A combined flexible and rigid ultrasonic transducer and its preparation method

Abstract

The present invention discloses a soft-hard combined integrated ultrasonic transducer and a preparation method thereof. Starting from the soft-hard combined ultrasonic transducer, the present invention studies the mechanical modeling and structural design under high pressure, and establishes a high-pressure self-adaptive method for the deep-sea integrated ultrasonic transducer in this embodiment, including a high-pressure self-adaptive cavity of soft structural material, an acoustic matching layer, a top electrode, a movable piezoelectric element sheet, a bottom electrode, and a lining sound absorption layer; and uses the integrated deep-sea high-pressure self-adaptive method.

Description

Technical Field

[0001] The present invention relates to the fields of ultrasonic detection imaging and deep-sea high-pressure environment exploration, and specifically relates to a combined rigid-flexible ultrasonic transducer and a preparation method thereof. Background Art

[0002] At present, in the deep sea, there are two means for detecting organisms: acoustics and optics. However, under the harsh working conditions in deep water, the optical detection method is often limited by the dissipation of light waves. To obtain a relatively clear optical image, a light beam with high energy and wide coverage is required, which may also disturb the organisms on the seabed or cause environmental damage. Therefore, the acoustic method has more obvious advantages in the deep-sea environment. To image and even perform in-vivo detection of organisms in unexplored areas of the deep sea, a new high-definition resolution acoustic imaging method is needed, which will become another pair of eyes for observing deep-sea organisms.

[0003] The extremely high hydrostatic pressure (at the level of 100 MPa) in the deep sea poses a huge challenge to human exploration and operation. How to protect the hardware equipment necessary for ultrasonic detection under high pressure is a problem that must be faced and urgently solved. At present, the mechanical design structure of combining rigidity and flexibility is an effective means to resist the ultra-high pressure in the deep sea. At the same time, in an ultrasonic transducer, a hard piezoelectric material (such as piezoelectric ceramics, PZT ceramics, etc.) is "embedded" in a relatively soft epoxy resin, and then adhesively bonded to the sound-absorbing substrate soft material polyurethane to form a combined rigid-flexible structure, which coincides with the anti-high-hydrostatic-pressure design for deep-sea work.

[0004] Under high pressure, materials will undergo non-linear deformation, which will affect the propagation, dissipation, etc. of sound waves (elastic waves) therein. At the same time, maintaining the integrity of the mechanical and electrical systems under high pressure is also the mechanical design content that needs to be solved. In terms of mechanical design, the idea of combining rigidity and flexibility has been widely applied to the structural design of electromechanical systems in harsh environments such as high-pressure resistance. Materials and robots combining rigidity and flexibility have been proven to have good self-adaptive pressure resistance under high pressure. The electromechanical system constructed by the combined rigid-flexible method and the soft robot driven by the force-electric coupling soft intelligent material can adapt to extremely high hydrostatic pressure (110 MPa) and achieve driving without a pressure-resistant shell.

[0005] Kohji IIDA et al. in Japan added an underwater acoustic camera hs2000 to assist the optical camera in the functions of underwater robots. It can be used to measure the size, shape and movement of living marine animals, as well as the tissue, shape and movement of internal organs. The water tank experiment successfully demonstrated that the acoustic camera has good observation effects on the inside of organisms, and the internal blood vessels of squids and fish can be clearly seen. However, the acoustic camera has only achieved experiments under a pressure of 100 m underwater and has not reached the scope of deep-sea exploration. At the same time, the pressure protection means for the acoustic camera are relatively traditional, using a rigid high-pressure-resistant shell to wrap the required camera hardware. Compared with the integrated ultrasonic transducer described in this article, it has defects such as large volume, large mass and high stiffness of the required pressure-resistant shell material.

