Ultrasonic endoscope transducer based on lead-free piezoelectric material as well as preparation method and application of ultrasonic endoscope transducer

Abstract

The invention discloses an ultrasonic endoscope transducer based on a lead-free piezoelectric ceramic material as well as a preparation method and application of the ultrasonic endoscope transducer. The ultrasonic transducer comprises an acoustic backing layer, a lead-free piezoelectric layer, an acoustic matching layer and a coaxial wire, the lead-free piezoelectric layer is made of lead-free piezoelectric ceramic or a lead-free piezoelectric ceramic composite material; according to the method, the matching layer is prepared by adopting a spin-coating method, so that the method has huge advantages in preparation of a micron-sized matching layer, and a new way is provided for preparation of the matching layer of the high-frequency ultrasonic transducer. A gradient matching material is used as an acoustic matching layer, and materials with low, medium and high acoustic impedances are prepared as the gradient acoustic matching layer, so that the sensitivity and the bandwidth can be effectively improved, and the performance of the transducer is improved; the lead-free piezoelectric ceramic and the lead-free piezoelectric ceramic composite material used for preparing the piezoelectric layer of the ultrasonic transducer have the advantages of being thin in thickness, high in dielectric constant, high in piezoelectric coefficient and the like, the amplitude is high, the sensitivity is high, the relative bandwidth is large, and the imaging effect of an ultrasonic endoscope system is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of ultrasonic transducers, and particularly relates to an ultrasonic endoscope transducer based on lead-free piezoelectric materials, a preparation method and application thereof. BACKGROUND

[0002] With the deepening of the aging trend and the worsening of environmental problems, the incidence of digestive and respiratory diseases is increasing, and the demand for ultrasonic endoscopy is gradually increasing. The incidence of digestive and respiratory cancer is also rising. People are increasingly paying attention to early screening of related cancers.

[0003] Surface cancer screening based on optical endoscopes cannot meet people's demand for health, and ultrasonic endoscope heads can penetrate deep into tissue structures to screen for internal lesions, and are favored by people. The core component of the ultrasonic endoscope head is the piezoelectric ultrasonic transducer. At present, the piezoelectric part of most ultrasonic transducers adopts zirconium titanate lead (PZT) ceramic material. PZT piezoelectric ceramics have high Curie temperature, strong piezoelectricity, easy doping modification, good stability and other characteristics, and have been the focus of attention and research since the 1960s. They are dominant in the field of piezoelectric ceramics. However, PZT-based ceramics contain a large amount of Pb, which can cause serious damage to the human ecological environment during production, use and disposal. Lead is a heavy metal element with neurotoxicity, and the younger the age, the more sensitive to lead toxicity. Fetuses are most susceptible to lead toxicity. Children with lead poisoning grow slowly, are short in stature, and have low intelligence. According to official data from the World Health Organization, more than 600,000 children worldwide suffer from lead poisoning and delayed intellectual development each year.

[0004] In medical ultrasonic transducers, the acoustic matching layer is a key component for achieving high-performance acoustic transmission. Its core function is to solve the large difference between the high acoustic impedance of piezoelectric materials and the low acoustic impedance of human tissues, and to widen the frequency band, improve sensitivity and resolution through impedance transition. At present, the traditional acoustic matching layer usually adopts a single-layer or double-layer structure. The theoretical optimal acoustic impedance of a single-layer matching layer is the geometric mean of the acoustic impedance of the piezoelectric material and the load medium, while a double-layer matching layer achieves wider frequency band matching through two specific impedance steps. The materials of these matching layers are mostly composites composed of epoxy resin and inorganic fillers such as tungsten powder, aluminum oxide or silicon dioxide. However, the available composite systems for adjustment are limited, and it is often difficult to accurately match this theoretical value. The inherent narrowband characteristics of single-layer structures limit their performance in wideband applications, and the design and preparation process of double-layer matching layers are more complex.

[0005] In terms of manufacturing processes, the most basic method is the "casting-curing-bonding" method, which involves mechanically mixing epoxy resin with fillers such as tungsten powder and alumina, pouring the mixture into a mold, curing it, and then bonding it to the piezoelectric material with an adhesive. This method is simple, but filler sedimentation is difficult to avoid, leading to poor material uniformity. Furthermore, the additional adhesive layer introduces unnecessary acoustic losses and performance variations. To improve film uniformity and thickness control, the doctor blade method and the casting method are widely used. The doctor blade method precisely sets the slurry thickness by controlling the gap between the doctor blade and the substrate, forming a matching layer after curing. The casting method goes a step further, spreading the slurry through a fixed blade or on a casting machine, enabling the production of large-area films with better thickness uniformity. Nevertheless, both methods still face significant challenges: First, to obtain specific high acoustic impedance, a high proportion of inorganic fillers is required, which can easily lead to a sharp increase in slurry viscosity and defects during the coating or casting process; second, they also face the problem of secondary bonding with piezoelectric elements, and interface loss is unavoidable; finally, for multilayer structures that require precise control of thickness and impedance gradient, traditional methods must rely on a cumbersome process of independent fabrication, polishing, and bonding of each layer, which not only leads to discontinuities in interlayer interface impedance and damage to acoustic performance, but also causes problems such as complex processes, low yield, and high costs, which seriously restrict the practical application and industrialization of high-performance multilayer gradient matching structures.

