A piezoelectric transducer and a method for manufacturing the same

Abstract

The present invention discloses a piezoelectric transducer and a preparation method thereof. The temperature stability of the piezoelectric transducer is greatly improved by doping perovskite-type high-temperature piezoelectric ceramics into PZT-based piezoelectric ceramics and designing a stepped amplitude structure with increasing diameter. The impedance matching condition of the piezoelectric transducer is set to achieve high electromechanical conversion efficiency and high output amplitude. The invention also has the advantages of simple process and suitability for mass production, and can well meet the needs of power ultrasonic equipment.

Description

Technical Field

[0001] The present invention relates to a transducer and a preparation method thereof, in particular to a piezoelectric transducer and a preparation method thereof, belonging to the technical field of power ultrasound. Background Art

[0002] Ultrasonic waves refer to sound waves with a frequency greater than 20KHz, which have the advantages of good directionality, strong reflection ability, and easy acquisition of concentrated sound energy. Ultrasonic technology generally includes power ultrasound and detection ultrasound. Power ultrasound technology is an application technology based on physics, mechanical vibration, electronic materials and other disciplines, which uses ultrasonic energy to change certain states of objects or object properties, including ultrasonic welding, cutting, cleaning, and spraying.

[0003] A power ultrasonic system is mainly composed of a generator, a piezoelectric transducer and a tool rod. Among them, the piezoelectric transducer is a device for energy conversion. It uses the piezoelectric effect of piezoelectric ceramics to convert the electrical energy generated by the ultrasonic generator into mechanical energy, so that the tool rod forms reciprocating telescopic vibration. As the core component of the power ultrasonic system, the characteristics of the piezoelectric transducer directly affect the performance of the entire system. The working conditions of power ultrasound often have the characteristics of high power and long cycle. Therefore, an ideal piezoelectric transducer should have the characteristics of high temperature stability. Temperature stability refers to the characteristics of the performance of the piezoelectric transducer that change with temperature. Taking the resonant frequency temperature stability as an example, it is defined as the relative change value of the resonant frequency caused by every 1°C change in temperature. The smaller the absolute value of the resonant frequency temperature stability, the less the resonant frequency of the piezoelectric transducer is affected by temperature, which is more conducive to the use of the piezoelectric transducer under high-power and long-term working conditions.

[0004] At present, the commonly used method to improve the temperature stability of piezoelectric transducers is to modify piezoelectric ceramics. Patent document 1 (CN101935215A) discloses a type of potassium sodium lithium niobate-based lead-free piezoelectric ceramic composite with good temperature stability, the general formula is: (1-x)(K 0.5 Na 0.5 ) 0.94 Li 0.06 NbO 3 -xY, where x = 0-0.05, Y is the perovskite structural element. Its characteristics are: good ferroelectricity, relatively high residual polarization intensity, relatively high piezoelectric performance, high Curie temperature, low room temperature dielectric loss and good temperature stability. It can meet the application in piezoelectric drivers, transducers, sensors and buzzers. But this lead-free (K 0.5 Na 0.5 )NbO 3 -LiNbO 3 The piezoelectric performance of piezoelectric ceramics based on d 33=108-212pC / N; kp = 33-41.6%, which cannot meet the application of power ultrasound. At the same time, since alkali metals are volatile at high temperatures, it is difficult to prepare dense (K 0.5 Na 0.5 )NbO 3 -LiNbO 3 Ceramics. Therefore, how to obtain a piezoelectric transducer with high temperature stability is an urgent problem to be solved. Summary of the invention

[0005] In order to solve the deficiencies in the prior art, the present invention provides a piezoelectric transducer and a method for preparing the same. The temperature stability of the piezoelectric transducer is greatly improved by doping perovskite-type high-temperature piezoelectric ceramics into PZT-based piezoelectric ceramics and designing a stepped amplitude structure with increasing diameter. The impedance matching conditions of the piezoelectric transducer are set to achieve high electromechanical conversion efficiency and high output amplitude. The invention also has the advantages of simple process and suitability for mass production, thereby overcoming the shortcomings of the above-mentioned process.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] The present invention provides a piezoelectric transducer, characterized in that it comprises a rear cover plate, a conductive sheet, a piezoelectric ceramic sheet, a front cover plate and bolts;

[0008] The rear cover plate is a circular ring with an outer diameter of 15 to 20 mm, an inner diameter of 4 to 6 mm, and a thickness of 10 to 12 mm;

