Composite piezoelectric structure, ultrasonic transducer and preparation method thereof

Abstract

The invention belongs to the technical field of composite piezoelectric materials, and discloses a composite piezoelectric structure, an ultrasonic transducer and a preparation method thereof. The composite piezoelectric structure comprises a piezoelectric material, a transverse middle kerf and a longitudinal middle kerf are formed in the piezoelectric material, and epoxy resin is injected into the transverse middle kerf and the longitudinal middle kerf. A plurality of transverse kerfs and a plurality of longitudinal kerfs are formed from the transverse middle kerfs and the longitudinal middle kerfs to the ends of the piezoelectric material, and tungsten-epoxy mixtures with different volume fractions are injected into the transverse kerfs and the longitudinal kerfs; the volume fractions of the tungsten-epoxy mixture in the plurality of transverse kerfs and the plurality of longitudinal kerfs are sequentially increased from the positions close to the transverse middle kerfs and the longitudinal middle kerfs to the positions away from the transverse middle kerfs and the longitudinal middle kerfs; the performance of the piezoelectric composite ultrasonic transducer can be improved, and the ultrasonic imaging quality is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of composite piezoelectric materials, and in particular to a composite piezoelectric structure, an ultrasonic transducer and a preparation method thereof. Background Art

[0002] In recent years, piezoelectric ultrasonic transducers have found widespread application in medical imaging, nondestructive testing, object ranging, sonar, and other fields, leveraging the physical effects of ultrasound in various media. For example, in medical imaging, ultrasound can penetrate human tissue and receive the returned information. By receiving and analyzing the returned ultrasound signal, two-dimensional, three-dimensional, and even four-dimensional images of the human body's internal structures can be obtained, with high resolution, contrast, and safety.

[0003] In recent years, type 1-3 piezoelectric composite structures have been widely used in the design of ultrasonic transducers due to their high electromechanical coupling coefficient and low acoustic impedance. However, with the increase in frequency, the groove width in the design rules of piezoelectric composite materials approaches the limit of the preparation process, making it impossible for the transducer vibration mode to achieve the desired effect. How to optimize the structure of the piezoelectric array element to improve the performance of the piezoelectric composite ultrasonic transducer and achieve high-quality ultrasonic imaging is a key issue in the innovation of ultrasonic technology. Summary of the Invention

[0004] The purpose of the present invention is to provide a composite piezoelectric structure, an ultrasonic transducer and a preparation method thereof to overcome the problems existing in the prior art. The present invention can optimize the structure of the piezoelectric array element to improve the performance of the piezoelectric composite ultrasonic transducer, and can also improve the energy conversion efficiency and energy transmission efficiency of the ultrasonic transducer, thereby significantly improving the quality of ultrasonic imaging.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a composite piezoelectric structure, comprising a piezoelectric material, wherein a transverse middle slit and a longitudinal middle slit are formed on the piezoelectric material, the intersection of the transverse middle slit and the longitudinal middle slit being located at the center point of the cross section of the piezoelectric material, and epoxy resin is injected into the transverse middle slit and the longitudinal middle slit; a plurality of transverse slits are formed from the transverse middle slit to the end of the piezoelectric material, and a plurality of longitudinal slits are formed from the longitudinal middle slit to the end of the piezoelectric material, and a tungsten-epoxy mixture having different volume fractions is injected into the plurality of transverse slits and the plurality of longitudinal slits, and the volume fraction of the tungsten-epoxy mixture in the plurality of transverse slits and the plurality of longitudinal slits increases successively from near the transverse middle slit and the longitudinal middle slit to far away from the transverse middle slit and the longitudinal middle slit; and the equivalent acoustic impedance of the epoxy resin and the tungsten-epoxy mixture exhibits a concave-valley gradient distribution; Furthermore, the angle between the transverse middle slit and the longitudinal middle slit is 90°; the plurality of transverse slits are arranged in parallel, and the plurality of longitudinal slits are arranged in parallel; Furthermore, the piezoelectric material is piezoelectric ceramic; and the equivalent acoustic impedance is the product of equivalent density and equivalent sound velocity.

[0006] In a second aspect, the present invention provides a composite piezoelectric ultrasonic transducer, comprising a metal housing, an acoustic lens mounted on the top of the metal housing, a first electrode layer mounted on the bottom of the acoustic lens, a piezoelectric composite array element mounted on the bottom of the first electrode layer, the bottom of the piezoelectric composite array element connected to an SMA connector via an electrical conductor, the piezoelectric composite array element, the electrical conductor, and the SMA connector being located inside the metal housing, and epoxy resin being filled between the piezoelectric composite array element and the metal housing; The piezoelectric composite array element includes a composite piezoelectric structure installed at the bottom of a first electrode layer. A second electrode layer and a backing layer are sequentially installed at the bottom of the composite piezoelectric structure. The backing layer is connected to an SMA connector via an electrical conductor.

