Piezoelectric high-frequency broadband transparent ultrasonic transducer and preparation method thereof

Abstract

The application provides a piezoelectric high-frequency wide-band transparent ultrasonic transducer and a preparation method thereof, and comprises a piezoelectric material layer, a matching layer, a backing layer and a grounding metal ring, wherein the piezoelectric material layer is located in the inner cavity of the grounding metal ring; the piezoelectric material layer and the upper surface of the grounding metal ring are provided with the backing layer; the lower surface of the piezoelectric material layer and the grounding metal ring is provided with the matching layer; the core sensing element of the transducer is designed to be light transparent, the light path can pass straight through, and the visible light transmittance is greater than 80%.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of ultrasonic transducers, and particularly relates to a piezoelectric high-frequency broadband transparent ultrasonic transducer and a preparation method thereof. BACKGROUND

[0002] Photoacoustic imaging is a biomedical imaging technique that has developed rapidly in recent years. It combines the advantages of ultrasonic imaging, such as deep detection, and optical imaging, such as high resolution, and can realize functional imaging of tissues. Photoacoustic signals are generated by laser pulses exciting light absorbers in biological tissues through the photothermal effect. The bandwidth of the ultrasonic signals generated in this way covers a wide range (over 100 MHz), and the signal strength is usually 2-3 orders of magnitude weaker than that of tissue ultrasonic echo signals. These two characteristics determine that the ultrasonic transducer used to detect photoacoustic signals needs to have sufficient frequency and bandwidth, i.e., the center frequency and the relative bandwidth are as high as possible, to ensure sufficient absolute detection bandwidth, so as to simultaneously obtain the low-frequency and high-frequency components of the photoacoustic signal and capture as much energy of the photoacoustic signal as possible, thereby improving the receiving sensitivity and signal-to-noise ratio.

[0003] An ultrasonic transducer is an important device for realizing ultrasonic wave reception and emission, and is widely used in biomedical, nondestructive testing, acoustic tweezers control and many other fields. A piezoelectric ultrasonic transducer uses the piezoelectric effect and inverse piezoelectric effect of piezoelectric materials to realize the mutual conversion between electrical energy and mechanical energy. The structure mainly includes piezoelectric materials, electrodes, matching layers, backing layers and metal shells. The core sensing element part (piezoelectric materials, electrodes, matching layers and backing) of the traditional piezoelectric ultrasonic transducer is made of non-transparent materials, so that the overall structure of the transducer is usually not transparent.

[0004] With the rapid development of photoacoustic imaging technology, the development of transparent ultrasonic transducers has become one of the research hotspots in recent years. The piezoelectric materials, electrodes, matching layers and backing layers in the transparent ultrasonic transducer are made of materials with good light transmission. Compared with traditional ultrasonic transducers, transparent ultrasonic transducers not only can realize ultrasonic wave reception and emission, but also can allow light to pass directly above the core sensing element of the transducer, thereby providing a necessary window for the intervention of various optical means and greatly simplifying the photoacoustic imaging device. Studies have shown that transparent transducers have great application value in multi-modal imaging such as fluorescence, two-photon, confocal, large-field optical scanning photoacoustic imaging, and cell ultrasonic stimulation. However, since the intensity of photoacoustic signals is 2-3 orders of magnitude weaker than that of tissue ultrasonic echo signals, and the signal bandwidth covers a wide range, the performance of the transparent transducer needs to be higher, i.e., the center frequency, relative bandwidth and sensitivity are as high as possible, to ensure sufficient signal-to-noise ratio.

