Photoacoustic transducer with gradient acoustic impedance matching layer, preparation method and test method

Abstract

The invention belongs to the technical field of ultrasound, and particularly relates to a photoacoustic transducer with a gradient acoustic impedance matching layer, a preparation method and a test method. The preparation method comprises the following steps: coating a photoacoustic transducer carrier with a mixed solution formed by polydimethylsiloxane and a carbon material, and heating and curing the photoacoustic transducer carrier coated with the mixed solution to obtain an initial photoacoustic transducer; infiltrating the initial photoacoustic transducer in a coupling agent solution, and coating the surface of the initial photoacoustic transducer infiltrated by the coupling agent with a matching solution to obtain the photoacoustic transducer with a gradient acoustic impedance matching layer; the matching liquid is a mixture of epoxy resin and metal or metal oxide. The opto-acoustic transducer prepared by the method has three matching layers with acoustic impedance gradients from low to high, and the matching layers can effectively improve the acoustic transmittance from an opto-acoustic material to a metal material, improve the ultrasonic propagation range of the opto-acoustic transducer and expand the application scene of the opto-acoustic transducer.

Description

Technical Field

[0001] The invention belongs to the field of ultrasonic technology, and in particular relates to a photoacoustic transducer with a gradient acoustic impedance matching layer, a preparation method and a testing method. Background Art

[0002] Photoacoustic transducers are an ideal solution for nondestructive testing, but they are limited by the intensity of the ultrasonic signal they excite, so it is difficult to be effectively promoted in nondestructive testing. There are two main methods to improve the intensity of ultrasonic signals in the prior art: improving the efficiency of light-heat-acoustic conversion from the material perspective, and improving the transmittance of ultrasound to the test piece from the structural perspective. At present, the materials are mainly carbon materials (graphite, graphene, carbon nanotubes and candle ash, etc.). After long-term research, it has become increasingly difficult to improve the efficiency. From a structural perspective, the academic community generally focuses on beam shaping and light trapping microstructures, which mainly apply a matching layer between the transducer and the test piece to increase the ultrasonic signal intensity by increasing the acoustic transmittance. The existing photoacoustic transducer has no acoustic impedance matching layer, resulting in a low acoustic transmittance from the photoacoustic material to the metal material. In addition, the existing acoustic impedance matching layer is a large acoustic impedance matching small acoustic impedance, which is not suitable for the application scenarios of photoacoustic transducers. Summary of the invention

[0003] The purpose of the present invention is to address the defect that the acoustic impedance matching layer in the prior art leads to a low acoustic transmittance of the photoacoustic material to the metal material, which is not suitable for the photoacoustic transducer, and thus proposes a photoacoustic transducer with a gradient acoustic impedance matching layer, a preparation method and a test method. The preparation method coats a mixed liquid formed by polydimethylsiloxane and a carbon material on a photoacoustic transducer carrier to prepare an initial photoacoustic transducer, and soaks the prepared initial photoacoustic transducer in a coupling agent, and coats the surface of the initial photoacoustic transducer treated with the coupling agent with a matching liquid mixed with epoxy resin and metal or epoxy resin and metal oxide. The photoacoustic transducer prepared by the method described in the present invention has three matching layers with an acoustic impedance gradient from low to high, which are composed of polydimethylsiloxane, a mixture of polydimethylsiloxane and epoxy resin, and a mixture of epoxy resin and metal or epoxy resin and metal oxide. The matching layer can effectively improve the acoustic transmittance of the photoacoustic material to the metal material, improve the ultrasonic propagation range of the photoacoustic transducer, and expand the application scenario of the photoacoustic transducer.

[0004] The first aspect of the present invention provides a method for preparing a photoacoustic transducer having a gradient acoustic impedance matching layer, the method comprising the following steps:

[0005] Coating a mixed liquid formed by polydimethylsiloxane and carbon material on a photoacoustic transducer carrier, and heating and curing the photoacoustic transducer carrier coated with the mixed liquid to obtain an initial photoacoustic transducer;

[0006] The initial photoacoustic transducer is immersed in a coupling agent solution, and the surface of the initial photoacoustic transducer treated with the coupling agent is coated with a matching liquid to obtain a photoacoustic transducer with a gradient acoustic impedance matching layer; the matching liquid is a mixture of epoxy resin and metal or metal oxide.

[0007] Preferably, the mass ratio of epoxy resin to metal or metal oxide is 100:2.5-12.5.

