Method for reducing array ultrasonic transducer crosstalk based on double flexible circuit boards

Abstract

The invention discloses a method for reducing crosstalk of an array ultrasonic transducer based on double flexible circuit boards. The array ultrasonic transducer based on the double flexible circuit boards comprises a matching layer, an upper flexible circuit board, a piezoelectric material layer, a lower flexible circuit board and a backing layer, the upper flexible circuit board, the lower flexible circuit board and the piezoelectric material layer are respectively bonded through a thin insulating adhesive with the thickness of not more than 5 microns; and the piezoelectric material layer is cut to form a plurality of separated independent vibration elements. According to the invention, by considering the electric excitation and potential measurement of the common electrode, the configured array only needs 2n interconnected elements to drive n2 vibration elements of the whole series. In addition, due to the polarization state of the piezoelectric material, each vibration element shows bias sensitive activity. According to the invention, a forced voltage bias is applied to the electrical coupling element through the column electrodes to minimize net polarization and piezoelectric activity, thereby reducing electrical crosstalk.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic transducers, and in particular to a method for reducing the crosstalk of array ultrasonic transducers by utilizing a double flexible circuit board. Background Art

[0002] Currently, the most common ultrasonic transducer is a single-vibrator. Single-vibrator ultrasonic transducers are usually used to generate ultrasonic waves with a fixed focus, so only one target can be processed at a time. The single-vibrator ultrasonic transducer must be mechanically moved to the next position of another target before it can continue processing, which means that the single-vibrator ultrasonic imaging system needs to include an electromagnetic motor that can drive the flexible shaft and then mechanically rotate the ultrasonic transducer to achieve 360-degree rotation in the endoscope to form a 2D image. Since the electromagnetic motor has a relatively complex structure and a large volume, it is usually located far away from the ultrasonic transducer. Therefore, for the endoscopic ultrasonic imaging system based on a single-vibrator, its imaging speed depends to a large extent on the rotation speed of the electromagnetic motor and the characteristics of the flexible shaft. For this reason, the imaging frame rate of the current endoscopic ultrasonic imaging system is usually limited by the mechanical rotation scanning method, and imaging is very time-consuming. In addition, in order to achieve real-time 3D ultrasonic imaging, it is even necessary to combine linear actuation components, which makes the entire 3D ultrasonic imaging system very complex and not suitable for integration into an endoscopic capsule to achieve ultrasonic imaging.

[0003] These shortcomings of single-element transducers can be overcome by using linear or planar array ultrasonic transducers. However, with the increasing demand for miniaturization and integration of ultrasonic transducers, it is inevitable to integrate more elements in a smaller size, so the spacing between elements will become smaller and smaller. As the number of array units increases and the spacing between elements decreases, the difficulty of exciting the elements increases exponentially.

[0004] For this reason, the current array ultrasonic transducer urgently needs to solve the problem of accurate excitation of multiple vibrators. In order to solve the problem of vibrator excitation of array ultrasonic transducers, technicians in this field have proposed connecting the vibrators by designing corresponding island bridge electrodes, but this method is only applicable to ultrasonic transducers with sparse vibrators. For independent vibrators formed by cutting a whole piece of piezoelectric material, due to the small spacing between the vibrators, it cannot be achieved through island bridge electrical connection. Researchers have also designed specific circuit boards to achieve the connection between the vibrators and the circuit board pads, but the processing technology of traditional conventional PCB circuit boards limits the vibrator spacing and size of the array ultrasonic transducer, and it is not easy to miniaturize. For high-frequency ultrasonic transducers with small vibrator size and a large number of vibrators, this connection method not only makes it very difficult to align and bond the pads on the circuit with the vibrators, resulting in vibrator failure, but also aggravates the crosstalk between the vibrators and reduces the imaging resolution. Summary of the invention

[0005] The main purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide an array ultrasonic transducer based on a double flexible circuit board and a method for reducing the crosstalk of an array ultrasonic transducer using a double flexible circuit board; the present invention can reduce the crosstalk level between elements, improve imaging resolution, and promote its application in fields such as endoscopes and industrial detection that require ultrasonic transducers to achieve precise imaging and detection.

