Acoustic transducer and method of manufacturing

Abstract

An acoustic transducer array and a method for manufacturing the same. A first metal layer is deposited on a first side of a piezoelectric composite material to form a common electrode, and a second metal layer is disposed on a corresponding side. Portions of the second metal layer are removed to produce a plurality of individual electrodes. A third metal layer may be deposited onto the plurality of individual electrodes, the third metal layer being thicker than the second metal layer. The individual electrodes extend out of the piezoelectric composite material in a vertical direction to produce electrode leads. The metal layers may be provided by photolithography, wireframes, or foils.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to UK application GB1915002.8 filed on October 17, 2019, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to acoustic transducers, and in particular piezoelectric transducers, which may be combined with imaging probes for use in medical examinations and non-destructive testing of structures such as pipes, wells, or manufactured parts. Background Art

[0004] Piezoelectric transducers are commonly used for non-destructive testing (NDT) and inspection of objects and structures by ultrasonically processing the object or structure with sound waves emitted by the transducer and receiving sound reflections from surface features and internal features. The received reflections are converted into electrical signals by the transducer, and these signals are processed by an audio and video processor.

[0005] Ultrasonic transducers are able to inspect at higher resolution (sub-millimeter) by inspecting features of an object with shorter wavelengths. Arrays of tens or hundreds of transducer elements can be manufactured together. There are many methods of manufacturing acoustic transducers. Patent application US20050000279A1 by Schlumberger entitled "Acoustic sensor for downhole measurement tool" discloses a method of manufacturing.

[0006] Figure 2 shows a known transducer stack in which a single PZT / epoxy composite block 22 is coated with thin gold layers 23, 25 on the top and bottom. Individual electrodes are defined by cutting through the top gold layer 25 and then soldering wires 24 to each electrode with solder 29.

[0007] After the transducer stack is manufactured, the electrical leads must be welded to the electrodes. This causes defects in transducers formed in this way. In high-resolution arrays, the fine spacing of the elements and leads makes it difficult to work and increases the possibility of short circuits between adjacent elements. The solder 29 and lead coverings of the piezoelectric elements produce anomalies in the transducer or the received signal. When the Curie temperature is exceeded, the heat used when welding to the transducer may affect the piezoelectric effect. The inventors have also observed that operation in certain harsh environments (such as high temperature, high pressure and the presence of chemicals) may cause the weld seam to crack. Summary of the invention

[0008] According to a first aspect of the present invention, a method for manufacturing an acoustic transducer array is provided, the method comprising the following steps: depositing a first metal layer on a first side of a piezoelectric composite material to form a common electrode; providing a carrier structure adjacent to a piezoelectric composite material substrate on a side of the composite material perpendicular to the first side; depositing a second metal layer on the carrier structure and on a second side of the piezoelectric composite material opposite to the first side using photolithography; selectively removing a portion of the second metal layer to produce a plurality of individual electrodes; depositing a third metal layer on the plurality of individual electrodes; wherein the third metal layer is thicker than the second metal layer and extends beyond the piezoelectric composite material [along the longitudinal direction of the element] to produce an electrode lead; and separating the carrier structure from a transducer stack comprising the piezoelectric composite material and the metal layer.

[0009] According to a second aspect of the present invention, a method for manufacturing an acoustic transducer array is provided, the method comprising the following steps: providing a piezoelectric composite substrate; depositing a first metal layer on a first side of the piezoelectric composite substrate to form a common electrode; depositing a second metal layer to a second side of the piezoelectric composite opposite to the first side; covering and connecting the second metal layer with a third metal layer, wherein the third metal layer is thicker than the second metal layer and extends beyond the piezoelectric composite [along the lateral direction of the composite]; and removing portions of the second metal layer and the third metal layer to produce a plurality of individual electrodes.

[0010] The method can manufacture at least two arrays in a single batch by providing at least two separate substrates or substrates sized to form at least two arrays, followed by depositing and forming thick electrodes extending beyond the substrates.

