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DESCRIPTION JP2014042355

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DESCRIPTION JP2014042355
Abstract: An ultrasonic matching layer and a transducer are provided. In one aspect, a matching
layer is provided for an ultrasound transducer stack having a matching layer comprising a matrix
material loaded with a plurality of micron-sized and nano-sized particles. In another aspect, the
matrix material is loaded with a plurality of heavy and light particles. In another aspect, an
ultrasound transducer stack comprises a piezoelectric layer and at least one matching layer. In
one aspect, the matching layer comprises a composite material comprising a matrix material
loaded with a plurality of micron-sized and nano-sized particles. In a further aspect, the
composite material also comprises a matrix material loaded with a plurality of heavy and light
particles. In further embodiments, the matching layer can also include cyanoacrylate. [Selected
figure] Figure 1
Ultrasonic matching layer and transducer
[0001]
Small animal imaging is an important area of research in many areas, including preclinical drug
development, developmental biology, cardiac research, and molecular biology. Several animal
models are widely used in these areas, the most common being mice and rats. High frequency
ultrasound at about 20 megahertz (MHz) to over 60 MHz is widely used for imaging in mouse
models. However, since rat has epidermal tissue, skin tissue and subcutaneous tissue which show
high attenuation and echo generation, the rat model has difficulty in imaging at high frequency
as compared with the mouse model.
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[0002]
In one aspect, a matching layer for an ultrasound transducer stack having a plurality of layers is
provided. The matching layer can comprise a composite material comprising a matrix material
loaded with a plurality of micron-sized and nano-sized particles. In another aspect, the composite
material also includes a matrix material loaded with a plurality of heavy and light particles. In
further embodiments, the matching layer can also include cyanoacrylate.
[0003]
Also provided is an ultrasound transducer stack comprising a plurality of layers, each layer
having a top surface and an opposite bottom surface, the plurality of layers including a
piezoelectric layer and at least one matching layer. The matching layer can be located in the
stack to cover the top surface of the piezoelectric layer. An exemplary stack comprises a
matching layer comprising a composite material loaded with a plurality of nano-sized and
micron-sized particles, a matching layer comprising a plurality of heavy and light particles, and a
matching layer comprising cyanoacrylate it can.
[0004]
Other systems, methods, and aspects and advantages of the present invention are described with
reference to the drawings and detailed description.
[0005]
The accompanying drawings, which are incorporated in and form a part of the specification,
illustrate certain aspects of the present invention and, together with the description, serve to
explain the principles of the present invention without limitation.
Like reference characters used in the drawings indicate like parts throughout the several
drawings. The present invention provides, for example, the following. (Item 1) A matching layer
of an ultrasonic transducer including a plurality of stacked layers, wherein at least one layer of
the plurality of stacked layers includes the matching layer, and the matching layer is
cyanoacrylate Including the matching layer. (Item 2) The matching layer according to item 1,
wherein the matching layer is an approximately 1/4 wave length matching layer. 3. The
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matching layer of claim 2, wherein the acoustic impedance of the matching layer is between
about 2.0 Mega Rail and about 3.5 Mega Rail. 4. The matching layer of claim 2, wherein the
acoustic impedance of the matching layer is between about 2.5 megarail and about 2.8 megarail.
5. The matching layer of claim 1, wherein at least one of the plurality of stacked layers comprises
a lens layer, the lens layer covering the matching layer and being bonded to the matching layer. .
6. The matching layer of claim 5, wherein the lens layer comprises TPX. 7. An ultrasonic
transducer stack comprising: a plurality of layers: a piezoelectric layer; at least one matching
layer comprising a first matching layer comprising cyanoacrylate; and a lens layer comprising
TPX A plurality of layers, each layer of the plurality of layers having a top surface and an
opposite bottom surface, the first matching layer being connected to the bottom surface of the
lens layer, under the bottom surface An ultrasonic transducer stack, wherein the piezoelectric
layer is below the bottom surface of the matching layer. 8. The ultrasonic transducer stack of
claim 7, wherein the first matching layer is an approximately 1⁄4 acoustic wave length matching
layer. 9. The ultrasonic transducer stack of claim 8, wherein the acoustic impedance of the first
matching layer is between about 2.0 Mega Rails (MR) and about 3.5 Mega Rails (MR). 10. The
ultrasonic transducer stack of claim 8, wherein the acoustic impedance of the first matching
layer is between about 2.5 Mega Rails (MR) and about 2.8 Mega Rails (MR). 11. The ultrasonic
transducer stack of claim 8, wherein the acoustic impedance of the lens layer is about 1.8
megarails (MR). 12. The ultrasonic transducer stack of claim 7, wherein the acoustic impedance
of the lens is substantially the same as the acoustic impedance of water. 13. The ultrasonic
transducer stack of claim 7, wherein the piezoelectric layer can generate ultrasonic waves at a
frequency of at least about 20 megahertz (MHz).
(Item 14) The piezoelectric layer is transmitted through the first matching layer, and then
transmitted through the lens layer, and is about 20 MHz, 25 MHz, 30 MHz, 35 MHz, 40 MHz, 45
MHz, 50 MHz, 55 MHz, 60 MHz. 14. An ultrasound transducer stack according to claim 13,
which is capable of producing ultrasound at or higher frequencies. 15. The ultrasonic transducer
stack of claim 7, further comprising a second matching layer positioned between the top surface
of the piezoelectric layer and the bottom surface of the first matching layer. 16. The ultrasonic
transducer stack of claim 15, wherein the top surface of the second matching layer is bonded to
the bottom surface of the first matching layer using an adhesive. 17. The ultrasonic transducer
stack of claim 16, wherein the adhesive forms an adhesive line layer between the first matching
layer and the second matching layer. 18. The ultrasonic transducer stack of claim 17, wherein
the adhesive line layer has a thickness in the height direction less than about 5 microns. 19. The
ultrasonic transducer stack of claim 17, wherein the adhesive line layer has a thickness in the
height direction of between about 1 micron and about 5 microns. 20. The ultrasonic transducer
stack of claim 17 wherein the adhesive line layer has a thickness in the height direction between
about 1 micron and about 3 microns. 21. The ultrasonic transducer stack of claim 17 wherein
the acoustic impedance of the adhesive line layer is substantially the same as the acoustic
impedance of the first matching layer. 22. The ultrasonic transducer stack of claim 16, wherein
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the adhesive is selected from the group consisting of epoxy or glue. 23. The ultrasonic transducer
stack of claim 22, wherein the adhesive is a low viscosity, room temperature cured epoxy. 24.
The ultrasonic transducer stack of claim 16, wherein the acoustic impedance of the second
matching layer is between about 3.5 megarail and about 6.0 megarail. 25. The ultrasonic
vibration of claim 15, further comprising a third matching layer, wherein the third matching
layer is located between the bottom of the second matching layer and the top of the piezoelectric
layer. Child stack. 26. The ultrasonic transducer of claim 25, wherein the acoustic impedance of
the third matching layer is between about 7.5 and about 12 megarails. 27. The ultrasonic
transducer of claim 25, wherein the acoustic impedance of the third matching layer is between
about 9.5 and about 10.5 mega rails.
28. The ultrasonic transducer of claim 25, further comprising a backing layer, wherein the top
surface of the backing layer is connected to the bottom surface of the piezoelectric layer and
under the bottom surface. 29. A process of producing an ultrasonic transducer stack comprising
a plurality of layers, each layer having a top surface and an opposite bottom surface, the process
comprising: providing a piezoelectric layer; Providing a lens layer comprising: adhering a first
matching layer comprising cyanoacrylate to a bottom surface of the lens layer; attaching the
adhered first matching layer and lens layer; Generating an ultrasonic transducer stack by
positioning at an overlying alignment. 30. Bonding the first matching layer to the bottom surface
of the lens layer, providing a release film, providing a plurality of spacers, and partially forming
the plurality of spacers. Positioning the top of the lens layer with substantially the entire bottom
surface of the lens layer with cyanoacrylate, and mounting the lens on the plurality of spacers in
spaced relation from the release film. The cyanoacrylate fills an internal volume defined between
the bottom surface of the lens layer and the release film to form the first matching layer. Process
described in. 31. The process of claim 30, wherein the release film is comprised of a low surface
energy metal film. 32. The process of claim 30, wherein the release film comprises aluminum foil.
33. The process of claim 30, wherein the release film is comprised of magnesium foil. (Item 34)
The step of adhering the first matching layer to the bottom surface of the lens applies a force to
the lens to compress the cyanoacrylate disposed between the bottom surface of the lens layer
and the release film. A process according to claim 30, further comprising the steps of: curing the
first matching layer comprising cyanoacrylate. 35. The method of claim 30, wherein adhering the
first matching layer to the bottom surface of the lens further comprises removing the release film
from the top surface on which the first matching layer is formed. Process described in 34. 36.