[0009] The piezoelectric ceramic piece is a ring, the outer diameter and inner diameter of the ring are the same as the outer diameter and inner diameter of the rear cover plate, the thickness of the ring is 4 to 8 mm, and the number of the piezoelectric ceramic pieces is 2 or 4;

[0010] The front cover plate comprises a small end cylindrical section with a threaded hole, a transition arc and a large end cylindrical section. The length of the small end cylindrical section is l 1 The length of the cylindrical section at the large end is l 2 The same, 15 ~ 20mm, the diameter of the small end cylindrical section D 1 The diameter of the cylindrical section at the large end is the same as the outer diameter of the piezoelectric ceramic. 2 =(1.2~1.5)*D 1 The diameter of the threaded hole is the same as the inner diameter of the piezoelectric ceramic piece, the length of the threaded hole is 3 to 5 mm, and the transition arc R = (0.3 to 0.4) D 1 ;

[0011] The rear cover plate material is Al-xZn-yMg-zCu, x is 4-6wt.%, y is 2-4wt.%, z is 1-2wt.%, and the density is 2700-2850kg / m 3, elastic modulus is 70~80GPa;

[0012] The piezoelectric ceramic material is a PZT-doped A composite piezoelectric ceramic, the mass fraction of A in the piezoelectric ceramic is ≤5.0%, and A is BiYbO 3 -PbTiO 3 and BiInO 3 -PbTiO 3 One of the following, with a density of 7600-7800 kg / m 3 , elastic modulus is 60~70GPa;

[0013] The front cover plate material is Fe-aCr-bNi-cMo, a is 16-20wt.%, b is 8-12wt.%, c is 1-4wt.%, and the density is 7900-8000kg / m 3 , elastic modulus is 195~210GPa;

[0014] The acoustic impedance of the rear cover plate * the acoustic impedance of the front cover plate = (1-1.2) the acoustic impedance of the piezoelectric ceramic * the acoustic impedance of the piezoelectric ceramic. The acoustic impedance Z of each part is calculated by the following formula: Where ρ is the part density and E is the part elastic modulus.

[0015] As a preferred embodiment, the present invention provides a piezoelectric transducer, characterized in that the rear cover plate is at the rear end of the piezoelectric transducer, the front cover plate is at the front end of the piezoelectric transducer, the conductive sheet and the piezoelectric ceramic sheet are arranged between the rear cover plate and the front cover plate, the bolts connect and fix the rear cover plate, the conductive sheet, the piezoelectric ceramic sheet and the front cover plate together, the material of the conductive sheet is one of pure copper and zinc white copper, and the material of the bolts is one of TC4 and TC11.

[0016] The present invention provides a method for preparing a piezoelectric transducer, characterized by comprising the following steps:

[0017] S1: Preparation of piezoelectric ceramics, which is obtained by powder making, compression molding, sintering and polarization in sequence, wherein the molding pressure is 300-600 MPa and the holding time is 30-60 min; the sintering process is: in a vacuum degree of ≤5×10 -3 Pa vacuum environment, heating to 1200-1300°C at a heating rate of 5-10°C / min, keeping warm for 1-4h, cooling to 100°C with the furnace and taking out of the furnace; the polarization process is: polarization voltage 2.5-3.5KV / mm, polarization temperature 130-150°C, polarization medium is methyl silicone oil, polarization time 25-35min;

[0018] S2: Preparation of bolts and conductive sheets, both of which are made of corresponding raw materials through fine processing to obtain parts;

[0019] S3: Preparation of rear cover plate, which is processed in sequence through batching, smelting and casting, homogenization treatment, rolling, solution treatment and aging treatment to obtain rods, and finally fine processing to obtain parts. The solution treatment process is: heat preservation at 400-460℃ for 6-12h, water quenching; the aging process is: heat preservation at 90-150℃ for 8-24h, and then cooling to room temperature before taking out of the furnace;

[0020] S4: Preparation of the front cover plate, which is processed in sequence through batching, smelting and casting, homogenization treatment, blanking and forging to obtain the bar, and finally fine processing to obtain the part;

[0021] S5: Assembling, firstly, surface treatment is performed on the rear cover plate, the conductive sheet, the piezoelectric ceramic sheet, the front cover plate and the bolts, then the above components are fixed together by bolts, and finally an aging treatment is performed to obtain the piezoelectric transducer.

