Acoustic emission sensor based on anti-reflection design and preparation method thereof

Abstract

The invention belongs to the technical field of acoustic emission sensor equipment, and particularly relates to an acoustic emission sensor based on anti-reflection design and a preparation method thereof.The acoustic emission sensor comprises a matching layer, multiple transition layers, an anti-reflection layer and a piezoelectric element, the multiple transition layers comprise multiple transition sub-layers arranged in a stacked mode, and the multiple transition sub-layers have multiple acoustic impedances; and the thickness of the anti-reflection layer is a quarter value of the wavelength of the typical longitudinal wave sound velocity of the center frequency of the acoustic emission sensor in the anti-reflection layer. By designing a multi-layer transition layer structure with different acoustic characteristics, good sound wave transmission can be realized in a wider frequency range, and stable passing of a target frequency is ensured; and through the design of the anti-reflection layer, destructive interference can be generated by waves, reflected on the surface of the anti-reflection layer, of sound wave signals of the center frequency based on the quarter-wavelength principle, so that reflection of sound waves is reduced, and the signal transmission efficiency in the frequency range near the center frequency is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of acoustic emission sensor equipment, and in particular relates to an acoustic emission sensor based on anti-reflection design and a preparation method thereof. Background Art

[0002] Acoustic emission sensors are widely used in the fields of non-destructive testing of materials and structural health monitoring. They work by converting mechanical vibrations generated on the surface of materials into electrical signals. An ideal acoustic emission sensor should be able to convert mechanical vibrations linearly over the entire frequency spectrum and have sufficient sensitivity to detect very small displacements.

[0003] The front end of the acoustic emission sensor generally includes a matching layer and a piezoelectric element. The matching layer is used to contact the surface of the object to be measured to ensure the effective transmission of the sound wave. The piezoelectric element is the core component of the acoustic emission sensor and is responsible for converting the mechanical vibration of the sound wave into an electrical signal. When the sound wave is transmitted from the matching layer to the piezoelectric element, if the acoustic impedance of the two materials is greatly different when the sound wave is transmitted at the interface of different layers of materials, the efficiency of the reflection and transmission of the sound wave will be reduced, and the sound wave may reverberate during the transmission process, resulting in signal distortion and increased noise, thereby affecting the effective transmission of the signal. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the defect of signal distortion in the transmission process of the acoustic wave signal of the acoustic emission sensor from the matching layer to the piezoelectric element in the prior art, thereby providing an acoustic emission sensor based on anti-reflection design and a preparation method thereof.

[0005] The present invention discloses an acoustic emission sensor based on anti-reflection design, the acoustic emission sensor comprises a matching layer, a multi-layer transition layer, an anti-reflection layer, and a piezoelectric element;

[0006] The matching layer is located at the front of the acoustic emission sensor, and the matching layer, the multi-layer transition layer, the anti-reflection layer, and the piezoelectric element are contacted and fixed in sequence from front to back;

[0007] The front end of the matching layer is used to contact the object to be measured to provide initial acoustic impedance matching;

[0008] The multi-layer transition layer includes a plurality of transition layers stacked in layers, and the plurality of transition layers have a variety of acoustic impedances;

[0009] The thickness of the anti-reflection layer is a quarter of the wavelength of the typical longitudinal wave speed of the acoustic emission sensor at the center frequency in the anti-reflection layer;

[0010] The piezoelectric element is used to convert the sound wave signal into an electrical signal.

[0011] Furthermore, the material of the matching layer includes one or more of epoxy resin, cobalt binder, nano tungsten powder, tungsten carbide powder, nano barium titanate, and nano silicon dioxide, and the acoustic impedance value of the matching layer is 3-50 MRayl.

[0012] Furthermore, the multi-layer transition layer includes at least three transition layers, each of which has a uniform acoustic impedance, and the acoustic impedance value of the transition layer gradually increases from the front to the back.

[0013] Furthermore, the transition layers of the multi-layer transition layer are provided with five layers, and the thickness of each transition layer is equal to a quarter of the wavelength of a typical longitudinal wave speed within which the center frequency of the acoustic emission sensor is located.

