Method for quantitatively controlling the acoustic impedance and radial stress of a fiber layer on the surface of a piezoceramic spherical shell

Abstract

The application provides a method for quantitatively controlling the acoustic impedance and radial stress of a fiber layer on a piezoelectric ceramic spherical shell, comprising determining the acoustic impedance of the fiber layer by the type and volume ratio of the fiber and the fiber binder, determining the pressure in a hot-pressing container by the thickness of the fiber binder layer and the prestress requirement, and then realizing the process of prestress application and fiber layer solidification. The application can coat the piezoelectric ceramic spherical shell with fiber material, realize the quantitative control of the radial prestress on the surface of the piezoelectric ceramic spherical shell through hot pressing, and has the advantages of low equipment requirement, simple method and wide application range.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic sensor technology, and specifically to a method for quantitatively controlling the acoustic impedance and radial stress of the fiber layer on the surface of a piezoelectric ceramic spherical shell. Background Technology

[0002] Piezoelectric ceramics possess unique electromechanical interchangeability, and when fabricated into ultrasonic sensors, they are widely used in medicine and have broad application value in the field of ultrasonic detection. When piezoelectric ceramics are fabricated into a spherical shell shape, they have a large directional opening angle, which is beneficial for achieving blind-zone-free detection with minimal transducers and the simplest layout. To improve the detection distance of the piezoelectric ceramic spherical shell, its acoustic emission capability needs to be improved. One effective method is to increase the voltage applied to the surface of the piezoelectric ceramic spherical shell. However, piezoelectric ceramics have low tensile strength, and excessive voltage can easily lead to brittle fracture. Applying prestress to increase the mechanical limit of the piezoelectric ceramic spherical shell can effectively improve its acoustic emission capability.

[0003] Meanwhile, the acoustic impedance of piezoelectric ceramics is typically much greater than that of their application medium, such as water, air, or skin, leading to complex acoustic reflections and resulting in sound energy loss. Adding a fiber layer effectively reduces the acoustic impedance of the composite piezoelectric ceramic spherical shell, thereby reducing the acoustic impedance mismatch between the piezoelectric ceramic and the target medium, and ultimately increasing the acoustic energy reaching the application medium. Summary of the Invention

[0004] To address the shortcomings of existing piezoelectric ceramic spherical shells, such as low tensile strength and acoustic impedance mismatch between the piezoelectric ceramic and the application medium, this invention provides a method for quantitatively controlling the acoustic impedance and radial stress of the fiber layer on the surface of the piezoelectric ceramic spherical shell using hot pressing. Quantitatively controlling the acoustic impedance of the fiber layer on the surface of the piezoelectric ceramic tube by utilizing the volume ratio of fiber to fiber binder helps reduce the impedance mismatch between the piezoelectric ceramic and the application medium. Quantitatively controlling the radial prestress on the surface of the piezoelectric ceramic using hot pressing helps improve the acoustic emission capability of the transducer.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for quantitatively controlling the acoustic impedance and radial stress of the fiber layer on the surface of a piezoelectric ceramic spherical shell includes the following steps:

[0007] (1) Determine the dimensions of the piezoelectric ceramic sphere shell, look up the acoustic impedance of the piezoelectric ceramic and the medium used, and then determine the range of values ​​for the acoustic impedance of the fiber layer. Take the middle value as the optimal acoustic impedance of the fiber layer, and determine the type and volume ratio of the fiber and fiber binder based on the acoustic impedance of the fiber layer;

[0008] (2) Prepare the fiber binder and impregnate the fiber cloth with the fiber binder according to the volume ratio of fiber to fiber binder;

[0009] (3) Use a hard mold to fill the sphere shell into a complete sphere, and use a porous adhesive to bond the gaps to prevent the fiber adhesive from overflowing into the inner cavity and contaminating the inner wall;

[0010] (4) The fibers impregnated with fiber binder are uniformly coated on the surface of the piezoelectric ceramic sphere shell;

[0011] (5) Use highly elastic materials to cover the fiber layer and the rigid mold to promote close contact between the fiber and the piezoelectric ceramic sphere shell;

[0012] (6) Determine the expected thickness of the fiber binder based on the thickness of the fiber, the outer radius of the piezoelectric ceramic sphere shell, and the volume ratio of the fiber to the fiber binder;

[0013] (7) Determine the pressure value that the hot-pressed container needs to reach based on the expected prestress requirements;

[0014] (8) Place the fiber-coated piezoelectric ceramic sphere into a hot press forming container and set the pressure value, curing temperature and curing time;

[0015] (9) After curing, remove the elastic coating film on the surface of the fiber layer, and remove the pore adhesive and mold.

