) is readily monitored and controlled by adjusting the drive parameters. Ingestion of gas bubbles and cavitation is readily controlled by adjusting the drive parameters or by running a “re-priming” procedure, that is, refilling the region above the plate (301) with bubble-free fluid. Blocked nozzles (304) are readily remedied by running an “unblocking” procedure. This may involve driving at high amplitude or at a different frequency for a short time. Alternatively, monitoring the blockage rate allows the operator to swap the plate (301) when a certain blockage threshold is reached. Selective ejection of certain components of the fluid (306) are also enabled by this monitoring arrangement. For example, passing biological cells may be ejected when it is detected that they are passing a nozzle (304). This may also be applied to other particles, such as fluorescently labelled cells or magnetic beads. This enables cell sorting and production of samples with one cell per droplet (307) for biological assays. For fluorescence detection, the illumination light would advantageously be either co-axial with the imaging (so that back-scattered fluorescence is detected) or at an oblique angle (i.e. accessing the region between the plate (101) and window or lens (314) from the side). These configurations minimise the amount of illumination light entering the detection optics and hence maximise the signal to background ratio. The optical access feature also enables other functions such as optical manipulation of particles (that is, optical tweezers) to position them for ejection and laser heating, for example, to help unblock nozzles by ablation or reduce local fluid viscosity by heating.

[0076] Referring to Figure 4, there is provided an exemplary atomiser according to a further embodiment of the invention, the atomiser comprising a sonotrode (405) with an acoustic focussing element (410) at its tip.

[0077] The acoustic focussing element (410) may take the form of a concave section, a curved boundary between a pair of materials with different acoustic impedances, an acoustic Fresnel lens, or other acoustic focussing element known to those skilled in the art. Optionally, a hollow core (411) is provided to facilitate priming and bubble removal. Preferably, the hollow core (411) is substantially longer in length than its diameter, so that it has a significant flow resistance and does not act to dissipate the pressure imparted by the motion (409) of the sonotrode (405). As with previous embodiments, a plate (401) is separated from the sonotrode (405) by a gap filled with the fluid (406). The nozzle plate (401) comprises one or more perforate regions (402), support regions (403) and nozzles (404) and, in operation, ejects fluid jets, droplets or slugs (407) into the gas (408). In the first operating mode, the sonotrode (405) is operated at a first frequency, typically in the range 20kHz to 120kHz. This mode is characterised by reduced focussing effect, due to the low numerical aperture of the acoustic lens. In this mode, a large area of nozzles (404), that is, the active area, are stimulated to eject droplets (407).

[0078] In a second operating mode, the sonotrode (405) is driven at a second frequency, typically in the range 1 MHz to 100MHz. In this mode, there is a significant focussing of the acoustic (and, optionally, ultrasonic) energy, as indicated by the dotted lines (412). In operation, this is used to eject droplets (407) from a single nozzle (404) or smaller (active) area of nozzles.

[0079] By these modes, the spray pattern and / or droplet size distribution can be adjusted. For example, the first mode may be used to produce a broad spray plume, whereas the second mode may be used for precise droplet deposition, providing adjustable deposition in an electronic painting system or a drug delivery device. Alternatively, one of the modes may be used to unblock nozzles (404) or perform other maintenance functions. Advantageously, the sonotrode (405) or focal spot may be moved relative to the plate (401), so that different nozzles or regions can be activated by the second mode.

[0080] Referring to Figure 5, there is provided an exemplary atomiser according to a further embodiment of the invention, the atomiser comprising a bending mode actuator (505).

[0081] In the illustrated example, the bending mode actuator (505) is a piezoelectric unimorph actuator comprising a substrate (505a) which is typically stainless steel, aluminium or ceramic and which is bonded to a piezoelectric material (505b). Bimorph and multi-layer piezoelectric actuators may also be used in the alternative, as may electro-strictive or magneto-strictive actuation methods.

[0082] As with previous embodiments, a plate (501) is separated from the bending mode actuator (505) by a gap filled with the fluid (506). The plate (501 ) is illustrated with one or more perforate regions (502), support regions (503) and nozzles (504) and, in operation, ejects fluid jets, droplets, or slugs (507) into the gas (508). In operation, the motion (509) of the actuator (505) imparts pressure oscillations on the fluid (506), which in turn causes the ejection of droplets (507), with the motion (509) preferably being substantially orthogonal to the plate (501).

