CN113714073A

CN113714073A - Electronic configuration and control for creating acoustic standing waves

Info

Publication number: CN113714073A
Application number: CN202111106334.3A
Authority: CN
Inventors: B·利普肯斯; R·穆夏克; D·米利; A·沙吉
Original assignee: Flodesign Sonics Inc
Current assignee: Flodesign Sonics Inc
Priority date: 2016-04-24
Filing date: 2017-04-24
Publication date: 2021-11-30
Anticipated expiration: 2037-04-24
Also published as: WO2017189435A1; CN109310933B; CN109310933A; CA3022040A1; CN113714073B

Abstract

Some aspects of the present invention relate to an apparatus for separating secondary fluids or particles from a primary fluid. The apparatus comprises a flow chamber with at least one inlet and at least one outlet. The drive circuit is configured to provide a drive signal and the filter circuit is configured to receive the drive signal and provide a transition drive signal. An ultrasonic transducer is disposed in co-operation with the flow chamber, and the transducer includes at least one piezoelectric element driven by a current drive signal to produce an acoustic standing wave in the flow chamber. At least one reflector is opposite the ultrasonic transducer to reflect acoustic energy.

Description

Electronic configuration and control for creating acoustic standing waves

The application is a divisional application with the application date of 2017, 4 and 24, and the invention name of Chinese invention patent application number 201780039257.X of 'electronic configuration and control for generating acoustic standing waves'.

Cross Reference to Related Applications

The present application claims priority from the following applications: U.S. provisional patent application serial No. 62/461,691(P-095) filed on day 21, 2, 2017, U.S. provisional patent application serial No. 62/446,356(P-094) filed on

day

13, 1, 2017, and U.S. provisional patent application serial No. 62/326,766(P-065) filed on day 24, 4, 2016. And this application is a continuation of the following U.S. patent applications: U.S. patent application serial No. 15/371,037, filed on 12/2016, which is a continuation of U.S. patent No. 9,512,395, filed on 5/11/2014 and claims priority to U.S. patent application serial No. 62/020,088, filed on 2/7/2014, and U.S. patent application serial No. 61/900,395, filed on 5/11/2013; U.S. patent application serial No. 15/285,349, filed on day 4, 10/2016, which is a continuation of U.S. patent No. 9,457,302, filed on day 8, 5/2015 and claims priority to U.S. patent application serial No. 61/990,168; and us patent application serial No. 14/026,413 filed on 9/13/2013, which is a continuation of us patent application No. 13/844,754 filed on 3/15/2013 and requires priority from us patent application No. 61/754,792 filed on 1/21/2013, us patent application No. 61/708,641 filed on 10/2/2012, us patent application No. 61/611,240 filed on 3/15/2012, and us patent application No. 61/611,159 filed on 3/15/2012; and U.S. patent application Ser. No. 15/284,529 filed on 3/10/2016, claiming priority from U.S. patent application Ser. No. 62/322,262 filed on 14/4/2016, U.S. patent application Ser. No. 62/307,489 filed on 12/3/2016, and U.S. patent application Ser. No. 62/235,614 filed on 1/10/2015; and U.S. patent No. 9,512,395, filed on 5/11/2014, which claims priority to U.S. patent application No. 62/020,088, filed on 2/7/2014, and U.S. patent application No. 61/900,635, filed on 6/11/2013. The entire contents of these applications are incorporated herein by reference.

Background

Acoustophoresis is the separation of particles and secondary fluids from a primary or host fluid using acoustic devices such as acoustic standing waves. When there is a difference in density and/or compressibility, also referred to as an acoustic contrast factor, the acoustic standing wave may exert a force on the particles in the fluid. The pressure profile in the standing wave contains regions of local minimum pressure amplitude at nodes of the standing wave and regions of local maxima at antinodes of the standing wave. Depending on the density and/or compressibility of the particles, the particles may be trapped at nodes or antinodes of the standing wave. Generally, the higher the standing wave frequency, the smaller the particles that can be captured.

On a microscopic scale, for example with structural dimensions on the order of microns, conventional acoustophoresis systems tend to use half-wavelength or quarter-wavelength acoustic chambers, whose thickness is typically less than one millimeter at frequencies of a few megahertz, and which operate at very slow flow rates (for example μ L/min). Such systems are not scalable as they benefit from extremely low reynolds numbers, laminar flow operation and minimal fluid dynamics optimization.

On a macroscopic scale, planar acoustic standing waves have been used in separation processes. However, a single planar wave tends to trap particles or secondary fluids, such that separation from the primary fluid is achieved by turning off or removing the planar standing wave. Removal of the planar standing wave may prevent continuous operation. Moreover, the amount of power used to generate the acoustic plane standing wave tends to heat the primary fluid through the waste energy, which may be detrimental to the material being processed.

Thus, conventional acoustophoresis devices have limited efficacy due to several factors, including heating, the use of planar standing waves, restricting fluid flow, and the inability to capture different types of materials.

Control of the power provided to the ultrasonic transducer is challenging to implement, particularly for efficient performance. Promoting multimode behavior in a resonant cavity system may depend on providing sufficient power to the ultrasonic transducers in the system.

Disclosure of Invention

The following presents a simplified summary in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to the description below.

Embodiments of the present invention relate to an apparatus for separating secondary fluids or particles from a primary fluid, comprising a flow chamber having opposing first and second walls, at least one inlet and at least one outlet. The control circuit provides a drive signal, and a scaling circuit (scaling circuit) receives the drive signal and provides an equivalent current source drive signal, wherein the scaling circuit provides an impedance and a source transformation (transition) with respect to the ultrasonic transducer. An ultrasonic transducer having a transducer input impedance and located within the flow chamber includes at least one piezoelectric element driven by the equivalent current source drive signal to produce an acoustic standing wave in the flow chamber. At least one reflector is located on a first wall of the flow chamber on a side opposite the at least one ultrasonic transducer.

The control circuit may comprise a voltage source.

The acoustic standing wave may comprise a multi-dimensional acoustic standing wave. The multi-dimensional acoustic standing wave may be generated by a single piezoelectric element or multiple piezoelectric elements, perturbed in higher order modes.

The scaling circuit may include: an inductor having a first terminal and a second terminal, wherein the first terminal receives a drive signal, and a capacitor having a third terminal and a fourth terminal, wherein the second terminal and the third terminal are connected, wherein the fourth terminal is connected to a reference potential, and wherein signals representative of the equivalent current source drive signal are provided at the second terminal and the third terminal.

The scaling circuit may be comprised of passive circuit components.

Some aspects of the invention also relate to an apparatus for separating secondary fluids or particles from a primary fluid that includes a flow chamber having opposing first and second walls, at least one inlet and at least one outlet. The circuit is configured to receive the drive signal and provide a transition drive signal. An ultrasonic transducer is located within the flow chamber, the transducer including at least one piezoelectric element that receives the transduction drive signal to generate an acoustic standing wave in the flow chamber. At least one reflector is located on a wall of a side of the flow chamber opposite the at least one ultrasonic transducer.

The acoustic standing wave may comprise a multi-dimensional acoustic standing wave.

The circuit may include a scaling circuit that receives the drive signal and provides a transformed drive signal, wherein the scaling circuit provides an impedance and a source transformation with respect to the ultrasound transducer.

The scaling circuit may include a first inductor, a first capacitor, and a second inductor that are cooperatively arranged as a low pass filter.

The scaling circuit may include: an inductor having a first terminal and a second terminal, wherein the first terminal receives a drive signal, and a capacitor having a third terminal and a fourth terminal, wherein the second terminal and the third terminal are connected, wherein the fourth terminal is connected to a reference potential, and wherein signals representative of an equivalent switched drive signal are provided at the second terminal and the third terminal.

The scaling circuit may be comprised of passive circuit components.

A first tap (tap) may sense a voltage across the ultrasonic transducer. The transducer may be constructed of or include a piezoelectric material, which may be embodied as a ceramic crystal, polycrystalline or other crystal, all of which may be collectively referred to herein as a crystal. The first tap may provide a sensed voltage signal indicative of a voltage across the transducer, and the current sensing coil may sense a current and provide a sensed current signal indicative of a crystal current.

A controller may receive and process the sensed current signal and the sensed voltage signal to control the drive signal.

The circuit may include: a first inductor having a first terminal and a second terminal, the first terminal receiving a signal representing a drive signal, a first capacitor having a third terminal and a fourth terminal, and a second inductor having a fifth terminal and a sixth terminal, wherein the second terminal is connected to the third terminal and the fifth terminal, the fourth terminal is connected to a reference voltage, and an output signal representing a current drive signal is provided on the sixth terminal.

Some aspects of the invention also relate to an apparatus for separating secondary fluids or particles from a primary fluid that includes a flow chamber having opposing first and second walls, and at least one inlet and at least one outlet. The drive circuit is configured to provide a drive signal, and the filter circuit is configured to receive the drive signal and provide a transition drive signal. An ultrasonic transducer is disposed in co-operation with the flow chamber, the transducer including one or more of at least one piezoelectric element driven by the current drive signal to generate an acoustic standing wave in the flow chamber. At least one reflector is located on the second wall opposite the ultrasonic transducer to receive the acoustic standing wave.

The filter circuit may include: an inductor having a first terminal and a second terminal, wherein the first terminal receives a drive signal, and a capacitor having a third terminal and a fourth terminal, wherein the second terminal and the third terminal are connected, wherein the fourth terminal is connected to a reference potential, and wherein signals representative of an equivalent current source drive signal are provided at the second terminal and the third terminal.

The filter circuit may include: a first inductor having a first terminal and a second terminal, wherein the first terminal receives a signal representative of the drive signal, a first capacitor having a third terminal and a fourth terminal, and a second inductor having a fifth terminal and a sixth terminal, wherein the second terminal is connected to the third terminal and the fifth terminal, wherein the fourth terminal is connected to a reference voltage, and wherein an output signal representative of a current drive signal is provided on the sixth terminal.

The filter may be comprised of passive circuit components.

The voltage drive signal may be substantially a square wave and the converted signal may be substantially a sine wave.

Drawings

The following is a brief description of the drawings, which are presented for the purpose of illustrating the exemplary embodiments disclosed herein and not for the purpose of limiting the same.

FIG. 1A is a schematic diagram illustrating the function of an acoustophoretic separator having a secondary fluid or particle that is less dense than the primary fluid.

FIG. 1B is a schematic diagram illustrating the function of an acoustophoretic separator having a secondary fluid or particle that is denser than the primary fluid.

Fig. 2 is a sectional view of a conventional ultrasonic transducer.

Fig. 3A is a cross-sectional view of an ultrasound transducer structure that may be used in the present invention. There is an air gap within the transducer and no backing layer or wear plate.

Figure 3B is a cross-sectional view of an ultrasound transducer structure that may be used in the present invention. There is an air gap within the transducer and there is a backing layer and wear plate.

Fig. 4 is a conventional one-piece monolithic piezoelectric crystal for use in an ultrasonic transducer.

Fig. 5 is an exemplary rectangular piezoelectric array having 16 piezoelectric elements for use in the transducer of the present invention.

Fig. 6 is another exemplary rectangular piezoelectric array having 25 piezoelectric elements for use in the transducer of the present invention.

Fig. 7 is a graph showing the relationship of acoustic radiation force, gravity/buoyancy, and Stokes' drag force to particle size. The horizontal axis is in micrometers (μm) and the vertical axis is in newtons (N).

Figure 8 is a graph of electrical impedance magnitude versus frequency for a square transducer driven at different frequencies.

FIG. 9A shows seven trapping line configurations from the smallest magnitude of FIG. 8 in a direction perpendicular to the fluid flow.

Fig. 9B is a perspective view showing the separator. Showing fluid flow direction and trapping lines.

Fig. 9C is a view from the fluid inlet along the direction of fluid flow (arrow 114) of fig. 9B, showing the capture node of the standing wave where the particle will be captured.