[0006] Therefore, the acoustic matching layers in the existing technology are structurally limited to simple single-layer or double-layer models, and their fabrication is hampered by material uniformity, layer thickness control, and interface problems when integrating multiple layers, making it difficult to meet the urgent needs of modern ultrasonic transducers for wider bandwidth, higher resolution, and consistency. Summary of the Invention

[0007] To address the aforementioned issues, this invention provides a method for fabricating and applying an ultrasonic transducer based on lead-free piezoelectric materials. The ultrasonic transducer in the ultrasonic endoscope is fabricated using lead-free sodium bismuth niobate-based ceramics, barium calcium titanate-based ceramics, barium titanate-based piezoelectric ceramics, or lead-free piezoelectric ceramic-based composite materials.

[0008] The first aspect of this invention provides an ultrasonic endoscope transducer based on lead-free piezoelectric material, comprising, from bottom to top, an acoustic backing layer, a lead-free piezoelectric layer, and an acoustic matching layer; the lead-free piezoelectric layer is connected to the coaxial line core wire, and the acoustic backing layer is connected to the coaxial line ground wire; The lead-free piezoelectric layer is a lead-free piezoelectric ceramic or a lead-free piezoelectric ceramic composite material; The acoustic matching layers are arranged in descending order of acoustic impedance, from bottom to top as a first acoustic impedance matching layer, a second acoustic impedance matching layer, and a third acoustic impedance matching layer; and the first acoustic impedance matching layer is connected to the lead-free piezoelectric layer. The third acoustic impedance matching layer is prepared by spin coating a mixture of polyvinylidene fluoride and polymethyl methacrylate in a mass ratio of 50~60:40~50. The second layer, the acoustic impedance matching layer, is prepared by adding 10% to 30% of ceramic powder by mass to the mixture and then spin-coating it. The first layer, the high acoustic impedance matching layer, is prepared by adding 50% to 65% of ceramic powder by mass to the mixture and then spin-coating it.

[0009] In another preferred embodiment, during the spin coating process for preparing the first acoustic impedance matching layer, the spin coating is performed at a speed of 1000 rpm to 1500 rpm for 10 to 20 seconds, and then adjusted to a speed of 2000 rpm to 3000 rpm for another 10 to 20 seconds. Specifically, polyvinylidene fluoride and polyglycerol methacrylate are dissolved in an organic reagent, and then lead-free ceramic powder is added to obtain a spin coating solution. The spin coating solution is first spin coated at a speed of 1000 rpm to 1500 rpm for 15 to 20 seconds, and then adjusted to a speed of 2000 rpm to 3000 rpm for another 10 to 15 seconds before drying. In the process of preparing the second acoustic impedance matching layer by spin coating, the spin coating is performed at a speed of 1000 rpm to 1500 rpm for 10 to 20 seconds, and then adjusted to a speed of 2000 rpm to 2500 rpm for 15 to 20 seconds. Specifically, polyvinylidene fluoride and polyglycerol methacrylate are dissolved in an organic reagent, and then lead-free ceramic powder is added to obtain a spin coating solution. The spin coating solution is first spin coated at a speed of 1000 rpm to 1500 rpm for 15 to 20 seconds, and then adjusted to a speed of 2000 rpm to 2500 rpm for 10 to 15 seconds, and then dried. In the process of preparing the third acoustic impedance matching layer by spin coating, the spin coating is performed at a speed of 1000 rpm to 1500 rpm for 10 to 20 seconds, and then adjusted to a speed of 2000 rpm to 3000 rpm for another 10 to 20 seconds. Specifically, polyvinylidene fluoride and polyglycerol methacrylate are dissolved in an organic reagent to obtain a spin coating solution. The spin coating solution is first spin coated at a speed of 1000 rpm to 1500 rpm for 10 to 20 seconds, and then adjusted to a high speed of 2000 rpm to 2500 rpm for another 10 to 20 seconds, followed by drying.

[0010] Since the matching layers need to be prepared with different thicknesses, the spin coating speed varies depending on the thickness. The faster the speed, the longer the spin coating time, and the thinner the prepared matching layer. Furthermore, the solutions prepared by the three matching layers have different concentrations, with the concentrations of the third, second, and first acoustic impedance matching layers increasing continuously. Therefore, in order to ensure that the first acoustic impedance matching layer is evenly dispersed on the piezoelectric layer, the rotation speed needs to be increased.

[0011] In another preferred embodiment, the acoustic impedance of the first acoustic impedance matching layer is 9.5 MRayls to 11.5 MRayls; The acoustic impedance of the second acoustic impedance matching layer is 4.5 MRayls to 7 MRayls; The acoustic impedance of the third acoustic impedance matching layer is 2.4 MRayls to 2.8 MRayls.

[0012] In another preferred embodiment, the thickness of the first acoustic impedance matching layer is 40 μm to 90 μm; The thickness of the second acoustic impedance matching layer is 35μm~80μm; The thickness of the third acoustic impedance matching layer is 25μm~35μm.

[0013] In another preferred embodiment, the lead-free piezoelectric ceramic is any one of sodium bismuth niobate-based ceramic, barium calcium titanate-based ceramic, barium titanate-based piezoelectric ceramic, sodium bismuth niobate-based lead-free piezoelectric textured ceramic, and barium calcium titanate-based lead-free piezoelectric textured ceramic.

[0014] In another preferred embodiment, the lead-free piezoelectric ceramic composite material refers to any one of the following: bismuth sodium niobate-based ceramics, barium calcium titanate-based ceramics, and barium titanate-based piezoelectric ceramics, used as the piezoelectric phase and epoxy resin as the matrix, resulting in any one of the 1-3, 2-3, and 2-2 type piezoelectric ceramic composite materials.

[0015] In another preferred embodiment, the frequency range of the lead-free piezoelectric layer is 8MHz to 25MHz, and the thickness is 70μm to 260μm; The lead-free piezoelectric layer is plated with metal electrodes on both its upper and lower surfaces. The metal electrode is formed by magnetron sputtering of nickel-chromium-gold or platinum materials to obtain a metal electrode with a thickness of 50nm~1000nm.

