Multi-frequency ultrasonic phased array probe and preparation method thereof

Abstract

The invention discloses a multi-frequency ultrasonic phased array probe and a preparation method thereof. Piezoelectric array elements in the multi-frequency ultrasonic phased array probe are selected from at least one of a zero-frequency array element, a frequency-doubled array element and a frequency-tripled array element and a fundamental-frequency array element; a fundamental frequency array element is used as a transmitting array element, and a zero frequency array element, a frequency doubling array element and a frequency tripling array element are used as receiving array elements, so that the receiving of nonlinear signals is enhanced; the matching layer is matched with the frequency of the corresponding piezoelectric array element according to the matching mechanism of lambda m / (4f), different frequencies correspond to different thicknesses of the matching layer, the transmission efficiency of multi-frequency sound waves is improved, the transmission efficiency of the multi-frequency sound waves can be larger than 80%, finally, the gradient porous backing layer is adopted, the sound absorption frequency is widened, signal aliasing is reduced, and the sound absorption effect is improved. Therefore, the multi-frequency ultrasonic phased array probe provided by the invention has high sensitivity, broadband response and accurate signal analysis in micron-sized crack detection.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrasonic phased array probes, and particularly relates to a multi-frequency ultrasonic phased array probe and a preparation method thereof. Background Art

[0002] Traditional ultrasonic phased array probes have significant limitations in detecting micron-sized cracks. They use single-frequency piezoelectric array elements and traditional subtractive manufacturing processes, resulting in insufficient sensitivity for detecting non-linear signals. In the prior art, piezoelectric wafers are formed into different thicknesses by mechanical cutting to achieve frequency differences. However, due to material brittleness and processing accuracy limitations, the yield of thin array elements is low and the frequency regulation range is limited. When a matching layer uses a composite material with a fixed thickness, it is difficult to adapt to the impedance matching requirements of multi-frequency sound waves, and the coupling between the matching layer interfaces of different frequency array elements is poor, resulting in a decrease in sound energy transmission efficiency and signal distortion. The backing layer, due to its uniform material system and simple structural design, has insufficient sound attenuation performance and a narrow bandwidth, making it difficult to achieve narrow pulse excitation. In addition, traditional manufacturing processes rely on multi-process machining and manual assembly, resulting in problems such as low array element size accuracy, large alignment deviations, and difficulty in forming complex structures, severely restricting the probe's ability to capture non-linear harmonic signals. These defects jointly caused by material properties, structural design, and manufacturing methods make it difficult for existing ultrasonic phased arrays to meet the core requirements of high sensitivity, wide-band response, and accurate signal analysis in micron-sized crack detection. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, the first object of the present invention is to provide a multi-frequency ultrasonic phased array probe. The multi-frequency ultrasonic phased array probe provided by the present invention has a matching layer with a frequency-thickness coupling characteristic, a wide-band backing layer with a special-shaped topology, and a multi-frequency piezoelectric array. It not only solves the problem of signal aliasing caused by poor thickness adaptability of the matching layer of multi-frequency array elements and the lack of impedance gradient in the backing layer in traditional processes, but also significantly improves the non-linear harmonic response sensitivity and detection bandwidth of the probe through the precise forming of the special-shaped acoustic structure, while reducing the assembly error, providing a new probe manufacturing solution with high sensitivity and wide-band response for non-linear ultrasonic detection of micron-sized cracks.

[0004] The second object of the present invention is to provide a preparation method for a multi-frequency ultrasonic phased array probe.

[0005] To achieve the above objects, the present invention adopts the following technical solutions:

[0006] A multi-frequency ultrasonic phased array probe of the present invention, the multi-frequency ultrasonic phased array probe includes a matching layer, a piezoelectric array, and a backing layer from bottom to top;

[0007] The piezoelectric array is composed of N groups of arrayed piezoelectric elements; the piezoelectric elements are selected from at least one of zero-frequency elements, second-harmonic elements, third-harmonic elements and fundamental-frequency elements;

[0008] The piezoelectric element is a PZT piezoelectric wafer with an Ag electrode on its surface;

[0009] The matching layer covers the upper part of the piezoelectric array, and the relationship between the thickness of the matching layer covering any piezoelectric element and the piezoelectric element is shown in Equation 1:

[0010] d = λ m / (4f) Equation 1,

[0011] where d is the thickness of the matching layer above the piezoelectric element, λ m is the wavelength corresponding to the sound velocity of the measured part material, and f is the operating frequency of the piezoelectric element;

[0012] The positioning card slot is arranged at the upper end of the backing layer, and the piezoelectric elements in the piezoelectric array are inserted into the positioning card slot; the backing layer is a gradient porous structure.