[0007] In a third aspect, the present invention provides a method for preparing a composite piezoelectric structure, comprising the following steps: Step 1: Grind the piezoelectric material once, and perform transverse and longitudinal slits based on the center point of the cross section of the piezoelectric material after the grinding, to obtain a transverse middle slit and a longitudinal middle slit, respectively; Step 2: vacuuming the prepared epoxy resin once, injecting the vacuumed epoxy resin into the transverse middle slit and the longitudinal middle slit by a siphon method, and performing a second vacuuming process to obtain a piezoelectric material injected with epoxy resin; Step 3: drying the piezoelectric material after injecting the epoxy resin, and performing secondary grinding on the dried piezoelectric material to obtain a secondary ground piezoelectric material; Step 4: Based on the horizontal middle slit of the piezoelectric material after the secondary grinding, a plurality of slits are made toward the horizontal ends of the piezoelectric material to obtain a plurality of horizontal slits; based on the longitudinal middle slit of the piezoelectric material after the secondary grinding, a plurality of slits are made toward the longitudinal ends of the piezoelectric material to obtain a plurality of longitudinal slits; Step 5: preparing tungsten-epoxy mixtures of different volume fractions, respectively, and injecting the tungsten-epoxy mixtures of different volume fractions into the transverse middle slit, the longitudinal middle slit, the plurality of transverse slits, and the plurality of longitudinal slits, respectively, to obtain a piezoelectric material injected with the tungsten-epoxy mixture; wherein the volume fractions of the tungsten-epoxy mixtures injected into the plurality of transverse slits and the plurality of longitudinal slits respectively increase gradually from close to the transverse middle slit and the longitudinal middle slit to farthest from the transverse middle slit and the longitudinal middle slit; Step 6: grinding the piezoelectric material injected with the tungsten-epoxy mixture three times to obtain a composite piezoelectric material; Furthermore, the piezoelectric material in step 1 is lead zirconate titanate piezoelectric ceramic (PZT5H); the first grinding in step 1 is specifically: grinding with 400-800 grit sandpaper until the thickness of the piezoelectric material is 250 μm; the depth of the horizontal middle slit and the vertical middle slit in step 1 is 190 μm, and the width is 55 μm; the angle between the horizontal middle slit and the vertical middle slit in step 1 is 90°; Furthermore, the time for the first vacuum treatment and the second vacuum treatment in step 2 is 10 to 15 minutes; The drying temperature in step 3 is 40-65° C. and the drying time is 12 h. The secondary grinding of the dried piezoelectric material in step 3 is specifically performed by grinding the top and bottom of the dried piezoelectric material with 800-grit sandpaper. Furthermore, the depth of the transverse slit and the longitudinal slit in step 4 is 190 μm, and the width is 95 μm; in step 4, the plurality of transverse slits are arranged in parallel, and the plurality of longitudinal slits are arranged in parallel; and in step 4, the angle between the transverse slit and the longitudinal slit is 90°; Furthermore, the volume fraction of the tungsten-epoxy mixture in step 5 is 10% to 45%; In step six, the piezoelectric material after injection of the tungsten-epoxy mixture is ground three times: the top surface of the piezoelectric material after injection of the tungsten-epoxy mixture is ground using 800-grit sandpaper, and the bottom surface of the piezoelectric material after injection of the tungsten-epoxy mixture is ground using 2000-grit sandpaper; the thickness of the composite piezoelectric material in step six is ​​190 μm.

[0008] In a fourth aspect, the present invention provides a method for preparing a composite piezoelectric ultrasonic transducer, comprising the following steps: Step 1: Using the composite piezoelectric structure as a piezoelectric layer, and plating electrodes on the top and bottom surfaces of the composite piezoelectric structure to form a first electrode layer and a second electrode layer, respectively; Step 2: obtain a piezoelectric material, enclose the piezoelectric material with a ceramic ring, and fill a conductive epoxy between the piezoelectric material and the ceramic ring to form a backing layer; Step 3: Connect an electrical conductor to the bottom of the backing layer, circumferentially install a metal shell on the outside of the piezoelectric layer, the second electrode layer, the backing layer, and the electrical conductor, install the first electrode layer on top of the metal shell, and fill epoxy resin between the piezoelectric layer, the second electrode layer, the backing layer, and the metal shell; In step 4, a gold electrode and a Parylene C film (poly(p-dichloroxylene)) are sputtered on the first electrode layer, the electrical conductors are connected to the SMA (Sub-Miniature A Connector) connector, and then an acoustic lens is installed on top of the first electrode layer after the sputtering of the gold electrode and the Parylene C film to complete the preparation of the composite piezoelectric ultrasonic transducer.

[0009] The above technical solution has the following advantages or beneficial effects: In the first aspect, the present invention provides a composite piezoelectric structure with the center of the piezoelectric ceramic PZT as the axis of symmetry, and a polymer mixture with gradient acoustic impedance is filled in the grooves on both sides thereof, presenting a concave-valley gradient distribution of acoustic impedance on the transverse cross-section of the piezoelectric element, which can effectively adjust the propagation characteristics of sound waves in the structure, reduce sound wave reflection and loss, and improve the efficiency of sound wave transmission; in the application of ultrasonic transducers, the sensitivity and bandwidth of the transducer can be enhanced, so that it can more accurately receive and transmit ultrasonic signals; during ultrasonic imaging, it can provide clearer, more accurate, and high-resolution images, which helps doctors diagnose diseases more accurately. It has important application value in the field of medical ultrasonic imaging and provides strong support for the development of ultrasonic diagnostic technology.

[0010] Secondly, the present invention provides a composite piezoelectric ultrasonic transducer. From an acoustic perspective, the piezoelectric composite array element achieves more efficient electrical-to-acoustic conversion, improving the transducer's sensitivity and bandwidth. This results in higher-quality ultrasonic signals and enhanced echo signal reception, thus laying the foundation for high-quality ultrasonic imaging. Structurally, the metal housing provides robust protection against external interference and damage, ensuring stable transducer operation. An acoustic lens focuses the ultrasonic signal, enhancing imaging focus and improving image clarity. Epoxy resin fills the gap between the piezoelectric composite array element and the metal housing, providing both stability and absorbing some clutter, reducing interference. Electrically, the transducer is reliably connected to external devices via electrical conductors and SMA connectors, ensuring stable signal transmission. A backing layer absorbs acoustic waves reflected from the back of the piezoelectric composite array element, reducing noise and further improving imaging quality. Overall, the synergistic operation of the transducer's components effectively improves the resolution, contrast, and depth of ultrasonic imaging. This transducer has significant application value in fields such as medical diagnosis and industrial nondestructive testing, helping to more accurately detect defects and lesions.