Affixing the first matching layer to the bottom surface of the lens, removing the plurality of
spacers, and removing the first matching layer until the first matching layer reaches a
predetermined thickness. 36. The process of claim 35, further comprising: polishing the formed
top surface of the layer.
37. The process of claim 30, wherein the spacer has a diameter between about 20 microns and
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about 30 microns. 38. The process of claim 30, wherein the spacer has a diameter of about 25
microns. 39. The process of claim 30, wherein the spacer has a diameter greater than a desired
predetermined thickness of the first matching layer. 40. The process of claim 37, 38 or 39,
wherein the spacer is a wire.
[0006]
FIG. 1 illustrates an exemplary transducer stack having multiple layers and is a schematic
diagram illustrating multiple matching layers. FIG. 2 is a schematic diagram showing a cross
section at the height dimension of an exemplary transducer stack. FIG. 3 is a block schematic
diagram of an exemplary transducer stack electrically connected. FIG. 4 is an enlarged schematic
view showing the layers of the exemplary transducer stack of FIG. 3 shown at an exemplary
scale. 5A-5C are block diagrams illustrating an exemplary method of manufacturing an
exemplary transducer stack. 5A-5C are block diagrams illustrating an exemplary method of
manufacturing an exemplary transducer stack. 5A-5C are block diagrams illustrating an
exemplary method of manufacturing an exemplary transducer stack.
[0007]
The present invention may be understood more readily by reference to the following detailed
description, examples, drawings, and claims, and the foregoing and following description.
However, unless specifically indicated otherwise before the present devices, systems, and / or
methods are disclosed and described, the present invention is not limited to the particular
devices, systems, and / or methods disclosed, and of course However, it should be understood
that it may change accordingly. It is also to be understood that the terminology used herein is for
the purpose of describing particular aspects only and is not intended to be limiting.
[0008]
The following description of the invention is provided as an enabling teaching of the invention in
the best known embodiment. To this end, those skilled in the relevant art will recognize and
understand that even with many modifications to the various aspects of the invention described
herein, the beneficial results of the invention can be obtained. will do. It will also be apparent that
some of the desirable benefits of the present invention can be obtained by selecting some of the
features of the present invention without utilizing other features. Accordingly, those skilled in the
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art will recognize that many modifications and adaptations to the present invention are possible
and, in some circumstances, even desirable, which are also part of the present invention. Thus,
the following description is provided as illustrative of the principles of the present invention, but
not in limitation thereof.
[0009]
As used herein, the singular forms include plural referents unless the context clearly indicates
otherwise. Thus, for example, the designation "layer" includes the aspect of having more than one
such layer, unless the context clearly indicates otherwise.
[0010]
Ranges are expressed herein as from "about" one particular value, and / or to "about" another
particular value. When such a range is expressed, another aspect includes from the one
particular value and / or to the other particular value. Similarly, when values are expressed as
approximations, it is understood that by using the antecedent "about," the specific values form
another aspect. Furthermore, each end point of the range is valid in connection with the other
end point and independently of the other end point.
[0011]
As used herein, "optional" or "optionally" means that the event or situation described below may
or may not occur, and the description is the event or It is meant to include when and when
conditions do occur.
[0012]
"Object" means an individual.
The term subject includes not only small animals or experimental animals but also primates,
including humans. Experimental animals include, but are not limited to, rodents such as mice or
rats. The term experimental animal is also used interchangeably with animal, including small
animals, small laboratory animals, or subjects, including mice, rats, cats, dogs, fish, rabbits,
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guinea pigs, rodents and the like. The term experimental animal does not indicate a particular
age or gender. Thus, adult and newborn animals, as well as fetuses (including embryos), whether
male or female, are included.
[0013]
The present invention may be understood more readily by reference to the following detailed
description of the preferred embodiments of the invention and the Examples included therein,
the Figures and the Description above and below.
[0014]
In one embodiment, the present invention is directed to a matching layer for an ultrasound
transducer stack having a plurality of layers.
The ultrasound transducer, or transducer stack, used for imaging utilizes an acoustic matching
layer located between the piezoelectric layer of the transducer and the lens or face layer. The
piezoelectric layer typically has high acoustic impedance (Z). The acoustic impedance of the
object being imaged is typically much lower. When the piezoelectric layer is pressed directly
against the object, considerable acoustic energy is lost due to the impedance mismatch between
the piezoelectric layer and the object. In ultrasound imaging techniques, a matching layer of
acoustic impedance between the piezoelectric layer and the lens layer or face layer is introduced
to the transducer stack to provide a transition from the higher impedance piezoelectric layer to
the lower impedance target.
[0015]
Thus, the matching layer provided herein can be used in an ultrasound transducer stack to
achieve an impedance transition from the piezoelectric layer to the lens layer or face layer.
Exemplary matching layers can have various acoustical impedances. One exemplary matching
layer can have an acoustic impedance of between about 7.0 MegaRayles and about 14.0 Mega
Rails. Other exemplary matching layers can have an acoustic impedance between about 3.0
megarails and about 7.0 megarails. Still other example matching layers can have an acoustic
impedance of between about 2.5 megarails and about 2.8 megarails. One skilled in the art will
appreciate that each exemplary matching layer may be a quarter wave matching layer.
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[0016]
Ultrasonic transducer stacks can be used to generate, oscillate and receive high frequency (more
than 20 megahertz) ultrasound. An exemplary ultrasound transducer stack comprises at least one
disclosed matching layer.
[0017]
A schematic of such an exemplary transducer stack is shown in FIG. FIG. 1 shows a transducer
stack 100 having a lithium niobate piezoelectric layer 102. The bottom surface of the
piezoelectric layer covers the top surface of the backing layer 104. Above the top surface of the
piezoelectric layer are the electrode layer 106, the three exemplary matching layers (108, 110
and 112), the epoxy adhesive layer 114, and the lens layer 116.
[0018]
In this embodiment, matching layer 108 is a higher impedance matching layer that can have an
acoustic impedance of between about 7.0 MegaRail and about 14.0 MegaRail. In other
embodiments, matching layer 108 can include nano-sized and micron-sized particles, as
described below.
[0019]
On top of the matching layer 108 is a matching layer 110 that has a lower impedance than the
matching layer 108. Matching layer 110 can have an acoustic impedance between about 3.0
megarails and about 7.0 megarails. In other embodiments, matching layer 110 can include light
and heavy particles, as described below.
[0020]
Matching layer 112 has a lower impedance than matching layer 110. Matching layer 112 has an
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acoustic impedance of between about 2.5 megarails and about 2.8 megarails. The matching layer
112 can include cyanoacrylate as described below. Matching layer 112 can be bonded to
underlying matching layer 110 using epoxy layer 114.
[0021]
The face layer of the exemplary transducer stack 100 includes a lens layer 116. The lens layer
can include TPX as described below. The lens layer 116 can be adhered directly to the matching
layer 112. Thus, in this example transducer stack 100, the matching layers (108, 110, and 112)
achieve a transition of impedance from the piezoelectric layer 102 to the lens layer 116.
[0022]
The transducer stacks exemplified herein can be used to image the subject or its anatomic site
using high frequency ultrasound. The generated image can have a high resolution. In one aspect,
the ultrasound transducer stack comprises a plurality of layers, each layer having a top surface
and an opposite bottom surface. In another aspect, the plurality of layers comprises a
piezoelectric layer and at least one matching layer. When disposed in the transducer stack, the
bottom surface of the given matching layer covers the top surface of the piezoelectric layer.
[0023]
The matching layer can comprise a composite material. In one aspect, the composite material can
include a matrix material loaded with a plurality of micron-sized and nano-sized particles. In
another aspect, the composite material can also include a matrix material loaded with a plurality
of first heavy particles and a plurality of second light particles. In further embodiments, the
matching layer can also include cyanoacrylate (CA).
[0024]
Acquisition of ultrasound data using an exemplary transducer stack includes the generation of
ultrasound, the emission of ultrasound to a subject, and the reception of ultrasound reflected
from the subject. Ultrasound data can be acquired using ultrasound of a wide range of
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frequencies. For example, ultrasound at a clinical frequency (less than 20 MHz) or ultrasound at
a high frequency (20 MHz or more) can be used. One skilled in the art can easily determine the
frequency to be used based on factors including, but not limited to, the depth of the image, or the
desired resolution, for example.
[0025]
High frequency ultrasound may be desirable if high resolution images are desired and the depth
of the imaged features in the object is not too great. Accordingly, acquiring ultrasound data may
include oscillating an ultrasonic wave having a frequency of at least 20 MHz and receiving a
portion of the oscillating ultrasonic wave reflected by the object. For example, transducers with
center frequencies of about 20 MHz, 30 MHz, 40 MHz, 50 MHz, 60 MHz or more can be used. In
one exemplary preferred embodiment, the transducer can have a center frequency of about 20
MHz (for a design frequency of 25 MHz, according to the general example of frequencies
described later herein).