[0006] ARIS (Adaptive Resolution Imaging Sonar) is an imaging sonar with adaptive resolution manufactured by Sound Metrics Corporation based on the existing product of didson. It has achieved the measurement of species-specific phenotypic characteristics (size) and behaviors (movement strategies; lip type, sub-vascular type and capillary type) under fish tank conditions. Denham Cook et al. established a "field fish length survey technology" using ARIS to achieve real-time underwater length measurement of single live fish (the ARIS 3000 Explorer imaging sonar has two working frequencies: 3 MHz, monitoring range 5 m; 1.8 MHz, monitoring range 15 m. The lower limits of the two distance resolutions are both between 3 mm and 19 mm). This camera is small in size, easy to use and has been integrated into commercial products. However, its high-pressure protection means are still wrapped with a pressure-resistant shell, and its pressure resistance ability still does not meet the experimental shooting requirements of the current full-depth or half-depth of the sea. Summary of the Invention

[0007] Aiming at the deficiencies of the prior art, the present invention starts from the integrated ultrasonic transducer of soft and hard combination, studies the mechanical modeling and structural design under high pressure, and proposes an integrated ultrasonic transducer of soft and hard combination and its preparation method.

[0008] The main technical solutions to achieve the object of the present invention are as follows:

[0009] The present invention provides a combined flexible and rigid ultrasonic transducer, which includes a soft material high-pressure adaptive cavity 1, an acoustic matching layer 2, a top electrode 3, a piezoelectric element module 4, a bottom electrode 5 and a backing acoustic absorption layer 6. The backing acoustic absorption layer 6, the bottom electrode 5, the piezoelectric element module 4 and the top electrode 3 are stacked in sequence from bottom to top. The acoustic matching layer 2 is coated on the exposed upper surfaces of the backing acoustic absorption layer 6, the bottom electrode 5, the piezoelectric element module 4 and the top electrode 3. The soft material high-pressure adaptive cavity 1 wraps the acoustic matching layer 2, the top electrode 3, the piezoelectric element module 4, the bottom electrode 5 and the backing acoustic absorption layer 6.

[0010] The piezoelectric element module 4 in this application includes a plurality of piezoelectric ceramic sheets, and the plurality of piezoelectric ceramic sheets are linearly arranged in a flexible polymer, and the flexible polymer is an epoxy resin material.

[0011] The materials of the top electrode and the bottom electrode in this application are copper, the thickness of the copper is 5 - 100 μm, and a titanium thin film is deposited thereon.

[0012] The material of the acoustic matching layer in this application is epoxy resin or modified epoxy resin, and the thickness is 1 / 4 of the wavelength at the detection frequency.

[0013] The material of the backing acoustic absorption layer in this application is polyurethane or tungsten powder modified epoxy resin.

[0014] The soft material high-pressure adaptive cavity 1 in this application is made of silicone rubber material. The soft material high-pressure adaptive cavity 1 is a cylinder with a radius of 10 mm and a height of 8 mm.

[0015] The piezoelectric element module uses materials such as piezoelectric ceramics. Electro-driven can generate high-frequency vibrations, receive and transmit voltage signals and acoustic signals, and convert the two. The preparation materials of the top electrode and the bottom electrode are copper. The material of the acoustic matching layer is a modified epoxy resin material, and its function is to impedance-match the moduli of the detected object and the piezoelectric element, that is, to reduce the reflection dissipation of sound waves at the interface through an intermediate substance. The thickness of the matching layer is one-fourth of the wavelength length of the sound wave in it. The substrate part is composed of polyurethane, and the purpose is to completely absorb the back elastic wave so as not to affect the signal due to the hard sound field boundary of the backing.

[0016] The combined flexible and rigid ultrasonic transducer is a combined flexible and rigid mechanical structure. By using the form of embedding rigid piezoelectric ceramics in a soft material such as silicone rubber polymer, it can effectively resist the deep water pressure of nearly 100 MPa and work normally.

[0017] This application uses a soft material to encapsulate the ultrasonic transducer structure. The piezoelectric elements are disassembled and dispersed and poured into epoxy resin to form a linear array, and then the whole is poured into silicone rubber for pressure protection, as Figure 2 shown.

[0018] This application also provides a method for preparing a hybrid ultrasonic transducer, including the following steps:

[0019] Step 1: Prepare a piezoelectric ceramic sheet and cut the piezoelectric ceramic into a uniform sheet structure.

[0020] Step 2: Prepare a piezoelectric element module. Arrange a plurality of piezoelectric ceramic sheets prepared in Step 1 in a linear array in a mold, and pour an epoxy resin flexible material into the mold until the top ends of the piezoelectric ceramic sheets are submerged to form a piezoelectric element module.