FIG. 9D is a view through the face of the transducer in the capture line configuration, along arrow 116 shown in FIG. 9B.

Figure 10A shows an acoustophoretic separator for separating floating materials.

Fig. 10B is an enlarged view of the fluid flow near the intersection of the profiled nozzle wall 129 and the collection conduit 137.

Fig. 11A shows an exploded view of an acoustophoretic separator used in a biopharmaceutical application.

Fig. 11B shows an exploded view of a stacked acoustophoretic separator having two acoustic chambers.

Fig. 12A is a graph showing the efficiency of Cell removal from media using a Beckman Coulter Cell Viability Analyzer (Beckman Coulter Cell Viability Analyzer) for one experiment.

Fig. 12B is a graph showing the efficiency of cell removal from media using a beckmann coulter cell viability analyzer for another experiment.

FIG. 13 shows a schematic diagram of a two-dimensional numerical model developed for simulation of an ultrasound transducer and transducer array.

Fig. 14A to 14D are schematic diagrams comparing the results of the numerical model (bottom) of fig. 13 with published data (top), showing the accuracy of the numerical model. Fig. 14A compares the acoustic potentials U. Fig. 14B compares the x-component of the Acoustic Radiation Force (ARF). FIG. 14C compares the y-component of ARF. Fig. 14D compares the absolute values of ARF.

FIG. 15 is a schematic diagram showing the amplitude of the acoustic standing wave generated by the monolithic piezoelectric crystal in the model of FIG. 13. The frequency was 2.245 MHz.

The horizontal axis is the position along the X-axis and the vertical axis is the position along the Y-axis between the transducer and the reflector.

Fig. 16 is a graph showing the amplitude of the acoustic standing wave generated by the 4-element piezoelectric array in the model of fig. 13. At a frequency of 2.245MHz, the phase between the elements changes.

Fig. 17 is a graph showing the amplitude of the acoustic standing wave generated by the 5-element piezoelectric array in the model of fig. 13. At a frequency of 2.245MHz, the phase between the elements changes.

FIG. 18 is a photograph of an acoustophoretic device having a 4X4 piezoelectric array made of a 2MHz PZT-8 crystal with a notch made in the crystal as shown in FIG. 5.

FIG. 19 is a comparison of a simulation of a out-of-phase piezoelectric array with an actual acoustophoretic test using the out-of-phase array. For the simulation, out-of-phase refers to the phase angle of the delivered voltage. For out-of-phase testing, the phase of the numerical model varied from 0-180-0-180. For the test, the elements were varied in a checkerboard pattern.

FIG. 20 is a comparison of a simulation of an in-phase piezoelectric array with an actual acoustophoretic test using the in-phase array. For the simulation, in-phase refers to the phase angle of the delivered voltage. For in-phase testing, the phase remains constant across all elements.

Fig. 21 is a picture showing a notched crystal (top) with a transducer array having piezoelectric elements (bottom) bonded together by a potting material.

FIG. 22 is a schematic diagram showing the out-of-phase mode tested for a 4 element array.

FIG. 23 is a schematic diagram showing the out-of-phase mode tested for a 5 element array.

Fig. 24 is a graph showing normalized Acoustic Radiation Force (ARF) from a monolithic piezoelectric crystal simulation.

Fig. 25 is a graph showing the ratio of ARF components (lateral to axial) for a monolithic piezoelectric crystal simulation.

Fig. 26 is a graph showing normalized Acoustic Radiation Force (ARF) for a 5-element simulation with varying phase.

Fig. 27 is a graph showing the ratio of ARF components (lateral to axial) for a 5-element simulation.

FIG. 28 is a schematic diagram showing phasing of the array during out-of-phase testing. Under test, the dark elements have a phase angle of 0 ° and the light elements have a phase angle of 180 °.

Fig. 29 is a circuit diagram of an RF power supply with an LCL network providing transducer drive signals to an ultrasonic transducer.

Fig. 30 is a graph showing a frequency response for an LC network.

Fig. 31 is a circuit diagram of a buck low pass filter for use with the RF power supply of fig. 29.

FIG. 32 is a block diagram illustrating a system for providing transducer drive signals to a transducer.

Fig. 33 is a graph showing a frequency response for an acoustic transducer.

FIG. 34 is a block diagram illustrating an alternative embodiment system for providing transducer drive signals to a transducer.

FIG. 35 is a block diagram illustrating a calculation technique for obtaining control parameters for an acoustic transducer.

Fig. 36 is a block diagram showing demodulation of a voltage or current signal.

FIG. 37 is a simplified schematic diagram of an RF power supply including an LC filter that provides a transducer drive signal.

Fig. 38 is a simplified schematic diagram of an alternative RF power supply including an LCL filter that provides the transducer drive signal.

Fig. 39 is a circuit diagram of an RF power supply providing a drive signal to an LCL filter, which provides a transducer drive signal to an ultrasound transducer.

Fig. 40 is a circuit diagram of an LCL filter circuit having a tap providing a current sense signal and a node providing a voltage sense signal that can be fed back to a controller (e.g., a DSP) to control the drive signal delivered to the transducer.

Fig. 41 is a schematic diagram of an embodiment of a power supply with an LCL filter network that provides transducer drive signals.

Detailed Description

The invention may be understood more readily by reference to the following detailed description of the required embodiments and the examples included therein. In the following specification and the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings.

The singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.

The term "comprising" is used herein to require the presence of the named component/step and to allow the presence of other components/steps. The term "comprising" should be interpreted as including the term "consisting of … …," which allows for the presence of only the named components/steps, as well as any impurities that may arise from the manufacture of the named components/steps.

Numerical values are to be understood as including: to the same number of significant digits and to deviate from the stated value in a manner that is less than the experimental error of conventional measurement techniques of the type described in this application to determine the value of that value.

All ranges disclosed herein are inclusive of the recited endpoint and independently combinable (e.g., ranges of "from 2 grams to 10 grams" are inclusive of the endpoints 2 grams and 10 grams and all intermediate values).

The terms "substantially" and "about" may be used to include any numerical value that can be changed without changing the basic function of the value. When used with a range, "substantially" and "about" also disclose the range defined by the absolute values of the two endpoints, e.g., the expression "from about 2 to about 4" also discloses the range "from 2 to 4". The terms "substantially" and "about" may refer to plus or minus 10% of the indicated number.

It should be noted that many terms are used herein as relative terms. For example, the terms "upper" and "lower" are positionally opposite one another, i.e., an upper component is at a higher elevation than a lower component in a given orientation, but these terms may vary if the device is inverted. The terms "inlet" and "outlet" are relative to the fluid flowing through them for a given structure, e.g., fluid flows into the structure through the inlet and out of the structure through the outlet. The terms "upstream" and "downstream" are relative to the direction in which fluid flows through the various components, i.e., fluid flows through an upstream component before flowing through a downstream component. It should be noted that in a loop, a first component may be described as being either upstream or downstream of a second component.

The terms "horizontal" and "vertical" are used to designate directions relative to an absolute reference (i.e., the ground plane). The terms "above" and "below" or "upward" and "downward" are also relative to absolute references; the upward flow is always against the earth's gravity.

The present application relates to "same order". If the quotient of the larger number divided by the smaller number is a value less than 10, the two numbers are of the same order.

The present invention's acoustophoretic separation technique employs an ultrasonic standing wave to capture particles or secondary fluids in a main fluid stream, even if it remains stationary. Depending on the acoustic contrast factor of the particulate or secondary fluid relative to the primary fluid, the particulate or secondary fluid collects at nodes or antinodes of the multi-dimensional acoustic standing wave to form clusters that eventually break away from the multi-dimensional acoustic standing wave when the clusters have grown to a size large enough to overcome the holding force of the multi-dimensional acoustic standing wave (e.g., by coalescence or aggregation). The dispersion of the acoustic field from the particles results in three-dimensional acoustic radiation forces that act as a three-dimensional trapping field. When the particles are small relative to the wavelength, the acoustic radiation force is proportional to the particle volume (e.g., the cube of the radius). Which is proportional to the frequency and the acoustic contrast factor. It also increases and decreases with acoustic energy (e.g., the square of the acoustic pressure amplitude). For harmonic excitation, the sinusoidal spatial variation of the force drives the particles to stable axial positions within the standing wave. When the acoustic radiation force acting on the particles is stronger than the combined effect of the fluid drag and buoyancy and gravity, the particles are trapped within the acoustic standing wave field. This continuous capture results in the concentration, agglomeration, clustering, agglomeration, and/or binding of the captured particles, which subsequently continuously detach from the multi-dimensional acoustic standing wave by gravity separation. This strong lateral force produces rapid clustering of the particles. By enhanced gravity separation, relatively large solids of one material may thus be separated from a different material, smaller particles of the same material and/or the host fluid.

In this regard, the contrast factor is the difference between the compressibility and density of the particles and the fluid itself. These properties are characteristic of the particles and the fluid itself. Most cell types exhibit higher density and lower compressibility than the medium in which they are suspended, so that the acoustic contrast factor between the cells and the medium is positive. As a result, axial Acoustic Radiation Force (ARF) drives cells with a positive contrast factor to the pressure nodal plane, while driving cells or other particles with a negative contrast factor to the pressure antinode plane. The radial or lateral component of the acoustic radiation force captures the cell. The radial or lateral component of the ARF is greater than the combined effect of fluid resistance and gravity. This radial or lateral component drives the cells/particles to a plane where they can cluster into larger groups, and then they will continuously gravitationally separate from the fluid.

As the cells agglomerate at the nodes of the standing wave, there is also a physical washout (scrubbing) of the cell culture medium that occurs, whereby more cells are captured when they come into contact with cells that have remained within the standing wave. This effect helps to separate the cells from the cell culture medium. The expressed (expressed) biomolecules remain in the nutrient stream (i.e. the cell culture medium).

For a three-dimensional sound field, the formula of Gor' kov can be used to calculate the acoustic radiation force F applicable to any sound field_ac. Primary acoustic radiation force F_acIs defined as a function of the field potential U,

wherein the field potential U is defined as:

and, f₁And f₂Are unipolar and bipolar contributions defined by:

where p is the acoustic pressure, u is the fluid particle velocity, and Λ is the cell density ρ_pAnd fluid density ρ_fA is the cell sound velocity c_pSpeed of sound c of fluid_fRatio of (A) to (B), V₀Is the volume of the cell, an<>Indicating the time over the period of the wave. The equation of Gor' kov applies to particles smaller than the wavelength. For larger particle sizes, illinskii provides a formula for calculating the 3D acoustic radiation force for any particle size. See Ilinskii, Acoustic Radiation Force on a Sphere in Tissue, The Journal of The Acoustic Society of America, 132,3,1954(2012), which is incorporated by reference into this application.

The acoustic transducer may be driven to generate acoustic waves. The acoustic wave may be reflected with another acoustic transducer or reflector to create an acoustic standing wave. Alternatively or additionally, two opposing acoustic transducers may be driven to create an acoustic standing wave therebetween. Perturbing the piezoelectric crystal in the ultrasound transducer in a multimode manner allows for the generation of a multi-dimensional acoustic standing wave. The piezoelectric material or crystal may be specifically designed to deform in a multimode manner at the design frequency, allowing a multi-dimensional acoustic standing wave to be generated. The multi-dimensional acoustic standing waves may be generated by different modes of the piezoelectric material or crystal, such as a 3x3 mode that can generate multi-dimensional acoustic standing waves. A large number of multi-dimensional acoustic standing waves may also be generated by allowing a piezoelectric material or crystal to vibrate via a number of different modal modes. Thus, the crystal will excite multiple modes, such as the 0x0 mode (i.e., piston mode) to lxl, 2x2, 1x3, 3x1, 3x3, and other higher order modes, and then cycle back to the lower modes of the crystal (not necessarily in direct order). This switching or dithering of the piezoelectric material or crystal between modes allows for the generation of various multi-dimensional waveforms, as well as single piston mode shapes, at a given time.