[0005] The main problems of the transparent ultrasonic transducer at present are two points, one is that the center frequency of the transducer is low, and the other is that the bandwidth of the transducer is low. These two problems directly lead to the low receiving sensitivity and signal-to-noise ratio of the transparent transducer to the photoacoustic signal, which seriously restricts the quality of photoacoustic imaging and hinders the further application and development of photoacoustic imaging in the field of photoacoustic imaging. In 2020, Ruimin Chen et al. prepared a high-frequency transparent ultrasonic transducer by using transparent lithium niobate piezoelectric crystal. The transparent ultrasonic transducer adopts a single-layer matching design, and the lithium niobate wafer plated with ITO transparent electrode is packaged into a metal shell with the wafer outward. The positive and negative electrodes are led out from both sides of the wafer by using conductive silver glue, and finally a certain thickness of Parylene is evaporated on the wafer outward as a matching layer. The center frequency of the transducer is 37MHz, and the-6dB relative bandwidth is about 30%. The preparation method of the transparent ultrasonic transducer has certain limitations, and only a single-layer matching layer structure can be realized, so the bandwidth of the transducer is low.

[0006] In the high-frequency ultrasonic transducer, the thickness of the wafer and the matching layer is very small, which is extremely difficult to prepare and requires high processing and assembly precision. The traditional high-frequency broadband transducer usually needs to adopt a double-layer matching design, the first layer of matching layer adopts silver powder doped epoxy resin, which has good conductivity and is convenient for leading out the electrode from the piezoelectric material, and the second layer is a Parylene film evaporated, which can be directly and uniformly wrapped on the surface of the transducer to form a waterproof and insulating protection. In the design of the transparent ultrasonic transducer, the transparent matching layer material with high acoustic impedance cannot meet the demand of conductivity, which makes it difficult to lead out the ground electrode of the piezoelectric material in the transparent transducer, so the preparation method of the traditional high-frequency broadband transducer cannot be applied to the preparation of the transparent ultrasonic transducer. SUMMARY

[0007] The purpose of the present application is to provide a piezoelectric high-frequency broadband transparent ultrasonic transducer and a preparation method thereof, which solves the above-mentioned deficiencies in the prior art.

[0008] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0009] The piezoelectric high-frequency broadband transparent ultrasonic transducer provided by the present application comprises a piezoelectric material layer, a matching layer, a backing layer and a grounding metal ring, wherein the piezoelectric material layer is located in the inner cavity of the grounding metal ring; the piezoelectric material layer and the upper surface of the grounding metal ring are provided with a backing layer; and the lower surface of the piezoelectric material layer and the grounding metal ring is provided with a matching layer.

[0010] Preferably, the matching layer is a double-layer structure, wherein the first layer of matching layer is quartz glass, and the second layer of matching layer is epoxy resin.

[0011] Preferably, the matching layer is a three-layer structure, wherein the first layer of the matching layer is glass, the second layer of the matching layer is polymethyl methacrylate, and the third layer of the matching layer is polystyrene.

[0012] Preferably, the backing layer is epoxy resin.

[0013] Preferably, the ground metal ring is a middle hollow metal sheet.

[0014] Preferably, one surface of the piezoelectric material layer is formed with a positive electrode, and the coaxial cable is connected to the positive electrode.

[0015] Preferably, a negative electrode is formed between the piezoelectric material layer and the lower surface of the ground metal ring and the matching layer.

[0016] A preparation method of a piezoelectric high-frequency broadband transparent ultrasonic transducer, comprising the following steps:

[0017] Step 1: mirror polishing the surface of the piezoelectric material layer to form a polished transparent piezoelectric layer;

[0018] Step 2: preparing a transparent electrode on the surface of the polished transparent piezoelectric layer to form a transparent electrode layer;

[0019] Step 3: cutting the transparent piezoelectric wafer on the side surface where the transparent electrode layer is formed according to the predetermined size to obtain a cut transparent piezoelectric wafer;

[0020] Step 4: placing the cut transparent piezoelectric wafer into the ground metal ring, and the side surface of the transparent piezoelectric wafer where the transparent electrode layer is formed is parallel to the bottom surface of the ground metal ring, and then fixing and packaging;

[0021] Step 5: grinding and polishing the side surface of the ground metal ring and the transparent piezoelectric wafer where the transparent electrode layer is not formed to the designed thickness of the piezoelectric wafer;

[0022] Step 6: preparing a transparent electrode layer on the polished side surface of the ground metal ring and the transparent piezoelectric wafer;

[0023] Step 7: preparing a matching layer on the transparent electrode layer;

[0024] Step 8: connecting an acoustic lens to the matching layer;

[0025] Step 9: connecting the core wire of the coaxial cable to the positive electrode of the transparent piezoelectric wafer, and connecting the shielding layer of the coaxial cable to the ground metal ring;

[0026] Step 10: forming a backing layer on the side of the ground metal ring and the transparent piezoelectric wafer where the positive electrode is formed to obtain a piezoelectric high-frequency broadband transparent ultrasonic transducer.