[0016] In another preferred embodiment, the thickness of the acoustic backing layer is 0.3 mm to 1.2 mm; the acoustic backing layer is an AB adhesive with conductive properties doped with metal powder.

[0017] The second aspect of this invention provides a method for fabricating the ultrasonic endoscopic transducer based on lead-free piezoelectric materials, comprising the following steps: Polyvinylidene fluoride and polymethyl methacrylate are mixed in a mass ratio of 50~60:40~50 to obtain a mixture; the mixture is then mixed with an organic solvent to obtain a spin-coating solution for the third acoustic impedance matching layer. Add 10% to 30% by weight of ceramic powder to the mixture and mix with an organic solvent to obtain a spin-coating solution for the second acoustic impedance matching layer. Add 50% to 65% by weight of ceramic powder to the mixture and mix with an organic solvent to obtain a spin-coating solution for the first high acoustic impedance matching layer; the organic solvent is N,N-dimethylformamide. Spin coating liquid of the first high acoustic impedance matching layer is applied to one side of the lead-free piezoelectric layer at a speed of 1000 rpm to 1500 rpm for 10 to 20 seconds, and then the speed is adjusted to 2000 rpm to 3000 rpm for 10 to 20 seconds to obtain a surface with the first high acoustic impedance matching layer. A second acoustic impedance matching layer is obtained by spin-coating a second acoustic impedance matching layer onto a surface with a first acoustic impedance matching layer at a speed of 1000 rpm to 1500 rpm for 10 to 20 seconds, and then at a speed of 2000 rpm to 2500 rpm for 15 to 20 seconds. A third acoustic impedance matching layer is then spin-coated onto the second acoustic impedance matching layer at a speed of 1000 rpm to 1500 rpm for 10 to 20 seconds, and then at a speed of 2000 rpm to 3000 rpm for 10 to 20 seconds. The conductive AB glue doped with metal powder is cast onto the other side of the lead-free piezoelectric layer to obtain the acoustic backing layer. A corner of the acoustic matching layer is scraped open to expose the metal electrode. The coaxial core wire is soldered to the electrode with solder beads, and the coaxial ground wire is bonded to the backing layer with conductive adhesive to obtain the ultrasonic endoscopic transducer made of the lead-free piezoelectric material.

[0018] The third aspect of the present invention provides the application of the aforementioned lead-free piezoelectric material-based ultrasonic endoscopic transducer in the fabrication of ultrasonic endoscopic probes.

[0019] Compared with the prior art, the present invention has the following beneficial effects: The piezoelectric layer used in this invention is a lead-free piezoelectric ceramic or a lead-free piezoelectric ceramic composite material, posing no threat to the environment or human health, especially for ultrasound endoscopes used for internal examinations. Furthermore, the gradient matching layer is prepared using a spin-coating method with three different acoustic impedance materials: low, medium, and high. The low acoustic impedance matching layer is prepared using a mixture of polyvinylidene fluoride (PVDF) and polymethyl methacrylate (PMMA), while the medium and high acoustic impedance matching layers are prepared using a mixture of PVDF, PMMA, and lead-free ceramic powder. This method not only produces a more uniform and thinner layer compared to traditional methods but also offers significant advantages in the preparation of micron-level matching layers, providing a new approach for the preparation of matching layers for high-frequency ultrasonic transducers and promoting the development of high-frequency transducers. The gradient matching layer used in this invention can effectively improve sensitivity and bandwidth, enhancing transducer performance.

[0020] The lead-free piezoelectric ceramics and lead-free piezoelectric ceramic composites used in the piezoelectric layer of the ultrasonic transducer in this invention have the characteristics of thin thickness, high dielectric constant, and high piezoelectric coefficient. The preparation method is simple and easy to mass-produce. Furthermore, the ultrasonic transducer made with lead-free piezoelectric materials has high amplitude, high sensitivity, and large relative bandwidth, which greatly improves the imaging effect of the ultrasonic endoscopy system. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the ultrasonic endoscope transducer of the present invention; in the figure: 1 is the acoustic matching layer; 2 is the lead-free piezoelectric layer; 3 is the acoustic backing layer; 4 is the coaxial core wire; and 5 is the coaxial ground wire.

[0022] Figure 2 This is a time-domain signal characteristic diagram of the ultrasonic endoscope transducer prepared in Example 2 of the present invention.

[0023] Figure 3 It is a frequency domain signal characteristic map of the ultrasonic endoscope transducer prepared in Embodiment 2 of the invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0026] A lead-free ceramic or lead-free piezoelectric ceramic composite material can be used to fabricate the ultrasonic transducer in an ultrasonic endoscope, such as Figure 1 As shown, it consists of a gradient matching layer 1, a lead-free piezoelectric layer 2, a doped backing layer 3, and coaxial lines 4 and 5.

[0027] The gradient matching layer is made of three different acoustic impedance materials: low, medium, and high. The low acoustic impedance matching layer is made of a mixture of PVDF and PMMA. The medium and high acoustic impedance matching layers are made of a mixture of PVDF, PMMA, and lead-free ceramic powder. The lead-free piezoelectric layer is made of lead-free piezoelectric ceramic material or lead-free piezoelectric ceramic composite material. The backing layer is made of metal-doped and modified conductive AB glue material, which comes from Zhonglixin Technology Co., Ltd.

[0028] The following is a detailed explanation of ultrasonic transducers made of lead-free piezoelectric materials.