[0016] Preferably, in step (1), the acoustic impedance Z of the fiber layer is between that of the piezoelectric ceramic and the acoustic impedance Z of the piezoelectric ceramic. c and target medium Z m Between, and satisfying:

[0017] ,

[0018] The middle value is usually taken. This represents the optimal acoustic impedance value for the fiber layer.

[0019] Preferably, the type of fiber in step (1) is glass fiber, nylon fiber, carbon fiber or aramid fiber.

[0020] Preferably, the fiber binder in step (1) is epoxy resin, unsaturated polyester resin, phenolic resin, polyacrylic resin or polyvinyl chloride resin.

[0021] Preferably, the method for determining the volume ratio of fiber and fiber binder in step (1) is as follows:

[0022] ① Query the sound velocity of the fiber and density Calculate its acoustic impedance :

[0023]

[0024] ② Query the sound velocity of the fiber adhesive. and density Calculate its acoustic impedance :

[0025]

[0026] ③Based on the acoustic impedance of the fiber layer Determine the volume ratio α of fiber and fiber binder based on the requirements:

[0027] .

[0028] Preferably, the rigid mold material in step (3) is wood, stainless steel or rigid polyurethane foam.

[0029] Preferably, the porous binder in step (3) is silicone rubber or silicone.

[0030] Preferably, in step (6), the thickness of the fiber is considered. Given the outer radius b of the spherical shell and the volume ratio α of the fiber to the binder, determine the expected thickness of the fiber binder. :

[0031] .

[0032] Preferably, the method for determining the pressure value of the autoclave in step (7) is as follows:

[0033] ① A resistance strain gauge is attached to the surface of a standard planar mold with a Young's modulus of E. The strain ε caused by the adhesive of the expected thickness is measured using a strain meter, and then the shrinkage stress T generated by the adhesive layer is calculated. s :

[0034] ;

[0035] ② Calculate the radial pressure P generated on the surface of the spherical shell by the shrinkage of the fiber layer based on the horizontal shrinkage stress of the binder layer. s :

[0036]

[0037] Where b is the outer radius of the piezoelectric ceramic spherical shell, and c is the outer radius of the fiber layer, satisfying... .

[0038] ③ Based on the prestress on the surface of the spherical shell Calculate the pressure value P of the autoclave:

[0039] .

[0040] Beneficial effects:

[0041] (1) By adjusting the volume ratio of fiber and fiber binder, quantitative control of acoustic impedance can be achieved over a wide range;

[0042] (2) By controlling the thickness of the fiber binder and adjusting the pressure inside the autoclave, the radial prestress on the surface of the piezoelectric ceramic sphere can be precisely applied;

[0043] (3) The fiber layer on the surface of the piezoelectric ceramic sphere is cured by hot pressing, resulting in uniform stress on the surface of the sphere, lower equipment requirements, and lower manufacturing cost;

[0044] (4) It has a wide range of applications and is suitable for piezoelectric ceramic spherical shells of different sizes and materials. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the piezoelectric ceramic spherical shell described in this invention;

[0046] Figure 2 This is a diagram of the hard mold described in this invention;

[0047] Figure 3 This is a schematic diagram of the prestressing application described in this invention;

[0048] Figure 4 The emission voltage response curves of the piezoelectric ceramic spherical shell before and after quantitative application of acoustic impedance and radial prestress using the present invention are shown.

[0049] Figure 5 The curves showing the change of sound source level with voltage before and after quantitative application of acoustic impedance and radial prestress to the piezoelectric ceramic spherical shell using the present invention are shown.