[0013] For the multi-frequency ultrasonic phased array probe provided by the present invention, the piezoelectric elements are selected from at least one of zero-frequency elements, second-harmonic elements, third-harmonic elements and fundamental-frequency elements; by using the fundamental-frequency element as the transmitting element and using the zero-frequency element, second-harmonic element and third-harmonic element as the receiving elements, the reception of non-linear signals is enhanced; and the matching layer is matched with the corresponding piezoelectric element frequency according to the matching mechanism of λ m / (4f), different frequencies correspond to different matching layer thicknesses, improving the transmission efficiency of multi-frequency sound waves, and the transmission efficiency of multi-frequency sound waves can be >80%. Finally, by adopting a gradient porous backing layer, the sound absorption frequency is broadened and signal aliasing is reduced, so that the multi-frequency ultrasonic phased array probe provided by the present invention has high sensitivity, wide-band response and accurate signal analysis in the detection of micron-scale cracks.

[0014] In a preferred solution, the length of the piezoelectric element is 2 mm to 15 mm.

[0015] In a preferred solution, the distance between any two elements is 100 μm to 500 μm.

[0016] In a preferred solution, the mode of the piezoelectric array is a linear array or a planar array.

[0017] In a preferred solution, the material of the matching layer is Al2O3 and / or resin.

[0018] In a preferred solution, the material of the backing layer contains tungsten.

[0019] Preferably, the pore diameter of the pores in the backing layer is 50-200 μm, and the porosity is 20-60%. In the present invention, by using a porous backing layer and controlling the pore diameter and porosity within the scope of the present invention, the signal aliasing rate can be reduced by 40%.

[0020] Preferably, the backing layer is a D-type triply periodic minimal surface (TPMS) structure. Using the D-type triply periodic minimal surface (TPMS) structure as the gradient porous structure, the performance of the finally obtained multi-frequency ultrasonic phased array probe is optimal.

[0021] Preferably, the multi-frequency ultrasonic phased array probe further includes a flexible circuit board, and the printed channels of the flexible circuit board correspond to each piezoelectric element one by one and are connected to the piezoelectric element through wires.

[0022] A preparation method of a multi-frequency ultrasonic phased array probe according to the present invention: establish an element model composed of a substrate A and N groups of piezoelectric elements arranged above the substrate A, and obtain a piezoelectric element blank by light-curing 3D printing of a slurry containing PZT ceramic powder according to the element model. The piezoelectric element blank is degreased and sintered to obtain a sintered blank, silver-plated for the first time, subjected to polarization treatment, the substrate A is removed, and silver-plated for the second time to obtain N groups of piezoelectric elements; according to the thickness of the matching layer, stretch a substrate B on the basis of the thickness of the matching layer to form a matching layer model, and obtain a matching layer containing the substrate B by light-curing 3D printing according to the matching layer model, then bond the piezoelectric element and the matching layer, and use light-curing 3D printing to obtain a backing layer with a positioning card slot at one end, assemble the backing layer and the piezoelectric element, and then remove the substrate B in the matching layer to obtain the product.

[0023] The preparation method of the present invention uses light-curing 3D printing technology to realize the manufacturing of high-precision special-shaped structures of the core functional layers of the probe. First, all the piezoelectric elements are integrally printed, which can not only improve the efficiency but also ensure the uniformity of polarization. Subsequently, a matching layer with frequency-thickness coupling characteristics is constructed by a digital forming method. According to the thickness of the matching layer, stretch a substrate B on the basis of the thickness of the matching layer to form a matching layer model, and obtain a matching layer containing the substrate B by light-curing 3D printing according to the matching layer model. Subsequently, a special-shaped topology broadband backing layer is formed by light-curing 3D printing. After assembling the backing layer and the piezoelectric element, the substrate B is precisely polished and removed to finally form the probe structure.

[0024] Preferably, the process of obtaining the piezoelectric element blank by light-curing 3D printing is as follows: mix PZT ceramic powder, a first light-curing monomer, and a first additive to obtain a slurry containing PZT ceramic powder, add the slurry containing PZT ceramic powder to a light-curing 3D printing device, and perform light-curing 3D printing according to the element model to obtain the piezoelectric element blank;

[0025] The PZT ceramic powder is composed of fine powder with a size of 100 - 500 nm and coarse powder with a particle size of 1 - 2 μm. By mass ratio, the fine powder:coarse powder = 2 - 5:5 - 8.

[0026] In the slurry containing PZT ceramic powder, the mass fraction of PZT ceramic powder is 80wt.% - 91wt.%, the mass fraction of the first photocurable monomer is 6wt.% - 17wt.%, and the mass fraction of the first additive is 1wt.% - 5wt.

