U.S. patent application number 17/198985 was filed with the patent office on 2021-11-04 for driver and control for variable impedence load.
The applicant listed for this patent is FloDesign Sonics, Inc.. Invention is credited to John Artis, Bart Lipkens, Dane Mealey, Ronald Musiak, Ali Shajii.
Application Number | 20210339169 17/198985 |
Document ID | / |
Family ID | 1000005712846 |
Filed Date | 2021-11-04 |
United States Patent
Application |
20210339169 |
Kind Code |
A1 |
Lipkens; Bart ; et
al. |
November 4, 2021 |
DRIVER AND CONTROL FOR VARIABLE IMPEDENCE LOAD
Abstract
An acoustic standing wave is utilized to separate components
from a multi-component fluid, such as oil from an oil-water
mixture, or cells entrained in a fluid, in a fluid flow scheme with
an acoustophoresis device. For example, the flow scheme and device
allows for trapping of the oil as the oil coalesces, agglomerates,
and becomes more buoyant than the water. A driver and controller
for the acoustophoretic device accommodate variable loading as the
components are separated, thereby improving separation
efficiency.
Inventors: |
Lipkens; Bart; (Bloomfield,
CT) ; Musiak; Ronald; (Westfield, MA) ;
Mealey; Dane; (Somers, CT) ; Artis; John;
(Santa Maria, CA) ; Shajii; Ali; (Weston,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FloDesign Sonics, Inc. |
Wilbraham |
MA |
US |
|
|
Family ID: |
1000005712846 |
Appl. No.: |
17/198985 |
Filed: |
March 11, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15872984 |
Jan 16, 2018 |
10967298 |
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17198985 |
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15621691 |
Jun 13, 2017 |
10350514 |
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15872984 |
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15000573 |
Jan 19, 2016 |
9675902 |
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15621691 |
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13943529 |
Jul 16, 2013 |
9272234 |
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15000573 |
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13844754 |
Mar 15, 2013 |
10040011 |
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13943529 |
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61754792 |
Jan 21, 2013 |
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61708641 |
Oct 2, 2012 |
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61611240 |
Mar 15, 2012 |
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61611159 |
Mar 15, 2012 |
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62446356 |
Jan 13, 2017 |
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61671856 |
Jul 16, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 21/283 20130101;
B01D 21/00 20130101; B01D 17/06 20130101; B01D 17/04 20130101 |
International
Class: |
B01D 17/04 20060101
B01D017/04; B01D 17/06 20060101 B01D017/06; B01D 21/00 20060101
B01D021/00; B01D 21/28 20060101 B01D021/28 |
Claims
1. An acoustophoresis system, comprising: a chamber for receiving a
fluid mixture that includes cells or particles in a fluid; an
ultrasonic transducer coupled to the chamber and configured to be
excited to generate an acoustic wave in the chamber; a driver
electrically connected to the ultrasonic transducer and configured
to provide an excitation to the ultrasonic transducer to generate
the acoustic wave in the chamber, the driver including an
amplifier; and a controller for controlling the amplifier based on
reactance determined from feedback signals from the ultrasonic
transducer.
2. The system of claim 1, wherein at least one ultrasonic
transducer comprises a plurality of transducers, each of the
plurality of transducers individually electrically connected to its
own amplifier.
3. The system of claim 1, wherein the amplifier further comprises
an inverter.
4. The system of claim 1, further comprising a capacitor
electrically connected between the amplifier and the at least one
ultrasonic transducer.
5. The system of claim 1, further comprising a filter electrically
connected between the amplifier and the at least one ultrasonic
transducer.
6. The system of claim 3, wherein the amplifier further comprises a
DC-DC converter coupled to an input of the inverter.
7. The system of claim 6, further comprising a filter between the
DC-DC converter and the inverter.
8. A method for controlling an acoustophoretic device that uses an
ultrasonic transducer, the method comprising: driving an amplifier
electrically connected to the ultrasonic transducer to send an
output signal to the ultrasonic transducer; receiving at a
controller a feedback signal from the ultrasonic transducer; and
adjusting the output signal from the amplifier with the controller
to obtain a desired reactance of the ultrasonic transducer.
9. The method of claim 8, further comprising determining the phase
angle of the impedance of the ultrasonic transducer.
10. A system for controlling an associated ultrasonic transducer,
comprising: an amplifier that produces an output signal to the
ultrasonic transducer; a controller connected to the amplifier for
controlling the amplifier; and the controller being electrically
connected to receive an impedance measurement from the ultrasonic
transducer.
11. The system of claim 10, further comprising the amplifier being
configured to produce an RF output.
12. The system of claim 10, further comprising the controller being
configured to measure power delivered to the ultrasonic transducer
and to control the amplifier to control a power level of the output
signal.
13. The system of claim 10, further comprising the controller being
configured to control a frequency of the output signal.
14. The system of claim 12, further comprising the controller being
configured to identify a frequency of the output signal that
produces a predetermined impedance measurement from the ultrasonic
transducer and to control the amplifier to provide the output
signal at the frequency.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 15/872,984, filed Jan. 16, 2018, which claims
the benefit of U.S. Provisional Application Ser. No. 62/446,356,
filed Jan. 13, 2017, and is a Continuation-in-Part of U.S. patent
application Ser. No. 15/621,691, filed Jun. 13, 2017, now U.S. Pat.
No. 10,350,514, which is a continuation of U.S. patent application
Ser. No. 15/000,573, filed Jan. 19, 2016, now U.S. Pat. No.
9,675,902, which is a continuation of U.S. patent application Ser.
No. 13/943,529, filed Jul. 16, 2013, now U.S. Pat. No. 9,272,234,
which claims priority to U.S. Provisional Patent Application Ser.
No. 61/671,856, filed on Jul. 16, 2012; and is a
Continuation-in-Part of U.S. Ser. No. 13/844,754, filed Mar. 15,
2013, now U.S. Pat. No. 10,040,011 which claims the benefit of U.S.
Provisional Patent Application Ser. No. 61/611,159, filed Mar. 15,
2012, and of U.S. Provisional Patent Application Ser. No.
61/611,240, also filed Mar. 15, 2012, and of U.S. Provisional
Patent Application Ser. No. 61/708,641, filed Oct. 2, 2012, and of
U.S. Provisional Patent Application Ser. No. 61/754,792, filed Jan.
21, 2013. The entire disclosure of each of which is incorporated
herein by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable
BACKGROUND
[0003] Acoustophoresis is the separation of materials using
acoustic waves. For example, particles and secondary fluids can be
separated from a primary or host fluid using acoustics, such as
acoustic standing waves. Acoustic standing waves can exert forces
on particles in a fluid when there is a differential in density
and/or compressibility, otherwise known as the acoustic contrast
factor. The pressure profile in a standing wave contains areas of
local minimum pressure amplitudes at standing wave nodes and local
maxima at standing wave anti-nodes. Depending on their density and
compressibility, the particles can be trapped at the nodes or
anti-nodes of the standing wave. Generally, the higher the
frequency of the standing wave, the smaller the particles that can
be trapped.
[0004] At a micro scale, for example with structure dimensions on
the order of micrometers, conventional acoustophoresis systems tend
to use half or quarter wavelength acoustic chambers, which at
frequencies of a few megahertz are typically less than a millimeter
in thickness, and operate at very slow flow rates (e.g.,
.mu.L/min). Such systems are not scalable since they benefit from
extremely low Reynolds number, laminar flow operation, and minimal
fluid dynamic optimization.
[0005] At the macro-scale, planar acoustic standing waves have been
used in separation processes. However, a single planar wave tends
to trap the particles or secondary fluid such that separation from
the primary fluid is achieved by turning off or removing the planar
standing wave. The removal of the planar standing wave may hinder
continuous operation. Also, the amount of power that is used to
generate the acoustic planar standing wave tends to heat the
primary fluid through waste energy, which may be disadvantageous
for the material being processed. Conventional drivers and
controllers used to generate acoustic waves may be designed for
static impedance loads with relatively low power output.
[0006] A number of industrial applications generate wastewater that
is contaminated with undesirable or hazardous fluid materials, such
as oil. These operations include oil drilling, mining and natural
gas fracking. Also, spills from oil rigs into seawater generate
emulsified oil in the water that is difficult to separate. The use
of methods such as hydrocyclones, absorptive media, mechanical
filtration, and chemical dispersion to separate the oil from the
water are both cost prohibitive and possibly injurious to the
environment.
SUMMARY
[0007] The present disclosure relates to systems, devices and/or
methods for acoustophoresis on preferably a large scale. The
devices use one or more distinct ultrasonic transducers as
described herein, or an array of such transducers. In some
examples, a transducer is driven at frequencies that produce
multi-dimensional standing waves. Acoustophoresis can employ high
intensity standing waves of sound to exert forces on particles. An
acoustic standing wave has a pressure profile that appears to
"stand" still in time. The pressure profile in a standing wave
varies from areas of low pressure (nodes) to areas of high pressure
(anti-nodes). Acoustic standing waves can be produced in acoustic
resonators. Acoustophoresis can be achieved using a piezoelectric
element as an ultrasonic transducer. The piezoelectric element
represents a variable impedance load during acoustophoretic
operations. In addition, the piezoelectric element may be driven at
radio frequencies (RF) to generate the desired acoustic waves that
influence material in the micrometer or smaller range.
[0008] A disclosed driver for such transducers produces relatively
high power at variable RF frequencies with a flexibility for
handling variable impedance loads. The driver includes a DC-DC
converter and an inverter. The converter provides a variable output
that is proportional to the input. The inverter produces an RF
drive signal given a DC input. The converter and inverter are
controlled with a controller that provides a desired level of power
and a desired frequency. A feedback loop from the load to the
controller provides feedback signals that permit the controller to
formulate control signals supplied to the driver to obtain a
desired output. The load can be a piezoelectric element in an
ultrasonic transducer, or can be an ultrasonic transducer in
combination with an acoustic chamber, which can be a resonant
chamber or system.
[0009] The load can be driven by the driver to obtain certain
characteristics, such as operating at a low or minimum reactance
point. As the load is driven, the impedance characteristics of the
load can change. The change in impedance can be due to a number of
factors, including temperature, fluid characteristics (e.g.,
density, compressibility, velocity), particle or fluid trapping in
an acoustic wave generated by the transducer, frequency, resonance
and any other variable that might influence the load. The driver
can be controlled based on feedback data from the load to adjust
output parameters such as frequency, power, voltage, current, phase
or any other parameter the driver can produce under control of the
controller.
[0010] Disclosed in some embodiments is an acoustophoresis device,
which includes a chamber with an inlet, an outlet, an ultrasonic
transducer coupled to the chamber, the ultrasonic transducer
including a piezoelectric material being configured to generate a
multi-dimensional standing wave in the flow chamber.
[0011] In some embodiments, a reflector may be provided on an
opposite side of the chamber from the ultrasonic transducer. The
chamber may be a flow chamber for accommodating a fluid flow that
transits past the ultrasonic transducer.
[0012] The device may include a plurality of device inlets spaced
about a first end of the device. The device may include a
longitudinal sidewall that is spaced apart from a contoured
wall.
[0013] The piezoelectric material of the ultrasonic transducer can
have a rectangular shape. The reflector can have a non-planar
surface.
[0014] In particular embodiments, the first end of the device has a
circular cross-section and the flow chamber has a rectangular
cross-section.
[0015] The multi-dimensional standing wave generated by the
transducer can result in an acoustic radiation force having an
axial force component and a lateral force component that are of the
same order of magnitude.
[0016] In some embodiments, the transducer comprises: a housing
having a top end, a bottom end, and an interior volume; and a
piezoelectric element at the bottom end of the housing having an
exposed exterior surface and an interior surface, the piezoelectric
element being able to vibrate when excited. The piezoelectric
element may be excited by application of an electrical signal.
[0017] Sometimes, no backing layer is present within the housing,
and a gap is present in the interior volume between the
piezoelectric element and a top plate at the top end of the
housing.
[0018] In other devices, the transducer includes a backing layer
contacting the interior surface of the piezoelectric element, the
backing layer being made of a substantially acoustically
transparent material. The substantially acoustically transparent
material can be balsa wood, cork, or foam. The substantially
acoustically transparent material may have a thickness of up to 1
inch.
[0019] The flow chamber can further comprise a transparent window
for viewing the interior of the flow chamber.
[0020] In particular embodiments, the device has a length L from
the at least one device inlet to a bottom of the longitudinal
sidewall, and a ratio of the length L to the first diameter is less
than 1.
[0021] Also disclosed herein are acoustophoresis devices for
retaining or trapping particles from a particle/host fluid mixture.
The particles may be cells. In some embodiments, an acoustophoresis
device comprises: a chamber; at least one ultrasonic transducer
coupled to the chamber, the at least one ultrasonic transducer
including a piezoelectric material configured to be excited to
generate a multi-dimensional acoustic standing wave in the chamber;
and a reflector coupled to the chamber opposite from the at least
one ultrasonic transducer; wherein the particles are continuously
trapped in the multi-dimensional acoustic standing wave,
agglomerate, aggregate, clump, or coalesce, and settle out of the
host fluid due to enhanced gravity forces, and exit the flow
chamber; and wherein the multi-dimensional standing wave results in
an acoustic radiation force having an axial force component and a
lateral force component that are of the same order of
magnitude.
[0022] Acoustophoretic systems are also disclosed. In particular
embodiments, an acoustophoresis system includes a chamber for
receiving a fluid mixture that includes cells or particles in a
fluid, an ultrasonic transducer coupled to the chamber and
configured to be excited to generate an acoustic wave in the
chamber, and a driver electrically connected to the ultrasonic
transducer and configured to provide an excitation to the
ultrasonic transducer to generate the acoustic wave in the chamber,
the driver including an amplifier.
[0023] In certain embodiments, the at least one ultrasonic
transducer can comprise a plurality of transducers, and each of the
plurality of transducers can be individually electrically connected
to its own amplifier.
[0024] In certain embodiments of the acoustophoretic system, a
function generator can be provided that drives the amplifier by
generating a signal (e.g., a low voltage sinusoidal voltage signal)
that is sent to the amplifier. A power resistor and/or a capacitor
can be electrically connected between the amplifier and the at
least one ultrasonic transducer. An oscilloscope can be provided
for measuring a first voltage before the power resistor and a
second voltage after the power resistor. Further yet, a particle
analyzer located downstream of the one or more flow chamber outlets
for characterizing the particles.
[0025] Further disclosed herein are methods for continuously
separating particles from a host fluid. In particular embodiments,
such a method comprises: flowing a mixture of the host fluid and
particles through an acoustophoresis device, the acoustophoresis
device comprising: a flow chamber including one or more inlets and
outlets; at least one ultrasonic transducer coupled to the flow
chamber; a reflector coupled to the flow chamber opposite from the
at least one ultrasonic transducer; and an amplifier electrically
connected to the at least one ultrasonic transducer. The method
further comprises driving the amplifier to produce an output signal
that drives the at least one ultrasonic transducer to create a
multi-dimensional acoustic standing wave in the flow chamber;
measuring a first voltage between the amplifier and a predetermined
first impedance; measuring a second voltage between the first
impedance and the at least one ultrasonic transducer; measuring a
current from the output signal between the measured first and
second voltages; determining an impedance of the at least one
ultrasonic transducer from the measured current and measured first
and second voltages.
[0026] In certain embodiments, the particles are continuously
trapped in the multi-dimensional acoustic standing wave, then
agglomerate, aggregate, clump, or coalesce, and eventually settle
out of the host fluid due to enhanced gravity forces, and exit the
flow chamber. In further embodiments, the multi-dimensional
standing wave results in an acoustic radiation force having an
axial force component and a lateral force component that are of the
same order of magnitude.
[0027] The impedance of the at least one ultrasonic transducer can
be proportional to the measured current. The impedance of the at
least one ultrasonic transducer can additionally be proportional to
the first impedance. The impedance of the at least one ultrasonic
transducer can be inversely proportional to the measured first and
second voltages. The method can further comprise determining the
phase angle of the impedance of the at least one ultrasonic
transducer. In some embodiments, the first impedance can be
predetermined across a power resistor electrically connected
between the amplifier and the at least one ultrasonic transducer.
In such embodiments, the predetermined first impedance across the
power resistor can be proportional to the first voltage and can be
inversely proportional to the second voltage.
[0028] The method can further comprise determining an electrical
power consumed by the at least one ultrasonic transducer from the
measured second voltage and the impedance of the at least one
ultrasonic transducer. The electrical power consumed by the at
least one ultrasonic transducer can be proportional to the measured
second voltage. The electrical power consumed by the at least one
ultrasonic transducer can be inversely proportional to the
impedance of the at least one ultrasonic transducer.
[0029] The amplifier can be driven by a function generator that
generates a signal (e.g., a low voltage sinusoidal voltage signal)
that is sent to the amplifier. The first and second voltages can be
measured by an oscilloscope. A particle analyzer located downstream
of the acoustophoretic device can be used for characterizing the
particles.
[0030] Discussed herein are systems and methods for acoustophoresis
for generating optimized particle clusters to improve gravity
separation and collection efficiency. Improved, continuous,
acoustophoresis devices using improved fluid dynamics are also
discussed, as well as control of the devices for desired
performance.
[0031] Control of the acoustic transducer can be implemented on the
basis of power setpoints. For example, a user can set a desired
power level for power delivered to the transducer. Performance of
acoustophoresis in an acoustic chamber using the acoustic
transducer can be modulated on the basis of modulated input power
to the acoustic transducer. In some instances, a power setpoint is
desired for operation, while other parameters, such as frequency,
for example, are modified. The power setpoint determines the power
output of an RF power supply or RF power amplifier. A power control
is provided to maintain the power setpoint, while other parameters
associated with operation of the acoustophoresis device are varied.
The power control senses signals provided to the acoustic
transducer, such as, for example, voltage and current. These
feedback signals are used to determine frequency and phase angle
for the power delivered to the transducer. In some examples, a buck
converter is used as the DC power supply. The buck converter has a
response bandwidth, which may influence the responsiveness of the
RF power control. For example, if the buck converter bandwidth is
relatively narrow, the system response for the RF power control may
be relatively slow for the desired operational performance
environment for the acoustophoresis device.
[0032] A number of different materials may be processed through the
acoustophoresis device, each of which may provide different load
characteristics on the acoustic transducer and acoustic chamber.