[0029] Example 1: An ultrasonic endoscope transducer made of lead-free piezoelectric material, wherein the ultrasonic endoscope probe transducer operates at a frequency of 8MHz.

[0030] The ultrasonic endoscopic transducer made of lead-free piezoelectric material consists of, from bottom to top, an acoustic backing layer, a lead-free piezoelectric layer, and an acoustic matching layer. The lead-free piezoelectric layer is connected to the coaxial cable core wire, and the acoustic backing layer is connected to the coaxial cable ground wire. The lead-free piezoelectric layer is made of lead-free piezoelectric ceramic material, specifically sodium bismuth niobate-based ceramic, with a thickness of 235 μm. Metal electrodes are plated on both the top and bottom surfaces of the lead-free piezoelectric layer. The metal electrodes are formed by magnetron sputtering of nickel-chromium-gold and platinum materials, with an electrode thickness of 200 nm. The acoustic matching layer is 200 μm thick.

[0031] The specific fabrication process of the ultrasonic endoscopic transducer made of the aforementioned lead-free piezoelectric material is as follows: S1. Take 12g of PVDF and dissolve it in 200mL of N,N-dimethylformamide. Mix and stir evenly. Add 8g of PMMA and continue stirring to obtain the mixture, which is the spin coating solution for the third acoustic impedance matching layer. Take 10 mL of the mixture and add 65% of the mixture's mass, i.e., 1.85 g of lead-free ceramic powder, and stir to obtain the spin coating solution for the first acoustic impedance matching layer; Take 10 mL of the mixture and add 30% of the mixture mass, i.e., 0.43 g of lead-free ceramic powder, and stir thoroughly to obtain the spin coating solution for the second acoustic impedance matching layer.

[0032] S2. After the lead-free piezoelectric layer is cleaned with plasma, it is used as a substrate and adsorbed in the center of the spin coater. Using a dropper, three to four drops of the spin coating liquid for the first acoustic impedance matching layer are applied to the piezoelectric layer. The spin coater is set to 1500 rpm for 20 seconds, then adjusted to a high speed of 2500 rpm for 20 seconds, until the adhesive is completely and evenly spread. The layer is then removed and cured in an oven at 60°C for 1 hour to obtain the first acoustic impedance matching layer with a thickness of approximately 45 μm. If the required matching layer thickness is not achieved, the above steps need to be repeated. Spin coat the layer again to achieve a thickness of 85 μm to 90 μm for the first acoustic impedance matching layer. A piezoelectric material with a first high acoustic impedance matching layer on its surface is used as a substrate and adsorbed onto the center of a spin coater. Three to four drops of the spin-coating liquid for the second acoustic impedance matching layer are applied onto the first acoustic impedance matching layer using a dropper. The spin coater is set to 1500 rpm for 20 seconds, then adjusted to a high speed of 2500 rpm for 15 seconds, until the adhesive is completely and evenly spread. The adhesive is then removed and cured in an oven at 60°C for 1 hour to obtain the desired second acoustic impedance matching layer with a thickness of approximately 40 μm. If the desired matching layer thickness is not achieved, the above steps need to be repeated, and the adhesive is then applied again to achieve a second acoustic impedance matching layer thickness of 75 μm to 80 μm. Three to four droplets of the spin-coating liquid for the third acoustic impedance matching layer are placed on the second acoustic impedance matching layer. The spin coating speed is set to 1200 rpm for 20 seconds, then adjusted to a high speed of 2500 rpm for 15 seconds, until the adhesive is completely and evenly spread. The adhesive is then removed and cured in an oven at 60°C for 1 hour to obtain the desired third acoustic impedance matching layer with a thickness of approximately 35 μm.

[0033] S3. Cast a conductive acoustic backing layer on the other side of the lead-free piezoelectric layer, controlling its thickness to 0.6 mm. The acoustic backing layer is made of conductive AB adhesive doped with metal powder, cut into 3 mm × 1.5 mm particles before casting. Scrape open a corner of the acoustic matching layer to expose the metal electrodes, and solder the coaxial cable core wire to the electrodes using solder balls. Attach the coaxial cable ground wire to the backing layer using conductive adhesive.

[0034] In this example, the acoustic impedance of the low acoustic impedance matching layer is 2.8 MRayls; the acoustic impedance of the medium acoustic impedance matching layer is 7 MRayls; and the acoustic impedance of the high acoustic impedance matching layer is 11.5 MRayls.

[0035] Example 2: A lead-free piezoelectric ultrasonic transducer with an operating frequency of 16MHz.

[0036] The ultrasonic transducer made of lead-free piezoelectric material consists of, from bottom to top, an acoustic backing layer, a lead-free piezoelectric layer, and an acoustic matching layer. The lead-free piezoelectric layer is connected to the coaxial cable core wire, and the acoustic backing layer is connected to the coaxial cable ground wire. The lead-free piezoelectric layer is made of lead-free piezoelectric ceramic material with a thickness of 120 μm. Metal electrodes are plated on both sides of the lead-free piezoelectric layer. The metal electrodes are formed by magnetron sputtering of nickel-chromium-gold and platinum materials, with an electrode thickness of 200 nm. The acoustic matching layer has a thickness of 120 μm.

[0037] The specific fabrication process of the ultrasonic endoscopic transducer made of the aforementioned lead-free piezoelectric material is as follows: S1. Take 12g of PVDF and dissolve it in 200mL of N,N-dimethylformamide solution. Mix and stir evenly. Take 8g of PMMA and continue stirring to obtain a mixture, which is the spin coating solution for the third acoustic impedance matching layer. Take 10 mL of the mixture and add 65% of the mixture's mass, i.e., 1.85 g of lead-free ceramic powder, and stir to obtain the spin coating solution for the first acoustic impedance matching layer.

