Acoustic Micropump Device Using Piezoelectric Transducers to Create a Directional Fluid Flow

The present application is a non-provisional patent application claiming priority to European Patent Application No. 24178366.1, filed May 28, 2024, the contents of which are hereby incorporated by reference.

The present disclosure relates to a micropump device. The micropump device is configured to create a net flow of a fluid inside a fluid channel along a flow direction. The net flow may be created between an inlet port and an outlet port of the fluid channel. For creating the net fluid flow, the micropump device employs piezoelectric transducers, which are controlled in at least three groups.

Micro fabrication has the ability to integrate various microscopic electromechanical components within a microelectromechanical system (MEMS). MEMS provides, for example, high functionality and performance, small size, low cost, and ease of fabrication. Micro fabrication has been increasingly popular in microfluidics systems, for example, for bioassays applications, wherein functional modules are miniaturized and integrated into one single micro-sized chip. Such systems are inexpensive, rapid in transportation of bio samples, and highly reproducible. Of integrated components, micropumps or micropump devices play an useful role in transporting the bio samples and reagents.

Various types of micropump devices have been developed based on different actuation mechanisms. One representative micropump device is the silicon-based diaphragm piezoelectric micropump device, which relies on the piezoelectric effect to deform a membrane to drive a fluid in a channel between an inlet and an outlet valve. This kind of micropump device can achieve a high pumping flow rate, however, it has some drawbacks. For instance, the micropump device has a rather complicated design including a complex fabrication of the inlet and outlet valves. Additionally, the micropump device works in a low frequency range (normally below 100 Hz), and has a high input power to pump the fluid (e.g., an AC signal having an amplitude of around 100 V is needed). Moreover, once the micropump device is fabricated, the flow direction of the fluid is fixed, which results in a limited flexibility of application.

In order to eliminate the impact of mechanical loss caused by moving parts, and to drive the fluid in a miniaturized microchannel, a phase shift vibrational membrane micropump device has been proposed. In this kind of micropump device, a vibrational wall composed of a thin piezoelectric film and square electrodes are fabricated on top of a straight fluid microchannel. By applying a phase delayed AC signal to the adjacent electrodes, a peristaltic mechanical vibrational wall motion is induced, which moves the fluid inside the microchannel unidirectionally. This kind of micropump device works in a moderate frequency range (e.g. at around 100 kHz), and with an AC signal that has a moderate amplitude (e.g. of around 20 V). However, the membrane displacement is in the order of a hundred nanometers, which results in a rather low pumping flow rate.

Apart from the above-mentioned mechanical actuation mechanisms, the development of wave-based acoustic streaming micropump devices has been carried out as well. Acoustic streaming refers to a fluid flow, which is induced by the force arising from the presence of a gradient in the time-averaged acoustic momentum flux inside the fluid domain. The acoustic streaming flow velocity is generally proportional to the acoustic wave amplitude and the wave frequency. Compared to the discrete mechanical micropump devices, the elastic wave motion is distributed along the length of the fluidic microchannel. Additionally, most of the acoustic energy of the elastic wave accumulates at the fluid-solid interface, which makes it more promising for fluid transportation inside a microchannel with a low channel height (e.g., of a few hundred micrometers). Furthermore, the fabrication process of this kind of micropump device is much less complicated, as it does not have moving parts, which are also prone to mechanical failure. With these improvements, acoustic streaming micropump devices have been widely used in various microfluidics applications including pumping, jetting, and manipulation of droplets or bio particles.

Surface acoustic wave (SAW) is a promising candidate for realizing acoustic steaming micropump devices. For example, an interdigitated transducer (IDT) composed of multiple comb-liked electrode finger pairs can be deposited on top of a piezoelectric film, and can be used to generate a SAW. The SAW propagates non-directionally at the electrode finger region and travels directionally to either side outside of the transducer region. A fluid chip with a bent channel may be bonded to one side of the IDT at a certain distance. In this design, the SAW first propagates along a substrate, through the microfluidic channel wall, and subsequently meets with the fluid inside the channel to induce acoustic streaming. A micropump device with this design does not have mechanical moving parts, but uses the SAW, which is easily generated, as the actuation force to pump the fluid.