[0008] Preferably, the gradient acoustic impedance matching layer comprises: a polydimethylsiloxane layer, a polydimethylsiloxane and epoxy resin layer, and an epoxy resin and metal or metal oxide layer, and the polydimethylsiloxane layer is attached to one side surface of the photoacoustic transducer carrier, and the polydimethylsiloxane and epoxy resin layer is attached between the polydimethylsiloxane layer and the epoxy resin and metal or metal oxide layer, and the acoustic impedance ratios of the polydimethylsiloxane layer, the polydimethylsiloxane and epoxy resin layer, and the epoxy resin and metal or metal oxide layer increase in sequence.

[0009] Preferably, the thickness of the gradient acoustic impedance matching layer is one quarter of the wavelength of an ultrasonic wave passing through the gradient acoustic impedance matching layer during detection, and the wavelength of the ultrasonic wave is 0.0075-7.5 mm.

[0010] Preferably, the thickness of the initial photoacoustic transducer is 10-500 μm, and the acoustic impedance of the initial photoacoustic transducer is 0.8-1.2 Mrayl.

[0011] Preferably, the coupling agent solution is a mixed solution of a coupling agent, anhydrous ethanol and water, and the volume ratio of the coupling agent, anhydrous ethanol and water is 10-40:10-40:20-80; the coupling agent is γ-aminopropyltriethoxysilane (KH-550) and / or γ-glycidyloxypropyltrimethoxysilane (KH-560).

[0012] The second aspect of the present invention provides a photoacoustic transducer with a gradient acoustic impedance matching layer prepared according to the above method, wherein the gradient acoustic impedance matching layer comprises: a polydimethylsiloxane layer, a polydimethylsiloxane and epoxy resin layer, and an epoxy resin and metal or metal oxide layer, and the polydimethylsiloxane layer is attached to one side surface of the photoacoustic transducer carrier, the polydimethylsiloxane and epoxy resin layer is attached between the polydimethylsiloxane layer and the epoxy resin and metal or metal oxide layer, and the acoustic impedance ratios of the polydimethylsiloxane layer, the polydimethylsiloxane and epoxy resin layer, and the epoxy resin and metal or metal oxide layer increase in sequence.

[0013] The third aspect of the present invention provides a method for testing acoustic impedance and acoustic transmittance of the photoacoustic transducer with a gradient acoustic impedance matching layer as described above, the method comprising: recording the initial signal strength of the ultrasonic pulse generator as E 0 , attach the ultrasonic pulse generator probe to the other side surface of the photoacoustic transducer carrier, place the test piece on the surface of the epoxy resin and the metal or metal oxide layer, turn on the ultrasonic pulse generator, and record the return time Δt and signal intensity E of the excitation ultrasonic pulse 1 , the acoustic impedance ratio of the epoxy resin and the metal or metal oxide layer is obtained according to the mass, volume, thickness of the initial photoacoustic transducer, the mass, volume, thickness of the photoacoustic transducer with the gradient acoustic impedance matching layer, and the return time of the exciting ultrasonic pulse, and the acoustic transmittance of the epoxy resin and the metal or metal oxide layer is obtained according to the initial signal strength of the ultrasonic pulse generator and the signal strength of the exciting ultrasonic pulse.

[0014] Preferably, the calculation formula of the acoustic impedance of the epoxy resin and the metal or metal oxide layer is as follows:

[0015]

[0016] In the formula, Z m is the acoustic impedance ratio of epoxy resin and metal or metal oxide layer, m 1 is the mass of the initial photoacoustic transducer, m 2 is the mass of the photoacoustic transducer with gradient acoustic impedance matching layer, V 1 is the volume of the initial photoacoustic transducer, V 2 is the volume of the photoacoustic transducer with gradient acoustic impedance matching layer, h 1 is the initial photoacoustic transducer thickness, h 2 is the thickness of the photoacoustic transducer with gradient acoustic impedance matching layer, Δt is the return time of the excitation ultrasonic pulse;

[0017] The formula for calculating the acoustic transmittance of epoxy resin and metal or metal oxide layer is as follows:

[0018]

[0019] Where T is the acoustic transmittance of the epoxy resin and the metal or metal oxide layer, E 0 is the initial signal strength of the ultrasonic pulse generator, E 1 is the signal intensity of the excitation ultrasonic pulse.

[0020] More preferably, the relationship between the acoustic transmittance of the epoxy resin and the metal or metal oxide layer and the acoustic impedance of the polydimethylsiloxane layer and the acoustic impedance of the test piece is as follows:

[0021]

[0022] Where, T is the acoustic transmittance of the epoxy resin and the metal or metal oxide layer, Z 1 is the acoustic impedance of the polydimethylsiloxane layer, Z 2 is the acoustic impedance of the device under test;

[0023] The relationship between the acoustic impedance of the polydimethylsiloxane layer, the acoustic impedance of the test piece, and the acoustic impedance of the epoxy resin and metal or metal oxide layer is shown in the following formula:

[0024]

[0025] Where, T max is the maximum acoustic transmittance value of the epoxy resin and metal or metal oxide layer, Z 1 is the acoustic impedance of the polydimethylsiloxane layer, Z 2 is the acoustic impedance of the device under test, Z m It is the acoustic impedance ratio of epoxy resin and metal or metal oxide layer.