In some embodiments of the invention, a single ultrasound transducer comprises a rectangular array of piezoelectric elements, which can be operated such that some components of the array will be out of phase with other components of the array. The phased array arrangement may also separate materials in the fluid stream. A single piezoelectric element may be used rather than a piezoelectric array.

One particular application of acoustophoretic devices is the treatment of bioreactor materials. In a fed-batch bioreactor, at the end of the production cycle, it is important to filter all cells and cell debris from the extrudate material located in the fluid stream. The extruded material consists of biomolecules, such as recombinant proteins or monoclonal antibodies, and is the desired product to be recovered. By using acoustophoresis, the separation of cells and cell debris is very efficient and results in very little loss of the extruded material. The use of acoustophoresis is an improvement over current filtration processes (depth filtration, tangential flow filtration, centrifugation) which exhibit limited efficiency at high cell densities, so that the loss of expressed material in the filter bed itself can be as high as 5% of the material produced by the bioreactor. The use of mammalian cell cultures, including Chinese Hamster Ovary (CHO), NS0 hybridoma cells, Baby Hamster Kidney (BHK) cells, and human cells, has proven to be a very efficient method for the production/expression (expression) of recombinant proteins and monoclonal antibodies required for pharmaceutical use. Filtration of mammalian cells and mammalian cell debris by acoustophoresis helps to greatly increase the yield of fed-batch bioreactors. The acoustophoretic process can also be combined with standard filtration processes, either upstream or downstream, by using multi-dimensional sound waves, such as depth filtration using diatomaceous earth, Tangential Flow Filtration (TFF), or other physical filtration processes.

Another type of bioreactor, the perfusion reactor, uses continuous expression of a target protein or monoclonal antibody from CHO cells. The continuity of the perfusion reactor allows for a much smaller footprint in the faster production cycle. The use of acoustophoresis in the production/expression of proteins to maintain CHO cells in a fluid stream is a very efficient and closed-loop production. It also allows for increased or maximal production efficiency of proteins and monoclonal antibodies, since no material is lost in the filter bed.

In a fed-batch bioreactor process, the acoustophoresis device uses a single or multiple standing waves to capture cells and cell debris. Cells and cell debris with a positive contrast factor move to nodes (rather than antinodes) of the standing wave. As cells and cell debris agglomerate at the nodes of the standing wave, there is also a physical washout (scrubbing) of the emerging fluid stream whereby more cells are captured as they come into contact with cells already held within the standing wave. When the cells in the multi-dimensional acoustic standing wave agglomerate to the point where their mass can no longer be maintained by the acoustic wave, the trapped aggregated cells and cell debris fall out of the fluid stream by gravity and can be collected separately. This effect allows cells to be separated in a continuous gravity separation process.

Advanced multi-physical and multi-scale computer models have been combined with high frequency (MHz), high power and high efficiency ultrasonic drivers with embedded controls to enable new designs of acoustic resonators driven by piezoelectric transducer arrays, yielding acoustophoretic separation devices that far exceed current capabilities.

Ideally, such transducers generate a multi-dimensional standing wave in the fluid that exerts a lateral force on the suspended particles/secondary fluid to accompany the axial force, thereby increasing the particle capture capacity of the acoustophoretic system. Typical results published in the literature indicate that transverse forces are two orders of magnitude less than axial forces. In contrast, the techniques disclosed in this application provide lateral forces that are of the same order of magnitude as axial forces.

The system may be driven by a controller and amplifier (not shown). System performance may be monitored and controlled by a controller. The excitation parameters of the transducer may be modulated. For example, the frequency, current, or voltage of the transducer excitation or drive signal may be modulated to change the characteristics of the generated acoustic standing wave. The amplitude modulation and/or frequency modulation may be controlled by a computer. The duty cycle of the standing wave propagation may also be used to achieve a particular result for the trapping material. The acoustic standing waves may be turned on and/or off at different frequencies to achieve the desired results.

The transverse force of the total Acoustic Radiation Force (ARF) generated by the ultrasound transducer of the present invention is significant and sufficient to overcome fluid resistance at high linear velocities up to 2cm/s and above. For example, the linear velocity through the apparatus of the present invention can be as small as or less than 4cm/min for separating cells/particles, and can be as high as 2cm/sec for separating oil/water phases. The flow rate may be as small as or less than 25mL/min, and may range up to 40mL/min to 1000mL/min, or even higher. These flow rates in the acoustophoretic system are applicable to batch reactors, fed-batch bioreactors, and perfusion bioreactors.

A schematic diagram of an embodiment for removing oil or other lighter than water material is shown in fig. 1A. The transducer 10 applies an excitation frequency typically in the range of hundreds of kHz to tens of MHz. One or more standing waves are generated between the transducer 10 and the reflector 11. The droplets or particles 12 are captured in a standing wave at a pressure antinode 14 where the droplets or particles 12 agglomerate, aggregate, agglomerate, or coalesce, and, in the case of a floating material, float to the surface and are discharged via an effluent outlet 16 located above the flow path. The purge fluid is discharged at outlet 18. The acoustophoretic separation technique enables multi-component particle separation to be accomplished at significantly reduced cost without fouling.

A schematic of an embodiment for removing contaminants or other heavier than water materials is shown in fig. 1B. The transducer 10 applies an excitation frequency typically in the range of hundreds of kHz to tens of MHz. At the pressure node 15 where the contaminants agglomerate, aggregate, clump or coalesce, the contaminants in the influent fluid 13 are captured in the standing wave and, in the case of heavier materials, sink to the bottom collector and are discharged via an effluent outlet 17 located below the flow path. The purified water is discharged at outlet 18.

Typically, the transducers are arranged such that they cover the entire cross-section of the flow path. In a particular embodiment, the acoustophoretic separation system of FIG. 1A or 1B has a square cross-section of 6.375 inches by 6.375 inches, at up to 5 Gallons Per Minute (GPM)Flow rate, or linear velocity of 12.5 mm/sec. The transducer 10 is a PZT-8 (lead zirconate titanate) transducer having a 1 inch by 1 inch square cross-section and a nominal 2 or 3MHz resonant frequency. Each transducer consumed approximately 60W of power for droplets at a flow rate of 5 GPM. This power consumption translates to 0.500kW hr/m³The energy cost of (a). This low power usage indicates that the energy cost of the technology is very low. Ideally, each transducer is powered and controlled by its own amplifier. One application of this embodiment is the conversion of particle size distribution into larger droplets by agglomeration, aggregation, agglomeration or coalescence of micron-sized oil droplets.

Fig. 2 is a sectional view of a conventional ultrasonic transducer. The transducer has a wear plate 50 at the bottom end, an epoxy layer 52, a ceramic crystal 54 (e.g. made of PZT), an epoxy layer 56 and a backing layer 58. On either side of the ceramic crystal, there are electrodes: a positive electrode 61 and a negative electrode 63. An epoxy layer 56 attaches a backing layer 58 to the crystal 54. The entire assembly is accommodated in a housing 60, which housing 60 may be made of aluminum, for example. An electrical adapter 62 provides a connection for wires to pass through the housing and connect with leads (not shown) attached to the crystal 54. Typically, the backing layer is designed to increase damping and form a broadband transducer with uniform displacement over a wide range of frequencies, and is designed to suppress excitation in specific natural modes of vibration. Wear plates are typically designed as impedance transformers to better match the characteristic impedance of the medium to which the transducer radiates.

Fig. 3A is a cross-sectional view of an ultrasonic transducer 81 of the present invention, which can be used in an acoustophoretic separator. The transducer 81 is in the shape of a disc or plate and has an aluminum housing 82. Piezoelectric crystals are a large number of perovskite ceramic crystals, each consisting of a smaller tetravalent metal ion (usually titanium or zirconium) in a lattice of larger divalent metal ions (usually lead or barium) and O2-ions. By way of example, a PZT (lead zirconate titanate) crystal 86 defines the bottom end of the transducer and is exposed from the exterior of the housing. The crystal is supported at its periphery by a small elastomeric layer 98 (e.g., silicone or similar material) located between the crystal and the housing. In other words, there is no wear layer.

The screws 88 attach the aluminum top plate 82a of the housing to the body 82b of the housing via threads. The top plate includes a connector 84 for powering the transducer. The top surface of PZT crystal 86 is connected to positive and

negative electrodes

90, 92 separated by insulating material 94. The electrodes may be made of any conductive material, such as silver or nickel. Power is supplied to the PZT crystal 86 through electrodes on the crystal. Note that as shown in fig. 2, the crystal 86 does not have a backing layer or epoxy layer. In other words, there is an air gap 87 between the aluminum top plate 82a and the crystal 86 in the transducer (i.e., the air gap is completely empty). In some embodiments, a relatively minimal backing 58 and/or wear plate 50 may be provided, as shown in fig. 3B.

The design of the transducer can affect the performance of the system. Typical transducers are layered structures in which a ceramic crystal is bonded to a backing layer and a wear plate. Due to the high mechanical impedance presented by the fluid to which the transducer is loaded, conventional design guidelines for wear plates, such as half wavelength thickness for standing wave applications or quarter wavelength thickness for radiation applications, and manufacturing methods may not be suitable. Rather, in one embodiment of the invention, the transducer does not have a wear plate or backing, so that a crystal (e.g., polycrystalline, piezoelectric, or single crystal (i.e., quartz)) vibrates in one of its eigenmodes with a high Q factor. The vibrating ceramic crystal/disk is directly exposed to the fluid flowing through the flow chamber.

Removing the backing (e.g., leaving the crystal back air) also allows the ceramic crystal to vibrate in higher order vibrational modes with little damping (e.g., higher order modal displacement). In a transducer having a crystal with a backing, the crystal vibrates with a more uniform displacement, like a piston. Removing the backing allows the crystal to vibrate in a non-uniform displacement mode. The higher the order of the mode shape of the crystal, the more the nodal lines of the crystal. Although the correlation of the trapping lines to the nodes is not necessarily one-to-one, higher order modal shifts of the crystal produce more trapping lines, while driving the crystal at higher frequencies does not necessarily produce more trapping lines. See discussion below regarding fig. 8-9D.

In some embodiments, the crystal may have a backing that may minimally affect the Q factor of the crystal (e.g., less than 5%). The backing may be made of a substantially acoustically transparent material, such as balsa wood, foam, or cork, which allows the crystal to vibrate with a higher order mode shape and maintain a high Q factor, while still providing some mechanical support for the crystal. The backing layer may be solid or may be a crystal lattice with holes through the layer such that the crystal lattice follows the nodes of the vibrating crystal in certain higher order modes of vibration, providing support at the node locations while allowing the rest of the crystal to vibrate freely. The goal of the lattice structure or acoustically transparent material is to provide support without lowering the Q factor of the crystal or interfering with the excitation of a particular mode shape.

Direct crystal contact with the fluid also contributes to the high Q factor by avoiding the damping and energy absorbing effects of the epoxy and wear plates. Other embodiments may have wear plates or wear surfaces to prevent lead-containing PZTs from contacting the primary fluid. In e.g. biological applications, such as separation of blood, it may be necessary to insert a layer on the PZT. These applications may use wear resistant layers such as chromium, electrolytic nickel or electroless nickel (electrolytic nickel). Chemical vapor deposition may also be used to coat a layer of poly (p-xylylene) (e.g., parylene) or other polymer. Organic and biocompatible coatings such as silicone or polyurethane may also be used as wear resistant surfaces. A glassy carbon abrasion resistant layer may also be used. Glassy carbon, also known as vitreous carbon (vitreous carbon), is a non-graphitizing carbon that combines the properties of glass and ceramics with those of graphite. The most important properties are high temperature resistance, hardness (7Mohs), low density, low electrical resistance, low friction and low thermal resistance. Vitreous carbon also has an extremely strong resistance to chemical attack and impermeability to gases and liquids.