[0027] In the present invention, the dual - particle - size grading strategy optimizes the rheological properties of the slurry. The coarse particle size reduces the viscosity of the slurry and improves its fluidity. At the same time, the dual - particle - size grading enhances the density of the piezoelectric wafer. Meanwhile, photocurable 3D printing is used to realize the continuous forming of sub - millimeter - thick wall piezoelectric wafers. The piezoelectric wafers obtained by the photocurable 3D printing of the present invention have a high density, and the piezoelectric coefficient d 33 is increased to 450 pC / N, and the deviation of the internal polarization uniformity of the wafer is <5%, solving the problem of weakened edge polarization caused by the traditional cutting process.

[0028] Further preferably, the first photocurable monomer is composed of dipentaerythritol hexaacrylate (DPHA), polyethylene glycol o - phenylphenyl ether acrylate (OPPEA), bisphenol A dimethacrylate (BPA4EODMA), and polyethylene glycol diacrylate (PEG200DA). By mass ratio, dipentaerythritol hexaacrylate (DPHA):polyethylene glycol o - phenylphenyl ether acrylate (OPPEA):bisphenol A dimethacrylate (BPA4EODMA):polyethylene glycol diacrylate (PEG200DA)=5 - 15:45 - 65:3.5 - 10:10 - 45.

[0029] Further preferably, the first additive is composed of a dispersant, an anti - settling agent, a leveling agent, an antifoaming agent, and a photoinitiator. By mass ratio, dispersant:anti - settling agent:leveling agent:antifoaming agent:photoinitiator = 1 - 3:0.1 - 3:1 - 3:0.1 - 3:0.1 - 5; the dispersant is Solsperse - 41000, the anti - settling agent is Sago - 8810, the leveling agent is Rad2500, the antifoaming agent is Sago - 1690, and the photoinitiator is ethyl 2,4,6 - trimethylbenzoyl - phenylphosphinate (TPO - L).

[0030] Further preferably, the PZT ceramic powder, the first photocurable monomer, and the first additive are mixed in a mixer under a vacuum environment. The mixing speed is 800 - 1500 rpm, and the mixing time is 5 - 20 min.

[0031] Further preferably, when photo-curing the 3D printed piezoelectric element blank, the exposure energy is controlled to be 8 - 30 mJ / cm², and the layer thickness is 10 - 30 μm.

[0032] Preferably, the debinding is carried out in a vacuum environment, the debinding temperature is 400 - 600 °C, and the debinding time is 2500 - 3000 min.

[0033] Preferably, the sintering temperature is 1230 - 1280 °C, and the sintering time is 1 - 3 h.

[0034] Preferably, the process of polarization treatment is as follows: placing the silver-coated sintered blank in silicone oil at 120 °C in an electric field of 2 - 5 kV / mm and polarizing for 30 - 60 min.

[0035] Preferably, the process of obtaining the matching layer containing the substrate B by photo-curing 3D printing is as follows: preparing a matching layer slurry by mixing Al2O3 ceramic powder, photo-curing monomer No. 2, and additive No. 2, adding the matching layer into a photo-curing 3D printing device, and performing photo-curing 3D printing according to the matching layer model to obtain the matching layer containing the substrate B;

[0036] In the slurry of the Al2O3 ceramic powder, the mass fraction of the Al2O3 ceramic powder is 0 wt.% - 75 wt.%, the mass fraction of the photo-curing monomer No. 2 is 20 wt.% - 99 wt.%, and the mass fraction of the additive No. 2 is 1 wt.% - 5 wt.%.

[0037] Further preferably, the particle size of the Al2O3 ceramic powder is 100 nm - 500 nm.

[0038] Further preferably, the photo-curing monomer No. 2 is composed of trimethylolpropane triacrylate (TMPTA), polyethylene glycol diacrylate (PEG200DA), and polyethylene glycol (PEG200). By mass ratio, trimethylolpropane triacrylate (TMPTA): polyethylene glycol diacrylate (PEG200DA): polyethylene glycol (PEG200) = 30 - 55: 20 - 65: 25 - 55.

[0039] Further preferably, the additive No. 2 is composed of a dispersant, an anti-settling agent, a leveling agent, an anti-foaming agent, and a photo-initiator. By mass ratio, dispersant: anti-settling agent: leveling agent: anti-foaming agent: photo-initiator = 1 - 3: 0.1 - 3: 1 - 3: 0.1 - 3: 0.1 - 5; the dispersant is Solsperse-41000, the anti-settling agent is Sago-8810, the leveling agent is Rad2500, the anti-foaming agent is Sago-1690, and the photo-initiator is ethyl-2,4,6-trimethylbenzoyl phenylphosphinate (TPO-L).