[0026]
The oscillation of high frequency ultrasound is often desirable for small animal imaging, in which
case high resolution can be achieved with acceptable penetration depth. Thus, the method can be
used at clinical frequencies or high frequencies for small animal subjects. Optionally, as
mentioned above, the small animal may be a rat or a mouse.
[0027]
The disclosed transducers can be operatively connected to an ultrasound imaging system for the
generation, transmission, reception, and processing of ultrasound data. For example, ultrasound
data can be transmitted, received, and processed using an ultrasound scanning device that can
provide ultrasound signals of at least about 20 MHz up to the maximum operating frequency.
Any ultrasound system or device operable at 20 MHz or higher may be used.
[0028]
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The matching layer described herein can be used with other devices capable of emitting and
receiving ultrasound at a desired frequency. For example, an ultrasound system using an array
transducer can be used.
[0029]
When imaging small animal subjects, illustratively, it can be located on a platform that can utilize
an anesthesia facility. Thus, the method can be used with platforms and devices used to image
small animals, including "rail guide" type platforms with steerable probe holder devices. For
example, the system described is described in U.S. Patent Application No. 10 / 683,168, entitled
"Integrated Multi-Rail Imaging System", U.S. Patent Application No. 10 / 053,748, entitled
"Integrated Multi-Rail Imaging System", U.S. Patent Application No. 10 / 683,870, now U.S.
Patent No. 6,851, 392 issued February 8, 2005, entitled "Small Animal Mount Assembly", and
U.S. Patent Application No. 11 / 053,653. Can be used with the multi-rail imaging system and the
small animal restraint assembly described in US Pat. No. “Small Animal Mount Assembly”,
which are incorporated herein by reference
[0030]
Small animals can be anesthetized during imaging and biophysiological parameters such as heart
rate and temperature can be monitored. Thus, the system can include means for collecting ECG
and temperature signals for processing and display. The system can also display physiological
waveforms, such as ECG, respiration, or blood pressure waveforms.
[0031]
Also provided is the use of the described transducer or matching layer in an ultrasound imaging
system using line based image reconstruction where high frame rates are desired. An example of
such a system may have the following components as described in US patent application Ser. No.
10 / 736,232, US patent application publication 2004/0236219 (incorporated herein by
reference): it can. The disclosed ultrasound imaging system, using line-based image
reconstruction, can provide ultrasound images having an effective frame rate greater than 200
frames per second. The system uses ultrasound to enable high temporal resolution, an ECG-based
technique that allows accurate depiction of rapidly moving structures such as the heart in small
animals such as mice, rats, rabbits, or other small animals. Prepare.
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[0032]
Many different target organs can be imaged, including dynamic organs having a lumen. For
example, the heart or portions thereof can be imaged using the methods and systems described
herein. However, it is contemplated that the method and system is not limited to imaging the
heart, but can image other organs or parts thereof, including other parts of the cardiovascular
system.
[0033]
Several animal models are widely used in the study, the most common being mice and rats. High
frequency ultrasound waves of about 20 MHz to over 60 MHz are widely used for imaging of
mouse models, and high effects have been obtained. However, because rat has epidermal tissue,
skin tissue, and subcutaneous tissue that show high attenuation and echogenicity, which
produces two major contrast impairments, the rat model has higher frequency imaging compared
to the mouse model. It has proven to be difficult. The first obstacle is the high attenuation of high
frequency ultrasound energy. The second obstacle is the generation of multiple reflections
leading to reverberant contrast artifacts. Both of these disorders can be alleviated by altering the
operating characteristics of the transducer used to image the rat.
[0034]
Exemplary operating characteristics for overcoming these imaging obstacles include high
sensitivity to overcome attenuation, combined lens systems to overcome reverberation, and / or
transducers and tissue to attenuate multiple reflections. Between the matching attenuation
layers. In addition, the transducers described for rat imaging can have a wide bandwidth so as
not to adversely affect the distance resolution.
[0035]
These three properties often offset one another and are generally regarded as a technical tradeoff. In one embodiment, higher sensitivity is generally at the expense of bandwidth. Similarly,
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better match often results in lossy lens material and adversely affects sensitivity, and bandwidth
is reduced when it is designed to be quarter wave match at the design frequency. Also, the
addition of a matched attenuation layer reduces the sensitivity of the primary signal level.
[0036]
Transducers incorporating acoustic matching to water, sensitivity, and wide bandwidth response
are described herein and are useful for imaging a target animal model. The transducer improves
high frequency ultrasound imaging on rats and other small animal models.
[0037]
In one aspect, a more efficient, more efficient transducer is described herein to overcome the rat
tissue property of high attenuation. In a further aspect, the transducer is relatively broadband,
such as, for example, a -6 dB bandwidth of about 80% or more.
[0038]
In another embodiment, a matching layer for an ultrasound transducer stack having a plurality of
layers is provided. In one aspect, the described matching layer may be an ultrasound transducer
stack that includes a piezoelectric layer. In alternative embodiments, the stack is, for example, but
not limited to, backing layers, other matching layers, lens layers, signal electrode layers, ground
electrode layers, adhesive layers, and / or other layers known to those skilled in the art. And
other layers can also be provided.
[0039]
In one embodiment of the present invention, the matching layer comprises a composite material.
In this aspect, the composite material can include a matrix material loaded with a plurality of
micron-sized and nano-sized particles. In an alternative embodiment, the composite material also
comprises a matrix material loaded with a plurality of heavy and light particles. In other
embodiments, the matching layer can also include cured cyanoacrylate.
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[0040]
An ultrasonic transducer stack comprising multiple layers is illustrated herein, each layer having
a top surface and an opposite bottom surface. In one aspect, the plurality of layers comprises a
piezoelectric layer and at least one matching layer. In this aspect, the matching layer can be
located in the stack to substantially cover the top surface of the piezoelectric layer. An exemplary
stack comprises a matching layer comprising a composite material loaded with a plurality of
nano-sized and micron-sized particles, a matching layer comprising a plurality of heavy and light
particles, and a matching layer comprising cyanoacrylate it can.
[0041]
Piezoelectric materials that can be used include, but are not intended to be limited to, for
example, ceramics, composite ceramic materials, single crystals, and the like. For example,
lithium niobate (LiNb) can be used in an exemplary single crystal mechanical scanning
transducer. In another embodiment, 36 degree Y-turn lithium niobate is an exemplary material
for the piezoelectric layer. LiNb has high efficiency mechanical bonding properties (Kt ~50%),
very low dielectric constant (ε r = 34), an efficient single can eliminate the need for additional
electrical matching networks The oscillator of the element can be obtained. Furthermore, lithium
niobate (LiNb) has a high Q value (in the region of 10,000) and can be a narrow band oscillator.
It is contemplated that the high Q factor is offset by the broadband matching structure and the
damping backing system acting to reduce the Q factor of the transducer.
[0042]
In a further aspect, a backing system can be used with the transducer stack and can be connected
to and / or below the piezoelectric layer on the bottom side. When used, the backing layer
achieves several points. First, it has an acoustic impedance that causes the transducer to resonate
at the desired bandwidth. Second, it has high attenuation so that the internal reflection of the
transducer itself is reduced or nonexistent. Finally, the backing layer can operate in contact with
the piezoelectric element.
[0043]
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In one exemplary embodiment, the acoustic impedance of the backing layer is chosen to be as
low as possible compared to LiNb Z in order to achieve high sensitivity while ensuring good
bandwidth. For example, an acoustic impedance of width between about 5 MR and 7 MR
provides the desired trade-off between sensitivity and bandwidth. For example, if higher
bandwidth is desired, a backing impedance of about 25 MR to 40 MR can be used.
[0044]
With respect to backing layer attenuation, the higher the attenuation, the thinner the backing
thickness required to eliminate internal reflection. Also, the thinner the backing layer, the less
weight and volume of the transducer.
[0045]
In alternative embodiments, the backing layer may be conductive or may be an insulator.
However, whether a conductor or insulator is used, the backing layer is operably connected to
the piezoelectric layer. As a result of the conductive backing layer, the manufacturing process
can be speeded up with a very narrow range of possible attenuation and available acoustic
impedance. Nonconductive backing layers offer a very wide range of damping and damping
possibilities.
[0046]
One exemplary backing layer is formed of Ablebond 16-1 conductive epoxy. The backing layer
material has an acoustic impedance of about 6.7 MR and an attenuation of greater than about
100 dB / mm at 30 MHz. Furthermore, this exemplary conductive epoxy exhibits excellent
conductivity at the bond line and makes a perfect connection with the piezoelectric layer.
[0047]
In alternative embodiments, materials such as, but not limited to, indium, tin, and indium alloys
are used to form the backing layer to create an ultra-high bandwidth design where lower
sensitivity is desired. It can be formed.
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[0048]
In other embodiments, a lens layer can be used.