In the present invention, the piezoelectric crystal used in each ultrasonic transducer is modified in the form of a segmented array of piezoelectric elements. The array is used to form a multi-dimensional acoustic standing wave(s) that can be used for acoustophoresis.

Fig. 4 shows a monolithic, single piece, single electrode piezoelectric crystal 200 for an ultrasound transducer. The piezoelectric crystal has a substantially square shape with a length 203 and a width 205 (e.g., about one inch) that are substantially equal to each other. The crystal 200 has an inner surface 202, and the crystal also has an outer surface 204 on the opposite side of the crystal that is typically exposed to fluid flowing through the acoustophoresis device. The area of the outer and inner surfaces is relatively large and the crystal is relatively thin (e.g., about 0.040 inches for a 2MHz crystal).

Fig. 5 shows a piezoelectric crystal 200' of the present invention. The inner surface 202 of the piezoelectric crystal 200' is divided into a piezoelectric array 206 having a plurality (i.e., at least two) piezoelectric elements 208. However, the array is still single crystalline. The piezoelectric elements 208 are separated from one another by one or more channels or cutouts 210 in the inner surface 202. The width of the channels (i.e., between the piezoelectric elements) may be on the order of about 0.001 inches to about 0.02 inches. The depth of the channels may be from about 0.001 inches to about 0.02 inches. In some cases, a potting material 212 (i.e., epoxy, silicone, etc.) may be inserted into the channels 210 between the piezoelectric elements. The potting material 212 is non-conductive, acts as an insulator between adjacent piezoelectric elements 208, and also serves to hold the individual piezoelectric elements 208 together. Here, the array 206 contains sixteen piezoelectric elements 208 (although any number of piezoelectric elements is possible) arranged in a rectangular 4x4 configuration (with squares being a subset of rectangles). Each piezoelectric element 208 has substantially the same dimensions as each other. The entire array 200' has the same length 203 and width 205 as the single crystal shown in fig. 4.

FIG. 6 illustrates another embodiment of a transducer 200 ". The transducer 200 "is substantially similar to the transducer 200' of fig. 5, except that the array 206 is formed from twenty-five piezoelectric elements 208 configured at 5x 5. Likewise, the entire array 200 "has the same length 203 and width 205 as the single crystal shown in FIG. 4.

Each piezoelectric element in the piezoelectric array of the present invention may have a separate electrical attachment (i.e., electrode) so that each piezoelectric element can be individually controlled for frequency and power. These elements may share a common ground electrode. This arrangement not only allows for the generation of a multi-dimensional acoustic standing wave, but also improves the control of the acoustic standing wave.

The piezoelectric array may be formed from a single piece of piezoelectric crystal by cutting across one surface to separate the surface of the piezoelectric crystal into individual elements. The cutting of the surface may be performed by using a saw, end mill or other means to remove material from the surface and leave discrete elements of the piezoelectric crystal between the channels/grooves formed thereby.

As described above, the potting material may be incorporated into the channels/grooves between the elements to form a composite material. For example, the potting material may be a polymer, such as an epoxy. In a particular embodiment, the piezoelectric elements 208 are individually physically isolated from each other. Such a structure may be obtained by filling the channels 210 with potting material and then cutting, grinding or milling the outer surface 204 into the channels. As a result, the piezoelectric elements are bonded to each other by the potting material, and each element is a separate component of the array. In other words, each piezoelectric element is physically separated from the surrounding piezoelectric elements by the potting material. Fig. 21 is a sectional view comparing these two embodiments. At the top, the crystal shown in fig. 5 is shown. The crystal is cut into four separate piezoelectric elements 208 on the inner surface 202, but the four elements share a common outer surface 204. At the bottom, the four piezoelectric elements 208 are physically isolated from each other by potting material 212. The four elements do not share a common surface therebetween.

In the present system, the system is operated at a voltage such that the particles are trapped in the ultrasonic standing wave, i.e. remain in a stationary position. The particles are collected along a defined trapping line spaced at half a wavelength. Within each nodal plane, the particles are trapped with minimal acoustic radiation potential. The axial component of the acoustic radiation force drives particles with a positive contrast factor to the pressure nodal surface, while particles with a negative contrast factor are driven to the pressure antinode surface. The radial or lateral component of the acoustic radiation force is the force that traps the particles. In systems using typical transducers, the radial or lateral component of the acoustic radiation force is typically several orders of magnitude smaller than the axial component of the acoustic radiation force. However, the lateral force in the device of the present invention can be significant, on the same order of magnitude as the axial force component, and sufficient to overcome the fluid resistance of linear velocities up to 1 cm/sec. As discussed above, the lateral force can be increased by driving the transducer in a higher order mode shape, as opposed to a vibrational mode in which the crystal effectively moves as a piston with uniform displacement. The sound pressure is proportional to the drive voltage of the transducer. The electrical power is proportional to the square of the voltage.

During operation, the piezoelectric array of the present invention can be driven such that the piezoelectric elements are in phase with each other. In other words, each piezoelectric element generates a multi-dimensional acoustic standing wave having the same frequency and without time shifting. In other embodiments, the piezoelectric elements may be out of phase with each other, i.e., there is a different frequency or time shift, or they have different phase angles. As will be described further below, in a more specific embodiment, the elements in the array are arranged in groups or sets that are out of phase by multiples of 90 ° (i.e., 90 ° and/or 180 °).

In embodiments, the pulsed voltage signal driving the transducer may have a sine wave, a square wave, a sawtooth wave, or a triangular waveform; and has a frequency of 500kHz to 10 MHz. The pulsed voltage signal may be driven with pulse width modulation that produces any desired waveform. The pulsed voltage signal may also have amplitude or frequency modulation start/stop capability to eliminate streaming.

Fig. 7 is a linear-logarithmic graph (linear y-axis, logarithmic x-axis) showing the calculated scale of acoustic radiation force, fluid resistance, and buoyancy force with particle radius. Buoyancy is applicable to negative contrast factor particles, such as the oil particles in this example. The calculated buoyancy may include an element of gravity. In embodiments using positive contrast factor particles (which may be certain types of cells), lines representing gravity are used in the figures for such positive contrast factor particles representing acoustic radiation force and fluid resistance. In this example shown in fig. 7, calculations were made for a typical SAE-30 oil drop used in the experiment. Buoyancy is a force that is dependent on particle volume, e.g. proportional to the radius cube, and is relatively negligible for particle sizes on the order of microns, but grows and becomes significant for particle sizes on the order of hundreds of microns. The fluid resistance varies linearly with the fluid velocity, for example proportional to the square of the radius, and typically exceeds the buoyancy of micron-sized particles, but has less effect on larger-sized particles on the order of hundreds of microns. Acoustic radiation force scaling works differently than fluid drag or buoyancy. When the particle size is small, the acoustic trapping force is proportional to the cube of the particle radius (volume) of the particle at a nearly linear ratio. Finally, as the particle size increases, the acoustic radiation force no longer increases linearly with the cube of the particle radius. As the particle size continues to increase, the acoustic radiation force decreases rapidly and, at some critical particle size, is a local minimum. To further increase the particle size, the magnitude of the radiation force is again increased, but with an opposite phase (not shown in the graph). This pattern is repeated to increase the particle size. The relationship of particle size to acoustic radiation force depends at least in part on the wavelength or frequency of the acoustic standing wave. For example, as the particles increase to a half wavelength size, the acoustic radiation force on the particles decreases. As the particle size increases to more than a half wavelength and less than a full wavelength, the acoustic radiation force on the particles increases.

Initially, as the suspension flows through the acoustic standing wave with the initially smaller micron-sized particles, the acoustic radiation force balances the combined effects of fluid drag and buoyancy to trap the particles in the standing wave. In FIG. 7, trapping occurs at a particle size of about 3.5 microns, labeled R_c1. According to the graph shown in FIG. 7, as the particle size continues to increase beyond R_c1Larger particles are trapped because the acoustic radiation force is increased compared to the fluid resistance. When smaller particles are trapped in the standing wave, particle agglomeration/caking/aggregation/agglomeration can occur, resulting in continued growth of the effective particle size. As larger particles are held and grow in size, other smaller particles continue to be driven into the trapping sites in the standing wave, resulting in continuous trapping. As the particle size increases, the acoustic radiation force on the particle increases until a first region of the particle size is reached. As the particle size increases beyond the first region, the acoustic radiation force on the particles begins to decrease. As the particle size continues to grow, the acoustic radiation force rapidly decreases until the buoyancy becomes dominant, which is defined by the second critical particle size R_c2It is indicated that particles of this size will rise or sink depending on their relative density or acoustic contrast factor with respect to the host fluid. When a particle rises or sinks and leaves an antinode (in the case of negative contrast factor) or a node (in the case of positive contrast factor) of the acoustic standing wave, the acoustic radiation force on the particle may be reducedTo a negligible amount. The acoustic radiation force continues to capture the smaller and larger particles and drives the captured particles to the capture location, which in this embodiment is located at the pressure antinode. The smaller particle size suffers from a reduced acoustic radiation force, which is reduced, for example, to that indicated at point R_c1Nearby acoustic radiation forces. The particle size is effectively increased as other particles become trapped and coalesced, agglomerated, aggregated, agglomerated, and/or clustered together at nodes or antinodes of the acoustic standing wave, so that the acoustic radiation force is increased and the cycle repeats. All particles do not escape from the acoustic standing wave and those remaining particles may continue to increase in size. Thus, fig. 7 explains how small particles are continuously trapped in a standing wave, grow into larger particles or clumps, and then eventually rise or settle due to the relationship between buoyancy, drag and acoustic radiation force and particle size.

The size, shape, and thickness of the transducer determine the displacement of the transducer at different excitation frequencies, which in turn affects the oil separation efficiency. Typically, the transducer operates at a frequency near the thickness resonance frequency (half wavelength). Gradients in transducer displacement typically result in locations where more oil is trapped. Higher order modal displacements produce a three-dimensional acoustic standing wave with a strong gradient in the acoustic field in all directions, resulting in an acoustic radiation force of the same intensity in all directions, resulting in a plurality of trapping lines, wherein the number of trapping lines is related to the specific modal shape of the transducer.

FIG. 8 shows the measured electrical impedance magnitude of a 1 "square PZT-82-MHz transducer as a function of frequency near the 2.2MHz transducer resonance. The minimum in the transducer electrical impedance corresponds to the acoustic resonance of the water column and represents the potential frequency for operation. Numerical modeling has shown that the transducer displacement profile varies significantly at these acoustic resonance frequencies, directly affecting the acoustic standing wave and the resulting trapping forces. Since the transducer operates near its thickness resonance, the displacements of the electrode surfaces are substantially out of phase. The typical displacement of the transducer electrodes is not uniform and varies depending on the excitation frequency. As an example, at one excitation frequency with a single drop trapping line, the displacement has a single maximum in the middle of the electrode, and a minimum near the transducer edge. At another excitation frequency, the transducer profile has multiple maxima, resulting in multiple drop capture lines. Higher order transducer displacement modes result in higher trapping forces and stable trapping lines for trapping oil droplets.

To investigate the effect of transducer displacement profile on acoustic trapping force and oil separation efficiency, the experiment was repeated 10 times with all conditions except excitation frequency being the same. Ten successive acoustic resonance frequencies, indicated by the circled numbers 1-9 and the letter a in fig. 8, are used as excitation frequencies. These oscillations in impedance correspond to the resonance of the acoustophoretic system. The length of the acoustophoretic system is 2", the oscillation interval is about 15 kHz. The conditions are as follows: the test duration was 30 minutes, an oil concentration of 1000ppm of about 5 micron SAE-30 oil droplets, a flow rate of 500 milliliters per minute (ml/min), and a 20W power applied in a cross section 1 inch wide by 2 inches long.