[0027] Compared with the prior art, the piezoelectric high-frequency wideband transparent ultrasonic transducer has the advantages that:

[0028] The piezoelectric high-frequency wideband transparent ultrasonic transducer provided by the application has the advantages that:

[0029] The piezoelectric high-frequency wideband transparent ultrasonic transducer provided by the application has the advantages that: BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a preparation process flowchart of the application;

[0031] Figure 2 is a transducer structure schematic diagram of the application;

[0032] Figure 3 is a piezoelectric material layer structure schematic diagram of the application;

[0033] Figure 4 is another piezoelectric material layer structure schematic diagram of the application;

[0034] Figure 5 is a matching layer structure schematic diagram of the application;

[0035] Figure 6 is another matching layer structure schematic diagram of the application;

[0036] Figure 7 is a transducer ultrasonic echo response test result of the application. DETAILED DESCRIPTION

[0037] The application will be further described in detail below with reference to the accompanying drawings.

[0038] The application provides a piezoelectric high-frequency broadband transparent ultrasonic transducer, which comprises an ultrasonic transducer body and a transducer shell.

[0039] As shown in the figure, Figure 2 The application provides a piezoelectric high-frequency broadband transparent ultrasonic transducer, which comprises an ultrasonic transducer body and a transducer shell.

[0040] As shown in the figure, Figure 5 、 Figure 6 The matching layer is a double-layer or double-layer-above structure, and the design principle is that the acoustic impedance gradually decreases in sequence.

[0041] When the matching layer is a double-layer structure, the first layer matching layer 2-1 is quartz glass, and the acoustic impedance is 12 Mrayl.

[0042] When the matching layer is a three-layer structure, the first layer matching layer 2-1 is glass, the acoustic impedance is 16 Mrayl, the second layer matching layer 2-2 is polymethyl methacrylate (PMMA), the acoustic impedance is 3.2 Mrayl, and the third layer matching layer 2-3 is polystyrene (PS), the acoustic impedance is 2.2 Mrayl.

[0043] The backing layer 3 is epoxy resin (Epo-tek 301).

[0044] One surface of the piezoelectric material layer is formed with a positive electrode, and the positive electrode is connected with a coaxial cable.

[0045] The lower surface of the piezoelectric material layer and the ground metal ring is formed with a negative electrode between the piezoelectric material layer and the matching layer.

[0046] As shown in the figure, Figure 1 The specific preparation process of the piezoelectric high-frequency broadband transparent ultrasonic transducer is as follows:

[0047] Step 1, mirror polishing the surface of the piezoelectric material layer with diamond polishing paste, the particle size of the polishing paste is reduced from 3um to 0.5um successively until no visible scratches are observed, forming a polished transparent piezoelectric layer;

[0048] Step 2, preparing an ITO transparent electrode on the surface of the polished transparent piezoelectric layer by a magnetron sputtering method to form a transparent electrode layer 5, with a thickness of 100nm;

[0049] Step 3, cutting the transparent piezoelectric wafer according to the preset size, the cutting depth is greater than the thickness of the transparent piezoelectric wafer;

[0050] Step 4, placing the cut transparent piezoelectric wafer into a grounded metal ring, ensuring that the bottom surface (positive electrode) of the transparent piezoelectric wafer is parallel to the bottom surface of the metal ring, and fixing and packaging with epoxy resin (Epo-tek301);

[0051] Step 5, fixing the grounded metal ring and the transparent piezoelectric wafer with paraffin on a glass substrate, grinding and polishing to the designed thickness of the piezoelectric wafer, i.e. the center frequency corresponds to half of the wavelength in the material, at this time the thickness of the grounded metal ring and the transparent piezoelectric wafer is the same;