For example, a lens that is acoustically substantially matched to water can be used. Such a lens
can have a sound velocity higher or lower than the sound velocity of water, but has a sound
velocity sufficiently different from water such that the actual curvature is achieved to achieve the
desired amount of focus. Exemplary lens materials that can be used are polymethylpentene or
TPX. The thermoplastic resin has an acoustic impedance of 1.8 MR and a longitudinal wave
propagation velocity of 2200 m / s. A convex lens (having a lower speed of sound than water)
can also be used.
[0049]
Although TPX has a large loss compared to some other alternatives (5.7 dB / mm at 30 MHz), it
has very good acoustic matching with water and tissue. The main problem in the use of TPX is
that adhesion to other layers of the ultrasound transducer stack is very difficult. For example,
Rexolite (thermosetting cross-linked polystyrene) has lower losses than TPX and only about 1.1
dB / mm at 30 MHz, but with an acoustic impedance of 2.6 MR. Rexolite can be used where
sensitivity is important and can withstand multiple reflections. Loss can be reduced by keeping
the lens thin and keeping the f-number on the high side of the normal range (typically between
about 2.5 and 3).
[0050]
In various embodiments, at least one exemplary quarter wave matching layer is used in an
ultrasound transducer stack. Conventionally, such quarter-wave matching layers are also known
simply as "matching layers". It should be noted that the term "matching layer" is used throughout
the description of the invention and has the same meaning as a quarter wave or wavelength
matching layer. The quarter wave matching layer affects both sensitivity and bandwidth.
[0051]
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At high frequencies, the matching layer can be on the order of about 5.0 μm to more than 50.0
μm thick, and typically has a low tolerance for the intermediate adhesive layer. For example,
layers greater than 500 nm may be detrimental to the design, and those greater than 1500 nm
may substantially cancel the effect of the stack. As will be apparent to those skilled in the art, for
quarter wave layers, the thickness depends on the desired oscillation frequency and the speed of
sound in the layer. Thus, one of ordinary skill in the art would determine the appropriate
thickness for the quarter wavelength of the matching layer, including heavy and light particles,
by routine testing of the speed of sound of the composite and knowledge of the desired design
frequency. Can.
[0052]
In one embodiment of the present invention, an exemplary lens layer comprises TPX connected
to a cyanoacrylate matching layer having an acoustic impedance of about 3 MR. As described
herein, a cyanoacrylate matching layer is adhered to the TPX lens layer to connect with the other
layers of the stack.
[0053]
In an exemplary embodiment, a matching layer of about 10 MR covers a matching layer having
an impedance between about 4.5 and 5 MR to improve bandwidth and maintain excellent
sensitivity. This is exemplarily achieved using two layers of tungsten-doped epoxy polished to the
desired thickness using a vacuum sander. In a further aspect, the low impedance layer may be
doped with SiC nanoparticles to prevent the tungsten powder from settling out during curing.
[0054]
As mentioned above, the other matching layer may be a cyanoacrylate (CA) layer laminated to
the TPX lens. The CA matching layer bonded to the lens layer can be bonded by the layer of
epoxy to the lower impedance matching layer located in the stack below the bottom of the CA
layer. In one aspect, the thickness in the height direction of the epoxy layer is about 5 μm or
less. Due to the acoustical similarity of the epoxy to the CA, this layer does not have a major
impact on the performance of the stack at a few micron thickness (<5 μm at 20 MHz). In one
aspect, the epoxy may be, for example, Epotek 301 epoxy, but is not intended to be limiting. In
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other embodiments, rubber reinforced CA (such as Loctite Black Max) that can have somewhat
lower acoustic impedance can be used.
[0055]
In an alternative embodiment of the present invention, the matching layer for an ultrasound
transducer stack comprising multiple layers can comprise a composite material having a matrix
material loaded with multiple micron-sized and nano-sized particles. In one aspect, the composite
material forms a matching layer of an ultrasound transducer stack. The matching layer may be a
quarter acoustic wavelength matching layer.
[0056]
The particles may be of various dimensions within the nano-sized and micron-sized areas,
respectively. In a preferred embodiment, the loaded particles have a maximum longitudinal
dimension or longest dimension less than the thickness of the matching layer. For example,
micron-sized particles have a maximum longitudinal dimension of about 5 μm, nano-sized
particles have a maximum longitudinal dimension of about 800 nm, and the thickness of the
matching layer is greater than 5 μm. One skilled in the art will understand that the smallest
possible particles are selected so that it is not possible to achieve the desired acoustic impedance.
Nominally, attenuation should be kept to a minimum in the matching layer, and the particle size
is much smaller than the wavelength. For example, a 5 μm particle in a 16.5 μm quarter wave
layer is about 1/13 of a wavelength.
[0057]
In one aspect, micron-sized and nano-sized particles can include high density metals. For
example, micron-sized and nano-sized particles can include tungsten, gold, platinum, or mixtures
thereof. Alternatively, if a nonconductive layer is desired, high density ceramics such as, for
example, PZT can be used.
[0058]
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In a further aspect, the matrix material may be a polymer. In one non-limiting example, the
polymer forming the matrix is an epoxy. For example, the epoxy may be a low viscosity room
temperature cure epoxy having a Tg above the maximum service temperature of the transducer.
Examples of some non-limiting epoxies include Epotek® 301 and 302 (Epotek, Inc., Billerica,
Mass.), Cotronics Duralco® 4461 (Cotronics, Inc., Brooklyn, NY), West Systems Epoxies (West
Systems) (Bay City, Mich.), And combinations of various Araldite® Epoxy. Alternatively, the
matching layer may be a thermoplastic resin, such as, for example, polymethyl methacrylate
(PMMA), such as acrylic, Plexiglas, Lucite, or polycarbonate (PC), such as, for example, Lexan.
[0059]
In an exemplary embodiment, micron-sized and nano-sized particles may be introduced into the
matrix material in a ratio of about 5: 1 to about 1: 5, in parts by weight of micron-sized particles
to nano-sized particles. For example, micron-sized and nano-sized particles may be introduced
into the matrix material at a ratio of about 1: 1, in terms of parts by weight of micron-sized
particles to nano-sized particles. In other aspects, the desired percentage of large particles can
increase as the desired acoustic impedance increases. For example, if a 10 MR matching layer is
desired, a 1: 1 ratio can be used. In other embodiments, a 2: 1 or 3: 1 micron size particle:
nanoparticle ratio can be used for the 12 MR layers.
[0060]
In certain exemplary embodiments, the nano-sized particles and the micron-sized particles of the
matching layer comprise about 10% to about 35% of the composite material on a volume basis.
In other embodiments, nano-sized particles and micron-sized particles can constitute about 25%
to about 30% of the composite material on a volume basis. In a preferred embodiment, the nanosized particles and the micron-sized particles make up about 25% of the composite material on a
volume basis.
[0061]
Matching layers with nanoparticles and micron particles can be designed to have the desired
acoustic impedance. For example, the acoustic impedance of the matching layer can be formed to
be between about 7.0 Mega Rail (MR) and 14.0 Mega Rail (MR). In a preferred aspect, the
acoustic impedance of the matching layer is about 10 MR.
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[0062]
In various embodiments, the matching layer can also vary in thickness. As will be appreciated by
those skilled in the art, the thickness to achieve a quarter-wave matching layer varies with the
speed of sound in the matching layer and the frequency of the ultrasound passing through the
matching layer. Thus, one of ordinary skill in the art can readily determine any desired
ultrasound oscillation frequency, including frequencies above 20 MHz, along with the
appropriate thickness of the matching layer, based on the teachings herein. In another exemplary
aspect, the speed of sound in the matching layer can be between about 1000 meters / second (m
/ s) and 3000 m / s. Furthermore, the thickness in the height direction of the matching layer can
be between about 4 μm and 30 μm.
[0063]
In one embodiment, a method of producing a nanoparticle / micron particle matching layer
comprises providing a matrix material, a plurality of micron-sized particles, and a plurality of
nano-sized particles. The matrix material is loaded with a plurality of micron-sized particles and a
plurality of nano-sized particles to form a composite material, and the formed composite material
is used to create a matching layer of an ultrasonic transducer stack . In one aspect, the micronsized and nano-sized particles can comprise the same substrate. Of course, it is also contemplated
that the micron-sized particles and the nano-sized particles consist of different substrates.
[0064]
As shown in FIG. 1, the nanoparticle / micron particle matching layer can be used as a matching
layer in the illustrated ultrasound transducer stack 100 having multiple layers. As shown, the
exemplary ultrasound stack 100 comprises a plurality of layers, each layer having a top surface
and an opposite bottom surface. The plurality of layers includes a piezoelectric layer 102 and at
least one matching layer. Of course, multiple matching layers (108, 110 and 112) can be used in
the transducer stack 100. The matching layer 108 comprises the quarter wave acoustic matching
layer described above.