[0006] The technical solution of the present invention is specifically described as follows.

[0007] The present invention provides an array ultrasonic transducer based on a double flexible circuit board, which comprises, from top to bottom, a matching layer, an upper flexible circuit board, a piezoelectric material layer, a lower flexible circuit board, an insulating structure and a backing layer; the upper flexible circuit board, the lower flexible circuit board and the piezoelectric material layer are bonded by an insulating adhesive; the piezoelectric material layer is cut to form a plurality of separate independent vibrators.

[0008] In the present invention, the piezoelectric material layer is cut to form an n×n vibrator array, where n is an integer greater than or equal to 2, the length and width of the vibrator are equal, the width of the vibrator is 3-10 times the spacing between adjacent vibrators, and the distance between the centers of two vibrators is less than or equal to the propagation wavelength λ of the ultrasonic transducer in water.

[0009] In the present invention, both the upper flexible circuit board and the lower flexible circuit board are single-layer boards. The upper flexible circuit board is wired in the horizontal direction and connected to n vibration element lead-out pads respectively. Meanwhile, the pads corresponding to the vibration elements in each row are connected through wiring. The lower flexible circuit board is wired in the longitudinal direction and connected to n lower flexible circuit board pads respectively. Meanwhile, the pads corresponding to the vibration elements in each column are connected through wiring. Pads are respectively arranged on the corresponding vibration elements of the upper flexible circuit board and the lower flexible circuit board, and are connected to the upper and lower surfaces of the piezoelectric material layer through the pads. Any vibration element in the vibration element array is taken as an excitation vibration element, and the vibration element lead-out pad of the row where the upper flexible circuit board pad corresponding to the excitation vibration element is located is connected to a driving electrical signal, the vibration element lead-out pad of the column where the lower flexible circuit board pad is located is grounded, and the remaining columns of the lower flexible circuit board pads are connected to column electrodes for applying a bias voltage.

[0010] In the present invention, the piezoelectric material layer is a 1-3 composite material composed of piezoelectric ceramic PZT-5H and epoxy resin, the insulating adhesive is epoxy resin adhesive Epotek301, and the thickness of the insulating adhesive layer does not exceed 5μm; the backing layer is obtained by high-temperature curing of Esolder3022; the matching layer is a polyparaxylene coating; and the insulating structure is prepared by mixing and curing the epoxy resin adhesive Epotek301.

[0011] In the present invention, the sizes of the vibrator lead-out pad, the upper flexible circuit board pad, and the lower flexible circuit board pad are equal to the length and width of the vibrator.

[0012] In the present invention, when the number of vibration elements exceeds 64, the vibration element lead-out pads of the upper and lower flexible circuit boards are directly set as connectors to achieve connection with the Verasonics Vantage ultrasonic experimental platform.

[0013] In the present invention, the array ultrasonic transducer is planar, or cylindrical with a matching layer, an upper flexible circuit board, a piezoelectric material layer, a lower flexible circuit board, a bonding structure and a backing layer arranged in sequence from the center to the outside radially.

[0014] The present invention also provides a method for preparing the above-mentioned array ultrasonic transducer based on a dual flexible circuit board, which is as follows:

[0015] When the array ultrasonic transducer is planar, the method comprises the following steps:

[0016] (1) The lower flexible circuit board and the bulk piezoelectric material are adhered by an insulating adhesive to ensure that the adhesive layer is evenly distributed on the entire surface of the flexible circuit board and the ultrasonic transducer; the central area of ​​the lower flexible circuit board corresponding to the ultrasonic transducer is pasted with an array of n×n pads, where n≥2; the lower flexible circuit board is wired in a vertical direction, and the vibrator lead-out pads are located on the upper side of the flexible circuit board, and the pads pasted corresponding to each column of vibrators on the lower flexible circuit board are connected by wiring;

