APPARATUS FOR AEROSOLISING A LIQUID

Abstract

 The present disclosure provides an apparatus for aerosolising a liquid (100) comprising one or more inputs (110), and a plurality of droplet ejectors (126) in fluid communication with the one or more inputs (110). Each droplet ejector comprises a nozzle portion and a piezoelectric actuator. The one or more inputs are for receiving one or more liquids. Each nozzle portion defines a nozzle outlet in fluid communication with the one or more inputs. Each piezoelectric actuator is operable to cause ejection of a liquid received by one of the one or more inputs through the respective nozzle outlet as one or more droplets to thereby generate an aerosol comprising the one or more droplets ejected by each droplet ejector.

Description

Field of the invention

[0001] The present invention relates to apparatus for aerosolising a liquid.

Background to the invention

[0002] There are a number of applications in which it is advantageous to convert a single volume of liquid into a plurality of droplets, such as an aerosol or a mist. Such a change may be done so as to increase the surface area of the liquid, and/or to provide droplets not exceeding a maximum size, and/or to allow the liquid to more easily be delivered to a target area by entraining within an airflow.

[0003] Prior techniques for producing a plurality of droplets (e.g. aerosols) can use an atomiser pressure nozzle, where a liquid is expelled through the nozzle under high pressure so as to form droplets. Another known nozzle technology is an ultrasonic nozzle where a given nozzle geometry and liquid will produce droplets having a predetermined median droplet size.

[0004] It is in this context that the present inventions have been devised.

Summary of the invention

[0005] An apparatus for aerosolising a liquid comprising: one or more inputs for receiving one or more liquids; and a plurality of droplet ejectors together in fluid communication with the one or more inputs. Each droplet ejector comprises: a nozzle portion defining a nozzle outlet in fluid communication with a one of the one or more inputs; and a piezoelectric actuator. Each piezoelectric actuator is operable to cause ejection of a liquid received by the one of the one or more inputs through the respective nozzle outlet as one or more droplets to thereby generate an aerosol comprising the one or more droplets ejected by each droplet ejector.

[0006] Thus, by providing the plurality of droplet ejectors, instead of a single droplet ejector, a given number of nozzle outlets are divided across the plurality of droplet ejectors. In other words, each droplet ejector causes ejection of the one or more liquids through fewer than the total number of nozzle outlets in the apparatus. As a result, undesired inhomogeneities in the ejection of droplets from different regions of the apparatus can be reduced, or even completely eliminated. Furthermore, it is possible to provide separate control signals to each of the piezoelectric actuators, allowing for a more finely controlled set of droplets to be ejected through the nozzle outlets. Accordingly, a larger proportion of the droplets present in the aerosol can be controlled to have sizes that more accurately reflect the desired ejection parameters. Typically, the size of the droplets ejected from a given droplet ejector will be dependent on a driving signal used to control the piezoelectric actuator of the given droplet ejector. In this way, the driving signal can be altered to cause different size droplets to be ejected (or even to cause the same size droplet to be ejected with different liquids).

[0007] It will be understood that the one or more liquids to be received by the one or more outputs and to be ejected as the aerosol by the apparatus can include solid particulates suspended in liquid in some examples.

[0008] In some examples, it may be that the apparatus is to be attached to one or more further components to be used. Specifically, any device that includes the plurality of droplet ejectors and one or more inputs described herein can typically be considered an apparatus for aerosolising a liquid. Put another way, it may be that the apparatus for aerosolising a liquid can be considered a refill for a larger apparatus that includes the one or more further components to provide a working device which can make use of the generated aerosol.

[0009] The term aerosol as used herein will be understood to mean substantially any droplets sufficiently small that they can be entrained within an airflow, for example, sufficiently small that they can be dispersed into the surrounding atmosphere/air. The term "apparatus for aerosolising" will be understood to mean any aerosoliser, that is, any device capable of producing an aerosol as described herein.

[0010] The one or more inputs typically receive a single liquid at a single respective input. However, in some examples, it may be that a first liquid is received at an input at a first time and a second liquid is received at the input at a second time, subsequent to the first time.

[0011] It will be understood that ejection of the one or more droplets through the nozzle outlets need not required that the droplets have sufficient momentum imparted thereto during ejection so as to travel a significant distance from the apparatus, only that the ejection of the droplets result in the formation of the aerosol.

[0012] The nozzle outlet defined by at least 50 per cent of the plurality of droplet ejectors may be among no more than one nozzle outlet defined by the respective droplet ejector. The nozzle outlet defined by each of the plurality of droplet ejectors may be among no more than one nozzle outlet defined by the respective droplet ejector. Thus, particularly effective control of the droplet size can be exercised since each piezoelectric actuator, when operated, causes ejection of droplets through only a single nozzle outlet. The nozzle outlet defined by each of the plurality of droplet ejectors may be in fluid communication with the one of the one or more inputs.

[0013] The apparatus may further comprise a storage portion defining one or more cavities for storing the one or more liquids, wherein the one or more cavities are together in fluid communication with each nozzle outlet and with the one or more inputs. Thus, the liquids can be stored in the one or more cavities before ejection by the droplet ejectors.

[0014] The storage portion may be removable. The storage portion may be replaceable. Thus, the liquids can be refilled easily by replacing an empty storage portion with a new, full, storage portion. Furthermore, the same apparatus can be used with multiple different liquids by replacing a first storage portion filled with a first liquid with a second storage portion filled with a second liquid. In other examples, the storage portion may be refillable. Thus, the apparatus can be re-used by refilling the storage portion. It will be appreciated that in many situations it is preferable to replace a storage portion instead of refilling the storage portion in situ, so as to ensure a protective environment is maintained (i.e. the liquids are not contaminated).

[0015] The apparatus may further comprise a housing to support the plurality of droplet ejectors. Typically, the housing provides an outer casing of the apparatus. Thus, the plurality of droplet ejectors may be considered to be in fluid communication with an external environment of the apparatus. The housing typically provides protection of internal components of the apparatus from an external environment, as well as providing a structural support on which components of the apparatus can be mounted.

[0016] The storage portion may be part of the housing. Thus, the storage portion can be held securely relative to the one or more inputs, thereby more easily maintaining fluid communication between the one or more cavities and the one or more inputs.

[0017] The apparatus may further comprise an outlet portion defining an aerosol outlet through which the aerosol can be output from the apparatus. Thus, the generated aerosol is output from the apparatus.

[0018] The outlet portion may be part of the housing. Thus, the aerosol can be conveniently output from the apparatus using a portion defined in the existing housing of the apparatus, without requiring a further, separate component.

[0019] The outlet portion may define an aerosol outlet channel to direct the aerosol to be output therefrom in a first direction out of the apparatus.

[0020] The apparatus may further comprise a power supply circuit portion. The power supply circuit portion is arranged to supply power to the piezoelectric actuator of each of the plurality of droplet ejectors. The power supply circuit portion may comprise a battery compartment arranged to receive a battery or a power supply port for connection of a power source thereto. The power supply circuit portion may comprise the power source, such as the battery. The battery may be a rechargeable battery. The apparatus may further comprise a power source to supply power to the power supply circuit portion. Thus, the apparatus can be easily moved to different locations. In some examples, the apparatus may be man-portable, such as hand-portable.

[0021] The power supply circuit portion may be supported by the housing. It may be that the power supply circuit portion is contained within the housing. Thus, protection of the power supply circuit portion can be at least partially provided by the housing.

[0022] The apparatus may further comprise a switch to activate the plurality of droplet ejectors. Thus, the plurality of droplet ejectors need only be activated when required. The switch may be user-operable or may be operated in dependence on control logic from a controller.

[0023] The switch may be a flow switch responsive to a flow through the aerosol outlet. Thus, it can be considered that the plurality of droplet ejectors may be configured to activate in response to a gas flow. The plurality of droplet ejectors may be configured to deactivate in response to cessation of the gas flow. In this way, wastage of the liquid to be aerosolised can be reduced or even entirely eliminated, as well as making it easier to determine the volume of the liquid having been provided as an aerosol.