[0022] As a preferred embodiment, the present invention provides a method for preparing a piezoelectric transducer, characterized in that the average particle size of the piezoelectric ceramic material powder is 200 to 400 nm, and the raw material powder Pb 3 O 4 、TiO 2 、ZrO 2 With BiYbO 3 -PbTiO 3 and BiInO 3 -PbTiO 3 One of them is made by mechanical alloying.

[0023] As a preferred embodiment, a method for preparing a piezoelectric transducer according to the present invention is characterized in that the rolling temperature of the rear cover plate is 400-460°C.

[0024] As a preferred embodiment, a method for preparing a piezoelectric transducer according to the present invention is characterized in that the temperature of the homogenization treatment of the front cover plate is 950-1050°C, and the blank forging temperature is 1000-1100°C.

[0025] As a preferred embodiment, a method for preparing a piezoelectric transducer according to the present invention is characterized in that the surface treatment is grinding and precision polishing the surface of the above-mentioned part to make its roughness Ra≤500nm.

[0026] As a preferred embodiment, the present invention provides a method for preparing a piezoelectric transducer, characterized in that the aging process is: heat preservation at 90-120° C. for 8-12 hours and cooling with the furnace.

[0027] The present invention provides a piezoelectric transducer and a preparation method thereof, wherein the resonant frequency temperature coefficient of the piezoelectric transducer is 50-100 ppm / °C, the output amplitude is 10-20 um, and the electromechanical coupling coefficient is 0.75-0.9.

[0028] Principles and advantages

[0029] In order to improve the temperature stability of the piezoelectric transducer, the present invention starts from two aspects: material modification and structural modification. First, the piezoelectric transducer is a device for energy conversion. It uses piezoelectric ceramics to convert the oscillating electrical signal generated by the ultrasonic generator into a mechanical vibration signal, that is, to convert electrical energy into mechanical energy. Therefore, the piezoelectric ceramic material directly affects the performance of the piezoelectric transducer.

[0030] The traditional lead zirconate titanate piezoelectric ceramics (PZT) are mostly used in the field of power ultrasound. It is composed of ferroelectric lead titanate (PbTiO 3 ) and the antiferroelectric lead zirconate (PbZrO 3 ) forms a continuous solid solution. Although PZT piezoelectric ceramics have the advantages of high piezoelectric coefficient and high mechanical strength, their Curie temperature Tc is only 360℃. When the service temperature exceeds 1 / 2Tc, the piezoelectric ceramics will be severely depolarized, resulting in the decline of piezoelectric performance or even failure, so their temperature stability is poor. Studies have found that Bi(Me)O 3 -PbTiO 3 High temperature piezoelectric ceramics are traditional perovskite structures with a general chemical formula of ABO 3 The perovskite structure can be represented by a simple cubic lattice, with the corners occupied by A ions, the body center occupied by B ions, and the six face centers occupied by O ions. During the technical development process, the inventor optimized the elements of Me and found that the use of Yb 3+ or In 3+ When the chemical formula is BiYbO 3 -PbTiO 3 and BiInO 3 -PbTiO 3 , the tolerance factor t at this time has a smaller value range, and the tolerance factor t is calculated by the following formula:

[0031]

[0032] In the formula, rA, rB, and rO are the radii of the A site, B site, and O ions, respectively. The smaller the tolerance factor, the higher the Curie temperature of the perovskite. Therefore, the present invention dopes a proper amount of BiYbO in the PZT-based piezoelectric ceramic. 3 -PbTiO 3 or BiInO 3 -PbTiO 3 High Curie temperature piezoelectric ceramics not only ensure higher piezoelectric performance, but also obtain a high Curie temperature, giving it better temperature stability.

[0033] In addition to the optimization of piezoelectric ceramic materials, the present invention also redesigned the materials of the front and rear covers. As we all know, when sound waves propagate from one medium to another, reflected waves and transmitted waves will be generated at the interface. Part of the sound energy is reflected back at the interface, and the other part of the sound energy penetrates the interface and continues to propagate in another medium. During the propagation of sound waves, it is assumed that the medium has no absorption. According to the acoustic propagation theory, when the sound wave is incident vertically from medium 1 to medium 2, the formulas for the transmittance R and reflectance T of the sound wave are:

[0034]