[0021] Step 3: Deposit a top electrode and a bottom electrode on the upper and lower end faces of the piezoelectric element module respectively.

[0022] Step 4: Wrap an acoustic matching layer on the top electrode and deposit a backing sound-absorbing layer at the lower end of the bottom electrode.

[0023] Step 5: Place the module prepared in Steps 1 - 4 as a whole in a mold, and slowly pour the stirred silicone rubber along the boundary into the mold until it is completely submerged.

[0024] Step 6: Place the mold together with the internal liquid silicone rubber in a vacuum box connected to a vacuum pump. After confirming the seal, use the vacuum pump to evacuate it.

[0025] The preparation method 1: Use a 3D printed acrylic mold and bond it with glue to form a box-shaped mold. After stirring, slowly pour the viscous colloidal silicone rubber along the boundary into the mold, immerse the piezoelectric array with the pulled-out and welded leads in the silicone rubber, use a solidified silicone rubber sheet as a gasket support at the bottom, and adjust the pouring angle so that the piezoelectric array is fully wrapped by the liquid silicone rubber. After complete immersion, place the mold together with the internal liquid silicone rubber in a vacuum box connected to a vacuum pump. After confirming the seal, use the vacuum pump to evacuate it. During this process, the small bubbles present in the liquid silicone rubber will float to the surface and expand and disappear due to the air pressure, fully reducing the pore defects such as bubbles inside the silicone rubber to avoid the influence of the small bubbles inside the gel on the material properties and compressive performance.

[0026] The described preparation method 2: Use a 3D-printed acrylic mold, and bond it with glue to form a film-like mold. Use a film stretching machine to form a film of VHB, cover it on the surface of the mold, and apply a release agent. Prepare a degassed aqueous solution of hydrogel. Place 100 g of the degassed sodium alginate aqueous solution (mass fraction 2%) in a test tube, add 22.2 g of acrylamide monomer, add 0.02 g of a cross-linking agent (such as 6,6′-bisamino-3,3′-methylenedibenzoic acid (MBAA)), add a small amount of glucose as a sustained-release agent, mix evenly, and finally mix it with calcium ions (calcium sulfate suspension). Pour the pre-gel solution prepared by this process into the mold, soak the piezoelectric sheet with the welded positive and negative electrodes used, lead out the welding wire, then seal the mold in a humid environment and store it for 1 h; after its physical cross-linking, separate the hydrogel from the mold and assemble the elastic tube; keep the ultraviolet chamber humid, irradiate it with ultraviolet light (365 nm UV; UVPCL-1000) for 1 h, and after the gel covalently cross-links and polymerizes, swell the hydrogel in water for at least 48 h to reach the equilibrium state.

[0027] The effectiveness of this protection method is given by the following method: The influence of the sound field under the protection of this soft material (elastic wave analysis) can be verified by referring to discontinuous medium mechanics: The main material selected in the previously used protective soft material is silicone rubber, which is a type of compressible material. The Ogden compressible material model is adopted for the model. Under this model, the strain energy function form of the hyperelasticity of the material is as follows: The main material selected in the previously used protective soft material is silicone rubber, which is a type of compressible material. The Ogden compressible material model is adopted for the model. Under this model, the strain energy function form of the hyperelasticity of the material is as follows:

[0028]

[0029] Among them, Ψ is the strain energy function, vol and iso The subscripts respectively represent the strain energy per unit volume of the volume change part and the isochoric change part. κ is the bulk modulus of the material, which is given by the Young's modulus and the Poisson's ratio. Under this model, generally take:

[0030]

[0031] For the further part, according to the model, select:

[0032]

[0033] where the constant

[0034] α1 = 1.3 μ1 = 6.3e5 N / m 2

[0035] α2 = 5.0 μ2 = 0.012e5 N / m2

[0036] α3 = -2.0, μ3 = -0.1e5 N / m 2

[0037] In this problem, the metamaterial model has been completely given, that is, the derivation of the constants related to material selection has been completely given. Therefore, according to the derivation, the expression of the elastic tensor can be obtained:

[0038]

[0039] The above formula shows that the elastic tensor of the silicone rubber soft material in a certain state is only related to the current deformation gradient and the adopted hyperelastic constitutive model. Further, the wave equation given by the elastic tensor is given

[0040]

[0041] where the relationship between the elastic tensor and the aforementioned elastic tensor is given by the following formula

[0042]

[0043] Prove that the high-voltage adaptive method has no impact on the transmission of sound waves (elastic waves) around the piezoelectric elements.