[0040] Further preferably, the Al2O3 ceramic powder, the second photocurable monomer, and the second additive are mixed in a mixer under a vacuum environment. The mixing speed is 800 - 1500 rpm, and the mixing time is 5 - 20 min.

[0041] Further preferably, when photocuring the matching layer containing the substrate B by 3D printing, the exposure energy is controlled to be 1.25 - 7.11 mJ / cm², and the layer thickness is 30 - 60 μm.

[0042] In a preferred solution, the piezoelectric element and the matching layer are bonded by epoxy resin using the micro-column positioning structure (accuracy ±50 μm) of the photocuring mold.

[0043] In a preferred solution, the flexible circuit board is connected to N groups of piezoelectric elements by conductive adhesive. When connecting, the channels on the flexible circuit board correspond to each piezoelectric element one by one. The lead electrodes are led out for easy wiring.

[0044] In a preferred solution, the process of obtaining the backing layer by photocuring 3D printing is as follows: tungsten powder, the third photocurable monomer, and the third additive are mixed to obtain the backing layer slurry. The backing layer slurry is added into the photocuring 3D printing equipment, and the backing layer is obtained by photocuring 3D printing according to the matching layer model.

[0045] In the backing layer slurry, the mass fraction of tungsten powder is 65 wt.% - 90 wt.%, the mass fraction of the third photocurable monomer is 5 wt.% - 34 wt.%, and the mass fraction of the third additive is 1 wt.% - 5 wt.%.

[0046] Further preferably, the particle size of the tungsten powder is 100 nm - 500 nm.

[0047] Further preferably, the third photocurable monomer is composed of trimethylolpropane triacrylate (TMPTA), polyethylene glycol o-phenylphenyl ether acrylate (OPPEA), and polyethylene glycol diacrylate (PEG200DA). By mass ratio: trimethylolpropane triacrylate (TMPTA): polyethylene glycol o-phenylphenyl ether acrylate (OPPEA): polyethylene glycol diacrylate (PEG200DA) = 20 - 45:30 - 65:15 - 25.

[0048] Further preferably, the No. 3 additive is composed of a dispersant, an anti-settling agent, a leveling agent, an anti-foaming agent, and a photoinitiator. By mass ratio, dispersant: anti-settling agent: leveling agent: anti-foaming agent: photoinitiator = 1-3: 0.1-3: 1-3: 0.1-3: 0.1-5; the dispersant is Solsperse-41000, the anti-settling agent is Sago-8810, the leveling agent is Rad2500, the anti-foaming agent is Sago-1690, and the photoinitiator is ethyl 2,4,6-trimethylbenzoyl phenylphosphinate (TPO-L).

[0049] Further preferably, tungsten powder, the No. 3 photocurable monomer, and the No. 3 additive are mixed in a mixer under a vacuum environment. The mixing speed is 800-1500 rpm, and the mixing time is 5-20 min.

[0050] Further preferably, when photocuring the 3D printing backing layer, the exposure energy is controlled to be 7.56-15 mJ / cm², and the layer thickness is 20-50 μm.

[0051] In a preferred solution, the backing layer and the piezoelectric element are assembled using an epoxy resin adhesive. During assembly, the assembly error is controlled to be <5 μm by die positioning.

[0052] Because the piezoelectric wafer generates high-frequency vibrations during operation, it is fixed together using an epoxy resin adhesive and a card slot to improve reliability.

[0053] Principle and advantages

[0054] The present invention realizes the manufacture of a high-precision special-shaped structure of the probe core functional layer through a photocuring 3D printing technology. Specifically, aiming at the key problems in the prior art such as impedance mismatch of the multi-frequency element matching layer, insufficient sound attenuation performance of the backing layer, and cumulative interlayer assembly error, a new process path with photocuring 3D printing as the core is proposed: constructing a matching layer with frequency-thickness coupling characteristics, a wide-frequency backing layer with special-shaped topology, and a thin-walled PZT piezoelectric array through a digital forming method. Among them, high-precision and high-performance piezoelectric wafers are realized by regulating the components and process parameters of the printing slurry, and sub-micron-level interlayer positioning accuracy is achieved by using the microstructural positioning characteristics of the photocuring mold. The method of the present invention not only solves the problems of poor thickness adaptability of the multi-frequency element matching layer and signal aliasing caused by the lack of impedance gradient in the backing layer in the traditional process, but also significantly improves the non-linear harmonic response sensitivity and detection bandwidth of the probe through the precise forming of the special-shaped acoustic structure, while reducing the assembly error, providing a new probe manufacturing solution with high sensitivity and wide-band response for the non-linear ultrasonic detection of micron-level cracks.