[0017] (2) cutting the bulk piezoelectric material to form separated n×n arrays, n≥2, and the cutting thickness is the thickness of the bulk piezoelectric material;

[0018] (3) using epoxy resin glue Epotek301 to mix and cure to prepare an insulating structure with the same length and width as the bulk piezoelectric material, and the thickness of the insulating structure is equal to the thickness of the bulk piezoelectric material, and the structure is bonded and fixed under the lower flexible circuit board; (4) using insulating adhesive to bond the backing layer;

[0019] (5) pasting the upper flexible circuit board with an insulating adhesive; the central area of ​​the upper flexible circuit board corresponding to the pasting of the ultrasonic transducer also includes an n×n pad array, where n≥2;

[0020] (6) applying a layer of paraxylene on the upper flexible circuit board as a matching layer;

[0021] (7) Wires are welded to the vibration element lead-out pads of the upper flexible circuit board and the lower flexible circuit board to connect to the ultrasonic transducer drive system.

[0022] When the array ultrasonic transducer is cylindrical, the steps include:

[0023] (1) Cut the rectangular block piezoelectric material into four identical material bodies with equal length and width;

[0024] (2) The lower flexible circuit board and the material body are pasted with an insulating adhesive to ensure that the adhesive layer is evenly distributed on the entire flexible circuit board and 1 / 4 of the ultrasonic transducer surface; at this time, the central area of ​​the lower flexible circuit board corresponding to the pasting of the ultrasonic transducer includes pad arrays, n≥4; the lower flexible circuit board is wired in the vertical direction, the vibrator lead-out pads are located on the upper side of the flexible circuit board, and the pads corresponding to each column of vibrators on the lower flexible circuit board are connected by wiring;

[0025] (3) Cutting the material body to form Independent oscillators, n≥4, the cutting thickness is the thickness of the material body;

[0026] (4) using an insulating adhesive to adhere the upper flexible circuit board and the material body with the lower flexible circuit board adhered thereto, and using a fixture to bend the material body into a 90° angle; wiring the upper flexible circuit board in a horizontal direction, and connecting the pads corresponding to each row of vibrators on the upper flexible circuit board through wiring;

[0027] (5) preparing a ring-shaped insulating structure and a backing layer, pasting them with an insulating adhesive, curing them, and placing them at room temperature to obtain structure B;

[0028] (6) Using insulating adhesive and a clamp, four 90° bent material bodies are adhered to the pre-prepared structure B to form a radial array transducer;

[0029] (7) applying a layer of paraxylene on the upper flexible circuit board as a matching layer;

[0030] (8) Wires are welded to the vibration element lead-out pads of the upper flexible circuit board and the lower flexible circuit board to connect to the ultrasonic transducer drive system.

[0031] In the present invention, the thickness of the adhesive layer formed by the insulating adhesive is not more than 5 μm.

[0032] Furthermore, the present invention provides a method for reducing ultrasonic transducer crosstalk by using the above-mentioned array ultrasonic transducer based on dual flexible circuit boards. During excitation, an orthogonal bias addressing method is adopted to activate the upper flexible circuit board pad corresponding to the vibrator to apply an excitation signal, the lower flexible circuit board pad corresponding to the column is grounded, and the remaining lower flexible circuit board pads connected to the column electrodes are applied with a bias voltage, and the bias voltage is the negative voltage of the coercive voltage. The ultrasonic transducer crosstalk is reduced by a forced bias voltage method.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention proposes a method for reducing crosstalk of array ultrasonic transducers based on a double flexible circuit board. Compared with the traditional array ultrasonic transducer, which requires n×n interconnections to access all the elements in the n×n array ultrasonic transducer, the present invention proposes a method for reducing crosstalk of array ultrasonic transducers based on a double flexible circuit board. By considering the electrical excitation and potential measurement of the common electrode, the configured array only needs 2n ​​interconnections to drive the full range of n elements. 2 In addition, due to the polarization state of the piezoelectric material, each oscillator exhibits bias-sensitive activity. The present invention applies a forced voltage bias to the electric coupling element through the column electrodes to minimize the net polarization and piezoelectric activity, thereby reducing electrical crosstalk. In addition, the structure attached under the flexible circuit board also helps to reduce crosstalk. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A top view of a single piezoelectric material formed by multiple cuts on its upper surface to form separate 3×3 array ultrasonic transducers.

