Preparation method of low-density ultrasonic transducer backing based on thermal expansion

Abstract

The invention provides a preparation method of a low-density ultrasonic transducer backing based on thermal expansion, which comprises the following steps of: 1, uniformly mixing epoxy resin, a curing agent and hollow microspheres before curing to obtain a mixed fluid; the hollow microspheres are made of polymer materials. And 2, adding the mixed fluid obtained in the step 1 into a soft mold which can expand under internal pressure, and heating and curing at 60-80 DEG C to obtain the ultrasonic transducer backing. Through a soft mold expansion method, the hollow microspheres are heated and expanded in the epoxy resin curing process to occupy the reserved space in the soft mold, and the soft mold and the epoxy resin are pushed to be expanded together after the hollow microspheres are filled in the soft mold, so that the density bottleneck of a traditional preparation scheme is broken through, and the density of the transducer backing is greatly reduced. In addition, a dense porous structure is formed in the transducer backing through expansion of the hollow microspheres, so that the sound attenuation coefficient of the transducer backing is increased while the density is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of acoustic materials, and in particular relates to a method for preparing a low-density ultrasonic transducer backing based on thermal expansion. Background Art

[0002] In recent decades, acoustic technology has developed significantly, and transducers are widely used in different fields such as medical ultrasound, sonar imaging, and non-destructive testing. The transducer consists of a piezoelectric element, a matching layer, a backing layer, and a circuit. The piezoelectric element allows the transducer to achieve the conversion between acoustic energy and electrical energy through the piezoelectric effect and the inverse piezoelectric effect. The matching layer is a layer or layers of materials with different acoustic impedances pasted on the piezoelectric element. The energy transmission efficiency and the working frequency band of the transducer are adjusted by acoustic impedance matching. The backing layer provides mechanical support for the transducer body and reduces the tailing of the transducer receiving signal through sound absorption, which improves the signal bandwidth to a certain extent. The backing can be divided into high acoustic impedance backing and low acoustic impedance backing according to the size of the acoustic impedance. The acoustic impedance of the high acoustic impedance backing is usually between 10-30 MRayl, which is similar to the acoustic impedance of the piezoelectric element material. The sound wave dissipates more energy into the backing, the sound wave is more attenuated, the interference pulse duration is short, but the sensitivity is low at the same time. The acoustic impedance of low acoustic impedance backing is less than 10 MRayl, which is quite different from the acoustic impedance of piezoelectric element materials. Its acoustic wave reflection energy is larger and its sensitivity is higher, but its acoustic attenuation ability is weaker than that of high acoustic impedance backing, and its interference pulse duration is longer. The ideal backing material should have low acoustic impedance to ensure high sensitivity while having a high acoustic attenuation coefficient to reduce the duration of interference pulses.

[0003] The traditional method of preparing transducer backing materials is to add solid powder (such as tungsten powder, tungsten oxide, hollow microspheres, etc.) to the main body of liquid epoxy resin, mix and solidify at low temperature (about 50°C). However, there are some problems with this method of preparing backing materials: the acoustic impedance of backing materials made with metal and metal oxide powders as fillers is large, usually greater than 2.5 MRayl; when hollow microspheres are used as fillers, as the mass fraction increases, the material mixing tends to be uneven, and there are limit values ​​for density and sound velocity. Its density is usually greater than 700kg / m^3, and the sound velocity is greater than 1700m / s, and the acoustic impedance of the backing material is greater than 1.2 MRayl.

[0004] In view of the above problems, the present invention uses a soft mold expansion method, uses a soft mold at high temperature, and changes the expansion volume of the internal hollow microspheres by adjusting the curing temperature, thereby reducing the density of the backing material and increasing the sound attenuation coefficient. The method proposed by the present invention ensures that the backing material is evenly distributed while generating dense small pores inside, and the prepared backing material has a lower acoustic impedance and a higher sound attenuation coefficient. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a low-density ultrasonic transducer backing based on thermal expansion, and a series of backing materials used in transducers are prepared by using a soft mold and changing the curing temperature of the backing material.