[0024] It may be that, in a first configuration, the switch is in a first state to cause activation of the piezoelectric actuators of the droplet ejectors to thereby cause aerosol to be generated, and in a second configuration, the switch is in a second state corresponding to no aerosol being generated by activation of the piezoelectric actuators. The apparatus may be configured to cause switching of the switch between the first state and the second state in dependence on detection of gas flow. Thus, the plurality of droplet ejectors may only be activated in the presence of a gas flow. This ensures that the entirety of the generated aerosol will be entrained within the gas flow, thereby reducing excess generation of aerosol.

[0025] The apparatus may further comprise a controller. The controller is to (e.g. configured to) control operation of the plurality of droplet ejectors. The control of the operation of the plurality of droplet ejectors may be in response to a sensor input, such as a state of a switch.

[0026] The controller may comprise one or more processors and a memory configured to store instructions which when executed by the one or more processors cause the apparatus to carry out the functions of the controller described herein. The memory may be non-transitory, computer readable memory. The memory may have the instructions stored thereon. The present invention extends to a non-transitory computer-readable medium (e.g., memory) having the instructions stored thereon to control the apparatus as described herein. The memory may be solid-state memory. The controller may be provided in a single device. In other example, the controller may be distributed, having a plurality of processors. A first processor may be separated from a second processor in a distributed manner. Where the controller is distributed over multiple separate devices, the apparatus may be formed from a plurality of separate devices.

[0027] The controller may be configured to cause generation of the liquid aerosol at a plurality of discrete times in response to an activation signal (e.g. one or more activation signals). Thus, the liquid aerosol may be arranged to be delivered in bursts, as appropriate.

[0028] The activation signal (e.g. the one or more activation signals) may be received from a remote device, separate from the apparatus. Thus, the activation of the apparatus may be controlled based on a signal received from a remote device. The remote device may be a sensor device. Alternatively, the remote device may be a user-operable device.

[0029] A first contiguous subset of the plurality of discrete times may be regularly spaced. A second contiguous subset of the plurality of discrete times, immediately following the first contiguous subset may be regularly spaced. The second contiguous subset may be spaced from the first contiguous subset by more than the spacing between the first contiguous subset. Thus, the aerosol may be generated as a plurality of discretely spaced bursts.

[0030] The one or more activation signals may cause generation of the liquid aerosol discretely or continuously over a period of more than 30 minutes. The first contiguous subset of the plurality of discrete times may extend over the period of more than 30 minutes. The period may be more than 1 hour. The period may be more than 12 hours. The period may be more than 24 hours. The period may be less than 1 year. The period may be less than 6 months.

[0031] At least one of the plurality of nozzle outlets may have a maximum cross-sectional extent less than 150 × 10^-6 metres (150 microns). More than 50 percent of the plurality of nozzle outlets may have a maximum cross-sectional extent less than 150 × 10^-6 metres (150 microns). Each of the plurality of nozzle outlets may have a maximum cross-sectional extent less than 150 × 10^-6 metres (150 microns).

[0032] At least one of the plurality of nozzle outlets may have a maximum cross-sectional extent less than 100 × 10^-6 metres (100 microns). More than 50 percent of the plurality of nozzle outlets may have a maximum cross-sectional extent less than 100 × 10^-6 metres (100 microns). Each of the plurality of nozzle outlets may have a maximum cross-sectional extent less than 100 × 10^-6 metres (100 microns).

[0033] At least one of the plurality of nozzle outlets may have a minimum cross-sectional extent greater than 0.1 × 10^-6 metres (0.1 microns). More than 50 percent of the plurality of nozzle outlets may have a minimum cross-sectional extent greater than 0.1 × 10^-6 metres (0.1 microns). Each of the plurality of nozzle outlets may have a minimum cross-sectional extent greater than 0.1 × 10^-6 metres (0.1 microns).

[0034] At least one of the plurality of nozzle outlets may have a minimum cross-sectional extent greater than 1 × 10^-6 metres (1 microns). More than 50 percent of the plurality of nozzle outlets may have a minimum cross-sectional extent greater than 1 × 10^-6 metres (1 microns). Each of the plurality of nozzle outlets may have a minimum cross-sectional extent greater than 1 × 10^-6 metres (1 microns).

[0035] At least one of the plurality of nozzle outlets may have a minimum cross-sectional extent greater than 5 × 10^-6 metres (5 microns). More than 50 percent of the plurality of nozzle outlets may have a minimum cross-sectional extent greater than 5 × 10^-6 metres (5 microns). Each of the plurality of nozzle outlets may have a minimum cross-sectional extent greater than 5 × 10^-6 metres (5 microns).

[0036] At least one of the plurality of nozzle outlets may have a minimum cross-sectional extent greater than 7 × 10^-6 metres (7 microns). More than 50 percent of the plurality of nozzle outlets may have a minimum cross-sectional extent greater than 7 × 10^-6 metres (7 microns). Each of the plurality of nozzle outlets may have a minimum cross-sectional extent greater than 7 × 10^-6 metres (7 microns).

[0037] At least one of the plurality of nozzle outlets may have a cross-sectional area less than 20 × 10^-9 m² (0.02 mm²). More than 50 percent of the plurality of nozzle outlets may have a cross-sectional area less than 20 × 10^-9 m² (0.02 mm²). Each of the plurality of nozzle outlets may have a cross-sectional area less than 20 × 10^-9 m² (0.02 mm²)

[0038] At least one of the plurality of nozzle outlets may have a cross-sectional area less than 10 × 10^-9 m² (0.01 mm²). More than 50 percent of the plurality of nozzle outlets may have a cross-sectional area less than 10 × 10^-9 m² (0.01 mm²). Each of the plurality of nozzle outlets may have a cross-sectional area less than 10 × 10^-9 m² (0.01 mm²).

[0039] At least one of the plurality of nozzle outlets may have a cross-sectional area greater than 0.02 × 10^-12 m² (0.02 µm²). More than 50 percent of the plurality of nozzle outlets may have a cross-sectional area greater than 0.02 × 10^-12 m² (0.02 µm²). Each of the plurality of nozzle outlets may have a cross-sectional area greater than 0.02 × 10^-12 m² (0.02 µm²).

[0040] At least one of the plurality of nozzle outlets may have a cross-sectional area greater than 25 × 10^-12 m² (25 µm²). More than 50 percent of the plurality of nozzle outlets may have a cross-sectional area greater than 25 × 10^-12 m² (25 µm²). Each of the plurality of nozzle outlets may have a cross-sectional area greater than 25 × 10^-12 m² (25 µm²).

[0041] Typically, each of the nozzle outlets will have a substantially similar cross-sectional shape. The cross-sectional shape of the nozzle outlets may be rounded, such as circular.

[0042] It will be understood that the nozzle outlet is where the nozzle portion ejects the one or more droplets from the droplet ejector. Thus, references to the cross-sectional extent or cross-section area of the nozzle outlet refer to the region of the nozzle portion which is last in contact with the liquid to be ejected as one or more droplets before the droplet is released from the droplet ejector.

[0043] A volume of at least 90% of the one or more droplets making up the liquid aerosol may be less than 2 × 10^-12 m³. A volume of each of the one or more droplets making up the liquid aerosol may be less than 2 × 10^-12 m³. A volume of at least 90% of the one or more droplets making up the liquid aerosol may be less than 2 × 10^-15 m³. A volume of each of the one or more droplets making up the liquid aerosol may be less than 2 × 10^-15 m³.

[0044] A volume of at least 90% of the one or more droplets making up the liquid aerosol may be greater than 0.5 × 10^-21 m³. A volume of each of the one or more droplets making up the liquid aerosol may be greater than 0.5 × 10^-21 m³. A volume of at least 90% of the one or more droplets making up the liquid aerosol may be greater than 2 × 10^-18 m³. A volume of each of the one or more droplets making up the liquid aerosol may be greater than 2 × 10^-18 m³.

[0045] In some examples, a volume of at least 90% of the one or more droplets making up the liquid aerosol may be less than 0.5 × 10^-18 m³. A volume of each of the one or more droplets making up the liquid aerosol may be less than 0.5 × 10^-18 m³. A volume of at least 90% of the one or more droplets making up the liquid aerosol may be greater than 2 × 10^-15 m³. A volume of each of the one or more droplets making up the liquid aerosol may be greater than 2 × 10^-15 m³.