[0083] Optionally, the bending mode actuator (505) may also be driven at a second frequency, typically above 1 MHz, in ‘thickness mode’, to enable the functions and features described in the text accompanying Figure 4. For this arrangement, an acoustic Fresnel lens may be formed into the substrate (505a) to provide the focussing function.

[0084] Referring to Figure 6, there is provided exemplary embodiments of the invention comprising mixing sonotrode designs.

[0085] Figure 6a illustrates a sonotrode (615) and its motion direction (619) which is substantially orthogonal to the plate (611). In this embodiment, the front face (613) of the sonotrode (615) is tilted (that is, obliquely angled) with respect to the plate (611). In operation, the vibration of the sonotrode (615) in the direction (619) encourages cross-flow, which may be understood to mean flows (612) of the fluid (616) parallel to the plate (611). The physical mechanism for this may be interpreted as an asymmetric flow resistance (valveless fluidic diodicity), such as that achieved in a Tesla valve or Liebau pump or as acoustic streaming behaviour, depending on the length scales, fluid properties and operation frequency.

[0086] Figure 6b illustrates a sonotrode (625) and its motion direction (629), which is substantially orthogonal to the plate (621). In this embodiment, the front face of the sonotrode (623) is corrugated. A saw-tooth corrugation is illustrated, which achieves a similar functionality to that in Figure 6a. In operation, the vibration encourages cross-flow, which may be understood to mean flow (622) of the fluid (626) parallel to the plate (621). The physical mechanism for this may be interpreted as an asymmetric flow resistance, such as that achieved in a Tesla valve or Liebau pump or as acoustic streaming behaviour, depending on the length scales, fluid properties and operation frequency.

[0087] Figure 6c illustrates two views of a sonotrode (635) and its motion direction (639), which is substantially orthogonal to a plate (631) containing a perforate region (632) where nozzles (634) are located. The front face of the sonotrode (635) comprises angled features (633) configured to encourage rotational mixing or centrifugal pumping. Optionally, the sonotrode (635) further comprises a fluidfeed channel (637) configured to provide input fluid for centrifugal mixing and / or jetting.

[0088] Figure 6d illustrates a sonotrode (645) and its motion direction (649), which is substantially orthogonal to a plate (641). The sonotrode (645) has a thinned or tapered region (643) which, in operation, is configured to flap (as indicated by the dashed lines) and thereby provide a pumping action, causing the fluid (646) to flow or mix in the direction (642). The thinned or tapered region (643) may be an asymmetric feature to induce cross-flow. Alternatively, the thinned tapered region (643) may be an axisymmetric fin, which may be used in combination with a central fluid port to induce radial flow. Advantageously, in this embodiment, flexibility may be incorporated into the tip of the sonotrode (645), in order to provide improved flow or mixing of the fluid (646) by a peristaltic motion.

[0089] Referring to Figure 7, there is provided an exemplary atomiser according to a further embodiment of the invention, the atomiser comprising a linear sonotrode (705) (also known in the art as a ‘sonotrode bar’) and an (optionally linear) array of perforate regions (704).

[0090] The atomiser further comprises a support region (702). The perforate regions (704) further comprise one or more nozzles (not shown) and are thinned regions to facilitate the fabrication of high quality nozzles with hydraulic low flow resistance. Together, the perforate regions (704) and support region (702) constitute, at least in part, the plate (701). The plate (701) is curved along an axis with a radius of curvature R (711) and an unsupported width W (712). The plate (701) is constrained at the edges by a mount (703). Advantageously, the plate (701) forms an extended sheet, so that fresh nozzles can be provided by sliding the plate (701) either along the longitudinal axis or around the curved axis.

[0091] Advantageously, the unsupported width W (712) is in the range 1mm to 5mm and the radius of curvature R (711) is less than 15mm in the case where the perforate region (704) is made of metal or less than 8mm in the case where the perforate region (704) is made of a polymer material. Advantageously, the thickness of the perforate region is between 0.04mm and 0.12mm when made of metal and between 0.04mm and 0.3mm when made from a polymer.

[0092] The linear sonotrode (705) (analogous to the sonotrode tip previously described) is located in the fluid behind the plate (701) and driven by one or more linear actuators (710) to vibrate in a direction (709) substantially orthogonal to the perforate regions (704). In operation, this imparts a pressure pulse or oscillation upon the fluid and causes the ejection of jets, slugs, or droplets of fluid from the nozzles (droplets are ejected substantially upwards away from the nozzles in this illustration).