[0036] Figure 2 A simplified diagram of the flexible circuit board for the separated 3×3 array ultrasound transducer.

[0037] Figure 3 This is a simplified diagram of the lower flexible circuit board of the 3×3 array ultrasonic transducer.

[0038] Figure 4 This is a schematic diagram of the first clamp structure in Example 2.

[0039] Figure 5 This is a schematic diagram of the second clamp structure in Example 2. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0041] Example 1

[0042] The present invention discloses an array ultrasonic transducer based on a double flexible circuit board, which comprises a matching layer, an upper flexible circuit board, a piezoelectric material, a lower flexible circuit board, a structure and a backing layer from top to bottom. The upper and lower flexible circuit boards and the piezoelectric material are bonded by epoxy resin glue Epotek301. During bonding, a threaded clamp is designed to tighten the thread at room temperature and cure at 40°C for 2 hours to ensure that the glue layer is evenly distributed on the entire flexible circuit board and the surface of the piezoelectric material, and the thickness of the glue layer does not exceed 5μm.

[0043] The piezoelectric material of the array ultrasonic transducer is a single block piezoelectric material that is cut multiple times on its upper surface to form separate vibrators, and the piezoelectric material is a 1-3 composite material composed of piezoelectric ceramic PZT-5H and epoxy resin. The cutting depth is the thickness of the entire material.

[0044] Figure 1 A single bulk piezoelectric material is cut multiple times on its upper surface to form a separate 3×3 array. Here, only a 3×3 array is used for subsequent description. In practical applications, the array can be n×n (n≥2). Among them, 11 is the vibration element spacing, 12 is the vibration element, the length and width of the vibration element are equal, the width of the vibration element 12 is 3-10 times the vibration element spacing 11, and the distance between the centers of the two vibration elements is less than or equal to the propagation wavelength λ of the ultrasonic transducer in water.

[0045] The upper and lower flexible circuit boards are both single-layer boards, and the upper flexible circuit board is wired in the horizontal direction. The circuit wiring diagram for the separated 3×3 array is as follows: Figure 2 As shown, 21 is a pad in the upper flexible circuit board for correspondingly bonding the separated vibration element of the ultrasonic transducer, and 22 is a vibration element lead-out pad.

[0046] The vibrator lead-out pad 22 is located on the right side of the flexible circuit board, and is used for externally connecting wires to the ultrasonic transducer drive system. The pads corresponding to each row of vibrators on the upper flexible circuit board are connected by wiring. The pads on the upper flexible circuit board corresponding to the separated vibrators of the ultrasonic transducer are of the same size.

[0047] The lower flexible circuit board is as follows Figure 3 As shown, the pad shown at 31 is Figure 1 The length and width of the ultrasonic transducer vibrator are equal, and the pads shown at 32-34 are used for external lead wires to connect to the ultrasonic transducer drive system.

[0048] When the number of vibrators exceeds 64, the vibrator lead-out pads of the upper and lower flexible circuit boards can also be directly set as connectors to achieve connection with the Verasonics Vantage ultrasonic experimental platform.