[0035] T=1-R

[0036] In the formula, Z 1 is the acoustic impedance of medium 1, Z 2 is the acoustic impedance of medium 2. It can be seen from the above two equations that when the sound wave propagates from medium 1 to medium 2, the reflectivity and transmittance of the sound wave generated at the interface are only related to the acoustic impedance of medium 1 and medium 2. For traditional piezoelectric transducers, it is assumed that medium 1 is piezoelectric ceramic and medium 2 is the back cover. We hope that the transmittance R of the sound wave is as small as possible, that is, the reflectivity T is as large as possible, so that as much sound energy as possible can be reflected back to reduce energy loss. Therefore, it is necessary to select a material with a large difference between the acoustic impedance of the back cover and the acoustic impedance of the ceramic, and then consider the problem of vibration velocity ratio, then Z2 should be much larger than Z1, such as stainless steel (1.5 to 2 times piezoelectric ceramic) and tungsten alloy (3 times piezoelectric ceramic). Assume that medium 1 is piezoelectric ceramic and medium 2 is the front cover. We hope that the reflectivity T of the sound wave is as small as possible, that is, the transmittance R is as large as possible, so that as much sound energy as possible can be radiated. Therefore, it is necessary to select a material whose acoustic impedance of the front cover is close to that of the ceramic. Considering the problem of vibration velocity ratio, Z3 should be slightly smaller than Z1, such as aluminum alloy and titanium alloy (0.7-0.8 times of piezoelectric ceramic). However, the disadvantage of doing so is that the amplification factor of the piezoelectric transducer is very large and the output amplitude is very high. Since the electromechanical conversion cannot be 100%, a lot of heat is generated, which in turn affects the temperature stability. Therefore, the inventors set the rear cover to aluminum alloy and the front cover to stainless steel to reduce the amplification factor and output amplitude of the piezoelectric transducer. At the same time, in order to ensure the optimal conditions for vibration propagation in the transducer and to achieve good impedance matching of various parts, the present invention found that the impedance of each component of the transducer needs to satisfy the following relationship: rear cover acoustic impedance * front cover acoustic impedance = (1-1.2) piezoelectric ceramic acoustic impedance * piezoelectric ceramic acoustic impedance. The acoustic impedance Z of each part is calculated by the following formula: In the formula, ρ is the density of the part, and E is the elastic modulus of the part. The density and elastic modulus of each part are adjusted to a suitable value through the coordinated cooperation of the composition and the preparation process. When the parts of the piezoelectric transducer meet this relationship, the transducer has the best impedance matching and high electromechanical conversion efficiency, which not only ensures the appropriate output amplitude, but also can well control the generation of heat and greatly improve the temperature stability.

[0037] In addition to the improvement in materials, in terms of the modification of the front cover structure, for traditional piezoelectric transducers, the role of the front cover is to amplify the displacement amplitude (or vibration velocity), or to concentrate the energy on a smaller area, that is, the energy-gathering effect. For example, in ultrasonic cutting, ultrasonic welding and metal processing, an amplitude of tens or even hundreds of microns is required, while the output displacement amplitude of piezoelectric ceramics is only a few microns. Therefore, the front cover must be used to amplify the mechanical action, so a stepped front cover with a decreasing diameter is often used to increase the output amplitude, but the larger output amplitude brings a significant increase in internal stress, the heating of the overall structure increases, and the energy loss also increases. Therefore, the inventor first designed the stepped front cover into an increasing diameter type, with a small diameter at the sound wave input end and a large diameter at the sound wave output end. This can properly control the amplitude increment and reduce heating. Secondly, due to the sudden change in the transition between the large end and the small end section of the stepped segment amplitude rod, it is easy to cause stress concentration, causing fatigue fracture at high temperature. Therefore, it is considered to set a transition arc at the cross-section mutation point of the stepped front cover plate, which can not only reduce stress concentration but also make the actual resonant frequency closer to the theoretical value. The present invention optimizes the transition arc parameters and finds that when R is 0.3 to 0.4 times the diameter of the small end cylindrical section, an optimal amplitude and heat generation performance can be obtained, thereby achieving improved temperature stability.

[0038] In addition, the assembly process of the piezoelectric transducer will also affect the temperature stability. 1) The surface roughness of the component. The smoother the surface of the part, the less mechanical loss will be generated between the interfaces, which is more conducive to the transfer of charge to the capacitor, so as to ensure that the charge transfer process will not produce unnecessary reduction, and improve the temperature stability; 2) The necessity of aging treatment. It was found in the experiment that the results of multiple measurements of the transducer varied greatly within a short period of time after the prestress was applied. The reason is that after the prestress is applied to the transducer, it takes a relatively long time for the distribution of the electric domain to become uniform, so that the state of the transducer is stable. Therefore, artificial aging is used to accelerate the process of uniform distribution of the electric domain and improve temperature stability.