[0011] In the third aspect, the present invention provides a method for preparing a composite piezoelectric structure. By accurately cutting the seams based on the center point of the cross section of the piezoelectric material and then continuing the processing based on the seams, the position of each seam can be guaranteed to be accurate, and the symmetry and uniformity of the final composite piezoelectric structure can be guaranteed, which is beneficial to improving the acoustic performance of the structure. By vacuuming the epoxy resin twice, the bubbles therein can be effectively removed. The siphon injection method can ensure that the epoxy resin is fully and evenly filled into the seam, avoiding uneven filling or voids, and enhancing the stability of the structure. By changing the doping concentration of tungsten powder particles in the epoxy resin mixture, the piezoelectric composite material can be broken. The periodic arrangement of piezoelectric composite materials breaks through the limitation of the periodic arrangement of piezoelectric composite materials on the groove width, effectively suppresses the first-order and second-order transverse resonances existing in traditional 1-3 piezoelectric composite materials, and further improves the energy conversion efficiency and energy transmission efficiency of the piezoelectric ultrasonic transducer. It is suitable for medical ultrasonic imaging and other imaging applications requiring high resolution and high contrast. The surface flatness of the piezoelectric material is guaranteed through multiple grinding processes, which is conducive to the close fitting of subsequent layers of materials, further improving the overall performance of the composite piezoelectric structure, and providing a reliable foundation for the preparation of high-performance piezoelectric composite ultrasonic transducers. It has important application value in fields such as ultrasonic imaging.

[0012] Furthermore, the volume fraction of the tungsten-epoxy mixture used is 10% to 45%. After the high-purity tungsten powder is fully doped with the epoxy resin, the mixture can have a gradient, effective acoustic impedance characteristic, and the mixture has a uniform texture.

[0013] In a fourth aspect, the present invention provides a method for preparing a composite piezoelectric ultrasonic transducer. By plating electrodes on the top and bottom of the composite piezoelectric structure to form first and second electrode layers, good electrical contact can be ensured, so that electrical signals are efficiently and stably transmitted in the transducer, energy loss is reduced, and the electrical-to-acoustic conversion efficiency of the transducer is improved. By using a ceramic ring to sheath the piezoelectric material and filling it with conductive epoxy to form a backing layer, the ceramic ring provides structural support, and the conductive epoxy not only absorbs back-reflected sound waves to reduce noise interference, but also enhances the electrical connection and mechanical stability between components, ensuring long-term stable operation of the transducer. The design of circumferential installation of the metal shell provides solid protection for the internal structure of the transducer to prevent external physical damage and electromagnetic interference. The epoxy resin filling further fixes the internal components, absorbs clutter, and improves imaging quality. By sputtering gold electrodes and Parylene C film on the first electrode layer, the gold electrode has good conductivity, and the Parylene C film is insulating and has good biocompatibility, providing a flat surface for the subsequent installation of the acoustic lens, and can also prevent leakage, ensuring safe use. The installation of the acoustic lens focuses the ultrasonic signal, improves the imaging resolution and clarity, and enables the transducer to work more accurately and efficiently in fields such as medical diagnosis and industrial testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic structural diagram of a composite piezoelectric structure of the present invention; Figure 2 A schematic diagram showing the trend of the density of the tungsten-epoxy mixture in a composite piezoelectric structure of the present invention and the acoustic impedance of the composite piezoelectric structure; Figure 3 Schematic diagram of the volume fraction distribution of a tungsten-epoxy mixture in a composite piezoelectric structure of the present invention; Figure 4 This is a schematic structural diagram of a composite piezoelectric ultrasonic transducer according to the present invention; Figure 5 is a cross-sectional view of a composite piezoelectric ultrasonic transducer of the present invention; Figure 6 This is a schematic flow chart of a method for preparing a composite piezoelectric structure according to the present invention; Figure 7 This is a characterization diagram of the electrical impedance and phase performance of a composite piezoelectric ultrasonic transducer of the present invention; Figure 8 This is a performance characterization diagram of the echo signal in the time domain and frequency domain of a composite piezoelectric ultrasonic transducer of the present invention; Figure 9 This is a characterization diagram of the electrical impedance and phase performance of the traditional 1-3 type ultrasonic transducer; Figure 10 The time domain and frequency domain performance characterization diagram of the echo signal of the traditional 1-3 type ultrasonic transducer; Figure 11 This is a schematic diagram of the tungsten filament imaging resolution test of the present invention; Figure 12 A schematic diagram of the horizontal position depth of the tungsten filament imaging resolution test results of the present invention; Figure 13 For the present invention Figure 12 Schematic diagram of the horizontal position amplitude of the tungsten filament imaging resolution test results in part A; Figure 14 Schematic diagram of a C-mode ultrasound imaging device; Figure 15 It is a schematic diagram of the structure of C-mode ultrasound imaging; In the figure, 1 is a backing layer; 2 is a composite piezoelectric structure; 3 is a first electrode layer; 31 is a second electrode layer; 4 is an acoustic lens; 5 is a metal housing; 6 is an electrical conductor; and 7 is an SMA connector. DETAILED DESCRIPTION