The RF power supply thus may be subjected to a wide range of loads,
which may place demands on both the Buck and RF power supply
supplies that are challenging to meet. For example, heavy loading
of the acoustic transducer and/or acoustic chamber experienced with
certain types of materials being processed may cause power supply
components to be overloaded, and/or overheated, or may cause trip
point thresholds to be met or exceeded. The heavy loading or trip
point thresholds crossings may cause faults to be identified in the
power control, causing the power supply to be shut down. In
addition, the power demands on the RF power supply may change
significantly with changes in other operational parameters, such as
temperature, frequency or loading characteristics, including
reactance. Power control based on a desired power level set levels
the point may thus imply other operational setpoints, such as
frequency, to manage operation of the power supply and
acoustophoresis device to handle a range of loads.
[0033] In some implementations, an RF linear amplifier is used to
supply RF power to the transducer. The linear amplifier may operate
by receiving an input AC signal, which may be AC or DC, and
amplifying the input signal in accordance with the operational
characteristics of the linear amplifier. Linear amplifiers are
typically designed to have a linear response, such that any input
signal is amplified by the same gain, regardless of the magnitude
of the input signal, within the operating parameters or
specifications of the linear amplifier. This linear operation can
be achieved through the use of techniques that contribute to
linearizing the response of the linear amplifier, potentially in
areas where non-ideal conditions tend to impose nonlinearities on
the response. However, linear operation is attained at the cost of
power regulation, usually generating significant heat losses as
well as incurring inefficient operation. Accordingly, linear
amplifiers tend to consume significant amounts of power, even when
the magnitude of the input signal is relatively small and/or when
the gain is relatively small. When demands are placed on the linear
amplifier to supply power in response to changing system
conditions, such as frequency or loading, challenges are presented
in terms of responsiveness and avoiding overloads.
[0034] In addition, linear amplifiers are designed for nominal
applications, for example, where a 50 ohm load is specified. The
load applied to the linear amplifier is thus intended to be
composed of mostly real impedance, or resistance, and tolerates a
relatively small amount of reactive impedance. In the case of
providing power to an acoustic transducer that is composed of a
piezoelectric material, the power supply sees a highly reactive
load, which limits the usefulness of an RF linear amplifier as the
source of RF power supply.
[0035] Discussed herein is a RF acoustic driver power supply and
method for providing power to an acoustic transducer composed of a
piezoelectric material, such as PZT-8. The piezoelectric material
may be formed as a poly-crystal, which is also referred to as a
crystal herein. The driver power supply provides RF power with a
relatively wide bandwidth of operation to permit responsive
operation with relatively high efficiency and with the ability to
accommodate a wide range of loads. The driver contains power supply
is a DC-DC converter that combines a power converter, such as a
buck, buck-boost or boost power converter, with an RF frequency
inverter which supplies RF AC to the PZT.
[0036] The system can be driven by a function generator and an
amplifier. The system performance can be monitored and controlled
by a computer. Excitation frequencies can be in the range of from
about hundreds of kilohertz to several megahertz.
[0037] The generation of an acoustic standing wave in a fluid
medium may be accomplished with the use of an oscillator or
function generator and an amplifier, which may be a linear
amplifier. The function generator or oscillator linear amplifier
provides an electronic input to a piezoelectric device such that
the piezoelectric device vibrates at the frequency that is set by
the function generator or oscillator connected to the input of the
amplifier. The amplifier also generates provides a certain amount
of power that is provided to the piezoelectric material, which
power can determine the strength of the acoustic wave that is set
by the frequency of the function generator or oscillator. A
controller implementing a control scheme is provided for the
amplifier and the function generator or oscillator to control the
generated and applied power.
[0038] A function generator is utilized to generate the initial
wave pattern that is imparted to the acoustic resonator system that
includes at least one acoustic transducer that is composed, for
example, of a piezoelectric material. The system may include
another transducer and/or one or more reflectors that are coupled
to an acoustic chamber. The signal from the function generator is
controlled for various parameters, such as, for example, amplitude.
For example, the signal from the function generator is amplified to
increase the amount of power applied to the transducer. The power
applied to the transducer determines, at least in part, the power
of the acoustic standing wave. The control of power applied to the
transducer can thus control the power of the acoustic standing
wave. The parameters of the signal from the function generator,
such as frequency, amplitude and phase, can be controlled with a
controller. The amplification of the signal from the function
generator can also be controlled by a controller, which may be the
same or different from the function generator controller.
[0039] The characteristics of the waveform oscillator input to the
piezoelectric material of the acoustic transducer can be modified
to permit various vibration modes of the piezoelectric material.
For example, a pure sine wave can induce a very succinct vibration
of the piezoelectric material, while a signal with harmonic content
can cause parasitic vibrations of the piezoelectric material. The
input to the piezoelectric material may influence the heat
generated or input into the fluid in which the acoustic standing
wave is formed. The input may generate more complicated motion in
the fluid coupled with the piezoelectric material.
[0040] Additionally, driving a piezoelectric material with a
current source rather than a voltage source may permit greater
electro-mechanical freedom in supporting and sustaining desirable
vibratory modes in the piezoelectric material. A drive and control
scheme can be provided to generate a low harmonic signal into the
piezoelectric material. The control of the acoustic transducer that
generates the acoustic standing wave in the fluid medium can
utilize a feedback loop and a computational processor. An
inductor-capacitor-inductor (LCL) or LC circuit configuration may
be used to generate a low harmonic function wave, such as a sine
wave, into the piezoelectric material. The low harmonic sine wave
permits less parasitic vibrations of the piezoelectric material.
Such a sine wave may also permit the piezoelectric material to
generate less heat when it vibrates.
[0041] An LCL configuration can act on the signal from the
amplifier as a filter to reduce the harmonic content speed of
response of the amplifier output. The LCL may thus act, at least in
part, as a low pass filter for the amplifier output. In some
examples, the LCL may cause the amplifier output to be filtered to
a pure sine wave form. As a result, the perturbation of the
piezoelectric material does not generate extra, parasitic
vibrations of the material. The output L of the LCL structure
provides a current source drive to the piezoelectric material. The
LCL input, and thus the current source, is controlled to improve
the piezoelectric material's performance in generating an acoustic
wave.
[0042] The acoustic transducer can be driven to create a
multi-dimensional acoustic standing wave in a coupled medium, where
the wave has at least non-zero acoustic forces in a direction
transverse to the propagation direction of the wave. The
multi-dimensional acoustic standing wave generation process takes
advantage of the higher-order vibratory modes of a loosely
suspended piezoelectric plate.
[0043] Piezoelectric material changes shape based on an electrical
signal applied to it, such as a voltage or current signal, or based
on a corresponding electric field permeating the material. The
electric field from external charges affects the fields of the
bound charges in the material and thereby affects the shape of the
material. The electrical signal can be from a voltage source. In
that case the amount of material deformation is related to the
voltage applied. For example, the deformation may be `voltage
clamped` or `voltage damped`. The amount of charge induced is
related to the applied voltage and the properties of the material.
This relationship can be expressed mathematically as Q=C*V, where Q
is charge, C is material capacitance, and V is the voltage of the
applied signal. Electrodes may be attached to the piezoelectric
material to provide a conduit for the applied charges signal. In
that case the resultant voltage, and the corresponding electric
field, is a function of the externally applied charges. Using the
above equation, the voltage can be express as V=Q/C. The resultant
voltage may be `unconstrained` in relation to operation of the
piezoelectric device. The `C` of the piezoelectric device is due to
its physical geometry and material properties. Since the material
changes shape as a function of the electric field permeating it,
the `C` of the device is a function of the electric field
permeating it. For a given Q, and driving the material with a
current source that is a time varying source of charge, C changes
as a function of electric field, which changes the voltage across
the device to `accommodate` the changed C. In a voltage driven
system, the electric field can determine the amount of charge,
which can determine the degree of deformation and correspondingly
the amount of change in C. To encourage multimode behavior in
piezoelectric material, the piezoelectric material can be
configured to be `free floating`, and in some examples, is made to
be as free floating as possible in both a mechanical and electrical
sense.
[0044] The LCL circuit can be implemented as an impedance matching
network which can amplify either current or voltage depending on
the value of the impedance being matched. One operation
implementation technique is to amplify voltage. In this case, power
may be transmitted through the LCL with little power loss with the
use of low loss inductors (L) and capacitors (C).
[0045] The harmonic frequencies are reduced or eliminated due the
arrangement of the elements used in the circuit and independent of
whether or not there is voltage amplification. The circuit
arrangement can be implemented as a low pass filter. Low pass
filters allow signals below a certain frequency, called the corner
frequency, to pass through the filter while blocking signals with
frequencies above the corner frequency. A square wave input into
such a network produces a sine wave output when the harmonics of
the square wave are at frequencies above the filter's corner
frequency.
[0046] Voltage amplification may or may not occur at certain
frequencies. Amplification can take place if the input impedance of
the LCL is smaller than the impedance the LCL is connected to,
within a certain range of frequencies. If a voltage gain is
applied, then there will be a corresponding current loss since the
voltage times the current (V*I) product going into the network must
equal the V*I product leaving that network, provided there are
negligible losses within the network itself. There is voltage
amplification when the system is operated at a piezoelectric
material's anti-resonance frequency, which produces large
impedances and the LCL is designed to present the inverse of those
impedances at its input. For example, suppose the piezoelectric
material or crystal's resistance at a particular frequency is 100
ohms and is absorbing 25 watts. The voltage at the crystal is 50
volts with a corresponding current of 0.5 amps (V*I=25). If the LCL
translates that 100 ohms to 9 ohms at its input then the drive
voltage is 15 volts with a corresponding current of 1.67 amps,
which equates to 25 watts. Thus, for a particular driver power, the
voltage into the LCL can be low and the current can be high, while
the current at the output of the LCL can be low and the voltage
output can be high, where the input and output V*I products are
equal, assuming negligible losses.
[0047] The control of the multi-dimensional acoustic standing wave
and the acoustic resonator or transducer is an important part of an
acoustophoresis process. For example, as a multi-dimensional
acoustic standing wave is utilized to trap biologic cells and cell
debris from a bioreactor process, the reactance of the resonator
changes. By sensing the voltage and current of the RF transmission
line to the piezoelectric element, the resonator can be properly
tuned to optimize the acoustophoresis process. The reactance and
power can be extracted from the voltage and current signals on the
piezoelectric element. For example, voltage and current signals can
be provided to a digital signal processor (DSP), which can be used
to calculate RF reactance and power. The measured and calculated
parameters of operation for the piezoelectric element can be used
to provide feedback for the tuning process. This tuning process may
consist of adjusting the gain of the amplifier to achieve a desired
power that is provided to the piezoelectric element and/or
adjusting the frequency of the drive signal to achieve a desired
reactance of the resonator, as examples.
[0048] The multi-dimensional acoustic standing wave is generated
through a multimode perturbation of the piezoelectric material by
electronic signal generated by a function generator or oscillator
and modified by an amplifier. The generation of the
multi-dimensional acoustic standing wave and the multimode
perturbation of the piezoelectric material is described in U.S.
Pat. No. 9,228,183 which is incorporated herein by reference.
[0049] An RF power driver or converter is provided to drive the
acoustic transducer. In some implementations, the driver power
converter is composed of a DC-DC converter coupled to a DC-AC
inverter. A filter is provided between the converter and inverter.
The output of the inverter may be supplied to the LCL matching
filter. The RF driver power converter has a number of advantages
over the linear amplifiers discussed above, including more
efficient operation, better responsiveness and the ability to drive
highly reactive loads.
[0050] The DC-DC converter may be a buck, buck-boost or boost
converter, as examples, although any type of DC-DC converter may be
used. The amplifier used in conjunction with the function generator
or oscillator discussed above can be can be implemented as the
converter can be implemented with a and filter. The filter can be
implemented as an RLC filter with a bandwidth that permits the
filter output, such as output voltage, to respond to dynamic
changes of the transducer and/or the acoustic cavity.
[0051] The function generator or oscillator discussed above can be
implemented as the DC-AC inverter. The inverter receives a DC input
and provides an RF frequency output. The inverter output can be
applied to a the LCL or LC matching filter, which smooths the
output of the inverter and provides an impedance match for the
output of the inverter to permit efficient electrical power
transfer.
[0052] A control, which may be a digital or analog control, is
provided that can receive inputs fed back from the acoustic
transducer or other system components and provide control signals
to various components of the RF driver power converter. The control
can provide control signals to vary the DC output of the converter,
and/or modify and control the amplitude of the power of the drive
signal for the acoustic transducer. Control signals provided by the
control can vary the operation of the inverter to modify and
control the frequency of the drive signal. The RF driver power
converter with the control permits control and modulation of the
acoustic transducer as a highly reactive load, while maintaining
desired transducer and acoustic chamber performance.
[0053] A control technique provides a system and method for
locating desired operating points for an acoustic transducer-cavity
combination, with or without loading, which loading may be highly
reactive. Feedback from the acoustic transducer can be used to
locate the resonance and anti-resonance frequencies of transducer
operation. According to some implementations, an operating
frequency less than the transducer anti-resonance is inspected for
minimum reactance as a point of operation. Some implementations
locate a frequency above the anti-resonance frequency, which
frequency is inspected for maximum reactance as a point of
operation. According to these implementations, a desired level of
efficiency can be obtained for acoustophoresis using the acoustic
transducer to generate an acoustic standing wave through fluid in
the acoustic chamber or cavity to which the transducer is coupled.
The points of operation that are determined according to a control
technique discussed herein can be frequency setpoints, which can be
dynamically maintained. For example, a desired point of operation
may change with characteristics of operation of the acoustic
chamber, such as a degree of material separation, temperature,
power delivered to the transducer, and other phenomena that may
influence or modify a desired operating point.
[0054] These and other non-limiting characteristics are more
particularly described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0055] The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawing(s) will be provided by the Office
upon request and payment of the necessary fee.
[0056] The following is a brief description of the drawings, which
are presented for the purposes of illustrating embodiments
disclosed herein and not for the purposes of limiting the same.
[0057] FIG. 1 is a front top perspective view of an exemplary
embodiment of a device of the present disclosure.
[0058] FIG. 2 is a front bottom perspective view of the device of
FIG. 1.
[0059] FIG. 3 is a right side view of the device of FIG. 1.
[0060] FIG. 4 is a front view of the device of FIG. 1.
[0061] FIG. 5 is a rear view of the device of FIG. 1.
[0062] FIG. 6 is a left side view of the device of FIG. 1.
[0063] FIG. 7 is a top view of the device of FIG. 1.
[0064] FIG. 8 is a bottom view of the device of FIG. 1.
[0065] FIG. 9 is a right side cross-sectional view of the device of
FIG. 1.
[0066] FIG. 10 is a cross-sectional diagram of an ultrasonic
transducer.
[0067] FIG. 11A is a cross-sectional side view of an acoustic
transducer with a free piezoelectric element;
[0068] FIG. 11B is a cross-sectional view of an acoustic transducer
with a damped piezoelectric element;
[0069] FIG. 12 is a photo of a square transducer and a circular
transducer suitable for use in the devices of the present
disclosure.
[0070] FIG. 13A is a graph illustrating force applied to a particle
in a fluid;
[0071] FIG. 13 is a graph of electrical impedance amplitude versus
frequency as a square transducer is driven at different
frequencies.
[0072] FIG. 14 illustrates the trapping line configurations for
seven of the peak amplitudes of FIG. 13.
[0073] FIG. 14A is an isometric view of an acoustic chamber;
[0074] FIG. 14B is a left side elevation view of the acoustic
chamber in FIG. 14A;
[0075] FIG. 14C is a front elevation view of the acoustic chamber
in FIG. 14A;
[0076] FIG. 15A illustrates a possible array configuration for a
group of transducers.
[0077] FIG. 15B illustrates another possible array configuration
for a group of transducers.
[0078] FIG. 16A is a general schematic of an impedance measurement
circuit.
[0079] FIG. 16B is a schematic of a circuit used for the
calibration of a power resistor.
[0080] FIG. 16C is a schematic of a circuit used to measure the
impedance of a transducer.
[0081] FIG. 16D is a schematic of an electronic system for
controlling an acoustophoretic device.
[0082] FIG. 17 is a computer model of an acoustophoretic separator
simulated to generate FIGS. 18-29.
[0083] FIG. 18 shows a simulation of the axial forces on a particle
in an acoustophoretic separator having a piezoelectric element
producing a single standing wave.
[0084] FIG. 19 shows a simulation of the lateral forces on a
particle in an acoustophoretic separator having a piezoelectric
element producing a single standing wave.
[0085] FIG. 20 shows a simulation of the axial forces on a particle
in an acoustophoretic separator having a piezoelectric element in a
multi-mode excitation.
[0086] FIG. 21 shows a simulation of the lateral forces on a
particle in an acoustophoretic separator a piezoelectric element in
a multi-mode excitation.
[0087] FIG. 22 shows a three dimensional computer generated model
of a mode shape calculation for a circular crystal driven at a
frequency of 1 MHz.
[0088] FIG. 23 shows the lateral (horizontal) acoustic radiation
force at 1.9964 MHz.
[0089] FIG. 24 shows the axial (vertical) component for a resonance
frequency of 1.9964 MHz.
[0090] FIG. 25 shows the acoustic pressure amplitude at 1.9964
MHz.
[0091] FIG. 26 shows the lateral force component at a resonance
frequency of 2.0106 MHz.
[0092] FIG. 27 shows the axial acoustic radiation force component
at a resonance frequency of 2.0106 MHz.
[0093] FIG. 28 shows the lateral force component at a resonance
frequency of 2.025 MHz.
[0094] FIG. 29 shows the axial acoustic radiation force component
at a resonance frequency of 2.025 MHz.
[0095] FIG. 30 is a picture showing the results of an oil/water
separation experiment.