[0011] According to a third aspect of the present invention, there is provided an acoustic transducer array, the array comprising: a piezoelectric composite material; a first metal layer on a first side of the piezoelectric composite material defining a common electrode; a second metal layer on a second side of the piezoelectric composite material opposite to the first side; a second metal layer connected to the first metal layer and extending outside the piezoelectric composite material, wherein the second metal layer is thicker than the first metal layer; and wherein the metal layers are formed to define a plurality of individual electrodes.

[0012] Thus, a more robust transducer can be produced that is able to withstand high temperatures and pressures. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Various objects, features and advantages of the present invention will become apparent from the following description of embodiments of the present invention and the accompanying drawings, which are not necessarily drawn to scale, emphasis instead being placed upon illustrating the principles of various embodiments of the present invention.

[0014] Figure 1 is a cross-sectional view of a transducer stack according to a preferred embodiment.

[0015] FIG. 2 is a cross-sectional view of a transducer stack according to the prior art.

[0016] Figure 3 is a cross-sectional view of a transducer stack according to an embodiment having a single metal layer addressable electrode.

[0017] Figure 4A are plan views of the transducer at various initial stages of lithography.

[0018] Figure 4B are plan views of the transducer at various subsequent stages of photolithography.

[0019] Figure 5 is a side view of a transducer stack with overlapping and cut wireframes.

[0020] Fig. 6A This is a plan view of the wireframe before cutting.

[0021] Figure 6B is an enlarged plan view of the addressable electrodes before cutting.

[0022] Fig. 7A This is the plan view of the wireframe after cutting.

[0023] Figure 7B is an enlarged plan view of the addressable electrodes after cutting.

[0024] Figure 8 Is a set of steps in the photolithography process used for transducers.

[0025] Fig. 9 is a flow chart for assembling a transducer array.

[0026] Fig. 10A is an illustration of a conical probe with a transducer array.

[0027] Fig. 10B is an illustration of a radial probe with a transducer array.

[0028] Fig.11 is a cross-sectional view of a downhole acoustic probe in a tubular.

[0029] Like reference numerals refer to like parts with the following key information:

[0030] 2. The surface to be studied;

[0031] 10 devices;

[0032] 11 scan lines;

[0033] 12 acoustic transducer array;

[0034] 15 frustoconical mount;

[0035] 21 matching layer;

[0036] 22Piezoelectric composite materials;

[0037] 23 common electrode;

[0038] 24 extension part / lead part;

[0039] 25 thin electrodes;

[0040] 26 thick electrode;

[0041] 27 electrode part;

[0042] 28 backing layer;

[0043] 29 solder;

[0044] 30 Wireframe;

[0045] 37 Carrier structure;

[0046] 42 Cutting piezoelectric composites;

[0047] 43 Photoresist;

[0048] 44 UV mask;

[0049] 45 Etching area

[0050] 46 Cured photoresist

[0051] 47 Thin metal seed layer;

[0052] 48 Thick metal plating;

[0053] 49 backbone / carrier frame;

[0054] 51 metal foil

[0055] 53 Cutting Line

[0056] 54 (Conductive) Adhesive

[0057] 55 Laser

[0058] 59 Cutting saw DETAILED DESCRIPTION

[0059] With reference to the accompanying drawings, a preferred embodiment of an acoustic transducer, its composition and construction are described. The transducer comprises a plurality of transducer elements arranged in a one-dimensional array. A single electrode on each transducer element extends as a continuous layer through the underlying piezoelectric composite material, thereby electrically and mechanically connecting to the wires of the drive circuit. The single electrode can be a single thick metal layer or comprise at least two metal layers (a seed layer and a thick metal layer).

[0060] Fabrication involves a combination of techniques for adding metal layers, and then selectively removing portions to form the individual electrodes of the element, in addition to other layers common to the acoustic stack, where portions extend outside the piezoelectric composite. Some methods use a support structure to deposit the layers.

[0061] Transducer array

[0062] The frequency of the acoustic waves generated by the transducer 12 is typically in the range of 200 kHz to 30 MHz and can be designed based on a variety of factors, including: the type of fluid, the velocity in the well, and the speed at which the imaging device is moved. In most applications, the wave frequency is ultrasonic, operating at a frequency of 1 to 10 MHz. Higher frequencies (shorter wavelengths) can distinguish finer features on the surface by returning different reflections from each feature.