[0026] The photoacoustic transducer with a gradient acoustic impedance matching layer, the preparation method and the testing method of the present invention have the following beneficial effects:

[0027] The present invention composites a photoacoustic material with low acoustic impedance, such as polydimethylsiloxane (PDMS), with a metal material with high acoustic transmittance, and prepares three matching layers consisting of polydimethylsiloxane with a low to high acoustic impedance gradient, a mixture of polydimethylsiloxane and epoxy resin, and a mixture of epoxy resin and metal or epoxy resin and metal oxide. The three matching layers with a low to high acoustic impedance gradient can allow ultrasonic waves to easily propagate from low acoustic impedance to high acoustic impedance (equivalent to the steps of a staircase). By introducing three acoustic impedance gradients, the loss of ultrasonic waves propagating between different media is gradually reduced, the acoustic transmittance from the photoacoustic material to the metal material is effectively improved, the ultrasound is more easily propagated from the photoacoustic material to the metal material, the intensity of the ultrasonic signal on the metal material is improved, the coverage range of the ultrasonic signal on the metal material is increased, and the application scenarios of the photoacoustic transducer are expanded. At the same time, the coupling efficiency of photoacoustic ultrasound (frequency is mainly above 1 MHz) from the photoacoustic transducer to the metal material is significantly improved. The preparation method is simple, has no environmental pollution, is not easy to damage, and has good reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of preparing a mixed solution of polydimethylsiloxane and carbon material in the present invention;

[0029] Figure 2 A schematic diagram of preparing a matching solution of epoxy resin and metal or metal oxide in the present invention;

[0030] Figure 3 It is a schematic diagram of coating a mixed liquid on a photoacoustic transducer carrier to prepare an initial photoacoustic transducer in the present invention;

[0031] Figure 4 It is a schematic diagram of the initial photoacoustic transducer being immersed in a coupling agent solution for treatment in the present invention;

[0032] Figure 5 The schematic diagram of the photoacoustic transducer having a gradient acoustic impedance matching layer obtained by coating the surface of the initial photoacoustic transducer treated with a coupling agent in the present invention with a matching liquid;

[0033] Figure 6 Schematic diagram of the chemical reaction formula between polydimethylsiloxane and epoxy resin at the interface in the present invention;

[0034] Figure 7 It is a schematic diagram of the photoacoustic transducer with a gradient acoustic impedance matching layer in the present invention propagating from the matching layer to the object to be tested (aluminum);

[0035] Figure 8 This is a test result diagram of the acoustic impedance and acoustic transmittance of epoxy resin and metal or metal oxide layer by the matching liquid with different mass fractions of silver powder in the present invention;

[0036] Fig. 9 is a curve diagram showing the relationship between the acoustic impedance and acoustic transmittance of the epoxy resin and the metal or metal oxide layer in the present invention;

[0037] Fig.10 Graphs showing the acoustic impedance test results of the polydimethylsiloxane layer, the polydimethylsiloxane and epoxy resin layer, the epoxy resin and metal or metal oxide layer, and the metal aluminum (test piece) in the embodiments.

[0038] Reference numerals

[0039] 1.1, polydimethylsiloxane; 1.2, carbon material; 1.3, mixed liquid; 2.1, epoxy resin; 2.2, metal or metal oxide; 2.3, matching liquid; 3.1, glass substrate; 3.2, optical fiber; 3.3, initial photoacoustic transducer prepared on glass substrate; 3.4, initial photoacoustic transducer prepared on optical fiber; 4.1, coupling agent solution; 5.1, glass substrate photoacoustic transducer with gradient acoustic impedance matching layer; 5.2, optical fiber photoacoustic transducer with gradient acoustic impedance matching layer. DETAILED DESCRIPTION

[0040] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0041] The first aspect of the present invention provides a method for preparing a photoacoustic transducer having a gradient acoustic impedance matching layer, the method comprising the following steps:

[0042] like Figure 1 As shown, polydimethylsiloxane 1.1 and carbon material 1.2 are mixed and stirred to obtain a mixed solution 1.3; Figure 2 As shown, epoxy resin 2.1 is mixed and stirred with metal or metal oxide 2.2 to obtain matching liquid 2.3;

[0043] In this article, the photoacoustic transducer carrier is a glass substrate 3.1 or an optical fiber 3.2, such as Figure 3 As shown, after the mixed solution 1.3 is coated on the glass substrate 3.1 or the optical fiber 3.2, the initial photoacoustic transducer 3.3 prepared on the glass substrate or the initial photoacoustic transducer 3.4 prepared on the optical fiber is obtained after heating and curing.