[0096] FIG. 31 is a graph illustrating transducer frequency
responses and frequencies with dominant modes;
[0097] FIG. 32 is a circuit and block diagram of an LCL
network;
[0098] FIG. 33 is a graph illustrating a frequency response for
load current;
[0099] FIG. 34 is a graph illustrating a frequency response for RMS
current;
[0100] FIG. 35 is a graph illustrating a frequency response for
output power;
[0101] FIG. 36 is a graph illustrating a frequency response for
output power;
[0102] FIG. 37 is a graph illustrating a frequency response for
output current;
[0103] FIG. 38 is a graph illustrating a frequency response for
projected output power;
[0104] FIG. 39 is a circuit diagram showing an RF power supply with
an LCL network;
[0105] FIG. 40 is a circuit diagram and graph illustrating a
frequency response for peak load current;
[0106] FIG. 41 is a circuit diagram and graph illustrating a
frequency response for peak load current;
[0107] FIG. 42 is a graph illustrating a frequency response with
and without an LCL network;
[0108] FIG. 43 is a circuit diagram of an RF power supply with an
LCL network;
[0109] FIG. 44 is a circuit diagram of a low pass filter used with
the RF driver power supply of FIG. 43;
[0110] FIG. 45 is a flowchart illustrating a method for controlling
an acoustic transducer;
[0111] FIG. 46 is a flowchart illustrating a method for
implementing an optimized low pass filter;
[0112] FIG. 47 is a graph illustrating a frequency response for an
acoustic transducer;
[0113] FIG. 48 is a graph illustrating a frequency response for an
acoustic transducer;
[0114] FIG. 49 is a block diagram illustrating a control technique
for an acoustic transducer;
[0115] FIG. 50 is a block diagram illustrating a control technique
for an acoustic transducer;
[0116] FIG. 51 is a block diagram illustrating a calculation
technique for obtaining control parameters for an acoustic
transducer;
[0117] FIG. 52 is a block diagram illustrating demodulation of a
voltage or current signal;
[0118] FIG. 53 is a flowchart illustrating a control technique for
an acoustic transducer;
[0119] FIG. 54 is a flowchart illustrating components of a control
technique for use with an acoustic transducer;
[0120] FIG. 55 is a graph illustrating a frequency response for an
LC network;
[0121] FIG. 56 is a graph illustrating power, reactance, resistance
and peak performance for an acoustic transducer;
[0122] FIG. 57 is a graph illustrating a resistance curve versus
frequency;
[0123] FIG. 58 is a graph illustrating reactance versus frequency,
with a number of different modes identified;
[0124] FIGS. 59, 60, 61 and 62 are graphs illustrating turbidity
and reactance for a given example of acoustophoresis;
[0125] FIG. 63 is a graph illustrating piezoelectric
displacement;
[0126] FIG. 64 is a graph illustrating power and impedance
amplitude;
[0127] FIG. 65 is a graph illustrating absolute impedance
amplitude;
[0128] FIG. 66 is a graph illustrating impedance phase;
[0129] FIG. 67 is a graph illustrating displacement normalized by
power;
[0130] FIG. 68 is a graph illustrating average pressure normalized
by power;
[0131] FIG. 69 shows two graphs illustrating axial and lateral
radiation force;
[0132] FIGS. 70A, 70B, 70C, 70D, and 70E collectively show[[s]]
five graphs illustrating displacement for various modes;
[0133] FIGS. 71, 72A and 72B are graphs illustrating relationships
between dimensions of piezoelectric material and number of
modes;
[0134] FIG. 73 is a graph illustrating turbidity, resistance,
reactance and real power versus time for a planar wave;
[0135] FIG. 74 is a graph illustrating turbidity, resistance,
reactance and real power versus time for multimode operation at a
minimum reactance point;
[0136] FIG. 75 is a graph illustrating resistance, reactance and
real power versus frequency;
[0137] FIG. 76 is a graph illustrating turbidity, resistance,
reactance and real power versus time for multimode operation at a
minimum reactance point that is zero or positive;
[0138] FIGS. 77, 78, 79 and 80 are flowcharts illustrating hardware
and software configurations;
[0139] FIGS. 81A and 81B show[[s]] graphs illustrating a frequency
sweep response;
[0140] FIG. 82 is a graph illustrating regions of operation;
[0141] FIG. 83 is a graph and text illustrating a control
technique; and
[0142] FIGS. 84, 85, 86, and 87 are graphs illustrating various
parameters versus frequency.
DETAILED DESCRIPTION
[0143] The present disclosure may be understood more readily by
reference to the following detailed description of desired
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.
[0144] The singular forms "a," "an," and "the" include plural
referents unless the context clearly dictates otherwise.
[0145] As used in the specification and in the claims, the term
"comprising" may include the embodiments "consisting of" and
"consisting essentially of."
[0146] Numerical values should be understood to include numerical
values which are the same when reduced to the same number of
significant figures and numerical values which differ from the
stated value by less than the experimental error of conventional
measurement technique of the type described in the present
application to determine the value.
[0147] All ranges disclosed herein are inclusive of the recited
endpoint and independently combinable (for example, the range of
"from 2 grams to 10 grams" is inclusive of the endpoints, 2 grams
and 10 grams, and all the intermediate values).
[0148] As used herein, approximating language may be applied to
modify any quantitative representation that may vary without
resulting in a change in the basic function to which it is related.
Accordingly, a value modified by a term or terms, such as "about"
and "substantially," may not be limited to the precise value
specified. The modifier "about" should also be considered as
disclosing the range defined by the absolute values of the two
endpoints. For example, the expression "from about 2 to about 4"
also discloses the range "from 2 to 4."
[0149] It should be noted that many of the terms used herein are
relative terms. For example, the terms "upper" and "lower" are
relative to each other in location, i.e. an upper component is
located at a higher elevation than a lower component in a given
orientation, but these terms can change if the device is flipped.
The terms "inlet" and "outlet" are relative to a fluid flowing
through them with respect to a given structure, e.g. a fluid flows
through the inlet into the structure and flows through the outlet
out of the structure. The terms "upstream" and "downstream" are
relative to the direction in which a fluid flows through various
components, i.e. the flow fluids through an upstream component
prior to flowing through the downstream component. It should be
noted that in a loop, a first component can be described as being
both upstream of and downstream of a second component.
[0150] The terms "horizontal" and "vertical" are used to indicate
direction relative to an absolute reference, i.e. ground level.
However, these terms should not be construed to require structures
to be absolutely parallel or absolutely perpendicular to each
other. For example, a first vertical structure and a second
vertical structure are not necessarily parallel to each other. The
terms "top" and "bottom" or "base" are used to refer to surfaces
where the top is always higher than the bottom/base relative to an
absolute reference, i.e. the surface of the earth. The terms
"upwards" and "downwards" are also relative to an absolute
reference; an upwards flow is always against the gravity of the
earth.
[0151] The present application refers to "the same order of
magnitude." Two numbers are of the same order of magnitude if the
quotient of the larger number divided by the smaller number is a
value of at least one and less than 10.
[0152] Example large volume flow rate acoustophoretic phase
separators using ultrasonic standing wave technology can be
configured to provide the benefit of having little or no
consumables, little or no generated waste, and/or low energy usage
or cost. The technology is efficient at removal of particles of
greatly varying sizes, including separation of micron and
sub-micron sized particles. Examples of acoustic filters/collectors
utilizing acoustophoresis can be found in commonly owned U.S.
patent application Ser. Nos. 12/947,757; 13/085,299; 13/216,049;
and Ser. No. 13/216,035, the entire disclosure of each being hereby
fully incorporated herein by reference. Generally, the
acoustophoretic systems discussed herein employ ultrasonic standing
waves to trap (i.e. hold stationary) secondary phase particles,
gases, or liquids that are suspended in a host fluid stream. The
secondary phase can be continuously separated out of the host fluid
as the mixture flows through the acoustophoretic system.
[0153] The acoustic radiation force is proportional to the particle
volume (e.g. the cube of the radius) when the particle is small
relative to the wavelength. It is proportional to frequency and the
acoustic contrast factor. It also scales with acoustic energy (e.g.
the square of the acoustic pressure amplitude). For harmonic
excitation, the sinusoidal spatial variation of the force is what
drives the particles to the stable positions within the standing
waves. When the acoustic radiation force exerted on the particles
is stronger than the combined effect of fluid drag force and
buoyancy/gravitational force, the particle is trapped within the
acoustic standing wave field. The action of the acoustic forces on
the trapped particles results in concentration, agglomeration
and/or coalescence of particles and droplets. Particles which are
denser than the host fluid are separated through enhanced
gravitational settling, and particles which are less dense than the
host fluid are separated through enhanced buoyancy.
[0154] Efficient and economic particle separation processes can be
useful in many areas of energy generation, e.g., producing water,
hydro-fracking, and bio-fuels, e.g, harvesting and dewatering.
Acoustophoretic technology can be used to target accelerated
capture of bacterial spores in water, oil-recovery, and dewatering
of bio-oil derived from micro-algae. Current technology used in the
oil recovery field does not perform well in recovery of small,
i.e., less than 20 micron, oil droplets. However, the
acoustophoretic systems described herein can enhance the capture
and coalescence of small oil droplets, thereby shifting the
particle size distribution resulting in an overall increased oil
capture. Practical, useful, large flow rates at a level of 15-20
gallons per minute (GPM) per square foot (cross-sectional area) are
desired. Another goal is the increased capture of oil droplets with
a diameter of less than 20 microns. Much prior work on
acoustophoretics only occurred at the microscale, in MEMS
applications in research settings. Industrial processes use high
flow rates and continuous operation.
[0155] Acoustophoretic separation can also be used to aid such
applications as advanced bio-refining technology to convert
low-cost readily available non-food biomass (e.g. municipal solid
waste and sewage sludge) into a wide array of chemicals and
secondary alcohols that can then be further refined into renewable
gasoline, jet fuel, or diesel. A water treatment technology is used
to de-water the fermentation broth and isolate valuable organic
salts for further processing into fuels. The dewatering process is
currently done through an expensive and inefficient
ultra-filtration method that suffers from frequent fouling of the
membranes, a relatively low concentration factor, and a high
capital and operating expense. Acoustophoretic separation can
filter out particles with an incoming particle size distribution
that spans more than three orders of magnitude, namely from 600
microns to 0.3 microns, allowing improvements in the concentration
of the separated broth with a lower capital and operational
expense.
[0156] Acoustophoretic separation is also useful for the
harvesting, oil-recovery, and dewatering of micro-algae for
conversion into bio-oil. Current harvesting, oil recovery, and
dewatering technologies for micro-algae suffer from high
operational and capital expenses. Current best estimates put the
price of a barrel of bio-oil derived from micro-algae at a minimum
of $200.00 per barrel. There is a desire in the art of micro-algae
biofuel for technologies that improve the harvesting, oil-recovery,
and dewatering steps of this process. Acoustophoretic separation is
one such technology.
[0157] Some other applications are in the areas of wastewater
treatment, grey water recycling, and water production. Other
applications are in the area of biopharmaceuticals, life sciences,
and medical applications, such as the separation of lipids from red
blood cells. This can be of critical importance during
cardiopulmonary bypass surgery, which involves suctioning shed
mediastinal blood. Lipids are unintentionally introduced to the
bloodstream when blood is re-transfused to the body. Lipid
micro-emboli can travel to the brain and cause various
neuro-cognitive disorders. Efforts have been undertaken to remove
the lipids and cleanse the re-transfused blood, however existing
methods can be relatively inefficient and/or harmful to red blood
cells.
[0158] Particular embodiments focus on the capture and growth of
sub 20 micron oil droplets. At least 80% of the volume of
sub-20-micron droplets are captured and then grown to droplets that
are bigger than 20 microns. The process involves the trapping of
the oil droplets in the acoustic standing wave, coalescence of many
small trapped droplets, and eventually release of the larger
droplets when the acoustic trapping force becomes smaller than the
buoyancy force.
[0159] Desirably, the ultrasonic transducers generate a
three-dimensional standing wave in the fluid that exerts a lateral
force on the suspended particles/secondary fluid to accompany the
axial force so as to increase the particle trapping capabilities of
a acoustophoretic system. Typical results published in literature
state that the lateral force is two orders of magnitude smaller
than the axial force. In contrast, the technology disclosed in this
application provides for a lateral force to be of the same order of
magnitude as the axial force.
[0160] The present disclosure relates to the use of an acoustic
standing wave generated by an ultrasonic transducer or transducers
to separate oil from processed water on a macro scale. The oil may
be partially emulsified with the water. The separation occurs by
trapping the oil particles at the pressure nodes and anti-pressure
nodes in a standing wave. As the oil is trapped at these nodes, it
agglomerates and, due to buoyancy, will move to an area of trapped,
concentrated oil. The buoyancy separation is accomplished through
fluid dynamics with the main fluid stream flowing in a downward
direction and the trapped, agglomerated and coalesced oil particles
floating upward, due to buoyancy, into a trap.
[0161] The oil particles are separated from the fluid stream at the
anti-pressure nodes of the acoustic standing wave due to the
difference in their acoustic contrast factors from the fluid
stream. The equation for determining the acoustic contrast factor
of an oil in a fluid is known, and is related to the density of the
fluid, the density of the oil in the fluid, the compressibility of
the fluid, and the compressibility of the oil in the fluid. Both
oil and emulsified oil typically have a negative contrast factor
(.PHI.).
[0162] In the present disclosure, a 3-D acoustic standing wave is
generated by causing the ultrasonic transducer to act in a
"drumhead" fashion as opposed to a "piston" fashion. The "drumhead"
operation of the piezoelectric element in the ultrasonic transducer
causes multiple standing waves to be generated in a 3-D space. This
is opposed to the action of the piezoelectric element in the
ultrasonic transducer acting in a "piston" fashion n where a single
standing wave is produced. Through the use of a 3-D multi-standing
wave, macro-scale trapping of oil particles may be accomplished.
This allows for high volumes of processed water to be treated and
the oil to be separated from the water,
[0163] The piezoelectric element in the ultrasonic transducer may
be directly interfaced with the fluid stream or may have a
protective layer or matching layer over the surface of the
piezoelectric element that is interfaced with the fluid stream, The
protective layer may be a coating, such as a polyurethane or epoxy.
The protective layer may also be plated onto the surface of the
piezoelectric element that is interfaced with the fluid stream. The
plated layer may be added to the surface of the piezoelectric
element through either electrolytic or electroless plating. The
plating material may be nickel, chrome, copper, indium or
combination of layers of these materials. Also, the secondary
material or matching layer may be adhered to the surface of the
piezoelectric element such that the matching layer is now
interfaced with the fluid stream. The matching layer may be a
material such as a stainless steel that is adhered to the
piezoelectric element through the use of a two-part epoxy
system.
[0164] FIGS. 1-9 show various views of an acoustophoresis device of
the present disclosure. Generally, the acoustophoresis device uses
the ultrasonic transducer to separate suspended oil
particles/droplets in a fluid stream into ordered, coalesced and
agglomerated particles trapped in a standing wave of the
acoustophoresis device. The flow of the fluid stream is from the
upper end downward (i.e. with gravity). The fluid stream can enter
the device through one of many inlets that surround a central
trapping device for the agglomerated and separated oil. The fluid
stream flows into the acoustophoresis separation device from a pump
through the inlet. The agglomerated and coalesced oil gains
buoyancy and rises into the central oil trapping device. The device
is shown here in an orientation where the flow direction is
downwards, which is used for separating less-dense particles from
the host fluid. However, the device may be essentially turned
upside down to allow separation of particles which are heavier than
the host fluid. Instead of a buoyant force in an upward direction,
the weight of the agglomerated particles due to gravity pulls them
downward.
[0165] The initial fluid stream is made up of a host fluid (e.g.
water) and a suspended phase (e.g. oil droplets/articles). The
fluid stream enters the device 200 through one or more device
inlets 206 into an annular plenum 220 at a first end 202 of the
device. The first end 202 includes an outer sidewall 222 and an
inner longitudinal sidewall 224. An end wall 212 is also visible,
from which the longitudinal sidewall extends. The term "annular,"
as used herein, only designates the area or volume between the
outer sidewall and the inner longitudinal sidewall, and should not
be construed as requiring the first end of the device to have a
circular cross-section. However, in contemplated embodiments the
first end of the device has a circular cross-section. The annular
plenum has an inner diameter 225 and an outer diameter 227. This
construction guides the fluid stream flow downwards in the
direction of the centerline, i.e. with little to no radial or
circumferential motion component. This helps to create laminar/plug
flow later downstream. One device inlet 206 is shown here, with
three other inlets spaced about the first end being shown in dotted
line. It is contemplated that any number of inlets may be provided
as desired. In particular embodiments, four inlets are used. The
inlets are radially oriented.
[0166] A contoured nozzle wall 230 reduces the outer diameter of
the flow path, which generates higher velocities near the wall and
reduces turbulence, producing near plug flow as the fluid velocity
profile develops and the fluid passes through the connecting duct
and into a flow/separation chamber. The contoured wall also adds a
radial motion component to the suspended particles, moving the
particles closer to the centerline of the device and generating
more collisions with rising, buoyant agglomerated particles. This
radial motion will allow for optimum scrubbing of the particles
from the fluid in the connecting duct prior to reaching the
separation chamber. The term scrubbing is used to describe the
process of particle/droplet agglomeration, aggregation, clumping or
coalescing, that occurs when a larger particle/droplet travels in a
direction opposite to the fluid flow and collides with smaller
particles, in effect scrubbing the smaller particles out of the
suspension. The contoured nozzle wall directs the fluid in a manner
that generates large scale vortices at the entrance of the first
device outlet to also enhance particle collection. Generally, the
flow area of the device is designed to be continually decreasing
from the device inlets to the separation chamber to assure low
turbulence and eddy formation for better particle separation,
agglomeration, and collection. Put another way, the contoured wall
230 has a wide end 232 and a narrow end 234. The first end of the
device/the wide end of the nozzle wall has a first diameter 235,
and the narrow end of the nozzle wall has a second diameter 237.
The second diameter is less than the first diameter. The connecting
duct 240 is downstream of the nozzle wall and connects to the inlet
256 of the flow chamber 250.
[0167] The flow/separation chamber 250 is downstream of the
connecting duct 240 and has an inlet 256 at a first end 252, and an
outlet 258 at a second end 254 opposite the first end. At least one
ultrasonic transducer 270 is present on a wall 260, and a reflector
272 is located on a wall 262 opposite the transducer. Multiple
transducers can be used, as desired. In use, standing waves are
created between the transducer 270 and reflector 272. These
standing waves can be used to agglomerate particles, and this
orientation is used to agglomerate particles that are buoyant (e.g.
oil). Fluid, containing residual particles, then exits through the
flow chamber outlet 258 and through a second device outlet 210
located at a second end 204 of the device opposite the first end
202 of the device. Also shown here is a transparent window 274 on a
third wall 264 of the flow chamber. It is contemplated that in
particular embodiments, the flow chamber has a rectangular
cross-section. The flow chamber inlet and outlets have a circular
cross-section for interfacing with the other components of the
device.
[0168] As the buoyant particles agglomerate, they eventually
overcome the combined effect of the fluid flow drag forces and
acoustic radiation force, and their buoyant force is sufficient to
cause the buoyant particles to rise upwards. In this regard, a
first device outlet or collection duct 208 is present at the first
end of the device 202, and is surrounded by the longitudinal
sidewall 224, or put another way is separated from the device
inlets 206 by the longitudinal sidewall 224, or put yet another way
the first device outlet is a hole in the end wall 212. The
agglomerated buoyant particles exit the device through the first
device outlet 208. The first device outlet and the second device
outlet are on opposite ends of the device.
[0169] It should be noted that the buoyant particles formed in the
separation chamber 250 subsequently pass through the connecting
duct 240. This causes the incoming fluid stream flow from the
device inlets 206 to flow over the rising agglomerated particles
due to the inward radial motion imparted by the contoured wall 230.