[0014] Furthermore, the multi-layer transition layer includes at least three transition layers, each of which has uniform acoustic impedance; the transition layers have at least two acoustic impedance values, and adjacent transition layers have different impedance values; the thickness of each transition layer is equal to one-fourth of the wavelength of the typical longitudinal wave speed of the center frequency of the acoustic emission sensor in the multi-layer transition layer.

[0015] Furthermore, the transition layers of the multi-layer transition layer are provided with six layers, and the acoustic impedance values ​​of adjacent transition layers are respectively greater than and less than the acoustic impedance value of the object under test.

[0016] Furthermore, the material of the piezoelectric element is one of modified lead zirconate titanate material and niobium indium magnesium lead titanate single crystal material.

[0017] A method for preparing an acoustic emission sensor based on an anti-reflection design, wherein the structure of the acoustic emission sensor prepared is as described above, and the method for preparing the matching layer comprises the following steps:

[0018] Step S1.1: measuring the acoustic impedance value of the object to be measured, and determining the target acoustic impedance value of the matching layer;

[0019] Step S1.2: Calculating the required composite material density based on the target acoustic impedance value;

[0020] Step S1.3: Calculating the filling ratio of the composite material based on the effective medium theory, and controlling the filling ratio so that the matching layer reaches the density of the composite material;

[0021] Step S1.4: using an acoustic measurement device to monitor the acoustic impedance value of the matching layer in real time, and adjusting the ratio so that the acoustic impedance value of the matching layer matches the target acoustic impedance value.

[0022] Furthermore, the method for preparing the multi-layer transition layer comprises the following steps:

[0023] Step S2.1: the number of transition layers of the multi-layer transition layer is five, the first transition layer to the fifth transition layer are stacked in sequence, the first transition layer is connected to the matching layer, and the fifth transition layer is connected to the piezoelectric element;

[0024] Step S2.2: preparing a fifth transition layer, wherein the composition weight ratio of the fifth transition layer is: 55-65% tungsten powder, 15-20% BaTiO3, 2-4% SiO2, 0.5-1% carbon nanotubes, and the balance is cobalt binder, and the acoustic impedance value is 40-45 MRayl;

[0025] Step S2.3: preparing a fourth transition layer, wherein the composition weight ratio of the fourth transition layer is: 40-50% tungsten powder, 20-25% BaTiO3, 3-5% SiO2, 0.1-0.3% graphene, and the balance is cobalt binder, and the acoustic impedance value is 30-35 MRayl;

[0026] Step S2.4: preparing a third transition layer, wherein the composition weight ratio of the third transition layer is: 25-35% tungsten powder, 25-30% BaTiO3, 4-6% SiO2, 1-2% Al2O3, and the balance is cobalt binder, and the acoustic impedance value is 20-25 MRayl;

[0027] Step S2.5: preparing a second transition layer, wherein the weight ratio of the components of the second transition layer is: 10-20% tungsten powder, 30-35% BaTiO3, 5-8% SiO2, 0.2-0.5% carbon nanotubes, and the balance is cobalt binder, and the acoustic impedance value is 10-15 MRayl;

[0028] Step S2.5: Prepare the first transition layer, the composition weight ratio of the first transition layer is: 5-15% tungsten powder, 35-40% BaTiO3, 6-9%, 0.05-0.1% graphene, and the balance is cobalt binder, and the acoustic impedance value is 5-10 MRayl.

[0029] Furthermore, the method for preparing the anti-reflection layer comprises the following steps:

[0030] Step S3.1: Calculate the thickness of the anti-reflection layer, where the thickness of the anti-reflection layer is a quarter of the wavelength of a typical longitudinal wave velocity in the anti-reflection layer at the center frequency of the acoustic emission sensor;

[0031] Step S3.2: Selecting the material of the anti-reflection layer, wherein the material of the anti-reflection layer is one of modified PZT ceramics, acoustic metamaterials, and composite functional materials.