The trapping lines of oil droplets were observed and characterized as the emulsion passed through the transducer. The observation of the number of trapped lines passing through the flow channel and the characteristics of the pattern are referred to for seven of the ten resonant frequencies identified in fig. 8, as shown in fig. 9A.

FIG. 9B shows an isometric view of the present system in which the location of the capture line is determined. Fig. 9C is a view of the system looking down at the entrance along arrow 114. FIG. 9D is a diagram presented by the present system when viewed directly at the transducer face along arrow 116. The trapping lines shown in fig. 9B to 9D are those generated at frequency 4 in fig. 8 and 9A.

The effect of the excitation frequency obviously determines the number of trapping lines, which varies from a single trapping line at the acoustic resonance excitation frequencies 5 and 9 to 9 trapping lines with respect to the acoustic resonance frequency 4. At other excitation frequencies, 4 or 5 trapping lines are observed. Different displacement profiles of the transducer can produce different (more) trapping lines in the standing wave, while larger gradients in the displacement profile generally produce higher trapping forces and more trapping lines.

Table 1 summarizes the findings of the oil capture test using a system similar to that of fig. 10A. An important conclusion is that the oil separation efficiency of an acoustic separator is directly related to the modal shape of the transducer. Higher order displacement profiles produce greater acoustic trapping force and more trapping lines, resulting in better efficiency. A second conclusion that is useful for scaling studies is that tests show that capturing 5 micron droplets at 500ml/min (milliliters/minute) implies that 10 watts of power is required per square inch of transducer area per 1 "of beam span. The main loss is the loss of the thermal viscous absorption in the total volume of the acoustic standing wave. The energy cost associated with this flow rate is 0.500 kilowatt-hours per cubic meter.

Table 1: capture mode efficiency study

A 4 "x 2.5" flow cross-sectional area, medium-scale apparatus 124 for separating a primary fluid from a floating fluid or particle is shown in fig. 10A. The acoustic path length is 4 ". The apparatus shown here is in a downward flow direction orientation that serves to separate low concentrations of particles from the primary fluid. However, the present apparatus may be substantially completely inverted to allow for the separation of particles heavier than the main stream. Instead of buoyancy in the upward direction, the weight of the agglomerated particles due to gravity pulls them downward. It should be noted that this embodiment is depicted as having an orientation in which the fluid flows vertically. However, it is also conceivable that the fluid flows in a horizontal direction or at an angle.

The fluid containing the particles enters the apparatus through inlet 126 into annular chamber (plenum) 131. The annular chamber has an annular inner diameter and an annular outer diameter. It should be noted that the term "annular" is used herein to refer to the region between two shapes, and the chamber need not be circular. Two inlets are seen in this illustration, although it is contemplated that any number of inlets may be provided as desired. In a particular embodiment, four inlets are used. The inlets are diametrically opposed and oriented.

The profile nozzle wall 129 reduces the outer diameter of the flow path in such a way that the closer to the wall region a higher velocity is generated and turbulence is reduced, thereby generating a near plug flow as the fluid velocity profile progresses, i.e. accelerating the fluid downwards in the direction of the centre line with little or no circumferential motion component and lower flow turbulence. This chamber flow profile is desirable for acoustic separation and particle collection. The fluid passes through connecting conduit 127 and into flow/separation chamber 128. It can be seen in the enlarged profiled nozzle 129 of fig. 10B that the nozzle wall also adds a radial component of motion to the suspended particles, moving the particles closer to the centerline of the apparatus and causing more collisions with the rising, floating, agglomerated particles. This radial movement allows the most advantageous washing out (scrubbing) of particles from the fluid in the connecting duct 127 before reaching the separation chamber. The contoured nozzle wall 129 directs the fluid in a manner that creates large scale vortices at the entrance of the collection duct 133, thereby also improving particle collection. In general, the flow area of the device 124 is designed to decrease continuously from the annular chamber 131 to the separation chamber 128 to ensure low turbulence and vortex formation, thereby facilitating better particle separation, agglomeration, and collection. The nozzle wall has a wide end and a narrow end. The term "wash out" is used to describe the process of particle/droplet agglomeration, aggregation, agglomeration or coalescence, which occurs when larger particles/droplets travel in a direction opposite to the fluid flow and collide with smaller particles, actually washing out the smaller particles out of suspension.

Returning to FIG. 10A, flow/separation chamber 128 includes a transducer array 130 and reflectors 132 located on opposite sides of the chamber. In use, a multi-dimensional standing wave 134 is generated between the transducer array 130 and the reflector 132. These standing waves can be used to agglomerate particles, and this orientation is used to agglomerate floating particles (e.g., oil). The fluid containing the remaining particles is then discharged through the flow outlet 135.

As the floating particles agglomerate, they eventually overcome the combined action of fluid flow resistance and acoustic radiation force, and their buoyancy 136 is sufficient to cause the floating particles to rise upward. In this regard, the collection conduit 133 is surrounded by the annular chamber 131. Larger particles will pass through this conduit and enter the collection chamber 140. The collection chamber may also be part of the outlet conduit. The collection conduit and the flow outlet are located at opposite ends of the apparatus.

It should be noted that the floating particles formed in the separation chamber 128 then pass through the connecting duct 127 and the nozzle wall 129. This arrangement allows the influent stream from the annular chamber to flow over the rising agglomerated particles due to the inward radial motion imparted by the nozzle wall.

The transducer configuration of the present invention generates a three-dimensional pressure field that includes a standing wave perpendicular to the fluid flow. The pressure gradient is large enough to generate an acoustophoretic force in a lateral direction, e.g., a direction orthogonal to the standing wave direction (i.e., the acoustophoretic force is parallel to the fluid flow direction), which is of the same order of magnitude as the acoustophoretic force in the wave direction. These forces enhance particle capture, collection and collection in the flow chamber and along well-defined capture lines, in contrast to conventional devices which capture particles only in the collection face. The particles have sufficient time to move towards the nodes or antinodes of the standing wave, creating regions where the particles can collect, agglomerate and/or coalesce, followed by buoyancy/gravity separation.

In some embodiments, the fluid flow has a reynolds number of up to 1500, i.e., laminar flow is occurring. For industrial applications, the reynolds number for flow through the system is typically 10 to 1500. The movement of the particles relative to the fluid motion produces reynolds numbers well below 1.0. The reynolds number represents the ratio of inertial flow effects to viscous effects in a given flow field. For reynolds numbers below 1.0, viscous forces are dominant in the flow field. This situation results in significant damping, where shear forces dominate the overall flow. This flow in which viscous forces prevail is called Stokes flow. The flow of molasses is an example. Under such conditions, wall profile control and streamlining are of only minor importance. These characteristics are associated with the flow of very viscous fluids or in very small channels (e.g., MEMS devices). The inlet profile control is of little importance. The flow of particles relative to the fluid in an acoustophoretic particle separator will be a Stokes flow because both the particle diameter and the relative velocity between the particles and the fluid are small. On the other hand, the reynolds number for the flow through the system will be much greater than 1.0, since the fluid velocity and inlet diameter are very large.

For reynolds numbers much greater than 1.0, viscous forces dominate where the flow contacts the surface. This viscous zone near the surface is called the boundary layer and is first recognized by Ludwig Prandtl. In a pipe flow, for a fully developed flow in the pipe, if the reynolds number is significantly above 1.0 and below 2300, the flow will be laminar. The wall shear stress at the wall will diffuse into the flow with distance. At the entrance of the pipe, the flow rate begins to deviate from uniform. As the flow moves down the pipe, the wall viscous forces will spread inward toward the centerline to produce a parabolic velocity profile. Such a parabolic profile will have a peak value that is twice the average velocity. The length of the conduit required for the development of the parabolic profile is a function of the reynolds number. For a Reynolds number of 20 (which is typical for CHO operation), the development length is 1.2 times the tube diameter. Thus, the fully developed flow occurs very quickly. Such a peak velocity in the center can be detrimental to acoustic particle separation. Also, at laminar reynolds numbers, turbulence may occur, and flow surface profiling is very important in controlling flow. For these reasons, the separator is designed with an annular inlet chamber and a collecting duct.

The large annular chamber is followed by an inlet wall nozzle that accelerates and directs the fluid inward toward the centerline, as shown in fig. 10B. The wall profile has a large influence on the distribution. The zone convergence increases the flow mean velocity, but it is the wall profile that determines the velocity profile. The nozzle wall profile will be streamlined and designed with a small radius of curvature in the separator.

The transducer(s) are used to create a pressure field that produces forces of equal magnitude in both the direction orthogonal to the standing wave direction and the standing wave direction. When these forces are of approximately equal magnitude, particles of sizes from 0.1 microns to 300 microns will move more efficiently toward the agglomeration zone ("capture line"). Because of the equally sized gradient in the orthogonal acoustophoretic force component, there are "hot spots" or particle collection regions that are not located in the conventional region between the transducer 130 and the reflector 132 in the direction of the standing wave. The hot spot is located at a minimum of the acoustic radiation potential. Such hot spots represent particle collection locations.

One application of acoustophoretic devices is the separation of biotherapeutic proteins from protein-producing biological cells. In this regard, existing separation methods utilize filtration or centrifugation, either of which can damage the cells while releasing protein debris and enzymes into the purification process and increasing the burden on downstream parts of the purification system. It is desirable to be able to process volumes with higher cell densities, as this allows for the collection of larger amounts of therapeutic protein and better cost effectiveness.

Fig. 11A and 11B are exploded views showing parts of the acoustophoretic separator. FIG. 11A has only one separation chamber, while FIG. 11B has two separation chambers.

Referring to fig. 11A, fluid enters separator 190 through four-port inlet 191. Here too the annular chamber can be seen. The transition piece 192 is provided to create plug flow through the separation chamber 193. The transition piece includes a profiled nozzle wall having a curved shape as shown in fig. 10A. The transducer 40 and reflector 194 are located on opposite walls of the separation chamber. Subsequently, the fluid exits the separation chamber 193 and the separator through the outlet 195. The separation chamber has a rectangular flow path geometry.

In fig. 11B there are two separation chambers 193. A system coupling 196 is disposed between the two chambers 193 to couple them together.

Acoustophoretic isolation has been tested on different strains of Chinese Hamster Ovary (CHO) cells. In one experiment, a solution with an initial cell density of 8.09x 106 cells/mL (cells/mL), 1,232NTU turbidity, and cell viability of about 75% was isolated using a system as depicted in fig. 11A. The transducer is a 2MHz crystal, operating at about 2.23MHz, consuming 24-28 watts. A flow rate of 25 milliliters per minute (mL/min) was used. The results of this experiment are shown in fig. 12A.

In another experiment, a solution with an initial cell density of 8.09x 106 cells/ml, 1,232NTU turbidity, and about 75% cell viability was isolated. This CHO cell line has a bimodal particle size distribution (at sizes 12 microns and 20 microns). The results are shown in fig. 12B.

FIGS. 12A and 12B are generated by a Beckman Coulter Cell Viability Analyzer (Beckman Coulter Cell Viability Analyzer). Other tests have shown that frequencies of 1MHz and 3MHz are not as effective as 2MHz in separating cells from a fluid.

In other tests performed at a flow rate of 10 liters/hour, 99% of the cells were captured and cell viability higher than 99% was confirmed. In other tests at a flow rate of 50 mL/min (i.e., 3 liters/hour), a final cell density of 3x 106 cells/mL (cells/mL) was obtained with nearly 100% viability and with little temperature rise. In still other tests, a 95% reduction in turbidity was obtained at a flow rate of 6 liters/hour.

The tests for calibration units (scaled units) shown in FIGS. 10A to 10B were performed on biological applications using yeast as a mimic for CHO. For these tests, different frequencies and power levels were tested at a flow rate of 15 liters/hour. Table 2 shows the results of the tests.