[0006] In a first aspect, the present invention provides a method for preparing a low-density ultrasonic transducer backing based on thermal expansion, which comprises the following steps: Step 1: Evenly mix the epoxy resin before curing, the curing agent and the hollow microspheres to obtain a mixed fluid. The hollow microspheres are made of polymer material.

[0007] Step 2: Add the mixed fluid obtained in step 1 into the mold, and reserve the space required for expansion in the mold; heat the mixed fluid added to the mold at 60° C. to 80° C. to expand and solidify, so as to obtain the ultrasonic transducer backing.

[0008] Preferably, the volume of the mixed fluid added to the mold in step 2 is 2 / 3 to 3 / 4 of the volume of the mold; the mold is a soft mold that can expand under internal pressure; the material of the soft mold is rubber or silicone.

[0009] Preferably, the mass fraction of the hollow microspheres in the epoxy resin, the curing agent and the hollow microspheres before curing is less than or equal to 9.1%.

[0010] Preferably, the mass ratio of the epoxy resin, the curing agent and the hollow microspheres before curing is (10-20):(0.1-4):(0.1-2).

[0011] Preferably, the hollow microspheres are made of one or more of polystyrene, phenolic resin, polyurethane, and cured epoxy resin.

[0012] Preferably, the particle size of the hollow microspheres is less than or equal to 15 μm.

[0013] Preferably, the epoxy resin comprises a rigid epoxy resin and a flexible epoxy resin. The Young's modulus of the rigid epoxy resin after curing is greater than the Young's modulus of the flexible epoxy resin after curing. The mass ratio of the rigid epoxy resin to the flexible epoxy resin is (8-15):5.

[0014] Preferably, the Young's modulus of the rigid epoxy resin after curing is 2 GPa (inclusive) to 5 GPa (inclusive); the Young's modulus of the flexible epoxy resin after curing is less than 2 GPa, preferably 1 GPa (inclusive) to 2 GPa (exclusive).

[0015] Preferably, in step 1, the epoxy resin, curing agent and hollow microspheres are mixed uniformly by centrifugation.

[0016] In a second aspect, the present invention provides a method for controlling the acoustic impedance of a transducer backing, comprising the following steps: Step 1: Evenly mix the epoxy resin before curing, the curing agent and the hollow microspheres to obtain a mixed fluid. The hollow microspheres are made of polymer material.

[0017] Step 2: Set the target curing temperature according to the target acoustic impedance. The larger the target acoustic impedance, the lower the target curing temperature. The target curing temperature range is 20°C to 80°C.

[0018] Step 3: Add the mixed fluid obtained in step 1 into a soft mold that is pressurized and expandable, and heat and cure it at the target curing temperature obtained in step 2 to obtain an ultrasonic transducer backing.

[0019] Preferably, the target curing temperature is obtained according to the target acoustic impedance and the relationship between the target curing temperature and the target acoustic impedance. The relationship between the target curing temperature and the target acoustic impedance is obtained through experiments.

[0020] In a third aspect, the present invention provides a method for controlling the acoustic attenuation coefficient of a transducer backing, which comprises the following steps: Step 1, uniformly mixing the epoxy resin before curing, the curing agent and the hollow microspheres to obtain a mixed fluid; the hollow microspheres are made of polymer material; Step 2: Set the target curing temperature according to the target acoustic attenuation coefficient; the larger the target acoustic attenuation coefficient, the larger the target curing temperature is set; the target curing temperature range is 20°C to 80°C; Step 3: Add the mixed fluid obtained in step 1 into a soft mold that is pressurized and expandable, and heat and cure it at the target curing temperature obtained in step 2 to obtain an ultrasonic transducer backing.