[0038] Take 10 mL of the mixture and add 30% of the mixture's mass, i.e., 0.43 g of lead-free ceramic powder, and stir thoroughly to obtain the spin coating solution for the second acoustic impedance matching layer; S2. After the lead-free piezoelectric layer is cleaned with plasma, it is used as a substrate and adsorbed in the center of the spin coater. Using a dropper, three to four drops of the spin coating liquid for the first acoustic impedance matching layer are applied to the piezoelectric layer. The spin coater is set to 1500 rpm for 20 seconds, then adjusted to a high speed of 2500 rpm for 20 seconds, until the adhesive is completely and evenly spread. The layer is then removed and cured in an oven at 60°C for 1 hour to obtain the desired high acoustic impedance matching layer with a thickness of approximately 45 μm.

[0039] The piezoelectric material with a first high acoustic impedance matching layer on its surface is used as a substrate and adsorbed in the center of the spin coater. Three to four drops of the spin coating liquid for the second acoustic impedance matching layer are applied to the first acoustic impedance matching layer using a dropper. The spin coater is set to 1500 rpm for 20 seconds, then adjusted to a high speed of 2500 rpm for 20 seconds, until the adhesive is completely and evenly spread. The adhesive is then removed and cured in an oven at 60°C for 1 hour to obtain the desired medium acoustic impedance matching layer with a thickness of approximately 40 μm.

[0040] A piezoelectric material with a second high acoustic impedance matching layer on its surface is used as a substrate and adsorbed in the center of a spin coater. Three to four drops of the spin coating liquid for the third acoustic impedance matching layer are applied to the second acoustic impedance matching layer using a dropper. The spin coater is set to 1200 rpm for 20 seconds, then adjusted to a high speed of 2500 rpm for 15 seconds until the adhesive is completely and evenly spread. The adhesive is then removed and cured in an oven at 60°C for 1 hour to obtain the desired low acoustic impedance matching layer with a thickness of approximately 35 μm.

[0041] S3. Cast a conductive backing layer on the other side of the lead-free piezoelectric layer, controlling its thickness to 0.6 mm. The acoustic backing layer is made of conductive AB adhesive doped with metal powder, cut into 3 mm × 1.5 mm particles before casting. Scrape open a corner of the matching layer to expose the metal electrodes, and solder the coaxial cable core wire to the electrodes using solder balls. Adhere the coaxial cable ground wire to the backing layer using conductive adhesive.

[0042] In this example, the acoustic impedance of the low acoustic impedance matching layer is 2.8 MRayls; the acoustic impedance of the medium acoustic impedance matching layer is 7 MRayls; and the acoustic impedance of the high acoustic impedance matching layer is 11.5 MRayls.

[0043] Example 3: An ultrasonic endoscope transducer made of lead-free piezoelectric material, wherein the ultrasonic endoscope probe transducer operates at a frequency of 20MHz.

[0044] The ultrasonic transducer made of lead-free piezoelectric material consists of, from bottom to top, an acoustic backing layer, a lead-free piezoelectric layer, and an acoustic matching layer. The lead-free piezoelectric layer is connected to the coaxial cable core wire, and the acoustic backing layer is connected to the coaxial cable ground wire. The lead-free piezoelectric layer is made of lead-free piezoelectric ceramic material with a thickness of 95 μm. Metal electrodes are plated on both sides of the lead-free piezoelectric layer. The metal electrodes are formed by magnetron sputtering of nickel-chromium-gold and platinum materials, with an electrode thickness of 200 nm. The acoustic matching layer is 100 μm thick.

[0045] The specific fabrication process of the ultrasonic endoscopic transducer made of the aforementioned lead-free piezoelectric material is as follows: S1. To prepare the PVDF and PMMA mixed solution, take 12g of PVDF and dissolve it in 200ml of N,N-dimethylformamide solution. Mix and stir evenly. Take 8g of PMMA and continue stirring to obtain the mixture, which is the spin coating solution for the third acoustic impedance matching layer. Take 10 mL of the mixture and add 65% of the mixture's mass, i.e., 1.85 g of lead-free ceramic powder, and stir to obtain the spin coating solution for the first acoustic impedance matching layer; Take 10 mL of the mixture and add 30% of the mixture mass, i.e., 0.43 g of lead-free ceramic powder, and stir thoroughly to obtain the spin coating solution for the second acoustic impedance matching layer.

[0046] S2. After the lead-free piezoelectric layer is cleaned with plasma, it is used as a substrate and adsorbed in the center of the spin coater. Using a dropper, three to four drops of the spin coating liquid for the first acoustic impedance matching layer are applied to the piezoelectric layer. The spin coater is set to 1500 rpm for 20 seconds, then adjusted to 3000 rpm for 15 seconds until the adhesive is completely and evenly spread. The layer is then removed and cured in an oven at 60°C for 1 hour to obtain the desired high acoustic impedance matching layer with a thickness of approximately 40 μm.

[0047] The piezoelectric material with a first high acoustic impedance matching layer on its surface is used as a substrate and adsorbed in the center of the spin coater. Three to four drops of the spin coating liquid for the second acoustic impedance matching layer are applied to the first acoustic impedance matching layer using a dropper. The spin coater is set to 1500 rpm for 20 seconds, then adjusted to a high speed of 3000 rpm for 15 seconds until the adhesive is completely and evenly spread. The adhesive is then removed and cured in an oven at 60°C for 1 hour to obtain the desired medium acoustic impedance matching layer with a thickness of approximately 35 μm.