[0052] Step 6, preparing a 100nm thick ITO transparent electrode on the polished side of the grounded metal ring and the transparent piezoelectric wafer by a magnetron sputtering method, so that the negative electrode of the wafer forms an electrical connection with the grounded metal ring;

[0053] Step 7, pasting a quartz glass sheet as the first matching layer on the ITO transparent electrode, using epoxy resin as the adhesive, and applying pressure during curing to ensure that the glue layer thickness is less than 1um;

[0054] Step 8, grinding and polishing the first matching layer to the required thickness, i.e. the center frequency corresponds to one quarter of the wavelength in the material;

[0055] Step 9, pouring epoxy resin as the second matching layer on the first matching layer, and grinding and polishing to the required thickness, i.e. the center frequency corresponds to one quarter of the wavelength in the material;

[0056] Step 10, pasting an acoustic lens on the second matching layer,

[0057] Step 11, heating and removing the grounded metal ring and the transparent piezoelectric wafer from the glass substrate, and fixing them in the metal shell with the other side up;

[0058] Step 12, cutting the transparent piezoelectric wafer according to the preset array unit on the surface of the transparent piezoelectric wafer, obtaining a divided array element transparent piezoelectric wafer, wherein the cutting depth is less than the thickness of the transparent piezoelectric wafer;

[0059] Step 13, the core wire of the coaxial cable is connected to the positive ITO electrode of the transparent piezoelectric wafer by using conductive silver glue (E-solder 3022), and the shielding layer of the coaxial cable is connected with the grounding metal ring and the metal shell to form a good electrostatic shield;

[0060] Step 14, epoxy resin is filled in the metal shell as a backing layer, and is polished to a required thickness, i.e. 4 to 6 times of the wavelength in the material corresponding to the center frequency;

[0061] Step 15, a standard SMA joint is welded at the other end of the coaxial cable;

[0062] Step 16, the assembled transducer is tested for ultrasonic pulse echo response, as shown in Figure 7 , the center frequency and bandwidth are calculated.

[0063] According to the present application, a high-frequency broadband transparent ultrasonic transducer and a preparation method thereof are provided, the center frequency of the transparent ultrasonic transducer can be greater than 25 MHz, and the -6dB bandwidth is relatively greater than 60%;

[0064] The preparation method introduces a grounding metal ring with the same thickness as the piezoelectric material, which is connected with the negative electrode of the transparent piezoelectric layer through a transparent electrode, so as to lead out the electrode of the piezoelectric material, and meanwhile does not affect the subsequent adhesion of the matching layer;

[0065] The material of the grounding metal ring according to the present application includes metal materials with good conductivity, such as stainless steel, aluminum alloy, brass, etc.

[0066] The grounding metal ring according to the present application is a metal sheet with a hollowed middle part, and the shape of the metal sheet and the hollowed middle part can be designed according to needs, including circular, square, polygon, etc.

[0067] The transparent piezoelectric layer according to the present application includes lithium niobate crystal, transparent piezoelectric ceramic / single crystal, etc.

[0068] The transparent piezoelectric layer according to the present application can include one or more than one piezoelectric element, as shown in Figure 3 and Figure 4 .

[0069] The transparent electrode according to the present application includes an oxide transparent electrode (such as indium tin oxide, ITO), a nano-metal transparent electrode (such as nano-silver wire), etc.

[0070] The transparent matching layer according to the present application is a structure of double layers or more than double layers.

[0071] The transparent matching layer material comprises transparent materials with high acoustic impedance, such as quartz glass, K9 optical glass and the like, and transparent polymer materials with low acoustic impedance, including epoxy resin, polymethyl methacrylate (PMMA), polystyrene (PS), parylene and the like.

[0072] The high acoustic impedance transparent matching layer material is connected with the piezoelectric wafer through an adhesive, and the adhesive comprises epoxy resin, acrylic resin and the like.

[0073] The adhesive is applied with pressure when being cured, so that the thickness of the adhesive layer is less than 1 mu m.