Table 2: results for a 2.5"x 4" system at a flow rate of 15 liters/hour

Frequency (MHz)	30W	37W	45 watt
				2.2211	93.9	81.4	84.0
2.2283	85.5	78.7	85.4
				2.2356	89.1	85.8	81.0
2.243	86.7	-	79.6

In biological applications, many components, such as tubing leading to or from the housing, the inlet, the exhaust plenum, and the access plenum, etc., may be disposable, with only the transducer and reflector being cleaned for reuse. Avoiding the centrifuge and filter allows for better separation of CHO cells without reducing cell viability. The shape factor of the acoustophoretic separator is also smaller than that of the filtration system, allowing CHO separations to be miniaturized. The transducer may also be driven to produce rapid pressure changes to avoid or clear blockages due to CHO cell agglomeration. The frequency of the transducer may also be varied to obtain optimum effectiveness at a given power.

The following examples are provided to illustrate the apparatus, components and methods of the present invention. These examples are merely illustrative and are not intended to limit the invention to the materials, conditions, or process parameters described therein.

Examples

A two-dimensional numerical model was developed for the acoustophoresis device using COMSOL simulation software. This model is shown in fig. 13. The device includes an aluminum wall 222 and a stainless steel reflector 224 opposite the wall. Embedded in the wall is a piezoelectric transducer 230. As shown, the transducer is in the form of a 4-element piezoelectric array. The wall 222 and reflector 224 define a flow chamber, and arrow 225 indicates the direction of flow of the fluid through the flow chamber. The piezoelectric transducer is in direct contact with the fluid. Channel/cut 210 and potting material 212 are also shown, although potting material was not used in the simulation.

The simulation software was run and its output compared to published data (Barmatz, J.Acoust.Soc.am.77,928, 1985). Fig. 14A compares the acoustic potentials U. Fig. 14B compares the x-component of the Acoustic Radiation Force (ARF). FIG. 14C compares the y-component of ARF. Fig. 14D compares the absolute values of ARF. In these figures, published data is at the top and numerical model results are at the bottom. As can be seen here, the results of the numerical model match the published data, which validates the numerical model and the subsequent calculations resulting therefrom.

Three different simulations were then run to model the separation of SAE 30 oil droplets from water using three different piezoelectric transducers: 1-element transducers (i.e., single crystals), 4-element transducers, and 5-element transducers. The transducers were operated at the same frequency and the following parameters were used for oil and water: oil particle radius (Rp) 10 μm; oil density (p)_p)＝865kg/m³(ii) a Velocity of sound in oil (c)_p) 1750 m/sec; particle velocity (. mu.)_f) 0.001kg/m sec; water density (. rho.)_f) 1000kg/m 3; and speed of sound in water (c)_f)＝1500m/sec。

For a 4-element transducer, each channel has a width of 0.0156 inches and a depth of 0.0100 inches, and each element has a width of 0.2383 inches (the total width of the transducer is 1 inch). For a 5-element transducer, each channel has a width of 0.0156 inches and a depth of 0.0100 inches, and each element has a width of 0.1875 inches.

FIG. 15 shows a simulation of the force on a particle using a 1-element transducer, which is a two-dimensional representation of a PZT crystal 200. Fig. 16 shows a simulation of the force on a particle using a 4-element transducer, which is a two-dimensional representation of a PZT crystal 200'. FIG. 17 shows a simulation of the force on a particle using a 5-element transducer, which is a two-dimensional representation of a PZT crystal 200 ". Each transducer has the same width regardless of the number of elements. The amplitude of the resulting multi-dimensional acoustic standing wave can be clearly seen (the amplitude of the lighter areas is higher than the amplitude of the darker areas).

Next, simulations were performed on the 4-element array to compare the effect of phase on the wave. The flow rate was 500mL/min, the reynolds number of the fluid was 220, the input voltage to each element was 2.5VDC, and the DC power to each element was 1 watt. In one simulation, the four elements are in phase with each other (i.e., out of phase) from 0-180-0-180. In another simulation, the four elements are in phase with each other. The simulation was then compared to actual testing with a transducer device having a 4x4 piezoelectric array as shown in fig. 18.

Fig. 19 compares the results of the out-of-phase simulation (left) with the picture (right), which shows the actual results when an out-of-phase array is used in the transducer arrangement of fig. 18. The results are very similar. Where the amplitude is high in the simulation, the captured particles can be seen in the actual picture.

Fig. 20 compares the results of in-phase simulation (left) and picture (right), which shows the actual results when an in-phase array is used in the transducer arrangement of fig. 18. The results are very similar.

Additional numerical modeling was performed using 4-element transducers and 5-element transducers, in phase or out of phase in different arrangements, over a sweep range of 2.19MHz to 2.25MHz for oil droplets of 20 microns diameter, as shown in table 3 below. Out of phase means that adjacent elements are excited with different phases.

FIG. 22 is a schematic diagram showing two out-of-phase modes simulated for a 4-element array. The 0-180-0-180 pattern is shown on the left side, while the 0-180-0 pattern is shown on the right side. Fig. 23 is a schematic diagram showing four out-of-phase modes simulated for a 5-element array. The upper left panel shows the 0-180-0-180-0 pattern. The upper right picture shows the 0-0-180-0-0 pattern. The bottom left diagram shows the 0-180-0 mode. The lower right panel shows the 0-90-180-90-0 pattern.

The ratio of the transverse (x-axis) force component to the axial (y-axis) force component of the acoustic radiation force is determined over this frequency range and the range of ratios is listed in table 3 below.

TABLE 3

Energy converter	Phase position	Minimum ratio	Maximum ratio
				1-element (Single Crystal)		～0.15	～0.75
4-element array	In phase	～0.08	～0.54
				4-element array	(0-180-0-180)	～0.39	～0.94
4-element array	(0-180-180-0)	～0.39	～0.92
				5-element array	In phase	～0.31	～0.85
5-element array	(0-180-0-180-0)	～0.41	～0.87
				5-element array	(0-0-180-0-0)	～0.41	～0.81
5-element array	(0-180-180-180-0)	～0.40	～0.85
				5-element array	(0-90-180-90-0)	～0.38	～0.81

Fig. 24 shows normalized Acoustic Radiation Force (ARF) from a single piezoelectric crystal simulation. The ARF value is normalized using the real power calculated from the measured voltage and current. Figure 25 shows the ratio of ARF components (lateral to axial) simulated for a single piezoelectric crystal over the frequency range tested. Fig. 26 shows the normalized Acoustic Radiation Force (ARF) from the 5-element simulation. Fig. 27 shows the ratio of ARF components (lateral to axial) simulated for the 5 elements over the frequency range tested. Comparing FIGS. 24-26, the peak ARF for the 1 element simulation was about 6e-11, while the peak ARF for the 5 element simulation was about 2 e-9. Comparing fig. 25-27, the force ratio is also more consistent, varying by about 0.60 as compared to about 0.40.

In general, 4-element and 5-element arrays produce high ratios, including some ratios greater than 0.9. Some simulations also have an acoustic radiation force amplitude that is almost two orders of magnitude higher than that produced by a 1-element transducer (used as a baseline).

The tentative 16 element arrays and 25 element arrays were then tested. The feed solution was a 3% packed cell pellet yeast solution used as a mimic of CHO cells for biological applications. For out-of-phase testing, a checkerboard pattern (checkerboard pattern) of 0 ° and 180 ° phases was used. For a 25 element array, 12 elements are 180 ° and 13 elements are 0 °. These checkerboard patterns are shown in FIG. 28. The left side is an array of 16 elements and the right side is an array of 25 elements, with different shading indicating different phase angles.

Turbidity of the feed, concentrate and permeate was measured after 30 minutes at various frequencies. The concentrate is the part that leaves the device, which contains the concentrated yeast, as well as some fluid. The permeate is the filtered part leaving the device, which is mainly liquid with a much lower yeast concentration. Lower turbidity indicates lower amounts of yeast. The capture efficiency was determined as (feed-permeate)/feed x 100%. The feed rate was 30mL/min and the concentrate flow rate was 5 mL/min. The power of the transducer was set to 8W.

Table 4 lists the results for a single element transducer, which is used as a baseline or control.

TABLE 4

Frequency (MHz)	2.225	2.244
			Concentrate (NTU)	15,400	15,400
Permeate (NTU)	262	327
			Feed (NTU)	4,550	5,080
Capture efficiency (%)	94.2	93.6

Table 5 lists the results of the 16 element in-phase test.

TABLE 5

Frequency (MHz)	2.22	2.225	2.23	2.242	2.243	2.244	2.255	2.26
									Concentrate (NTU)	22,700	24,300	22,500	24,600	23,100	28,100	27,400	23,800
Permeate (NTU)	205	233	241	201	249	197	244	165
									Feed (NTU)	5,080	4,850	5,100	4,830	4,810	5,080	4,940	4,830
Capture efficiency (%)	96.0	95.2	95.3	95.8	94.8	96.1	95.1	96.6

Table 6 lists the results of the 16 element out of phase tests.

TABLE 6

Frequency (MHz)	2.22	2.225	2.23	2.242	2.243	2.244	2.255	2.26
									Concentrate (NTU)	40,900	21,400	26,000	49,300	19,100	55,800	22,100	35,000
Permeate (NTU)	351	369	382	1,690	829	761	397	581
									Feed (NTU)	5,590	4,870	5,860	5,160	5,040	4,870	4,800	5,170
Capture efficiency (%)	93.7	92.4	93.5	67.2	83.6	84.4	91.7	88.8

Comparing the results and control of the 16 element arrays with each other, the in-phase array maintains high capture efficiency over the entire frequency range, while the out-of-phase array falls rapidly around 2.24 MHz. The efficiency results are very similar to the control of most in-phase tests. The in-phase efficiency is higher than the out-of-phase efficiency at each frequency.

Table 7 lists the results of the 25 element in-phase test.

TABLE 7

Frequency (MHz)	2.2190	2.2300	2.2355	2.2470	2.2475	2.2480	2.2485	2.2615
									Concentrate (NTU)	13,300	19,800	20,900	21,400	13,700	17,300	19,000	19,500
Permeate (NTU)	950	669	283	1,044	1,094	1,164	688	797
									Feed (NTU)	4,930	4,930	4,910	5,010	4,950	5,220	5,010	5,110
Capture efficiency (%)	80.7	86.4	94.2	79.2	77.9	77.7	86.3	84.4

Table 8 lists the results of the 25 element out of phase test.

TABLE 8

Frequency (MHz)	2.2190	2.2300	2.2355	2.2470	2.2475	2.2480	2.2485	2.2615
									Concentrate (NTU)	14,605	-	21,700	18,025	23,425	22,575	21,900	22,450
Permeate (NTU)	2,568	2,541	1,484	1,134	1,005	987	905	2,034
									Feed (NTU)	5,610	6,020	5,200	6,010	5,880	5,840	5,860	5,880
Capture efficiency (%)	54.2	57.8	71.5	81.1	82.9	83.1	84.6	65.4

Comparing 25 the results and control of the element arrays to each other, both arrays are less efficient than control. The 25-element in-phase array peaks around 95% and then falls off in both directions. The peak efficiency of the out-of-phase array is about 85% and drops dramatically. The efficiency results are very similar to the control. It should be noted that the high peak amplitudes found using numerical models have not passed experimental testing.