[0046] The plurality of droplet ejectors may be formed on a common substrate. In other words, both the nozzle portions and the piezoelectric actuators of all of the plurality of droplet ejectors may be formed on the common substrate.

[0047] Typically, the substrate has a first surface and an opposite second surface. The substrate comprises a CMOS control circuit, a plurality of layers on the first surface of the substrate, the piezoelectric actuator being formed by one or more said layers and the nozzle portion defining a hole (e.g. the nozzle outlet) through the one or more said layers, such that the piezoelectric actuator displaces the one or more said layers and the nozzle portion in use to thereby eject droplets. Thus, the droplet ejectors are typically configured to eject droplets in an inertial mode. It may be that the hole extends through the piezoelectric actuator.

[0048] The piezoelectric actuator typically operates to cause displacement of a resiliently deformable membrane defining at least a portion of the nozzle outlet in such a way as to cause ejection of the droplets from said nozzle portion on operation of said actuator. In this way, it can be considered that the resiliently deformable membrane is part of the nozzle portion.

[0049] In this way, typically the piezoelectric actuator is coupled to the respective nozzle portion. Thus, deformation of the piezoelectric actuator during use leads to movement of a region of the nozzle portion, in turn causing ejection of the droplets from the nozzle outlet. Typically, the resiliently deformable membrane comprises the piezoelectric actuator and defines at least a region of the nozzle portion. Thus, the resiliently deformable membrane defines at least part (e.g., a wall) of a chamber in fluid communication with the nozzle outlet. Typically, the piezoelectric actuator is disposed adjacent to, for example around, the nozzle outlet. Typically, actuation of the piezoelectric actuator deflects the resiliently deformable membrane, which defines the nozzle outlet. Thus, the resiliently deformable membrane and nozzle portion move in use to eject droplets from within the chamber out through the nozzle outlet. Typically, the apparatus comprises a nozzle-defining layer formed on the substrate, the nozzle-defining layer comprising the piezoelectric actuator and defining the nozzle outlet. The nozzle-defining layer typically comprises at least one piezoelectric layer and one or more electrodes in electrical contact with the at least one piezoelectric layer.

[0050] In other possible arrangements, the piezoelectric actuator is in distal association with the nozzle outlet, and/or the nozzle outlet and piezoelectric actuator are on different walls of the chamber (e.g. the nozzle outlet is on one wall of the fluid chamber, and the actuator is on the opposing wall of the same chamber such that the piezoelectric actuator is far away from the nozzle outlet). Where the piezoelectric actuator is not coupled to the nozzle outlet/is away from the nozzle outlet requires a large actuation force to compress almost the entire liquid stored in the chamber in order to eject the droplets through the nozzle outlet. This operation thus depends upon compressibility mode. By contrast, the use of the inertial mode avoids disturbing the majority of the liquid in the chamber, and only requires a small actuation force to displace the liquid in the nozzle outlet. The liquid is then ejected as a droplet mainly by inertial force (i.e. inertial ejection) from the nozzle outlet. Herein, ejection by inertial force can also be referred to as inertial ejection or ejection by inertial mode. Where the piezoelectric actuator is coupled to the respective nozzle portion, ejection of the liquid (from the respective nozzle) is permitted by inertial mode instead of by compressibility mode.

[0051] It will be understood that ejection by inertial mode (i.e. inertial ejection) has a number of closely associated benefits. It permits the use of low-temperature processable piezoelectric materials having lower piezoelectric constants (i.e. piezoelectric materials which are processable below 450 degrees Celsius or below 300 degrees Celsius) since only a small actuation force is initially required. The small force exerted by a piezoelectric actuator comprising low-temperature processable piezoelectric materials gives relatively low fluid pressure such that an acoustic cross talk problem (i.e. neighbouring actuators and fluid chambers interact with one another through pressure waves in the fluid) is partially or even completed mitigated. Lower levels of acoustic cross talk in turn permit close integration of neighbouring ejectors for a compact configuration of the apparatus.

[0052] It may be that all of the plurality of droplet ejectors for the apparatus are provided on a single droplet ejector chip, for example on a single substrate.

[0053] The nozzle portion and the piezoelectric actuator for each droplet ejector may be formed together by fabrication.

[0054] The apparatus may further comprise driving circuitry to control operation of the piezoelectric actuator responsive to control signals received thereat. Thus, the piezoelectric actuators can be individually activated by the driving circuitry. The driving circuitry may be fabricated at least partially with the piezoelectric actuators. Thus, costs of manufacture for the apparatus can be advantageously constrained because the multiple components required to both provide and allow control of the plurality of droplet ejectors can be formed together, rather than each droplet ejector needing to be formed separately, or the driving circuitry needing to be separately attached to a pre-formed plurality of droplet ejectors.

[0055] The plurality of droplet ejectors may be at least four droplet ejectors. The plurality of droplet ejectors may be at least 25 droplet ejectors. The plurality of droplet ejectors may be at least 100 droplet ejectors. The plurality of droplet ejectors may be at least 500 droplet ejectors. The plurality of droplet ejectors may be fewer than 10,000 droplet ejectors. The plurality of droplet ejectors may be fewer than 1,000 droplet ejectors. Thus, aerosols having relatively high densities of droplets can be generated.

[0056] The plurality of droplet ejectors may be arranged such that the nozzle outlets are provided in a grid arrangement. Thus, the generated droplets have a distribution which is particularly simple to predict, making it simpler to generate aerosols having a desired set of properties, such as droplet density.

[0057] It may be that the plurality of droplet ejectors are arranged such that the nozzle outlets are provided in a regular arrangement. The plurality of droplet ejectors may define a substantially rectilinear arrangement, such as a rectangular or square arrangement. In some examples, the plurality of droplet ejectors may define a substantially quadrilateral arrangement, such as arranged substantially in a parallelogram.

[0058] The apparatus further comprises a signal generator configured to generate a driving signal having a repeating waveform, and driving circuitry configured to relay the driving signal to the piezoelectric actuators via a plurality of switches and to control the plurality of switches to selectively apply the driving signal to individual piezoelectric actuators to thereby eject droplets of the liquid. It may be that the driving signal can be determined so as to cause the piezoelectric actuators to eject droplets of different volumes and/or velocities as indicated by control signals.

[0059] Suitably, the driving circuitry configured to relay the driving signal is comprised in the apparatus. In other words, the driving circuitry can be part of the apparatus. Furthermore, the complexity of wiring connections in the apparatus can be reduced, because separate control wiring to each piezoelectric actuator need only be provided from the driving circuitry, rather than being provided into the apparatus; the control instructions for any piezoelectric actuators in a apparatus can be provided to the apparatus via a single wiring connection to the driving circuitry on the apparatus (should these need to be externally received).

[0060] The driving circuitry may comprise a CMOS circuit (i.e. a complementary metal oxide semiconductor) and a plurality of circuit elements each associated with a droplet ejector.

[0061] The driving circuitry may be integrally formed with the nozzle portions. In other words, formation of the driving circuitry, the nozzle portions and (optionally) the piezoelectric actuators can be provided at the same time, without requiring assembly of multiple component parts assembled separately. By providing the driving circuitry using an integrated circuit, the driving circuitry can be provided adjacent the nozzle portions, thereby ensuring the apparatus is compact.

[0062] It may be that the driving circuitry comprises (a) a digital register. It may be that the driving circuitry comprises (b) a voltage trimming calculation circuit and/or register. It may be that the driving circuitry comprises (c) a temperature measurement circuit. It may be that the driving circuitry comprises (d) a fluid chamber fill detection circuit.

[0063] The digital register may be a shift register, or a latch register, for example. In operation, it may be that data is stored in or read from a register within the driving circuitry. In operation, it may be that temperature is measured using a temperature sensitive component of the temperature measurement circuit. In operation, it may be that the fill level of a fluid chamber is measured.

[0064] It may be that the driving circuitry is configured to modify the voltage pulses applied to one or more electrodes of one or more piezoelectric actuators responsive to data stored by the driving circuitry or measurements from one or more sensors, which are typically within the apparatus. In operation, it may be that the driving circuitry measures the voltage pulses applied to one or more electrodes of one or more piezoelectric actuators responsive to data stored by the driving circuitry or measurements from one or more sensors, which are typically within the apparatus.