[0032] Beneficial effects: The present invention discloses an acoustic emission sensor based on an anti-reflection design, including a matching layer, a multi-layer transition layer, an anti-reflection layer, and a piezoelectric element. The multi-layer transition layer includes a plurality of transition layers stacked in a stack, and the plurality of transition layers have a variety of acoustic impedances. The thickness of the anti-reflection layer is a quarter of the wavelength of the typical longitudinal wave speed of the center frequency of the acoustic emission sensor in the anti-reflection layer. By designing a multi-layer transition layer structure with different acoustic properties, good acoustic wave transmission can be achieved in a wider frequency range to ensure the stable passage of the target frequency; and through the design of the anti-reflection layer, based on the quarter-wavelength principle, the sound wave signal of the center frequency reflected on the surface of the anti-reflection layer can produce destructive interference, thereby reducing the reflection of the sound wave and significantly improving the signal transmission efficiency in the frequency range near the center frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0035] Explanation of the reference numerals: 1. matching layer; 2. multi-layer transition layer; 3. anti-reflection layer; 4. piezoelectric element. DETAILED DESCRIPTION

[0036] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0037] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0038] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0039] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0040] Embodiment 1:

[0041] Reference Figure 1 As shown, this embodiment discloses an acoustic emission sensor based on anti-reflection design, the acoustic emission sensor includes a matching layer 1, a multi-layer transition layer 2, an anti-reflection layer 3, and a piezoelectric element 4; the matching layer 1 is located at the front of the acoustic emission sensor, and the matching layer 1, the multi-layer transition layer 2, the anti-reflection layer 3, and the piezoelectric element 4 are contacted and fixed in sequence from front to back; the front end of the matching layer 1 is used to contact the object to be measured to provide initial acoustic impedance matching; the multi-layer transition layer 2 includes a plurality of transition layers stacked, and the plurality of transition layers have a variety of acoustic impedances; the thickness of the anti-reflection layer 3 is a quarter of the wavelength of the typical longitudinal wave speed of the center frequency of the acoustic emission sensor in the anti-reflection layer 3; the piezoelectric element 4 is used to convert the acoustic wave signal into an electrical signal.

[0042] The present embodiment discloses an acoustic emission sensor based on an anti-reflection design, comprising a matching layer 1, a multi-layer transition layer 2, an anti-reflection layer 3, and a piezoelectric element 4. The multi-layer transition layer 2 comprises a plurality of transition layers stacked in a stack, and the plurality of transition layers have a variety of acoustic impedances. The thickness of the anti-reflection layer 3 is a quarter of the wavelength of a typical longitudinal wave velocity of the center frequency of the acoustic emission sensor in the anti-reflection layer 3. By designing a multi-layer transition layer 2 structure with different acoustic properties, good acoustic wave transmission can be achieved in a wider frequency range, ensuring the stable passage of the target frequency; and through the design of the anti-reflection layer 3, based on the quarter-wavelength principle, the sound wave signal of the center frequency reflected on the surface of the anti-reflection layer 3 can produce destructive interference, thereby reducing the reflection of the sound wave and significantly improving the signal transmission efficiency in the frequency range near the center frequency.

[0043] Specifically, in this embodiment, the material of the matching layer 1 includes one or more of epoxy resin, cobalt binder, nano tungsten powder, tungsten carbide powder, nano barium titanate, and nano silicon dioxide, and the acoustic impedance value of the matching layer 1 is 3 to 50 MRayl. As a preferred embodiment of this embodiment, the acoustic impedance value of the matching layer 1 is close to the contacted object to be measured.

[0044] In this embodiment, the longitudinal wave speed in PZT (lead zirconate titanate) ceramics is usually in the range of 3700-4600m / s, and for PZT-5H, its typical speed is about 4350m / s. Calculate 1 / 4 wave of 1MHz wave, define thickness, λ=v / f, where λ is wavelength, v is speed of sound, and f is frequency; for f=1MHz=1,000,000Hz, v≈4350m / s (using the typical value of PZT-5H)λ=4350 / 1,000,000=0.00435m=4.35mm; 1 / 4 wavelength=λ / 4=4.35 / 4=1.0875mm≈1.09mm. Therefore, in this embodiment, the thickness of the anti-reflection layer 3 is 1.09mm. Thus, by using a specific thickness and structural design, the designed anti-reflection layer 3 can produce constructive interference at a frequency near 1MHz and enhance signal strength.