This allows the rising particles to also trap smaller particles in
the incoming flow, increasing scrubbing effectiveness. The length
of the connecting duct and the contoured nozzle wall thus increase
scrubbing effectiveness. Especially high effectiveness is found for
particles with a size of 0.1 microns to 10 microns, where
efficiency is very low for conventional methods. As noted here, the
distance from the device inlets 206 to the bottom of the
longitudinal sidewall 224 is marked as length (L). The first
diameter is marked as D1 (reference numeral 235). This
length-to-diameter ratio here (i.e. L/D1) is less than 1.
[0170] The design here results in low flow turbulence at the flow
chamber inlet, a scrubbing length before (i.e. upstream of) the
flow chamber to enhance particle agglomeration and/or coalescence
before acoustic separation, and the use of the collection vortices
to aid particle removal upstream of the flow chamber.
[0171] The ultrasonic transducer(s) are arranged to cover the
entire cross-section of the fluid stream flowpath. In certain
embodiments, the flow chamber has a square cross section of 6
inches.times.6 inches which operates at flow rates of up to 3
gallons per minute (GPM), or a linear velocity of 8 mm/sec. The
transducer can be a PZT-8 (Lead Zirconate Titanate) transducer with
a 1-inch diameter and a nominal 2 MHz resonance frequency. Each
transducer consumes about 28 W of power for droplet trapping at a
flow rate of 3 GPM. This translates in an energy cost of 0.25 kW
hr/m3. This is an indication of the very low cost of energy of this
technology. Desirably, when multiple transducers are present, each
transducer is powered and controlled by its own amplifier. This
device shifts the particle size distribution in the host fluid
through agglomeration of smaller oil droplets into larger oil
droplets.
[0172] FIG. 10 is a cross-sectional diagram of a conventional
ultrasonic transducer. This transducer has a wear plate/protective
layer 50 at a bottom end, epoxy layer 52, piezoelectric material 54
(made of, e.g. PZT), an epoxy layer 56, and a backing layer 58. The
epoxy layer 56 attaches backing layer 58 to the crystal 54. The
entire assembly is contained in a housing 60 which may be made out
of, for example, aluminum. A connector 62 provides connection for
wires to pass through the housing and connect to leads (not shown)
which attach to the piezoelectric material 54. Typically, backing
layers are designed to add damping and to create a broadband
transducer with uniform displacement across a wide range of
frequency and are designed to suppress excitation at particular
vibrational eigen-modes. Wear plates are usually designed as
impedance transformers to better match the characteristic impedance
of the medium into which the transducer radiates, and face in the
direction in which the wave is generated. The piezoelectric
material can be, for example, a ceramic crystal.
[0173] FIG. 11 is a cross-sectional view of an ultrasonic
transducer 81 of the present disclosure, which can be used with the
acoustophoretic device of FIGS. 1-9. Transducer 81 has an aluminum
housing 82. A PZT crystal 86 defines the bottom end of the
transducer, and is exposed from the exterior of the housing. The
crystal is supported on its perimeter by the housing, with a small
elastic layer, e.g. silicone or similar material, located between
the crystal and the housing.
[0174] Screws (not shown) attach an aluminum top plate 82a of the
housing to the body 82b of the housing via threads 88. The top
plate includes a connector 84 to pass power to the PZT crystal 86.
The bottom and top surfaces of the PZT crystal 86 each contain an
electrode. A wrap-around electrode tab 90 connects to the bottom
electrode and is isolated from the top electrode. Electrical power
is provided to the PZT crystal 86 through the electrodes, with the
wrap-around tab 90 being the ground connection point. Note that the
crystal 86 has no backing layer or epoxy layer as is present in
FIG. 5. Put another way, there is an air gap 87 in the transducer
between aluminum top plate 82a and the crystal 86. A minimal
backing may be provided in some embodiments.
[0175] The transducer design can affect performance of the system.
A typical transducer is a layered structure with the ceramic
crystal bonded to a backing layer and a wear plate. Because the
transducer is loaded with the high mechanical impedance presented
by the standing wave, the traditional design guidelines for wear
plates, e.g., half wavelength thickness for standing wave
applications or quarter wavelength thickness for radiation
applications, and manufacturing methods may not be appropriate.
Rather, in one embodiment of the present disclosure the
transducers, there is no wear plate or backing, allowing the
crystal to vibrate 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.
[0176] Removing the backing (e.g. making the crystal air backed)
also permits the ceramic crystal/piezoelectric material to vibrate
higher order modes of vibration (e.g. higher order modal
displacement) with little damping. 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
order the mode shape of the crystal, the more nodal lines the
crystal has. The higher order modal displacement of the crystal
creates more trapping lines, although the correlation of trapping
line to node is not necessarily one to one, and driving the crystal
at a higher frequency will not necessarily produce more trapping
lines. In the present disclosure, the transducers are driven so
that the piezoelectric element vibrates in higher order modes of
the general formula (m, n), where m and n are independently 1 or
greater. In practice, the transducers of the present disclosure
will vibrate at higher orders than (1,2).
[0177] In some embodiments, the crystal may have a backing that
minimally affects 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 in a higher order mode shape and maintains a high
Q-factor while still providing some mechanical support for the
crystal. In another embodiment, the backing may be a lattice work
that follows the nodes of the vibrating crystal in a particular
higher order vibration mode, providing support at node locations
while allowing the rest of the crystal to vibrate freely. The goal
of the lattice work 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.
[0178] Placing the crystal in direct contact with the fluid also
contributes to the high Q-factor by avoiding the dampening and
energy absorption effects of the epoxy layer and the wear plate.
Other embodiments may have wear plates or a wear surface/protective
layer to prevent the PZT, which contains lead, contacting the host
fluid. This may be desirable in, for example, biological
applications such as separating blood. Such applications might use
a wear layer such as chrome, electrolytic nickel, or electroless
nickel. Chemical vapor deposition could also be used to apply a
layer of poly(p-xylxyene) (e.g. Parylene) or other polymer. Organic
and biocompatible coatings such as silicone or polyurethane are
also contemplated for use as a wear surface.
[0179] FIG. 12 illustrates two different ultrasonic transducers
that can be used in the devices of the present disclosure. The
transducer on the right shows a circular-shaped PZT-8 crystal 110
that is 1 inch in diameter. The transducer on the right shows a
rectangular-shaped crystal, which here is a square 1 inch by 1 inch
crystal. The effect of transducer shape on oil separation
efficiency was investigated, and Table 1 shows the results.
TABLE-US-00001 TABLE 1 Results of Investigation of Round and Square
Transducer Shape Total Power Capture Transducer Input Flowrate
Duration Efficiency Shape (Watts) (ml/min) (min) (%) Round 20 500
45 59% Square 20 500 30 91%
[0180] The results indicate that the square transducer 112 provides
better oil separation efficiencies than the round transducer 110,
explained by the fact that the square transducer 112 provides
better coverage of the flow channel with acoustic trapping forces,
and that the round transducer only provides strong trapping forces
along the centerline of the standing wave.
[0181] The size, shape, and thickness of the transducer determine
the transducer displacement at different frequencies of excitation,
which in turn affects oil separation efficiency. Typically, the
transducer is operated at frequencies near the thickness resonance
frequency (half wavelength). Gradients in transducer displacement
typically result in more places for oil to be trapped. Higher order
modal displacements generate three-dimensional acoustic standing
waves with strong gradients in the acoustic field in all
directions, thereby creating equally strong acoustic radiation
forces in all directions, leading to multiple trapping lines, where
the number of trapping lines correlate with the particular mode
shape of the transducer.
[0182] FIG. 13 shows the measured electrical impedance amplitude of
the transducer as a function of frequency in the vicinity of the
2.2 MHz transducer resonance. The minima in the transducer
electrical impedance correspond to acoustic resonances of the water
column and represent potential frequencies for operation. Numerical
modeling has indicated that the transducer displacement profile
varies significantly at these acoustic resonance frequencies, and
thereby directly affects the acoustic standing wave and resulting
trapping force. Since the transducer operates near its thickness
resonance, the displacements of the electrode surfaces are
essentially out of phase. The typical displacement of the
transducer electrodes is not uniform and varies depending on
frequency of excitation. As an example, at one frequency of
excitation with a single line of trapped oil droplets, the
displacement has a single maximum in the middle of the electrode
and minima near the transducer edges. At another excitation
frequency, the transducer profile has multiple maxima leading to
multiple trapped lines of oil droplets. Higher order transducer
displacement patterns result in higher trapping forces and multiple
stable trapping lines for the captured oil droplets.
[0183] To investigate the effect of the transducer displacement
profile on acoustic trapping force and oil separation efficiencies,
an experiment was repeated ten times, with all conditions identical
except for the excitation frequency. Ten consecutive acoustic
resonance frequencies, indicated by circled numbers 1-9 and letter
A on FIG. 13, were used as excitation frequencies. The conditions
were an experiment duration of 30 min, a 1000 ppm oil
concentration, a flow rate of 500 ml/min, and an applied power of
20 W.
[0184] As the emulsion passed by the transducer, the trapping lines
of oil droplets were observed and characterized. The
characterization involved the observation and pattern of the number
of trapping lines across the fluid channel, as shown in FIG. 14,
for seven of the ten resonance frequencies identified in FIG.
13.
[0185] The effect of excitation frequency clearly determines the
number of trapping lines, which vary from a single trapping line at
the excitation frequency of acoustic resonance 5 and 9, to nine
trapping lines for acoustic resonance frequency 4. At other
excitation frequencies four or five nodal trapping lines are
observed. Different displacement profiles of the transducer can
produce different (more) trapping lines of the standing waves, with
more gradients in displacement profile generally creating higher
trapping forces and more trapping lines.
[0186] Table 2 summarizes the findings from an oil trapping
experiment using a system similar to FIGS. 1-9. An important
conclusion is that the oil separation efficiency of the acoustic
separator is directly related to the mode shape of the transducer.
Higher order displacement profiles generate larger acoustic
trapping forces and more trapping lines resulting in better
efficiencies. A second conclusion, useful for scaling studies, is
that the tests indicate that capturing 5 micron oil droplets at 500
ml/min uses 10 Watts of power per square-inch of transducer area
per 1'' of acoustic beam span. The main dissipation is that of
thermo-viscous absorption in the bulk volume of the acoustic
standing wave. The cost of energy associated with this flow rate is
0.667 kWh per cubic meter.
TABLE-US-00002 TABLE 2 Trapping Pattern Capture Efficiency Study
Resonance Total Power # of Capture Peak Input Trapping Flowrate
Duration Efficiency Location (Watts) Lines (ml/min) (min) (%) 4 20
9 500 30 91% 8 20 5 500 30 58% A 20 4 500 30 58% 9 20 2 500 30
37%
[0187] In larger systems, different transducer arrangements are
feasible. FIG. 15A shows a transducer array 120 including three
square 1''.times.1'' crystals 120a, 120b, 120c. Two squares are
parallel to each other, and the third square is offset to form a
triangular pattern and get 100% acoustic coverage. FIG. 15B shows a
transducer array 122 including two rectangular 1''.times.2.5''
crystals 122a, 122b arranged with their long axes parallel to each
other. Power dissipation per transducer was 10 W per 1''.times.1''
transducer cross-sectional area and per inch of acoustic standing
wave span in order to get sufficient acoustic trapping forces. For
a 4'' span of an intermediate scale system, each 1''.times.1''
square transducer consumes 40 W. The larger 1''.times.2.5''
rectangular transducer uses 100 W in an intermediate scale system.
The array of three 1''.times.1'' square transducers would consume a
total of 120 W and the array of two 1''.times.2.5'' transducers
would consume about 200 W. Arrays of closely spaced transducers
represent alternate potential embodiments of the technology.
Transducer size, shape, number, and location can be varied as
desired to generate desired three-dimensional acoustic standing
waves.
[0188] When multiple transducers are connected in series, the
amplifier(s) used to power and control the transducers delivers
more voltage at increased current draws. When multiple transducers
are connected in parallel, the voltage remains similar to single
transducer operation, but the current draw increased proportionally
to the number of transducers connected. Typical amplifiers may be
more limited in the slew rate of current than in voltage. Also,
typical amplifiers only operate up to 100 W, which assumes perfect
impedance matching (i.e., a load impedance of 50 Ohm), which may
not occur in practice. Another complicating factor is that when
multiple transducers are connected to the same amplifier, the
transducers are excited at the same frequency. Impedance
measurements of the transducers has shown small changes in the
resonance frequency of each transducer, which can make it difficult
to find an excitation frequency that is optimal for each
transducer. Thus, it would be desirable to develop custom-made
electronics for powering and controlling the acoustic transducer(s)
and the resulting acoustic standing waves of the present
disclosure.
[0189] A circuit layout of two electrical impedances in series is
used to characterize the transducer. From voltage measurements, the
electrical impedance and electrical power consumed by the
transducer can be derived. The circuit consists of a series
combination of two impedances, as shown in FIG. 16A. The impedances
can consist of resistances, capacitance, and/or inductance, and are
specified later. The voltages are measured before and after
impedance Z1. Because resistors are passive devices (i.e., they
neither produce nor consume electrical energy), the ratio of
voltage to current in these circuits depends upon the frequency and
phase angle (.phi.) of the supply. Because the AC impedance (Z) is
equivalent to DC resistance (R), in these circuits, R=Z.
[0190] The measurement between the amplifier and impedance Z1 is
voltage V1, and the measurement between impedance Z1 and impedance
Z2 is voltage V2. Two cases are distinguished. In the first case,
impedance Z2 is a known impedance, typically a pure resistance, and
is used along with voltage measurements to obtain impedance Z2.
Since the elements can be reactive, the voltages and currents can
be treated as vectors (i.e., phasors, with amplitude and phase). In
the second case, a known impedance Z1 is used with the voltage
measurements to obtain impedance Z2, which is then the unknown
transducer. The general circuit equations that can be used to solve
the circuit are Kirchoff's equation for voltage:
{right arrow over (V)}.sub.1-{right arrow over
(V)}.sub.2=Z.sub.1{right arrow over (i)}
[0191] and the relationship between voltage and current:
{right arrow over (V)}.sub.2=Z.sub.2{right arrow over (i)}
[0192] When the above equations are combined, the following
relationship between the measured voltages and circuit impedances
is obtained:
V 2 .fwdarw. V 1 .fwdarw. = 1 1 + Z 1 Z 2 ##EQU00001##
[0193] In a typical setup, a power resistor of a known resistance
is used to measure and characterize the transducer. The power
resistor behaves like a series combination of a resistor and
inductance at typical ultrasonic frequencies because at the
ultrasonic frequencies of the present disclosure, the resistor is
no longer a pure resistor. As such, the first step in the
calibration process is to determine the value of the resistance and
inductance of the power resistor. This can be done, for example, by
completing the circuit with a known termination resistance,
typically 50 or 75 Ohm. Such a circuit is shown in FIG. 16B.
[0194] Solving the following relationship between the measured
voltages and circuit impedances yields the following equation for
impedance Z1:
Z 1 = R 2 .function. [ V 1 .fwdarw. V 2 .fwdarw. - 1 ]
##EQU00002##
[0195] From the above equation, the real and imaginary parts
representing the resistance and inductance of the power resistor
can be obtained. First, the real part of the above equation,
represent the resistance of the power resistor, can be found by the
following equation:
R 1 = Re .times. { Z 1 } = R 2 .function. [ V 1 V 2 .times. cos
.times. .times. .phi. 1 .times. 2 - 1 ] ##EQU00003##
[0196] and the imaginary part of the above equation, representing
the inductance of the power resistor, can be found by the following
equation:
.omega. .times. .times. L = Im .times. { Z 1 } = R 2 .function. [ V
1 V 2 .times. sin .times. .times. .phi. 1 .times. 2 - 1 ]
##EQU00004##
[0197] where .omega. is the work/energy and L is the
self-inductance of the power resistor.
[0198] From the two above equations, a first estimate of R1 and L
can be obtained. The computer program LabVIEW can be used to
calculate these values as the average of all of the predicted
values at each frequency. Next, a more accurate estimate of these
values can be obtained by comparing the measure voltage amplitude
ration of V2/V1 and the phase difference between V1 and V2. The
voltage amplitude ratio can be obtained by the following
equation:
V 2 V 1 = 1 ( 1 + R 1 R 2 ) 2 + ( .omega. .times. L R 2 ) 2
##EQU00005##
and the phase difference can be obtained by the following
equation:
.phi. 2 .times. 1 = - a .times. .times. tan .times. .times. 2
.times. ( 1 + R 1 R 2 , .times. .omega. .times. L R 2 )
##EQU00006##
[0199] Using the LabVIEW computer program, the values of R1 and L
can be iterated until the best fit is obtained. At that point, the
resistance and inductance values of the power resistor have been
determined. For exemplary purposes, typical values for a 10 Ohm
power resistor in the frequency range of about 2 MHz are a
resistance of 9.6 Ohm and an inductance of 9.7.times.10-7
Henry.
[0200] Once the power resistor is characterized, the impedance of
the transducer can be measured with the schematic shown in FIG.
16C. Impedance Z1 is now known, while impedance Z2 remains unknown,
which is the transducer impedance Zt. Using the same equations
provided above, the following equations are obtained:
Z t = Z 1 [ V 1 .fwdarw. V 2 .fwdarw. - 1 ] .times. .times. Z 1 = R
1 + j .times. .omega. .times. L ##EQU00007##
Using these equations, the following equation for Z.sub.t is
obtained:
Z t = R 2 + .omega. 2 + L 2 ( V 1 V 2 ) 2 - 2 .times. V 1 V 2
.times. cos .times. .times. .phi. 1 .times. 2 + 1 ##EQU00008##
and the following equation for the phase of Z.sub.t is
obtained:
.phi. Z t = a .times. .times. tan .times. .times. 2 .times. ( R ,
.omega. , ) - a .times. .times. tan .times. .times. 2 .times. ( V 1
V 2 .times. cos .times. .times. .phi. 1 .times. 2 - 1 , V 1 V 2
.times. sin .times. .times. .phi. 1 .times. 2 ) ##EQU00009##
The electrical power consumed by the transducer is given by the
following equation:
P E .times. l = V 2 2 2 .times. Z t ##EQU00010##
From the power consumed, the real power is given by the following
equation:
P E .times. l = V 2 2 2 .times. Z t .times. cos .times. .times.
.phi. Z t ##EQU00011##
and the reactive power is given by the following equation:
P E .times. l = V 2 2 2 .times. Z t .times. sin .times. .times.
.phi. Z t ##EQU00012##
[0201] These equations can be programmed in a LabVIEW computer
program that measures the voltages V1 and V2 and deduces therefrom
the electrical properties of the transducer.