[0055] Compared with the prior art, the present invention combines the photocuring 3D printing technology with innovative structural design to achieve breakthrough technical effects in the field of manufacturing multi-frequency ultrasonic phased array probes:

[0056] 1. Precision structure manufacturing advantages. Based on the particle size distribution of PZT slurry and the refined regulation of process parameters, piezoelectric wafers with high piezoelectricity and polarization uniformity are achieved. The piezoelectric coefficient d 33 reaches 450 pC / N, the polarization uniformity deviation < 5%, effectively eliminating the edge polarization decay phenomenon caused by traditional cutting processes. At the same time, through the digital forming of the λ / 4 wavelength matching layer (0.1 - 0.5 mm), the acoustic energy transmission efficiency of multi-frequency sound waves > 90%. Using the micro-column positioning characteristics of the light-curing mold and the connection substrate structure design, the element pitch accuracy is ±50 μm.

[0057] 2. Improvement of multi-frequency acoustic performance. The innovative frequency-thickness coupling matching layer structure (d = λ m / (4f) adjustment) combined with the broadband sound-absorbing back lining layer, the -6dB detection bandwidth of the probe ≥ 75%. Description of the Drawings

[0058] Figure 1 is a schematic structural diagram of a multi-frequency ultrasonic phased array probe based on PZT piezoelectric ceramics.

[0059] Figure 2 is a piezoelectric ceramic wafer diagram based on light-curing 3D printing provided in Example 1.

[0060] Figure 3 is an Al2O3 matching layer diagram based on light-curing 3D printing provided in Example 1.

[0061] Figure 4 is a porous back lining layer diagram based on tungsten powder and light-curing 3D printing provided in Example 1.

[0062] Figure 5 is a schematic process flow diagram of the preparation method of a multi-frequency ultrasonic phased array probe based on PZT piezoelectric ceramics provided in Example 1.

[0063] Figure 6 is a comparison of the -6dB bandwidth between the multi-frequency ultrasonic phased array probe based on PZT piezoelectric ceramics provided in Example 1 and the single-frequency probe, Figure 6 (a) is the 0.5 MHz element -6dB bandwidth in Example 1, Figure 6 (b) is the 3 MHz element -6dB bandwidth in Example 1, Figure 6 (c) is the element -6dB bandwidth in Comparative Example 1. Detailed Embodiments

[0064] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0065] Example 1:

[0066] Step 1: Photocuring 3D printing of PZT piezoelectric wafers. PZT piezoelectric wafers with a thickness of 0.68 mm (0.5 MHz) and 4 mm (3 MHz) are respectively prepared. Take 70 g of PZT ceramic powder with a particle size of 2 μm, 30 g of PZT powder with a particle size of 100 nm, 2.285 g of DPHA, 9.900 g of OPPEA, 0.762 g of BPA4EODMA, 2.285 g of PEG200DA, 4 g of Solsperse-41000, 0.7 g of Sago-8810, 0.5 g of Rad2500, 0.5 g of Sago-1690, and 0.228 g of TPO-L. Mix all the raw materials and use a vacuum mixer to mix for 20 minutes under the condition of 1200 min / revolution to obtain the required ceramic slurry. The solid content of this ceramic slurry is 50 vol%. Using an energy of 29.8 mJ / cm 2 and a slice thickness of 20 μm, one-time forming of piezoelectric wafers with thicknesses of 0.68 mm and 4 mm is achieved. After gradient degreasing (600 °C / 3000 min), high-temperature sintering (1250 °C / 3 h), and polarization in a silicone oil environment (120 °C / 5 kV / mm), the density of the wafer reaches 93.2% after testing, and the piezoelectric constant d 33 = 450 pC / N, and the polarization uniformity deviation < 3%, which is especially suitable for the requirements of alternating thin and thick arrangements of 0.5 - 3 MHz array elements.

[0067] Step 2: Photocuring 3D printing of the Al2O3 matching layer

[0068] Take 100 g of Al2O3 ceramic powder, 22.27 g of TMPTA, 33.753 g of PEG200DA, 14.851 g of PEG200, 4.433 g of Solsperse-41000, 1.008 g of Sago-8810, 1.008 g of Rad2500, 2.015 g of Sago-1690, and 0.354 g of TPO-L. Mix all the raw materials and use a vacuum mixer to mix for 20 minutes under the condition of 1200 min / revolution to obtain the required ceramic slurry. The solid content of this ceramic slurry is 25 vol%. Using an energy of 2.58 mJ / cm 2The energy, the process parameters with a slice thickness of 50 μm, achieve the precise manufacturing of a matching layer with a thickness of 0.57 mm at 0.5 MHz and a thickness of 0.2 mm at 3 MHz (thickness tolerance ±10 μm). This process adjusts the thickness according to the formula d = λ m / (4f), so that the sound energy transmission efficiency of the 0.5 MHz array element reaches 92.5%, and the interface reflection loss of the 3 MHz array element is reduced to 3.8 dB. As shown in Figure 3 the printed structure edge clarity shown is better than ±20 μm.