[0021] Preferably, the target curing temperature is obtained according to the target acoustic attenuation coefficient and the relationship between the target curing temperature and the target acoustic attenuation coefficient. The relationship between the target curing temperature and the target acoustic attenuation coefficient is obtained through experiments.

[0022] The beneficial effects of the present invention are: 1. The present invention uses the soft mold expansion method to utilize the heating expansion of hollow microspheres during the epoxy resin curing process to occupy the reserved space in the soft mold, and after filling the soft mold, the soft mold and epoxy resin are pushed to expand together, thereby breaking through the density bottleneck of the traditional preparation scheme and greatly reducing the density of the transducer backing. The soft mold can adapt to the difference in the expansion amount of epoxy resin in each processing, avoiding the problem of uneven top and bottom of the finished product due to too much reserved space, or avoiding the problem of excessive obstruction of expansion due to too little reserved space.

[0023] 2. The present invention forms a dense porous structure inside the transducer backing by expanding the hollow microspheres, thereby reducing the density and increasing the acoustic attenuation coefficient of the transducer backing.

[0024] 3. The present invention obtains transducer backings with different acoustic impedances and acoustic attenuation coefficients by regulating the curing temperature: the regulation range of the acoustic impedance of the transducer backing reaches 0.87 Mrayl to 2.07 Mrayl, and the regulation range of the acoustic attenuation coefficient reaches 4.41 dB / mm to 16.41 dB / mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a density variation diagram of the transducer backing prepared in Examples 1-4 of the present invention.

[0026] Figure 2 This is a diagram showing the sound velocity variation of the transducer backings prepared in Examples 1-4 of the present invention.

[0027] Figure 3 The acoustic impedance change diagram of the transducer backing prepared in Examples 1-4 of the present invention.

[0028] Figure 4 This is a graph showing the change in acoustic attenuation coefficient of the transducer backing prepared in Examples 1-4 of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings.

[0030] Example 1 A method for preparing an ultrasonic transducer backing comprises the following steps: S1. Preliminary mixing of rigid epoxy resin A, flexible epoxy resin B, curing agent, and hollow microspheres with a particle size of 15 μm in a mass ratio of 10:5:2:0.5 was performed, and then placed in a blender for centrifugal stirring for 1 min. After each component was fully stirred, a mixed fluid was formed. Rigid epoxy resin A and flexible epoxy resin B use the main resin component of bisphenol A epoxy resin with different Young's modulus. Bisphenol A epoxy resins with different molecular structures have different Young's moduli. The Young's modulus of rigid epoxy resin A after curing is greater than that of flexible epoxy resin B after curing. In this embodiment, the Young's modulus of rigid epoxy resin A after curing is 2 to 5 GPa, and the Poisson's ratio is 0.35 to 0.4. The Young's modulus of flexible epoxy resin B after curing is less than 2 GPa, and the Poisson's ratio is 0.4 to 0.5.

[0031] In some embodiments, the hollow microspheres are made of one or more of polystyrene, phenolic resin, polyurethane, and epoxy resin.

[0032] In some embodiments, the Young's modulus of the rigid epoxy resin A and the flexible epoxy resin B after curing is, for example: (A is 5 GPa, B is 2 GPa), or (A is 4 GPa, B is 1.5 GPa), or (A is 3 GPa, B is 1 GPa), or (A is 2 GPa, B is 1 GPa), or (A is 5 GPa, B is 1 GPa), and other reasonable values ​​may also be taken.

[0033] In some other embodiments, the particle size of the hollow microspheres 5 can also be other values ​​less than 15μm, such as 14μm, 13.5μm, 13μm, 12.5μm, 12μm, 11.5μm, 11μm, 10.5μm, 10μm, 9.5μm, 9μm, 8.5μm, 8μm, 7.5μm, 7μm, 6.5μm, 6μm, or other reasonable values.

[0034] In some other embodiments, the centrifugal stirring time may be other values ​​other than 1 min, such as 2 min, 3 min, 10 min, 15 min, or other time that allows the components to be evenly mixed.

