Dual Frequency Ultrasonic Transducer

Abstract

To provide a manufacturing method of a dual frequency ultrasound transducer that is easier and / or less costly to manufacture.SOLUTION: A dual frequency ultrasound transducer includes a high frequency (HF) transducer with a piezoelectric layer 50, and a low frequency (LF) transducer that is positioned behind the HF transducer and has a piezoelectric layer 70. An intermediate layer 150 is positioned between the LF transducer and the HF transducer to absorb HF ultrasound signals. An alignment feature on the LF transducer is positioned with respect to a fiducial point that is marked at a known position with respect to HF transducer elements of the HF transducer to align LF transducer elements of the LF transducer with the HF transducer elements.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application is related to and claims the benefit of U.S. Provisional Patent Application No. 62 / 666,519, filed May 3, 2018, and U.S. Patent Application No. 16 / 051,060, filed July 31, 2018, which are hereby incorporated by reference in their entireties.

[0002] Statement on Federally Sponsored Research The subject matter of this application was made with Government support under Grant No. 5100220-Federal Report and Grant No. RO1CA189479 awarded by the National Institutes of Health (NIH). The United States Government has certain rights in the invention.

[0003] The disclosed technology relates to ultrasonic transducers, and more particularly, to dual frequency ultrasonic transducers. [Background technology]

[0004] In conventional ultrasound imaging, an ultrasound acoustic signal is directed at a region of interest and corresponding reflected echo signals are detected. Characteristics of the echo signals, such as their amplitude, phase shift, Doppler shift, power, etc., are analyzed and quantified into pixel data that is used to generate an image or representation of the flow. In conventional single transducer ultrasound imaging, the received ultrasound echo signals are in the same frequency range as the transmitted ultrasound signal.

[0005] Another approach to performing ultrasound imaging is to apply an ultrasound acoustic signal at one frequency to a region of interest and capture and analyze received echo signals at another frequency, such as one or more harmonics of the transmitted ultrasound signal. Typically, the harmonics have a frequency three to five times that of the transmitted signal. One particular application of harmonic imaging is imaging of tissues with contrast agents. Contrast agents are typically encapsulated microbubbles of fluid or lipid sized to resonate at a particular transmitted ultrasound frequency. Upon exposure to ultrasound in the body at the resonant frequency of the microbubbles, the bubbles burst and generate nonlinear ultrasound echoes that have a much higher frequency than the applied ultrasound. For example, nonlinear microbubbles resonate at 1-6 MHz, but can be designed to generate echo signals in the range of 10-30 MHz. The high frequency echo signals allow detailed images of tissue structures, such as the microvasculature surrounding tumors in clinical or preclinical settings, to be generated and observed.

[0006] The most common way to perform dual frequency imaging is with a mechanically scanned single element transducer with confocal low and high frequency transducer elements. Although such transducers work well, faster scans can be performed with transducer arrays that can be steered electronically. Such transducers typically have low and high frequency transducer arrays aligned with each other. One issue with dual frequency transducers is the alignment of the low and high frequency arrays. For a 30 MHz high frequency phased array, the element size (e.g., 1 / 2A or less) is about 25 microns. At 50 MHz, the element size is about 15 microns. For comparison, a typical human hair is about 80 microns in diameter. The procedure required to align the arrays often requires making fine adjustments to the positions of the high and low frequency transducers on a wet bench, then gluing them together when the best match is found. This is both time consuming and expensive. The technology described herein relates to an improved dual frequency transducer that is easier and / or less expensive to manufacture. Summary of the Invention

[0007] The dual frequency ultrasonic transducer includes a high frequency transducer and a low frequency transducer positioned behind the high frequency transducer. Alignment features on the low frequency transducer are positioned relative to a reference point marked at a known location positioned relative to the high frequency transducer. In one embodiment, one or more reference points are marked on an intermediate layer positioned between the high frequency transducer and the low frequency transducer. The intermediate layer is configured to absorb high frequency ultrasonic signals while passing lower frequency ultrasonic signals.