[0063] The number of individual elements in the transducer array affects the resolution of the image produced. Typically, each transducer array consists of 32 to 2048 elements, preferably 128 to 1024 elements. Using a relatively large number of elements can produce high-resolution images of the object. The circuits to drive and capture these arrays are also generally available commercially.

[0064] 2 shows a side view of an exemplary transducer stack prepared according to known methods, which includes: a common electrode 23, a piezoelectric composite block 22, a top electrode 20 and a matching layer 21. Electrical leads 24 are attached to the top electrode 25 by solder 29, so that the element can be activated individually. Due to the irregular geometry and the loss of piezoelectric effect when soldering exceeds the Currie temperature, the part of the element close to the solder 29 and the lead 24 will emit acoustic anomalies.

[0065] Thus, in a preferred transducer and manufacturing method, the electrodes are placed substantially continuously over the entire height (elevation) of the element and extend beyond the piezoelectric substrate in the vertical direction. Thus, connection to the leads by welding or clamping occurs at a location away from the piezoelectric region. Preferably, the extension 24 extends beyond the composite material by at least 2 mm in the vertical direction of the transducer.

[0066] Figure 1A side view of a single element transducer stack is shown, where the array of elements would extend into the page. A first major surface of the piezoelectric composite 22 is coated with a conductive material to serve as a common electrode 23 for the array. The opposing second surface is coated with a second conductive material on a per element basis to form addressable (thin) electrodes 25. These electrodes activate the piezoelectric posts in the composite 22, causing them to vibrate generally perpendicular to the first and second surfaces.

[0067] One of the electrode surfaces may be designated as the transmission surface within the probe, designed to face the subject of study, while the other electrode surface is designated as the backside. A backing layer 28 may be attached to the backside to provide structural and acoustic damping for the transducer and / or adhesion to secure the transducer to the probe. The backing layer 28 may be conductive (e.g., tungsten impregnated epoxy) or non-conductive (e.g., glass-filled polyetheretherketone).

[0068] The matching layer 21 covers the transmission surface and is preferably designed to have an acoustic impedance value that is the geometric mean of the lens and the composite material and a thickness that is one quarter of the design wavelength of the transducer. This is to allow the acoustic wave to be transmitted through the matching layer with maximum energy and minimum artifacts. The matching layer can be an epoxy resin filled with Al2O3.

[0069] As an example, a stack may include: a composite material 0.3 mm thick; a backing layer 10 mm thick; a sputtered thin electrode 0.6 μm thick; and a thick electrode 15 to 40 μm thick.

[0070] For simplicity, we assume that the composite material 22 is a plate made of piezoelectric pillars, which are cut along the thickness of the plate, surrounded by a matrix of softer material (such as epoxy resin), which is currently available on the market. This ensures that the combined vibration of all pillars is perpendicular to the main surface of the plate. The composite material can be a commonly available 2-2 or 1-3 PZT.

[0071] Figure 1 The stack further comprises a thick conductive layer 26 in electrical contact or partial electrical contact with the thin electrode layer 25. Thus, the full electrode of each element comprises a first thin layer 25 and a second thick layer 26. Typically, layer 26 is at least one order of magnitude thicker than layer 25. Both layers extend through the height of each transducer element to activate the underlying piezoelectric material, and layer 26 extends through the piezoelectric composite material, typically continuing in the height dimension to form a lead portion 24.

[0072] Layers 25 and 26 are made of a conductive material (usually a metal) and may be the same material. Good choices for these materials include: gold, chromium, silver, copper and nickel. As described below, the choice may be determined by material cost and manufacturability of a given step in the process.