[0044] like Figure 4 As shown, the initial photoacoustic transducer 3.3 prepared on the glass substrate or the initial photoacoustic transducer 3.4 prepared on the optical fiber is immersed in a coupling agent solution 4.1 for treatment;

[0045] like Figure 5 As shown, the surface of the initial photoacoustic transducer 3.3 prepared on the glass substrate or the initial photoacoustic transducer 3.4 prepared on the optical fiber after being treated with a coupling agent is coated with a matching liquid 2.3, and after heating and curing, a glass substrate photoacoustic transducer 5.1 with a gradient acoustic impedance matching layer or an optical fiber photoacoustic transducer 5.2 with a gradient acoustic impedance matching layer is obtained respectively.

[0046] In a specific embodiment of the preparation method of the present invention, the mass ratio of polydimethylsiloxane 1.1 to carbon material 1.2 is 100:1-20. When the mass ratio of polydimethylsiloxane 1.1 to carbon material 1.2 is less than 100:1, the carbon material is unsaturated in laser absorption. When the mass ratio of polydimethylsiloxane 1.1 to carbon material 1.2 is greater than 100:20, polydimethylsiloxane is difficult to solidify. The stirring rate of polydimethylsiloxane 1.1 and carbon material 1.2 is 100-400r / min. When the stirring rate is less than 100r / min, the carbon material cannot be completely dispersed in the polydimethylsiloxane. When the stirring rate is greater than 400r / min, the torque is insufficient and it is difficult to stir. In this article, the carbon material 1.2 is graphite, graphene or carbon nanotubes.

[0047] In a specific embodiment of the preparation method of the present invention, the mass ratio of epoxy resin 2.1 to metal or metal oxide 2.2 is 100:2.5-12.5. When the mass ratio of epoxy resin 2.1 to metal or metal oxide 2.2 is less than 100:2.5, the acoustic impedance is too low, far below the ideal acoustic impedance, resulting in less than 1% increase in acoustic transmittance. When the mass ratio of epoxy resin 2.1 to metal or metal oxide 2.2 is greater than 100:12.5, the acoustic impedance is too high, exceeding the ideal acoustic impedance, resulting in a decrease in acoustic transmittance. Specifically, the mass ratio of epoxy resin 2.1 to metal or metal oxide 2.2 can be 100:2.5, 100:5.0, 100:7.5, 100:10.0 or 100:12.5. In a preferred embodiment, the mass ratio of epoxy resin 2.1 to metal or metal oxide 2.2 is 100:7.5-12.5.

[0048] The stirring rate of the epoxy resin 2.1 and the metal or metal oxide 2.2 is 100-400 r / min. When the stirring rate is less than 100 r / min, the metal or metal oxide cannot be completely dispersed in the epoxy resin. When the stirring rate is greater than 400 r / min, the torque is insufficient and stirring is difficult.

[0049] In this article, the epoxy resin 2.1 is selected from one or more of novolac epoxy resin, epoxy ester resin, bisphenol A epoxy resin and bisphenol F epoxy resin. Specifically, the acoustic impedance of the epoxy resin 2.1 is 1.0-2.5 Mrayl. When the acoustic impedance of the epoxy resin 2.1 is less than 1.0 Mrayl, the acoustic impedance is too low to generate an acoustic impedance gradient. When the acoustic impedance of the epoxy resin 2.1 is greater than 2.5 Mrayl, it is difficult to obtain such epoxy resin. The metal or metal oxide is silver or aluminum oxide. Specifically, the acoustic impedance of the metal or metal oxide is 16-30 Mrayl. When the acoustic impedance of the metal or metal oxide is less than 16 Mrayl, the acoustic impedance is not significantly improved, and a large amount of the material needs to be added, which affects the curing of the epoxy resin. When the acoustic impedance of the metal or metal oxide is greater than 30 Mrayl, too little of the material is added, resulting in difficulty in completely dispersing it in the epoxy resin.