[0202] FIG. 16D schematically illustrates an experimental setup for
an acoustophoretic device according to the present disclosure and
the electronics for controlling the ultrasonic transducer(s) of the
device and acoustic standing wave(s) created therein. As seen in
FIG. 16D, a function generator (Tektronix AFG 3022B) is used to
generate a signal (e.g., a low voltage sinusoidal voltage signal)
that is sent to an amplifier (AR Model 100A250A). The amplifier
output signal is electrically connected to a power resistor, which
is in turn electronically connected to the ultrasonic transducer of
the acoustic wave separator (AWS) device. The voltage before the
resistor (first voltage V1) and the voltage after the resistor
(second voltage V2) are measured. As seen in FIG. 16D, an
oscilloscope (Agilent Technologies DSO5014A) is used to measure the
voltages. The power resistor is used to measure and characterize
the performance of the transducer, as previously explained. A
computer running the computer program LabVIEW is used to
communicate with the function generator and oscilloscope (e.g., via
USB cables). A particle analyzer (Jorin VIPA) is used to
characterize the particles in the emulsion.
[0203] FIG. 17 is a computer model of an acoustophoretic separator
92 simulated to produce FIGS. 18-29. The piezo ceramic crystal 94
is in direct contact with the fluid in the water channel 96. A
layer of silicon 98 is between the crystal 94 and the aluminum top
plate 100. A reflector 102 reflects the waves to create standing
waves. The reflector is made of a high acoustic impedance material
such as steel or tungsten, providing good reflection. For
reference, the Y-axis 104 will be referred to as the axial
direction. The X-axis 106 will be referred to as the radial or
lateral direction. The acoustic pressure and velocity models were
calculated in COMSOL including piezo-electric models of the PZT
transducer, linear elastic models of the surrounding structure
(e.g. reflector plate and walls), and a linear acoustic model of
the waves in the water column. The acoustic pressure and velocity
was exported as data to MATLAB. The radiation force acting on a
suspended particle was calculated in MATLAB using Gor'kov's
formulation. The particle and fluid material properties, such as
density, speed of sound, and particle size, are entered into the
program, and used to determine the monopole and dipole scattering
contributions. The acoustic radiation force is determined by
performing a gradient operation on the field potential U, which is
a function of the volume of the particle and the time averaged
potential and kinetic energy of the acoustic field.
[0204] FIGS. 18-21 show simulations of the difference in trapping
pressure gradients between a single acoustic wave and a multimode
acoustic wave. FIG. 18 shows the axial force associated with a
single standing acoustic wave. FIG. 19 shows the lateral force due
to a single standing acoustic wave. FIG. 20 and FIG. 21 show the
axial force and lateral force, respectively, in a multi-mode
(higher order vibration modes having multiple nodes) piezoelectric
element excitation where multiple standing waves are formed. The
electrical input is the same as the single mode of FIG. 18 and FIG.
19, but the trapping force (lateral force) is 70 times greater
(note the scale to the right in FIG. 19 compared to FIG. 21). The
figures were generated by a computer modeling simulation of a 1 MHz
piezo-electric transducer driven by 10 V AC potted in an aluminum
top plate in an open water channel terminated by a steel reflector
(see FIG. 17). The field in FIG. 18 and FIG. 19 is 960 kHz with a
peak pressure of 400 kPa. The field in FIG. 20 and FIG. 21 is 961
kHz with a peak pressure of 1400 kPa. In addition to higher forces,
the 961 kHz field has more gradients and focal spots.
[0205] FIG. 22 shows a three dimensional computer generated model
of a mode shape calculation showing the out-of-plane displacement
for a circular crystal driven at a frequency of 1 MHz.
[0206] FIGS. 23-29 are based on the model of FIG. 17 with a PZT-8
piezo-electric transducer operating at 2 MHz. The transducer is 1''
wide and 0.04'' thick, potted in an aluminum top plate (0.125''
thick) in a 4''.times.2'' water channel terminated by a steel
reflector plate (0.180'' thick). The acoustic beam spans a distance
of 2''. The depth dimension, which is 1'', is not included in the
2D model. The transducer is driven at 15V and a frequency sweep
calculation is done to identify the various acoustic resonances.
The results of the three consecutive acoustic resonance
frequencies, i.e., 1.9964 MHz (FIGS. 23-25), 2.0106 MHz (FIG. 26
and FIG. 27), and 2.025 MHz (FIG. 28 and FIG. 29), are shown. The
acoustic radiation force is calculated for an oil droplet with a
radius of 5 micron, a density of 880 kg/m3, and speed of sound of
1700 m/sec. Water is the main fluid with a density of 1000 kg/m3,
speed of sound of 1500 m/sec, and dynamic viscosity of 0.001
kg/msec.
[0207] FIG. 23 shows the lateral (horizontal) acoustic radiation
force. FIG. 24 shows the axial (vertical) component for a resonance
frequency of 1.9964 MHz. FIG. 25 shows the acoustic pressure
amplitude. FIG. 23 and FIG. 24 show that the relative magnitude of
the lateral and axial component of the radiation force are very
similar, about 1.2e-10 N, indicating that it is possible to create
large trapping forces, where the lateral force component is of
similar magnitude or higher than the axial component. This is a new
result and contradicts typical results mentioned in the
literature.
[0208] A second result is that the acoustic trapping force
magnitude exceeds that of the fluid drag force, for typical flow
velocities on the order of mm/s, and it is therefore possible to
use this acoustic field to trap the oil droplet. Of course,
trapping at higher flow velocities can be obtained by increasing
the applied power to the transducer. That is, the acoustic pressure
is proportional to the driving voltage of the transducer. The
electrical power is proportional to the square of the voltage.
[0209] A third result is that at the frequency shown, high trapping
forces associated with this particular trapping mode extend across
the entire flow channel, thereby enabling capture of oil droplets
across the entire channel width. Finally, a comparison of the
minima of the acoustic trapping force field, i.e., the locations of
the trapped particles, with the observed trapping locations of
droplets in the standing wave shows good agreement, indicating that
COMSOL modeling is indeed an accurate tool for the prediction of
the acoustic trapping of particles. This will be shown in more
detail below.
[0210] FIG. 26 shows the lateral force component at a resonance
frequency of 2.0106 MHz, and FIG. 27 shows the axial acoustic
radiation force component at a resonance frequency of 2.0106 MHz.
FIG. 26 and FIG. 27 exhibit higher peak trapping forces than FIG.
23 and FIG. 24. The lateral acoustic radiation forces exceed the
axial radiation force. However, the higher trapping forces are
located in the upper part of the flow channel, and do not span the
entire depth of the flow channel. It would therefore represent a
mode that is effective at trapping particles in the upper portion
of the channel, but not necessarily across the entire channel.
Again, a comparison with measured trapping patterns indicates the
existence of such modes and trapping patterns.
[0211] FIG. 28 shows the lateral force component at a resonance
frequency of 2.025 MHz, and FIG. 29 shows the axial acoustic
radiation force component at a resonance frequency of 2.025 MHz.
The acoustic field changes drastically at each acoustic resonance
frequency, and therefore careful tuning of the system is important.
Two-dimensional models are used for relatively accurate prediction
of the acoustic trapping forces.
[0212] Two-dimensional axisymmetric models were developed to
calculate the trapping forces for circular transducers. The models
were used to predict acoustic trapping forces on particles, which
can then be used to predict particle trajectories in combination
with the action of fluid drag and buoyancy forces. The models
clearly show that it is possible to generate lateral acoustic
trapping forces that can be used to trap particles and overcome the
effects of buoyancy and fluid drag. The models also show that
circular transducers do not provide for large trapping forces
across the entire volume of the standing wave created by the
transducer, indicating that circular transducers only yield high
trapping forces near the center of the ultrasonic standing wave
generated by the transducer, but provide much smaller trapping
forces toward the edges of the standing wave. This further
indicates that the circular transducer only provides limited
trapping for a small section of the fluid flow that would flow
across the standing wave of the circular transducer, and no
trapping near the edges of the standing wave.
[0213] FIG. 30 is a picture showing the separation attained by an
apparatus of FIGS. 1-9 after 30 minutes of operation. This picture
is taken in a column attached to the first device outlet. An air
layer is present at the top, followed by an oil layer and a water
column. The oil is clearly separated from the water column.
[0214] The acoustophoretic devices of the present disclosure create
a three dimensional pressure field which includes standing waves
perpendicular to the fluid flow. The pressure gradients are large
enough to generate acoustophoretic forces orthogonal to the
standing wave direction (i.e., the acoustophoretic forces are
parallel to the fluid flow direction) which are of the same order
of magnitude as the acoustophoretic forces in the wave direction.
This permits better particle trapping and collection in the flow
chamber and along well-defined trapping lines, as opposed to merely
trapping particles in collection planes as in conventional devices.
The particles have significant time to move to nodes or anti-nodes
of the standing waves, generating regions where the particles can
concentrate, agglomerate, and/or coalesce.
[0215] In some embodiments, the fluid flow has a Reynolds number of
up to 500, i.e. laminar flow is occurring. For practical
application in industry, the Reynolds number is usually from 10 to
500 for the flow through the system. The particle movement relative
to the fluid motion generates a Reynolds number much less than 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
results in significant damping where shear forces are predominant
throughout the flow. This flow where viscous forces are dominant is
called Stokes flow. The flow of molasses is an example.
[0216] Wall contouring and streamlining have very little importance
to the flow of very viscous fluids or the flow in very tiny
passages, like MEMS devices. The flow of the particles relative to
the fluid in MEMS devices will be Stokes flow because both the
particle diameters and the relative velocities between the
particles and fluid are very small. On the other hand, the Reynolds
number for the flow through the present system will be much greater
than 1.0 because the fluid velocity and inlet diameter are much
larger. For Reynolds numbers much greater than 1.0, viscous forces
are dominant only where the flow is in contact with the surface.
This viscous region near the surface is called a boundary layer and
was first recognized by Ludwig Prandtl (Reference 2). In duct flow,
the flow will be laminar if the Reynolds number is significantly
above 1.0 and below 2300 for fully developed flow in the duct. The
flow velocity starts off uniform. As the flow moves down the duct,
the effect of wall viscous forces will diffuse inward towards the
centerline to generate a parabolic velocity profile. This parabolic
profile may have a peak value that is twice the average velocity.
The length of duct or passage for the parabolic profile to develop
is a function of the Reynolds number. For a Reynolds number of 20,
the development length will be 1.2 duct diameters. Thus, fully
developed flow happens very quickly. This peak velocity in the
center can be detrimental to acoustic particle separation. Also,
turbulence can occur and so flow surface contouring is very
important in controlling the flow. Thus, the shape of the contoured
nozzle wall will have a large effect on the final velocity profile.
The area convergence increases the flow average velocity, but it is
the wall contour that determines the velocity profile. The nozzle
wall contour will be a flow streamline, and is designed with a
small radius of curvature.
[0217] The transducer(s) is/are used to create a pressure field
that generates forces of the same order of magnitude both
orthogonal to the standing wave direction and in the standing wave
direction. When the forces are roughly the same order of magnitude,
particles of size 0.1 microns to 300 microns will be moved more
effectively towards regions of agglomeration ("trapping lines").
Because of the equally large gradients in the orthogonal
acoustophoretic force component, there are "hot spots" or particle
collection regions that are not located in the regular locations in
the standing wave direction between the transducer and the
reflector. Such hot spots are located in the maxima or minima of
acoustic radiation potential. Such hot spots represent particle
collection locations which allow for better wave transmission
between the transducer and the reflector during collection and
stronger inter-particle forces, leading to faster and better
particle agglomeration.
[0218] In biological applications, many parts, e.g. the tubing
leading to and from the device, may all be disposable, with only
the transducer and reflector to be cleaned for reuse. Avoiding
centrifuges and filters allows better separation of cells without
lowering the viability of the cells. The form factor of the
acoustophoretic device is also smaller than a filtering system,
allowing cell separation to be miniaturized. The transducers may
also be driven to create rapid pressure changes to prevent or clear
blockages due to agglomeration of cells. The frequency of the
transducers may also be varied to obtain optimal effectiveness for
a given power.
[0219] One or more multi-dimensional acoustic standing waves are
created between an ultrasonic transducer and a reflector.
Acoustically transparent or responsive materials may also be used
with the transducer or reflector to modify and/or control the
standing wave. Two transducers facing each other can be used to
generate a standing wave therebetween, e.g., the reflector can be
replaced by a transducer. The acoustic waves generated by the
transducer(s) are bulk acoustic standing waves that propagate
through large volume, e.g., the volume of an acoustic chamber.
[0220] As the fluid mixture flows through acoustic chamber with an
active ultrasonic transducer, particles or secondary fluid cluster,
collect, agglomerate, aggregate, clump, or coalesce at the nodes or
anti-nodes of the multi-dimensional acoustic standing wave,
depending on the particles' or secondary fluid's acoustic contrast
factor relative to the host fluid. The particles form clusters that
eventually exit the multi-dimensional acoustic standing wave nodes
or anti-nodes when the clusters have grown to a size large enough
to overcome the holding force of the multi-dimensional acoustic
standing wave (e.g. coalescence or agglomeration overcomes gravity
or buoyancy forces). For fluids/particles that are more dense than
the host fluid (such as cells), the clusters sink to the bottom and
can be collected separately from the clarified host fluid. For
fluids/particles that are less dense than the host fluid, the
buoyant clusters float upwards and can be collected.
[0221] The scattering of the acoustic field off the particles
results in a secondary acoustic radiation force that tends to draw
particles together. The multi-dimensional acoustic standing wave
produces a multi-dimensional acoustic radiation force, which acts
as a multi-dimensional trapping field. The multi-dimensional
features can be active in at least two or three dimensions. The
acoustic radiation force is proportional to the particle volume
(e.g. the cube of the radius) when the particle is small relative
to the wavelength. The force is proportional to frequency and the
acoustic contrast factor. The force scales with acoustic energy
(e.g. the square of the acoustic pressure amplitude). When the
acoustic radiation force exerted on the particles is stronger than
the combined effect of fluid drag force and buoyancy and
gravitational force, the particles are trapped within the acoustic
standing wave field. The particle trapping in a multi-dimensional
acoustic standing wave results in clustering, concentration,
agglomeration and/or coalescence of the trapped particles.
Relatively large solids of one material can thus be separated from
smaller particles of a different material, the same material,
and/or the host fluid through enhanced gravitational/buoyancy
separation.
[0222] The multi-dimensional standing wave generates acoustic
radiation forces in both the axial direction (e.g., in the
direction of the standing wave, between the transducer and the
reflector, which may be at an angle across the flow direction, and
in some instances may be perpendicular to the flow direction) and
the lateral direction (e.g., in the flow direction or transverse to
the direction between the transducer and the reflector). As the
mixture flows through the acoustic chamber, particles in suspension
experience a strong axial force component in the direction of the
standing wave. Since this acoustic force is across (e.g.
perpendicular to) the flow direction and the drag force, it quickly
moves the particles to pressure nodal planes or anti-nodal planes,
depending on the contrast factor of the particle. The lateral
acoustic radiation force acts to move the concentrated particles
towards the center of each planar node, resulting in clustering,
agglomeration or clumping. The lateral acoustic radiation force
component can overcome fluid drag for such clumps of particles, to
continually grow the clusters, which can exit the mixture due to
gravity or buoyancy. The drop in drag per particle as the particle
cluster increases in size, as well as the drop in acoustic
radiation force per particle as the particle cluster grows in size,
may separately or collectively influence operation of the acoustic
separator device. In the present disclosure, the lateral force
component and the axial force component of the multi-dimensional
acoustic standing wave are of the same or different order of
magnitude. In this regard, it is noted that in a multi-dimensional
acoustic standing wave generated by a single transducer, the axial
force is stronger than the lateral force, but the lateral force of
such a multi-dimensional acoustic standing wave is much higher than
the lateral force of a planar standing wave, usually by two orders
of magnitude or more.
[0223] Particle drag and acoustic radiation force effects may
influence optimal operation of the systems and methods of the
present disclosure. At low Reynolds numbers of less than 10,
laminar flow dominates, and viscous forces are much stronger than
inertial forces.
[0224] As the particles are trapped by the multi-dimensional
ultrasonic acoustic standing wave, they begin to aggregate and form
a clump of particles. The drag on this clump of particles is a
function of the geometry of the clump and is not merely the sum of
the drag of the individual particles that make up the clump.
[0225] For laminar flow, the Navier Stokes equation is expressed
as:
.rho. ( .differential. V .differential. t + ( V .gradient. )
.times. V ) ) = - .gradient. P + .mu. .times. .gradient. 2 .times.
V ##EQU00013##
where
.differential. V .differential. t ##EQU00014##
represents unsteady motion, (V.gradient.)V) represents inertial
motion, -.gradient.P represents pressure motion, and
.mu..gradient..sup.2V represents viscous motion.
[0226] For low Reynolds numbers, the unsteady motion and inertial
motion terms can be ignored (i.e. set equal to zero), and the
equation can be simplified to:
.gradient.P=.mu..gradient..sup.2V
[0227] For a particle of diameter a, the following equations
hold:
.gradient. P .varies. .mu. .times. V a .times. .times. F = 6
.times. .pi. .times. .mu. .times. a .times. V ##EQU00015##
where P is pressure, .mu. is the dynamic viscosity, a is the
particle diameter, V is the flow velocity, and F is the Stoke's
drag.
[0228] Prior to discussing further optimization of the systems, it
is helpful to provide an explanation now of how multi-dimensional
acoustic standing waves are generated. The multi-dimensional
acoustic standing wave used for particle collection is obtained by
driving an ultrasonic transducer composed of a piezoelectric
material at a frequency that generates the acoustic standing wave
and excites a fundamental 3D vibration mode of the transducer. The
transducer may be composed of various materials that may be
perturbed to generate an ultrasonic wave. For example, the
transducer may be composed of a piezoelectric material, including a
piezoelectric crystal or poly-crystal. Perturbation of the
piezoelectric material, which may be a piezoelectric crystal or
poly-crystal, in the ultrasonic transducer to achieve a multimode
response allows for generation of a multi-dimensional acoustic
standing wave. A piezoelectric material can be specifically
designed to deform in a multimode response at designed frequencies,
allowing for generation of a multi-dimensional acoustic standing
wave. The multi-dimensional acoustic standing wave may be generated
with distinct modes of the piezoelectric material such as a
3.times.3 mode that generates multi-dimensional acoustic standing
waves. A multitude of multi-dimensional acoustic standing waves may
also be generated by allowing the piezoelectric material to vibrate
through many different mode shapes. Thus, the material can be
selectively excited to operate in multiple modes such as a
0.times.0 mode (i.e. a piston mode), 1.times.1, 2.times.2,
1.times.3, 3.times.1, 3.times.3, and other higher order modes. The
material can be operated to cycle through various modes, in a
sequence or skipping past one or more modes, and not necessarily in
a same order with each cycle. This switching or dithering of the
material between modes allows for various multi-dimensional wave
shapes, along with a single piston mode shape to be generated over
a designated time.