[0073] Overall Manufacturing

[0074] Similar to known methods, the present transducer array is constructed in layers, removing areas of the layer where the material is not needed. Figure 4A The initial stages of fabrication are shown starting with a piezoelectric composite plate 22 that has been ground flat on both major surfaces. Since the plate is typically quite wide relative to a single array, multiple strips 42 of composite material are cut (step 2) and then placed separately on a base, preferably held in place and separated by a temporary sacrificial support 37 (step 3). The support material can be a wax, metal, epoxy, or plastic frame. The support structure can have voids in it to accommodate the composite strips. The support material not only holds the strips in place, but also provides a means to accept metal atoms and support electrode layers, where the electrode layers extend beyond the composite strips. The support structure can be a material that is placed near or molded around the composite and then ground to be coplanar with the composite. In an alternative embodiment, the piezoelectric composite strip 42 is wider than the width required for the transducer for active use. This additional "sacrificial" portion provides a carrier for accepting and supporting the metal layers 25 and / or 26, and the "sacrificial" portion is machined near the end of the manufacturing process to expose the extension 24.

[0075] like Figure 4B As shown, a thin layer 47 of conductive material is deposited on the top and bottom of the composite surface as electrodes 23, 25, and on a carrier 37. These layers can be added to the composite plate early in the process, which is generally the same as commercially available piezoelectric composites. Since the composite is not conductive, a form of electroless deposition is used to add the thin electrode layer, such as vacuum deposition (including physical / chemical vapor deposition, evaporative deposition and sputtering), electroless plating by immersion or adhesion of foil or fine wire frame. This layer 47 may be thin (i.e., 0.2μm to 3μm) and weak, but its purpose is to form a bond between the composite and subsequent layers. The thin layer 47 may actually include a continuously changing layer of different metals or multiple sub-layers.

[0076] On top of the thin layer 47, a thick electrode layer 48 is added to provide strength and stability at elevated temperatures and high pressures. This layer forms the electrode 26, extending beyond the composite stack to provide an electrode lead portion 24 that can then be connected to a flexible circuit conductor. The carrier 37 provides a ground to deposit and hold the extension, especially when an addressable element is present or formed.

[0077] Alternatively, the common electrode layer 23 is coated with an adhesive layer 28, preferably a conductive adhesive layer, so that when assembled in a device, the common electrode can be easily contacted by electrical leads. The common electrode may be 0.6 μm thick and provided with a composite material.

[0078] The electrode layer 26 is either preformed from separate electrodes, each having extensions 24, or is formed after the layer is coupled to the thin electrode. Figure 4B The intermediate step of FIG. 4 shows the removal (by etching or cutting) of region 45, leaving intact electrode 26 on each piezoelectric element. More preferably, electrode 26 is patterned (by etching or ablation) to form an extension 24 on the composite material that is narrower than portion 27 (see FIG. Figure 7B ). This narrowing creates more space between the leads, facilitating subsequent connection to electrical leads or creating traces in a circuit (see below). For example, the array may have a pitch of 400 μm, and the transducer elements (and therefore electrode portions 27) are only 75 microns apart, making welding or clamping very difficult. Therefore, the extension portion 24 may be narrowed to less than 150 μm to create a separation of at least 250 μm.

[0079] The number of transducer elements, their spacing and the drive frequency λ affect the imaging quality. In acoustic transducers, a useful rule is that the spacing should range from λ / 2 to λ to minimize grating lobes. Thus, in one embodiment, there may be 128 elements, spaced 300 μm apart (equal to λ), driven at 5 MHz in water. In very high resolution arrays, the spacing may be 150 μm.

[0080] The transducer array can be separated by removing the carrier (i.e., melting the wax or pulling off the frame). Figure 4B As shown in the last step, multiple arrays 12 have been made in one batch. For rigidity, the extensions can be connected together by transverse "skeleton" portions 49, which will be cut when connected to the electrical leads (see Figure 8 skeleton 49).

[0081] The matching layer 21 is molded, ground and shaped separately and then bonded to the thick electrode 26. The multiple arrays can then be removed from the carrier 37 and separated from each other.

[0082] The array is bonded to a backing layer after it is formed. The flat stack is then shaped to match the shape of the device housing, typically a cone or ring. Leads from the flex circuit are connected to separate extensions by soldering or ultrasonic welding. The lens is coupled to a matching layer using a material selected to have an impedance value similar to that of the fluid in the well.