[0065]
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In an exemplary embodiment, the piezoelectric layer can generate ultrasound at a center
frequency of at least about 20 megahertz (MHz) to transmit the first matching layer. Such high
oscillation center frequencies may be particularly desirable for imaging small animals, including
rats. Thus, in an exemplary aspect, the piezoelectric layer is at least about 20 MHz, 25 MHz, 30
MHz, 35 MHz, 40 MHz, 45 MHz, 50 MHz, 55 MHz, 60 MHz, 65 MHz, 70 MHz or more to
transmit the first matching layer. It is possible to generate ultrasound at a higher center
frequency.
[0066]
In another aspect, the piezoelectric layer can have an acoustic impedance of 20 MR or more. As
mentioned above, one exemplary type of piezoelectric layer that can be used includes lithium
niobate having an impedance of about 34 MR. In another embodiment, the piezoelectric layer can
include PZT having an impedance of about 33-35 MR.
[0067]
Of course, in addition to the nanoparticle / micron particle matching layer described herein,
other matching layers can also be used. One exemplary matching layer of an ultrasound
transducer stack having a plurality of layers comprises a composite material comprising a matrix
material loaded with a plurality of first heavy particles and a plurality of second light particles.
However, it should be noted that in the present embodiment, there is no limitation on the size of
light particles and heavy particles. Thus, the matching layer comprising light and heavy particles
can comprise a mixture of nanoparticles and micron particles. For example, light particles may be
micron-sized or nano-sized, heavy particles may be micron-sized or nano-sized, and any
combination thereof may be added to the matrix material.
[0068]
The matching layer with heavy and light particles can include a quarter acoustic wavelength
matching layer. In certain non-limiting examples, the light particles have a density of about 4.0
grams per cubic centimeter (g / cc) or less, and the heavy particles have a density of greater than
about 4.0 g / cc. For example, the light particles can have a density between about 2.5 g / cc and
14-04-2019
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about 4.0 g / cc. Heavy particles can have, for example, a density of 10.0 g / cc or more.
[0069]
For example, the first heavy particles can comprise micron-sized or nano-sized particles selected
from the group consisting of tungsten particles and lead zirconate titanate particles or mixtures
thereof. In a further embodiment, the second light particles comprise micron-sized or nano-sized
particles selected from the group consisting of silicon carbide particles and alumina particles or
mixtures thereof. Additionally, the density of the second light particles can be between about
100% and 200% of the density of the final complex of heavy particles and matrix.
[0070]
As mentioned above, the size of the heavy and light particles may be different. In various
embodiments, the heavy or light particles can be less than 1 micron. In a preferred embodiment,
the loaded particles have a maximum longitudinal dimension or longest dimension of less than
1/50 of the wavelength in the matching layer in which they are contained. Heavy and light
particles can be introduced into a matrix material that can include, for example, a polymer such
as an epoxy. In one embodiment, the plurality of particles introduced may comprise at least
about 11.0% by volume of the composite material. For example, the plurality of particles can
comprise between about 11.0% and about 20.0% by volume of the composite material. In a
preferred embodiment, about 5.5% by volume of the composite material comprises a plurality of
heavy nanosized particles and about 5.5% by volume of the composite material comprises a
plurality of light nanosized particles. In this preferred embodiment, as in the other exemplary
embodiments, the heavy particles may be tungsten particles, PZT particles, gold particles, or
platinum particles, and the light particles are silicon carbide particles or alumina particles. May
be
[0071]
The acoustic impedance of matching layers comprising heavy and light particles can be varied.
For example, the acoustic impedance of this layer can be between about 3.0 and 7.0 megarails. In
an exemplary embodiment, the acoustic impedance is about 4.5 MR.
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[0072]
The thickness of the matching layer can also vary. Thus, one skilled in the art can determine the
appropriate thickness for the quarter wavelength of the matching layer, including heavy and light
particles, by routine testing for sound velocity and knowledge of the desired oscillation
frequency. In one embodiment, the matching layer can have a speed of sound between about
1500 m / s and about 4500 m / s. In another embodiment, the speed of sound in the matching
layer is between about 1800 m / s and about 2500 m / s. In a preferred embodiment, the speed
of sound in the matching layer is about 2100 m / s. In various embodiments, it is contemplated
that the thickness of the illustrated matching layer comprising heavy and light particles can be
between about 4.0 microns and 30 microns. For example, a design frequency of 25 MHz,
including an exemplary mixture of about 5.5% by volume of nano-sized first heavy particles of
the composite and about 5.5% by volume of nano-sized second light particles of the composite
Whereas in the exemplary transducer where the center frequency is 20 MHz, the matching layer
is approximately 22.0 microns thick in the height dimension of the ultrasound transducer stack.
[0073]
In one embodiment of the present invention, a method of producing a light particle / heavy
particle matching layer includes providing a matrix material, a plurality of first heavy particles,
and a plurality of second light particles. In this aspect, the matrix material is charged with a
plurality of first heavy particles and a plurality of second light particles to form a composite
material used as a matching layer of the ultrasound transducer stack.
[0074]
The ultrasound transducer stack can comprise a matching layer comprising light and heavy
particles as described above. This matching layer comprises the lower impedance matching layer
of the transducer stack which also comprises the higher impedance matching layer. In this
regard, higher impedance matching layers include similar weights of nanoparticles and micron
particles, and / or materials as lower impedance matching layers.
[0075]
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Thus, the exemplary stack 100 can comprise multiple layers, each layer having a top surface and
an opposite bottom surface. The plurality of layers can include a piezoelectric layer 102 and at
least one matching layer. Matching layer 110 may comprise a composite material comprising a
matrix material loaded with a plurality of first heavy particles and a plurality of second light
particles, and the bottom surface of matching layer 110 is a top surface of piezoelectric layer
102. cover. The ultrasound transducer stack 100 may further comprise a matching layer 108
having an impedance higher than the impedance of the matching layer 110, the matching layer
108 being located between the top surface of the piezoelectric layer 102 and the bottom surface
of the matching layer 110. Do.
[0076]
The piezoelectric layer can generate ultrasound at a center frequency of at least about 20
megahertz (MHz) to pass through the one or more matching layers. For example, the
piezoelectric layer produces ultrasound at a center frequency of at least about 25 MHz, 30 MHz,
35 MHz, 40 MHz, 45 MHz, 50 MHz, 55 MHz, 60 MHz, 65 MHz, 70 MHz or more to transmit one
or more matching layers can do. The ultrasound may pass through the matching layer 108 and
then through the matching layer 110.
[0077]
Also provided herein is a backing layer 104 of an ultrasound transducer stack 100 having a
plurality of layers. The backing layer can comprise a composite material having a matrix material
loaded with a plurality of micron-sized and nano-sized particles. Also provided is a backing layer
104 of an ultrasonic transducer stack 100 comprising a composite material having a matrix
material loaded with a plurality of first heavy particles and a plurality of second light particles.
[0078]
EXPERIMENTAL The following examples provide a person of ordinary skill in the art with a full
disclosure and description of how the compounds, compositions, articles, devices, and / or
methods claimed herein can be evaluated. And are intended to be purely exemplary of the
present invention, and not intended to limit the scope of what we regard as our invention. Efforts
have been made to ensure accuracy with respect to numbers (quantity, temperature etc), but
some errors and deviations should also be taken into account. Unless indicated otherwise, parts
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are parts by weight, temperature is in degrees Centigrade, or ambient temperature, and pressure
is at or near atmospheric pressure.
[0079]
Example 1: Fabrication of an exemplary LiNb 20-25 MHz transducer stack with a TPX lens Figure
5 shows a method of fabricating an exemplary LiNb 20-25 MHz transducer with a TPX lens FIG.
The manufacturing process is described in the following three exemplary sections. First, the
fabrication of matching layers and piezoelectric layers to form a stack is described. Next, the
preparation of the lens layer and the cyanoacrylate matching layer is described. Finally, adhesion
of the lens and cyanoacrylate layer to the transducer stack is described.
[0080]
Preparation of Matching Layer and Piezoelectric Layer As shown in block 504, LiNb crystals for
the piezoelectric layer are prepared. A 36 degree Y-cut LiNb crystal is lapped to a thickness of
0.4 lambda at the desired center frequency to offset the mass loading. The crystals are plated
with 3000 A of gold using suitable means such as E-beam evaporation or sputtering. As
appreciated by those skilled in the art, typically a thin layer of Cr or Ni can be used to improve
the adhesion of the gold layer. The gold side of the LiNb crystals is washed with acetone. After
washing, place the crystals in a clean place until further manipulation.
[0081]
Nanoparticle and micron particle loaded epoxy is prepared for the quarter wave matching layer.
At block 506, a high impedance matching layer having an impedance greater than about 8 MR is
prepared. The formation of input epoxy composites with acoustic impedances greater than 8 MR
is typically limited by the maximum volume ratio of powders that can be wetted with epoxy.