[0093] This embodiment has the advantage that uniform pressure generation and hence droplet generation can be achieved for an arbitrarily long linear array. A further advantage is in the enabling the use of a low cost polymer plate (701 ) with a linear spray configuration.

[0094] The mount (703) may be permanently joined to the plate (701) or separably clamped onto it. Advantageously, a clamped arrangement enables the simple replacement of blocked or damaged plates (701) without replacing the whole apparatus.

[0095] Referring to Figure 8(a), there is provided an exemplary atomiser according to a further embodiment of the invention, the atomiser comprising a separable enclosed fluid chamber and a sonotrode (805). In operation, the sonotrode (805) vibrates in a motion direction (809) substantially orthogonal to the plate (801). The fluid (806) is contained in an enclosed fluid chamber between the plate (801) and a rear wall (812). The plate (801) comprises one or more support regions (803) and one or more perforate regions (802). The perforate regions (802) are perforated with nozzles (804). In operation, the acoustic (and, optionally, ultrasonic) energy from the sonotrode (805) is coupled through the rear wall (812) which in turn imparts a pressure disturbance upon the fluid (806) resulting in the ejection of fluid droplets, jets, or slugs (807) from the nozzles (804) into the gas (808).

[0096] A coupling layer (810) (comprising adhesive, gel or fluid) may be advantageously used to connect the sonotrode (805) to the rear wall (812) to in order to couple the acoustic (and, optionally, ultrasonic) energy into the fluid (806) reliably. It will be noted that in operation, the rear wall (812) hence effectively becomes part of the actuator.

[0097] The enclosed fluid chamber comprises at least the nozzle plate (801) and rear wall (812) and may be pre-loaded with fluid (806) for some applications. The enclosed fluid chamber optionally comprises a flow channel, a cartridge, a microfluidic chip or a bioreactor vessel, which can accommodate fluid cross-flow and be separable from the sonotrode (805). This enables the use of a low-cost fluid-containing cartridge which does not need to include the expensive acoustic or ultrasonic actuator (of which the sonotrode tip is illustrated here). The enclosed fluid chamber may be hygienical ly separated from the sonotrode (805).

[0098] In the illustrated embodiment, the entrance side of the nozzles (804) are substantially flush with the inner wall of the flow channel (the region of fluid 806). In operation, this has the advantage of allowing a smooth cross-flow (813) of fluid (806) with straight streamlines and minimal recirculation, stagnation, or turbulent zones. Advantageously, the edge of the perforate region (802) is tapered to facilitate imaging and cleaning of the droplet (807) generation zone and fluid meniscus (811) at the exit side of the nozzles (804). Preferably, this flow channel approach is combined with the hollow sonotrode of Figure 3 in order to enable cells or particles from the flow channel to be ejected upon detection. This is enabled by the addition of an optical access path (814) and optical window or lens (815).

[0099] Figure 8(b) illustrates an exemplary atomiser according to a further embodiment of the invention, the atomiser comprising a separable fluid flow chamber (827), referred to here as the “fluidic chip”, and a sonotrode (815). In this embodiment, the fluidic chip (827) takes the form of a flow cell, such as a microfluidic chip or moulded flow channel.

[0100] In operation, the sonotrode (815) vibrates in a motion direction (819) substantially orthogonal to the surface of the fluid chamber (827). The fluid is contained in an enclosed channel (816) of the fluid chamber (827). The channel is perforated by one or more nozzles (814), wherein the nozzles may be any of the hitherto described nozzles. The region away from the nozzles (814) functions as the support region as hitherto described. In operation, the acoustic (and, optionally, ultrasonic) energy from the sonotrode (815) may be coupled through the upper wall of the flow channel (816) which in turn imparts the pressure disturbance upon the fluid resulting in the ejection of fluid droplets, jets, or slugs (817) from the nozzles (814).

[0101] A coupling layer (820) (optionally comprising adhesive, gel or fluid) may be advantageously used to connect the sonotrode (815) to the upper wall of the flow channel (816) to in order to reliably couple the acoustic (and, optionally, ultrasonic) energy into the fluid to be ejected.