[0039] Compared with the prior art, the advantages of the present invention are as follows:

[0040] 1) High temperature stability. Doping perovskite-type high-temperature piezoelectric ceramics in PZT-based piezoelectric ceramics and designing a stepped amplitude structure with increasing diameters can greatly improve the temperature stability of the piezoelectric transducer, which is twice as high as the existing technology;

[0041] 2) High electromechanical conversion efficiency. Design the impedance matching conditions of the piezoelectric transducer. When the acoustic impedance of the rear cover plate * the acoustic impedance of the front cover plate = (1-1.2) the acoustic impedance of the piezoelectric ceramic * the acoustic impedance of the piezoelectric ceramic, a good electromechanical conversion efficiency is obtained, which is 30% higher than the existing technology;

[0042] 3) The process is simple and suitable for mass production. Piezoelectric ceramics are made using powder metallurgy, and the remaining metal parts are basically made using traditional ingot metallurgy, without any special and complex processes, which is suitable for industrial production.

[0043] In summary, the present invention provides a piezoelectric transducer and a preparation method thereof. By doping perovskite-type high-temperature piezoelectric ceramics into PZT-based piezoelectric ceramics and designing a stepped amplitude structure with increasing diameter, the temperature stability of the piezoelectric transducer is greatly improved, and the impedance matching conditions of the piezoelectric transducer are set to achieve high electromechanical conversion efficiency and high output amplitude. At the same time, it has the advantages of simple process and suitability for mass production, and can well meet the needs of power ultrasonic equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of a piezoelectric transducer, wherein 1-bolt, 2-rear cover plate, 3-conductive sheet, 4-piezoelectric ceramic, 5-front cover plate, and 6-arc. DETAILED DESCRIPTION

[0045] The method of the present invention is further described below with reference to two examples.

[0046] Embodiment 1:

[0047] A piezoelectric transducer and a method for preparing the same, the process is as follows:

[0048] S1: Preparation of piezoelectric ceramics, PZT+5%BiYbO with an average particle size of 200nm 3 -PbTiO 3 The ceramic powder is molded and sintered to obtain a piezoelectric ceramic sheet. The molding pressure of the molding is 400MPa and the holding time is 50min. The sintering process is as follows: in a vacuum degree of ≤5×10 -3 Pa vacuum environment, the temperature was raised to 1250℃ at a rate of 5℃ / min, kept at this temperature for 3h, and then cooled to 100℃ and taken out of the furnace; the polarization voltage was 3KV / mm, the polarization temperature was 130℃, the polarization medium was methyl silicone oil, and the polarization time was 25min; the outer and inner diameters of the piezoelectric ceramic piece were 16mm and 6mm respectively, the thickness was 5mm, and the density was 7650kg / m 3 , elastic modulus is 65GPa;

[0049] S2: bolts and conductive sheets are prepared by finishing TC4 titanium alloy and pure copper respectively;

[0050] S3: Preparation of rear cover plate. Al-4Zn-2.5Mg-1Cu (wt.%) alloy is successively subjected to batching, smelting and casting, homogenization treatment, rolling, solution treatment and aging treatment to obtain rods, and finally fine processing to obtain parts. The rolling temperature is 450°C, the solution treatment process is: 400°C insulation for 6h, water quenching; the aging process is: 120°C insulation for 16h, and then cooled to room temperature. The outer and inner diameters of the rear cover plate are 16mm and 6mm respectively, the thickness is 10mm, and the density is 2800kg / m 3 , elastic modulus is 72GPa;

[0051] S4: Preparation of front cover plate. Fe-18Cr-10Ni-2Mo (wt.%) alloy is successively subjected to batching, smelting and casting, homogenization treatment, and blank forging to obtain rods, and finally fine processing to obtain parts. The homogenization temperature is 1000℃, and the blank forging temperature is 1050℃. The front cover plate includes three parts: a small end cylindrical section with a threaded hole, a transition arc, and a large end cylindrical section. The length of the small end cylindrical section is l 1 The length of the cylindrical section at the large end is l 2 The same, 15mm, the diameter of the small end cylindrical section D 1 The diameter of the cylindrical section at the large end is 16 mm. 2 The diameter of the threaded hole is 20.8mm, the length of the threaded hole is 6mm, the transition arc R is 6.4mm, and the density is 7950kg / m 3 , elastic modulus is 200GPa;