[0035] In some other embodiments, the centrifugal stirring speed may be 10000 r / min, 12000 r / min, 15000 r / min, or other reasonable speeds that can uniformly mix the components.

[0036] In some other embodiments, centrifugal stirring can be replaced by other methods to promote mixing, as long as the components can be mixed evenly.

[0037] In some other embodiments, under the condition that the mass fraction of hollow microspheres is less than or equal to 9.1%, the mass ratio of rigid epoxy resin A, flexible epoxy resin B, curing agent, and particle size of 15 μm can be other reasonable ratios other than 10:5:2:0.5, for example: 10:1:0.1:0.1, 10:10:4:2, 10:5:2:1, 10:5:2:0.5, 10:5:2:0.5, 10:8:2:0.5.

[0038] In some other embodiments, the flexible epoxy resin B may not be used, that is, only the rigid epoxy resin A, the curing agent, and the particle size of 15 μm are mixed according to a set mass ratio.

[0039] S2. After introducing the obtained mixed fluid into the soft mold, put it into an oven and heat it at a constant temperature of 50°C for 4 hours to solidify. The volume of the mixed fluid introduced into the soft mold is 2 / 3 to 3 / 4 of the initial volume of the soft mold, so that there is space in the soft mold for the expansion of the mixed fluid; at the same time, the soft mold itself can also expand under internal pressure; during the heating and curing process of the mixed fluid, the hollow microspheres expand, so that the mixed fluid has an expansion trend, and the expanded mixed fluid can occupy the space reserved in the soft mold, and after filling the internal space of the soft mold, the soft mold is squeezed from the inside to the outside, so that the soft mold expands together to meet the expansion requirements of the mixed fluid; during this process, the density of the mixed fluid decreases. The use of a soft mold enables the mold to adapt to the difference in the amount of expansion of the mixed fluid in each processing, avoiding the problem of uneven top and bottom of the finished product due to too much reserved space, or avoiding the problem of excessive obstruction of expansion due to too little reserved space.

[0040] In some embodiments, the soft mold is made of rubber or silicone.

[0041] S3. Take out the solidified product from the soft mold, put it under a grinder and process it to a specified thickness to obtain a transducer backing.

[0042] The transducer backing obtained in this embodiment was tested for performance, and the obtained performance indicators are as follows: density is 855kg / m 3 , the sound velocity is 2185m / s, the acoustic impedance is 1.83MRayl, and the acoustic attenuation is 4.89dB / mm.

[0043] Example 2 A method for preparing an ultrasonic transducer backing comprises the following steps: S1. Preliminary mixing of rigid epoxy resin A, flexible epoxy resin B, curing agent, and hollow microspheres with a particle size of 15 μm in a mass ratio of 10:5:2:0.5 was performed, and then placed in a blender for centrifugal stirring for 1 min. After each component was fully stirred, a mixed fluid was formed. Rigid epoxy resin A and flexible epoxy resin B use the main resin component of bisphenol A epoxy resin with different Young's modulus. The Young's modulus of rigid epoxy resin A after curing is greater than that of flexible epoxy resin B after curing. In this embodiment, the Young's modulus of rigid epoxy resin A after curing is 2 to 5 GPa, and the Poisson's ratio is 0.35 to 0.4. The Young's modulus of flexible epoxy resin B after curing is less than 2 GPa, and the Poisson's ratio is 0.4 to 0.5.

[0044] S2. The obtained mixed fluid is introduced into a soft mold and then placed in an oven, and heated at a constant temperature of 60° C. for 4 hours to solidify.

[0045] S3. Take out the solidified product from the mold, put it under a grinder and process it to a specified thickness to obtain a transducer backing.

[0046] The performance indicators of the obtained transducer backing are as follows: density is 585kg / m^3, sound velocity is 2060m / s, acoustic impedance is 1.20MRayl, and acoustic attenuation is 9.08dB / mm.