[0065] Modifying the voltage pulses may comprise shifting them in time. Modifying the voltage pulses may comprise compressing or expanding them. Modifying the voltage pulses may comprise modifying their magnitude. Modifying the voltage pulses may comprise swapping between a plurality of (typically repeating) sequences of received actuator drive pulses with different profiles. The driving circuitry is typically configured to modify the voltage pulses applied to one or more electrodes of one or more individual piezoelectric actuators responsive to data relating to that individual piezoelectric actuator stored by the driving circuitry or measurements from one or more sensors.

[0066] The driving circuitry comprises a plurality of circuit elements each associated with a droplet ejector. The circuit element can be an ejection transistor. The ejection transistor is typically in direct electrical communication (without intervening switched semiconductor junction) with an electrode of the piezoelectric actuator. In operation, it may be that the ejection transistor is controlled to cause a potential output from the ejection transistor to be applied directly to an electrode of the piezoelectric actuator.

[0067] The driving circuitry may be configured to receive input control signals from outside the plurality of droplet ejectors, such as from outside the apparatus and to output actuator control signals to each of the plurality of actuators to control ejection of the droplets from the plurality of nozzle outlets.

[0068] It may be that the apparatus further comprises an electrical input for receiving actuator drive pulses. In operation, the apparatus may receive actuator drive pulses.

[0069] The apparatus may comprise a controller for controlling the apparatus. The controller may comprise one or more microcontrollers or microprocessors, which may be integrated or distributed, in communication with or comprising a memory storing program code.

[0070] It may be that the controller comprises a signal generator configured to generate (typically a sequence of) actuator drive pulses. Each apparatus typically comprises an electrical input connected to the controller through which the actuator drive pulses are received. In operation, an apparatus assembly may generate actuator drive pulses (e.g. in a controller) and conduct them to the apparatus through an electrical connection.

[0071] The actuator drive pulses are typically analogue signals. The actuator drive pulses typically comprise periodic repeating voltage waveforms.

[0072] It may be that the driving circuitry is configured to switchedly connect or disconnect at least one electrode of the or each of a plurality of piezoelectric actuators to the received actuator drive pulses to thereby selectively actuate the piezoelectric actuators. In operation, it may be that the apparatus switchedly connects or disconnects at least one electrode of the or each of a plurality of piezoelectric actuators to the received actuator drive pulses to thereby selectively actuate the piezoelectric actuators.

[0073] It may be that the controller comprises one or more pulse generators which generate a plurality of sequences of actuator drive pulses, and electrical inputs of the plurality of droplet ejectors receive the plurality of sequences of actuator drive pulses (generated by the one or more pulse generators) through a plurality of electrical connections to the controller, and the driving circuitry is configured to switchedly connect or disconnect at least one electrode of the or each of a plurality of piezoelectric actuators to received actuator drive pulses selected from a plurality of different received sequences of actuator pulses. In operation, it may be that the apparatus generates a plurality of different sequences of actuator drive pulses (e.g. in a controller) and conducts them to the plurality of droplet ejectors through separate electrical connections, and switchedly connects or disconnects at least one electrode of the or each of a plurality of piezoelectric actuators to one or more received actuator drive pulses received from a variable (and selectable) one of the plurality of different sequences of actuator drive pulses.

[0074] The selection as to which received sequence of actuator pulses at least one electrode of piezoelectric actuator is connected to may be responsive to stored data specific to the respective piezoelectric actuator and/or responsive to measurements of operation of the respective piezoelectric actuator. Accordingly, the driving circuitry can typically select whether or not each piezoelectric actuator ejects a droplet at each of a sequence of periodic droplet ejection decision points. By a decision point we refer to a time prior to the start of an actuator drive pulses where it is determined whether or not to communicate that actuator drive pulse to at least one electrode of a specific piezoelectric actuator.

[0075] Typically, the actuator drive pulses repeat periodically. It may be that the actuator drive pulses are amplified by the controller. It may be that the actuator drive pulses are not amplified by the apparatus. It may be that the apparatus does not generate actuator drive pulses.

[0076] Typically, pulses from the pulse generator are conducted to a plurality of control circuits. Thus a single pulse generator circuit may drive multiple piezoelectric transducers on the same substrate.

[0077] The digital actuation control signals are typically received from a controller. The digital actuation control signals are typically received through one or more flexible connectors. The digital actuation control signals may be received in serial form and converted to parallel control signals using a shift register within the driving circuitry.

[0078] It may be that the controller comprises a pulse generator configured to generate actuator drive pulses which are conducted to the plurality of droplet ejectors and digital control signals which are conducted to the plurality of droplet ejectors and the digital control signals are processed in the driving circuitry of the apparatus to determine which actuator drive pulses are conducted to at least one electrode of the piezoelectric actuators of the plurality of droplet ejectors to cause droplet ejection.

[0079] In operation, it may be that the apparatus generates actuator drive pulses (e.g. at a controller) and digital control signals, and conducts both the actuator drive pulses and the digital control signals to the driving circuitry of the apparatus and the driving circuitry processes the digital control signals and, responsive thereto, conducts selected actuator drive pulses to at least one electrode of the piezoelectric actuators of the plurality of droplet ejectors to cause droplet ejection.

[0080] Thus, typically analogue actuator drive pulse and digital control signals are input by the driving circuitry. Typically the digital control signals are used to selectively switch the analogue actuator drive pulses to thereby selectively transmit them to the piezoelectric actuators.

[0081] In some embodiments, the driving circuitry is configured to switchedly connect one or more of ground and a single fixed non-zero voltage line, or multiple fixed voltage lines of different voltages (one or more of which may be ground) to one or both electrodes of a piezoelectric actuator to cause droplet ejection of liquid. For example, the driving circuitry may switch an electrode between a connection to ground and a connection to a fixed voltage or multiple fixed voltage lines of different voltages and back to ground again in order to cause a droplet ejection.

[0082] Switching an electrode between a connection to ground and a connection to a fixed voltage or between fixed voltage lines may comprise operating a latch.

[0083] It may be that the driving circuitry is configured to individually and selectively actuate at least double the number of piezoelectric actuator elements than signal conductors through which the driving circuitry receives actuation control signals.

[0084] It may be that the said driving circuitry is configured to individually and selectively actuate at least 128 (or at least 256) piezoelectric actuator elements and the driving circuitry receives actuation control signals through at most 64 (or at most 32) signal conductors.

[0085] The driving circuitry may comprise a serial to parallel conversion circuit configured to convert a digital signal received in serial form through one or more signal conductors into a selection of piezoelectric actuators to be actuated to carry out a droplet ejection simultaneously (i.e. in parallel). The serial to parallel conversion circuit typically comprises one or more shift registers.

[0086] A one of the one or more liquids may be a non-aqueous solution. In other words, at least one of the one or more liquids may comprise a liquid other than water. It may be that each of the one or more liquids is a non-aqueous solution.

[0087] The apparatus may be fixedly mounted to a support member. It may be that the apparatus is fixedly mounted inside a reaction chamber, or on a wall of a building.

[0088] The apparatus may be an industrial apparatus. It will be understood that an industrial apparatus is an apparatus for use in an industrial process, such as a chemical reaction process. It will be understood that an industrial process is typically any process for manufacturing an item (e.g. a product or a material). Typically, industrial processes are carried out on a large scale.

[0089] The power supply may be a mains power supply. Thus, the apparatus need not be battery powered.

[0090] The apparatus may comprise an airflow generator for entraining the generated aerosol therein and conveying the aerosol away from the apparatus. The airflow generator may be a fan.

[0091] In one example, the aerosolising apparatus may be an air freshener.

[0092] The present disclosure further extends to a liquid adapted for use with the apparatus described herein. The disclosure extends to a refill capsule for use with the apparatus described herein. The refill capsule may comprise the liquid.

[0093] The present disclosure also extends to a method of controlling an apparatus for aerosolising a liquid as described herein. The apparatus is substantially as described hereinbefore. The method comprises: receiving a control signal indicative of a demand to start aerosolisation; and causing ejection of a plurality of droplets of liquid from the apparatus. The ejection of the plurality of droplets is caused by activation of the plurality of droplet ejectors, for example, by applying the driving waveform described herein (or another driving waveform) to the piezoelectric actuators of a plurality of the plurality of droplet ejectors. In another aspect, the present disclosure can also further be considered to extend to a method of aerosolising a liquid, using an apparatus as described herein.