[0229] Some further explanation of the ultrasonic transducers used
in the devices, systems, and methods of the present disclosure may
be helpful as well. In this regard, the transducers may be composed
of a piezoelectric material, such as a piezoelectric crystal or
poly-crystal, which may be made of PZT-8 (lead zirconate titanate).
Such crystals may have a major dimension on the order of 1 inch and
larger. The resonance frequency of the piezoelectric material may
nominally be about 2 MHz, and may be operated at one or more
frequencies. Each ultrasonic transducer module can have only one
crystal, or can have multiple crystals that each act as a separate
ultrasonic transducer and are either controlled by one or multiple
controllers, which controllers may include signal amplifiers. The
piezoelectric material can be square, rectangular, irregular
polygon, or generally of any arbitrary shape. The transducer(s)
is/are used to create a pressure field that generates forces of the
same order of magnitude both orthogonal to the standing wave
direction (lateral) and in the standing wave direction (axial).
[0230] FIG. 10 is a cross-sectional diagram of a conventional
ultrasonic transducer. This transducer has a wear plate 50 at a
bottom end, epoxy layer 52, ceramic crystal 54 (made of, e.g. PZT),
an epoxy layer 56, and a backing layer 58. On either side of the
ceramic crystal, there is an electrode: a positive electrode 61 and
a negative electrode 63. The epoxy layer 56 attaches backing layer
58 to the crystal 54. The entire assembly is contained in a housing
60 which may be made out of, for example, aluminum. An electrical
adapter 62 provides connection for wires to pass through the
housing and connect to leads (not shown) which attach to the
crystal 54. Typically, backing layers are designed to add damping
and to create a broadband transducer with uniform displacement
across a wide range of frequency and are designed to suppress
excitation at particular vibrational eigen-modes. Wear plates are
usually designed as impedance transformers to better match the
characteristic impedance of the medium into which the transducer
radiates.
[0231] FIG. 11A is a cross-sectional view of an ultrasonic
transducer 81 according to an example of the present disclosure.
Transducer 81 is shaped as a disc or a plate, and has an aluminum
housing 82. The piezoelectric crystal is a mass of perovskite
ceramic crystals, each consisting of a small, tetravalent metal
ion, usually titanium or zirconium, in a lattice of larger,
divalent metal ions, usually lead or barium, and O2-ions. As an
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 has an interior surface and an exterior
surface. The crystal is supported on its perimeter by a small
elastic layer 98, e.g. silicone or similar material, located
between the crystal and the housing. Put another way, no wear layer
is present. In particular embodiments, the crystal is an irregular
polygon, and in further embodiments is an asymmetrical irregular
polygon.
[0232] Screws 88 attach an 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 the
PZT crystal 86 is connected to a positive electrode 90 and a
negative electrode 92, which are separated by an insulating
material 94. The electrodes can be made from any conductive
material, such as silver or nickel. Electrical power is provided to
the PZT crystal 86 through the electrodes on the crystal. Note that
the crystal 86 has no backing layer or epoxy layer. Put another
way, there is an air gap 87 in the transducer between aluminum top
plate 82a and the crystal 86 (i.e. the housing is empty). A minimal
backing 58 (on the interior surface) and/or wear plate 50 (on the
exterior surface) may be provided in some embodiments, as seen in
FIG. 11B.
[0233] The transducer design can affect performance of the system.
A typical transducer is a layered structure with the ceramic
crystal bonded to a backing layer and a wear plate. Because the
transducer is loaded with the high mechanical impedance presented
by the standing wave, the traditional design guidelines for wear
plates, e.g., half wavelength thickness for standing wave
applications or quarter wavelength thickness for radiation
applications, and manufacturing methods may not be appropriate.
Rather, in one embodiment of the present disclosure the
transducers, there is no wear plate or backing, allowing the
crystal to vibrate in one of its eigenmodes (i.e. near
eigenfrequency) with a high Q-factor. The vibrating ceramic
crystal/disk is directly exposed to the fluid flowing through the
acoustic chamber.
[0234] Removing the backing (e.g. making the crystal air backed)
also permits the ceramic crystal to vibrate at higher order modes
of vibration 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 order the mode shape of the crystal,
the more nodal lines the crystal has. The higher order modal
displacement of the crystal creates more trapping lines, although
the correlation of trapping line to node is not necessarily one to
one, and driving the crystal at a higher frequency will not
necessarily produce more trapping lines.
[0235] In some embodiments, the crystal may have a backing that
minimally affects 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 in a higher order mode shape and maintains a high
Q-factor while still providing some mechanical support for the
crystal. The backing layer may be a solid, or may be a lattice
having holes through the layer, such that the lattice follows the
nodes of the vibrating crystal in a particular higher order
vibration mode, providing support at node locations while allowing
the rest of the crystal to vibrate freely. The goal of the lattice
work 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.
[0236] Placing the crystal in direct contact with the fluid also
contributes to the high Q-factor by avoiding the dampening and
energy absorption effects of the epoxy layer and the wear plate.
Other embodiments may have wear plates or a wear surface to prevent
the PZT, which contains lead, from contacting the host fluid. This
may be desirable in, for example, biological applications such as
separating blood. Such applications might use a wear layer such as
chrome, electrolytic nickel, or electroless nickel. Chemical vapor
deposition could also be used to apply a layer of poly(p-xylylene)
(e.g. Parylene) or other polymers or polymer films. Organic and
biocompatible coatings such as silicone or polyurethane are also
usable as a wear surface.
[0237] FIG. 13A is a log-log graph (logarithmic y-axis, logarithmic
x-axis) that shows the scaling of the acoustic radiation force,
fluid drag force, and buoyancy force with particle radius, and
provides an explanation for the separation of particles using
acoustic radiation forces. The buoyancy force is a particle volume
dependent force, and may therefore be negligible for particle sizes
on the order of micron, but grows, and becomes significant for
particle sizes on the order of hundreds of microns. The fluid drag
force (Stokes drag force) scales linearly with fluid velocity, and
therefore typically exceeds the buoyancy force for micron sized
particles, but is negligible for larger sized particles on the
order of hundreds of microns. The acoustic radiation force scaling
is different. When the particle size is small, Gor'kov's equation
is accurate and the acoustic trapping force scales with the volume
of the particle. Eventually, when the particle size grows, the
acoustic radiation force no longer increases with the cube of the
particle radius, and will rapidly vanish at a certain particle
size. For further increases of particle size, the radiation force
increases again in magnitude but with opposite phase (not shown in
the graph). This pattern repeats for increasing particle sizes.
[0238] Initially, when a suspension is flowing through the system
with primarily small micron sized particles, the acoustic radiation
force balances the combined effect of fluid drag force and buoyancy
force to permit a particle to be trapped in the standing wave. In
FIG. 13A this trapping happens at a particle size labeled as Rc1.
FIG. 13A indicates that all larger particles will be trapped as
well. Therefore, when small particles are trapped in the standing
wave, particle
clustering/coalescence/clumping/aggregation/agglomeration takes
place, resulting in continuous growth of effective particle size.
As particles cluster, the total drag on the cluster is much lower
than the sum of the drag forces on the individual particles. In
essence, as the particles cluster, they shield each other from the
fluid flow and reduce the overall drag of the cluster. As the
particle cluster size grows, the acoustic radiation force reflects
off the cluster, such that the net acoustic radiation force
decreases per unit volume. The acoustic lateral forces on the
particles may be larger than the drag forces for the clusters to
remain stationary and grow in size.
[0239] Particle size growth continues until the buoyancy force
becomes dominant, which is indicated by a second particle size,
Rc2. The buoyancy force per unit volume of the cluster remains
constant with cluster size, since it is a function of the particle
density, cluster concentration and gravity constant. Therefore, as
the cluster size increases, the buoyancy force on the cluster
increases faster than the acoustic radiation force. At the size
Rc2, the particles will rise or sink, depending on their relative
density with respect to the host fluid. At this size, acoustic
forces are secondary, gravity/buoyancy forces become dominant, and
the particles naturally drop out or rise out of the host fluid.
Some particles may remain in the acoustic wave as clusters of
others drop out, and those remaining particles and new particles
entering the acoustic chamber with the flow of a fluid mixture
continue to move to the three-dimensional nodal locations,
repeating the growth and drop-out process. Clusters can grow larger
than a half wavelength of the acoustic wave, which results in
periodic and sharp changes in acoustic radiation force on the
clusters. This phenomenon explains the quick drops and rises in the
acoustic radiation force beyond size Rc2. Thus, FIG. 13A explains
how small particles can be trapped continuously in a standing wave,
grow into larger particles or clumps, and then eventually will rise
or settle out because of increased buoyancy/gravity force.
[0240] In some examples, the size, shape, and thickness of the
transducer can determine the transducer displacement at different
frequencies of excitation. Transducer displacement with different
frequencies may affect particle separation efficiency. Higher order
modal displacements can generate three-dimensional acoustic
standing waves with strong gradients in the acoustic field in all
directions, thereby creating strong acoustic radiation forces in
all directions, which forces may, for example be equal in
magnitude, leading to multiple trapping lines, where the number of
trapping lines correlate with the particular mode shape of the
transducer.
[0241] FIG. 14A shows an isometric view of the system in which the
trapping line locations are being determined. FIG. 14B is a view of
the system as it appears when looking down the inlet, along arrow
114. FIG. 14C is a view of the system as it appears when looking
directly at the transducer face, along arrow 116.
[0242] The effect of excitation frequency clearly determines the
number of trapping lines, which vary from a single trapping line at
the excitation frequency of acoustic resonance 5 and 9, to nine
trapping lines for acoustic resonance frequency 4. At other
excitation frequencies four or five trapping lines are observed.
Different displacement profiles of the transducer can produce
different (more) trapping lines in the standing waves, with more
gradients in displacement profile generally creating higher
trapping forces and more trapping lines. It is noted that although
the different trapping line profiles shown in FIG. 14 were obtained
at the frequencies shown in FIG. 13, these trapping line profiles
can also be obtained at different frequencies.
[0243] FIG. 14 shows the different crystal vibration modes possible
by driving the crystal to vibrate at different fundamental
frequencies of vibration. The 3D mode of vibration of the crystal
is carried by the acoustic standing wave across the fluid in the
chamber all the way to the reflector and back. The resulting
multi-dimensional standing wave can be thought of as containing two
components. The first component is a planar out-of-plane motion
component (uniform displacement across crystal surface) of the
crystal that generates a standing wave, and the second component is
a displacement amplitude variation with peaks and valleys occurring
in lateral directions across the crystal surface. Three-dimensional
force gradients are generated by the standing wave. These
three-dimensional force gradients result in lateral radiation
forces that stop and trap the particles with respect to the flow by
overcoming the viscous drag force. In addition, the lateral
radiation forces are responsible for creating tightly packed
clusters of particles. Therefore, particle separation and
gravity-driven collection depends on generating a multi-dimensional
standing wave that can overcome the particle drag force as the
mixture flows through the acoustic standing wave. Multiple particle
clusters are formed along trapping lines in the axial direction of
the standing wave, as presented schematically in FIG. 14.
[0244] The piezoelectric crystals of the transducers described
herein can be operated at various modes of response by changing the
drive parameters, including frequency, for exciting the crystal.
Each operation point has a theoretically infinite number of
vibration modes superimposed, where one or more modes are dominant.
In practice, multiple vibration modes are present at arbitrary
operating points of the transducer, with some modes dominating at a
given operating point. FIG. 52 presents COMSOL results for crystal
vibration and lateral radiation forces on a typical particle size.
The ratio of lateral to axial radiation force is plotted versus
operating frequency. Points are labeled on the curve where a
specific mode of vibration is dominant. Mode I represents the
planar vibration mode of the crystal designed to generate a 2 MHz
standing wave in a mixture. Mode III represents the 3.times.3 mode
operation of a 1.times.1 crystal. These analytical results show
that the 3.times.3 mode can be dominant with different levels of
lateral radiation force. More specifically, operating the example
system at a frequency of 2.283 MHz generates the lowest lateral
force ratio of about 1.11 for a 3.times.3 mode. This operating
point generates the largest cluster size and the best collection
operation for the example system. Operating the devices and systems
described herein at a frequency for a given configuration that
produces a desired 3D mode with the lowest lateral force ratio is
desirable to achieve the most efficient separation.
[0245] FIG. 32 shows an inductor-capacitor-inductor system that is
utilized to smooth the electronic impulses that are sent to the
piezoelectric material. The step is a critical part of the process
as otherwise parasitic vibrations of the piezoelectric material
will generate heat into the system and reduce the overall
efficiency of the acoustic resonator when generating a
multidimensional acoustic standing wave. The circuit of FIG. 32
depicts the use of a current source to drive the crystal for
enhanced performance for the specific application. FIG. 32 also
shows a digital signal processor (DSP) that may be utilized to
optimize the performance of the acoustic resonator by detecting
degradation of the acoustic wave and assess the performance of the
resonator system, adjusting the system for optimum performance.
FIG. 32 illustrates the use of VI-sensing to control the frequency
and delivered power to optimize performance, to detect degradation,
and to assess performance.
[0246] FIG. 33 shows the use of a load current in amps over various
frequencies and at different resistances. The highest current load
at about 2.4 MHz is at the lowest resistance of 5 ohms.
[0247] FIG. 34 shows three root mean squared (RMS) currents plotted
against frequencies from 2.1 MHz to 2.3 MHz where the currents are
at different voltages from 25 V to 35 V.
[0248] FIG. 35 shows the output to the crystal in power (measured
in Watts) at 25 V over frequencies from 2.1 MHz to 2.3 MHz. The
plot also shows the resistance of the piezoelectric material over
the same frequency range.
[0249] FIG. 36 shows the output into the piezoelectric material in
Watts over a 2.1 MHz to 2.3 MHz range and at three different
voltage levels (25 V, 30 V, 35 V).
[0250] FIG. 37 shows the output in RMS current to the piezoelectric
material over the range of 2.1 MHz to 2.3 MHz at three different
voltages (25 V, 30 V, 35 V).
[0251] FIG. 38 shows the projected output power into the
piezoelectric material where there are three measured power output
numbers and a fourth projected power number, the fourth power
number being at 45 V over the frequency range of 2.1 MHz to 2.3
MHz.
[0252] FIG. 39 shows a schematic of the Buck book voltage, the
inverter, and the inductor-capacitor inductor (LCL) tank.
[0253] FIG. 40 shows the configuration of the LCL circuit and plots
peak current loads over the range of 2 MHz to 3 MHz.
[0254] FIG. 41 shows the LCL circuit and the peak load current
plotted over the frequency range of 2.2 MHz to 2.3 MHz at various
resistance levels.
[0255] The-effect of the LCL circuit is shown in FIG. 42 which
shows the higher frequency harmonics being filtered out of the
electronic signal that is sent to the piezoelectric material. The
smaller a particular spectral line is the better the filtering
operation. As a result, the parasitic vibrations that would have
been generated in the piezoelectric material are reduced or
eliminated.
[0256] FIG. 43 is a diagram of an RF driver power converter
composed of a DC-DC converter, a converter filter, [[A]] a DC-AC
inverter and an LCL matching filter. [[s]]Switches S1a and S1b of
the converter are driven by complementary clocking signals that
have the same frequency and duty cycle. Switches S1a and S1b may
not be both closed at the same time. The switches may be operated
to avoid being both closed at the same time. The action of switches
S1a and S1b produces a `chopped` voltage Vb across switch S1b. The
output of the converter is a chopped signal with an average DC
voltage that is dependent on the duty cycle of the switches.
[0257] The output of the converter is provided to an RLC filter
that averages the output of the converter. The RLC filter may be
implemented as a buck filter that filters the `chopped` Vb so that
its average value appears across capacitor C2. The chopped output
of the converter appears as an average DC signal across the output
of the filter. The filter's bandwidth or response is sufficient to
follow or keep up with changes in the duty cycle of the clocking
signals provided to the switches of the converter. The duty cycle
of the clocking signals, or the DC output of the converter, is
related to control of the dynamic characteristics of the acoustic
transducer, for example, the reactive nature of the piezoelectric
material. The filter's bandwidth allows the voltage across
capacitor C2 to `follow` changes in the duty cycle of the clocking
signals which is related to the dynamic changes in the acoustic
cavity.
[0258] The output of the filter is provided to the DC-AC inverter.
The inverter includes switches that are driven by complementary
clocking signals that are switched at a frequency that is related
to the operation of the acoustic transducer and cavity system.
Switches S2a and S2b are driven by complementary clocking signals
that have the same frequency as the PZT-CAVITY system. The action
of switches S2a and S2b constitutes a DC to AC inverter. The DC
input to the inverter is used as a control signal for RF power
conversion, where the inverter provides an RF signal with a power
level that is controlled by the DC input.
[0259] The output of the inverter is applied to an LCL matching
filter, which is connected to the acoustic transducer. The LCL
matching filter smooths the output of the inverter and provides a
load match for the inverter output. The LCL matching filter
provides the dual purpose of smoothing the output of the inverter
and matching the PZT to the inverter for optimum electrical power
transfer.
[0260] An example of the filter interposed between the converter
and inverter in the RF driver power converter is illustrated in
FIG. 44. The filter may be implemented as a low pass filter, with a
response time or bandwidth that is sufficient to react to changes
in duty cycle of the complementary signals used to drive the DC-DC
converter switches. As can be seen in FIG. 44, resistor Rg is 0.1
ohms, inductor L1 is 10 microhenries, capacitor C1 is 90 .mu.F and
resistor R1 is 1.0 ohms. The output of the filter is provided to a
high-frequency roll off element, implemented here as capacitor C2,
which has a value of 3 .mu.F. The filter contributes to interfacing
the DC-DC converter, which operates on a duty cycle basis, with the
DC-AC inverter, which operates as a function generator or
oscillator that translates the DC input from the converter into an
RF amplified signal that can be used to drive the acoustic
transducer. The filter thus performs several functions, including
smoothing the response of the output of the DC-DC converter and
averaging the chopped output of the converter to provide a
well-regulated DC signal that is related to the operation, for
example, the feedback data, of the acoustic transducer.