[0045] In some implementations of this embodiment, the total thickness of the multi-layer transition layer 2 is equal to the wavelength of the typical longitudinal wave sound velocity of the center frequency of the acoustic emission sensor in the multi-layer transition layer 2; the multi-layer transition layer 2 includes at least three transition layers, each of which has a uniform acoustic impedance, and the acoustic impedance value of the transition layer gradually increases from front to back.

[0046] The transition layers of the multi-layer transition layer 2 are provided with five layers, and the thickness of each transition layer is equal to one-quarter of the wavelength of the typical longitudinal wave speed within the center frequency of the acoustic emission sensor. The center frequency of the acoustic emission sensor is 1MHz, and the target frequency band is 0.8MHz to 1.2MHz. As a preferred embodiment of this embodiment, the acoustic impedance values ​​of the five transition layers from front to back are 10MRayl, 15MRayl, 22MRayl, 30MRayl, and 40MRayl, respectively. The sound velocity of each transition layer is obtained, and the wavelength of the sound wave of each transition layer is calculated based on the sound velocity and the center frequency. The thickness of each transition layer is one-quarter of the wavelength of the sound wave passing through it. This transition structure with a thickness of one-quarter of the wavelength of the sound wave can produce a destructive interference, so that the wave returning from the interlayer interface is opposite to the incident wave in phase and cancels each other, thereby reducing the total reflection, thereby maintaining good transmission performance within the characteristic frequency range.

[0047] Specifically, in this embodiment, the first transition layer to the fifth transition layer are stacked in sequence from front to back, the first transition layer is connected to the matching layer 1, and the fifth transition layer is connected to the piezoelectric element 4; first, the material ratio is determined based on the designed acoustic impedance value of each layer, and then the composite density is determined based on the material ratio, and then the sound velocity v=Z / ρ is determined based on the acoustic impedance value and the composite density, and finally the sound wave wavelength is determined based on the sound velocity and the center frequency to calculate the thickness λ / 4; wherein Z is the acoustic impedance and ρ is the composite density. The material ratio of the first transition layer is epoxy resin: 60wt%; nano tungsten powder: 35wt%; nano silicon dioxide: 35wt%, so that the composite density is 2.86g / cm 3 , the sound velocity is 3496m / s, and the thickness is 0.874mm. The material ratio of the second transition layer is epoxy resin: 50wt%; nano tungsten powder: 45wt%; nano barium titanate: 5wt%, so the composite density is 3.97g / cm 3 , the sound velocity is 3778m / s, and the thickness is 0.944mm. The material ratio of the third transition layer is epoxy resin: 40wt%; nano tungsten powder: 55wt%; tungsten carbide powder: 5wt%, so the composite density is 5.61g / cm 3 , the sound velocity is 3922m / s, and the thickness is 0.981mm. The material ratio of the fourth transition layer is epoxy resin: 30wt%; nano tungsten powder: 65wt%; cobalt binder: 5wt%, so the composite density is 7.28g / cm 3 , the sound velocity is 4121m / s, and the thickness is 1.030mm. The material ratio of the fifth transition layer is epoxy resin: 20wt%; nano tungsten powder: 75wt%; cobalt binder: 5wt%, so the composite density is 9.30g / cm 3 , the speed of sound is 4301m / s, and the thickness is 1.075mm. In this embodiment, the value of the material density is: the epoxy resin density is 1.2g / cm 3 , nano tungsten powder is 19.3g / cm 3 , silicon dioxide is 2.65g / cm 3 , nano barium titanate is 6.02g / cm 3 , tungsten carbide is 15.63g / cm 3 , cobalt binder is 8.9g / cm 3 , and then calculate its composite density according to the material ratio.

[0048] The quarter wavelengths of the target frequency band boundaries 0.8 MHz and 1.2 MHz are calculated as follows: 0.8 MHz: λ / 4 = (4350 / 800,000) / 4 = 1.36 mm, 1.2 MHz: λ / 4 = (4350 / 1,200,000) / 4 = 0.91 mm, which means that within the entire target frequency band, at least one layer of the transition layer has a thickness close to a quarter wavelength, thereby effectively improving the transmission efficiency.

[0049] In some other implementations of this embodiment, the multilayer transition layer 2 includes at least three transition layers, each of which has a uniform acoustic impedance; the transition layers have at least two acoustic impedance values ​​in total, and adjacent transition layers have different impedance values; the thickness of each transition layer is equal to one-fourth of the wavelength of the typical longitudinal wave speed of the center frequency of the acoustic emission sensor in the multilayer transition layer 2.