[0008] In one embodiment, the high frequency transducer includes a support frame including alignment posts that fit into cooperating slots or keyways on the intermediate layer to align the intermediate layer with the support frame and the high frequency transducer element. One or more reference points on the intermediate layer are positioned relative to the high frequency transducer element to align the low frequency transducer to the high frequency transducer element. [Brief description of the drawings]

[0009] [Figure 1A] FIG. 2 is a top view of a piezoelectric layer of a high frequency (HF) transducer in accordance with some embodiments of the disclosed technology. [Figure 1B] FIG. 2 is a top view of a piezoelectric layer of a low frequency (LF) transducer according to some embodiments of the disclosed technology. [Diagram 2] 1 is a partial isometric view of a conductive frame and piezoelectric layer of a high frequency transducer array in accordance with some embodiments of the disclosed technology; [Diagram 3] 1 is an isometric view of a piezoelectric layer, a flex circuit, and a conductive frame with alignment features formed on the back surface of the frame in accordance with some embodiments of the disclosed technology. [Figure 4] 1 is an isometric view of an intermediate layer that may be disposed between a low-frequency transducer and a high-frequency transducer according to some embodiments of the disclosed technology. [Diagram 5] FIG. 1 is a cross-sectional view of a dual frequency transducer with an intermediate layer in place over a high frequency transducer. [Figure 6] 6A-6D are top, side, and end views of an intermediate layer aligned with a radio frequency transducer according to an embodiment of the disclosed technology. [Figure 7A] FIG. 1 illustrates an isometric view of a piezoelectric layer of a low frequency transducer in accordance with some embodiments of the disclosed technology. [Figure 7B] FIG. 1 illustrates one embodiment of a low frequency transducer element dicing pattern in accordance with an embodiment of the disclosed technology. [Figure 8]FIG. 1 illustrates an isometric view of a low frequency transducer in accordance with some embodiments of the disclosed technology. [Figure 9] 9A-9C are end, top, and side views of a low-frequency transducer according to some embodiments of the disclosed technology. [Figure 10A] and [Figure 10B] FIG. 13 illustrates how connections are made between ground and signal traces in a flex circuit to electrodes for low frequency transducer elements and a common transducer ground electrode in accordance with one embodiment of the disclosed technology. [Figure 11] 1 is a cross-sectional view of a dual frequency transducer illustrating alignment of high frequency and low frequency transducer elements according to some embodiments of the disclosed technology. [Figure 12] FIG. 1 illustrates a housing for a dual frequency transducer according to an embodiment of the disclosed technology. [Figure 13] 13A-13H are diagrams illustrating multiple beam plots from a low frequency transducer in accordance with an embodiment of the disclosed technology. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The technology shown in the figures and described below relates to a dual frequency ultrasonic transducer. For purposes of illustrating how to make and use the disclosed technology, the components of a dual frequency transducer are shown. It will be understood that the figures are not necessarily drawn to scale.

[0011] FIG. 1 is a top view of a piezoelectric layer 50 for a high frequency ultrasonic transducer according to one embodiment of the disclosed technology. In one embodiment, the layer 50 has an outer frame 52 surrounding a sheet 54 of PZT, single crystal piezoelectric material, or other known piezoelectric material. In one embodiment, the frame 52 is a pre-machined non-conductive alumina ceramic with a central cutout area slightly larger than the outer dimensions of the sheet 54 of piezoelectric material. In other embodiments, the frame 52 can be made of a conductive material such as molybdenum or graphite. The frame 52 preferably has a similar coefficient of thermal expansion as the piezoelectric material to prevent the piezoelectric material from cracking during manufacturing, handling, or use. An adhesive 56, such as EPO-TEK 301 epoxy, fills the gap between the frame and the piezoelectric material. The piezoelectric material 54 is diced with a patterning laser or dicing saw to produce a large number (e.g., 128, 256, or fewer, or more) of piezoelectric elements (not shown separately). By surrounding the sheet 54 of piezoelectric material with a frame 52, the kerf cuts that define the individual transducer elements can extend across the entire width of the sheet of piezoelectric material.