[0049] In this embodiment, a planar radial array transducer is provided, and the specific preparation steps are as follows:

[0050] 1. The lower flexible circuit board and the bulk piezoelectric material are pasted with epoxy resin glue Epotek301. During the bonding, a threaded fixture is designed to tighten the threads at room temperature and cure at 40°C for 2 hours to ensure that the glue layer is evenly distributed on the entire flexible circuit board and the surface of the ultrasonic transducer, and the thickness of the glue layer does not exceed 5μm. The material of the fixture is polytetrafluoroethylene, and its length and width are 2-3 times that of the bulk piezoelectric material. Subsequently, it is placed at room temperature for 24 hours in a tightened state and then removed from the fixture. At this time, the central area of ​​the lower flexible circuit board corresponding to the pasted ultrasonic transducer contains an array of n×n (n≥2) pads, and the length and width of the pads are equal to the length and width of a single vibrator that is subsequently cut and separated from the ultrasonic transducer. In addition, the lower flexible circuit board is wired in the vertical direction, and the vibrator lead-out pad is located on the upper side of the flexible circuit board. The pads corresponding to the pasted vibrators in each column on the lower flexible circuit board are connected by wiring.

[0051] 2. Cutting the bulk piezoelectric material to form separated n×n (n≥2) arrays, and the cutting thickness is the thickness of the bulk piezoelectric material.

[0052] 3. Use epoxy resin glue Epotek301 to prepare an insulating structure with the same length and width as the bulk piezoelectric material after mixing and curing, and its thickness is equal to the thickness of the bulk piezoelectric material. Subsequently, the cured insulating structure is adhered to the piezoelectric material area of ​​the ultrasonic transducer corresponding to the lower bottom surface of the lower flexible circuit board by epoxy resin glue Epotek301. During bonding, a threaded fixture is designed to tighten the threads at room temperature and cure at 40°C for 2 hours to ensure that the glue layer is evenly distributed on the lower surface of the entire lower flexible circuit board, and the thickness of the glue layer does not exceed 5μm. Finally, place it at room temperature for 24 hours in a tightened state, and then remove it from the fixture.

[0053] 4. Use epoxy resin glue Epotek301 to bond the backing layer. During bonding, tighten the threads at 40°C with a threaded clamp and cure at high temperature for 2 hours to ensure that the glue layer is evenly distributed on the lower surface of the entire insulating structure and the upper surface of the backing layer, and the thickness of the glue layer does not exceed 5μm. Then, place it at room temperature for 24 hours in a tightened state and then take it out of the clamp. The backing layer is obtained by high-temperature curing of Esolder3022, and its length and width are equal to those of the bulk piezoelectric material, and its thickness is 3mm.

[0054] 5. Use the epoxy resin glue Epotek301 to stick the upper flexible circuit board. When bonding, tighten the threads at room temperature with a threaded clamp and cure at 40°C for 2 hours to ensure that the glue layer is evenly distributed on the entire flexible circuit board and the surface of the ultrasonic transducer, and the thickness of the glue layer does not exceed 5μm. Then, place it at room temperature for 24 hours in a tightened state and then remove it from the clamp. At this time, the central area of ​​the upper flexible circuit board corresponding to the ultrasonic transducer also contains an array of n×n (n≥2) pads, and the length and width of the pads are equal to the length and width of a single vibrator of the ultrasonic transducer after cutting and separation.

[0055] 6. Coat 1 μm thick para-xylene as a matching layer using the Diener PARYLENE coating system. Connect the ultrasonic transducer drive system by welding wires on the vibration element lead pads of the upper and lower flexible circuits.

[0056] In the present invention, during excitation, in order to reduce the crosstalk between the vibration elements and allow the activation of the target element, an orthogonal bias addressing method is adopted. Specifically, an excitation signal is applied to the upper flexible circuit board pad 22 corresponding to the activation vibration element 21, the corresponding lower flexible circuit board pad 32 is grounded, and a bias voltage is applied to the lower flexible circuit board pads 33 and 34, and the bias voltage is a negative voltage of the coercive voltage.