However, there are still several drawbacks. Firstly, the amplitude of the SAW is typically extremely low (in the sub nanometer range), which results in an extremely low pumping flow rate. Secondly, since the SAW amplitude is extremely low, a high input power is needed. Thirdly, since a directional SAW is needed to drive the fluid motion, the microchannel has to be placed at one side of the channel. Consequently, (e.g., only) half of the acoustic energy generated by the IDT is used, which is energy inefficient and increases the energy consumption of the micropump device. Lastly, the SAW has a severe acoustic attenuation inside the necessarily elastic fluid channel material before it meets the fluid, wherein over 90% of the acoustic energy may be lost.

In view of the above, an objective of this disclosure is to provide an acoustic micropump device, which provides improvements as described. An objective is, in particular, to achieve a high pumping velocity and thus a large pumping flow rate with the micropump device. Another objective is to provide (e.g., enable) low input power for the micropump device.

These and other objectives are achieved by the solutions provided in the independent and dependent claims.

A first example embodiment of this disclosure provides an acoustic micropump device for creating a net flow of fluid along a flow direction. The acoustic micropump device comprises a fluid channel for the fluid and a plurality of piezoelectric transducers arranged adjacent to the fluid channel, wherein the piezoelectric transducers are organized into a set comprising at least three groups. The groups are consecutively arranged along the flow direction, and each group comprising at least one piezoelectric transducer, wherein each piezoelectric transducer comprises a respective membrane, which is configured to vibrate when the piezoelectric transducer is electrically actuated and to acoustically couple to the fluid channel. The device further includes a controller configured to actuate the plurality of piezoelectric transducers using at least three periodic electrical control signals. Each electrical control signal is associated with one group of the at least three groups of piezoelectric transducers of the set. The controller is configured to consecutively delay the at least three electrical control signals to another, in accordance with the consecutively arranged groups of the set associated with the electrical control signals, to create the net flow of fluid along the flow direction.

The fluid channel may be configured to hold and provide (e.g., enable) transport of the fluid. The fluid channel may have at least two ports, wherein one port may act as inlet port, the other port may act as outlet port, and the flow direction may be provided (e.g., defined) from inlet to outlet port. The function of inlet and outlet port may be reversed. In this case, the controller may be configured to change the delay between the at least three control signals to reverse the net fluid flow. The controller may be configured to set the delay(s) between respectively the at least three control signals in a variable manner, so as to achieve different flow directions of the net fluid flow in the fluid channel. For instance, changing a sign of the respective delays between the control signals may reverse the flow direction. The fluid channel may be straight and the flow direction may be along the fluid channel length. The fluid channel may also be bent or curved, and the flow direction may lie arbitrarily within fluid channel or may follow the bend or curve of the fluid channel.

The fluid usable with the micropump device may be a liquid, such as water or an aqueous solution. Since the micropump device may be used for bio-applications, the liquid may also be or comprise blood, pharmaceutical compounds, cell culture media, and various buffers as used in diagnostic and therapeutic procedures. The fluid is not a part of the micropump device, and may be supplied externally to the fluid channel of the micropump device.

The delayed electrical control signals provided by the controller may be time-delayed with respect to each other and/or may be phase-delayed with respect to each other. For instance, the electrical control signals may be identical or similar pulsed signals, wherein the pulses of different electrical control signals appear at different time instances, i.e., with a time delay. The electrical control signals may also be sinusoidal signals and/or AC signals with a phase difference between different electrical control signals. For example, each electrical control signal may have a phase shift with respect to a common periodic electrical control signal (providing a reference phase). The common electrical control signal may be one of the electrical control signals used. The electrical control signals may all have the same shape and/or amplitude and/or frequency. The delay may be the same between any two consecutively arranged groups of piezoelectric transducers of the set. However, the delays between respective pairs of consecutively arranged groups of the set may also differ. That is, equidistant or non-equidistant delays may be used.