Description of the Drawings

[0094] An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

Figures 1 and 2 show a perspective view and a cross-sectional view respectively of an apparatus for aerosolising a liquid in accordance with an embodiment of the present invention;

Figure 3 shows a perspective view of an aerosoliser chip in accordance with an embodiment of the present invention;

Figure 4 shows a top-down view of a portion of the aerosoliser chip of Figure 3, focusing on a subset of the plurality of droplet ejectors of the aerosoliser chip of Figure 3;

Figure 5 shows a perspective cross-sectional view of one of the droplet ejectors shown in Figure 4;

Figure 6 is a schematic diagram showing an arrangement of a piezoelectric actuator, nozzle portion and driving circuitry as disclosed herein;

Figures 7(a) and 7(b) show actuator states for a piezoelectric actuator as used in an example of the present invention;

Figure 8 shows a possible drive waveform for driving a piezoelectric actuator in accordance with an example of the present invention;

Figure 9 shows a simplified manufacturing process flow for forming a droplet ejector in accordance with an example of the present invention;

Figure 10 shows a system diagram for an apparatus for aerosolising a liquid according to an example of the present invention; and

Figure 11 shows a flowchart illustrating a method of operating an apparatus for aerosolising a liquid according to an example of the present invention.

Detailed Description of an Example Embodiment

[0095] Figure 1 shows a perspective view of an apparatus for aerosolising a liquid in accordance with an embodiment of the present invention. Figure 2 shows a cross-sectional view of the apparatus shown in Figure 1. The apparatus 100 comprises a housing 102 enclosing internal components of the apparatus 100. The housing 102 comprises a front portion 104 in the form of a front side wall 104, and an upper portion 106. The upper portion 106 of the housing 102 is movable (specifically, removable) relative to the front portion 104 of the housing so as to expose an opening of a cavity 110 (best illustrated in Figure 2). The cavity 110 can receive and store a liquid therein for supplying an input of the apparatus 100. The apparatus 100 is further provided with an aerosol outlet 108. The aerosol outlet 108 is defined by an aerosol outlet wall 109 extending inwardly within the housing 102 from an opening defined by the front portion 104 of the housing 102 and is in fluid communication with the external environment therethrough.

[0096] The aerosol outlet 108 is in fluid communication with the cavity 110 via a droplet ejector portion 112. As shown in Figure 2, the droplet ejector portion 112 comprises a liquid channel 124 directing liquid from the cavity 110 towards a aerosoliser chip 126 comprising a plurality of droplet ejectors (also part of the droplet ejector portion 112, though not shown in Figures 1 and 2). On operation of the plurality of droplet ejectors, a plurality of droplets is generated from the liquid in the cavity 110 and the liquid channel 124 and are ejected into the aerosol outlet 108. The plurality of droplet ejectors is described further with reference to further Figures hereinafter.

[0097] The apparatus 100 further comprises control circuitry 114 configured to provide control signals to the plurality of droplet ejectors to control aerosolisation thereby. The control circuitry typically comprises a circuit board 115 on which electronic components are mounted, including a processor 116 in the form of a microprocessor 116, such as an integrated circuit chip 116. The control signals for the plurality of droplet ejectors are communicated from the control circuitry 114 via a wired connection 118. As will be described further hereinafter, the aerosoliser chip 126 may itself include further control circuitry to convert the control signals received from the control circuitry 114 via the wired connection 118, into individual control signals to directly control each respective droplet ejector. Specifically, it may be that each droplet ejector comprises a dedicated control circuit such that a plurality of control circuits is provided on the aerosoliser chip 126.

[0098] The apparatus 100 further comprises a switch 120 mounted on the front portion 104 of the housing 102, and an external electrical connector 122 also mounted on the housing 102. Although not shown, the switch 120 and the electrical connector 122 are each electrically connected to the control circuitry 114.

[0099] It will be understood that one or more gas inlets (not shown) will be provided at the aerosol outlet wall 109and in fluid communication with the external environment. In this way, a gas can flow through the aerosol outlet 108 as will be described further hereinafter.

[0100] The operation of the apparatus 100 to produce a liquid aerosol will now be described. For a pre-filled apparatus 100, having liquid provided in the cavity 110, the apparatus 100 is oriented such that the liquid is able to enter the droplet ejector portion 112 via the liquid channel 124 such that the liquid is in contact with a side of the aerosoliser chip 126 exposed to the liquid channel 124. The apparatus 100 is activated via electrical switch 120 to cause operation of the control circuitry 114 in an operating configuration. In the operating configuration, the control circuitry 114 communicates control signals to the plurality of droplet ejectors to cause them to eject a plurality of droplets of the liquid into the aerosol outlet 108. A flow of gas is supplied through the aerosol outlet 108 via the one or more air inlets. Droplets of the liquid aerosol, ejected into the aerosol outlet 108 from the plurality of droplet ejectors, are entrained within the gas flow, and therefore travel from the aerosol outlet 108 into the external environment.

[0101] The apparatus 100 can then be deactivated using the switch 120.

[0102] It will be understood that the control signals sent from the control circuitry 114 to the aerosoliser chip 126 may be determined based on a desired regimen for the liquid stored within the cavity 110. The desired regimen (or data indicative thereof) is typically communicated to the control circuitry 114 via the electrical connector 122. The apparatus 100 shown in Figures 1 and 2 is refillable, though it will be understood that non-refillable (i.e. single use) versions may also be desirable in certain applications. To refill the liquid in the apparatus 100, the upper portion 106 of the housing 102 is partially or even fully removed to allow further liquid to be added to the cavity 110.

[0103] Figure 3 shows a perspective view of an aerosoliser chip in accordance with an embodiment of the present invention. Figure 4 shows a top-down view of a portion of the aerosoliser chip of Figure 3, focusing on a subset of the plurality of droplet ejectors of the aerosoliser chip of Figure 3. Figure 5 shows a perspective cross-sectional view of one of the droplet ejectors shown in Figure 4. The aerosoliser chip 226 shown in Figures 3 to 5 is an example of the aerosoliser chip 126 of Figures 1 and 2.

[0104] The aerosoliser chip 226 comprises a substrate 240 in the form of a silicon substrate 240 with a plurality of droplet ejectors 242 situated thereon. The plurality of droplet ejectors 242 are arranged in a plurality of rows, including a first row 244 and a second row 246. Each row is parallel to each and every other row, and is mutually aligned, such that the plurality of rows of droplet ejectors 242 are arranged in a rectangular grid.

[0105] The aerosoliser chip 226 further comprises a plurality of lower portion bond pads 248 arranged in a line running perpendicular to the rows of the plurality of droplet ejectors 242 and situated adjacent to the plurality of droplet ejectors 242 on a first side thereof to communicate control signals between the plurality of droplet ejectors 242 and further control circuitry located separate to the aerosoliser chip 226 (not shown in Figure 3). The aerosoliser chip 226 further comprises a plurality of upper portion bond pads 250 arranged in a line running parallel to the plurality of lower portion bond pads 248 and situated adjacent to the plurality of droplet ejectors 242 on a second side thereof. The plurality of upper portion bond pads 250 are spaced from the plurality of lower portion bond pads 248. The plurality of upper portion bond pads 250 are to communicate control signals between the plurality of droplet ejectors 242 and further control circuitry located separate to the aerosoliser chip 226 (not shown in Figure 3). The first and second sides are opposite to one another such that the rows of the plurality of droplet ejectors 242 extend from the first side to the second side. The plurality of lower portion bond pads 248 includes a first lower portion bond pad 252 to communicate control signals to the first two rows 244, 246 of the plurality of droplet ejectors 242 and the further control circuitry located separate to the aerosoliser chip 226 (not shown in Figure 3). The plurality of upper portion bond pads 250 comprises a first upper portion bond pad 254 to communicate control signals between the first two rows 244, 246 of the plurality of droplet ejectors 242 and the further control circuitry located separate to the aerosoliser chip 226 (not shown in Figure 3).