[0012] If the frame 52 is made of a non-conductive material, the cutout areas or notches 60 on one or both sides of the frame can be filled with conductive epoxy or can include a number of conductive vias to provide an electrical path from the front side of the frame to the rear side of the frame. Further details regarding the construction of ultrasonic transducers with peripheral frames can be found in commonly owned U.S. Patent Application No. 151993,156, filed May 30, 2018, and U.S. Provisional Application No. 62 / 612,169, filed December 29, 2017, which are incorporated herein by reference in their entireties.

[0013] FIG. 1B shows a piezoelectric layer 70 of a low frequency ultrasonic transducer, which in one embodiment is constructed similarly to the piezoelectric layer of the high frequency transducer shown in FIG. 1A. An alumina frame 72 surrounds a sheet 74 of piezoelectric material. The frame 72 has a central opening sized to form a gap between the edge of the opening and the edge of the piezoelectric sheet 74. The gap is filled with a non-conductive epoxy 76. The low frequency array has fewer transducer elements than the high frequency transducer. In one embodiment, the low frequency transducer has 32 individually addressable transducer elements, but can have fewer or more elements. A pair of cut-out areas or notches 80 on either side of the frame 72 can be filled with conductive epoxy or can include conductive vias through the frame to provide an electrical path from the front of the low frequency array to the rear of the frame.

[0014] FIG. 2 is an isometric view of a conductive support frame 100 that may be secured to the rear surface of a piezoelectric layer 50 of a high frequency transducer. The frame 100 supports one or more flex circuits (not shown) having signal traces that are electrically connected to corresponding electrodes on each high frequency transducer element. Additionally, the support frame 100 provides electromagnetic shielding for the rear surface of the transducer elements. A common ground electrode on the front surface of the piezoelectric layer 50 is connected to a ground plane in the flex circuit through a conductive path that includes the conductive support frame 100. In one embodiment, the support frame 100 is secured to the piezoelectric layer 50 with conductive epoxy. Also shown in FIG. 2 are one or more matching layers and lenses disposed in front of (e.g., in front of) the piezoelectric layer 50.

[0015] FIG. 3 shows one flex circuit 104 attached to the support frame 100. In some embodiments, the high frequency transducer includes two flex circuits with one flex circuit signal traces electrically coupled to the even numbered transducer elements and the other flex circuit signal traces electrically connected to the odd numbered transducer elements. Electrical connections are made from the individual transducer elements on the rear surface of the piezoelectric layer to metal signal traces in the flex circuit. The connections between the transducer elements and the metal signal traces in the flex circuit can be made using techniques described in U.S. Patent Publication No. 2017 / 0144192 or U.S. Patent No. 8,316,518, which are incorporated by reference in their entireties. After the connections are made, the open rear side of the support frame is filled with an epoxy material 110, such as EPO-TEK 301. In one embodiment, the height of the epoxy 110 in the frame extends above the edge of the support frame 100. As shown in FIG. 3, the epoxy 110 is molded or laser machined to form a pair of alignment posts 112a, 112b and a recessed area 114 behind the high frequency transducer element. In one embodiment, the recessed area 114 is about 4.2 mm deep. The alignment posts 112a, 112b are configured to align the intermediate layer over the high frequency transducer, as described below. A pair of reference points 120a, 120b are laser marked on each alignment post at a known distance from the high frequency transducer element. The reference points 120a, 120b serve as references so that other components of the dual frequency transducer can be placed in known positions relative to the high frequency transducer element.