[0057] In a specific embodiment, the block piezoelectric material is cut to form a separated 16×16 vibrator array, the width of the vibrator 12 is 3 times the vibrator spacing 11, and the distance between the centers of the two vibrators is equal to the propagation wavelength λ of the ultrasonic transducer in water. The forced voltage bias method can reduce the crosstalk between the elements by 7.25dB.

[0058] Example 2

[0059] This embodiment provides a cylindrical radial array transducer, and the specific preparation steps are as follows:

[0060] 1. Cut the rectangular block of piezoelectric material into 4 identical material bodies with equal length and width.

[0061] 2. Use the epoxy resin glue Epotek301 to stick the lower flexible circuit board and 1 / 4 bulk piezoelectric material (material body). During bonding, design a clamp with threads to tighten the threads at room temperature and cure at 40°C for 2 hours to ensure that the glue layer is evenly distributed on the entire flexible circuit board and 1 / 4 ultrasonic transducer surface, and the thickness of the glue layer does not exceed 5μm. The material of the clamp is polytetrafluoroethylene, and its length and width are 2-3 times that of the 1 / 4 bulk piezoelectric material (material body). Then, place it at room temperature for 24 hours in a tightened state and then remove it from the clamp. At this time, the center area of ​​the lower flexible circuit board corresponding to the pasted ultrasonic transducer includes The lower flexible circuit board is wired in a vertical direction, the vibrator lead-out pads are located on the upper side of the flexible circuit board, and the pads corresponding to each column of vibrators on the lower flexible circuit board are connected by wiring.

[0062] 3. Cut 1 / 4 of the bulk piezoelectric material (material body) vibrator to form An independent oscillator, the cutting thickness is the thickness of the material body.

[0063] 4. Place the upper flexible circuit board and the material body with the lower flexible circuit board attached Figure 4 The first fixture shown is made of polytetrafluoroethylene; the central angle corresponding to the arc portion in the middle of the fixture is 90°, and the arc length is equal to 1 / 4 of the length of the bulk piezoelectric material (material body). The upper flexible circuit board and the material body with the lower flexible circuit board are attached using epoxy resin glue Epotek301, and the threads are tightened at 80°C to bend the material body into 90°. In addition, the upper flexible circuit board is wired in the horizontal direction, and the pads corresponding to each row of vibrators on the upper flexible circuit board are connected by wiring.

[0064] 5. Then, cure at 40°C for 2 hours, place at room temperature for 24 hours in a tightened state, and then remove from the fixture. Repeat this process 4 times to form 4 90° bent material bodies, on which the upper and lower flexible circuit boards are attached.

[0065] 6. Prepare the annular insulating structure and backing layer in advance, stick them with epoxy resin glue Epotek301, cure them at 40°C for 2 hours, place them at room temperature for 24 hours in a tightened state, and then take them out of the fixture to form structure B.

[0066] 7. Using Epotek301 and Figure 5 The second fixture shown is used to paste four 90° bent material bodies onto the pre-prepared structure B to form a radial array transducer. Similarly, it is cured at 40°C for 2 hours, and placed at room temperature for 24 hours in a tightened state before being removed from the fixture. There are four 90-degree alignment lines on the top surface of the fixture to ensure the precise connection of the four independent units. At the same time, in order to observe the alignment degree of the four 90° bent material bodies, the material of the fixture is selected as transparent glass. The structure B is cylindrical, and its outer diameter is equal to the inner diameter of the fixture.

[0067] 8. Coat 1 μm thick para-xylene as a matching layer using the Diener PARYLENE coating system. Connect the ultrasonic transducer drive system by welding wires on the vibration element lead pads of the upper and lower flexible circuits.

[0068] When the number of vibrators exceeds 64, the vibrator lead-out pads of the upper and lower flexible circuit boards can also be directly set as connectors to achieve connection with the Verasonics Vantage ultrasonic experimental platform.