[0052] S5: Assembly, firstly, the rear cover plate, the conductive sheet, the two piezoelectric ceramic sheets, the front cover plate and the bolts are ground and precisely polished to make the roughness Ra of 400nm, then the above components are fixed together by bolts, and finally the piezoelectric transducer is aged. The aging process is: 120℃ insulation for 8h, followed by furnace cooling;

[0053] S6: Performance test, the resonant frequency temperature coefficient of the piezoelectric transducer is 60ppm / ℃, the output amplitude is 15um, and the electromechanical coupling coefficient is 0.8.

[0054] Embodiment 2:

[0055] A piezoelectric transducer and a method for preparing the same, the process is as follows:

[0056] S1: Preparation of piezoelectric ceramics, PZT + 3% BiYbO with an average particle size of 250nm 3 -PbTiO 3 The ceramic powder is molded and sintered to obtain a piezoelectric ceramic sheet. The molding pressure of the molding is 400MPa; the holding time is 50min, and the sintering process is: in a vacuum degree of ≤5×10-3 Pa vacuum environment, the temperature was raised to 1280℃ at a rate of 5℃ / min, kept at this temperature for 2h, and then cooled to 100℃. The polarization voltage was 3KV / mm, the polarization temperature was 140℃, the polarization medium was methyl silicone oil, and the polarization time was 30min. The outer and inner diameters of the piezoelectric ceramic piece were 16mm and 6mm respectively, the thickness was 5mm, and the density was 7680kg / m 3 , elastic modulus is 66GPa;

[0057] S2: bolts and conductive sheets are made of TC11 titanium alloy and pure copper respectively through fine machining to obtain parts;

[0058] S3: Preparation of rear cover plate. Al-4.5Zn-2Mg-1Cu (wt.%) alloy is successively subjected to batching, smelting and casting, homogenization treatment, rolling, solution treatment and aging treatment to obtain rods, and finally fine processing to obtain parts. The rolling temperature is 450°C, the solution treatment process is: 400°C insulation for 6h, water quenching; the aging process is: 120°C insulation for 16h, and then cooled to room temperature before being taken out of the furnace; the outer and inner diameters of the rear cover plate are 16mm and 6mm respectively, the thickness is 10mm, and the density is 2850kg / m 3 , elastic modulus is 70GPa;

[0059] S4: Preparation of front cover plate. Fe-16Cr-11Ni-1Mo (wt.%) alloy is successively subjected to batching, smelting and casting, homogenization treatment, blank forging to obtain rods, and finally fine processing to obtain parts. The homogenization temperature is 1000℃, and the blank forging temperature is 1050℃. The front cover plate includes three parts: a small end cylindrical section with a threaded hole, a transition arc and a large end cylindrical section. The length of the small end cylindrical section is l 1 The length of the cylindrical section at the large end is l 2 The same, 15mm, the diameter of the small end cylindrical section D 1 The diameter of the cylindrical section at the large end is 16 mm. 2 The diameter of the threaded hole is 20.8mm, the length of the threaded hole is 6mm, the transition arc R is 6.4mm, and the density is 7980kg / m 3 , elastic modulus is 202GPa;

[0060] S5: Assembly, firstly, the rear cover plate, the conductive sheet, the two piezoelectric ceramic sheets, the front cover plate and the bolts are ground and precisely polished to make the roughness Ra of 400nm, then the above components are fixed together by bolts, and finally the piezoelectric transducer is aged. The aging process is: 120℃ insulation for 8h, followed by furnace cooling;

[0061] S6: Performance test, the resonant frequency temperature coefficient of the piezoelectric transducer is 65ppm / ℃, the output amplitude is 16um, and the electromechanical coupling coefficient is 0.82.