[0016] FIG. 4 shows one embodiment of the intermediate layer 150 that is placed behind the high frequency transducer. In one embodiment, the intermediate layer 150 is composed of silicone powder doped EPO-TEK 301 epoxy. The size of the silicone powder is in the nanometer range to highly attenuate high frequency (HF) ultrasound and pass low frequency (LF) ultrasound. The intermediate layer is sized to absorb high frequency ultrasound up to a certain level, such as 65 dB, but pass low frequency signals transmitted from or received by the low frequency transducer. The top of the intermediate layer 150 includes a pair of slots or keyways 152a, 152b that cooperate with alignment posts 112a, 112b on the back side of the frame 100 to align the intermediate layer 150 in a known position relative to the transducer elements of the high frequency transducer. In one embodiment, the intermediate layer 150 is secured to the frame 100 using the same epoxy that fills the back side of the frame to avoid acoustic discontinuities at the bond line.

[0017] Once the intermediate layer is secured to the frame 100, additional datums 154a, 154b can be placed on the intermediate layer as measured from datums 120a, 120b marked on the support frame (i.e., on the filled epoxy on the backside of the support frame).

[0018] FIG. 5 shows a cross section of a high frequency transducer with an intermediate layer 150 fixed to the back of a support frame 100. As shown, the high frequency transducer includes a lens 130 designed to focus high frequency ultrasonic signals at a specific depth. Typical lens materials include polymethylpentene (TPX), cross-linked polystyrene (Rexolite) or polybenzimidazon (Celezole). However, other non-damping plastic materials can be used. Behind the lens are one or more quarter-wave matching layers 132 that match the impedance of the piezoelectric layer 50 to that of the lens 130. The matching layer or layers are typically formed by adding particles to an epoxy to adjust its acoustic impedance. A metal (e.g., gold or gold+chrome) common ground electrode is deposited on the front of the piezoelectric layer 50 and is electrically coupled to the conductive support frame 100 through a slot or via in the frame 52 that surrounds the PZT material. An applied metallization on the rear or proximal surface of the piezoelectric layer provides a conductive path from the individual transducer elements to the signal traces in the flex circuit. A layer of epoxy 110 covers the proximal side of the transducer elements and fills the rear side of the support frame. In one embodiment, recesses 114 formed in the epoxy behind the high frequency transducer array are sized such that the intermediate layer is larger in the elevation and azimuth dimensions of the transducer than the size of the transducer elements, such that the intermediate layer extends over the ends of the high frequency transducer elements.

[0019] 6A-6D show paired reference points 154a, 154b marked on the top surface of the intermediate layer 150. The reference points 154a, 154b are measured against reference points 112a, 112b marked on the epoxy in the support frame. The reference points 154a, 154b are marked on the intermediate layer once it is secured to the support frame behind the high frequency transducer. In the illustrated embodiment, the reference points 112a, 112b, 154a, 154b are laser-made crosses.

[0020] FIG. 7A illustrates one embodiment of a piezoelectric layer 70 for a low frequency transducer. In the illustrated embodiment, the piezoelectric layer 70 also includes an alumina frame that surrounds a sheet of PZT or other piezoelectric material. In one embodiment, the sheet of PZT is diced into multiple rows of triangular prisms as a 1-3 composite, as best shown in FIG. 7B. In the illustrated example, each row 72a, 72b, 72c of triangular elements 74 is treated as a single transducer element. In FIG. 7B, only 12 rows of transducer elements are shown for illustration purposes. In one embodiment, the low frequency transducer includes 32 rows of triangular elements. However, the low frequency transducer can include fewer or more rows, as desired. Additionally, each transducer element in the low frequency transducer may have other shapes, such as small square or rectangular shaped elements.

[0021] FIG. 8 is an isometric view of a low-frequency transducer according to one embodiment of the disclosed technology. The low-frequency transducer includes a piezoelectric layer 70, one or more matching layers 160 disposed in front of (e.g., in front of) the piezoelectric layer 70, and a backing layer 170 disposed behind the transducer elements. A flex circuit 180 includes signal traces that are electrically connected to the individual low-frequency transducer elements. The low-frequency transducer also includes a pair of alignment tabs 162a, 162b. In one embodiment, the alignment tabs are Kapton® sheets inserted into the epoxy matching layer at a location away from the location of the low-frequency transducer elements so as not to interfere with the operation of the low-frequency transducer elements. Other materials for the alignment tabs, such as alumina, can also be used. Holes 164a, 164b are located in the alignment tabs at a known distance from the low-frequency transducer elements. The holes are located over reference points on the high-frequency transducer to precisely align the low-frequency transducer elements relative to the high-frequency transducer elements.