Fig. 29 is a circuit diagram of an RF power supply 300 having an LCL filter network 302 that provides a transducer drive signal on line 304 to an ultrasonic transducer 306. In this embodiment, the DC-DC converter 308 receives a first DC voltage from a power supply 310 and switches 312, 314 (e.g., power MOSFETs) are cooperatively switched under the control of a controller (not shown) to produce a Pulse Width Modulated (PWM) signal provided on line 316. The

switches

312, 314 are driven by a first complementary clock signal generated by the controller and have the same frequency and duty cycle. The switches may not be closed at the same time and the switching action produces a chopped voltage V across switch 314_b. The resultant PWM signal on line 316 is received by a filter 318 (e.g., a buck filter) that filters the signal on line 318 so as to be across a capacitor C₂An average voltage is present at 320 and the resultant PWM signal is provided on line 322 to a DC-AC inverter 324. The bandwidth of the filter 318 is selected so that the voltage on line 322 follows the change in duty cycle of the clock signal that drives the

switches

312, 314 based on the dynamic changes in the acoustic cavity 326. The second complementary clock signal generated by the controller drives the

switches

328, 330 to perform the DC to AC conversion and provides a resultant AC signal on line 332. The AC signal is then input to a matched filter network 302 (e.g., LC, LCL, etc.) that filters the input to attenuate the higher frequency components of the input and provides a periodic signal, such as a sine wave, on line 304 to drive a transducer 306. In this embodiment, the LCL filter 302 includes inductors L2, L2, 334, 336, respectively, connected in series, and a capacitor C3338 that extends from the node between the

inductors

334, 336 to ground. The LCL circuit 302 filters the output of the inverter 324 and matches the transducer 306 to the inverter 324 to improve power transfer.

The matched filter 302 provides impedance scaling (impedance scaling) to obtain the appropriate load for the inverter driver. The matched filter may be considered a network that is tuned to provide a desired power transfer (e.g., optimized power transfer) through the transducer 306 and into the resonant cavity 326. Considerations for implementing the filter 302 (e.g., LC or LCL) include the combined response of the transducer 306 and the resonant cavity 326. According to one embodiment, the filter allows a desired power transfer, e.g. an optimized power transfer, when the acoustic transducer is operated in a multi-dimensional mode or a multi-mode, e.g. in a plurality of overlapping vibration modes resulting in one or more primary or main vibration modes. The desired mode of operation is at a frequency corresponding to a lower or very small reactance point of the response of the transducer, and/or the response of the transducer/resonator combination.

For a fixed resonant frequency, the matched filter 302 may deliver different power values based on the system resonance(s) according to the inductor and capacitance value combinations used to form the matched filter network. Fig. 30 shows the response curve of a matched filter configured as an LC network with an inductance value of 1.596uH and a capacitance value of 3.0 nF. The resonant frequency of the LC network is 2.3 MHz. Referring to fig. 30, the resistive impedance is labeled a, the reactive impedance (reactive impedance) is labeled B, the input active power is labeled C, and the acoustic active power entering the cavity is labeled D. With respect to the power delivered to the system, increasing the capacitance with the same resonance will boost the power entering the system. In general, changing the values of the inductors and/or capacitors can affect the resonant frequency of the LC network. Changing the resonant frequency of the LC network changes the frequency at which optimal power transfer occurs and may affect transfer efficiency. For example, the frequency for optimum power transfer relative to the lower or lowest reactance point of the input impedance of the system (labeled B) is affected by the resonant frequency of the LC network.

The graph in fig. 30 shows points on the input active power (C) and the acoustic active power (D) at the reactance minimum. The input active power and the acoustic active power are reasonably matched, indicating efficient power transfer. If the value of the inductor becomes 0.8uH and the value of the capacitor becomes 6.0nF, the same reactance minimum results in greater power transfer with slightly less efficiency. When the input active power (C) is significantly different from the acoustic active power (D) (the former is greater than the latter), the efficiency of power transfer becomes low. In some cases, depending on the inductance and capacitance values, power transfer may be efficient, however the frequency operating point may not be at the point of very little reactance (B). Accordingly, a choice may be made between operating the transducer to obtain efficient separation in the acoustic chamber, implying very small reactive points, and obtaining efficient power transfer to the chamber. For a given material being separated and a given transducer, the LC network can be selected at a resonant frequency that achieves efficient power transfer to the acoustic cavity, thereby improving overall system efficiency.

Fig. 31 is a circuit diagram of one embodiment of the buck filter 318 shown in fig. 29. The component values shown in fig. 31 are presented by way of example, and other values and component combinations may be used to provide the desired filtering.

Fig. 32 is a block diagram of a system 350 for providing transducer drive signals on line 352 to an acoustic transducer 354. Referring to fig. 32, a system 350 controls a transducer 354 coupled to an acoustic chamber 356. Acoustic transducer 354 is driven by an RF power converter consisting of a DC power source 358 (e.g., 48 volts DC), a DC-DC converter 360 (e.g., a buck converter), and an RF DC-AC inverter 362. The inverter output drive signal on line 364 is input to a low pass filter 365 (e.g., an LC or LCL matched low pass filter as shown in fig. 29) and the resultant filtered signal on line 367 is sensed to obtain a voltage sense signal on line 366 and a current sense signal on line 368, which are fed back to the controller 370. The controller 370 provides control signals to the converter 360 and the inverter 362 to control the drive signals on line 364.

The signal provided by the controller 370 to the converter 360 is a pulse width measurement that determines the duty cycle of the switching signal in the converter 360. The duty cycle determines the DC level on the converter output signal on line 372, which is applied to the inverter 362. For example, the larger the duty cycle, the higher the DC output on line 372. Controller 370 provides control signals to inverter 362 that determine the operating frequency of the inverter. The control signal provided to the inverter 362 may be a switching signal for switching a switch (e.g., FET) in the inverter, an example of such a switch being shown in fig. 29. Alternatively or additionally, the controller 370 may provide control signals to the inverter 362 indicating the desired switching frequency, and circuitry internal to the inverter interprets the control signals and switches the internal switches in accordance with the interpreted control signals.

The voltage sense signal on line 366 and the current sense signal on line 368 are provided as feedback signals to controller 370 to control the drive signal provided to acoustic transducer 354 on line 364. The controller 370 operates and calculates the feedback signals on the

lines

366, 368, for example, to obtain a power measurement P ═ V × I, or to obtain a phase angle θ ═ arctan (X/R).

The controller 370 is equipped with a control scheme that receives process settings, such as power output, frequency operating range, or other user selectable parameters, and provides control signals to the converter 360 and inverter 362 based on the process settings and feedback values. For example, as described above, the controller may sequence a plurality of frequencies in the frequency range provided to the inverter 362, thereby scanning the frequency range and determining the characteristics of the transducer 354 or the characteristics of the transducer 354 in combination with the acoustic chamber 356, which may be under load. The results of the frequency sweep in terms of voltage and current obtained from the feedback signals on

lines

366, 368 are used to identify the characteristics of the impedance curve of the component or system, as shown in fig. 33. Fig. 33 is a graph showing a frequency response for an acoustic transducer.

The frequency sweep may be implemented to occur at set-up, and/or at intervals during operation of the illustrated system. During steady state operation, a frequency sweep may be performed to identify a desired set point for operation, such as power or frequency, based on user settings and feedback values. Thus, the control scheme implemented by controller 370 is dynamic and responsive to changing conditions in the system, such as frequency drift, temperature changes, load changes, and any other system parameter changes that may be encountered. The dynamic nature of the control scheme allows the controller to respond or compensate for non-linearities such as may be encountered as a component ages or loses tolerance. Accordingly, the control scheme is adaptive and can adapt to system variations.

Still referring to fig. 32, some embodiments of system operation include driving the acoustic transducer 354 to create an acoustic standing wave (e.g., a multi-dimensional acoustic standing wave) in the acoustic chamber 356. For example, a 3D acoustic wave may be excited by driving an acoustic transducer 354, which may be implemented as a piezoelectric crystal near its anti-resonant frequency, which is sometimes referred to herein as PZT. The cavity resonance modulates the impedance distribution of the PZT and affects its resonance modes. Under the influence of the 3D acoustic field, suspended particles in the liquid medium in the acoustic chamber 356 are forced into agglomerated sheets and then strings of "beads" of agglomerated material. Once the particle concentration reaches a critical size, gravity will dominate and the agglomerated material falls out of the acoustic field and reaches the bottom of the chamber. Changes in the concentration of the agglomerated material and the dropping of the material can affect the resonance of the chamber, which in turn can change the acoustic load on the PZT and its corresponding electrical impedance. The dynamic changes in the collected material detune the cavity and PZT, reducing the effect of the 3D waves in the purification medium. In addition, variations in the media and chamber temperature can also detune the chamber, thereby reducing the cleaning effect. To track the resonant changes that occur in the chamber, a control technique is used to follow the changes in the electrical properties of the PZT.

By driving the PZT at a frequency whose input impedance is complex (real and imaginary), a strong 3D sound field can be generated. However, chamber dynamics may cause the impedance values to vary significantly in an irregular manner. The change in impedance is due, at least in part, to a change in the load applied to the acoustic transducer 354 and/or the acoustic chamber 356. As the particles or secondary fluid separate from the primary or primary fluid, the load on the acoustic transducer and/or acoustic chamber may change, which in turn affects the impedance of the acoustic transducer and/or acoustic chamber.

To correct for the detuning, the controller 370 calculates the PZT impedance from the feedback signals on

lines

366, 368 to change the operating frequency to compensate for the detuning. Since frequency variations can affect the power delivered to the chamber 356, the controller 370 also determines how to adjust the output voltage of the (dynamic) converter 360 to maintain a desired amount of power output from the RF DC-AC inverter 362 to the acoustic transducer 354 and/or the acoustic chamber 356.

Converter 360 (e.g., a buck converter) is an electronically adjustable DC-DC power source and is the power source for inverter 362. The inverter 362 converts the DC voltage on line 372 to a high frequency AC signal on line 364, which is filtered by the filter 365 to produce a transducer drive signal that drives the PZT 354. The dynamics in the chamber 356 occur at rates corresponding to frequencies in the bass frequency band. Thus, the converter 360, controller 370, and DC-AC inverter 362 can operate at a faster rate than the bass band, allowing the controller to track chamber dynamics and keep the system tuned.

The controller 370 can simultaneously vary the frequency of the DC-AC inverter 362 and the DC voltage out of the buck converter 360 to track the chamber dynamics in real time. The control bandwidth of the system is a function of the RF bandwidth of the inverter and the cutoff frequency of the filter system (see, e.g., filter 318 in fig. 29) of the buck converter.

As an example, the controller 370 may be implemented as a DSP (digital signal processor) controller, a microcontroller, a microcomputer, etc., or as an Application Specific Integrated Circuit (ASIC) or Field Programmable Gate Array (FPGA) control. The controller may be implemented with multiple channels to allow parallel processing (e.g., analysis) of active and/or reactive impedance, voltage, current, and power.

The acoustic dynamics of chamber 356 affect the electrical characteristics of PZT 354, which in turn affects the voltage and current exhibited by the PZT. The sensed PZT voltage and current fed back on

lines

366, 368 are processed by the controller 370 to calculate the real-time power consumed by the PZT and its instantaneous impedance (subject to acoustic dynamics). Based on the user set point, controller 370 adjusts in real time the DC power provided on line 372 to inverter 362 and adjusts the frequency at which the inverter is operated to track the chamber dynamics and maintain the user set point. A filter 365 (e.g., LC or LCL, etc.) is used to impedance match the output impedance of the inverter 362 to increase power transfer efficiency.

The controller 370 samples the feedback signals on lines 366,368 quickly enough to detect changes in chamber performance (e.g., through changes in PZT impedance) in real time. For example, the controller 370 may sample the feedback signals on

lines

366, 368 at one hundred million samples per second. Signal processing techniques are performed to allow a wide dynamic range of system operation to accommodate a wide variation in chamber dynamics and applications. The DC-DC converter 360 may be configured to have a fast response time to follow signal commands from the controller 370. The inverter 362 may drive a wide range of loads that require different amounts of active and reactive power over time. An electronic package for implementing the system shown in fig. 32 may be configured to meet or exceed UL and CE specifications for electromagnetic interference (EMI).