[0050] Figure 6 The curves showing the change of sound source level with voltage pulse width before and after quantitative application of acoustic impedance and radial prestress to a piezoelectric ceramic spherical shell using the present invention are shown.

[0051] Wherein 1-piezoelectric ceramic spherical shell, 2-rigid mold, 3-fiber, 4-fiber binder, 5-elastic material, 6-hot press container, a-inner radius of spherical shell, b-outer radius of spherical shell, h-height of spherical shell, c-outer radius of mold, h f - Fiber thickness, h t -Fiber binder thickness. Detailed Implementation

[0052] Example 1:

[0053] A method for quantitatively controlling the acoustic impedance and radial stress of the fiber layer on the surface of a piezoelectric ceramic spherical shell, the method comprising the following steps:

[0054] (1) Prepare a piezoelectric ceramic sphere shell with dimensions of a42.3*b45*h45mm, with a clean surface and no defects in the electrodes;

[0055] (2) Acoustic impedance of piezoelectric ceramics The query result is 31.5Mrayls, target medium. Since the acoustic impedance of the fiber layer is 1.5 Mrayls, the range of acoustic impedance values ​​for the fiber layer is 2.07~6.21 Mrayls, and the optimal value for the acoustic impedance of the fiber layer is 4.14 Mrayls.

[0056] (3) Glass fiber and epoxy resin were selected for fiber layer composite. The density of epoxy resin is 1100 kg·m³. -3 The sound velocity is 2250 m / s, and the calculated acoustic impedance is 2.48 Mrayls; the density of glass fiber is 2500 kg·m³. -3 The sound velocity is 2740 m / s, and the calculated acoustic impedance is 6.85 Mrayls. The calculated volume ratio of glass fiber to epoxy resin is 0.75.

[0057] (4) According to the required volume ratio of fiber to epoxy resin, impregnate the fiber in epoxy resin;

[0058] (5) Attach strain gauges to the surface of the piezoelectric ceramic sphere shell, combine the piezoelectric ceramic sphere shell with the rigid polyurethane mold to form a complete sphere, and fill the gaps with 704 silicone rubber.

[0059] (6) Coating the surface of the piezoelectric ceramic sphere with fibers;

[0060] (7) Use rubber balls to tightly wrap the fiber layer and the hard mold;

[0061] (8) The thickness h of the selected fiber f The value is taken as 0.80 mm. Based on the fiber thickness, the outer radius of the piezoelectric ceramic sphere shell, the volume ratio of the fiber to the fiber binder, and the expected thickness h of the fiber binder. t The calculated value is 1.07 mm.

[0062] (9) A resistance strain gauge was attached to the surface of an aluminum planar mold. The Young's modulus of aluminum is 71.7 GPa and the Poisson's ratio is 0.33. The horizontal stress generated by the shrinkage of the 1.07 mm thick epoxy resin during curing is measured to be 5.736 MPa, corresponding to the radial pressure P. s The required radial stress is 0.47 MPa. If the expected radial stress requirement for the piezoelectric ceramic sphere shell is 1 MPa, then the pressure P of the hot pressing device should be set to 0.53 MPa.

[0063] (10) Place the fiber-coated piezoelectric ceramic sphere into a hot press molding container, set the pressure value to 0.6 MPa, and set the curing temperature to 80°C and the curing time to 8 hours according to the resin curing requirements.

[0064] (11) Remove the elastic coating film on the surface of the fiber layer, and remove the pore adhesive and mold;

[0065] (12) The Young's modulus E of the piezoelectric ceramic is 85 GPa. The horizontal stress generated on the surface of the piezoelectric ceramic by the shrinkage of the epoxy resin and the pressure during hot pressing is calculated using the strain value ε. The horizontal stress on the surface of the piezoelectric ceramic spherical shell is combined with the surface pressure P of the ceramic. c The relationship between the pressure values ​​P and the pressure values ​​P is calculated. c for:

[0066] =0.94MPa, which differs from the expected target stress value of 1MPa by 0.06MPa. Where a and b are the inner and outer radii of the piezoelectric ceramic spherical shell.