[0261] Referring to FIG. 45, a flow chart is illustrated for a
process for locating a minimum and/or maximum reactance for the
acoustic transducer and/or the transducer/acoustic chamber
combination, which may be under load. The load can be a fluid in
the acoustic chamber, and/or particulates or a secondary fluid that
is separated from the primary or host fluid. As the particulates or
secondary fluid is separated from the primary or host fluid, the
characteristics of the fluid in the acoustic chamber change, which
can impact the operation of the transducer and/or
transducer/acoustic chamber combination. The process for locating
an operating point for driving the transducer begins by scanning
through frequencies applied to the transducer, for example, by
applying a range of frequencies to the transducer and measuring
feedback data from the transducer. The range of frequencies to be
scanned can be provided by user settings. Data for the reactance,
X, and resistance, R, of the transducer is collected. One technique
for collecting reactance and resistance data is to measure voltage,
current and phase angle on the transducer. Resistance is determined
as the real part of the voltage divided by the current, while
reactance is determined as imaginary part of the voltage divided by
the current.
[0262] As the data for the frequency scan is collected, a number of
resonance and anti-resonance frequencies can be determined. The
data can be passed through a low pass filter and peaks can be
identified using a derivative function. A maximum peak for the
anti-resonance is also identified. The method can accept an input
setting of the number of reactances from anti-resonance to locate a
minimum reactance. Based on the collected and calculated data, the
desired minimum reactance below anti-resonance or desired maximum
reactance above anti-resonance is determined, in this case as an
index of the minimum or maximum reactances. Once the frequency of
the desired reactance is located, the frequency of the RF driver
power converter is set to the located frequency. The located
frequency can be an operating setpoint for operating the
transducer.
[0263] After a period of time, such as a number of milliseconds up
to a number of tens of seconds, the process is repeated. By
repeating the process, variations in the system can be dynamically
identified, such as changes to reactance caused by temperature
shifts, and the desired operating setpoints can be modified
accordingly in keeping with the process.
[0264] Referring to FIG. 46, a flow chart illustrates a process for
implementing a low-pass filter for use in the frequency
determination process described above. The filter characteristics
can be modified in accordance with the illustrated process to
contribute to optimizing detection of the desired frequency
setpoints. The process begins by using an existing cut off or
corner frequency in conjunction with the data collected from the
frequency scan. A zero phase low-pass Butterworth filter is used to
filter the collected data with the cutoff frequency. The derivative
of the data is taken to determine minimums and/or maximums, and
positive to negative zero crossings are identified and counted. The
positive to negative zero crossings are indicative of detected
peaks in the frequency response. If the process detects more peaks
than expected, the cutoff frequency is increased and the process is
repeated. If the count is less than the expected number of peaks,
the filtered data is provided to the minimum/maximum reactance
detection process.
[0265] FIG. 47 illustrates a frequency scan for a slightly damped
1.times.3 piezoelectric transducer coupled to an acoustic cavity
through which a fluid containing CHO (Chinese hamster ovary) cells
was flowed. As illustrated, peak anti-resonance is located, and a
minimum reactance two away from the anti-resonance is selected for
a frequency setpoint. In the figure, anti-resonance is
approximately 2.278 MHz, and the selected frequency setpoint is
approximately 2.251 MHz.
[0266] FIG. 48 illustrates a frequency scan for a highly damped 2
MHz 1.times.3 transducer coupled to an acoustic chamber containing
CHO. The peak anti-resonance is identified and the minimum
reactance two away from the anti-resonance frequency is selected
for an operating setpoint. Although a minimum reactance two away
from the anti-resonance frequency is chosen as an operating
setpoint, any reactance or index away from anti-resonance can be
chosen for an operating setpoint.
[0267] Through experimental testing of the large scale acoustic
filtration system, it has been determined that the 1 MHz and 2 MHz
1.times.3 transducer may have an optimal efficiency when operating
at the minimum reactance points at frequencies below the transducer
anti-resonances, as well as operating at the maximum reactance
points above the anti-resonance of the transducer. The technique
described herein provides an automated method to set the frequency
of the RF drive to the transducer, so it is operating at a minimum
reactance point below the anti-resonance or a maximum reactance
above the anti-resonance. According to a feature, the technique
maintains the desired operating point. The technique can be used to
set the frequency of the RF drive, such as the inverter, function
generator or oscillator discussed above.
TABLE-US-00003 TABLE 3 Functions and Variable Inputs and Outputs
Name Type Description Scan Function Function Steps through a range
of frequencies and captures Resistance and Reactance data from the
Voltage and Current measurements of the RF drive. Inputs: Range
(+-50 kHz around anti-res) Step Size (500 Hz) Step Interval (1 ms)
Output: Array of Frequency, R, and X Estimated Number Input Double
Expected number of resonances of Resonances over the full scan
range Number of Reactance Input Signed If negative the method will
Minima/Maxima from Integer pick the frequency of that
Anti-Resonance many minima below the anti- resonance. If positive
the method will pick the frequency of that many maxima above the
anti- resonance Frequency to Set Output Double The frequency that
the method picks to set the RF drive Wait Time Input Double
Specifies the amount of time between scans
[0268] The method begins by running a sweep of frequencies and
collecting resistance and reactance data for each frequency step.
The resistance and reactance data is extrapolated from the voltage
and current measurements of the RF drive. The sweep range is
specified by the user, but is targeted to be 50 kHz above and 50
kHz below the anti-resonance of the transducer. The step size and
step interval are also variables that can be altered. When the
sweep is complete it outputs the frequency, resistance, and
reactance at each step.
[0269] The data from the sweep is then filtered utilizing a
zero-phase low pass Butterworth filter. The reactance enters a loop
where the low cutoff frequency of the filter is constantly
increased, until the number of peaks of the filtered data, equals
the number of estimated peaks. This number of estimated peaks is
entered by the user. The resistance data is filtered using a
zero-phase low-pass Butterworth filter, however the low cutoff
frequency is increased until there is one peak. The peak value of
the filtered resistance data is interpreted as the anti-resonance
of the transducer.
[0270] The derivative of the filtered reactance data is calculated
and is used to find all the maximum or minimum points of the
reactance curve. If the number of reactance minima/maxima from the
anti-resonance data input is negative the method will look for the
minimum reactance points below the anti-resonance. The method does
this by identifying the negative to positive zero crossings, in
other words, the upward slope zero crossings of the derivative of
the filtered reactance curve. If this number is positive the method
will look for the positive to negative zero crossings above the
anti-resonance, which are the maximum points of the reactance
curve. The absolute value of the number of reactance minima/maxima
from the anti-resonance data input is the number of minimum or
maximum points from the anti-resonance. The index of this point is
used to determine the frequency to set the RF drive.
[0271] The RF drive is set and the method waits for a designated
amount of time set by the user. Once this time period has elapsed
the method then scans and start the sequence over again. Sample
data of both slightly and highly damped data can be seen in FIG. 47
and FIG. 48. In both these examples the method was selected to pick
two minimum reactance points below the anti-resonance. The set
frequency is indicated by the red line. It can be seen that this
line falls on the negative to positive zero crossing of the
derivative of the filtered reactance data curve, and at the local
minimum of the filtered reactance data curve.
[0272] Referring to FIG. 49, a diagram of a control configuration
for controlling an acoustic transducer 112 coupled to an acoustic
chamber 114 is illustrated. Acoustic transducer 112 is driven by an
RF driver power converter composed of DC source 110, DC-DC
converter 116 and RF DC-AC inverter 118. The output drive signal
provided by inverter 118 is inspected or sensed to obtain voltage
sense 122 and current sense 124, which are fed back to a controller
120. Controller 120 provides control signals to converter 116 and
inverter 118 to modulate the drive signal provided to the acoustic
transducer 112.
[0273] The signal provided by controller 120 to converter 116 is a
pulse width measure, which determines the duty cycle of the
switching signals in converter 116. The duty cycle determines the
DC level of the output of converter 116, which is applied to
inverter 118. For example, the greater the duty cycle, the higher
the DC output that is generated by converter 116. Controller 120
also provides control signals to inverter 118 that determine the
frequency of operation of inverter 118. The control signals
provided to inverter 118 may be switching signals, for switching
switches in inverter 118, an example of such switches being shown
in FIG. 43. Alternately, or in addition, controller 120 can provide
a control signal to inverter 118 that is used to indicate a desired
switching frequency, and circuitry internal to inverter 118
interprets the control signal and switches the internal switches in
accordance with the interpreted control signal.
[0274] Voltage sense 122 and current sense 124 produce signals that
are provided to controller 120 as feedback signals to control the
drive signal provided to acoustic transducer 112. Controller 120
performs operations and calculations on the signals provided by
voltage sense 122 and current sense 124, for example, to obtain a
power measure, P=V*I, or to obtain a phase angle, .theta.=arctan
(X/R).
[0275] Controller 120 is provisioned with a control scheme that
accepts process settings, such as power output, range of frequency
operation, or other user selectable parameters, and provides
control signals to converter 116 and inverter 118 based on the
process settings and the feedback values. For example, as described
above, controller 120 can sequence through a number of frequencies
in a range of frequencies that are provided to inverter 118 to scan
through the frequency range and determine the characteristics of
transducer 112 or transducer 112 in combination with acoustic
chamber 114, which may be under load. The results of the frequency
scan in terms of voltage and current obtained from the voltage
sense 122 and current sense 124, respectively, are used to identify
characteristics of the impedance curves for the components or the
system, such as is illustrated in FIG. 47. The frequency scan can
be implemented to occur at set up, and/or at intervals during
operation of the illustrated system. During steady-state operation,
the frequency scanned can be conducted to identify desired
setpoints for operation, such as power or frequency, based on user
settings and feedback values. The control scheme implemented by
controller 120 is thus dynamic, and responds to changing conditions
in the system, such as may be encountered with frequency drift,
temperature change, load changes and any other system parameter
changes. The dynamic nature of the control scheme permits the
controller to respond to or compensate for nonlinearities, such as
may be encountered as components age or lose tolerance.
Accordingly, the control scheme is adaptive and can accommodate
system changes.
[0276] Some examples of system operation include driving acoustic
transducer 112 to produce a multidimensional acoustic standing wave
in the acoustic chamber 114. A 3D acoustic wave is stimulated by
driving acoustic transducer 112, which may be implemented as a
piezoelectric crystal, sometimes referred to herein as a PZT, near
its anti-resonance frequency. Cavity resonances modulate the
impedance profile of the PZT as well as affect its resonance modes.
Under the influence of the 3D acoustic field, suspended particles
in the liquid medium in the acoustic cavity 114 are forced into
agglomerated sheets and then into strings of `beads` of
agglomerated material. Once particle concentrations reach a
critical size, gravitational forces take over and the agglomerated
material drops out of the acoustic field and to the bottom of the
chamber. The changing concentrations of agglomerated material as
well as the dropping out of that material affects the cavity's
resonances which in turn change the acoustic loading on the PZT and
its corresponding electrical impedance. The changing dynamics of
the collected material detunes the cavity and PZT reducing the
effects of the 3D wave in clarifying the medium. Additionally,
changes in the medium and cavity temperature also detune the cavity
so that clarification is reduced. To track the resonance changes
occurring in the cavity, a control technique is used to follow
changes in the PZT's electrical characteristics.
[0277] A strong 3D acoustic field can be generated by driving the
PZT at a frequency where its input impedance is a complex (real and
imaginary) quantity. However, cavity dynamics can cause that
impedance value to change significantly in an erratic manner. The
changes in impedance are due, at least in part, to changes in the
load applied to the acoustic transducer 112 and/or acoustic chamber
114. As particles or secondary fluid is separated from a primary or
host fluid, the loading on acoustic transducer 112 and/or acoustic
chamber 114 changes, which in turn can influence the impedance of
the acoustic transducer 112 and/or acoustic chamber 114.
[0278] To correct for detuning, controller 120 calculates the PZT
impedance from the voltage and current sensed at the PZT using
voltage sense 122 and current sense 124 and determines which way to
change the operating frequency to compensate for the detuning.
Since frequency changes affect power delivered to the chamber, the
controller also determines how to adjust the output voltage of
(dynamic) buck converter 116 to maintain the desired amount of
power output from RF DC-AC inverter 118 and into the acoustic
transducer 112 and/or acoustic chamber 114.
[0279] Buck converter 116 is an electronically adjustable DC-DC
power supply and is the power source for inverter 118. RF DC-AC
inverter 118 converts the DC voltage out of converter 116 back to a
high-frequency, AC signal to drive the PZT. The dynamics in the
chamber occur at rates corresponding to frequencies in the low
audio band. Consequently, the converter 116, controller 120, and
DC-AC inverter 118 are capable of working at rates faster than the
low audio band to permit controller 120 to track chamber dynamics
and keep the system in tune.
[0280] Controller 120 can simultaneously change the frequency of
DC-AC inverter 118 and the DC voltage coming out of buck converter
116 to track cavity dynamics in real time. The control bandwidth of
the system is a function of the RF bandwidth of inverter 118 and
the cutoff frequency of the filtering system of buck converter
116.
[0281] Controller 120 can be implemented as a DSP (digital signal
processor) control, or as an FPGA (field programmable gate array)
control, as examples. Controller 120 may be implemented with two
channels, to permit parallel processing, for example to analyze
real and/or reactive impedance, voltage, current and power.
[0282] The acoustic dynamics of the cavity affects the electrical
characteristics of the PZT which affects the voltage and current
drawn the PZT. The sensed PZT voltage and current is processed by
the controller to compute the real-time power consumed by the PZT
as well as its instantaneous impedance (affected by acoustic
dynamics). Based on user set points the controller adjusts, in
real-time, the DC power supplied to inverter 118 and the frequency
at which inverter 118 is operated to track cavity dynamics and
maintain user set points. An LCL network is used to match the
output impedance of inverter t 118 to increase power transfer
efficiency.
[0283] Controller 120 samples sensor signals fast enough to detect
changes in cavity performance (via changes in PZT impedance) in
real time. For example, controller 120 may sample the feedback
values from the voltage sense 122 and current sense 124 at one
hundred million samples per second. Signal processing techniques
are implemented to permit a wide dynamic range for system operation
to accommodate wide variations in cavity dynamics and applications.
Converter 116 can be configured to have a fast response time to
follow the signal commands coming from controller 120. Inverter 118
can drive a wide range of loads that demand varying amounts of real
and reactive power that change over time. The electronics package
used to implement the system illustrated in FIG. 49 may be
configured to meet or exceed UL and CE requirements for
electromagnetic interference (EMI).
[0284] Referring to FIG. 50, controller 120 may be implemented with
very-high-speed parallel digital-signal-processing loops using RTL
(Register Transfer Level) which is realized in actual digital
electronic circuits inside a field-programmable-gate-array (FPGA).
Two high speed digital proportional integral (PI) loops adjust the
frequency and amplitude control signals generated by controller 120
to track power and reactance. A linear amplifier 132 is used to
amplify the output signal from controller 130 (which can be
implemented as controller 120) in preparation for driving the PZT.
The voltage and current sense is used to sense the voltage and
current at the transducer. A calculation is performed in series by
controller 130 to generate control signals provided to linear
amplifier 132. The FPGA can be operated with a clocking signal of
100 MHz. The clocking speed contributes to obtaining fast enough
sampling to monitor and adapt to conditions of the PZT in
real-time. In addition, the structure of the FPGA permits each gate
component to have a propagation delay commensurate with the
clocking speed. The propagation delay for each gate component can
be less than one cycle, or 10 ns with a clocking speed of 100
MHz.
[0285] Referring to FIG. 51, a diagram illustrates parallel and
sequential operations for calculating control signals. Controller
130 may be configured to calculate the following parameters.
VRMS=sqrt(V12+V22+ . . . +Vn2)
IRMS=sqrt(I12+I22+ . . . +In2)
Real Power (P=V-Inst..times.I-Inst Integrated over N Cycles)
Apparent Power (S=VRMS.times.IRMS)
[0286] Controller 130 may be configured to calculate reactive power
and bipolar phase angle by decomposing sensed voltage and current
into in-phase and quadrature-phase components. FIG. 52 illustrates
the in-phase and quadrature-phase demodulation of the voltage and
current to obtain a four-quadrant phase, reactive power and
reactance. The calculations for reactive power and phase angle can
be simplified using the in-phase and quadrature-phase
components.
VPhase Angle=Arctan(QV/IV)
IPhase Angle=Arctan(QI/II)
Phase Angle=VPhase-Iphase
Reactive Power=(Q=Apparent Power.times.Sine(Phase Angle)
[0287] Controller 130 may implement a control scheme that begins
with a frequency sweep to determine system performance parameters
at discrete frequencies within the frequency sweep range. The
control scheme may accept inputs of a start frequency, a frequency
step size and number of steps, which defines the frequency sweep
range. Controller 130 provides control signals to linear amplifier
132 to modulate the frequency applied to the PZT, and the voltage
and current of the PZT are measured using the voltage sense and the
current sense. The control scheme of controller 130 may repeat the
frequency sweep a number of times to determine the system
characteristics, for example, reactance, with a relatively high
level of assurance.
[0288] A number of reactance minimums can be identified as a result
of analysis of the data obtained in the frequency sweep. The
control technique can be provided with an input that specifies a
certain frequency range where a desired reactance minimum is
located, as well as being provided with a resistance slope (+/-)
that can be used for tracking a desired point of operation based on
resistance tracking that corresponds to a desired minimum
reactance. The resistance slope may be constant near the minimum
reactance, which may provide a useful parameter for use with a
tracking technique. By tracking resistance at a desired frequency,
a robust control can be attained for operating at a minimum
reactance point.
[0289] The control technique may take the derivative of the
resistance/reactance values to locate zero slope derivatives, which
are indicative of maximums and minimums. A
proportional-integral-differential (PID) controller loop may be
used to track the resistance to obtain a frequency setpoint at
which a desired minimum reactance occurs. In some implementations,
the control may be a proportional-integral (PI) loop. With the FPGA
operating at 100 MHz, adjustments or frequency corrections can be
made every 10 ns to compensate for changes in the tracked
resistance. This type of control can be very accurate and
implemented in real-time to manage control of the PZT in the
presence of a number of changing variables, including reactance,
load and temperature, for examples. The control technique can be
provided with an error limit for the frequency of the reactance
minimum or frequency setpoint, to permit the control to adjust the
output to linear amplifier 132 to maintain the frequency within the
error limit.
[0290] A fluid mixture, such as a mixture of fluid and
particulates, may be flowed through the acoustic chamber to be
separated. The fluid mixture flow may be provided via a fluid pump,
which may impose perturbations on the fluid, as well as the PZT and
chamber. The perturbations can create a significant fluctuation in
sensed voltage and current amplitudes, indicating that the
effective impedance of the chamber fluctuates with pump
perturbations. However, owing to the speed of the control
technique, the fluctuations can be almost completely canceled out
by the control method. For example, the perturbations can be
identified in the feedback data from the PZT and can be compensated
for in the control output from the controller. The feedback data,
for example the sensed voltage and current, may be used to track
the overall acoustic chamber pressure. As the characteristics of
the transducer and/or acoustic chamber change over time and with
various environmental parameters, such as pressure or temperature,
the changes can be sensed and the control technique can compensate
for the changes to continue to operate the transducer and acoustic
chamber at a desired setpoint. Thus, a desired setpoint for
operation can be maintained with very high accuracy and precision,
which can lead to optimized efficiency for operation of the
system.