[0015] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it. In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention. It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0016] Example: See also Figure 1 The present invention provides a composite piezoelectric structure, comprising a piezoelectric material, wherein a transverse middle slit and a longitudinal middle slit are provided on the piezoelectric material, wherein the intersection of the transverse middle slit and the longitudinal middle slit is located at the center point of the cross section of the piezoelectric material, the angle between the transverse middle slit and the longitudinal middle slit is 90°, and epoxy resin is injected into the transverse middle slit and the longitudinal middle slit; a plurality of transverse slits are provided from the transverse middle slit as the starting point to the end of the piezoelectric material, the plurality of transverse slits are arranged in parallel, and a plurality of longitudinal slits are provided from the longitudinal middle slit as the starting point to the end of the piezoelectric material The longitudinal slits are arranged in parallel, and a tungsten-epoxy mixture with different volume fractions is injected into the plurality of transverse slits and the plurality of longitudinal slits. The volume fraction of the tungsten-epoxy mixture in the plurality of transverse slits and the plurality of longitudinal slits increases successively from the position close to the transverse middle slit and the longitudinal middle slit to the position farthest from the transverse middle slit and the longitudinal middle slit. The equivalent acoustic impedance of the epoxy resin and the tungsten-epoxy mixture presents a concave-valley gradient distribution. The concave-valley gradient trend of the equivalent acoustic impedance is caused by the change in the volume fraction of the tungsten-epoxy mixture, and is flexibly adjusted by doping with a 0-3 type polymer. See Figure 2The equivalent acoustic impedance is the product of the equivalent density and the equivalent sound velocity, and its change changes with the change of the tungsten powder concentration in the tungsten-epoxy composite material. The tungsten content in the tungsten-epoxy composite material is distributed in a two-dimensional axisymmetric manner on the transverse section. The slit filled with epoxy resin without tungsten powder particles is the symmetrical central slit, and the edge slit is filled with tungsten-epoxy composite material with a tungsten volume concentration of 45%, increasing from the center to both sides. The equivalent acoustic impedance of the slit filler is distributed in a two-dimensional axisymmetric gradient manner on the transverse section. The equivalent acoustic impedance of the central symmetric axis slit filler is the smallest, and the equivalent acoustic impedance of the slit filler increases from the center to both sides on the transverse section, and the equivalent acoustic impedance of the edge slit filler is the largest. Preferably, the piezoelectric material is lead zirconate titanate piezoelectric ceramic (PZT5H).

[0017] See also Figure 3 By uniformly doping tungsten powder particles, the tungsten powder-epoxy resin mixture has a gradual change in transverse and longitudinal sound velocity, which will further optimize the vibration mode of the piezoelectric element.

[0018] See also Figure 4 and Figure 5 In one embodiment of the present invention, a composite piezoelectric ultrasonic transducer, also known as a 1-3 type GDPC ultrasonic transducer (acoustic impedance gradient distribution 1-3 type high-frequency composite ultrasonic transducer), is provided, comprising an acoustic lens 4, a first electrode layer 3, a piezoelectric composite array element, an electrical conductor 6, an SMA connector 7, and a metal housing 5; the piezoelectric composite array element comprises a composite piezoelectric structure 2, a second electrode layer 31, and a backing layer 1; An acoustic lens 4 is mounted on top of a metal housing 5. A first electrode layer 3 is mounted on the bottom of the acoustic lens 4. A piezoelectric composite array element is mounted on the bottom of the first electrode layer 3. The bottom of the piezoelectric composite array element is connected to an SMA connector 7 via an electrical conductor 6. The piezoelectric composite array element, the electrical conductor 6, and the SMA connector 7 are located inside the metal housing 5. The metal housing 5 is arranged circumferentially along the piezoelectric composite array element. Epoxy resin is filled between the piezoelectric composite array element and the metal housing 5 for fixation. The piezoelectric composite array element includes a composite piezoelectric structure 2 mounted on the bottom of the first electrode layer 3. A second electrode layer 31 and a backing layer 1 are sequentially mounted on the bottom of the composite piezoelectric structure 2. The backing layer 1 is connected to the SMA connector 7 via an electrical conductor 6. Preferably, the acoustic lens 4 is made of high-density epoxy resin with a curvature of f # is 2; Preferably, the structural parameters of the composite piezoelectric layer 2 are determined by a three-dimensional finite element simulation model constructed using COMSOL Multiphysics software to accurately simulate the vibration mode and impedance spectrum of the element; Preferably, the change in the volume fraction of the slit filler in the composite piezoelectric layer 2 will affect the change in the equivalent sound velocity, and the arrangement of the equivalent sound velocity will further affect the vibration mode of the array element, wherein the first-order and second-order transverse resonance frequencies 、 Equivalent sound speed v s The calculation formula is as follows: ; ; Where, d Indicates width; p represents epoxy; The impedance gradient structure can break the periodic arrangement of the piezoelectric composite array elements, suppress the first-order and second-order resonances of the 1-3 type GDPC ultrasonic transducer, and break through the limitations of the structural parameters of the traditional composite ultrasonic transducer on the device frequency.

[0019] See also Figures 7 to 10 , which are respectively the electrical impedance and phase performance characterization diagram and the echo signal time domain and frequency domain performance characterization diagram of a composite piezoelectric ultrasonic transducer of the present invention, and the electrical impedance and phase performance characterization diagram and the echo signal time domain and frequency domain performance characterization diagram of a traditional 1-3 type ultrasonic transducer. By performing performance characterization on the developed 1-3 type GDPC ultrasonic transducer and its control group transducer of the same size, it was found that the 1-3 type GDPC ultrasonic transducer has a thickness mode resonant frequency of 8.39 MHz and a thickness mode electromechanical coupling coefficient of 0.64. Compared with the traditional 1-3 type piezoelectric composite ultrasonic transducer with similar frequency (thickness mode electromechanical coupling coefficient of 0.58), it effectively suppresses the non-ideal first-order and second-order lateral vibrations and improves the energy conversion efficiency of the device.