[0050] Specifically, the transition layers of the multi-layer transition layer are provided with six layers, and the acoustic impedance values ​​of adjacent transition layers are respectively greater than and less than the acoustic impedance value of the object under test. The center frequency of the acoustic emission sensor is 1MHz. In this embodiment, the material of the multi-layer transition layer 2 is lead zirconate titanate ceramic of type PZT-5H, and the typical longitudinal wave sound velocity is 4350m / s. Therefore, the wavelength of the center frequency λ=v / f=4.35mm, and the quarter wavelength of the center frequency is defined as the thickness of each transition layer of the multi-layer transition layer 2, so that the thickness of each transition layer is λ / 4=(4350 /

[0051] 1,000,000) / 4=1.09mm. In this embodiment, the acoustic impedance value of each layer is first designed, the material ratio is determined, the sound speed is determined based on the material ratio, the wavelength is determined based on the sound speed and the center frequency, and finally the thickness is calculated according to the wavelength, so that the six transition layers are: the first transition layer: 34MRayl, sound speed 4350m / s, thickness 1.09mm; the second transition layer: 15MRayl, sound speed 4000m / s, thickness 1.00mm; the third transition layer: 34MRayl, sound speed 4350m / s, thickness 1.09mm; the fourth transition layer: 15MRayl, sound speed 4000m / s, thickness 1.00mm; the fifth transition layer: 34MRayl, sound speed 4350m / s, thickness 1.09mm; the sixth transition layer: 15MRayl, sound speed 4000m / s, thickness 1.00mm, that is, the total thickness = 1.09mm*6 = 6.54mm. This structure can achieve a bandwidth of about 30%, then: lower limit frequency = 1MHz*(1-0.15) = 0.85MHz upper limit frequency = 1MHz*(1+0.15) = 1.15MHz, calculate the quarter wavelength of the boundary frequency: 0.85MHz: λ / 4 = (4350 / 850,000) / 4 = 1.28mm 1.15MHz: λ / 4 = (4350 / 1,150,000) / 4 = 0.95mm, so the multi-layer transition layer can have good transmission characteristics in the range of 0.85MHz to 1.15MHz. This multi-layer alternating structure can provide a smoother acoustic impedance transition, thereby conducting energy from the material under test to the target piezoelectric element as much as possible, and provide higher temperature stability and structural stability. In some structures of this embodiment, multiple transition layers form acoustic Bragg reflectors, thereby more effectively passing sound waves of the center frequency.

[0052] As a preference of this embodiment, the material of the piezoelectric element 4 is one of modified lead zirconate titanate material and niobium indium magnesium lead titanate single crystal material.

[0053] Embodiment 2:

[0054] This embodiment discloses a method for preparing an acoustic emission sensor based on an anti-reflection design. The structure of the acoustic emission sensor prepared is as described above. In some specific implementations of this embodiment, the method for preparing the matching layer 1 includes the following steps:

[0055] Step S1.1: measuring the acoustic impedance value of the object to be measured, and determining the target acoustic impedance value of the matching layer 1;

[0056] Step S1.2: Calculating the required composite material density based on the target acoustic impedance value;

[0057] Step S1.2.1: Design the target acoustic impedance Z;

[0058] Step S1.2.2: Based on the target acoustic impedance Z, estimate the acoustic velocity c of the composite material according to empirical data or simple experiments;

[0059] Step S1.2.3: Calculate the target density ρ based on the relationship Z=ρc;

[0060] Step S1.2.4: Selecting a suitable material combination based on the target density;

[0061] Step S1.2.5: Calculate the density of the composite material under different material ratios based on the mixing rule;

[0062] Step S1.2.6: Adjust the material ratio so that the calculated density is close to the target density.

[0063] Step S1.3: Calculating the filling ratio of the composite material based on the effective medium theory, and controlling the filling ratio so that the matching layer 1 reaches the density of the composite material;

[0064] Step S1.4: using an acoustic measurement device to monitor the acoustic impedance value of the matching layer 1 in real time, and adjusting the ratio so that the acoustic impedance value of the matching layer 1 matches the target acoustic impedance value.