[0069] The present invention proposes a method for reducing crosstalk of array ultrasonic transducers based on a double flexible circuit board. Compared with the traditional array ultrasonic transducer, which requires n×n interconnections to access all the elements in the n×n array ultrasonic transducer, the present invention proposes a method for reducing crosstalk of array ultrasonic transducers based on a double flexible circuit board. By considering the electrical excitation and potential measurement of the common electrode, the array configured by the present invention only needs 2n ​​interconnections to drive the full range of n elements. 2 In addition, each element exhibits bias-sensitive activity due to the polarization state of the piezoelectric material. A forced voltage bias is applied to the electrically coupled element through the column electrodes to minimize the net polarization and piezoelectric activity, thereby reducing electrical crosstalk. In addition, the structure attached under the flexible circuit board also helps to reduce crosstalk.

Claims

1. An array ultrasonic transducer based on a double flexible circuit board, characterized in that: It includes a matching layer, an upper flexible circuit board, a piezoelectric material layer, a lower flexible circuit board, an insulating structure and a backing layer from top to bottom; the upper flexible circuit board, the lower flexible circuit board and the piezoelectric material layer are bonded by insulating adhesives; the piezoelectric material layer is cut to form a number of separate independent vibrators.

2. The array ultrasonic transducer based on a double flexible circuit board according to claim 1, characterized in that: The piezoelectric material layer is cut to form an n×n vibrator array, where n is an integer greater than or equal to 2, the length and width of the vibrator are equal, the width of the vibrator is 3-10 times the spacing between adjacent vibrators, and the distance between the centers of two vibrators is less than or equal to the propagation wavelength λ of the ultrasonic transducer in water.

3. The array ultrasonic transducer based on a double flexible circuit board according to claim 2, characterized in that: The upper flexible circuit board and the lower flexible circuit board are both single-layer boards. The upper flexible circuit board is wired in the horizontal direction and connected to n vibration element lead-out pads respectively. At the same time, the pads corresponding to the vibration elements in each row are connected through wiring. The lower flexible circuit board is wired in the longitudinal direction and connected to n lower flexible circuit board pads respectively. At the same time, the pads corresponding to the vibration elements in each column are connected through wiring. Pads are respectively arranged on the corresponding vibration elements of the upper flexible circuit board and the lower flexible circuit board, and are connected to the upper and lower surfaces of the piezoelectric material layer through the pads. Any vibration element in the vibration element array is taken as an excitation vibration element, and the vibration element lead-out pad of the row where the upper flexible circuit board pad corresponding to the excitation vibration element is located is connected to a driving electrical signal, the vibration element lead-out pad of the column where the lower flexible circuit board pad is located is grounded, and the lower flexible circuit board pads of all remaining columns are connected to column electrodes for applying a bias voltage.

4. The array ultrasonic transducer based on a double flexible circuit board according to claim 1, characterized in that: The piezoelectric material layer is a 1-3 composite material composed of piezoelectric ceramic PZT-5H and epoxy resin, the insulating adhesive is epoxy resin adhesive Epotek301, and the thickness of the insulating adhesive layer does not exceed 5 μm; the backing layer is Esolder3022 obtained after high temperature curing; The matching layer is a polyparaxylene coating; the insulating structure is prepared by mixing and curing the epoxy resin adhesive Epotek301.

5. The array ultrasonic transducer based on a double flexible circuit board according to claim 1, characterized in that: The array ultrasonic transducer is planar, or cylindrical in shape with a matching layer, an upper flexible circuit board, a piezoelectric material layer, a lower flexible circuit board, an insulating structure and a backing layer arranged in sequence from the center of the circle to the outside radially.