[0067] (13) The fiber layer prepared using the same process was tested, and the average density of the fiber layer was 1698 kg / m³. 3 The average sound velocity is 2338 m / s, and the acoustic impedance of the fiber layer is 3.97 Mrayls, which differs from the optimal value by 0.17 Mrayls, and is within the allowable range of the acoustic impedance of the fiber layer.

[0068] (14) The composite piezoelectric ceramic fiber shell was used as a transducer and its performance was tested in an anechoic water tank. It was found that compared with the transducer without quantitative control of acoustic impedance and prestress, the emission voltage response was significantly improved at different frequencies, with a maximum increase of 2.7 dB; the sound source level increased by 2.3 dB at 250 V as the voltage increased; the sound source level decreased as the voltage pulse width increased, and the sound source level after acoustic impedance and prestressing was still higher than before the treatment, with an increase of 1.7 dB at a pulse width of 20 ms.

[0069] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for quantitatively controlling the acoustic impedance and radial stress of the fiber layer on the surface of a piezoelectric ceramic spherical shell, characterized in that, Includes the following steps: (1) Determine the range of acoustic impedance values ​​for the fiber layer, and determine the type and volume ratio of fiber and fiber binder based on the optimal acoustic impedance value; acoustic impedance of the fiber layer Due to the acoustic impedance of piezoelectric ceramics and target media Between, and satisfying: ； Take the median value The optimal acoustic impedance value for the fiber layer; (2) Impregnate the fiber cloth with the fiber binder according to the volume ratio of fiber to fiber binder; (3) Use a hard mold to fill the spherical shell into a complete sphere, and use a porous adhesive to bond the gaps; (4) The fibers impregnated with fiber binder are uniformly coated on the surface of the piezoelectric ceramic sphere shell; (5) Use highly elastic materials to cover the fiber layer and rigid mold; (6) Based on the thickness of the fiber Given the outer radius b of the piezoelectric ceramic sphere shell and the volume ratio α of the fiber to the fiber binder, determine the expected thickness of the fiber binder. : ； (7) Determine the pressure value that the thermoforming container needs to reach based on the expected prestress requirements and the fiber binder thickness; (8) Place the fiber-coated piezoelectric ceramic sphere into a hot press forming container and set the pressure value, curing temperature and curing time; (9) After curing, remove the elastic coating film on the surface of the fiber layer, and remove the pore adhesive and mold.

2. The method according to claim 1, characterized in that, The type of fiber in step (1) is glass fiber, nylon fiber, carbon fiber or aramid fiber.

3. The method according to claim 1, characterized in that, In step (1), the fiber binder is epoxy resin, unsaturated polyester resin, phenolic resin, polyacrylic resin or polyvinyl chloride resin.

4. The method according to claim 2, characterized in that, The method for determining the volume ratio of fiber and fiber binder in step (1) is as follows: ① Query the sound velocity of the fiber and density Calculate its acoustic impedance : ； ② Query the sound velocity of the fiber adhesive. and density Calculate its acoustic impedance : ； ③Based on the acoustic impedance of the fiber layer Determine the volume ratio α of fiber and fiber binder based on the requirements: 。 5. The method according to claim 1, characterized in that, In step (3), the rigid mold material is wood, stainless steel, or rigid polyurethane foam.

6. The method according to claim 1, characterized in that, In step (3), the porous binder is silicone rubber or silicone.

7. The method according to claim 1, characterized in that, The method for determining the pressure value of the autoclave in step (7) is as follows: ① When Young's modulus is Resistance strain gauges are adhered to the surface of a standard flat mold, and strain gauges are used to measure the strain caused by the adhesive of the expected thickness. Then, the horizontal shrinkage stress generated by the adhesive layer is calculated. : ； ② Calculate the radial pressure generated on the surface of the spherical shell by the shrinkage of the fiber layer based on the horizontal shrinkage stress of the binder layer. : ； Where b is the outer radius of the piezoelectric ceramic spherical shell, and c is the outer radius of the fiber layer, satisfying... ; ③ Based on the prestress on the surface of the spherical shell Calculate the pressure value P of the autoclave: 。

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