[0065] The method for preparing the multi-layer transition layer 2 comprises the following steps:

[0066] Step S2.1: the multi-layer transition layer 2 has five transition layers, the first transition layer to the fifth transition layer are stacked in sequence, the first transition layer is connected to the matching layer 1, and the fifth transition layer is connected to the piezoelectric element 4;

[0067] Step S2.2: preparing a fifth transition layer, wherein the composition weight ratio of the fifth transition layer is: 55-65% tungsten powder, 15-20% BaTiO3, 2-4% SiO2, 0.5-1% carbon nanotubes, and the balance is cobalt binder, and the acoustic impedance value is 40-45 MRayl;

[0068] Step S2.3: preparing a fourth transition layer, wherein the composition weight ratio of the fourth transition layer is: 40-50% tungsten powder, 20-25% BaTiO3, 3-5% SiO2, 0.1-0.3% graphene, and the balance is cobalt binder, and the acoustic impedance value is 30-35 MRayl;

[0069] Step S2.4: preparing a third transition layer, wherein the composition weight ratio of the third transition layer is: 25-35% tungsten powder, 25-30% BaTiO3, 4-6% SiO2, 1-2% Al2O3, and the balance is cobalt binder, and the acoustic impedance value is 20-25 MRayl;

[0070] Step S2.5: preparing a second transition layer, wherein the weight ratio of the components of the second transition layer is: 10-20% tungsten powder, 30-35% BaTiO3, 5-8% SiO2, 0.2-0.5% carbon nanotubes, and the balance is cobalt binder, and the acoustic impedance value is 10-15 MRayl;

[0071] Step S2.5: Prepare the first transition layer, the composition weight ratio of the first transition layer is: 5-15% tungsten powder, 35-40% BaTiO3, 6-9%, 0.05-0.1% graphene, and the balance is cobalt binder, and the acoustic impedance value is 5-10 MRayl.

[0072] The method for preparing the anti-reflection layer 3 comprises the following steps:

[0073] Step S3.1: Calculate the thickness of the anti-reflection layer 3, where the thickness of the anti-reflection layer 3 is a quarter of the wavelength of a typical longitudinal wave velocity in the anti-reflection layer 3 at the center frequency of the acoustic emission sensor;

[0074] Step S3.2: Select the material of the anti-reflection layer 3, wherein the material of the anti-reflection layer 3 is one of modified PZT ceramics, acoustic metamaterials, and composite functional materials.

[0075] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0076] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. An acoustic emission sensor based on anti-reflection design, characterized in that: The acoustic emission sensor comprises a matching layer, a multi-layer transition layer, an anti-reflection layer, and a piezoelectric element; The matching layer is located at the front of the acoustic emission sensor, and the matching layer, the multi-layer transition layer, the anti-reflection layer, and the piezoelectric element are contacted and fixed in sequence from front to back; The front end of the matching layer is used to contact the object to be measured to provide initial acoustic impedance matching; The multi-layer transition layer includes a plurality of transition layers stacked in layers, and the plurality of transition layers have a variety of acoustic impedances; The thickness of the anti-reflection layer is a quarter of the wavelength of the typical longitudinal wave speed of the acoustic emission sensor at the center frequency in the anti-reflection layer; The piezoelectric element is used to convert the sound wave signal into an electrical signal.

2. The acoustic emission sensor based on anti-reflection design according to claim 1, characterized in that: The material of the matching layer includes one or more of epoxy resin, cobalt binder, nano tungsten powder, tungsten carbide powder, nano barium titanate, and nano silicon dioxide. The acoustic impedance value of the matching layer is 3-50 MRayl.

3. The acoustic emission sensor based on anti-reflection design according to claim 1, characterized in that: The multi-layer transition layer includes at least three transition layers, each of which has a uniform acoustic impedance, and the acoustic impedance value of the transition layer increases gradually from the front to the back.

4. The acoustic emission sensor based on anti-reflection design according to claim 3, characterized in that: The transition layers of the multi-layer transition layer are provided with five layers, and the thickness of each transition layer is equal to a quarter of the wavelength of a typical longitudinal wave speed within which the center frequency of the acoustic emission sensor is located.