[0020] See also Figures 11 to 13 , which are schematic diagrams of the tungsten filament imaging resolution test, the lateral position depth of the test results, and the lateral position amplitude of the test results of the present invention, respectively. An ultrasonic imaging application experiment was designed to verify the performance of the above-mentioned concave valley gradient acoustic impedance distribution 1-3 type high-frequency composite ultrasonic transducer (hereinafter referred to as 1-3 type GDPC transducer). First, ultrasonic scanning imaging was performed on the tungsten filament model, and the transducer imaging resolution was calculated. Four tungsten filaments with a diameter of 50 μm were tied to a stepped fixture with a lateral distance of 1.5 mm and a vertical distance of 0.5 mm. The transducer was focused on the second tungsten filament. The calculated lateral resolution was 153.7 μm. A customized high-precision metal resolution plate was used to further intuitively test the imaging capability of the 1-3 type GDPC transducer.

[0021] See also Figure 14 and Figure 15, respectively, are schematic diagrams of the C-mode ultrasonic imaging device and structure. The sample to be imaged is placed in deionized water, and the prepared ultrasonic transducer is moved horizontally to complete the scanning process. Post-processing generates the image. The resolution plate features five pairs of slits with equal widths and spacings of 0.1, 0.2, 0.3, 0.4, and 0.5 mm, respectively; a spiral with a line width of 0.5 mm; and multiple circles with diameters of 0.5 mm and 1.2 mm. As can be seen from the figure, the 0.1 mm slit width exceeds the device's imaging capability, rendering the two slits indistinguishable in the imaging results. Therefore, the imaging resolution limit of the designed device is to distinguish between two slits with a width of 0.2 mm and a spacing of 0.2 mm. The above imaging experiments demonstrate the device's excellent imaging capabilities and further confirm that the design approach for this GDPC composite material can effectively improve device performance, enabling integrated, high-efficiency acoustic wave transmission and reception.

[0022] See also Figure 6 In one embodiment of the present invention, a method for preparing a composite piezoelectric structure is provided, comprising the following steps: Step 1: Grind the lead zirconate titanate piezoelectric ceramic (PZT5H) with 400-grit sandpaper until the thickness of the lead zirconate titanate piezoelectric ceramic is 250 μm. Use a cutting machine to perform transverse and longitudinal slits based on the center point of the cross section of the lead zirconate titanate piezoelectric ceramic after the first grinding, to obtain a transverse middle slit and a longitudinal middle slit, respectively. The depth of the transverse middle slit and the longitudinal middle slit are 190 μm and the width is 55 μm. The angle between the transverse middle slit and the longitudinal middle slit is 90°. Step 2: The prepared epoxy resin is vacuumed for 10 minutes using an oil pump to remove bubbles in the epoxy resin. The epoxy resin after the vacuuming is injected into the horizontal middle slit and the vertical middle slit by a siphon method, and a second vacuuming is performed for 10 minutes to obtain the piezoelectric material after the epoxy resin is injected. Step 3: Dry the epoxy resin-injected piezoelectric material at 40°C for 12 hours, and grind the top and bottom of the dried lead zirconate titanate piezoelectric ceramic using 800-grit sandpaper to remove excess epoxy resin covering the top surface and the ceramic support at the bottom, thereby obtaining a second-grinded lead zirconate titanate piezoelectric ceramic. Step 4: Taking the transverse middle slit of the lead zirconate titanate piezoelectric ceramic after the secondary grinding as the reference, 5 slits are made to the transverse ends of the lead zirconate titanate piezoelectric ceramic to obtain 10 transverse slits, and the 10 transverse slits are arranged in parallel. Taking the longitudinal middle slit of the lead zirconate titanate piezoelectric ceramic after the secondary grinding as the reference, 5 slits are made to the longitudinal ends of the lead zirconate titanate piezoelectric ceramic to obtain 10 longitudinal slits, and the 10 longitudinal slits are arranged in parallel. The depth of the transverse slit and the longitudinal slit is 190 μm, the width is 95 μm, and the angle between the transverse slit and the longitudinal slit is 90°; Step 5: tungsten powder and epoxy resin are respectively prepared into tungsten-epoxy mixtures with volume fractions of 10%, 20%, 30%, 40%, and 45%, and the tungsten-epoxy mixtures with volume fractions of 10%, 20%, 30%, 40%, and 45% are respectively injected into the transverse middle slit, the longitudinal middle slit, a plurality of transverse slits, and a plurality of longitudinal slits to obtain lead zirconate titanate piezoelectric ceramics injected with the tungsten-epoxy mixture; wherein the volume fractions of the tungsten-epoxy mixtures injected into the 10 transverse slits and the 10 longitudinal slits respectively increase gradually from close to the transverse middle slit and the longitudinal middle slit to away from the transverse middle slit and the longitudinal middle slit; Step 6: Use 800-grit sandpaper to grind the top surface of the piezoelectric material after the tungsten-epoxy mixture is injected, and use 2000-grit sandpaper to grind the bottom surface of the piezoelectric material after the tungsten-epoxy mixture is injected to remove the ceramic support at the bottom and the excess epoxy resin covering the top surface, so that there are no obvious scratches on the surface of the piezoelectric material, and obtain a composite piezoelectric material with a thickness of 190 μm.