[0291] The FPGA may be implemented as a standalone module and maybe
coupled with a class-D driver. Each module may be provided with a
hardcoded address so that it can be identified when connected to a
system. The module can be configured to be hot-swappable, so that
continuous operation of the system is permitted. The module may be
calibrated to a particular system and a transducer, or may be
configured to perform a calibration at particular points, such as
upon initialization. The module may include long-term memory, such
as an EEPROM, to permit storage of time in operation, health, error
logs and other information associated with operation of the module.
The module is configured to accept updates, so that new control
techniques can be implemented with the same equipment, for
example.
[0292] Referring now to FIG. 53, a method for controlling an
acoustic transducer is illustrated with a flowchart. The
illustrated method may be implemented on or with controller 120 or
130. The method uses a low voltage output during a frequency sweep
that drives the acoustic transducer over a range of frequencies.
Feedback from the acoustic transducer is used to determine the
resistance and reactance response of the transducer over the range
of frequencies at the low voltage output. Once the data for the
transducer responses collected, the frequency at which the minimum
reactance occurs below anti-resonance is identified. The resistance
at the minimum reactance is identified and the frequency setpoint
is set to establish operation at this resistance. A real power
setpoint for the frequency setpoint is established, which may be
based on user input. The establishment of the operating setpoints,
the method causes the power control signals to be output for the
linear amplifier or the converter-inverter power supply.
[0293] The method performs a loop in which voltage and current are
measured at the acoustic transducer, real power and resistance are
calculated and provided to a proportional-integral (PI) controller.
The output of the PI controller is used to adjust the amplitude and
frequency of the signal supplied to the transducer. The loop is
repeated, resulting in the amplitude of the power provided to the
transducer being controlled and tracked, and the frequency of the
power provided to the transducer being controlled and tracked. The
loop permits the controller to dynamically adjust to changes in the
system, including changes related to loading of the transducer
and/or the transducer/acoustic cavity combination or changes
related to temperature, as examples.
[0294] FIG. 54 illustrates an example method for processing
information to implement a transducer control. The method uses
desired operating points for real power and a minimum reactance,
which may be obtained from user input. Data is received from the
transducer, including drive voltage and drive current. The data
received from the transducer is conditioned to improve the quality
of the information and calculations derived there from. For
example, the data representing drive voltage and drive current is
deskewed, provided with an offset and scaled for use with
subsequent calculations. The condition data is used to calculate
real power, resistance and reactance of the transducer. These
parameters are compared to operating points received in the method,
and a PI controller is used to generate a signal that can adjust
the real power and frequency of the drive signal provided to the
transducer. Note that the conditioned feedback parameters can be
used to generate an error signal in conjunction with the desired
operating point information, with the error signal being provided
to an amplifier that adjusts the signal provided to the RF driver
power supply, whether linear amplifier or converter-inverter
combination.
[0295] An LCL matching filter is discussed above, such as with
respect to FIG. 43. According to another example, and LC matching
filter is provided between the converter output and the PZT. The LC
matching filter provides impedance scaling to obtain inappropriate
load for the inverter drive. The LC combination can be considered a
network, which is tuned to provide desired power transfer, such as
optimized power transfer, through the transducer and into the
resonant cavity. Considerations for implementing the LCL filter or
the LC filter include the combined response of the transducer and
the resonant cavity. According to one example, a filter is
implemented to permit desired power transfer, such as optimized
power transfer, when the acoustic transducer is operated in a
multi-dimensional mode, or in a multi-mode, for example, with
multiple overlaid vibrational modes that produce one or more
primary or dominant vibrational modes. As discussed above, a
desired mode of operation is at a frequency that corresponds to a
minimum reactance point of the response of the transducer, and/or
the response of the transducer/resonant cavity combination.
[0296] For a fixed resonant frequency, the LC network can deliver
different amounts of power based on the system resonances
residences in accordance with the combination of inductor and
capacitor values that are used to form the LC network. FIG. 55
illustrates a response curve for an LC network with an inductor
value of 1.596 uH and a capacitor value of 3.0 nF. The resonant
frequency of the LC network is 2.3 MHz, the resistive impedance (A)
is shown in blue, the reactive impedance (B) is shown in red, the
input real power (C) is shown in yellow and the acoustic real power
(D) into the cavity is shown in purple. With regard to the power
delivered into the system, increasing the capacitor value with the
same resonance increases power into the system. In general,
changing the values of the inductor and/or capacitor can influence
the resonant frequency of the LC network. Changing the resonant
frequency of the LC network changes the frequency at which optimum
power transfer occurs, and can impact the efficiency of the
transfer. For example, the frequency for optimum power transfer
relative to minimum reactance points (B) of the input impedance of
the system is influenced by the resonance frequency of the LC
network.
[0297] The plot in FIG. 55 shows the points on the input real power
(C) and the acoustic real power (D) at a reactance minimum. The
input real power and acoustic real power are fairly well matched,
indicating efficient transfer of power. If the value of the
inductor is changed to 0.8 uH and the value of the capacitor is
changed to 6.0 nF, the same reactance minimum produces a greater
power transfer with somewhat less efficiency. The power transfer
becomes less efficient when the input real power (C) is
significantly different (greater) than the acoustic real power (D).
In some instances, depending on the inductor and capacitor values,
power transfer can be highly efficient, however, the frequency
operating point may not be at a minimum reactance point (B).
Accordingly, trade of choices can be made between operating the
transducer to obtain highly efficient separation in the acoustic
chamber, implying a minimum reactance point, and obtaining
efficient power transfer into the chamber. For a given material
being separated and a given transducer, an LC network can be
selected with a resonance frequency to obtain efficient power
transfer into the acoustic cavity, improving overall system
efficiency.
[0298] FIG. 57 is a graph illustrating a resistance curve versus
frequency, with a number of different modes identified. Higher
order modes are obtained along the graph line locations where
resistance is above a minimum. FIG. 58 is a graph illustrating
reactance versus frequency, with a number of different modes
identified. In FIGS. 57-58, solid circles are pure modes and hollow
circles are where the mode first occurs and disappears. Higher
order modes are illustrated as available along a number of
locations on the graph line. FIGS. 59, 60, 61 and 62 are graphs
illustrating turbidity and reactance for a given example of
acoustophoresis. The graphs in FIGS. 59, 60, 61 and 62 show
turbidity and reactance average values over a range of frequencies,
where the sample frequency ran for twenty minutes. The acoustic
transducer in FIG. 62 was operated at 1 MHz.
[0299] The acoustic radiation force exerted on the particles in the
fluid can be calculated and/or modeled. For example, a COMSOL model
was created and used to predict linear acoustic standing wave
fields. The model implemented models for piezo-electricity,
elasticity and acoustics. The model was used to predict acoustic
radiation forces on particles that are small compared to
wavelength, which includes using the Gorkov equation, and larger
particles, which includes using the Yurii-Zhenia equations. In some
instances, it may be helpful to normalized the results, for
example, by normalizing with respect to power. The effect on the
particles of the acoustic radiation forces can be studied, and in
particular used for determining transducer configurations, and for
controlling the transducer and/or transducer/cavity
combination.
[0300] FIG. 63 is a graph illustrating piezoelectric displacement.
FIG. 64 is a graph illustrating power and impedance amplitude. FIG.
65 is a graph illustrating absolute impedance amplitude. A number
of modes are identified along the line of the graph. Higher order
modes can be attained near peak absolute impedance amplitudes. FIG.
66 is a graph illustrating impedance phase. Again, a number of
modes are illustrated along the line of the graph. FIG. 67 is a
graph illustrating displacement normalized by power. Again, a
higher order multimode operation can be attained at higher
displacement values. FIG. 68 is a graph illustrating average
pressure normalized by power. FIG. 69 shows two graphs illustrating
axial and lateral radiation force.
[0301] FIGS. 70A, 70B, 70C, 70D, and 70E collectively show[[s]]
five graphs illustrating displacement for various modes. FIGS. 71,
72 are graphs illustrating relationships between dimensions of
piezoelectric material and number of modes. FIG. 73 is a graph
illustrating turbidity, resistance, reactance and real power versus
time for a planar wave. FIG. 74 is a graph illustrating turbidity,
resistance, reactance and real power versus time for multimode
operation at a minimum reactance point. FIG. 75 is a graph
illustrating resistance, reactance and real power versus frequency.
FIG. 76 is a graph illustrating turbidity, resistance, reactance
and real power versus time for multimode operation at a minimum
reactance point that is zero or positive.
[0302] The performance illustrated in FIG. 73 is fairly poor, with
a minimum turbidity of approximately 1000, and typical turbidity
performance being much higher. The performance illustrated in FIG.
73 is illustrated in FIG. 75 and zero phase. The acoustic
transducer in this case is producing a planar mode acoustic
standing wave, which can be envisioned as piston operation.
[0303] The turbidity performance in FIG. 74 is a significant
increase over that illustrated in FIG. 73, with minimum turbidity
being often less than 500. The acoustic transducer in this case is
operated at a reactance minimum, illustrated in the graph of FIG.
75 at point X-1. Point X-1 represents multimode operation, which
can produce axial and lateral forces on particles in the fluid
through which the acoustic standing wave passes. These acoustic
forces are illustrated in an example in FIG. 69. Thus, providing a
control technique for operating the acoustic transducer at a
reactance minimum can attain desired performance. The desired
performance can be attained even at zero phase when operating in
multimode, as illustrated with point X-4 in FIG. 75. Point X-4 is a
reactance minimum with zero phase, which can achieve desired
performance due to multimode operation, unlike the zero phase
planar wave operation. FIG. 76 is a graph illustrating turbidity,
resistance, reactance and real power versus time for multimode
operation at a minimum reactance point that is zero or
positive;
[0304] FIGS. 77, 78, 79 and 80 are flowcharts illustrating hardware
and software configurations. FIG. 80 shows graphs illustrating a
frequency sweep response. FIGS. 81A and 81B show[[s]] graphs
illustrating a frequency sweep response. The sweep settings range
from 2.22 MHz to 2.26 MHz, with steps of 2 kHz. Each frequency in
the sweep was held for 5 minutes, with a constant voltage of 65 V.
The measured AC values seemed to correlate with the DC readings.
Several studies were run on MM CHO and Yeast, both show max
efficiency near max current. FIG. 82 is a graph illustrating
regions of operation.
[0305] FIG. 83 is a graph illustrating a control technique that
works as follows. When the transducer is powered on, the voltage
ramps up to the desired voltage, and a frequency scan commences.
The scan parameters are: Start, where the bit word value on the
coarse DAC is set to 20 units below the current value .about.-15
kHz; End, where the bit word value on the coarse DAC is set to 20
units above the current value .about.+15 kHz; Increment, which is a
1 bit word value on the coarse DAC .about.1 kHz; Step Duration=250
ms; and Total Duration=10 seconds. The current and frequency data
are used to fit a Gaussian Peak. The frequency center of the peak
is the resonance frequency. An Upper Cutoff Limit is set to 95% of
the peak. An average of all current data from the scan is the Lower
Cutoff Limit. The data shown in the plot in FIG. 83 is recorded at
1 Hz, the actual data that is used to fit the Gaussian Peak is
captured at 4 Hz.
[0306] The control technique includes, after the scan, the system
sets the frequency to the resonance frequency and waits 10 seconds
before monitoring. The current data is continually monitored at 5
Hz and a running average of 20 points is calculated. If the running
average stays above the Upper Cutoff limit, the system will
continue to monitor. If the running average drops below the Upper
Cutoff limit, the frequency is increased by 1000 Hz. If the running
average drops below the Lower Cutoff limit, a scan is commenced.
Frequency can be changed at any point. The system will change the
frequency, wait 10 seconds, and continue monitoring at the new
frequency. When the voltage is changed a new scan will be
initiated. Tracking range is set from 2.2 MHz to 2.26 MHz, and If
tracking algorithm moves the frequency out of this range, it resets
the frequency to 2.23 MHz.
[0307] FIGS. 84, 85, 86, and 87 are graphs providing plots of
various parameters versus frequency. FIG. 84 is a graph with a
left-hand scale measuring a ratio of lateral-to-axial forces for
various frequencies (solid line), and a right-hand scale measuring
reactance (dashed line). Identified on the ratio graph lines are
locations and ranges for various modes of multimode operation. A
range of a given mode for multimode operation (A, B, C, or D) is
identified as existing between open circles, with a primary or
dominant frequency for that mode being identified as a solid
circle.
[0308] FIG. 85 is a graph with a left-hand scale measuring average
pressure per power for various frequencies (solid line), and a
right-hand scale measuring reactance (dashed line). Identified on
the pressure graph line are locations and ranges for various modes
of multimode operation (A, B, C, or D). A given mode for multimode
operation is identified as a circle that represents a primary or
dominant frequency for that mode.
[0309] FIG. 86 is a graph showing reactance versus frequency, with
a number of modes for multimode operation being identified as
locations and ranges on the graph line. A range of a given mode for
multimode operation is identified as existing between open circles,
with a primary or dominant frequency for that mode being identified
as a solid circle.
[0310] FIG. 87 is a graph showing resistance versus frequency, with
a number of modes for multimode operation being identified as
locations and ranges on the graph line. A range of a given mode for
multimode operation is identified as existing between open circles,
with a primary or dominant frequency for that mode being identified
as a solid circle.
[0311] As can be seen with FIGS. 84-87, multimode operation is
strong near minimum reactance. FIG. 84 shows a force ratio plot
with a ratio of >0.1 at minimum reactance points. Along with
these simulation results, experimental data showing minimum
reactance gives the best performance. Note that the tests
illustrated in FIGS. 84-87 reflect steady state tests.
[0312] The acoustophoretic devices of the present disclosure, can
be used in a filter "train," in which multiple different filtration
steps are used to clarify or purify an initial fluid/particle
mixture to obtain the desired product and manage different
materials from each filtration step. Each filtration step can be
optimized to remove a particular material, improving the overall
efficiency of the clarification process. An individual
acoustophoretic device can operate as one or multiple filtration
steps. For example, each individual ultrasonic transducer within a
particular acoustophoretic device can be operated to trap materials
within a given particle range. In particular, the acoustophoretic
device can be used to remove large quantities of material, reducing
the burden on subsequent downstream filtration steps/stages.
Additional filtration steps/stages can be placed upstream or
downstream of the acoustophoretic device. Multiple acoustophoretic
devices can be used as well. Desirable biomolecules or cells can be
recovered/separated after such filtration/purification.
[0313] The outlets of the acoustophoretic devices of the present
disclosure (e.g. clarified fluid and concentrated cells) can be
fluidly connected to any other filtration step or filtration stage.
Such filtration steps can include various methods such as depth
filtration, sterile filtration, size exclusion filtration, or
tangential filtration. Depth filtration uses physical porous
filtration mediums that can retain material through the entire
depth of the filter. In sterile filtration, membrane filters with
extremely small pore sizes are used to remove microorganisms and
viruses, generally without heat or irradiation or exposure to
chemicals. Size exclusion filtration separates materials by size
and/or molecular weight using physical filters with pores of given
size. In tangential filtration, the majority of fluid flow is
across the surface of the filter, rather than into the filter.
[0314] Chromatography can also be used, including cationic
chromatography columns, anionic chromatography columns, affinity
chromatography columns, mixed bed chromatography columns. Other
hydrophilic/hydrophobic processes can also be used for filtration
purposes.
[0315] Desirably, flow rates through the devices of the present
disclosure can be a minimum of 4.65 mL/min per cm2 of
cross-sectional area of the acoustic chamber. Even more desirably,
the flow rate can be as high as 25 mL/min/cm2, and can range as
high as 40 mL/min/cm2 to 270 mL/min/cm2, or even higher. This is
true for batch reactors, fed-batch bioreactors and perfusion
bioreactors, with which the acoustophoretic devices and transducers
discuss herein may be used. For example, the acoustophoretic
devices may be interposed between a bioreactor and a downstream
filtration device, such as those discussed above. The
acoustophoretic devices may be configured to be downstream of a
filtration device coupled to a bioreactor, and may be upstream of
other filtration devices. In addition, the acoustophoretic devices
and/or other filtration devices can be configured to have a
feedback to the bioreactor.
[0316] The methods, systems, and devices discussed above are
examples. Various configurations may omit, substitute, or add
various procedures or components as appropriate. For instance, in
alternative configurations, the methods may be performed in an
order different from that described, and that various steps may be
added, omitted, or combined. Also, features described with respect
to certain configurations may be combined in various other
configurations. Different aspects and elements of the
configurations may be combined in a similar manner. Also,
technology evolves and, thus, many of the elements are examples and
do not limit the scope of the disclosure or claims.
[0317] Specific details are given in the description to provide a
thorough understanding of example configurations (including
implementations). However, configurations may be practiced without
these specific details. For example, well-known processes,
structures, and techniques have been shown without unnecessary
detail to avoid obscuring the configurations. This description
provides example configurations only, and does not limit the scope,
applicability, or configurations of the claims. Rather, the
preceding description of the configurations provides a description
for implementing described techniques. Various changes may be made
in the function and arrangement of elements without departing from
the spirit or scope of the disclosure.
[0318] Also, configurations may be described as a process that is
depicted as a flow diagram or block diagram. Although each may
describe the operations as a sequential process, many of the
operations can be performed in parallel or concurrently. In
addition, the order of the operations may be rearranged. A process
may have additional stages or functions not included in the
figure.
[0319] Having described several example configurations, various
modifications, alternative constructions, and equivalents may be
used without departing from the scope of the disclosure. For
example, the above elements may be components of a larger system,
wherein other structures or processes may take precedence over or
otherwise modify the application of the invention. Also, a number
of operations may be undertaken before, during, or after the above
elements are considered. Accordingly, the above description does
not bound the scope of the claims.
[0320] A statement that a value exceeds (or is more than) a first
threshold value is equivalent to a statement that the value meets
or exceeds a second threshold value that is slightly greater than
the first threshold value, e.g., the second threshold value being
one value higher than the first threshold value in the resolution
of a relevant system. A statement that a value is less than (or is
within) a first threshold value is equivalent to a statement that
the value is less than or equal to a second threshold value that is
slightly lower than the first threshold value, e.g., the second
threshold value being one value lower than the first threshold
value in the resolution of the relevant system.
* * * * *