5. The acoustic emission sensor based on anti-reflection design according to claim 1, characterized in that: The multi-layer transition layer includes at least three transition layers, each of which has uniform acoustic impedance; the transition layers have at least two acoustic impedance values ​​in total, and adjacent transition layers have different impedance values; the thickness of each transition layer is equal to one-fourth of the wavelength of the typical longitudinal wave speed of the center frequency of the acoustic emission sensor in the multi-layer transition layer.

6. The acoustic emission sensor based on anti-reflection design according to claim 5, characterized in that: The transition layers of the multi-layer transition layer are provided with six layers, and the acoustic impedance values ​​of adjacent transition layers are respectively greater than and less than the acoustic impedance value of the object to be measured.

7. The acoustic emission sensor based on anti-reflection design according to claim 1, characterized in that: The material of the piezoelectric element is one of modified lead zirconate titanate material and niobium indium magnesium lead titanate single crystal material.

8. A method for preparing an acoustic emission sensor based on an anti-reflection design, wherein the acoustic emission sensor structure prepared by the method is as described in any one of claims 1 to 7, characterized in that: The method for preparing the matching layer comprises the following steps: Step S1.1: measuring the acoustic impedance value of the object to be measured, and determining the target acoustic impedance value of the matching layer; Step S1.2: Calculating the required composite material density based on the target acoustic impedance value; Step S1.3: Calculating the filling ratio of the composite material based on the effective medium theory, and controlling the filling ratio so that the matching layer reaches the density of the composite material; Step S1.4: using an acoustic measurement device to monitor the acoustic impedance value of the matching layer in real time, and adjusting the ratio so that the acoustic impedance value of the matching layer matches the target acoustic impedance value.

9. The method for preparing an acoustic emission sensor based on anti-reflection design according to claim 8, characterized in that: The preparation method of the multi-layer transition layer comprises the following steps: Step S2.1: the number of transition layers of the multi-layer transition layer is five, the first transition layer to the fifth transition layer are stacked in sequence, the first transition layer is connected to the matching layer, and the fifth transition layer is connected to the piezoelectric element; Step S2.2: preparing a fifth transition layer, wherein the composition weight ratio of the fifth transition layer is: 55-65% tungsten powder, 15-20% BaTiO3, 2-4% SiO2, 0.5-1% carbon nanotubes, and the balance is cobalt binder, and the acoustic impedance value is 40-45 MRayl; Step S2.3: preparing a fourth transition layer, wherein the composition weight ratio of the fourth transition layer is: 40-50% tungsten powder, 20-25% BaTiO3, 3-5% SiO2, 0.1-0.3% graphene, and the balance is cobalt binder, and the acoustic impedance value is 30-35 MRayl; Step S2.4: preparing a third transition layer, wherein the composition weight ratio of the third transition layer is: 25-35% tungsten powder, 25-30% BaTiO3, 4-6% SiO2, 1-2% Al2O3, and the balance is cobalt binder, and the acoustic impedance value is 20-25 MRayl; Step S2.5: preparing a second transition layer, wherein the weight ratio of the components of the second transition layer is: 10-20% tungsten powder, 30-35% BaTiO3, 5-8% SiO2, 0.2-0.5% carbon nanotubes, and the balance is cobalt binder, and the acoustic impedance value is 10-15 MRayl; Step S2.5: Prepare the first transition layer, the composition weight ratio of the first transition layer is: 5-15% tungsten powder, 35-40% BaTiO3, 6-9%, 0.05-0.1% graphene, and the balance is cobalt binder, and the acoustic impedance value is 5-10 MRayl.

10. The method for preparing an acoustic emission sensor based on anti-reflection design according to claim 8, characterized in that: The method for preparing the anti-reflection layer comprises the following steps: Step S3.1: Calculate the thickness of the anti-reflection layer, where the thickness of the anti-reflection layer is a quarter of the wavelength of a typical longitudinal wave velocity in the anti-reflection layer at the center frequency of the acoustic emission sensor; Step S3.2: Selecting the material of the anti-reflection layer, wherein the material of the anti-reflection layer is one of modified PZT ceramics, acoustic metamaterials, and composite functional materials.

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