[0083] Foil Lamination:

[0084] Figure 5 The electrodes 26 are provided on the side of the array using foil. The foil 51 is a thin, ductile sheet of metal bonded to the top of the stack 23 / 22 / 25, preferably by a conductive adhesive 54, and the end portions extend beyond the ceramic 22. The adhesive may comprise an epoxy, such as a B-stage epoxy, and may contain silver and other conductive particles to electrically couple the thin electrode layer 25 to the foil 51. This may comprise a 50 μm thick epoxy and a 15 μm thick foil. An example of a suitable adhesive is Loctite TM Ablestik TM CF3350、Mereco's TM Metacase TM 401 and Rogers Corporation's TM CoolSpan TM TECA film.

[0085] The foil 51 may be formed into a single electrode prior to bonding (similar to Fig. 6A The common connector 49 provides a framework for holding the components together during assembly, which is then removed by cutting or severing after the electrodes have been bonded, as shown by line 53.

[0086] Alternatively, individual electrodes are formed in the foil after bonding, each electrode including a portion extending outside the composite material. The electrodes may be formed by chemical etching, laser ablation or cutting. Figure 5 As shown, laser 55 patterns the electrode by ablating the foil ends to overhang. If desired, the overhanging portion can be supported by a carrier pad (not shown) during laser cutting. Foil 51 is cut by saw 59 to form a single thick electrode / lead 26 that is thicker and stronger than thin electrode 25. During this step, cuts are made through layers 25, 26, 54 and a small amount into composite material 22. The depth of the cut can be 10-200 μm. This separates the composite material into individual transducer elements, which can be individually addressed by the electrodes 26 bonded thereto.

[0087] Single wireframe

[0088] In a preferred embodiment, the wire frame 30 can be manufactured separately and placed on the cut composite material with the thin electrodes 25. Fig. 6A As shown in FIG. 6B, a separately manufactured wireframe 30 may include an array of preformed leads 24 connected together by a skeleton 49. The leads 24 are spaced and sized to align with each transducer element that has been (or will be) produced by cutting the composite material. The end portion of each lead may be ultrasonically welded or soldered to the end of a thin electrode 25.

[0089] This connection can be weak and affect the piezoelectric effect, but it can be minimized by connecting the ends with minimal overlap and then strengthening the connection by electroplating a thick conformal layer over the leads 24 and thin electrodes 25. The wireframe and composite are placed in a copper ion bath and the cathode is connected to the bobbin 49. The plated layer becomes the thick electrode 26.

[0090] The wireframe is made of a thin layer of conductive material, for example 15-40 μm copper foil. Before connection to the stack, the undesired areas of conductive material around the electrodes are removed, preferably by etching, cutting away or laser ablation.

[0091] Lithography:

[0092] like Figure 8 As shown, the electrodes can also be produced by additional photolithography. Starting from the cut epoxy resin filled composite material 22, a negative resist 43 is spin-coated on the composite top surface 22 and the carrier 37. The carrier 37 surrounds the composite material to keep it in place and provides a substrate for constructing the electrode extension portion 24. A transparent field mask 44 is placed on the composite material, and UV light is applied through the transparent field mask 44 to selectively cure the resist. The uncured area defines the area that will be covered by the electrode 25, which can be patterned to include a wide electrode portion, a narrow extended lead portion, and a skeleton 49 that connects the leads together. The uncured photoresist is then washed off with a detergent (e.g., 2% tetramethylammonium hydroxide).

[0093] A thin metal layer 47 is electrolessly deposited (e.g. by vapor deposition) over the existing resist, carrier and composite material. The metal may be copper, chromium, gold or a combination that can form some bond with the composite material and carrier.