[0044] Further, following the above partial differential equation, discretize it and use the finite element simulation method to evaluate the influence of this protection method on the sound field, and at the same time verify its working state under high voltage. Conduct acoustic signal transmission and reception experiments on the prepared prototype. Apply an alternating current with an amplitude of 100V and a frequency of 10kHz - 50kHz to the positive electrode of the transmitting piezoelectric sheet, and the negative electrode is grounded. One pole of the transmitting and receiving piezoelectric sheets is supported to restrict its longitudinal vibration.

[0045] Compared with the prior art, the present invention has the following advantages: adopting a fusion design instead of a mechanical structure of a pressure-resistant shell, combined with the inherent embedded structure of the ultrasonic transducer, enables the ultrasonic transducer to obtain effective soft body high-pressure working ability. It is an innovative design of a deep-sea high-pressure acoustic detection ultrasonic transducer, and this design and protection method have the advantages of ultra-high pressure resistance, high flexibility, and self-adaptation. Brief Description of the Drawings

[0046] Figure 1 It is a schematic diagram of the structure of the fusion ultrasonic transducer;

[0047] Figure 2 It is a schematic cross-sectional view of the structure of the fusion ultrasonic transducer;

[0048] Figure 3 It is a schematic diagram of the transducer working under high pressure;

[0049] Figure 4 Schematic diagram of the hydrogel fusion ultrasonic transducer structure of Example 2 Detailed implementation mode

[0050] The present invention will be described in detail below in conjunction with the drawings and specific embodiments.

[0051] As Figure 1 shown, the present invention provides a high-pressure-resistant soft-hard combined fusion ultrasonic transducer, including a soft material high-pressure adaptive cavity 1, an acoustic matching layer 2, a top electrode 3, a piezoelectric element module 4, a bottom electrode 5 and a back lining sound absorption layer 6. The back lining sound absorption layer 6, the bottom electrode 5, the piezoelectric element module 4 and the top electrode 3 are stacked in sequence from bottom to top. The acoustic matching layer 2 is coated on the exposed upper surfaces of the back lining sound absorption layer 6, the bottom electrode 5, the piezoelectric element module 4 and the top electrode 3. The soft material high-pressure adaptive cavity 1 wraps the acoustic matching layer 2, the top electrode 3, the piezoelectric element module 4, the bottom electrode 5 and the back lining sound absorption layer 6.

[0052] The piezoelectric element module 4 in this application includes a plurality of piezoelectric ceramic sheets, and the plurality of piezoelectric ceramic sheets are linearly arranged in a flexible polymer, and the flexible polymer is an epoxy resin material.

[0053] The materials of the top electrode and the bottom electrode in this application are copper, the thickness of the copper is 5-100 μm, and a titanium thin film is deposited on it.

[0054] The material of the acoustic matching layer in this application is epoxy resin or modified epoxy resin, and the thickness is 1 / 4 of the wavelength at the detection frequency.

[0055] The material of the back lining sound absorption layer in this application is polyurethane or tungsten powder modified epoxy resin.

[0056] The soft material high-pressure adaptive cavity 1 in this application is made of silicone rubber material. The soft material high-pressure adaptive cavity 1 is a cylinder, its radius is 10 mm, and its height is 8 mm.

[0057] The preparation material of the back lining sound absorption layer is polyurethane or tungsten powder modified epoxy resin, which greatly absorbs the dissipated sound waves at the back. The epoxy resin and the curing agent are heated and melted, tungsten powder is incorporated, and the mixture is stirred with a glass rod while heating. After stirring, the mixture is cooled evenly to prepare.