[0062] Embodiment 3:

[0063] A piezoelectric transducer and a method for preparing the same, the process is as follows:

[0064] S1: Preparation of piezoelectric ceramics, PZT + 3% BiInO with an average particle size of 250nm 3 -PbTiO 3 The ceramic powder is molded and sintered to obtain a piezoelectric ceramic sheet. The molding pressure of the molding is 400MPa; the holding time is 50min, and the sintering process is: in a vacuum degree of ≤5×10 -3 Pa vacuum environment, the temperature was raised to 1300℃ at a rate of 5℃ / min, kept at that temperature for 1h, and then cooled to 100℃. The polarization voltage was 3.5KV / mm, the polarization temperature was 130℃, the polarization medium was methyl silicone oil, and the polarization time was 25min. The outer and inner diameters of the piezoelectric ceramic piece were 16mm and 6mm respectively, the thickness was 5mm, and the density was 7750kg / m 3 , elastic modulus is 68GPa;

[0065] S2: bolts and conductive sheets are prepared by finishing TC11 titanium alloy and zinc-nickel copper respectively;

[0066] S3: Preparation of rear cover plate. Al-4.5Zn-2Mg-1Cu (wt.%) alloy is successively subjected to batching, smelting and casting, homogenization treatment, rolling, solution treatment and aging treatment to obtain rods, and finally fine processing to obtain parts. The rolling temperature is 450°C, the solution treatment process is: 400°C insulation for 6h, water quenching; the aging process is: 120°C insulation for 16h, and then cooled to room temperature before being taken out of the furnace; the outer and inner diameters of the rear cover plate are 16mm and 6mm respectively, the thickness is 10mm, and the density is 2850kg / m 3 , elastic modulus is 70GPa;

[0067] S4: Preparation of front cover plate. Fe-16Cr-11Ni-1Mo (wt.%) alloy is successively subjected to batching, smelting and casting, homogenization treatment, blank forging to obtain rods, and finally fine processing to obtain parts. The homogenization temperature is 1000℃, and the blank forging temperature is 1050℃. The front cover plate includes three parts: a small end cylindrical section with a threaded hole, a transition arc and a large end cylindrical section. The length of the small end cylindrical section is l 1 The length of the cylindrical section at the large end is l 2 The same, 15mm, the diameter of the small end cylindrical section D 1 The diameter of the cylindrical section at the large end is 16 mm. 2 The diameter of the threaded hole is 20.8mm, the length of the threaded hole is 6mm, the transition arc R is 6.4mm, and the density is 7980kg / m3 , elastic modulus is 202GPa;

[0068] S5: Assembly, firstly, the rear cover plate, the conductive sheet, the two piezoelectric ceramic sheets, the front cover plate and the bolts are ground and precisely polished to make the roughness Ra of 450nm, then the above components are fixed together by bolts, and finally the piezoelectric transducer is aged. The aging process is: 90℃ for 12h, followed by furnace cooling;

[0069] S6: Performance test, the resonant frequency temperature coefficient of the piezoelectric transducer is 70ppm / ℃, the output amplitude is 18um, and the electromechanical coupling coefficient is 0.85.

[0070] The above-described examples are only preferred implementation methods of the present invention, and therefore cannot be used to limit the scope of implementation of the present invention. Other equivalent changes, modifications, substitutions and combinations made in accordance with the principles and contents of the present invention still fall within the protection scope of the present invention.

Claims

1. A piezoelectric transducer, characterized in that, it includes a rear cover plate, a conductive sheet, a piezoelectric ceramic sheet, a front cover plate and a bolt; The rear cover plate is a ring, the outer diameter of the ring is 15 - 20 mm, the inner diameter of the ring is 4 - 6 mm, and the thickness of the ring is 10 - 12 mm; The piezoelectric ceramic sheet is a ring, the outer diameter and the inner diameter of the ring are the same as the outer diameter and the inner diameter of the rear cover plate respectively, the thickness of the ring is 4 - 8 mm, and the number of piezoelectric ceramic sheets is 2 or 4; The front cover plate includes a small end cylindrical section with a threaded hole, a transition arc and a large end cylindrical section. The length of the small end cylindrical section is l 1 The length of the cylindrical section at the large end is l 2 The same, 15 ~ 20mm, the diameter of the small end cylindrical section D 1 The diameter of the cylindrical section at the large end is the same as the outer diameter of the piezoelectric ceramic. 2 =(1.2~1.5)*D 1 The diameter of the threaded hole is the same as the inner diameter of the piezoelectric ceramic piece, the length of the threaded hole is 3 to 5 mm, and the transition arc R = (0.3 to 0.4) D 1 ; The rear cover material is Al-xZn-yMg-zCu, where x is 4-6wt.%, y is 2-4wt.%, z is 1-2wt.%, and the density is 2700-2850kg / m 3 , elastic modulus is 70~80GPa; The piezoelectric ceramic sheet material is PZT doped with A composite piezoelectric ceramic, the mass fraction of A in the piezoelectric ceramic is ≤5.0%, and A is BiYbO 3 -PbTiO 3 and BiInO 3 -PbTiO 3 One of the following, with a density of 7600-7800 kg / m 3 , elastic modulus is 60~70GPa; The front cover material is Fe-aCr-bNi-cMo, a is 16-20wt.%, b is 8-12wt.%, c is 1-4wt.%, and the density is 7900-8000kg / m 3 , elastic modulus is 195~210GPa; The acoustic impedance of the rear cover plate * the acoustic impedance of the front cover plate = (1-1.2) the acoustic impedance of the piezoelectric ceramic * the acoustic impedance of the piezoelectric ceramic. The acoustic impedance Z of each part is calculated by the following formula: Where ρ is the part density and E is the part elastic modulus.