[0102] In operation, a cross-flow of fluid is provided in the flow channel (816) from the inlet (823) to the outlet (824). The sonotrode (815) may be provided with an optical access path (826) through its centre. Optical detection is used to detect when a particle or substance of interest (e.g. a labelled cell) is passing or passing through the nozzle (814), and the control system then drives the sonotrode (815) to eject the particle or substance in a droplet (817). Advantageously, the channel (816) may have a width between 0.05mm and 0.5mm, so that passing particles or substances of interest may be ejected from the nozzle (814), which may have an outlet diameter of between 0.05mm and 0.25mm. The embodiment illustrated in figure 8(b) may be used in combination with a mechanism to focus the particles towards a central streamline. Inertial, optical, and / or acoustic focussing methods or other such methods known to those skilled in the art may be used for this purpose. When used in combination with any of the hitherto described focussing methods, the channel width may be significantly larger than the nozzle diameter. The upper wall of the flow channel (816) is preferably sufficiently flexible that pressure waves are transmitted through it with low loss. A polymer capping layer of thickness less than 0.1 mm and preferably around 0.05mm has been found to work in practice. Stiffer upper walls may also be used, for example to obtain pressure amplification from mechanical resonance of the channel structure.

[0103] Figure 8(c) illustrates an embodiment of the invention utilising a separable fluidcontaining capsule and a sonotrode (835). In applications such as pharmaceutical compound screening and drug delivery, it is advantageous to provide a low cost container from which material can be dispensed / atomised with a low risk of crosscontamination or loss of sterility.

[0104] The capsule comprises a liquid (836) contained within a nozzle plate (831), chamber walls (833), and rear wall (832) which takes the form of a deformable separator or membrane. A peelable film (838) may be used to seal the capsule prior to first use and help avoid loss of fluid or loss of sterility. In operation, a coupling layer (830) may optionally be used to couple the sonotrode (835) to the capsule, so that acoustic energy may be coupled to the liquid (836), causing ejection of droplets from the nozzle (834). The deformable separator (832) may be configured so that is moved towards the nozzle plate (831) as the remaining volume of liquid (836) decreases. This has the advantage that a high proportion of the liquid (836) can be utilized in the process and waste is reduced. This is particularly advantageous in combination with high value fluids such as pharmaceuticals. Figure 8(d) illustrates a further embodiment of the invention comprising a separable fluid container (851) comprised in the fluid accommodating vessel, and a sonotrode (845). In applications such as chemical compound library storage, it is advantageous to provide a low cost container from which material can be dispensed in a non-contact manner with a low risk of cross-contamination.

[0105] The fluid container (851 ) comprises a variable volume liquid reservoir (843), which is able to expand or contract due to a flexible upper surface, a liquid feed channel (852), and a nozzle-bearing region (842) (i.e., plate) including a nozzle (844). In operation, an optional coupling layer (850), for example a water or gel, may optionally provide coupling of acoustic energy from a sonotrode (845), which may be configured to vibrate in a direction (849) substantially orthogonal to nozzlebearing region (842). The oscillating acoustic pulses may be configured to cause the ejection of droplets (847) from the nozzle (844). In order to help maintain purity, and to prevent evaporation and accidental dispense, the nozzle can be protected by a removable film or cap, or can be laser drilled at the time of first dispense. Multiple feed channels (852), nozzle-bearing regions (842) and / or nozzles (844) may be used to allow single-use operation of each nozzle-bearing region (842). Nozzle-bearing regions (842) can then be isolated after use, for example by heat-sealing across the feed channel (852). This further reduces the risk of contamination or sample loss. The use of multiple nozzle bearing regions (842) can also be used to enable different dispense locations or different dispense volumes from the same fluid container (851).

[0106] The embodiments in Figures 8(a) to 8(d) are well-suited to working in a drop-on- demand operating mode, as opposed to a continuous sinusoidal drive waveform, as will be apparent to those skilled in the art. Drop-on-demand operating modes have been found to operate well with centre frequencies in the range 5kHz to 12 kHz. Advantageously, a multi-layer piezoelectric actuator may be used to create the comparatively large impulses required for drop-on-demand operation. As will be appreciated by a person skilled in the art, the above embodiments and examples demonstrate in detail the wide applicability and inventiveness of the present invention, and its benefits in providing a more efficient and easily manufactured atomiser. Though the description of each embodiment has its own emphasis, for any aspect or feature that is not described in relation to one embodiment, reference may be made to related descriptions of any other embodiments.