[0023] In one embodiment of the present invention, a method for preparing a composite piezoelectric structure is provided, comprising the following steps: Step 1: Grind the lead zirconate titanate piezoelectric ceramic (PZT5H) with 600-grit sandpaper until the thickness of the lead zirconate titanate piezoelectric ceramic is 250 μm. Use a cutting machine to perform transverse and longitudinal slits based on the center point of the cross section of the lead zirconate titanate piezoelectric ceramic after the first grinding, to obtain a transverse middle slit and a longitudinal middle slit, respectively. The depth of the transverse middle slit and the longitudinal middle slit are 190 μm and the width is 55 μm. The angle between the transverse middle slit and the longitudinal middle slit is 90°. Step 2: The prepared epoxy resin is vacuumed for 13 minutes using an oil pump to remove bubbles in the epoxy resin. The epoxy resin after the vacuuming is injected into the horizontal middle slit and the vertical middle slit by a siphon method, and a second vacuuming is performed for 13 minutes to obtain the piezoelectric material after the epoxy resin is injected. Step 3: Dry the epoxy resin-injected piezoelectric material at 50°C for 12 hours, and grind the top and bottom of the dried lead zirconate titanate piezoelectric ceramic using 800-grit sandpaper to remove excess epoxy resin covering the top surface and the ceramic support at the bottom, thereby obtaining a second-grinded lead zirconate titanate piezoelectric ceramic. Step 4: Taking the transverse middle slit of the lead zirconate titanate piezoelectric ceramic after the secondary grinding as the reference, 5 slits are made to the transverse ends of the lead zirconate titanate piezoelectric ceramic to obtain 10 transverse slits, and the 10 transverse slits are arranged in parallel. Taking the longitudinal middle slit of the lead zirconate titanate piezoelectric ceramic after the secondary grinding as the reference, 5 slits are made to the longitudinal ends of the lead zirconate titanate piezoelectric ceramic to obtain 10 longitudinal slits, and the 10 longitudinal slits are arranged in parallel. The depth of the transverse slit and the longitudinal slit is 190 μm, the width is 95 μm, and the angle between the transverse slit and the longitudinal slit is 90°; Step 5: tungsten powder and epoxy resin are respectively prepared into tungsten-epoxy mixtures with volume fractions of 10%, 20%, 30%, 40%, and 45%, and the tungsten-epoxy mixtures with volume fractions of 10%, 20%, 30%, 40%, and 45% are respectively injected into the transverse middle slit, the longitudinal middle slit, a plurality of transverse slits, and a plurality of longitudinal slits to obtain lead zirconate titanate piezoelectric ceramics injected with the tungsten-epoxy mixture; wherein the volume fractions of the tungsten-epoxy mixtures injected into the 10 transverse slits and the 10 longitudinal slits respectively increase gradually from close to the transverse middle slit and the longitudinal middle slit to away from the transverse middle slit and the longitudinal middle slit; Step 6: Use 800-grit sandpaper to grind the top surface of the piezoelectric material after the tungsten-epoxy mixture is injected, and use 2000-grit sandpaper to grind the bottom surface of the piezoelectric material after the tungsten-epoxy mixture is injected to remove the ceramic support at the bottom and the excess epoxy resin covering the top surface, so that there are no obvious scratches on the surface of the piezoelectric material, and obtain a composite piezoelectric material with a thickness of 190 μm.

[0024] In one embodiment of the present invention, a method for preparing a composite piezoelectric structure is provided, comprising the following steps: Step 1: Grind the lead zirconate titanate piezoelectric ceramic (PZT5H) with 800-grit sandpaper until the thickness of the lead zirconate titanate piezoelectric ceramic is 250 μm. Use a cutting machine to perform transverse and longitudinal slits based on the center point of the cross section of the lead zirconate titanate piezoelectric ceramic after the first grinding, to obtain a transverse middle slit and a longitudinal middle slit, respectively. The depth of the transverse middle slit and the longitudinal middle slit are 190 μm and the width is 55 μm. The angle between the transverse middle slit and the longitudinal middle slit is 90°. Step 2: The prepared epoxy resin is vacuumed for 15 minutes using an oil pump to remove bubbles in the epoxy resin. The epoxy resin after the vacuuming is injected into the horizontal middle slit and the vertical middle slit by a siphon method, and a second vacuuming is performed for 15 minutes to obtain the piezoelectric material after the epoxy resin is injected. Step 3: Dry the epoxy resin-injected piezoelectric material at 65°C for 12 hours, and grind the top and bottom of the dried lead zirconate titanate piezoelectric ceramic using 800-grit sandpaper to remove excess epoxy resin covering the top surface and the ceramic support at the bottom, thereby obtaining a second-grinded lead zirconate titanate piezoelectric ceramic. Step 4: Based on the horizontal middle slit of the lead zirconate titanate piezoelectric ceramic after the secondary grinding, 8 slits are made to the horizontal ends of the lead zirconate titanate piezoelectric ceramic to obtain 16 horizontal slits, and the 16 horizontal slits are arranged in parallel. Based on the longitudinal middle slit of the lead zirconate titanate piezoelectric ceramic after the secondary grinding, 8 slits are made to the longitudinal ends of the lead zirconate titanate piezoelectric ceramic to obtain 16 longitudinal slits, and the 16 longitudinal slits are arranged in parallel. The depth of the horizontal slit and the longitudinal slit is 190 μm, the width is 95 μm, and the angle between the horizontal slit and the longitudinal slit is 90°; Step 5: tungsten powder and epoxy resin are respectively prepared with volume fractions of 10%, 15%, 20%, 25%, 30%, 35%, 40%, and 45% of tungsten-epoxy mixtures, and the tungsten-epoxy mixtures with volume fractions of 10%, 15%, 20%, 25%, 30%, 35%, 40%, and 45% are respectively injected into the transverse middle slit, the longitudinal middle slit, a plurality of transverse slits, and a plurality of longitudinal slits to obtain lead zirconate titanate piezoelectric ceramics injected with the tungsten-epoxy mixture; wherein the volume fractions of the tungsten-epoxy mixtures injected into the 16 transverse slits and the 16 longitudinal slits respectively show a gradually increasing trend from close to the transverse middle slit and the longitudinal middle slit to away from the transverse middle slit and the longitudinal middle slit; Step 6: Use 800-grit sandpaper to grind the top surface of the piezoelectric material after the tungsten-epoxy mixture is injected, and use 2000-grit sandpaper to grind the bottom surface of the piezoelectric material after the tungsten-epoxy mixture is injected to remove the ceramic support at the bottom and the excess epoxy resin covering the top surface, so that there are no obvious scratches on the surface of the piezoelectric material, and obtain a composite piezoelectric material with a thickness of 190 μm.