2. The piezoelectric transducer according to claim 1, characterized in that, The rear cover plate is at the rear end of the piezoelectric transducer, the front cover plate is at the front end of the piezoelectric transducer, the conductive sheet and the piezoelectric ceramic sheet are arranged between the rear cover plate and the front cover plate, and the bolt connects and fixes the rear cover plate, the conductive sheet, the piezoelectric ceramic sheet and the front cover plate together. The material of the conductive sheet is one of pure copper and nickel silver, and the material of the bolt is one of TC4 and TC11.

3. The preparation method of the piezoelectric transducer according to claim 1 or 2, characterized in that, it includes the following steps: S1: Preparation of piezoelectric ceramics. The piezoelectric ceramic products are obtained through powder making, die pressing, sintering, and poling in sequence. The forming pressure for die pressing is 300 - 600 MPa, and the pressure holding time is 30 - 60 min. The sintering process is as follows: in a vacuum environment with a vacuum degree ≤ 5×10 - 3 Pa, the temperature is raised to 1200 - 1300 °C at a heating rate of 5 - 10 °C / min, held for 1 - 4 h, and then cooled to 100 °C in the furnace and taken out. The poling process is: the poling voltage is 2.5 - 3.5 KV / mm, the poling temperature is 130 - 150 °C, the poling medium is methyl silicone oil, and the poling time is 25 - 35 min; S2: Preparation of the bolt and the conductive sheet, and parts are obtained by precision machining using corresponding raw materials; S3: Preparation of the rear cover plate, a bar is obtained by successively going through batching, melting and casting, homogenization treatment, rolling, solution treatment and aging treatment, and finally a part is obtained by precision machining. The solution process is: heat preservation at 400 - 460 °C for 6 - 12 h, water quenching; the aging process is: heat preservation at 90 - 150 °C for 8 - 24 h, furnace cooling to room temperature and then taking out of the furnace; S4: Preparation of the front cover plate, a bar is obtained by successively going through batching, melting and casting, homogenization treatment, and cogging forging, and finally a part is obtained by precision machining; S5: Assembly, first perform surface treatment on the rear cover plate, the conductive sheet, the piezoelectric ceramic sheet, the front cover plate and the bolt, then fix the above components together by bolts, and finally perform aging treatment to obtain the piezoelectric transducer. The surface treatment is to grind and precisely polish the surfaces of the above parts to make the surface roughness Ra ≤ 500 nm.

4. The preparation method of the piezoelectric transducer according to claim 3, characterized in that, The average particle size of the piezoelectric ceramic sheet material powder is 200-400nm. 3 O 4 、TiO 2 、ZrO 2 With BiYbO 3 -PbTiO 3 and BiInO 3 -PbTiO 3 One of them is made by mechanical alloying.

5. The preparation method of the piezoelectric transducer according to claim 3, characterized in that, The rolling temperature of the rear cover plate is 400 - 460 °C.

6. The preparation method of the piezoelectric transducer according to claim 3, characterized in that, The temperature of the homogenization treatment of the front cover plate is 950 - 1050 °C, and the cogging forging temperature is 1000 - 1100 °C.

7. The preparation method of the piezoelectric transducer according to claim 3, characterized in that, The aging process is: heat preservation at 90 - 120 °C for 8 - 12 h, furnace cooling.

8. The preparation method of the piezoelectric transducer according to claim 3, characterized in that, The resonance frequency temperature coefficient of the piezoelectric transducer is 50 - 100 ppm / °C, the output amplitude is 10 - 20 μm, and the electromechanical coupling coefficient is 0.75 - 0.9.

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