[0022] In one embodiment, the holes 164a, 164b in the alignment tabs 162a, 162b are positioned over reference points on the intermediate layer. If the alignment tabs are long enough, the holes in the alignment tabs can be positioned over reference points marked on the support frame to align the low frequency transducer with respect to the high frequency transducer.

[0023] FIG. 9A is a cross-sectional view of a low-frequency transducer according to one embodiment of the disclosed technology. The transducer includes a piezoelectric layer 70 and two matching layers 160 disposed in front of the piezoelectric layer. The matching layers match the impedance of the low-frequency piezoelectric element to the impedance of the intermediate layer to which the low-frequency transducer is fixed. A backing layer 170 is disposed behind the low-frequency transducer element. As shown in FIG. 9C, alignment tabs 162a, 162b are part of the matching layer in front of the low-frequency transducer element. The alignment tab holes 164a, 164b are positioned a known distance from the low transducer element as seen in FIG. 9B. A flex circuit 180 extends from underneath the backing layer where connections are made to the transducer elements.

[0024] 10A and 10B show one way of connecting the signal and ground traces of the flex circuit to the corresponding electrodes of the low frequency array. As shown in FIG. 10A, the flex circuit 180 includes a number of signal traces 182 and ground traces 184. The ground traces 184 are electrically connected to the ground electrodes on the front side of the low frequency array with conductive epoxy 186 bonded to conductive epoxy 188 in the notch 80 of the frame 70 or vias in the frame. As shown in FIG. 10B, the exposed ends of the signal traces 182 can be adhesively secured to the transducer elements with conductive epoxy. Because the transducer elements of the low frequency transducer are relatively large, they can be easily aligned with the signal traces 182 in the flex circuit 180.

[0025] FIG. 11 is a cross-sectional view of a dual frequency transducer according to one embodiment of the disclosed technology. The low frequency transducer element 71 is directly aligned with the high frequency transducer element 51 by locating the holes on the alignment tabs 162a, 162b over reference points on the intermediate layer. The holes on the alignment tabs are located in known positions relative to the low frequency transducer element, and the reference points are precisely located in known positions relative to the high frequency transducer element. Thus, locating the holes over the reference points on the intermediate layer precisely positions the low frequency transducer element relative to the high frequency transducer element without the need to align the transducers on a wet bench.

[0026] FIG. 12 illustrates one embodiment of a transducer housing 200 enclosing a dual frequency transducer array. In the illustrated embodiment, the housing includes separate cables 202, 204 connecting the low frequency transducer and the high frequency transducer. In one embodiment, the low frequency transducer can be used alone to image tissue with low frequency ultrasound (e.g., in the 4-10 MHz frequency range). Similarly, the high frequency transducer can be used to image tissue with high frequency ultrasound (e.g., in the 20-50 MHz frequency range). Alternatively, both transducers can be used to perform imaging such as harmonic or contrast imaging where the region of interest is non-harmonic with the signal from the low frequency transducer and ultrasound echo signals at harmonics of the excitation frequency are detected at the high frequency transducer.

[0027] 13A-13H are sample beam plots of a portion of a low-frequency transducer operating in plane wave imaging mode. In one embodiment, a 32-element low-frequency transducer is placed behind a 256-element high-frequency transducer. Electrical matching with a 1:3 mini-transformer brings the impedance of the low-frequency transducer elements from about 500 ohms to about 47.2 +1-2.6 ohms, with a phase of minus 60.1 +1-5.5 degrees. The single low-frequency element peak-peak pressure measured 1.7 mm from the lens increased from 0.77 kPaN without matching to 1.51 kPa / V with matching ranging from 6 to 140 V, with a variation of about +5°. / .0 across the element. In plane wave imaging, the pressure is 3 times higher than for the single element. Focusing is observed in the 5.5 mm elevation plane with a 6 dB beamwidth of 2.7 mm (FIGS. 13A, 130). Past the focus, the pressure drops as the wavefront diverges (Figure 13E). In the azimuth direction, the beam is relatively uniform (no apodization) with a 2 dB variation from the maximum on the edges (Figures 13B, 13D). Beam steering is achieved for angles of +1-18 degrees (Figures 13F-13H), allowing planar compounding.