Claims

CLAIMS1 . An atomiser arranged in use to atomise a fluid, the atomiser comprising: a vessel for accommodating the fluid; a plate comprising a perforate region and a support region, wherein at least one perforation is provided in the perforate region, and wherein the perforate region has a lower thickness than that of the support region; and an actuator arranged in use to impart a pressure disturbance on the fluid, wherein the actuator is disposed at least in part in the vessel, and wherein the pressure disturbance ejects at least some of the fluid through the at least one perforation, thereby atomising the at least some of the fluid.

2. The atomiser of claim 1 , wherein the atomiser comprises an ultrasonic atomiser, and the actuator comprises a piezoelectric axial mode actuator comprising a sonotrode.

3. The atomiser of claim 2, wherein the sonotrode is configured to be driven to vibrate in a substantially orthogonal direction to a plane of the plate whereby to impart a pressure disturbance on the fluid.

4. The atomiser of claim 2 or 3, wherein the sonotrode further comprises one or more embedded channels configured to permit heat exchange whereby to permit control of a temperature of one or more of the sonotrode, the accommodated fluid, and the plate.

5. The atomiser of any preceding claim, wherein the actuator and the plate are separable.

6. The atomiser of any preceding claim, wherein the plate is at least in part domed or curved.

7. The atomiser of any preceding claim, wherein the plate comprises one or more of a polymer, ceramic, or glass material.

8. The atomiser of any preceding claim, wherein the plate further comprises a sensor for detecting an obstruction in the at least one perforation.

9. The atomiser of any preceding claim, wherein the at least one perforation provided in the perforate region comprises a nozzle configured to protrude outwardly from the plate in a direction in which fluid may be ejected.

10. The atomiser of any preceding claim, wherein the perforate region has a thickness between 0.025mm and 0.5mm and preferably between 0.1 mm and 0.3mm, and wherein the perforate region has an unsupported span between 0.5mm and 4mm and preferably between 1 mm and 2mm.

11. The atomiser of any preceding claim, wherein the perforate region comprises a flow channel arranged in use for accommodating a flow channel fluid, the flow channel being configured to permit cross-flow of the flow channel fluid with respect to the at least one perforation.

12. The atomiser of any preceding claim, wherein the actuator is configured at least in part to transmit light through the actuator.

13. The atomiser of any preceding claim, wherein the actuator comprises an optical access path configured such that an inward surface of the plate is viewable through the actuator in use.

14. The atomiser of claim 13, wherein the optical access path is configured to be provided by a hollow core of the actuator.

15. The atomiser of any preceding claim, wherein the plate is configured to be at least in part optically transparent.

16. The actuator of any preceding claim, wherein the actuator comprises an acoustic focussing element whereby the actuator is configured to transmit acoustic energy having frequencies between 20kHz and 120kHz.

17. The atomiser of claim 16, wherein the acoustic focussing element is configured to be provided by a convex portion of the part of the actuator disposed in the vessel.

18. The atomiser of any preceding claim, the atomiser further comprising a fluidic cartridge comprising a rear wall arranged in use to accommodate the fluid and transmit acoustic energy from an actuator.

19. The atomiser of any preceding claim, wherein the atomiser further comprises one or more fluid reservoirs comprising a flexible outer surface, the one or more fluid reservoirs being configured to feed fluid to be ejected to the at least one perforation.

20. The atomiser of any preceding claim, wherein the plate further comprises one or more flow channels embedded therein, the one or more flow channels being configured to guide the accommodated fluid across the at least one perforation, wherein the one or more flow channels is configured to be coupled with the actuator whereby to couple acoustic energy from the actuator to the fluid to be ejected.21 . The atomiser of any preceding claim, wherein the actuator is configured to be disposed at least in part in the to-be-atomised fluid.

22. A method of using an atomiser for atomising a fluid, the atomiser comprising a plate comprising a perforate region and a support region, wherein at least one perforation is provided in the perforate region, and wherein the perforate region has a lower thickness than that of the support region, and the method comprising: accommodating the fluid in a vessel; and imparting, by an actuator disposed at least in part in the vessel, a pressure disturbance on the fluid, wherein the pressure disturbance ejects at least some of the fluid through the at least one perforation and thereby atomises the at least some of the fluid.

Images