The vibration of the respective membranes of the piezoelectric transducers, which can be coupled acoustically to the fluid channel, may create a traveling acoustic wave, for example a SAW like flexural plate wave, at the interface of the fluid and the fluid channel (wall), and may cause the directional net flow of the fluid in the fluid channel. A flexural plate wave is a type of acoustic wave that travels along, for instance, a thin plate, bending the plate as it goes. In the present disclosure, this plate may be a wall and/or elastic layer of the fluid channel. In this way, a pumping of the fluid can be achieved along the fluid channel. Since the travelling wave displacement (amplitude), for example, the flexural plate wave displacement, may be in the sub-micrometer range, i.e. can be much larger than that of the SAW, which is typically (e.g., only) in the sub-nanometer range, a much higher acoustic pressure and acoustic streaming velocity can be achieved as for conventional actuation mechanisms based on SAW. Thereby, also a relatively low input power is used (e.g., needed) for the electrical control signals. The piezoelectric transducers may be PMUTs, piezoelectric diaphragm transducers, or the like.

In an implementation of the acoustic micropump device, the piezoelectric transducers are organized into two or more sets. The sets are consecutively arranged along the flow direction, wherein each set comprises at least three groups of piezoelectric transducers, which are consecutively arranged along the flow direction. The controller is configured to actuate the piezoelectric transducers of each set using the same at least three electrical control signals. Each electrical control signal is associated with one group of the set to create the net flow of fluid along the flow direction.

That is, there is more than one set of piezoelectric transducers in the plurality of piezoelectric transducers. Using more than one set allows for transporting of the fluid along the fluid direction over a longer distance, providing (e.g., allowing) for longer fluid channels. Thereby, the electrical control signals used for the first set can be re-used for other sets, and little extra power is used (e.g., required). The multiple sets of piezoelectric transducers can be arranged one after the other parallel to the flow direction, and within each of the sets the at least three groups of piezoelectric transducers (e.g., each having one or more piezoelectric transducers) can be arranged parallel to the flow direction as well.

In an implementation of the acoustic micropump device, the at least three groups of the set comprise a first group, a second group, and a third group, which are arranged in this order along the flow direction. The at least three electrical control signals are phase-shifted versions of a common periodic electrical control signal. The at least three electrical control signals are phase-shifted to another in accordance with the consecutively arranged groups associated with the electrical control signals. The at least three electrical control signals comprise a first periodic electrical control signal having a phase shift in a range of −120° to −70°, and being associated with the first group, a second periodic electrical control signal having a phase shift of 0°, and being associated with the second group, and a third periodic electrical control signal having a phase shift in a range of +70° to +120°. The at least three electrical control signals are associated with the third group.

For example, the phase shift of the first control signal may be around −120°, the phase shift of the second control signal may be around 0° (e.g. ±10°), wherein the second control signal may be used as a reference for the other control signals, and the phase shift of the third control signal may be around +120°. The phase difference between the first control signal and the second control signal is 120°, and is the same as the phase difference between the second control signal and the third control signal. The phase shifts may be relative to a common electrical control signal, which may be (e.g., substantially) identical to the second electrical control signal. The amplitude and frequency may be the same for each electrical control signal. If there are more than three groups in a set of piezoelectric transducers, then the phase shift may consecutively change by up to 90° between adjacent groups (e.g. in case of four groups or more) or (e.g., only) by up to 60° between adjacent groups (e.g. in case of six groups or more), or (e.g., even only) by up to 30° between adjacent groups (e.g., in case of twelve groups or more).

However, also non-equidistant phase shifts are possible. For instance, the phase shift of the first control signal could be around −120°, the phase shift of the second control signal could be in a range of −60° to −10°, and the phase shift of the third control signal could be in a range of +130° to +180°. In this case, the phase difference between the first control signal and the second control signal may be in a range of 60-110°, and the phase difference between the second control signal and the third control signal is in a range of 140°-240°. It is further possible that the phase shift of the first control signal is about 0°, and the phase shifts of the second control signal, the third control signal, and potentially further control signals for the set are consecutively increased in an equidistant or in a non-equidistant manner. In the end, the phase differences between the control signals may be decisive, not the “absolute” phase shifts regarding a certain reference. For instance, the situation −120°, 0°, and +120° for the three control signals, as described above, may be (e.g., substantially) identical to the situation 0°, +120°, and +240° for the same three control signals.

In an implementation of the acoustic micropump device, the piezoelectric transducers are organized into an array of rows and columns, wherein each row of piezoelectric transducers is one group of piezoelectric transducers, or wherein each row of piezoelectric transducers comprises at least three groups of piezoelectric transducers.