[0106] The aerosoliser chip 226 further comprises a plurality of lower portion interconnects 258 extending between the plurality of lower portion bond pads 248 and the plurality of droplet ejectors 242 and providing electrical communication therebetween. In this way, control signals and/or power signals received at the plurality of lower portion bond pads 248 can be communicated to the plurality of droplet ejectors 242. Similarly, feedback signals from the plurality of droplet ejectors 242 can be communicated to the plurality of lower portion bond pads 248 via the plurality of lower portion interconnects 258. The plurality of lower portion interconnects 258 comprises a first lower portion interconnect 260 extending between the first lower portion bond pad 252 and the first and second rows 244, 246 of the plurality of droplet ejectors 242. The first lower portion interconnect 260 comprises a trunk portion 260A extending from the first lower portion bond pad 252, a first branch portion 260B extending from the aforementioned trunk portion 260A to the first row 244 of the plurality of droplet ejectors 242, and a second branch portion 260C extending from the aforementioned trunk portion 260A to the second row 246 of the plurality of droplet ejectors 242.

[0107] The aerosoliser chip 226 further comprises a plurality of upper portion interconnects 262 extending between the plurality of upper portion bond pads 250 and the plurality of droplet ejectors 242 and providing electrical communication therebetween. In this way, control signals and/or power signals received at the plurality of upper portion bond pads 250 can be communicated to the plurality of droplet ejectors 242. Similarly, feedback signals from the plurality of droplet ejectors 242 can be communicated to the plurality of upper portion bond pads 250 via the plurality of upper portion interconnects 262. The plurality of upper portion interconnects 262 comprises a first upper portion interconnect 264 extending between the first upper portion bond pad 254 and the first and second rows 244, 246 of the plurality of droplet ejectors 242 providing electrical communication therebetween. The first upper portion interconnect 264 comprises a trunk portion 264A extending from the first upper portion bond pad 254, a first branch portion 264B extending from the aforementioned trunk portion 264A to the first row 244 of the plurality of droplet ejectors 242, and a second branch portion 264C extending from the aforementioned trunk portion 264A to the second row 246 of the plurality of droplet ejectors 242.

[0108] The second row 246 of the plurality of droplet ejectors 242 comprises a droplet ejector 270 comprising an actuator portion 272 (best illustrated in Figures 4 and 5) in electrical communication with the second branch portion 260C of the first lower portion interconnect 260 via a lower portion metallisation contact 274 of the droplet ejector 270 and in electrical communication with the second branch portion 264C of the first upper portion interconnect 264 via an upper portion metallisation contact 276 of the droplet ejector 270. The droplet ejector 270 further comprises an outer passivation layer 278 encasing the actuator portion 272 and providing electrical stability thereto. The lower and upper portion metallisation contacts 274, 276 are in electrical communication with the actuator portion 272 via apertures in the outer passivation layer 278 through which the lower and upper portion metallisation contacts 274, 276 extend.

[0109] The actuator portion 272 comprises a lower electrode 280 in electrical communication with the lower portion metallisation contact 274 and an upper electrode 282 in electrical communication with the upper portion metallisation contact 276 such that a potential difference can be applied across a piezoelectric layer 284 situated therebetween to cause contraction or expansion thereof, whereby to cause actuation of the actuator portion 272 in a direction transverse to a plane of the piezoelectric layer.

[0110] The droplet ejector 270 is formed upon a foundational passivation layer 286 in the form of a nozzle-defining layer 286, which defines the inner portion of a nozzle outlet 290. The external portion of the nozzle outlet 290 is defined by a protective front surface 288, provided to cover and protect the droplet ejector 270 and abutting against a surface 286A of the foundational passivation layer 286.

[0111] A droplet ejector cavity 292 is defined within the droplet ejector 270, in fluid communication with the nozzle outlet 290. As will be described further hereinafter with reference to Figure 6, in operation, liquid in the droplet ejector cavity 292 is expelled out of the nozzle outlet 290 on operation of the droplet ejector 270.

[0112] Figure 6 is a schematic diagram showing an arrangement of a piezoelectric actuator, nozzle portion and driving circuitry for a droplet ejector to be used in embodiments of the present disclosure. Although Figure 6 is substantially schematic, it will be understood that the features and operation of the droplet ejector are equally applicable to the examples described previously with reference to Figures 3 to 5 apart from those described differently hereinafter, unless inherently incompatible therewith. The droplet ejector 301 shown in Figure 6 comprises a silicon substrate 340 comprising driving circuitry 330 on the first surface 340A of the silicon substrate 340. The driving circuitry 330 is for receiving control signals and generating driving signals to control operation of the piezoelectric actuator. The driving circuitry 330 is typically an integrated circuit 330 in the form of a CMOS circuit 330. The person skilled in the art will appreciate that a CMOS circuit comprises both doped regions of the substrate and metallisation layers and interconnections formed on the first surface of the substrate. A plurality of layers shown generally as 332 are formed on the first surface 340A of the silicon substrate 340. Layer 332 is the CMOS metallisation layer and comprises metal conductive traces and a passivation insulator such as SiO₂, SiN, SiON. The droplet ejector 301 further comprises an actuator portion 372 in the form of a piezoelectric actuator 372 comprising a piezoelectric layer 384 which in this example is formed of AIN or ScAIN but may be formed of another suitable piezoelectric material which is processable at a temperature of below 450°C. The piezoelectric actuator 372 forms a diaphragm with layers of materials such as silicon, silicon oxide, silicon nitride or derivatives thereof and has a passivation layer 386 (sometimes referred to as a nozzle outlet defining layer 386 or referred to as a nozzle plate 386) which prevents applied electrical potentials from contacting liquid.

[0113] At least one metallisation layer 332 includes interconnects conducting signals from an external controller via a bond pad 352 to a first portion 330A of the driving circuitry 330 and from second and third portions 330B, 330C of the driving circuitry 330 to the piezoelectric actuator 372 via electrical interconnects 360, in particular to lower electrodes 380 and upper electrodes 382 arranged to apply an electrical potential difference across and thereby actuate the piezoelectric layer 384. An opening 384A is defined in the piezoelectric layer 384 for passage of the electrical interconnect 360 between the third portion 330C of the driving circuitry 330 and the upper electrode 382.

[0114] The piezoelectric actuator 372 and accompanying nozzle outlet defining layer 386 defines a wall of a droplet ejector cavity 392 in the form of a liquid chamber 392 which receives liquid through a liquid chamber inlet 394 in fluid communication with at least one of the one or more inputs described hereinbefore. The liquid chamber 392 is further in fluid communication with a nozzle outlet 390 for ejecting liquid. The piezoelectric actuator 372 and the nozzle outlet defining layer 386 further define a wall of the nozzle outlet 390. The liquid chamber inlet 394 forms at least part of a liquid manifold providing a liquid communication pathway between a cavity (not shown in Figure 6) and the nozzle outlet 390 (as well as, in typical examples, further nozzle outlets, not shown in Figure 6), via the liquid chamber 392. The liquid chamber inlet 394 is defined by the silicon substrate 340, the metallisation layer 332 and the nozzle outlet defining layer 386. A protective front surface 388 provides the external surface of the droplet ejector 301, provided to cover and protect the piezoelectric actuator 372, and abutting against a surface 386A of the nozzle outlet defining layer 386. The protective front surface 388 has apertures which define the nozzle outlet 390 (as well as further nozzle outlets, not shown in Figure 6). The piezoelectric actuator 372, liquid chamber 392 and nozzle outlet 390 together form the droplet ejector 301.

[0115] Typically, the CMOS control circuit comprises patterned regions of doped silicon and metallisation layers. The number of metallisation layers depends on the complexity of the CMOS control circuit, but three layers should suffice for many applications.

[0116] Although only one nozzle outlet 390 and piezoelectric actuator 372 is shown in Figure 6 for clarity, it will be understood that a plurality of nozzle outlets 390 and corresponding piezoelectric actuators 372 are typically provided together as a plurality of droplet ejectors, but on the same substrate 340. Each piezoelectric actuator 372 is configured to control ejection of liquid from the respective nozzle outlet 390.