[0025] In one embodiment of the present invention, a method for preparing a composite piezoelectric ultrasonic transducer is provided, comprising the following steps: Step 1: Using the composite piezoelectric structure 2 as a piezoelectric layer, electrodes are plated on the top and bottom surfaces of the composite piezoelectric structure 2 to form a first electrode layer 3 and a second electrode layer 31, respectively. Step 2: obtain a piezoelectric material, enclose the piezoelectric material with a ceramic ring, and fill a conductive epoxy between the piezoelectric material and the ceramic ring to form a backing layer 1; Step 3: Connect the electrical conductor 6 to the bottom of the backing layer 1, circumferentially install the metal shell 5 outside the piezoelectric layer, the second electrode layer 31, the backing layer 1 and the electrical conductor 6, install the first electrode layer 3 on the top of the metal shell 5, and fill the space between the piezoelectric layer, the second electrode layer 31, the backing layer 1 and the metal shell 5 with epoxy resin; In step 4, a gold electrode and a Parylene C film are sputtered on the first electrode layer 3, the electrical conductor 6 is connected to the SMA connector 7, and then an acoustic lens 4 is installed on the top of the first electrode layer 3 after the gold electrode and the Parylene C film are sputtered to complete the preparation of the composite piezoelectric ultrasonic transducer.

[0026] The core of the present invention lies in a piezoelectric ceramic / polymer composite material with a new structure. The center of the piezoelectric ceramic PZT is used as the symmetry axis, and a polymer mixture with gradient acoustic impedance is filled in the grooves on both sides of the piezoelectric ceramic PZT, presenting a concave-valley gradient distribution of acoustic impedance on the transverse cross-section of the piezoelectric element. By changing the doping concentration of tungsten powder particles in the epoxy resin mixture, the periodic arrangement of the piezoelectric composite material is broken, and the limitation of the periodic arrangement of the piezoelectric composite material on the groove width is broken, and the first-order and second-order transverse resonances existing in the traditional 1-3 piezoelectric composite material are effectively suppressed, further improving the energy conversion efficiency and energy transmission efficiency of the piezoelectric ultrasonic transducer, making it suitable for medical ultrasonic imaging and other imaging applications requiring high resolution and high contrast. Through finite element simulation and device preparation, the structural size limitation introduced by the periodic arrangement of the piezoelectric composite structure and the periodicity of the traditional 1-3 composite material are broken, pseudo vibration is suppressed, and the energy conversion efficiency and energy transmission efficiency of the ultrasonic transducer are improved, solving the problems faced by high-frequency piezoelectric composite ultrasonic transducers in frequency enhancement, single vibration mode and its energy conversion efficiency.

[0027] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite piezoelectric structure, characterized in that: The invention comprises a piezoelectric material, wherein a transverse middle slit and a longitudinal middle slit are provided on the piezoelectric material, the intersection of the transverse middle slit and the longitudinal middle slit is located at the center point of the cross section of the piezoelectric material, and epoxy resin is injected into the transverse middle slit and the longitudinal middle slit; a plurality of transverse slits are provided from the transverse middle slit as a starting point to the end of the piezoelectric material, and a plurality of longitudinal slits are provided from the longitudinal middle slit as a starting point to the end of the piezoelectric material; a tungsten-epoxy mixture with different volume fractions is injected into the plurality of transverse slits and the plurality of longitudinal slits, and the volume fraction of the tungsten-epoxy mixture in the plurality of transverse slits and the plurality of longitudinal slits increases successively from close to the transverse middle slit and the longitudinal middle slit to far away from the transverse middle slit and the longitudinal middle slit; and the equivalent acoustic impedance of the epoxy resin and the tungsten-epoxy mixture presents a concave-valley gradient distribution.

2. A composite piezoelectric structure according to claim 1, characterized in that: The angle between the transverse middle slit and the longitudinal middle slit is 90°; the plurality of transverse slits are arranged in parallel, and the plurality of longitudinal slits are arranged in parallel.

3. The composite piezoelectric structure according to claim 1, characterized in that: The piezoelectric material is piezoelectric ceramic; the equivalent acoustic impedance is the product of equivalent density and equivalent sound velocity.