An array of piezoelectric transducers provides (e.g., enables) flexible selection of the flow direction by the controller, such as by controlling the transducers with suitable electrical control signals and delays. In this implementation, a horizontal or vertical flow direction may be achieved (e.g., vertical may be along the column direction). It may be possible that each piezoelectric transducer of the array can be controlled individually. The controller would thus be able to selectively control certain piezoelectric transducers as groups with the same electrical control signal, and could “regroup” the piezoelectric transducers if useful (e.g., needed).

In an implementation of the acoustic micropump device, the piezoelectric transducers are organized into an array of rows and columns, wherein the at least one piezoelectric transducer of each group of the at least three groups of the set is arranged in a different row and in a different column than the at least one piezoelectric transducer of the other groups of the at least three groups of the set.

In this implementation, a diagonal flow direction through the array may be achieved.

In an implementation of the acoustic micropump device, the fluid channel is bonded to the array of piezoelectric transducers.

For instance, the fluid channel may be attached to or coupled to the vibrating membranes of the piezoelectric transducers, so that membrane vibrations can be transferred to vibration(s) of the fluid channel.

In an implementation of the acoustic micropump device, the fluid channel extends at least (e.g., predominantly) along the flow direction.

This may be beneficial if a fixed flow direction is desired, for instance, from a dedicated inlet port to a dedicated outlet port.

In an implementation of the acoustic micropump device, the respective membrane of each piezoelectric transducer comprises a piezoelectric layer, which is sandwiched between a bottom electrode and a top electrode, and the fluid channel comprises an elastic layer attached to the respective membrane and/or to the top electrode.

In an implementation of the acoustic micropump device, at least the piezoelectric transducers of the same group have a common piezoelectric layer.

The piezoelectric layer may also be shared by more or even all piezoelectric transducers.

In an implementation of the acoustic micropump device, the electrical control signals are applied to the top electrodes of the piezoelectric transducers and the bottom electrodes of the piezoelectric transducers are grounded, or the electrical control signals are applied to the bottom electrodes of the piezoelectric transducers and the top electrodes of the piezoelectric transducers are grounded.

In an implementation of the acoustic micropump device, the top electrodes or the bottom electrodes of two or more piezoelectric transducers of the same group are commonly connected to the controller for receiving the same electrical control signal.

In an implementation of the acoustic micropump device, the electrical control signals are applied to the top electrodes of the piezoelectric transducers, and the acoustic micropump device further comprises a grounded shielding layer arranged between the top electrodes and the fluid channel.

The shielding layer allows reducing dielectrophoresis forces, which may be induced by applying the control signals to the top electrodes.

In an implementation of the acoustic micropump device, the respective membrane of each piezoelectric transducer is suspended in a cavity formed in a substrate of the piezoelectric transducer; wherein the cavity has a width in a range of 10-150 μm, and/or wherein a spacing between any two adjacent piezoelectric transducers is at least 50-200 μm.

For instance, the membranes may be formed from the piezoelectric layer, which may be shared by two or more piezoelectric transducers. The membrane is in this case provided (e.g., defined) by the part of the piezoelectric layer being suspended in the cavity. The substrate in which the cavities are formed may be rigid. The piezoelectric transducers may share the rigid substrate. Due to the rigid substrate, (e.g., only) the membranes suspended over the cavities are able to vibrate, which leads to a discontinuous membrane vibration. The membranes' vibrations may correspond to local deformations of the parts of the piezoelectric layer above the cavities.

The width of the cavity may be the maximum extension (can be shape-dependent) of the cavity along the direction in which multiple piezoelectric transducers are arranged one after the other, e.g., along the flow direction. The spacing between the two adjacent piezoelectric transducers is the spacing between the cavities of these two piezoelectric transducers. The spacing may be in a range of 50-200 μm, or may be larger.

In an implementation of the acoustic micropump device, the piezoelectric transducers are piezoelectric micromachined ultrasonic transducers (PMUTs).

A PMUT works by utilizing the piezoelectric effect, where the application of an electrical voltage to a piezoelectric material causes it to deform, emitting ultrasonic waves. The piezoelectric material may be the membrane, and the electrical voltage may be the electrical control signal applied by the controller.