[0047] Example 3 A method for preparing an ultrasonic transducer backing comprises the following steps: S1. Preliminary mixing of rigid epoxy resin A, flexible epoxy resin B, curing agent, and hollow microspheres with a particle size of 15 μm in a mass ratio of 10:5:2:0.5 was performed, and then placed in a blender for centrifugal stirring for 1 min. After each component was fully stirred, a mixed fluid was formed. Rigid epoxy resin A and flexible epoxy resin B use the main resin component of bisphenol A epoxy resin with different Young's modulus. The Young's modulus of rigid epoxy resin A after curing is greater than that of flexible epoxy resin B after curing. In this embodiment, the Young's modulus of rigid epoxy resin A after curing is 2 to 5 GPa, and the Poisson's ratio is 0.35 to 0.4. The Young's modulus of flexible epoxy resin B after curing is less than 2 GPa, and the Poisson's ratio is 0.4 to 0.5.

[0048] S2. The obtained mixed fluid is introduced into a soft mold and then placed in an oven, and heated at a constant temperature of 70° C. for 4 hours to solidify.

[0049] S3. Take out the solidified product from the mold, put it under a grinder and process it to a specified thickness to obtain a transducer backing.

[0050] The performance indicators of the obtained transducer backing are as follows: density is 522kg / m^3, sound velocity is 1909m / s, acoustic impedance is 0.99MRayl, and acoustic attenuation is 12.48dB / mm.

[0051] Example 4 A method for preparing an ultrasonic transducer backing comprises the following steps: S1. Preliminary mixing of rigid epoxy resin A, flexible epoxy resin B, curing agent, and hollow microspheres with a particle size of 15 μm in a mass ratio of 10:5:2:0.5 was performed, and then placed in a blender for centrifugal stirring for 1 min. After each component was fully stirred, a mixed fluid was formed. Rigid epoxy resin A and flexible epoxy resin B use the main resin component of bisphenol A epoxy resin with different Young's modulus. The Young's modulus of rigid epoxy resin A after curing is greater than that of flexible epoxy resin B after curing. In this embodiment, the Young's modulus of rigid epoxy resin A after curing is 2 to 5 GPa, and the Poisson's ratio is 0.35 to 0.4. The Young's modulus of flexible epoxy resin B after curing is less than 2 GPa, and the Poisson's ratio is 0.4 to 0.5.

[0052] S2. The obtained mixed fluid is introduced into a soft mold and then placed in an oven, and heated at a constant temperature of 80° C. for 4 hours to solidify.

[0053] S3. Take out the solidified product from the mold, put it under a grinder and process it to a specified thickness to obtain a transducer backing.

[0054] The performance indicators of the obtained transducer backing are as follows: density is 480kg / m^3, sound velocity is 1820m / s, acoustic impedance is 0.87MRayl, and acoustic attenuation is 16.41dB / mm.

[0055] Comparative Example 1 A method for preparing an ultrasonic transducer backing comprises the following steps S1. Preliminary mixing of rigid epoxy resin A, flexible epoxy resin B, curing agent, and hollow microspheres with a particle size of 15 μm in a mass ratio of 10:5:2:0.5 was performed, and then placed in a blender for centrifugal stirring for 1 min. After each component was fully stirred, a mixed fluid was formed. Rigid epoxy resin A and flexible epoxy resin B use the main resin component of bisphenol A epoxy resin with different Young's modulus. The Young's modulus of rigid epoxy resin A after curing is greater than that of flexible epoxy resin B after curing. In this embodiment, the Young's modulus of rigid epoxy resin A after curing is 2 to 5 GPa, and the Poisson's ratio is 0.35 to 0.4. The Young's modulus of flexible epoxy resin B after curing is less than 2 GPa, and the Poisson's ratio is 0.4 to 0.5.