[0058] The high-pressure adaptive overall structure in this embodiment: outside the piezoelectric ceramic with relatively high rigidity, an acoustic matching layer and a first layer of soft material protection (the first layer of protection material is epoxy resin) are wrapped, and then after being adhered to another layer of soft substrate material polyurethane, a second layer of protective high polymer silicone rubber is wrapped outside.

[0059] In the structure of this embodiment:

[0060] Piezoelectric ceramic: Young's modulus E pzt = 76500 MPa, Poisson's ratio μ pzt = 0.32

[0061] Polyurethane: Young's modulus E Tpu = 50 MPa, Poisson's ratio μ Tpu = 0.47

[0062] Epoxy resin: Young's modulus E ep = 1 GPa, Poisson's ratio μ ep = 0.38

[0063] Silicone rubber: Young's modulus E silicone = 5 MPa, Poisson's ratio μ silicone = 0.48

[0064] Preparation method of the high-pressure adaptive soft material cavity structure in this embodiment: Use a 3D printed acrylic mold and bond it with glue to form a box-shaped mold. After stirring, slowly pour the viscous colloidal silicone rubber along the boundary into the mold. Immerse the ultrasonic transducer with the pulled-out leads welded in the silicone rubber, and use the solidified silicone rubber sheet as a gasket support at the bottom. Adjust the pouring angle so that the ultrasonic transducer is fully wrapped by the liquid silicone rubber. After complete immersion, place the mold together with the internal liquid silicone rubber in a vacuum box connected to a vacuum pump. After confirming the seal, use the vacuum pump to evacuate it. During this process, the small bubbles existing in the liquid silicone rubber will float to the surface and expand and disappear due to the air pressure, fully reducing the bubble and other pore defects inside the silicone rubber to avoid the influence of the small bubbles inside the gel on the material properties and compressive performance. After evacuation, put the fusion transducer into the oven to dry and solidify to obtain the embodiment.

[0065] In the stress analysis, the maximum von Mises stress appears at the root of the strain gauge, indicating that this part of the structure may be damaged when subjected to hydrostatic high pressure. The maximum von Mises stress is 250 MPa. At this stress level, the piezoelectric ceramic will not yield, but may depolarize due to mechanical strength. At the same time, observe the bending deformation of the overall structure, and calculate the overall bending angle through the maximum deformation at the outermost end of the array.

[0066] Define two deformation measurement data under this deformation:

[0067] Bending angle θ bend :

[0068]

[0069] Represents the degree of bending of the overall part under this pressure.

[0070] Matching layer shrinkage ratio κ coupling :

[0071]

[0072] It represents the change in the thickness h of the matching layer under this pressure. The results show that under this condition, the thickness of the matching layer decreases by 95.3% from 0.415 mm to 0.395 mm.

[0073] As Figure 3 shown, the high hydrostatic pressure environment working tests of Examples 1 and 2 under high-pressure self-adaptation are carried out. The examples are placed in a high-pressure water environment. An alternating current with an amplitude of 100 V and a frequency of 10 kHz - 50 kHz is applied to the positive electrode of the transmitting piezoelectric sheet, and the negative electrode is grounded. The receiving piezoelectric sheet is connected to a receiving test circuit such as an oscilloscope at the back end to display the response electrical signal.

[0074] As Figure 3 shown. In the high-pressure water environment, after a transmitting voltage of 100 V is applied, the receiving end can obtain a response voltage of 0.5 - 3 V, and the response frequency can include the level of 100 Khz - 5 MHz.

[0075] As Figure 4 shown, the high-pressure self-adaptation method of the deep-sea fusion ultrasonic transducer in Example 2 includes a VHB film frame (1), a soft material high-pressure self-adaptation cavity (2), a top electrode (3), a vibrating piezoelectric thin sheet (4), and a bottom electrode (5); the fusion body deep-sea high-pressure self-adaptation method is used.