A second example embodiment of this disclosure provides a method of operating an acoustic micropump device according to the first example embodiment or any of its implementations, so as to create the net flow of the fluid along the flow direction. The method comprises actuating the plurality of piezoelectric transducers using the at least three periodic electrical control signals, wherein each electrical control signal is used to actuate all piezoelectric transducers of one group of the at least three groups of the set, and consecutively delaying the at least three electrical control signals to another in accordance with the consecutively arranged groups of the set associated with the electrical control signals.

In an example embodiment of the acoustic micropump device, the at least three electrical control signals are phase-shifted versions of a common periodic electrical control signal. A first electrical control signal of the at least three electrical control signals has a phase shift in a range of −120° to −70°, and is used to actuate all piezoelectric transducers of a first group of the at least three groups of piezoelectric transducers of the set. A second electrical control signal of the at least three electrical control signals has a phase shift of 0°, and is used to actuate all piezoelectric transducers of a second group of the at least three groups of piezoelectric transducers of the set. A third electrical control signal of the at least three electrical control signals has a phase shift in a range of +70° to +120°, and is used actuate all piezoelectric transducers of a third group of the at least three groups of piezoelectric transducers of the set. The first group, the second group, and the third group are arranged in this order along the flow direction.

In an example embodiment of the method, the first electrical control signal is further used to actuate all piezoelectric transducers of a fourth group of piezoelectric transducers of a further set. The second electrical control signal is further used to actuate all piezoelectric transducers of a fifth group of piezoelectric transducers of the further set. The third electrical control signal is further used actuate all piezoelectric transducers of a sixth group of piezoelectric transducers of the further set, wherein the fourth group, the fifth group, and the sixth group are arranged in this order along the flow direction after the first group, the second group, and the third group.

The method of the second example embodiment achieves the same improvements as the micropump device of the first example embodiment, and may be extended by respective implementations as described above for the micropump device of the first example embodiment.

Another example embodiment of this disclosure is related to a computer program comprising instructions which, when the program is executed by the controller of the micropump device of the first example embodiment, causes the control to perform the method of the second example embodiment.

In summary, this disclosure proposes a micropump device that employs piezoelectric transducers, which are actuated by respectively delayed control signals, in order to realize a net fluid flow in a fluid channel with an improvement of the pumping velocity over other acoustic streaming micropump devices. As the piezoelectric transducers, PMUTs may be used. The piezoelectric transducers can be controlled to generate a travelling wave—e.g. a SAW like unidirectional flexural plate wave—in the fluid channel, which causes a streaming of the fluid inside the fluid channel. This disclosure provides (e.g., enables) a high pumping flow rate of several hundreds of μL/min for the micropump device.

The figures are schematic, not necessarily to scale, and generally show parts used to elucidate example embodiments, wherein other parts may be omitted or merely suggested.

Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings. That which is encompassed by the claims may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example. Furthermore, like numbers refer to the same or similar elements or components throughout.

show schematically an acoustic micropump deviceaccording to this disclosure. The acoustic micropump deviceis configured to create a directional net flow of a fluid, wherein the fluid may be a liquid. For example, the liquid may be water or an aqueous solution. In particular,shows a sectional view of the acoustic micropump device, andB shows a top view of the micropump device.

The acoustic micropump devicecomprises a fluid channel. The fluid channelis suitable to hold and transport the fluid, for example, liquid. The fluid channelmay be provided (e.g., defined) by channel walls, wherein the material of these channel walls may be elastic and may be suitable to be displaced to create plate waves. The net flow of the fluid is created by the micropump devicein the fluid channeland along a flow direction. The fluid channelmay, to this end, extend at least predominantly along the flow direction, or may even extend (e.g., strictly) along the flow direction, especially if this flow directionis fixed. The flow directiondoes not have to be as indicated in. The flow directionmay be provided (e.g., defined) from a first port of the fluid channelto a second port of the fluid channel, for example, from an inlet port to an outlet port. The micropump devicemay, however, be configured to create a net flow of fluid along different selectable flow directions, for instance, it may be configured to reverse the flow directionto be from the second port to the first port.