Achieving a volume ratio of more than 20% with particles small enough to fit a 25 MHz design is
difficult due to the large surface area to volume ratio of the fine powder. Due to the 20% volume
ratio limitation, and also using tungsten powder, it is difficult to form composites with acoustic
impedances greater than about 8-9 MR. For example, Martha G. Grewe, T. R. Gururaha, Thomas R
Shrout, and Robert E Newnham, "Acoustic Properties of Particle / Polymer Composites for
Ultrasonic Transducer Backing Applications", IEEE Trans. on Ultrasonics, Ferroelectrics and
Frequency Control, Vol. 37, no. 6, November 1990.
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[0082]
The use of a low viscosity epoxy (preferably less than 1000 cps) allows the largest proportion by
volume of powder added to the epoxy before the mixture becomes too dry to use. An example of
such an epoxy known in the art is Epotek 301. For example, Haifeng Wang, Tim Ritter, Wenwu
Cao, and K.W. Kirk Shung, "Passive Materials for High Frequency Ultrasound Transducers" SPIE
Conf. on Ultrasonic Transducer Engineering, San Diego, California, February 1999, SPIE Vol. See
3664. The epoxy is thoroughly mixed before adding the powder.
[0083]
The powder 25% volume ratio in the epoxy matrix is used to form an exemplary 10 megarail
matching layer. To achieve this volume ratio, relatively large 5 μm particles are used. However,
such large particles do not match the frequency of the transducer since only three particles are
allowed in the thickness direction of the matching layer. Submicron tungsten (W) powder mixed
with 5 μm powder to a ratio of 1: 1 is also used. This is valid over a range of at least 1: 6 to 2: 1
by weight. The upper limit of density that can be achieved in powder loaded epoxy is limited by
the ability to wet the surface of all powder particles. As the particle size increases, the volume
ratio of powdered material to surface area increases linearly. Thus, as the size of the powder
particles is increased, the volume ratio of powder to epoxy which can be fully wetted into a voidfree mixture is increased. However, as the particle size increases, the problem arises that
sedimentation causes the interaction between the individual particles and the wavelength of the
ultrasonic energy to increase rapidly.
[0084]
The particle size can be small compared to the wavelength of the matrix (epoxy) in order to
reduce the attenuation in the matching layer and also for the predictable acoustic impedance of
the matrix and the powder as formulation material. In order to make a quarter wave matching
layer, the particle size can be made sufficiently small so that the composite contains at least 15
or more particles in its thickness direction.
[0085]
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The illustrated use of a mixture of nanoparticles and larger particles enables high density input
particles with both high volume fraction of input particles and excellent control over settling.
Sedimentation is controlled by adjusting the amount of nanoparticles to control the viscosity and
the thixotropic index of the resulting paste. In addition to the upper limit to the achievable
volume fraction and the advantages obtained in reducing the sedimentation of relatively large
particles, the nanoparticles allow a quarter wave layer (eg 16.5 μm thickness at 25 MHz) to be
of any cross section In the present invention, it is possible to have more particles, and even a
spatial distribution of powder particles (ie, there is no large epoxy area between large particles as
in the case of large particles alone).
[0086]
A mixture of large and small particles is preferred. With nanoparticles only, the upper limit
possible is less than 20% by volume, but with 5.0 μm particles only, or even with 2.0 μm or 3.0
μm particles only, a wider interparticle space compared to the wavelength Due to, a matching
layer having high attenuation with unclear acoustic impedance is obtained. An exemplary Wdoped epoxy preparation comprises a mixed batch of 3: 1 volume ratio of Epotek 301 epoxy to
tungsten powder (5 μm: less than 1 μm but 50%: 50%). This is a highly thixotropic paste, an
85% by weight tungsten mixture with a density of 5.7 g / cc and a volume fraction of tungsten of
25%. Due to the small size of the nanosized particles, it has up to 50 particles in its thickness
direction. For example, the mixture can be weighed as 0.5 g of mixed 301 epoxy (0.1 g of curing
agent, 0.4 g of resin), 1.5 g of W powder less than 1 μm, 1.5 g of 5 μmW powder.
[0087]
An intermediate acoustic impedance matching layer between about 3.5 MR and 6 MR is
produced by mixing light particles with heavy particles, as shown in block 514. The formation of
the intermediate acoustical impedance matching layer can achieve high to mid impedance in this
range using a high volume fraction of single light particles. However, using a single material with
a particle size small enough to form an intermediate acoustic impedance typically involves the
difficult task of finding an appropriate density of material available with a suitable powder
particle size is necessary. The high volume fraction makes mixing, degassing and spreading /
coating very difficult as a high viscosity and high thixotropy paste is formed, leading to
manufacturing problems. However, since the volume fraction of powder is typically kept higher
than 11% in order to keep the attenuation low, often a compromise is achieved between
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achieving the ideal acoustic impedance and the ideal physical properties, Otherwise you have to
explore new materials and start the process again.
[0088]
Thus, the combined use of light and heavy particles allows a solution that isolates the problem of
achieving the desired acoustical impedance from the problems of viscosity, wettability and
thixotropy index. Heavy materials are mixed in volume proportions to obtain the desired acoustic
impedance, and then light nanoparticles are added until the desired viscosity and thixotropic
index are achieved (i.e., easily wet but do not flow or settle). In one embodiment, commercially
available SiC light weight nanoparticles can be used as light weight particles. SiC p = 3.2 g / cc
and alumina p = 3.9 g / cc etc to isolate the problems of wettability, viscosity and thixotropy from
the problem of achieving a given acoustic impedance, but not limited to them Some particles of
are available.
[0089]
In this way, the acoustic impedance of the matching layer is controlled only by approximately the
volume fraction of heavy particles, which has a large settling problem. However, the viscosity and
uniformity of the complex mixture, as well as the settling, are controlled only by the substantially
light particles. In this regard, the lightweight particles are selected such that the density is
between about 100% and 200% of the desired composite density of the heavy particle-epoxy
mixture.
[0090]
For example, in an exemplary 25 MHz 4.5 MR matching layer, 5.5% volume fraction tungsten
powder nanoparticles in a room temperature cured low viscosity epoxy suitable to achieve an
acoustic impedance between about 4.5 MR and 5 MR Used for Then, SiC nanoparticles are added
to achieve an exemplary 11% volume fraction.
[0091]
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This exemplified mixture is easy to operate, has very good wettability, and does not appreciably
settle during the 24 hour cure period in which the epoxy cures. Before the addition of the SiC
particles, the mixture settles completely in a few seconds, but when the SiC is added, the mixture
becomes thixotropic and does not precipitate. Although the change in acoustic impedance due to
the addition of SiC particles is slight, the viscosity changes significantly and the mixture does not
settle. Any desired acoustic impedance can be achieved in the middle range, and using two
readily available powdered materials, the desired behavior without settling and without requiring
a very high volume fraction Characteristics are maintained. Also, the size of the nanoparticles
minimizes attenuation and scattering and provides an excellent matching layer.
[0092]
As shown at block 508, W-doped epoxy can be added to the stack. The application of the
matching layer requires careful consideration, as cavities in the matching layer can generally
cause a bad stack. Cavities near the interface between the piezoelectric crystals and the powder
loaded epoxy can be detrimental.
[0093]
In order to prevent the cavity, the input epoxy is spread evenly and the cavity is pushed out to
the mixture surface. In general, the thixotropic paste used to make the matching layer is difficult
to "flush out" to certain parts and usually requires agitation to flow like a liquid. Thus, a vibrating
manipulator (eg, an engraver with a portion of a 22 gauge wire attached) can be used to spread
the paste over the crystal surface so that it flows and wets the entire surface. Furthermore, the
vibrations promote the cavity to rise to the surface of the paste, which can be removed by
grinding. This allows the use of highly thixotropic pastes that do not settle after being spread out
as desired.
[0094]
In one example, an engraver tip converted into a 22 gauge hard tempered copper wire L-shaped
tip under a microscope for better wettability and to promote floating of the cavity onto the
surface Move the thixotropic paste smoothly onto the top. Typically, an engraver chip is used on
the entire surface of the aperture and set to a low amplitude high frequency setting (about 7,200
spm). In one aspect, a small portion (about 0.25 mm) of the edge around the end coats the LiNb
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crystal surface without coating so that it can be used for later grounding. With the epoxy on the
edge, it can not be cleaned effectively unless the entire batch is removed from the face of the
transducer.
[0095]
The epoxy is allowed to cure at room temperature, as indicated at block 510, and then raised for
post-cure. Room temperature curing epoxy can be used to prevent significant shrinkage of the
layers that cause the piezoelectric crystals to strain. Because high Tg is preferred, an epoxy
compatible with high temperature post cure in an oven is selected. The epoxy cures at room
temperature for about 18 hours or more (24 hours preferred). In addition, the cured epoxy is
subjected to a post cure at 65 ° C. for about 3 hours or more in an incubator.