4. A composite piezoelectric ultrasonic transducer, characterized in that: A composite piezoelectric structure according to any one of claims 1 to 3, comprising a metal shell (5), an acoustic lens (4) mounted on the top of the metal shell (5), a first electrode layer (3) mounted on the bottom of the acoustic lens (4), a piezoelectric composite array element mounted on the bottom of the first electrode layer (3), the bottom of the piezoelectric composite array element being connected to an SMA connector (7) via an electrical conductor (6), the piezoelectric composite array element, the electrical conductor (6) and the SMA connector (7) being located inside the metal shell (5), and epoxy resin being filled between the piezoelectric composite array element and the metal shell (5); The piezoelectric composite array element comprises a composite piezoelectric structure (2) mounted on the bottom of a first electrode layer (3), a second electrode layer (31) and a backing layer (1) being mounted in sequence on the bottom of the composite piezoelectric structure (2), and the backing layer (1) being connected to an SMA connector (7) via an electrical conductor (6).

5. A method for preparing a composite piezoelectric structure, characterized in that: A composite piezoelectric structure according to any one of claims 1 to 3, comprising the following steps: S1, grinding the piezoelectric material once, and performing transverse slits and longitudinal slits based on the center point of the cross section of the piezoelectric material after the grinding, to obtain transverse middle slits and longitudinal middle slits, respectively; S2, vacuuming the prepared epoxy resin once, injecting the vacuumed epoxy resin into the transverse middle slit and the longitudinal middle slit by a siphon method, and vacuuming the epoxy resin twice to obtain a piezoelectric material injected with epoxy resin; S3, drying the piezoelectric material after the epoxy resin injection, and performing secondary grinding on the dried piezoelectric material to obtain a secondary ground piezoelectric material; S4, making a plurality of slits toward both ends of the piezoelectric material in the transverse direction based on the transverse middle slit of the piezoelectric material after the secondary grinding, thereby obtaining a plurality of transverse slits; making a plurality of slits toward both ends of the piezoelectric material in the longitudinal direction based on the longitudinal middle slit of the piezoelectric material after the secondary grinding, thereby obtaining a plurality of longitudinal slits; S5, preparing tungsten-epoxy mixtures of different volume fractions, respectively, and injecting the tungsten-epoxy mixtures of different volume fractions into the transverse middle slit, the longitudinal middle slit, the plurality of transverse slits, and the plurality of longitudinal slits, respectively, to obtain piezoelectric materials injected with the tungsten-epoxy mixtures; wherein the volume fractions of the tungsten-epoxy mixtures injected into the plurality of transverse slits and the plurality of longitudinal slits increase gradually from being closer to the transverse middle slit and the longitudinal middle slit to being farther away from the transverse middle slit and the longitudinal middle slit, respectively; S6, grinding the piezoelectric material injected with the tungsten-epoxy mixture three times to obtain a composite piezoelectric material.

6. The method for preparing a composite piezoelectric structure according to claim 5, wherein: The piezoelectric material in S1 is lead zirconate titanate piezoelectric ceramic; the first grinding in S1 is specifically: using 400-800 mesh sandpaper to grind until the thickness of the piezoelectric material is 250 μm; the depth of the horizontal middle slit and the longitudinal middle slit in S1 is 190 μm, and the width is 55 μm; the angle between the horizontal middle slit and the longitudinal middle slit in S1 is 90°.

7. The method for preparing a composite piezoelectric structure according to claim 5, wherein: The time for the first vacuum treatment and the second vacuum treatment in S2 is 10-15 minutes; The drying temperature in S3 is 40-65° C. and the drying time is 12 h. The secondary grinding of the dried piezoelectric material in S3 specifically comprises: grinding the top and bottom of the dried piezoelectric material using 800-grit sandpaper.

8. The method for preparing a composite piezoelectric structure according to claim 5, wherein: The depth of the transverse slit and the longitudinal slit in S4 is 190 μm, and the width is 95 μm; the plurality of transverse slits in S4 are arranged in parallel, and the plurality of longitudinal slits are arranged in parallel; the angle between the transverse slit and the longitudinal slit in S4 is 90°.

9. The method for preparing a composite piezoelectric structure according to claim 5, characterized in that: The volume fraction of the tungsten-epoxy mixture in S5 is 10% to 45%; In the S6, the piezoelectric material after the tungsten-epoxy mixture is injected is ground three times, specifically: the top surface of the piezoelectric material after the tungsten-epoxy mixture is ground using 800-grit sandpaper, and the bottom surface of the piezoelectric material after the tungsten-epoxy mixture is ground using 2000-grit sandpaper; the thickness of the composite piezoelectric material in the S6 is 190 μm.

10. A method for preparing a composite piezoelectric ultrasonic transducer, characterized in that: A composite piezoelectric ultrasonic transducer according to claim 4, comprising the following steps: The composite piezoelectric structure (2) is used as a piezoelectric layer, and electrodes are plated on the top and bottom surfaces of the composite piezoelectric structure (2) to form a first electrode layer (3) and a second electrode layer (31), respectively; Obtain a piezoelectric material, encase the piezoelectric material with a ceramic ring, and fill a conductive epoxy between the piezoelectric material and the ceramic ring to form a backing layer (1); An electric conductor (6) is connected to the bottom of the backing layer (1), a metal shell (5) is circumferentially mounted on the outside of the piezoelectric layer, the second electrode layer (31), the backing layer (1) and the electric conductor (6), the first electrode layer (3) is mounted on the top of the metal shell (5), and epoxy resin is filled between the piezoelectric layer, the second electrode layer (31), the backing layer (1) and the metal shell (5); A gold electrode and a Parylene C film are sputtered on the first electrode layer (3), an electric wire (6) is connected to an SMA connector (7), and then an acoustic lens (4) is installed on the top of the first electrode layer (3) after the gold electrode and the Parylene C film are sputtered, thereby realizing the preparation of a composite piezoelectric ultrasonic transducer.

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