[0117] The droplet ejector 301 of Figure 6 ejects liquid through the nozzle outlet 390. The piezoelectric actuator 372 is in the nozzle outlet defining layer 386 which moves with the nozzle outlet 390. Thus, the surface of the liquid chamber 392 that includes the nozzle outlet 390 is the surface that moves during actuation. This contrasts with devices in which the surface that includes the nozzle outlet does not move and another surface, e.g., the opposite surface, is actuated. As a result, only a small actuation force is required to displace the liquid in the nozzle outlet portion. The liquid is then ejected mainly by inertial force (i.e. inertial ejection) from the nozzle outlet. Herein, ejection by inertial force can also be referred to as inertial ejection or ejection by inertial mode. The ejection of the liquid is dictated predominantly by the density and viscosity of the liquid - not by compressibility as would be the case if another surface was actuated and the liquid in the chamber was displaced as a whole in order to cause the ejection.

[0118] In use, the droplet ejector 301 is mounted on a support including a liquid manifold that supplies liquid to the liquid chamber inlet 394. Fluid pressure is typically slightly negative at the liquid chamber inlet 394 and the liquid chamber 392 typically "primes" or fills with liquid by surface tension driven capillary action. The nozzle outlet 390 primes up to the outer surface of the protective front surface 388 due to capillary action once the liquid chamber 392 is primed. The liquid does not move onto the outer surface of the protective front surface 388 past the nozzle outlet 390 due to the combination of negative fluid pressure and the geometry of the nozzle outlet 390.

[0119] The second and third portions 330B, 330C of the driving circuitry 330 control the application of a voltage pulse to the lower electrode 380 and upper electrode 382, respectively, according to a timing signal from the first portion 330A of the driving circuitry 330. The application of electrode voltage across the piezoelectric layer 384 creates an electric field. The application of this electric field causes a deformation of the piezoelectric layer 384. The deformation can either be tensile or compressive strain depending on the orientation of the electric field with respect to the direction of polarisation in the piezoelectric material. The induced strain caused by the expansion or contraction of the piezoelectric layer 384 induces a strain gradient through the thickness of the nozzle plate 386, piezoelectric actuator 372 and the protective front surface 388 causing a movement or displacement in a direction parallel to an axis defined by the nozzle outlet 390.

[0120] The piezoelectric properties of the piezoelectric material can be characterized in part by the transverse piezoelectric constant d₃₁. d₃₁ is the particular component of the piezoelectric coefficient tensor which relates the electric field applied across the piezoelectric material in a first direction to the strain induced in the piezoelectric material along a second direction perpendicular to said first direction. The piezoelectric actuator 372 shown is configured such that the applied electric field induces a strain in the material in a direction perpendicular to the direction in which the field is applied and is therefore characterized by the d₃₁ constant.

[0121] The application of a DC or constant electric field can cause a net positive or negative displacement of the nozzle plate 386. A positive displacement of the nozzle plate is shown in Figure 7(a).

[0122] The application of a pulsed electric field can cause an oscillation of the nozzle plate 386. This oscillation of the nozzle plate 386 induces a pressure in the liquid chamber 392 under the nozzle plate 386 which causes droplet ejection out of the nozzle outlet 390. The frequency and amplitude of the oscillation of the nozzle plate 386 is primarily a function of the mass and stiffness characteristics of the nozzle plate 386, the piezoelectric actuator 372, and the protective front surface 388, the properties of the liquid (for example, the density, viscosity (either Newtonian or non-Newtonian), and surface tension), the geometries of the nozzle outlet 390 and the liquid chamber 392, and the configuration of the drive pulses to the piezoelectric actuators.

[0123] Figures 7(a) and 7(b) show movement of a piezoelectric actuator. Voltage pulses are applied across lower electrode 380 and upper electrode 382 to cause the movements shown. The electric field direction is labelled as E and the deflection is labelled as X.

[0124] The application of a steady state or DC electric field across the electrodes causes a contraction in the piezoelectric layer 384 and a steady state deflection of the nozzle plate 386 away from the liquid chamber inlet 394 as shown in Figure 7(a). The fluid pressure under the nozzle plate 386 is the same as the supply pressure from the liquid chamber inlet 394. Strain energy is stored in the nozzle plate 386, the piezoelectric actuator 372 and the protective front surface 388.

[0125] Subsequently, the electric field is removed, and a reverse electric field pulse is applied. This causes both a release of the stored strain energy and the application of additional expansion of the piezoelectric material of piezoelectric layer 384. The piezoelectric actuator 372 moves towards the liquid chamber inlet 394 as shown in Figure 7(b). This causes a positive pressure in the liquid chamber inlet 394 and nozzle region which causes droplet ejection out of the nozzle outlet 390. The reverse electric field pulse may come immediately after the removal of the DC pulse or at a slightly delayed duration.

[0126] The final removal of the electric field across the piezoelectric layer 384 causes the nozzle plate 386 to return to a position with no induced strain.

[0127] The control of two electrodes for any nozzle-actuator-nozzle plate in the device facilitates directional switching of the applied electric fields in relation to the inherent polarisation of the piezoelectric material. This allows the device to incorporate stored strain energy into the nozzle plate 386 and piezoelectric actuator 372 structure. The release and integration of this stored strain energy augments volumetric displacements during a nozzle plate droplet ejection oscillation. The increased volumetric displacement is achieved without having to increase applied voltages and electric fields.

[0128] It is also possible to replace the DC electric field configuration described hereinbefore with a pulse field configuration. This has the advantage of minimizing any applied strain effects over longer durations. An additional advantage of the dual pulsed approach is enabled by the timing of the field pulse switching application. The application of the first pulse will induce an oscillation with an initial nozzle plate movement away from the liquid inlet as shown in Figure 7(a). This oscillation will introduce a negative fluid pressure under the nozzle plate which introduces a net liquid flow towards the nozzle which can additionally augment the liquid ejection flows through the nozzle.

[0129] Figure 8 shows a possible drive waveform for use in driving the piezoelectric actuators described herein. The x-axis is time (in microseconds, µs), the right y-axis is the amplitude of the signal (in volts, V), and the left y-axis is the resulting displacement of the piezoelectric actuator (in micrometres, µm). The signal has an initial voltage of 0 V at point A and is initially raised to a positive potential difference peaking at point B (to cause deformation of the piezoelectric actuator in one direction), and then lowered to a negative potential difference having a trough at point C (to cause greater deformation of the piezoelectric actuator in the opposite direction). The signal is further returned to a positive potential difference having a peak at point D, before being lowered and held at a magnitude of around 35 V for approximately 1.2 µs between point E and point F. Subsequently, the signal is lowered back to 0 V at point G, and held there, as shown in point H. The use of a driving waveform of this shape causes displacement of the actuator as depicted by the broken line of Figure 8, with droplet ejection occurring between point E and point G. In this way, it can be seen that the displacement of the piezoelectric actuator follows the initial stages of the voltage amplitude of the input signal between points A to E with a slight delay, growing in amplitude as the input signal grows. The displacement of the piezoelectric actuator damps once the input signal drops to 0 at point G. Of course, it will be understood that other driving waveforms can be used and may be different for different liquids and geometries of the droplet ejector.

[0130] Figure 9 illustrates stages in a simplified manufacturing process flow for forming a droplet ejector in accordance with examples described herein. The droplet ejector 401 is substantially similar to the droplet ejector 301 shown in Figure 6, apart from the hereinafter described differences. Like features are illustrated with like reference numbers, with the first digit changing from 3 to 4, to indicated that the feature is relevant to Figure 9 instead of Figure 6 (e.g., the nozzle plate 386 of Figure 6 is the nozzle plate 486 of Figure 9). Specifically, the droplet ejector 401 includes a silicon substrate 440, first and second portions 430A, 430B of driving circuitry 430, a bond pad 452, a nozzle plate 486, a piezoelectric actuator 472, a protective front surface 488, a liquid chamber 492 and a liquid chamber inlet 494.

[0131] A first manufacturing step, as shown in Figure 9(a), is to create the driving circuitry 430 and an interconnect layer 433, for example CMOS driving circuitry 430 and interconnects 433, on a surface of a silicon substrate 440. The CMOS driving circuitry 430 is formed by standard processes - for example ion implantation on p-type or n-type substrates followed by the creation of a wiring interconnect layer by standard CMOS fabrication processes (e.g. ion implantation, chemical vapour deposition (CVD), physical vapour deposition (PVD), etching, chemical-mechanical planarization (CMP) and/or electroplating).