[0094] Thick metal layer 48 is electroplated to thin metal layer 47 to produce full electrode 26. This thick metal layer 48 is coupled to thin layer 47 in a conductive and mechanical manner, and substantially covers layer 47 (on each electrode 25). Therefore, the voltage applied to lead 24 excites the entire electrode and the composite material below it, and the uniform covering ensures that the wave is uniformly transmitted through the metal layer. Skeleton 49 can provide electrical connection with the cathode in the electroplating bath, and the electroplating bath contains metal ions, such as copper. Preferably, relative to electroplating layers 47, 48, the photoresist layer is thick enough so that the metal on the cured and uncured photoresist layer will not bridge. Similarly, the metal ion concentration and the electroplating rate should be low enough so that no bridging occurs between the separated electrodes.

[0095] Acetone can be used to remove the cured photoresist, and also removes the thin and thick metal layers attached thereto. The entire stack with the extended leads 24 is then removed from the carrier 37 for subsequent soldering to the circuit and cutting of the skeleton 49.

[0096] Single electrode layer

[0097] In certain preferred embodiments, a single electrode is formed as a layer 26, such as Figure 3 Here, the thick layer 26 provides both mechanical strength for connecting the electrical leads to the transducer stack and a uniform layer through which the waves can propagate. The metal layer 26 can be formed by electroless plating, vacuum deposition (VD), or by bonding a foil or wireframe directly to the top of the composite material using an adhesive layer 54. In all cases, the electrode will extend out of the composite material in the vertical direction to connect to a single lead of a circuit connector. The thickness of the metal layer can be 10-40 μm.

[0098] Advantageously, certain transducers made using this method will be easier to make and provide a more consistent layer through which waves can propagate.

[0099] Arc array

[0100] Conical radial transducer arrays are fabricated by placing the array backing on a truncated cylindrical surface (see Fig. 10A ) to arrange the elements facing radially outward and partially longitudinally (i.e., downward or upward). There are certain geometric challenges in producing this array from a flat laminate structure. Fig. 6A As shown, a flat wireframe curved in a plane may be provided, which, after the stack is created, is then conformally molded around the frustoconical base 15 of the device. The entire circular array may be constructed from two or more curved segments to cover individual portions around the cone (e.g., Fig. 6A Each segment is 180° (as shown in FIG), and then each is wired to a flexible circuit for use as a single array.

[0101] In this case, the cutting operation can be performed on a flat stack by varying the relative angle of the cutting saw in fractions of a degree relative to the stack. This operation is preferably performed using a jig for holding the stack and indexed at multiple angles from -45° to +45°.

[0102] Circuit

[0103] The device includes a circuit board, electrical components, and a terminal connector. The terminal connector may be a flexible circuit whose conductor traces connect to the extension 24 at the distal end of the composite laminate. The circuit may have electrical components, conditioned signal components, ADC, drivers, and processors. This facilitates locating certain electrical components as close to the transducer as possible, reducing the introduction of additional noise, and simplifying the connection to the rest of the probe. Other components are located in a pressurized housing of the device to protect it from extreme environmental conditions.

[0104] In one manufacturing implementation, circuit traces are laid out along with the individual component electrodes, for example by photolithography.

[0105] application

[0106] Transducers and fabrications of the compositions of the present invention may be used in various probes for use in applications such as medical inspections, wells, and pipelines. Fig.11 An imaging device for wells and pipelines is described and includes an array of transducers operable in a phased array. The transducer has particular advantages in applications with large physical strains, such as high pressure or high temperature, which would normally fracture the electrodes during use.

[0107] Fig.11 An imaging device 10 is shown that can be deployed in a well or pipeline 2. The imaging device 10 generally includes at least one ultrasonic transducer 12 and optionally one or more centralizers 20. The well or pipeline 2 can be used to transport or obtain water, oil or gas. The term is intended to include: cased wells, tubeless wells, open holes, boreholes, water lines, oil lines, pipes, and boiler tubes.

[0108] like Fig. 10A and 10B As shown, a radial transducer is a one-dimensional array of transducer elements 12 spaced radially about the body of the device. The geometry of the transducer (including any lenses and reflectors) directs the pulses outward to ultrasonically treat the surface of the well, pipe, or manufactured part.