[0096]
As indicated at block 510, polishing and / or lapping of the first matching layer is performed.
Remove excess material to achieve a quarter wave matching layer. Several methods (such as
lapping or polishing) can be used to remove excess material and obtain a 1⁄4 wavelength thick
matching layer. The first matching layer is polished to a thickness of λ / 4 (c = 1600 m / s)
using a polishing system (this is 16-17 μm thick at 25 MHz). Since the tolerance of an
exemplary device at 20 MHz for a design frequency of about 25 MHz is in the range of 2-3 μm,
ie 16.5 μm + 2 μm / -1 μm, care should be taken in sample attachment and measurement.
[0097]
As indicated at block 514, a relatively low impedance second layer is fabricated and applied.
Once the first matching layer is complete, apply a second paste of intermediate acoustic
impedance to the first layer and repeat the process of spreading, curing, and material removal to
form a second quarter wave layer . The batch is mixed as follows: W powder doped epoxy using
Epotek 301 and a 17: 1 volume ratio or (51 wt% W) mixture of tungsten powder less than 1 μm.
Add 50% of the mass of the mixture in SiC powder less than 1 μm and mix until a smooth paste
is obtained. Any lumps in the paste can be removed by lightly kneading with a mortar and pestle.
The mixture can be weighed as 0.5 g of mixed 301 epoxy, 0.52 g of less than 1 μm W powder,
0.2 g of less than 1 μm SiC powder. The second layer is applied as a first layer using an
engraver with an L-shaped tip for uniform spreading of the paste and good wettability. The
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mixture is allowed to cure at room temperature for about 18 to 24 hours and then post cured at
65 ° C. for about 3 more hours.
[0098]
As shown at block 516, polishing and / or lapping the second matching layer is performed.
Polish the material to a thickness of λ / 4 using c = 2100 m / s (in the 25 MHz design frequency
example, this thickness is about 18-19 μm thick +/- 1 μm).
[0099]
As shown in blocks 518 and 520, the support structure of the stack is prepared and the crystals
are adhered to the support structure. In one aspect, the stack is disposed within the housing. It
has an ID that matches the desired transducer opening and height, and an OD that matches the
desired Ti transducer housing specifications, so that the top of the insert is about 1.5 mm below
the edge of the Ti housing , Ultem 1000 (polyetherimide) inserts can be used. Clean the front of
the insert and inspect it for cleanness, burrs and bumps. For example, the insert can be first
cleaned with an ultrasonic cleaner and detergent, and further rinsed with isopropyl alcohol just
prior to use.
[0100]
A small amount of a suitable low temperature cure medium viscosity epoxy (such as Loctite E20HP) is prepared and applied as a very thin film to the front of the cleaned insert using a cotton
swab tip. The epoxy is not applied thick enough to form a meniscus across the thickness of the
insert wall. In practice, the crystal is placed on the epoxy coated side of the insert, stack side up,
and centered on the insert. In one embodiment, lithium niobate crystals are applied to the insert
using a vacuum adsorption tool. A small force is applied to press the crystals against the face of
the insert, which causes the epoxy to flow to the end of the insert below. The centered crystals
are placed in an incubator and cured at about 40 ° C. for about 3 hours.
[0101]
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After curing, the insert / crystal assembly is inspected to ensure that the crystals are centered
and completely adhered to the insert. Next, the edge of the insert / crystal assembly is cleaned.
Check that the diameter of the Ultem insert has not increased by sliding this part into the
exemplary housing.
[0102]
At this stage, one skilled in the art will understand that the acoustic stack can be placed on a
suitable support structure and that the back electrode and backing material with suitable
damping can be applied as shown in blocks 522 and 524. will do. These functions can be
combined by using conductive epoxy as a backing layer.
[0103]
In one example, the illustrated insert / crystal assembly can be successfully installed on a clean
smooth machined surface with the crystal layer down. The air gap on the back is filled with
Ablebond 16-1 silver conductive epoxy. The void is first filled by dropping epoxy into the center
of the cavity using an epoxy syringe and an applicator tip. Apply epoxy over the back of the
crystal, making sure that the backing material does not trap any voids. Use an epoxy syringe and
continue filling with the tip of the applicator below the epoxy surface so that no cavity is formed
in the epoxy during filling. Fill the void until the conductive epoxy is about 0.5 mm below the
edge of the insert.
[0104]
Here, the backed stack, referred to as a "pill", can be housed in a suitable housing, taking into
account the expected weight, temperature, RF shielding etc depending on the application for
which the device is intended And are attached as shown at blocks 526 and 528.
[0105]
The pill is placed on the fixture of the housing with the epoxy not cured on top.
Apply a small amount of Loctite E-20 HP to the back of the pills in several places so as not to join
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each other. The completed housing is then placed on the pill until the pill contacts the back of the
housing. The fixture clamps are then placed on the housing and held in place and allowed to cure
at room temperature for about 18 hours or more. The assembly is then placed in an incubator
and post cured at 65 ° C. for about 3 hours. Typically, the surface of the pill is parallel to the
floor and facing down to help prevent the backing layer from flowing in the housing.
[0106]
The adhesive layer can then be applied. In this example, when the epoxy is completely cured,
beads of epoxy are applied to the periphery of the crystal such that there is a continuous smooth
surface between the crystal and the Ti housing. Here, a very small amount of Epotek 301 epoxy
is applied over the perimeter of the LiNb crystal and the inside diameter of the housing. The
crystal surface is preferably about 1.25 mm below the chamfer on the Ti housing to obtain an
epoxy negative meniscus between the crystal and the Ti housing. Both the surface is clean and no
epoxy is present, as crystal and Ti can sputter gold on both surfaces. In practice, high
magnification (20 ×, preferably higher) is used to apply the epoxy beads. In one embodiment,
the epoxy can be applied at three locations on the perimeter and allowed to flow around the
perimeter using gravity and capillary action. In a further embodiment, a fine gauge wire (per 26
gauge) can be attached to the end of the sharp Q-tip to improve control to help the adhesive flow
around the entire circumference. The resulting structure is allowed to cure for about 12-18
hours at room temperature. The adhesion procedure may be repeated, curing the structure at
room temperature for about 18 hours, and then incubating at 65 ° C. for about 3 hours to
perform post curing. After the epoxy cures, inspect the edge of the Ti enclosure for epoxy. The
epoxy found at the edge is removed.
[0107]
As will be appreciated, as shown at block 530, a ground connection to the return path of the
signal is provided at the exposed gold edge of the acoustic stack. Again, one skilled in the art will
recognize several methods of attaching such electrodes, such as sputtering of conductive ink and
epoxy, direct mechanical contact with good conductors.
[0108]
In one embodiment of the ultrasound stack, the stack formed as described above can then be
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adhered to the third low impedance matching layer and the lens. A lens with good integrity is
selected. As mentioned above, in a preferred embodiment, the lens matches well with water in
terms of acoustic impedance and can reduce echo artifacts. In addition, the lens material may
have low damping and may have a sound velocity sufficiently different from water so as to be
able to create a focusing effect without extreme curvature. There are many exemplary materials
used to form lenses for ultrasound transducers. Furthermore, many transducer designs utilize
hardened piezoelectric elements, or array structures, as an alternative to lenses.
[0109]
For the purpose of imaging rats, reverberation artifacts are a major problem in lens design. TPX
is recognized as a preferred lens material with acoustic matching with water, although there are
other materials with higher losses and lower losses or higher refractive indices at high
frequencies. TPX is one of the polyolefin based and has acoustic impedance matching closer to
water and tissue compared to most resins. TPX has an acoustic impedance between about 1.78
MR and 1.85 MR. For example, Alan R. Selfridge, "Approximate Material Properties in Isotropic
Materials" IEEE Trans. Sonics and Ultrasonics、Vol. SU-32, no. See 3,
May 1985. The impedance of water is Z = 1.5 MR.
[0110]
It is well known that TPX is difficult to bond with epoxy and most other adhesives. Most in the
industry TPX is used as a release film. That is, TPX is recognized as a material to which most
substances do not stick. Although some surface treatment techniques can be used to increase
adhesion strength, in fact, even with adhesion promoters, primers, or even corona etching, TPX is
not bondable in demanding applications Often they must be joined by mechanical means, heat
sealing or welding. Timothy Ritter, K.I. Kirk Shung, Xuecang Geng, Pat Lopath, Richard Tutwiler,
and Thomas Shrout, “Proceedings of SPIE-Volu me 3664 Medical Imaging 1999” Ultrasonic
Transducer Engineering, K. Kirk Shung, Editor, June 1999, pp. See 67-75.
[0111]
The adhesive line between the lens and the acoustic stack in the contrast transducer experiences
temperature swings of over 40 ° C. and rapid cooling in minutes, periodically in use.
Furthermore, it is constantly exposed to ultrasound energy. Poor adhesion generally results in
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delamination and dead spots in the transducer. For this reason, high quality adhesive lines are
desirable for assembly of the transducer.