[0050] In a specific embodiment of the preparation method of the present invention, Figure 3As shown, after coating the mixed solution 1.3 on the glass substrate 3.1 or the optical fiber 3.2, respectively, the initial photoacoustic transducer 3.3 prepared on the glass substrate or the initial photoacoustic transducer 3.4 prepared on the optical fiber is obtained after heating and curing at 80-150° C. In this article, the thickness of the initial photoacoustic transducer 3.3 prepared on the glass substrate or the initial photoacoustic transducer 3.4 prepared on the optical fiber is 10-500 μm. When the thickness of the initial photoacoustic transducer is less than 10 μm, the light absorption is insufficient and the ultrasonic intensity is too low. When the thickness of the initial photoacoustic transducer is less than 10 μm, the light absorption is insufficient and the ultrasonic intensity is too low. When the thickness is greater than 500 μm, it is too thick, resulting in excessive ultrasonic transmission loss. The acoustic impedance of the initial photoacoustic transducer 3.3 prepared on the glass substrate or the initial photoacoustic transducer 3.4 prepared on the optical fiber is 0.8-1.2 Mrayl. Since the acoustic impedance of polydimethylsiloxane is 0.8 Mrayl, the acoustic impedance of the initial photoacoustic transducer cannot be less than 0.8 Mrayl. When the acoustic impedance of the initial photoacoustic transducer is greater than 1.2 Mrayl, it means that too much carbon material has been added, making it difficult for polydimethylsiloxane to solidify.

[0051] In a specific embodiment of the preparation method of the present invention, the coupling agent solution is a mixed solution of a coupling agent, anhydrous ethanol and water, and the volume ratio of the coupling agent, anhydrous ethanol and water is 10-40:10-40:20-80; the coupling agent is γ-aminopropyltriethoxysilane and / or γ-glycidyloxypropyltrimethoxysilane.

[0052] In the specific operation process, the initial photoacoustic transducer 3.3 prepared on the glass substrate or the initial photoacoustic transducer 3.4 prepared on the optical fiber after being treated with the coupling agent is heated at a temperature above 80° C. to remove excess ethanol and deionized water on the surface.

[0053] In a specific embodiment of the preparation method of the present invention, Figure 5 As shown, the surface of the initial photoacoustic transducer 3.3 prepared on the glass substrate or the initial photoacoustic transducer 3.4 prepared on the optical fiber after being treated with a coupling agent is coated with a matching liquid 2.3, and after heating and curing, a glass substrate photoacoustic transducer 5.1 with a gradient acoustic impedance matching layer or an optical fiber photoacoustic transducer 5.2 with a gradient acoustic impedance matching layer is obtained respectively. In the specific operation process, the heating and curing temperature is 100-150° C., and the heating and curing time is 10-60 min.

[0054] like Figure 6 As shown, after being treated with a coupling agent, the surface of the initial photoacoustic transducer 3.3 prepared on the glass substrate or the initial photoacoustic transducer 3.4 prepared on the optical fiber is coated with a matching liquid 2.3, and the polydimethylsiloxane on the glass substrate or the optical fiber will undergo a bonding reaction with the epoxy resin in the matching liquid 2.3 to obtain a mixture of polydimethylsiloxane and epoxy resin.

[0055] In this article, Figure 7 As shown, the gradient acoustic impedance matching layer includes: a polydimethylsiloxane layer, a polydimethylsiloxane and epoxy resin layer, and an epoxy resin and metal or metal oxide layer, and the polydimethylsiloxane layer is attached to one side surface of the photoacoustic transducer carrier, and the polydimethylsiloxane and epoxy resin layer is attached between the polydimethylsiloxane layer and the epoxy resin and metal or metal oxide layer, and during the detection process, the ultrasonic wave is transmitted from the matching layers (the polydimethylsiloxane layer, the polydimethylsiloxane and epoxy resin layer, and the epoxy resin and metal or metal oxide layer in sequence) to the photoacoustic transducer to be detected. Part (aluminum); specifically, the thickness of the gradient acoustic impedance matching layer is one quarter of the wavelength of the ultrasonic wave passing through the gradient acoustic impedance matching layer during detection, the ultrasonic wave wavelength is 0.0075-7.5 mm, and the acoustic impedance rate of the gradient acoustic impedance matching layer is 1.0-8.0 Mrayl. When the acoustic impedance rate of the gradient acoustic impedance matching layer is less than 1.0 Mrayl, the acoustic impedance rate is too small, and the improvement of ultrasonic transmittance is too low. When the acoustic impedance rate of the gradient acoustic impedance matching layer is greater than 8.0 Mrayl, the acoustic impedance rate is too large, exceeding the acoustic impedance rate of the ideal matching layer, and the improvement of ultrasonic transmittance is too low.

[0056] In a preferred embodiment, the acoustic impedance rates of the polydimethylsiloxane layer, the polydimethylsiloxane and epoxy resin layer, and the epoxy resin and metal or metal oxide layer increase successively. The three matching layers with acoustic impedance gradients from low to high can allow ultrasonic waves to easily propagate from low acoustic impedance to high acoustic impedance (equivalent to the steps of stairs). By introducing three acoustic impedance gradients, the loss of ultrasonic waves propagating between different media is gradually reduced, and the acoustic transmittance from the photoacoustic material to the metal material is effectively improved, making it easier for ultrasound to propagate from the photoacoustic material to the metal material, thereby improving the intensity of the ultrasonic signal on the metal material, increasing the coverage of the ultrasonic signal on the metal material, and expanding the application scenarios of the photoacoustic transducer.