[0109] When the array is facing in a purely radial direction (called a thickness probe), the reflections indicate the distance to the surface and defects in the wall. When the radial array is formed on a frustoconical surface with a 20-40° cone angle, the peaks are partially pointed toward the longitudinal axis and reflect surface and depth features from the focus point.

[0110] Although certain models and scientific theories have been used to explain the above-described apparatus and methods for the sake of clarity, the present invention is not limited to the correctness of these theories or to implementations that conform to these theories.

[0111] Terms such as "top", "bottom", "distal", "near", "adjacent", "below", "above", and "upper" are used herein to simplify the description of the relative positioning of the transducer stack elements as shown in the drawings or with reference to a surface reference. Although the present invention has been described and illustrated with respect to preferred embodiments thereof and preferred uses thereof, the present invention is not limited thereto, as modifications and variations of the present invention may be made by those skilled in the art within the full intended scope of the present invention.

Claims

1. A method for manufacturing an acoustic transducer array, the method comprising: depositing a first metal layer on the first side of the piezoelectric composite material to form a common electrode; depositing a second metal layer on a second side of the piezoelectric composite opposite the first side; covering the second metal layer with a third metal layer, wherein the third metal layer is thicker than the second metal layer and includes an extension portion extending outside the piezoelectric composite material in a vertical direction of the acoustic transducer; and Then, a portion of the metal layer on the second side is selectively removed to define a plurality of individual electrodes, each of which has an electrical lead at the extended portion, The step of selectively removing a portion of the metal layer on the second side patterns the single electrode to include a portion located above the composite material that is wider than a width of the extended portion.

2. The method of claim 1, wherein: For the second metal layer and the third metal layer, different techniques are used to remove the selectively removed portions.

3. The method of claim 1, wherein: The third metal layer is deposited by electroplating to the second metal layer or by bonding the foil to the second metal layer using an adhesive.

4. The method of claim 1, wherein: The third metal layer includes a wireframe defining a plurality of electrical leads extending from a common carrier frame, and wherein covering the second metal layer includes bonding the wireframe to the second metal layer and then removing the common carrier frame.

5. The method of claim 1, wherein: Covering the second metal layer includes bonding wires at edges of the second metal layer and electroplating metal on the wires and the second metal layer to form a third layer, wherein the wires are bonded to the second metal layer by one of the following means: conductive adhesive, welding, and ultrasonic welding.

6. The method of claim 1, wherein the third metal layer is a foil bonded to the second metal layer by an adhesive and then processed to selectively remove the second metal layer and the third metal layer together to produce a plurality of individual electrodes.

7. The method of claim 1 further comprising a matching layer bonded to the third metal layer, wherein: The matching layer is shaped to match the acoustic transducer and then bonded to the third metal layer.

8. An acoustic transducer array, comprising: Piezoelectric composite materials; a first metal layer defining a common electrode on a first side of the piezoelectric composite; a second metal layer on a second side of the piezoelectric composite material opposite the first side; a third metal layer conductively connected to the second metal layer and substantially covering the second metal layer, and including an extension portion extending outside the piezoelectric composite material along a vertical direction of the acoustic transducer; as well as Matching layer, bonded to the third metal layer, The third metal layer is thicker than the second metal layer. The second metal layer and the third metal layer are formed to define a plurality of individual electrodes, and The portion of the single electrode located above the composite material is wider than the width of the extended portion.

9. The acoustic transducer array of claim 8, wherein: The third metal layer is one of the following: electrodeposited foil, rolled foil, and electroplated layer.

10. The acoustic transducer array of claim 8, further comprising an adhesive between the second metal layer and the third metal layer.

11. The acoustic transducer array of any one of claims 8 to 10, further comprising a matching layer covering the individual electrodes.

12. The acoustic transducer array according to any one of claims 8 to 10, further comprising a backing layer covering the common electrode.

13. The acoustic transducer array according to any one of claims 8 to 10, wherein: The thickness of the second metal layer is between 0.2 μm and 3 μm, and wherein the thickness of a single electrode is between 15 μm and 40 μm.

14. The acoustic transducer array according to any one of claims 8 to 10, wherein: The metal layer includes one or more of the following: copper, gold, nickel, and silver.

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