[0112]
In an exemplary high frequency ultrasound transducer, the lens always remains in contact with
the stack. Even slight detachment can cause transducer dead spots.
[0113]
In an exemplary embodiment, a cyanoacrylate (CA) based adhesive is adhered to the TPX lens. CA
forms a strong bond to TPX, for example, by using a suitable primer such as Verik AC 77, some
toluene based primers etc but not intended to be limiting. However, CA is not used in transducer
stacks because the cure properties of cyanoacrylates are very catastrophic and depend on the
substrate and environmental conditions. With very thin adhesive lines used to make high
frequency ultrasound stacks, immediate curing of the adhesive can occur suddenly. The addition
of adhesive line spacers is often not used for CA adhesives as it results in immediate curing of the
material due to the large surface area. For the same reason, CA can not be loaded with powder,
which makes it even less likely to be a candidate for transducer production. In addition, the
acoustic properties of CA can not be found in the literature, as this material can not be cured in
thick enough pieces for standard testing. In addition, material properties that can be used
acoustically as a model of CA can not be exploited for the same reasons.
[0114]
In spite of the lack of technology and the disadvantages known in the art, CA can be cured over a
narrow range of thickness. The curable range of CA can be used to form a quarter wave matching
layer for frequencies ranging from 5 MHz to over 60 MHz. The acoustical properties of CA were
determined using it as a matching layer and associated with the model using PiezoCAD software
based on the KLM model available from Sonic Concepts (Woodinville, Wash., USA). The results
showed that CA could be used as a matching layer with an acoustic impedance between about
2.5 MR and 2.8 MR.
[0115]
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One exemplary method of adhering TPX to a quarter wave matching system utilizes CA. As a
result of testing the adhesion between the TPX layer and the CA layer, the interface between the
CA layer and the TPX layer was at least as strong as TPX alone. However, for the reasons
described above, the thickness of the bond can not be controlled and is prone to misalignment
with the air gap, which can ruin the nearly complete transponder stack in the final stages of
assembly, Direct bonding to the stack is not suitable.
[0116]
In one exemplary process, a quarter wavelength thick cured CA layer is applied to the back (flat
side) of the TPX lens layer, and then the formed structure is conventionally applied to the top of
the preformed stack. Bonded with epoxy. The epoxy adheres easily to the CA layer so that the CA
layer is adhered to the TPX lens layer. The CA layer thus forms a quarter wave matching layer
from the top of the stack to the TPX lens layer. For the exemplary stack, the top surface of the
stack has an acoustic impedance of 4.5 MR, CA is Z = 2.5-2.8, and the TPX lens layer is Z = 1.8.
This results in a transducer having a -6 dB bandwidth of 85% to 90% and a bi-directional
insertion loss of between about -41 dB and -42 dB at 25 MHz re1 V / V.
[0117]
In one embodiment, as shown in blocks 534 and 536, some amount of CA adhesive, such as, for
example, Verik PR40, is coated on the back of the TPX lens using an aluminum foil release layer
and a wire spacer. In practice, the release film is placed on a flat surface (preferably on the
vacuum plate so that the foil is flat). In one aspect, the aluminum foil is clean and free of oil and
moisture. The wires are arranged in a pattern on the release film. In one aspect, the wires are
arranged in a radiation pattern such that the wires do not meet at a common vertex. These wires
are used as spacers for the layers of CA. In an exemplary 25 MHz stack, wires of about 25 μm
diameter are used to form a CA layer with a resulting thickness of about 23 μm to 25 μm. This
is slightly thicker than the desired quarter wavelength thickness of CA, which is between about
21 μm and 23 μm in a 25 MHz design frequency oscillator. At this point, the longitudinal wave
velocity in CA is estimated to be between about 2100 m / s and 2200 m / s. 1-3 μm during the
grinding process, which also serves to treat the surface of the CA layer to improve the adhesion
of the epoxy used to affix the lens layer to which the CA layer is adhered to the stack below it
Excess material is removed.
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[0118]
In fact, the back of the TPX lens layer is ground with SiC sandpaper of suitable particle size to
improve surface adhesion, as shown in block 532, for example, suitable for Verik AC 77, toluene
based primer etc. It is treated with a CA polyolefin primer. The back of the lens is then coated
with a large amount of CA so that substantially the entire surface is wetted, as shown at block
536. The CA does not cure rapidly if a relatively thick meniscus is formed on the back of the lens,
so a large amount of CA will allow enough time for the lens to be placed on a treated release film
/ wire configuration Is obtained.
[0119]
Subsequently, the CA coated lens layer is placed on the release film and lightly compressed as
shown in block 538 so that the lens "pins" the wire between the underlying release film and the
lens layer. Ru. After curing for about 2 hours, the lens and the attached release film are removed
from the vacuum plate and the release film is peeled away from the lens layer as shown at block
542. Next, the CA layer is cured for about 24 hours as shown in block 540, and then 1-3 μm of
CA is removed with a sandpaper, as shown in step 544, and the surface of the newly formed CA
layer Grind and prepare for adhesion to the stack.
[0120]
As shown in blocks 548, 550 and 552, the lens layer / CA layer formed composite is bonded to
the transducer stack. In one example, a lens layer / CA layer composite is bonded to the
underlying stack using a suitable low viscosity room temperature cure epoxy, such as Epotek
301, which has an acoustic impedance value close to that of the CA layer. In one aspect, a fixture
is used to hold the lens in place to maintain a pressure of at least about 100 kPa during curing of
the epoxy. In order to cure the epoxy with a thin bond line as described above, a further post
cure at high temperature using an external heat source is performed, which ensures the
formation of a bond line of less than 5 μm, preferably 1 μm to 3 μm. As the acoustic
impedance of the epoxy is similar to that of CA, it will be appreciated that the contribution of this
adhesive layer to the stack is negligible if at all.
[0121]
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The above-described exemplary method can be used to form a transducer stack in which the
center frequency of the piezoelectric layer ranges from about 5 MHz to about 60 MHz or more.
Such transducers can be used for imaging small animals, including rats, using high oscillation
frequencies (20 MHz and higher).
[0122]
Example 2: General high frequency design of an exemplary wide bandwidth (85 to 95%-6 dB
bandwidth) LiNb transducer with TPX lens Table 1 shows the different layers that make up the
exemplary transducer stack Indicates This stack design can be used for transducers with center
frequencies above about 20 MHz to 60 MHz.
[0123]
The design center frequency fD is chosen to be higher than the desired operating center
frequency f0 of the device to offset the mass loading which reduces the center frequency of the
device. fD is the frequency at which the device operates in air with no lens or air backing. In this
exemplary design, fD is chosen to be approximately 1.15 to 1.25 times the desired center
frequency of the final transducer. For example, for a 20 MHz device, fD = about 23-25 MHz is
chosen because of the relationships shown in Table 1 below.
[0124]
Throughout this application, various publications have been referenced. The disclosures of these
publications in their entireties are hereby incorporated by reference in order to more fully
describe the state of the art to which this invention pertains.
[0125]
Since modifications within the scope of the appended claims and their equivalents will be
apparent to those skilled in the art, the above detailed description is provided only to understand
exemplary practices of the present invention. It should not be understood as an unnecessary
limitation.
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[0126]
The above description of the present invention is provided as a teaching that enables the present
invention in the best presently known embodiment.
To this end, those skilled in the relevant art will recognize and understand that even with many
modifications to the various aspects of the invention described herein, the beneficial results of
the invention can be obtained. will do. It will also be apparent that some of the desirable benefits
of the present invention can be obtained by selecting some of the features of the present
invention without utilizing other features. Corresponding structures, materials, acts and
equivalents of all means or steps and functional elements in the following claims for performing
functions in combination with other claimed elements as specifically claimed. Intended to include
structures, materials, or acts.
[0127]
Unless expressly stated otherwise, it is not at all intended to be construed that for the methods
described herein, the steps should be performed in a particular order. Thus, if a method claim
does not actually list the order in which the steps should follow, or if it is not specifically stated
in the claims or description that the steps should be limited to a particular order: There is no
intention to imply order at any point. This may be, for example, any possible implicit
interpretation, such as a logical problem with regard to the arrangement of steps or operational
flow, a simple meaning derived from grammar constructs or punctuation marks, and the number
of types of embodiments described in the specification. The same holds true for the standard.
[0128]
Accordingly, those skilled in the art will recognize that many modifications and adaptations to
the present invention are possible and, in some circumstances, even desirable, which are also
part of the present invention. Other embodiments of the invention will be apparent to those
skilled in the art, given the specification and practice of the invention disclosed herein. Thus, the
above description is provided as an illustration of the principles of the present invention, but not
as a limitation. It is intended that the specification and examples be considered as exemplary
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only, with the true scope and spirit of the invention being indicated by the following claims.
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