[0132] Subsequent manufacturing steps are implemented to define features and structures of the droplet ejector device. Subsequent steps are chosen not to damage structures formed in previous steps. A key manufacturing parameter is the peak processing temperature. Problems associated with processing CMOS at high temperatures include the degradation of dopant mobility and interconnect wiring schemes. CMOS electronics are known to survive temperatures of 450°C. However, a much lower temperature (i.e., below 300°C) is desirable for high yield.

[0133] The nozzle plate 486, piezoelectric actuator 472, protective front surface 488 and bond pad 452 are formed on top of the interconnect layer 433 as shown in Figure 9(b). The nozzle plate 486 is deposited using a CVD or PVD process.

[0134] The formation of a CMOS compatible piezoelectric material within the piezoelectric actuator 472 is of particular interest as this is the key driving element of the actuator. ZnO, AIN and AIN compounds (such as ScAIN) materials can be deposited using low-temperature PVD (e.g. sputtering) processes that do not require post processing such as annealing. These materials also do not require poling.

[0135] ZnO, AIN and AIN compounds (e.g. ScAIN) materials are therefore commercially viable materials for the fabrication of a monolithic droplet ejector device. However, the value of d₃₁ for these materials is significantly lower than that of PZT. The particular configuration of the nozzle (i.e. the actuatable nozzle plate), which improves ejection efficiency, and the use of two control electrodes, which improves actuation efficiency, counter the lower d₃₁ value associated with these materials.

[0136] Piezoelectric electrode materials are deposited using a CMOS compatible process such as PVD (including low-temperature sputtering). Typical electrode materials may include titanium (Ti), platinum (Pt), aluminium (Al), tungsten (W) or alloys thereof. The electrodes of the piezoelectric actuator 472 are defined by standard patterning and etch methods.

[0137] Protective materials can be deposited and patterned using a spin on and cure method (suitable for polyimides or other polymeric materials). Some materials, such as PTFE, may require more specific deposition and patterning approaches.

[0138] Bond pads are deposited using methods such as CVD or PVD (e.g. sputtering).

[0139] The liquid chambers and liquid chamber inlets are defined using high aspect ratio Deep Reactive Ion Etching (DRIE) methodologies to arrive at the shape shown in Figure 9(c). The liquid chambers are aligned to the nozzle outlets using a wafer front-back side alignment tool. The wafer may be mounted on a handle wafer during the front-back alignment and etch steps.

[0140] Figure 10 is a schematic illustration of an apparatus for aerosolising a liquid according to an example of the present invention. The apparatus 500 comprises a plurality of components, including a plurality of droplet ejectors 510, and a controller 520. The controller 520 is configured to exchange signals 515 with the plurality of droplet ejectors 510 to control the plurality of droplet ejectors 510 in accordance with input signals received by the controller 520, for example from a regimen preprogrammed into the apparatus 500. The controller 520 in this example is realised by one or more processors 530 and a computer-readable memory 540. The memory 540 stores instructions which, when executed by the one or more processors 530, cause the apparatus 500 to operate as described herein.

[0141] Figure 11 is a flowchart illustrating a method of controlling an apparatus for aerosolising a liquid as described herein. The method 600 is a method of controlling an apparatus having a plurality of droplet ejectors for generating an aerosol from a liquid provided thereto. Specifically, the method 600 comprises receiving 610 a control signal. The control signal may be received from a computer program stored in memory or may be received as a result of a user input indicative of a demand to start aerosolisation or may be received from an external device. The method 600 further comprises causing 620 ejection of a plurality of droplets of liquid from the apparatus. The ejection of the plurality of droplets is caused by activation of the plurality of droplet ejectors, for example, by applying the driving waveform described herein (or another driving waveform) to the piezoelectric actuator of a plurality of the plurality of droplet ejectors.

[0142] In summary, the present disclosure provides an apparatus for aerosolising a liquid (100) comprising one or more inputs (110), and a plurality of droplet ejectors (126) in fluid communication with the one or more inputs (110). Each droplet ejector comprises a nozzle portion and a piezoelectric actuator. The one or more inputs are for receiving one or more liquids. Each nozzle portion defines a nozzle outlet in fluid communication with the one or more inputs. Each piezoelectric actuator is operable to cause ejection of a liquid received by one of the one or more inputs through the respective nozzle outlet as one or more droplets to thereby generate an aerosol comprising the one or more droplets ejected by each droplet ejector.

[0143] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to and do not exclude other components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0144] Features, integers, characteristics or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. An apparatus for aerosolising a liquid, comprising:

one or more inputs for receiving one or more respective liquids; and

a plurality of droplet ejectors together in fluid communication with the one or more inputs, each droplet ejector comprising:

a nozzle portion defining a nozzle outlet in fluid communication with a one of the one or more inputs; and

a piezoelectric actuator,

wherein each piezoelectric actuator is operable to cause ejection of a respective liquid received by the one of the one or more inputs through the respective nozzle outlet as one or more droplets to thereby generate a liquid aerosol comprising the one or more droplets ejected by each droplet ejector.

2. The apparatus according to claim 1, wherein the nozzle outlet defined by each of the plurality of droplet ejectors is among no more than one nozzle outlet defined by the respective droplet ejector and in fluid communication with the one of the one or more inputs.

3. The apparatus according to claim 1 or claim 2, further comprising a storage portion defining one or more cavities for storing the one or more respective liquids, wherein the one or more cavities are together in fluid communication with each nozzle outlet and with the one or more inputs, optionally wherein the storage portion is removable.

4. The apparatus according to any preceding claim, further comprising a housing to support the plurality of droplet ejectors, optionally wherein the storage portion is part of the housing.

5. The apparatus according to any preceding claim, further comprising an outlet portion defining an outlet through which the liquid aerosol can be output from the apparatus, optionally wherein the outlet portion is part of the housing.

6. The apparatus according to any preceding claim, further comprising a power supply circuit portion to supply power to the piezoelectric actuator of each of the plurality of droplet ejectors, optionally wherein the power supply circuit portion is supported by the housing, and additionally or alternatively wherein the apparatus further comprises a power source to supply power to the power supply circuit portion.

7. The apparatus according to any preceding claim, further comprising a switch to activate the plurality of droplet ejectors, optionally wherein the switch is a flow switch responsive to a flow through the outlet.

8. The apparatus according to any preceding claim, further comprising a controller to control operation of the plurality of droplet ejectors, optionally wherein the controller is configured to cause generation of the liquid aerosol at a plurality of discrete times, in response to one or more activation signals, further optionally wherein the one or more activation signals are received from a remote device, separated from the apparatus, and additionally or alternatively wherein a first contiguous subset of the plurality of discrete times are regularly spaced, and additionally or alternatively wherein the one or more activation signals cause generation of the liquid aerosol discretely or continuously over a period of more than 30 minutes, and optionally wherein the first contiguous subset of the plurality of discrete times extend over the period of more than 30 minutes.

9. The apparatus according to any preceding claim, wherein at least one, for example more than 50 percent, such as each, of the plurality of nozzle outlets has a maximum cross-sectional extent less than 100 x 10^-6 metres (100 microns), and additionally or alternatively wherein at least one, for example more than 50 percent, such as each, of the plurality of nozzle outlets has a maximum cross-sectional extent greater than 5 x 10^-6 metres (5 microns).

10. The apparatus according to any preceding claim, wherein, for each droplet ejector, the nozzle portion and the piezoelectric actuator are formed together by fabrication, and additionally or alternatively wherein the apparatus further comprises driving circuitry to control operation of the piezoelectric actuator responsive to one or more control signals received thereat.

11. The apparatus according to any preceding claim, wherein the plurality of droplet ejectors are at least 100 droplet ejectors, optionally wherein the plurality of droplet ejectors are at least 500 droplet ejectors.

12. The apparatus according to any preceding claim, wherein the plurality of droplet ejectors are arranged such that the nozzle outlets are provided in a grid arrangement.

13. The apparatus according to any preceding claim, wherein a one of the one or more liquids is a non-aqueous solution.

14. The apparatus according to any preceding claim, wherein the apparatus is fixedly mounted to a support member.

15. The apparatus according to any preceding claim, wherein the apparatus is an industrial apparatus for use in an industrial process.

Drawing