[0057] The second aspect of the present invention provides a photoacoustic transducer with a gradient acoustic impedance matching layer prepared according to the above method, wherein the gradient acoustic impedance matching layer comprises: a polydimethylsiloxane layer, a polydimethylsiloxane and epoxy resin layer, and an epoxy resin and metal or metal oxide layer, and the polydimethylsiloxane layer is attached to one side surface of the photoacoustic transducer carrier, the polydimethylsiloxane and epoxy resin layer is attached between the polydimethylsiloxane layer and the epoxy resin and metal or metal oxide layer, and the acoustic impedance ratios of the polydimethylsiloxane layer, the polydimethylsiloxane and epoxy resin layer, and the epoxy resin and metal or metal oxide layer increase in sequence.

[0058] The third aspect of the present invention provides a method for testing acoustic impedance and acoustic transmittance of the photoacoustic transducer with a gradient acoustic impedance matching layer as described above, the method comprising: recording the initial signal strength of the ultrasonic pulse generator as E 0 , attach the ultrasonic pulse generator probe to the other side surface of the photoacoustic transducer carrier, place the test piece on the surface of the epoxy resin and the metal or metal oxide layer, turn on the ultrasonic pulse generator, and record the return time Δt and signal intensity E of the excitation ultrasonic pulse 1 , the acoustic impedance ratio of the epoxy resin and the metal or metal oxide layer is obtained according to the mass, volume, thickness of the initial photoacoustic transducer, the mass, volume, thickness of the photoacoustic transducer with the gradient acoustic impedance matching layer, and the return time of the exciting ultrasonic pulse, and the acoustic transmittance of the epoxy resin and the metal or metal oxide layer is obtained according to the initial signal strength of the ultrasonic pulse generator and the signal strength of the exciting ultrasonic pulse.

[0059] In a specific embodiment of the method of the present invention, the calculation formula of the acoustic impedance ratio of the epoxy resin and the metal or metal oxide layer is as follows:

[0060]

[0061] In the formula, Z m is the acoustic impedance ratio of epoxy resin and metal or metal oxide layer, m 1 is the mass of the initial photoacoustic transducer, m 2 is the mass of the photoacoustic transducer with gradient acoustic impedance matching layer, V 1 is the volume of the initial photoacoustic transducer, V 2 is the volume of the photoacoustic transducer with gradient acoustic impedance matching layer, h 1 is the initial photoacoustic transducer thickness, h 2 is the thickness of the photoacoustic transducer with gradient acoustic impedance matching layer, Δt is the return time of the excitation ultrasonic pulse;

[0062] The formula for calculating the acoustic transmittance of epoxy resin and metal or metal oxide layer is as follows:

[0063]

[0064] Where T is the acoustic transmittance of the epoxy resin and the metal or metal oxide layer, E 0 is the initial signal strength of the ultrasonic pulse generator, E 1 is the signal intensity of the excitation ultrasonic pulse.

[0065] In a specific embodiment of the method of the present invention, the relationship between the acoustic transmittance of the epoxy resin and the metal or metal oxide layer and the acoustic impedance of the polydimethylsiloxane layer and the acoustic impedance of the test piece is as follows:

[0066]

[0067] Where, T is the acoustic transmittance of the epoxy resin and the metal or metal oxide layer, Z 1 is the acoustic impedance of the polydimethylsiloxane layer, Z 2 is the acoustic impedance of the device under test;

[0068] The relationship between the acoustic impedance of the polydimethylsiloxane layer, the acoustic impedance of the test piece, and the acoustic impedance of the epoxy resin and metal or metal oxide layer is shown in the following formula:

[0069]

[0070] Where, T max is the maximum acoustic transmittance value of the epoxy resin and metal or metal oxide layer, Z 1 is the acoustic impedance of the polydimethylsiloxane layer, Z 2 is the acoustic impedance of the device under test, Z m It is the acoustic impedance ratio of epoxy resin and metal or metal oxide layer.

[0071] The experimental methods or test methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are obtained from conventional commercial channels or prepared by conventional methods unless otherwise specified.