[0074] The material of the acoustic lens comprises transparent materials such as epoxy resin, polymethyl methacrylate (PMMA), polystyrene (PS) and TPX (methylpentene copolymer).

[0075] The acoustic lens comprises a curved surface acoustic lens and a Fresnel plane acoustic lens based on artificial acoustic structure.

[0076] The transparent backing layer material comprises transparent polymer materials such as epoxy resin, polymethyl methacrylate (PMMA) and polystyrene (PS).

[0077] The metal shell can be designed according to the application needs, including a hollow cylinder and a hollow prism.

Claims

1. A piezoelectric high frequency broadband transparent ultrasound transducer, characterized in that, The piezoelectric material layer, the matching layer, the backing layer and the grounding metal ring, wherein the piezoelectric material layer is located in the inner cavity of the grounding metal ring; the piezoelectric material layer and the upper surface of the grounding metal ring are provided with the backing layer; the lower surface of the piezoelectric material layer and the grounding metal ring is provided with the matching layer; The thickness of the grounding metal ring is the same as the thickness of the piezoelectric material layer, and the grounding metal ring is electrically connected with the negative electrode of the piezoelectric material layer through a transparent electrode layer; The matching layer, the backing layer and the electrode are all made of transparent material, so that the light transmittance of the transducer in the visible light band is greater than 80%.

2. A piezoelectric high frequency wideband transparent ultrasound transducer according to claim 1, characterized in that, The matching layer is a double-layer structure, wherein the first layer of the matching layer is quartz glass, and the second layer of the matching layer is epoxy resin.

3. A piezoelectric high frequency wideband transparent ultrasonic transducer according to claim 1, characterized in that, The matching layer is a three-layer structure, wherein the first layer of the matching layer is glass, the second layer of the matching layer is polymethyl methacrylate, and the third layer of the matching layer is polystyrene.

4. A piezoelectric high frequency wideband transparent ultrasonic transducer according to claim 1, characterized in that, The backing layer is epoxy resin.

5. A piezoelectric high frequency wideband transparent ultrasonic transducer according to claim 1, characterized in that, The grounding metal ring is a metal sheet with a hollow middle part.

6. A piezoelectric high frequency wideband transparent ultrasonic transducer according to claim 1, characterized in that, A positive electrode is formed on one surface of the piezoelectric material layer, and the positive electrode is connected with a coaxial cable.

7. A piezoelectric high frequency wideband transparent ultrasonic transducer according to claim 1, characterized in that, A negative electrode is formed between the lower surface of the piezoelectric material layer and the grounding metal ring and the matching layer.

8. A method of manufacturing a piezoelectric high frequency broadband transparent ultrasound transducer, characterized in that, The method comprises the following steps: Step 1: mirror polishing the surface of the piezoelectric material layer to form a polished transparent piezoelectric layer; Step 2: preparing a transparent electrode on the surface of the polished transparent piezoelectric layer to form a transparent electrode layer; Step 3: cutting the side surface of the transparent piezoelectric wafer with the transparent electrode layer according to the preset size to obtain a cut transparent piezoelectric wafer; Step 4: placing the cut transparent piezoelectric wafer into the grounding metal ring, and fixing and packaging the side surface of the transparent piezoelectric wafer with the transparent electrode layer parallel to the bottom surface of the grounding metal ring; Step 5: grinding and polishing the side surface of the transparent piezoelectric wafer without the transparent electrode layer to the designed thickness of the piezoelectric wafer; Step 6: preparing a transparent electrode layer on the polished side of the grounding metal ring and the transparent piezoelectric wafer; Step 7: preparing a matching layer on the transparent electrode layer; Step 8: connecting an acoustic lens on the matching layer; Step 9: connecting the core wire of the coaxial cable to the positive electrode of the transparent piezoelectric wafer, and connecting the shielding layer of the coaxial cable with the grounding metal ring; Step 10: forming a backing layer on the side of the grounding metal ring and the transparent piezoelectric wafer with the positive electrode to obtain a piezoelectric high-frequency broadband transparent ultrasonic transducer.

Images