[0056] S2. After introducing the obtained mixed fluid into the soft mold, let it stand at room temperature for 12 hours to solidify.

[0057] S3. Take out the solidified product from the mold, put it under a grinder and process it to a specified thickness to obtain a transducer backing.

[0058] The performance indicators of the obtained transducer backing are as follows: density is 948kg / m^3, sound velocity is 2185m / s, acoustic impedance is 2.07MRayl, and acoustic attenuation is 4.41dB / mm.

[0059] The difference between the above-mentioned embodiments 1 to 4 and comparative example 1 is that the curing temperature during the preparation process is different; the density, sound velocity, acoustic impedance and acoustic attenuation of the transducer backing obtained in embodiments 1 to 4 and comparative example 1 vary with temperature as shown in the following table: Figures 1 to 4 Shown: From Figure 1 It can be seen that the density of the backing material obtained after high temperature expansion is 948kg / m 3 Reduced to 480kg / m 3 , the density decreases significantly; from Figure 2It can be seen that the sound velocity in the backing material obtained after high-temperature expansion is significantly reduced. Since acoustic impedance = density × sound velocity, a better curing temperature can reduce both density and sound velocity, indicating that the adjustment of the curing temperature can achieve the regulation of the angle amplitude of the backing acoustic impedance.

[0060] from Figure 3 and Figure 4 It can be seen that the acoustic impedance and acoustic attenuation coefficient of the transducer backing material obtained at different curing temperatures have a large variation range. Therefore, the acoustic impedance and acoustic attenuation coefficient of the obtained acoustic transducer backing can be changed by adjusting the curing temperature, thereby achieving effective regulation of the acoustic impedance and acoustic attenuation coefficient.

[0061] Example 5 A method for controlling the acoustic impedance of a transducer backing comprises the following steps: S1. Preliminarily mix the rigid epoxy resin A, the flexible epoxy resin B, the curing agent, and the hollow microspheres with a particle size of 15 μm, and then put them into a blender for centrifugal stirring for 1 minute. After all the components are fully stirred, a mixed fluid is formed.

[0062] S2. Set the target curing temperature according to the target acoustic impedance; the larger the target acoustic impedance, the smaller the target curing temperature. The target curing temperature range is 20°C to 80°C. The value relationship between the target acoustic impedance and the target curing temperature is obtained through a numerical relationship curve or a numerical relationship table. The numerical relationship table is obtained through advance experiments; the numerical relationship curve is obtained through advance experiments and fitting the obtained discrete values.

[0063] S3, introducing the mixed fluid obtained in step S1 into the soft mold and then putting it into an oven, and heating the mixed fluid at a constant temperature for 4 hours according to the target curing temperature set in step S2, so that the mixed fluid is cured.

[0064] S4. Take out the solidified product from the mold, put it under a grinder and process it to a specified thickness to obtain a transducer backing with a target acoustic impedance.

[0065] Example 6 A method for regulating the acoustic attenuation coefficient of a transducer backing comprises the following steps: S1. Preliminarily mix the rigid epoxy resin A, the flexible epoxy resin B, the curing agent, and the hollow microspheres with a particle size of 15 μm, and then put them into a blender for centrifugal stirring for 1 minute. After all the components are fully stirred, a mixed fluid is formed.

[0066] S2. Set the target curing temperature according to the target acoustic attenuation coefficient. The larger the target acoustic attenuation coefficient, the larger the target curing temperature. The target curing temperature range is 20°C to 80°C. The value relationship between the target acoustic attenuation coefficient and the target curing temperature is obtained through a numerical relationship curve or a numerical relationship table. The numerical relationship table is obtained through advance experiments; the numerical relationship curve is obtained through advance experiments and fitting the obtained discrete values.

[0067] S3, introducing the mixed fluid obtained in step S1 into the soft mold and then putting it into an oven, and heating the mixed fluid at a constant temperature for 4 hours according to the target curing temperature set in step S2, so that the mixed fluid is cured.