6. A method for preparing an array ultrasonic transducer based on a dual flexible circuit board according to any one of claims 1 to 5, characterized in that: When the array ultrasonic transducer is planar, the following steps are included: (1) The lower flexible circuit board and the bulk piezoelectric material are adhered by an insulating adhesive to ensure that the adhesive layer is evenly distributed on the entire surface of the flexible circuit board and the ultrasonic transducer; the central area of ​​the lower flexible circuit board corresponding to the ultrasonic transducer is pasted with an array of n×n pads, where n≥2; the lower flexible circuit board is wired in a vertical direction, and the vibrator lead-out pads are located on the upper side of the flexible circuit board, and the pads pasted corresponding to each column of vibrators on the lower flexible circuit board are connected by wiring; (2) cutting the bulk piezoelectric material to form separated n×n arrays, n≥2, and the cutting thickness is the thickness of the bulk piezoelectric material; (3) using epoxy resin glue Epotek301 to mix and cure to prepare an insulating structure with the same length and width as the bulk piezoelectric material, and the thickness of the insulating structure is equal to the thickness of the bulk piezoelectric material, and the structure is bonded and fixed under the lower flexible circuit board; (4) bonding the backing layer with an insulating adhesive; (5) pasting the upper flexible circuit board with an insulating adhesive; the central area of ​​the upper flexible circuit board corresponding to the pasting of the ultrasonic transducer also includes an n×n pad array, where n≥2; (6) applying a layer of paraxylene on the upper flexible circuit board as a matching layer; (7) Wires are welded to the vibration element lead-out pads of the upper flexible circuit board and the lower flexible circuit board to connect to the ultrasonic transducer drive system.

7. A method for preparing an array ultrasonic transducer based on a dual flexible circuit board according to any one of claims 1 to 5, characterized in that: When the array ultrasonic transducer is cylindrical, the steps include: (1) Cut the rectangular block piezoelectric material into four identical material bodies with equal length and width; (2) The lower flexible circuit board and the material body are glued together with an insulating adhesive to ensure that the adhesive layer is evenly distributed on the entire flexible circuit board and 1 / 4 of the ultrasonic transducer surface; at this time, the central area of ​​the lower flexible circuit board corresponding to the ultrasonic transducer is included. pad arrays, n≥4; the lower flexible circuit board is wired in the vertical direction, the vibrator lead-out pads are located on the upper side of the flexible circuit board, and the pads corresponding to the vibrators in each column on the lower flexible circuit board are connected by wiring; (3) Cutting the material body to form Independent oscillators, n≥4, the cutting thickness is the thickness of the material body; (4) using an insulating adhesive to adhere the upper flexible circuit board and the material body with the lower flexible circuit board adhered thereto, and using a fixture to bend the material body into a 90° angle; wiring the upper flexible circuit board in a horizontal direction, and connecting the pads corresponding to each row of vibrators on the upper flexible circuit board through wiring; (5) preparing a ring-shaped insulating structure and a backing layer, pasting them with an insulating adhesive, curing them, and placing them at room temperature to obtain structure B; (6) Using insulating adhesive and a clamp, four 90° bent material bodies are adhered to the pre-prepared structure B to form a radial array transducer; (7) applying a layer of paraxylene on the upper flexible circuit board as a matching layer; (8) Wires are welded to the vibration element lead-out pads of the upper flexible circuit board and the lower flexible circuit board to connect to the ultrasonic transducer drive system.

8. The method for preparing an array ultrasonic transducer based on a dual flexible circuit board according to claim 6 or 7, characterized in that: The thickness of the adhesive layer formed by the insulating adhesive shall not exceed 5 μm.

9. A method for reducing ultrasonic transducer crosstalk using the array ultrasonic transducer based on a dual flexible circuit board according to any one of claims 1 to 5, characterized in that: During excitation, an orthogonal bias addressing method is adopted to apply an excitation signal to the upper flexible circuit board pad corresponding to the activated vibrator, the lower flexible circuit board pad corresponding to the column is grounded, and a bias voltage is applied to the remaining lower flexible circuit board pads connected to the column electrode. The bias voltage is the negative voltage of the coercive voltage, and the crosstalk of the ultrasonic transducer is reduced by the forced bias voltage method.

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