[0069] Step 3: Stereolithography 3D printing of the backing layer

[0070] Take 100 g of tungsten powder, 9.199 g of TMPTA, 27.179 g of OPPEA, 6.899 g of PEGDA, 3.591 g of Solsperse-41000, 0.518 g of Sago-8810, 0.518 g of Rad2500, 0.518 g of Sago-1690, and 0.214 g of TPO-L. Mix all the raw materials and use a vacuum mixer to mix for 20 minutes under the condition of 1200 min / revolution to obtain the required slurry. Use an exposure energy of 9.34 mJ / cm² and a layer thickness of 20 μm to print a gradient porous D-type TPMS structure backing layer with a porosity of 30 - 60%. Increase the -6 dB bandwidth to 75% of the center frequency and reduce the signal aliasing rate by 30%.

[0071] Step 4: Multi-frequency array sub-micron assembly method.

[0072] The multi-frequency ultrasonic phased array probe of the present invention includes a matching layer, an Ag lower electrode, a piezoelectric wafer, an Ag upper electrode, a flexible circuit board, and a backing layer stacked in sequence from bottom to top; wherein the matching layer is matched with the corresponding piezoelectric array element frequency according to the λ / 4 matching mechanism, the lower electrode will be turned over to the upper surface of the piezoelectric wafer, the printed channels of the flexible circuit board correspond to the array element electrodes one by one, and the flexible circuit board is used to lead out the wiring of the ultrasonic phased array probe for easy connection with external devices. Its preparation and assembly method includes the following steps:

[0073] ① In this embodiment, the PZT piezoelectric ceramic array includes an array of 32 array elements, the spacing between each array element is 100 μm, the 0.5 MHz array elements and the 3 MHz array elements are arranged alternately, with 16 array elements each. The thickness of the 0.5 MHz array element is 4 mm and the width is 12 mm, the thickness of the 3 MHz array element is 0.68 mm and the width is 12 mm. The 0.5 MHz array element is used as the zero-frequency array element, and the 3 MHz array element is used as the fundamental-frequency array element.

[0074] ② After printing the piezoelectric array by stereolithography 3D printing technology, degreasing is carried out in a vacuum environment at a temperature of 600 °C for 3000 min. After sintering at 1250 °C for 3 h, electrode preparation is carried out. Then, in a silicone oil environment at 120 °C under an electric field of 5 kV / mm, polarization is carried out for 60 min. The excess ceramics at the bottom are polished, and electrode preparation is carried out again to obtain a piezoelectric wafer group with uniform polarization;

[0075] ③ The alumina (Al2O3) matching layer is printed by stereolithography 3D printing technology. The printed model is stretched by a 2-mm substrate on the basis of the design size of the traditional λ / 4 matching mechanism to connect the element matching layers;

[0076] ④ The piezoelectric element and the matching layer are adhesively bonded with epoxy resin by using the micro-column positioning structure (accuracy ±50 μm) of the stereolithography mold;

[0077] ⑤ The flexible circuit board is connected to the flipped electrode with conductive adhesive, so that the channels on the flexible circuit board correspond to each element, and the electrodes are led out for easy wiring;

[0078] ⑥ The tungsten powder backing layer is printed by stereolithography 3D printing technology. A gradient porous D-type TPMS structure tungsten powder backing layer with a porosity of 30 - 60% and positioning slots is printed. The assembly error is realized to be <15 μm by using the mold limit feature and assembled with the above parts with epoxy resin adhesive;

[0079] ⑦ The 2-mm substrate in the matching layer is polished off, and finally a multi-frequency ultrasonic phased array probe is formed.

[0080] Comparative Example 1

[0081] Other conditions are the same as those in Example 1, except that the 0.5-MHz element is changed to a 3-MHz element, and finally a single-frequency ultrasonic phased array probe is prepared.

[0082] For the probes in the examples and comparative examples, ultrasonic waves are emitted by a single element and the reflected echoes are received, and the spectra of the echo signals are analyzed. It is obtained that Figure 6 (a) and (b) are the -6 dB bandwidths of the zero-frequency element and the fundamental-frequency element of the multi-frequency ultrasonic phased array probe, Figure 6 (c) is the -6 dB bandwidth of the element of the single-frequency ultrasonic phased array probe. The -6 dB bandwidth of the zero-frequency element of the multi-frequency ultrasonic phased array probe is 0.195 MHz - 0.945 MHz, and the -6 dB bandwidth of the fundamental-frequency element is 1.12 MHz - 4.98 MHz, and zero-frequency signals can be received. The -6 dB bandwidth of the element of the single-frequency ultrasonic phased array probe is 1.20 MHz - 4.95 MHz, and it is extremely insensitive to zero-frequency signals.