[0048] Three to four droplets of the spin-coating liquid for the third acoustic impedance matching layer are placed on the second acoustic impedance matching layer. The spin coating speed is set to 1200 rpm for 20 seconds, then adjusted to a high speed of 3000 rpm for 15 seconds, until the adhesive is completely and evenly spread. The layer is then removed and cured in an oven at 60°C for 1 hour to obtain the desired low acoustic impedance matching layer with a thickness of approximately 25 μm.

[0049] S3. Cast a conductive acoustic backing layer on the other side of the lead-free piezoelectric layer, controlling its thickness to 0.6 mm. The acoustic backing layer is made of conductive AB adhesive doped with metal powder, cut into 3 mm × 1.5 mm particles before casting. Scrape open a corner of the matching layer to expose the metal electrodes, and solder the coaxial cable core wire to the electrodes using solder balls. Attach the coaxial cable ground wire to the backing layer using conductive adhesive.

[0050] In this example, the acoustic impedance of the low acoustic impedance matching layer is 2.8 MRayls; the acoustic impedance of the medium acoustic impedance matching layer is 7 MRayls; and the acoustic impedance of the high acoustic impedance matching layer is 11.5 MRayls.

[0051] Example 4: Lead-free piezoelectric ultrasonic transducer, the ultrasonic transducer of which operates at a frequency of 8MHz.

[0052] The ultrasonic transducer made of lead-free piezoelectric material consists of, from bottom to top, an acoustic backing layer, a lead-free piezoelectric layer, and an acoustic matching layer. The lead-free piezoelectric layer is connected to the coaxial cable core wire, and the acoustic backing layer is connected to the coaxial cable ground wire. The lead-free piezoelectric layer is a lead-free piezoelectric ceramic composite material with a thickness of 175 μm. Metal electrodes are plated on both sides of the lead-free piezoelectric layer. The metal electrodes are formed by magnetron sputtering of nickel-chromium-gold and platinum materials, with an electrode thickness of 200 nm. The acoustic matching layer is 200 μm thick.

[0053] The specific fabrication process of the ultrasonic endoscopic transducer made of the aforementioned lead-free piezoelectric material is as follows: S1. Take 10g of PVDF and dissolve it in 200mL of N,N-dimethylformamide solution. Mix and stir evenly. Add 10g of PMMA and continue stirring to obtain a mixture, which is the spin coating solution for the third acoustic impedance matching layer. Take 10 mL of the mixture and add 50% of the mixture mass, i.e., 1 g of lead-free ceramic powder, and stir to obtain the spin coating solution for the first acoustic impedance matching layer. Take 10 mL of the mixture and add 10% of the mixture mass, i.e., 0.11 g of lead-free ceramic powder, and stir thoroughly to obtain the spin coating solution for the second acoustic impedance matching layer.

[0054] S2. After plasma cleaning, the lead-free piezoelectric layer is used as a substrate and adsorbed in the center of the spin coater. Using a dropper, three to four drops of the spin coating liquid for the first acoustic impedance matching layer are applied to the piezoelectric layer. The spin coater is set to 1500 rpm for 20 seconds, then adjusted to a high speed of 2500 rpm for 15 seconds, until the adhesive is completely and evenly spread. The layer is then removed and cured in an oven at 60°C for 1 hour to obtain the desired high acoustic impedance matching layer with a thickness of approximately 45 μm. If the desired matching layer thickness is not achieved, the above steps need to be repeated, and the spin coater is applied again to achieve a high acoustic impedance matching layer thickness of 85 μm to 90 μm.

[0055] A piezoelectric material with a first high acoustic impedance matching layer on its surface is used as a substrate and adsorbed onto the center of a spin coater. Three to four drops of the spin-coating liquid for the second acoustic impedance matching layer are applied onto the first acoustic impedance matching layer using a dropper. The spin coater is set to 1500 rpm for 15 seconds, then adjusted to a high speed of 2500 rpm for 15 seconds, until the adhesive is completely and evenly spread. The adhesive is then removed and cured in an oven at 60°C for 1 hour to obtain the desired medium acoustic impedance matching layer with a thickness of approximately 40 μm. If the desired matching layer thickness is not achieved, the above steps need to be repeated, and the adhesive is spin-coated again to achieve a medium acoustic impedance matching layer thickness of 75 μm to 80 μm.

[0056] Three to four droplets of the spin-coating liquid for the third acoustic impedance matching layer are placed on the second acoustic impedance matching layer. The spin coating speed is set to 1500 rpm for 20 seconds, then adjusted to a high speed of 3000 rpm for 15 seconds, until the adhesive is completely and evenly spread. The adhesive is then removed and cured in an oven at 60°C for 1 hour to obtain the desired low acoustic impedance matching layer with a thickness of approximately 35 μm.

[0057] S3. Cast a conductive acoustic backing layer on the other side of the lead-free piezoelectric layer, controlling its thickness to 0.6 mm. The acoustic backing layer is made of conductive AB adhesive doped with metal powder, cut into 3 mm × 1.5 mm particles before casting. Scrape open a corner of the matching layer to expose the metal electrodes, and solder the coaxial cable core wire to the electrodes using solder balls. Attach the coaxial cable ground wire to the backing layer using conductive adhesive.

[0058] In this example, the acoustic impedance of the low acoustic impedance matching layer is 2.4 MRayls; the acoustic impedance of the medium acoustic impedance matching layer is 4.5 MRayls; and the acoustic impedance of the high acoustic impedance matching layer is 9.5 MRayls.

[0059] Example 5: An ultrasonic endoscope transducer made of lead-free piezoelectric material, wherein the ultrasonic endoscope probe transducer operates at a frequency of 20MHz.