[0072] Example

[0073] Fabrication of photoacoustic transducer with gradient acoustic impedance matching layer:

[0074] A mixed solution of polydimethylsiloxane 1.1 and graphene (carbon material 1.2) is coated on a glass substrate 3.1, wherein the mass ratio of polydimethylsiloxane 1.1 to graphene is 100:5, and then cured at 120°C to obtain an initial photoacoustic transducer;

[0075] The initial photoacoustic transducer is immersed in a coupling agent solution for 10 minutes, wherein the coupling agent solution is a mixed solution of γ-aminopropyltriethoxysilane, anhydrous ethanol and water, and the volume ratio of γ-aminopropyltriethoxysilane, anhydrous ethanol and water is 1:10:30, and then heated at 80°C to remove excess ethanol and deionized water on the surface, and the surface of the initial photoacoustic transducer treated with the coupling agent is coated with a matching liquid, wherein the matching liquid is a mixture of epoxy resin and silver powder, and the mass fraction of the silver powder is used as a variable. In the matching liquid, the silver powder The mass fraction of the silver powder is 0%, 2.5%, 5%, 7.5%, 10% and 12.5%, and then cured at 120°C for 40 minutes to obtain 6 groups of photoacoustic transducers with gradient acoustic impedance matching layers with different mass fractions of silver powder, respectively. The gradient acoustic impedance matching layer includes a polydimethylsiloxane layer, a polydimethylsiloxane and epoxy resin layer, and an epoxy resin and silver powder layer. The polydimethylsiloxane layer is attached to one side surface of the glass substrate 3.1, and the polydimethylsiloxane and epoxy resin layer is attached between the polydimethylsiloxane layer and the epoxy resin and silver powder layer.

[0076] Application Examples

[0077] Measure the initial photoacoustic transducer mass m 1 、Volume V 1 and thickness h 1 , and the mass m of the photoacoustic transducer with a gradient acoustic impedance matching layer with a mass fraction of silver powder of 0%, 2.5%, 5%, 7.5%, 10% and 12.5% ​​respectively. 2 、Volume V 2 and thickness h 2 , record the initial signal strength of the ultrasonic pulse generator as E 0 , attach the ultrasonic pulse generator probe to the other side surface of the glass substrate 3.1, place metal aluminum on the surface of the epoxy resin and silver powder layer, turn on the ultrasonic pulse generator, and record the return time Δt and signal intensity E of the excitation ultrasonic pulse 1 According to formulas (1) and (2), the acoustic impedance and acoustic transmittance of the epoxy resin and silver powder layer in the photoacoustic transducer with a gradient acoustic impedance matching layer prepared by matching solutions with silver powder mass fractions of 0%, 2.5%, 5%, 7.5%, 10% and 12.5% ​​were calculated respectively. The test results are shown in Figures 8-9 As shown by Figures 8-9 It can be seen that the maximum acoustic transmittance value T of the epoxy resin and silver powder layer is max The acoustic impedance of the epoxy resin and silver powder layer is 36.6%. At this time, the acoustic impedance of the epoxy resin and silver powder layer is 3.8 Mrayl, the mass fraction of the silver powder is 10.0%, and the acoustic impedance test results of the three acoustic impedance gradients (polydimethylsiloxane layer, polydimethylsiloxane and epoxy resin layer, epoxy resin and silver powder layer) and metal aluminum are as follows Fig.10 shown.

[0078] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing a photoacoustic transducer having a gradient acoustic impedance matching layer, characterized in that: The preparation method comprises the following steps: Coating a mixed liquid formed by polydimethylsiloxane and carbon material on a photoacoustic transducer carrier, and heating and curing the photoacoustic transducer carrier coated with the mixed liquid to obtain an initial photoacoustic transducer; The initial photoacoustic transducer is immersed in a coupling agent solution, and the surface of the initial photoacoustic transducer treated with the coupling agent is coated with a matching liquid to obtain a photoacoustic transducer with a gradient acoustic impedance matching layer; the matching liquid is a mixture of epoxy resin and metal or metal oxide.

2. The method for preparing a photoacoustic transducer having a gradient acoustic impedance matching layer according to claim 1, characterized in that: The mass ratio of epoxy resin to metal or metal oxide is 100:2.5-12.

5.

3. The method for preparing a photoacoustic transducer with a gradient acoustic impedance matching layer according to claim 1, characterized in that: The gradient acoustic impedance matching layer includes: a polydimethylsiloxane layer, a polydimethylsiloxane and epoxy resin layer, and an epoxy resin and metal or metal oxide layer, and the polydimethylsiloxane layer is attached to one side surface of the photoacoustic transducer carrier, the polydimethylsiloxane and epoxy resin layer is attached between the polydimethylsiloxane layer and the epoxy resin and metal or metal oxide layer, and the acoustic impedance ratios of the polydimethylsiloxane layer, the polydimethylsiloxane and epoxy resin layer, and the epoxy resin and metal or metal oxide layer increase in sequence.