[0083] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A multi-frequency ultrasonic phased array probe, characterized in that: The multi-frequency ultrasonic phased array probe includes a matching layer, a piezoelectric array, and a backing layer from bottom to top; The piezoelectric array is composed of N groups of arrayed piezoelectric elements; the piezoelectric elements are selected from at least one of zero-frequency elements, second-harmonic elements, and third-harmonic elements and fundamental-frequency elements; The piezoelectric element is a PZT piezoelectric wafer coated with an Ag electrode on the surface; The matching layer covers the upper part of the piezoelectric array, and the relationship between the thickness of the matching layer covering any piezoelectric element and the piezoelectric element is shown in Equation 1: d = λ m / (4f) Equation 1, where d is the thickness of the matching layer above the piezoelectric element, λ m is the wavelength corresponding to the sound velocity of the material of the DUT, and f is the operating frequency of the piezoelectric element; A positioning slot is provided at the upper end of the backing layer, and the piezoelectric elements in the piezoelectric array are inserted into the positioning slot; the backing layer is a gradient porous structure.

2. The multi-frequency ultrasonic phased array probe according to claim 1, wherein: The length of the piezoelectric element is 2 mm to 15 mm; The distance between any two piezoelectric elements is 100 μm to 500 μm; The mode of the piezoelectric array is a linear array or a planar array; The material of the matching layer is Al2O3 and / or resin; The material of the backing layer contains tungsten.

3. The multi-frequency ultrasonic phased array probe according to claim 1 or 2, wherein: The pore diameter of the pores in the backing layer is 50 to 200 μm, and the porosity is 20 to 60%; The backing layer is a D-type three-period minimal surface structure.

4. The multi-frequency ultrasonic phased array probe according to claim 1 or 2, wherein: The multi-frequency ultrasonic phased array probe further includes a flexible circuit board. The printed channels of the flexible circuit board correspond to each piezoelectric element one by one and are connected to the piezoelectric elements through wires.

5. A method for preparing a multi-frequency ultrasonic phased array probe according to any one of claims 1-4, characterized in that: An element model composed of a substrate A and N groups of piezoelectric elements arranged above the substrate A is established. According to the element model, a piezoelectric element blank is obtained by photocuring 3D printing of a slurry containing PZT ceramic powder. The piezoelectric element blank is degreased and sintered to obtain a sintered blank, silver-plated for the first time, subjected to polarization treatment, the substrate A is removed, and silver-plated for the second time to obtain N groups of piezoelectric elements; according to the thickness of the matching layer, a substrate B is stretched on the basis of the thickness of the matching layer to form a matching layer model. According to the matching layer model, a matching layer containing the substrate B is obtained by photocuring 3D printing. Then, the piezoelectric elements and the matching layer are bonded, and a backing layer with a positioning slot at one end is obtained by photocuring 3D printing. The backing layer and the piezoelectric elements are assembled, and then the substrate B in the matching layer is removed to obtain the product.

6. The preparation method of a multi-frequency ultrasonic phased array probe according to claim 5, characterized in that: The process of obtaining the piezoelectric element blank by photocuring 3D printing is as follows: PZT ceramic powder, a first photocuring monomer, and a first additive are mixed to obtain a slurry containing PZT ceramic powder. The slurry containing PZT ceramic powder is added to a photocuring 3D printing device, and photocuring 3D printing is carried out according to the element model to obtain the piezoelectric element blank; The PZT ceramic powder is composed of fine powder with a particle size of 100 to 500 nm and coarse powder with a particle size of 1 to 2 μm. By mass ratio, the fine powder:coarse powder = 2 to 5:5 to 8; In the slurry containing PZT ceramic powder, the mass fraction of PZT ceramic powder is 80wt.% - 91wt.%, the mass fraction of the first photocurable monomer is 6wt.% - 17wt.%, and the mass fraction of the first additive is 1wt.% - 5wt.%. The first photocurable monomer is composed of DPHA, OPPEA, BPA4EODMA, and PEG200DA. By mass ratio, DPHA:OPPEA:BPA4EODMA:PEG200DA = 5 - 15:45 - 65:3.5 - 10:10 - 45. The first additive is composed of a dispersant, an anti-settling agent, a leveling agent, an anti-foaming agent, and a photoinitiator. By mass ratio, dispersant:anti-settling agent:leveling agent:anti-foaming agent:photoinitiator = 1 - 3:0.1 - 3:1 - 3:0.1 - 3:0.1 - 5; the dispersant is Solsperse-41000, the anti-settling agent is Sago-8810, the leveling agent is Rad2500, the anti-foaming agent is Sago-1690, and the photoinitiator is TPO-L. When photocuring 3D printing the piezoelectric element blank, the exposure energy is controlled to be 8 - 30mJ / cm², and the layer thickness is 10 - 30μm. The debinding is carried out in a vacuum environment. The debinding temperature is 400 - 600°C, and the debinding time is 2500 - 3000min. The sintering temperature is 1230 - 1280°C, and the sintering time is 1 - 3h. The process of polarization treatment is as follows: The silver-coated sintered blank is placed in silicone oil at 120°C and polarized in an electric field of 2 - 5kV / mm for 30 - 60min.