[0028] From the foregoing it will be appreciated that, although specific embodiments of the invention have been described for purposes of illustration, various modifications may be made without deviating from the scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.

Claims

1. 1. A method for manufacturing a dual frequency transducer, comprising: Providing a high frequency (HF) transducer having a first sheet of piezoelectric material including an HF transducer element, one or more first matching layers, and a high frequency frame; affixing a surface of the first sheet of piezoelectric material to a support frame comprising an epoxy material; forming at least one alignment post in the epoxy material; marking one or more reference points on the at least one alignment post; disposing an intermediate layer on a first side of the HF transducer element, the intermediate layer configured to absorb HF ultrasonic signals, the intermediate layer including at least one slot configured to engage the at least one alignment post; aligning the one or more reference points with a low frequency (LF) transducer, the LF transducer including one or more tabs having alignment features for aligning the LF transducer with the one or more reference points, a second sheet of piezoelectric material including LF transducer elements, and one or more second matching layers; affixing the one or more second matching layers to the intermediate layer; A method comprising:

2. The method of claim 1 , wherein the alignment features include holes on alignment tabs at known positions relative to the LF transducer elements of the LF transducer.

3. The method of claim 1 , wherein the intermediate layer is comprised of an epoxy doped with silicone powder.

4. The method of claim 3 , wherein a surface of the support frame is filled with epoxy having a recess into which a portion of the intermediate layer is recessed.

5. The method of claim 4 , wherein the intermediate layer is adhered to the recess with the same epoxy in which the recess is formed.

6. The method of claim 1 , wherein the intermediate layer is disposed over an area of ​​the HF transducer element within a piezoelectric material of the HF transducer.

7. 2. The method of claim 1, wherein the intermediate layer includes at least one reference point marked at a known position relative to the HF transducer element, and the alignment feature on the LF transducer is aligned with the at least one reference point on the intermediate layer.

8. The method of claim 1 , wherein at least one of the tabs includes a hole for placement over the one or more reference points on the HF transducer.

9. The method of claim 1 , wherein the one or more tabs of the LF transducer are embedded in the one or more second matching layers of the LF transducer.

10. the first sheet of piezoelectric material further comprising a periphery having an edge; 2. The method of claim 1 , wherein the support frame surrounds the periphery of the first sheet of piezoelectric material and is spaced from the edge of the periphery such that kerf cuts defining individual transducer elements of the first sheet of piezoelectric material extend across an entire width of the first sheet of piezoelectric material.

11. 1. A method for manufacturing a dual frequency transducer, comprising: providing a high frequency (HF) transducer comprising a sheet of piezoelectric material including a plurality of HF transducer elements; disposing an intermediate layer on a first side of the HF transducer element, the intermediate layer being configured to absorb HF ultrasonic signals and pass low frequency (LF) ultrasonic signals; providing one or more reference points marked on the first side of the HF transducer element at known positions relative to the HF transducer element; providing a low frequency (LF) transducer including a plurality of LF transducer elements including one or more alignment tabs aligned using the one or more reference points to align the LF transducer elements with the HF transducer elements; fixing the LF transducer to the intermediate layer; A method comprising:

12. The method of claim 11 , further comprising incorporating the one or more alignment tabs of the LF transducer into a matching layer of the LF transducer.

13. The method of claim 12 , further comprising inserting the one or more alignment tabs into an epoxy layer that forms the matching layer.

14. 14. The method of claim 13, further comprising aligning the LF transducer element with respect to the HF transducer element by positioning holes in the one or more alignment tabs over the one or more reference points.

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