FIG. 34 is a block diagram of an alternative embodiment system 380 for providing a transducer drive signal 352 to a transducer 354. The embodiment of fig. 34 is substantially the same as the embodiment of fig. 32, with the primary difference being that the DC-DC converter 360 and DC-AC inverter 362 of fig. 32 have been replaced with a linear amplifier 382 (fig. 32). In addition, the output of the controller 384 will be an analog sine wave on line 386, which is input to the linear amplifier 382. Referring to fig. 35, the controller 384 may be implemented by a parallel digital signal processing loop at very high speed using an RTL (register transfer level) implemented in actual digital electronic circuitry within a Field Programmable Gate Array (FPGA). Two high-speed digital Proportional Integral (PI) loops adjust the frequency of the sinusoidal output signal on line 386. The linear amplifier 382 amplifies the output signal on line 386 and provides an amplified output signal on line 388, which is filtered using a low pass filter 365. The combined voltage and current from the low pass filter 365 is fed back to the controller 384 on

lines

366 and 368. The calculations may be performed serially by the controller 384 to generate control signals to the linear amplifier 382. The linear amplifier may have a variable gain set by the controller 384. The controller 384 (e.g., an FPGA) may operate with a 100MHz clock signal, for example. In a real-time system, the clock speed (e.g., sampling rate, control loop update rate, etc.) may be fast enough to properly monitor and adapt to the conditions of PZT 354 and/or chamber 356. In addition, the architecture of the FPGA allows each gate component to have a propagation delay commensurate with the clock speed. The propagation delay for each gate component may be less than one cycle or, for example, 10ns for a clock speed of 100 MHz.

Referring to fig. 35, a diagram illustrates parallel and sequential operations for computing control signals. The controller 384 may be configured to calculate the following parameters.

VRMS＝sqrt(Vl²+V2²+...+Vn²)

IRMS＝sqrt(Il²+I2²+...+In²)

Active power (P ═ V-Inst. x I-Inst integral over N cycles)

Equipment power (S ═ VRMS x IRMS)

The controller 384 may be configured to calculate the reactive power and the bipolar phase angle by decomposing the sensed voltage and current into in-phase and quadrature-phase components. Fig. 36 shows in-phase and quadrature-phase demodulation of voltage and current to obtain four-quadrant phase, reactive power and reactance. The use of in-phase and quadrature-phase components can simplify the calculation of reactive power and phase angle.

VPhase Angle＝Arctan(QV/IV)

IPhase Angle＝Arctan(QI/II)

Phase angle VPhase-IPhase

Reactive power (Q is the sine of the phase angle of the power x of the device)

The controller 384 may implement a control scheme that begins with a frequency sweep to determine system performance parameters at discrete frequencies within a frequency sweep range. The control scheme may accept inputs of a start frequency, a frequency step size, and a number of steps, which define a frequency sweep range. The controller provides a control signal to the linear amplifier 382 to modulate the frequency applied to the PZT 354, and the voltage and current of the PZT is fed back to the controller on

lines

366, 368. The control scheme of the controller 384 may repeat the frequency sweep multiple times to determine system characteristics, such as reactance, with a relatively high level of assurance.

A plurality of reactance minima may be identified as a result of an analysis of the data obtained in the frequency sweep. The control technique may be provided with an input specifying a particular frequency range within which a desired reactance minimum is located, and with a resistance slope (+/-), which may be used to track a desired operating point based on tracking resistance corresponding to the desired minimum reactance. The resistance slope may be constant around a very small reactance, which may provide a useful parameter for tracking techniques. By tracking the resistance of the desired frequency, robust control for operation at very small reactance points can be obtained.

The control technique may use the derivative of the resistance/reactance value to locate the zero slope derivative representing the maximum and minimum values. A proportional-integral-derivative (PID) controller loop can be used to track the resistance to obtain a frequency set point at which the desired minimum reactance occurs. In some implementations, the control may be a Proportional Integral (PI) loop. By operating the FPGA at 100MHz, adjustments or frequency corrections can be made every 10ns to compensate for changes in tracking resistance. This type of control can be very accurate and implemented in real time to manage the control of the PZT in the presence of multiple varying variables, such as reactance, load, and temperature. The control technique may be provided with an error limit for the frequency or frequency set point of the reactance minimum to allow the controller to adjust the output to the linear amplifier 382 to maintain the frequency within the error limit.

A fluid mixture, such as a mixture of fluid and particles, may flow through the acoustic chamber for separation. The flow of the fluid mixture may be provided by a fluid pump which may apply turbulence to the fluid and the PZT and the chamber. The disturbance can produce significant fluctuations in the sensed voltage and current amplitudes, indicating that the effective impedance of the chamber fluctuates with the pump disturbance. However, due to the speed of the control technique, the fluctuations can be almost completely cancelled out by the control method. For example, the disturbance may be identified in the feedback data from the PZT, and the disturbance may be compensated in the control output from the controller. Feedback data, such as sensed voltage and current, can be used to track the entire acoustic chamber pressure. As the characteristics of the transducer and/or acoustic chamber change over time and with various environmental parameters (e.g., pressure or temperature), changes may be sensed and control techniques may compensate for these changes to continue operating the transducer and acoustic chamber at desired set points. Thus, the desired operational set points may be maintained with very high accuracy and precision, which may result in optimized efficiency for system operation.

The FPGA may be implemented as a stand-alone module and may be coupled with a class D driver. Each module may be provided with a hard coded address so that the module can be identified when connected to the system. The module may be configured to be hot pluggable in order to allow continuous operation of the system. The module may be calibrated for a particular system and transducer, or may be configured to perform calibration at a particular point, for example, at initialization. The module may include long-term memory, such as an EEPROM, to allow storage of operating time, health, error logs, and other information related to the operation of the module. The module is configured to accept updates so that, for example, new control techniques can be implemented using the same device.

Fig. 37 is a simplified circuit diagram of an RF power supply 396 including a voltage source 398 that provides a signal on line 400 to an LC matched filter 402 that provides a transducer drive signal on line 404 to an ultrasonic transducer 406. Fig. 38 is a simplified circuit diagram of an RF power supply 408 that is substantially identical to the power supply shown in fig. 36, except that it is an LCL matched filter 410 instead of the LC filter 402 shown in fig. 36.

Fig. 39 is a circuit diagram of an RF power supply 412 providing a drive signal on line 414 to an LCL low pass filter 416 which provides a transducer drive signal on line 418 to an ultrasonic transducer 420. A controller (see, e.g., controller 370 in fig. 32) provides complementary control signals to the first FET switch 422 and the second FET switch 424 of the DC-AC inverter 426 and provides a resultant AC drive signal on line 414. The frequency of the complementary control signals applied to the

switches

422, 424 is controlled by the controller to set the frequency of the signal on line 414. The signal on line 414 is low pass filtered to attenuate high frequency components and ideally to provide a sine wave on line 418. Fig. 39 also shows an example of a dynamic model of the ultrasound transducer 420.

FIG. 40 is a simplified circuit diagram of an LCL filter circuit 430 having a current sense signal I provided_RFA tap of,And providing a voltage sense signal V_RFThe node (c). Signal I_RFAnd V_RFIs fed back to a controller 431 (e.g., a DSP) to control the transducer drive signals (e.g., frequency and power) applied to the transducer 434 on line 432.

Fig. 41 is a schematic diagram of an embodiment of a power supply including an inverter 440, the inverter 440 receiving a switching signal on line 442 and its complement (complement) on line 444 from a controller (not shown), and the complement being used to drive a first FET 446 and a second FET 448. The resultant AC signal on line 450 is input to the LCL filter 452 and the resultant filtered signal is output to drive the transducer. The filter 452 serves as a current source to drive the transducer.

It is envisioned that the drivers and filters disclosed herein may be used to generate plane waves.

The invention has been described with reference to exemplary embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

1. A method of operating an acoustophoretic system, comprising:

receiving a feedback signal from the acoustic transducer over a frequency range;

determining a reactance minimum or a reactance maximum in the frequency range;

controlling the frequency of the drive signal applied to the acoustic transducer at the determined reactance minimum or reactance maximum.

2. The method of claim 1, further comprising locating an anti-resonance frequency.

3. The method of claim 2, further comprising locating a reactance minimum or a reactance maximum near the anti-resonance frequency.

4. The method of claim 3, further comprising:

identifying a reactance minimum from the reactance minima or a reactance maximum from the reactance maxima; and

the drive signal is set at a first frequency associated with the reactance minimum or the reactance maximum.

5. The method of claim 4, further comprising:

scanning the frequency range for a new reactance minimum or a new reactance maximum when the reactance value of the acoustic transducer changes during operation; and

a new frequency associated with the new reactance minimum or new reactance maximum is selected.

6. The method of claim 1, further comprising determining a reactance minimum or a reactance maximum by taking a derivative value of the reactance.

7. The method of claim 1, further comprising determining one or more of a voltage, a current, a resistance, a reactance, a power, or a phase angle from the feedback signal.

8. The method of claim 1, further comprising controlling the drive signal to maintain a power setpoint.

9. The method of claim 1, further comprising:

flowing a mixture of the primary fluid and the particles or a mixture of the primary fluid and the secondary fluid into an acoustophoresis system; and

the frequency of the drive signal is adjusted based on the reactance minimum or reactance maximum.

10. The method of claim 9, further comprising:

generating sound waves with an acoustic transducer;

changing the retention of material in the acoustic wave such that the load on the acoustic transducer changes; and

controlling a drive signal applied to the acoustic transducer based on a new reactance minimum or reactance maximum associated with a change in a load on the acoustic transducer.

11. An acoustophoretic system, comprising:

an acoustic chamber;

an acoustic transducer coupled to the acoustic chamber and configured to generate an acoustic standing wave in the acoustic chamber;

wherein the acoustic transducer is controlled according to the method of claim 1.

12. A method for controlling an acoustic transducer, comprising:

determining a very small or very large reactance frequency of the acoustic transducer;

providing a power signal to an acoustic transducer at the infinitesimal reactance frequency or the infinitesimal reactance frequency;

determining a reactance value of the acoustic transducer during operation; and

adjusting a frequency of a power signal provided to the acoustic transducer to a minimum reactance value or a maximum reactance value based on the determined reactance value during operation.

13. A method for determining an operating set point of an acoustic system, the acoustic system comprising an acoustic transducer and an acoustic chamber, the method comprising:

determining reactance values of the acoustic transducer with respect to at least some of the frequency ranges such that a minimum reactance value or a maximum reactance value is determined with respect to the frequency range; and

applying a drive signal to an acoustic transducer at a frequency related to the minimum or maximum reactance value;

determining a reactance value of the acoustic transducer during operation; and

adjusting the frequency of the drive signal applied to the acoustic transducer to a minimum reactance value or a maximum reactance value based on the determined reactance value during operation.

14. A driver for providing a drive signal to an acoustic transducer, comprising:

a DC-DC converter;

an RF inverter coupled to an output of the DC-DC converter;

an output of an RF converter, an output of the RF converter coupled to an acoustic transducer; and

a controller coupled to the DC-DC converter, the RF inverter, and the acoustic transducer for controlling the drive signal provided to the acoustic transducer.

15. The driver of claim 14, further comprising a filter interposed between the DC-DC converter and the RF inverter.

16. The driver of claim 15, wherein the filter comprises a low pass filter to provide an average voltage of the output of the DC-DC converter to the RF inverter.

17. The driver of claim 14, further comprising a matched filter interposed between the RF inverter and the acoustic transducer.

18. The driver of claim 14, further comprising the DC-DC converter configured to generate a pulse width modulated signal on the output.

19. The driver of claim 14, further comprising feedback from the acoustic transducer to the controller.

20. The driver of claim 19, wherein the controller is configured to provide a control signal to the RF inverter to control a frequency of a drive signal provided to the acoustic transducer based on feedback from the acoustic transducer.

21. The driver of claim 20, wherein the controller is configured to implement the method of claim 1.