[0076] The preparation method adopted in Example 2: Use a 3D printed acrylic mold, and bond it with glue to form a film-like mold. Use a film stretching machine to form a VHB film, cover it on the surface of the mold, and apply a release agent. Prepare a degassed aqueous solution of hydrogel. Place 100 g of the degassed sodium alginate aqueous solution (mass fraction 2%) in a test tube, add 22.2 g of acrylamide monomer, add 0.02 g of cross-linking agent (such as 6,6'-bisamino-3,3'-methylenedibenzoic acid (MBAA)), add a small amount of glucose as a slow-release agent, mix evenly, and finally mix it with calcium ions (calcium sulfate suspension). Pour the pre-gel solution prepared by this process into the mold, soak the piezoelectric sheet with the positive and negative electrodes welded, lead out the welding wire, then seal the mold in a humid environment and store it for 1 h; after its physical cross-linking, separate the hydrogel from the mold and assemble the elastic tube; keep the ultraviolet chamber humid, irradiate it with ultraviolet light (365 nm UV; UVP CL-1000) for 1 h, and after the gel covalently cross-links and polymerizes, swell the hydrogel in water for at least 48 h to reach the equilibrium state. Take it out from the mold to obtain the self-adaptive fusion ultrasonic thin sheet transducer.

[0077] The specific embodiments described above have elaborated in detail on the technical solutions and beneficial effects of the present invention. It should be understood that the above is only the most preferred embodiment of the present invention and is not used to limit the present invention. Any modifications, supplements, equivalent replacements, etc. made within the principle scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A combined flexible and rigid ultrasonic transducer, comprising a soft material high-pressure adaptive cavity, an acoustic matching layer, a top electrode, a piezoelectric element module, a bottom electrode, and a backing acoustic absorption layer. The backing acoustic absorption layer, bottom electrode, piezoelectric element module, and top electrode are stacked in sequence from bottom to top. The acoustic matching layer is coated on the exposed upper surfaces of the backing acoustic absorption layer, bottom electrode, piezoelectric element module, and top electrode. The soft material high-pressure adaptive cavity wraps the acoustic matching layer, top electrode, piezoelectric element module, bottom electrode, and backing acoustic absorption layer. The soft material high-pressure adaptive cavity is made of silicone rubber material.

2. The hybrid flexible ultrasonic transducer according to claim 1, wherein The piezoelectric element module includes a plurality of piezoelectric ceramic sheets, and the plurality of piezoelectric ceramic sheets are linearly arrayed in a flexible polymer, and the flexible polymer is an epoxy resin material.

3. A combined rigid-flexible integrated ultrasonic transducer according to any one of claims 1-2, characterized in that, The top electrode and the bottom electrode are made of copper, and the thickness of the copper is 5 - 100 μm, and a titanium thin film is deposited thereon.

4. A combined rigid-flexible integrated ultrasonic transducer according to any one of claims 3, characterized in that The material of the acoustic matching layer is epoxy resin or modified epoxy resin, and the thickness is 1 / 4 of the wavelength at the detection frequency.

5. A hybrid ultrasonic transducer according to any one of claims 4, characterized in that, The material of the backing acoustic absorption layer is polyurethane or tungsten powder modified epoxy resin.

6. A combined rigid-flexible integrated ultrasonic transducer according to any one of claims 5, characterized in that The soft material high-pressure adaptive cavity is a cylinder, with a radius of 10 mm and a height of 8 mm.

7. The preparation method of a soft-hard combined integrated ultrasonic transducer according to any one of claims 1, It includes the following steps. Step 1, prepare piezoelectric ceramic sheets, and cut the piezoelectric ceramics into uniform sheet structures. Step 2, prepare the piezoelectric element module. Linearly array the plurality of piezoelectric ceramic sheets prepared in Step 1 in a mold, and pour an epoxy resin flexible material into the mold to submerge the tops of the piezoelectric ceramic sheets, forming the piezoelectric element module. Step 3, lay the top electrode and the bottom electrode on the upper and lower end faces of the piezoelectric element module respectively. Step 4, wrap the acoustic matching layer on the top electrode, and lay the backing acoustic absorption layer at the lower end of the bottom electrode. Step 5, place the modules prepared in Steps 1 - 4 as a whole in a mold, and slowly pour the stirred silicone rubber along the boundary into the mold until it is completely submerged. Step 6, place the mold together with the internal liquid silicone rubber in a vacuum box connected to a vacuum pump. After confirming the seal, use the vacuum pump to evacuate it.

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