7. The preparation method of a multi-frequency ultrasonic phased array probe according to claim 5, characterized in that: The process of photocuring 3D printing to obtain the matching layer containing substrate B is as follows: Mix Al2O3 ceramic powder, the second photocurable monomer, and the second additive to obtain the matching layer slurry. Add the matching layer into the photocuring 3D printing equipment and perform photocuring 3D printing according to the matching layer model to obtain the matching layer containing substrate B. In the matching layer slurry, the mass fraction of Al2O3 ceramic powder is 0wt.% - 75wt.%, the mass fraction of the second photocurable monomer is 20wt.% - 99wt.%, and the mass fraction of the second additive is 1wt.% - 5wt.%. The particle size of the Al2O3 ceramic powder is 100nm - 500nm. The second photocurable monomer is composed of TMPTA, PEG200DA, and PEG200. By mass ratio, TMPTA:PEG200DA:PEG200 = 30 - 55:20 - 65:25 - 55. The second additive is composed of a dispersant, an anti-settling agent, a leveling agent, an anti-foaming agent, and a photoinitiator. By mass ratio, dispersant:anti-settling agent:leveling agent:anti-foaming agent:photoinitiator = 1 - 3:0.1 - 3:1 - 3:0.1 - 3:0.1 - 5; the dispersant is Solsperse-41000, the anti-settling agent is Sago-8810, the leveling agent is Rad2500, the anti-foaming agent is Sago-1690, and the photoinitiator is TPO-L. When photo-curing the matching layer containing the substrate B, control the exposure energy to be 1.25 - 7.11 mJ / cm² and the layer thickness to be 30 - 60 μm.

8. The preparation method of a multi-frequency ultrasonic phased array probe according to claim 5, characterized in that: Adhere the piezoelectric element and the matching layer with epoxy resin by using the micro-column positioning structure of the photo-curing mold; Connect the flexible circuit board and N groups of piezoelectric elements with conductive adhesive, and make the channels on the flexible circuit board correspond to each piezoelectric element one by one during connection.

9. The preparation method of a multi-frequency ultrasonic phased array probe according to claim 5, characterized in that: The process of obtaining the backing layer by photo-curing 3D printing is as follows: Mix tungsten powder, photo-curing monomer No. 3, and additive No. 3 to obtain the backing layer slurry. Add the backing layer slurry into the photo-curing 3D printing equipment and perform photo-curing 3D printing according to the matching layer model to obtain the backing layer; In the backing layer slurry, the mass fraction of tungsten powder is 65wt.% - 90wt.%, the mass fraction of photo-curing monomer No. 3 is 5wt.% - 34wt.%, and the mass fraction of additive No. 3 is 1wt.% - 5wt.%; The particle size of the tungsten powder is 100nm - 500nm; The photo-curing monomer No. 3 is composed of TMPTA, OPPEA, and PEG200DA. By mass ratio, TMPTA:OPPEA:PEG200DA = 20 - 45:30 - 65:15 - 25; The additive No. 3 is composed of a dispersant, an anti-settling agent, a leveling agent, an anti-foaming agent, and a photo-initiator. By mass ratio, dispersant:anti-settling agent:leveling agent:anti-foaming agent:photo-initiator = 1 - 3:0.1 - 3:1 - 3:0.1 - 3:0.1 - 5; The dispersant is Solsperse-41000, the anti-settling agent is Sago-8810, the leveling agent is Rad2500, the anti-foaming agent is Sago-1690, and the photo-initiator is TPO-L. When photo-curing 3D printing the backing layer, control the exposure energy to be 7.56 - 15 mJ / cm² and the layer thickness to be 20 - 50 μm.

10. The preparation method of a multi-frequency ultrasonic phased array probe according to claim 5, characterized in that: Assemble the backing layer and the piezoelectric element with epoxy resin adhesive, and control the assembly error < 5 μm by mold limit during assembly.

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