[0068] S4. Take out the solidified product from the mold, put it under a grinder and process it to a specified thickness to obtain a transducer backing with a target sound attenuation coefficient.

Claims

1. A method for preparing a low-density ultrasonic transducer backing based on thermal expansion, characterized in that: The following steps are involved: Step 1, uniformly mixing the epoxy resin before curing, the curing agent and the hollow microspheres to obtain a mixed fluid; the hollow microspheres are made of polymer material; Step 2: Add the mixed fluid obtained in step 1 into the mold, and reserve the space required for expansion in the mold; heat the mixed fluid added to the mold at 60° C. to 80° C. to expand and solidify, so as to obtain the ultrasonic transducer backing.

2. The method for preparing a low-density ultrasonic transducer backing based on thermal expansion according to claim 1, characterized in that: The volume of the mixed fluid added to the mold in step 2 is 2 / 3 to 3 / 4 of the volume of the mold; the mold is a soft mold that can expand under internal pressure; the material of the soft mold is rubber or silicone.

3. The method for preparing a low-density ultrasonic transducer backing based on thermal expansion according to claim 1, characterized in that: In the epoxy resin, the curing agent and the hollow microspheres before curing, the mass fraction of the hollow microspheres is less than or equal to 9.1%.

4. The method for preparing a low-density ultrasonic transducer backing based on thermal expansion according to claim 1, characterized in that: The hollow microspheres are made of one or more of polystyrene, phenolic resin, polyurethane and cured epoxy resin.

5. The method for preparing a low-density ultrasonic transducer backing based on thermal expansion according to claim 1, characterized in that: The particle size of the hollow microspheres is less than or equal to 15 μm.

6. The method for preparing a low-density ultrasonic transducer backing based on thermal expansion according to claim 1, characterized in that: The epoxy resin comprises a rigid epoxy resin and a flexible epoxy resin; the Young's modulus of the rigid epoxy resin after curing is greater than the Young's modulus of the flexible epoxy resin after curing; and the mass ratio of the rigid epoxy resin to the flexible epoxy resin is (8-15):

5.

7. The method for preparing a low-density ultrasonic transducer backing based on thermal expansion according to claim 6, characterized in that: The Young's modulus of the rigid epoxy resin after curing is 2 GPa to 5 GPa; the Young's modulus of the flexible epoxy resin after curing is less than 2 GPa.

8. The method for preparing a low-density ultrasonic transducer backing based on thermal expansion according to claim 1, characterized in that: In step 1, the epoxy resin, the curing agent and the hollow microspheres are mixed uniformly by centrifugation.

9. A method for controlling the acoustic impedance of a transducer backing, characterized in that: The following steps are involved: Step 1, uniformly mixing the epoxy resin before curing, the curing agent and the hollow microspheres to obtain a mixed fluid; the hollow microspheres are made of polymer material; Step 2: Set the target curing temperature according to the target acoustic impedance; the larger the target acoustic impedance, the lower the target curing temperature is set; the target curing temperature range is 20°C to 80°C; Step 3: Add the mixed fluid obtained in step 1 into a soft mold that is pressurized and expandable, and heat and cure it at the target curing temperature obtained in step 2 to obtain an ultrasonic transducer backing.

10. A method for controlling the acoustic attenuation coefficient of a transducer backing, characterized in that: The following steps are involved: Step 1, uniformly mixing the epoxy resin before curing, the curing agent and the hollow microspheres to obtain a mixed fluid; The hollow microspheres are made of polymer material; Step 2: Set the target curing temperature according to the target acoustic attenuation coefficient; the larger the target acoustic attenuation coefficient, the larger the target curing temperature is set; the target curing temperature range is 20°C to 80°C; Step 3: Add the mixed fluid obtained in step 1 into a soft mold that is pressurized and expandable, and heat and cure it at the target curing temperature obtained in step 2 to obtain an ultrasonic transducer backing.

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