4. The method for preparing a photoacoustic transducer with a gradient acoustic impedance matching layer according to claim 1, characterized in that: The thickness of the gradient acoustic impedance matching layer is one quarter of the wavelength of the ultrasonic wave passing through the gradient acoustic impedance matching layer during detection, and the wavelength of the ultrasonic wave is 0.0075-7.5 mm.

5. The method for preparing a photoacoustic transducer with a gradient acoustic impedance matching layer according to claim 1, characterized in that: The thickness of the initial photoacoustic transducer is 10-500 μm, and the acoustic impedance of the initial photoacoustic transducer is 0.8-1.2 Mrayl.

6. The method for preparing a photoacoustic transducer with a gradient acoustic impedance matching layer according to claim 1, characterized in that: The coupling agent solution is a mixed solution of coupling agent, anhydrous ethanol and water, and the volume ratio of coupling agent, anhydrous ethanol and water is 10-40:10-40:20-80; The coupling agent is γ-aminopropyltriethoxysilane and / or γ-glycidyloxypropyltrimethoxysilane.

7. A photoacoustic transducer having a gradient acoustic impedance matching layer prepared according to the method of any one of claims 1 to 6, characterized in that: The gradient acoustic impedance matching layer includes: a polydimethylsiloxane layer, a polydimethylsiloxane and epoxy resin layer, and an epoxy resin and metal or metal oxide layer, and the polydimethylsiloxane layer is attached to one side surface of the photoacoustic transducer carrier, the polydimethylsiloxane and epoxy resin layer is attached between the polydimethylsiloxane layer and the epoxy resin and metal or metal oxide layer, and the acoustic impedance ratios of the polydimethylsiloxane layer, the polydimethylsiloxane and epoxy resin layer, and the epoxy resin and metal or metal oxide layer increase in sequence.

8. A method for testing acoustic impedance and acoustic transmittance of a photoacoustic transducer having a gradient acoustic impedance matching layer according to claim 7, characterized in that: The method includes: The initial signal strength of the ultrasonic pulse generator is recorded as E0, the ultrasonic pulse generator probe is attached to the other side surface of the photoacoustic transducer carrier, the test piece is placed on the surface of the epoxy resin and the metal or metal oxide layer, the ultrasonic pulse generator is turned on, and the return time Δt and the signal strength E1 of the exciting ultrasonic pulse are recorded. The acoustic impedance of the epoxy resin and the metal or metal oxide layer is obtained according to the mass, volume, thickness of the initial photoacoustic transducer, and the mass, volume, thickness of the photoacoustic transducer with the gradient acoustic impedance matching layer and the return time of the exciting ultrasonic pulse, and the acoustic transmittance of the epoxy resin and the metal or metal oxide layer is obtained according to the initial signal strength of the ultrasonic pulse generator and the signal strength of the exciting ultrasonic pulse.

9. The method according to claim 8, characterized in that The calculation formula of the acoustic impedance ratio of the epoxy resin and the metal or metal oxide layer is as follows: In the formula, Z m is the acoustic impedance ratio of epoxy resin to metal or metal oxide layer, m1 is the mass of the initial photoacoustic transducer, m2 is the mass of the photoacoustic transducer with gradient acoustic impedance matching layer, V1 is the volume of the initial photoacoustic transducer, V2 is the volume of the photoacoustic transducer with gradient acoustic impedance matching layer, h1 is the thickness of the initial photoacoustic transducer, h2 is the thickness of the photoacoustic transducer with gradient acoustic impedance matching layer, Δt is the return time of the excitation ultrasonic pulse; The formula for calculating the acoustic transmittance of epoxy resin and metal or metal oxide layer is as follows: Where T is the acoustic transmittance of the epoxy resin and the metal or metal oxide layer, E0 is the initial signal strength of the ultrasonic pulse generator, and E1 is the signal strength of the exciting ultrasonic pulse.

10. The method according to claim 9, characterized in that The relationship between the acoustic transmittance of the epoxy resin and the metal or metal oxide layer and the acoustic impedance of the polydimethylsiloxane layer and the acoustic impedance of the test piece is shown in the following formula: Wherein, T is the acoustic transmittance of the epoxy resin and the metal or metal oxide layer, Z1 is the acoustic impedance of the polydimethylsiloxane layer, and Z2 is the acoustic impedance of the test piece; The relationship between the acoustic impedance of the polydimethylsiloxane layer, the acoustic impedance of the test piece, and the acoustic impedance of the epoxy resin and metal or metal oxide layer is shown in the following formula: Where, T max is the maximum acoustic transmittance value of the epoxy resin and the metal or metal oxide layer, Z1 is the acoustic impedance of the polydimethylsiloxane layer, Z2 is the acoustic impedance of the test piece, and Z m It is the acoustic impedance ratio of epoxy resin and metal or metal oxide layer.

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