[0060] The ultrasonic transducer made of lead-free piezoelectric material consists of, from bottom to top, an acoustic backing layer, a lead-free piezoelectric layer, and an acoustic matching layer. The lead-free piezoelectric layer is connected to the coaxial cable core wire, and the acoustic backing layer is connected to the coaxial cable ground wire. The lead-free piezoelectric layer is primarily a lead-free piezoelectric ceramic composite material with a thickness of 70 μm. Metal electrodes are plated on both sides of the lead-free piezoelectric layer. The metal electrodes are formed by magnetron sputtering of nickel-chromium-gold and platinum materials, with a thickness of 200 nm. The acoustic matching layer is 100 μm thick.

[0061] The specific fabrication process of the ultrasonic endoscopic transducer made of the aforementioned lead-free piezoelectric material is as follows: S1. Take 10g of PVDF and dissolve it in 200mL of N,N-dimethylformamide solution. Mix and stir evenly. Add 10g of PMMA and continue stirring to obtain a mixture, which is the spin coating solution for the third acoustic impedance matching layer. Take 10 mL of the mixture and add 50% of the mixture mass, i.e., 1 g of lead-free ceramic powder, and stir to obtain the spin coating solution for the first acoustic impedance matching layer. Take 10 mL of the mixture and add 10% of the mixture mass, i.e., 0.11 g of lead-free ceramic powder, and stir thoroughly to obtain the spin coating solution for the second acoustic impedance matching layer.

[0062] S2. After the lead-free piezoelectric layer is cleaned with plasma, it is used as a substrate and adsorbed in the center of the spin coater. Using a dropper, three to four drops of the spin coating liquid for the first acoustic impedance matching layer are applied to the piezoelectric layer. The spin coater is set to 1500 rpm for 20 seconds, then adjusted to 3000 rpm for 15 seconds until the adhesive is completely and evenly spread. The layer is then removed and cured in an oven at 60°C for 1 hour to obtain the desired high acoustic impedance matching layer with a thickness of approximately 40 μm.

[0063] The piezoelectric material with a first high acoustic impedance matching layer on its surface is used as a substrate and adsorbed in the center of a spin coater. Three to four drops of the spin coating liquid for the second acoustic impedance matching layer are applied to the first acoustic impedance matching layer using a dropper. The spin coater is set to a speed of 1500 rpm for 20 seconds, then adjusted to a high speed of 3000 rpm for 15 seconds, until the adhesive is completely and evenly spread. The adhesive is then removed and cured in an oven at 60°C for 1 hour to obtain the desired medium acoustic impedance matching layer with a thickness of approximately 35 μm.

[0064] Three to four droplets of the spin coating liquid for the third acoustic impedance matching layer are placed on the second acoustic impedance matching layer. The spin coating speed is set to 1500 rpm for 20 seconds, then adjusted to a high speed of 3000 rpm for 20 seconds, until the adhesive is completely and evenly spread. The adhesive is then removed and cured in an oven at 60°C for 1 hour to obtain the desired low acoustic impedance matching layer with a thickness of approximately 25 μm.

[0065] S3. Cast a conductive acoustic backing layer on the other side of the lead-free piezoelectric layer, controlling its thickness to 0.6 mm. The acoustic backing layer is made of conductive AB adhesive doped with metal powder, cut into 3 mm × 1.5 mm particles before casting. Scrape open a corner of the matching layer to expose the metal electrodes, and solder the coaxial cable core wire to the electrodes using solder balls. Attach the coaxial cable ground wire to the backing layer using conductive adhesive.

[0066] In this example, the acoustic impedance of the low acoustic impedance matching layer is 2.4 MRayls; the acoustic impedance of the medium acoustic impedance matching layer is 4.5 MRayls; and the acoustic impedance of the high acoustic impedance matching layer is 9.5 MRayls.

[0067] Examples 1 through 5 above all yielded ultrasonic endoscopic transducers made of lead-free piezoelectric material, with comparable performance. The ultrasonic endoscopic transducer made of lead-free piezoelectric material prepared in Example 2 is used as an example for characterization. Pulse echo waveforms and spectra were obtained using a pulse receiver (5073PR, Olympus, Japan) and an oscilloscope (Tektronik 3012). The results are as follows: Figure 2 and Figure 3 As shown.

[0068] from Figure 2 It can be seen that the echo peak voltage is high, indicating that the transducer has high sensitivity. From Figure 3 It can be seen that the center frequency of the transducer is 16MHz, and the transducer bandwidth can reach 75%. In summary, the ultrasonic transducer made of lead-free piezoelectric material has high amplitude, high sensitivity, and large relative bandwidth, which greatly improves the imaging effect of the ultrasonic endoscopy system.

[0069] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An ultrasonic endoscopic transducer based on lead-free piezoelectric materials, characterized in that, From bottom to top, the layers are an acoustic backing layer, a lead-free piezoelectric layer, and an acoustic matching layer; the lead-free piezoelectric layer is connected to a coaxial core wire, and the acoustic backing layer is connected to a coaxial ground wire. The lead-free piezoelectric layer is a lead-free piezoelectric ceramic or a lead-free piezoelectric ceramic composite material; The acoustic matching layers are arranged in descending order of acoustic impedance, from bottom to top as a first acoustic impedance matching layer, a second acoustic impedance matching layer, and a third acoustic impedance matching layer; and the first acoustic impedance matching layer is connected to the lead-free piezoelectric layer. The third acoustic impedance matching layer is prepared by spin coating a mixture of polyvinylidene fluoride and polymethyl methacrylate in a mass ratio of 50~60:40~50. The second acoustic impedance matching layer is prepared by adding 10% to 30% ceramic powder by mass of the mixture to the mixture and then preparing it by spin coating. The first high acoustic impedance matching layer is prepared by adding 50% to 65% ceramic powder by mass of the mixture to the mixture and then preparing it by spin coating.

2. The ultrasonic endoscopic transducer based on lead-free piezoelectric material according to claim 1, characterized in that, During the preparation of the first acoustic impedance matching layer by spin coating, the spin coating is performed at a speed of 1000 rpm to 1500 rpm for 10 s to 20 s, and then adjusted to a speed of 2000 rpm to 3000 rpm for 10 s to 20 s. During the preparation of the second acoustic impedance matching layer by spin coating, spin coating is performed at a speed of 1000 rpm to 1500 rpm for 10 s to 20 s, and then adjusted to a speed of 2000 rpm to 2500 rpm for 15 s to 20 s. During the preparation of the third acoustic impedance matching layer by spin coating, the spin coating is performed at a speed of 1000 rpm to 1500 rpm for 10 to 20 seconds, and then adjusted to a speed of 2000 rpm to 3000 rpm for another 10 to 20 seconds.

3. The ultrasonic endoscopic transducer based on lead-free piezoelectric material according to claim 1, characterized in that, The acoustic impedance of the first acoustic impedance matching layer is 9.5 MRayls to 11.5 MRayls; The acoustic impedance of the second acoustic impedance matching layer is 4.5 MRayls to 7 MRayls; The acoustic impedance of the third acoustic impedance matching layer is 2.4 MRayls to 2.8 MRayls.

4. The ultrasonic endoscopic transducer based on lead-free piezoelectric material according to claim 1, characterized in that, The thickness of the first acoustic impedance matching layer is 40μm~90μm; The thickness of the second acoustic impedance matching layer is 35μm~80μm; The thickness of the third acoustic impedance matching layer is 25μm~35μm.

5. The ultrasonic endoscopic transducer based on lead-free piezoelectric material according to claim 1, characterized in that, The lead-free piezoelectric ceramic is any one of sodium bismuth niobate-based ceramics, barium calcium titanate-based ceramics, barium titanate-based piezoelectric ceramics, sodium bismuth niobate-based lead-free piezoelectric textured ceramics, and barium calcium titanate-based lead-free piezoelectric textured ceramics.

6. The ultrasonic endoscopic transducer based on lead-free piezoelectric material according to claim 1, characterized in that, The lead-free piezoelectric ceramic composite material refers to any one of the following: bismuth sodium niobate-based ceramics, barium calcium titanate-based ceramics, and barium titanate-based piezoelectric ceramics, as the piezoelectric phase, and epoxy resin as the matrix, resulting in any one of the 1-3, 2-3, and 2-2 type piezoelectric ceramic composite materials.

7. The ultrasonic endoscopic transducer based on lead-free piezoelectric material according to claim 1, characterized in that, The frequency range of the lead-free piezoelectric layer is 8MHz~25MHz, and the thickness is 70μm~260μm; The lead-free piezoelectric layer is plated with metal electrodes on both its upper and lower surfaces. The metal electrode is formed by magnetron sputtering of nickel-chromium-gold and platinum materials to obtain a metal electrode with a thickness of 50nm~1000nm.

8. The ultrasonic endoscopic transducer made of lead-free piezoelectric material according to claim 1, characterized in that, The thickness of the acoustic backing layer is 0.3mm~1.2mm; The acoustic backing layer is an AB adhesive with conductive properties, doped with metal powder.

9. A method for fabricating an ultrasonic endoscopic transducer based on lead-free piezoelectric materials as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Polyvinylidene fluoride (PVDF) and polymethyl methacrylate (PMMA) are mixed in a mass ratio of 50-60:40-50 to obtain a mixture; the mixture is then mixed with an organic solvent to obtain a spin-coating solution for the third acoustic impedance matching layer. Add 10% to 30% by weight of ceramic powder to the mixture and mix with an organic solvent to obtain a spin-coating solution for the second acoustic impedance matching layer. Add 50% to 65% by weight of ceramic powder to the mixture and mix with an organic solvent to obtain a spin-coating solution for the first high acoustic impedance matching layer. Spin coating liquid of the first high acoustic impedance matching layer is applied to one side of the lead-free piezoelectric layer at a speed of 1000 rpm to 1500 rpm for 10 to 20 seconds, and then the speed is adjusted to 2000 rpm to 3000 rpm for 10 to 20 seconds to obtain a surface with the first high acoustic impedance matching layer. A second acoustic impedance matching layer is obtained by spin-coating a second acoustic impedance matching layer onto a surface with a first acoustic impedance matching layer at a speed of 1000 rpm to 1500 rpm for 10 to 20 seconds, and then at a speed of 2000 rpm to 2500 rpm for 15 to 20 seconds. A third acoustic impedance matching layer is then spin-coated onto the second acoustic impedance matching layer at a speed of 1000 rpm to 1500 rpm for 10 to 20 seconds, and then at a speed of 2000 rpm to 3000 rpm for 10 to 20 seconds. The conductive AB glue doped with metal powder is cast onto the other side of the lead-free piezoelectric layer to obtain the acoustic backing layer. A corner of the acoustic matching layer is scraped open to expose the metal electrode. The coaxial core wire is soldered to the electrode with solder beads, and the coaxial ground wire is bonded to the backing layer with conductive adhesive to obtain the ultrasonic endoscopic transducer made of the lead-free piezoelectric material.

10. The application of the ultrasonic endoscope transducer based on lead-free piezoelectric material as described in any one of claims 1 to 8 in the fabrication of an ultrasonic endoscope probe.

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