High-response acoustic emission sensor based on acoustic structure

Abstract

The invention discloses a high-response acoustic emission sensor based on an acoustic structure, and belongs to the technical field of acoustic emission sensors. The invention solves the problems of weak response to an acoustic emission source, small amplitude of received signals and low signal-to-noise ratio of acoustic emission signals generated by early wear, fatigue cracks and other defects and received by the traditional acoustic emission sensor when the environmental noise is relatively large in the existing acoustic emission sensor. Comprising a shell, an acoustic structure cavity, a Fresnel lens, a circular-truncated-cone-shaped piezoelectric element, a connector and a distance adjusting bolt, the shell is fixedly buckled on the Fresnel lens, the acoustic structure cavity comprises an installation plate and at least one first circular ring fixedly installed on the lower end face of the installation plate, and when the number of the first circular rings is multiple, the first circular ring is connected with the connector. The diameters of the first circular rings are different, and the first circular rings are sequentially and coaxially arranged from inside to outside. According to the invention, the response capability of the sensor to an acoustic emission source, the amplitude of a received signal and the signal-to-noise ratio are obviously improved.

Description

TECHNICAL FIELD

[0001] The application relates to a high-response acoustic emission sensor based on an acoustic structure and belongs to the technical field of acoustic emission sensors. BACKGROUND

[0002] Acoustic emission is a phenomenon that stress waves are generated due to rapid energy release caused by changes in the internal state of materials. At present, rotating machinery is widely used in various occasions such as rail transportation, aerospace, power transmission and power equipment, and often works in harsh conditions such as high speed or high load. This increases the possibility of failure of rotating machinery. Once obvious wear or cracks occur inside, it will seriously affect the reliability and safety of mechanical equipment, leading to equipment damage and shutdown. Therefore, it is of great significance to carry out fault diagnosis on rotating machinery.

[0003] The acoustic emission fault diagnosis method has the advantages of real-time dynamic monitoring, insensitivity to environmental noise, sensitivity to crack propagation and wear particles, sensitivity to fault type and fault location, etc. Therefore, the acoustic emission technology is widely used in the field of fault diagnosis.

[0004] The acoustic emission sensor is a key component in fault monitoring. Considering the characteristics of the acoustic emission signal of the rotating machinery damage, a piezoelectric sensor is often used in fault diagnosis. This type of sensor mainly consists of a piezoelectric element, a matching layer, a backing layer and a shell. The piezoelectric element is the core part of the sensor. For a receiving type acoustic emission sensor, the piezoelectric element works in the positive piezoelectric effect mode and can convert the mechanical signal of the acoustic emission wave into an electrical signal. The matching layer can achieve acoustic impedance matching between the piezoelectric element and the measured object, and at the same time protect the piezoelectric element. The backing layer mainly absorbs the reflected echo excited by the piezoelectric element.

[0005] The acoustic emission signal can directly represent the defects of the equipment, so the response ability of the sensor to the acoustic emission source and the amplitude of the received signal are crucial in fault diagnosis. When the equipment fails, such as crack propagation in the material and intensified friction between parts, the amplitude of the acoustic emission signal usually changes. For the same acoustic emission source, the higher the amplitude of the received signal of the sensor, the higher the sensitivity, and it will have a better response to early defects that are difficult to monitor, and potential risks can be discovered earlier.

[0006] Due to the large noise in the working environment of the rotating machinery, the acoustic emission signals generated by early wear and fatigue cracks and other defects received by the traditional acoustic emission sensor have the problems of weak response to the acoustic emission source, small amplitude of the received signal and low signal-to-noise ratio. SUMMARY

[0007] The application aims at solving the problem that the acoustic emission sensor in the prior art has weak response to the acoustic emission source, small amplitude of the received signal and low signal-to-noise ratio when the environmental noise is large.

[0008] The application adopts the technical scheme that: The application discloses a high-response acoustic emission sensor based on an acoustic structure. The bottom end of the Fresnel lens is provided with a plurality of coaxially distributed annular grooves, and the annular grooves are filled with phase inversion materials, so that phase inversion zones are formed in the annular grooves. The Fresnel lens is internally fixed with at least one second annular ring, and the second annular ring is arranged in radial misalignment with the first annular ring. The circular-truncated-cone-shaped piezoelectric element is coaxially mounted on the Fresnel lens inside the innermost second annular ring. The distance adjusting bolt is sequentially threaded on the shell and the mounting plate from top to bottom, and the axial distance between the acoustic structure cavity and the Fresnel lens is adjusted through the distance adjusting bolt. The circular-truncated-cone-shaped piezoelectric element is connected with an external device through the connector.

[0009] Further, when the number of the first annular rings and the second annular rings is multiple, the spacing between each adjacent first annular ring and second annular ring is the same.

[0010] Further, the upper surface diameter of the circular-truncated-cone-shaped piezoelectric element is larger than the lower surface diameter, and the material of the circular-truncated-cone-shaped piezoelectric element is PZT-5.

[0011] Further, the shell is in a barrel shape.

[0012] Further, the mounting plate is provided with a threaded hole, the lower end of the distance adjusting bolt is threadedly connected with the mounting plate, the upper inner wall of the Fresnel lens is provided with a limiting clamping groove, and the outer wall of the outermost first annular ring in the acoustic structure cavity is provided with a tenon matched with the limiting clamping groove.

[0013] Further, the mounting plate is provided with a wire hole.

[0014] Further, the first annular ring and the second annular ring have the same thickness, and the minimum thickness is 1mm, and the maximum thickness is half of the interval between the adjacent first annular ring and the second annular ring.

[0015] Further, the Fresnel lens is made of copper, and the phase inversion region is made of aluminum oxide.

[0016] Further, the first annular ring and the second annular ring are made of aluminum.

[0017] Further, the shell is made of stainless steel.

[0018] Compared with the prior art, the present application has the following effects: The Fresnel lens is located at the bottom of the sensor and is used to focus the acoustic emission wave on the lower surface of the circular truncated cone piezoelectric element; the circular truncated cone piezoelectric element is used to realize electromechanical conversion; the connector connects the inside and outside of the sensor and is used to connect with external equipment. The distance adjusting bolt is used to adjust the axial distance between the acoustic structure cavity and the Fresnel lens, and then control the size of the Z-shaped bending path.

[0019] Compared with the traditional acoustic emission sensor, the present application is based on the acoustic structure cavity, and the annular pair formed by the first annular ring and the second annular ring forms one or more continuous Z-shaped structures to amplify the amplitude of the sound signal. Since the acoustic emission signal is not always vertically incident on the lower surface of the acoustic emission sensor, the Z-shaped structure forces the acoustic emission signal incident on both ends to pass along the bending path first, and the increased path length can reduce the peak frequency of the acoustic signal. By adjusting the length of the Z-shaped path, the peak frequency of the incident acoustic emission signal can be gradually adjusted. For acoustic emission signals outside the resonant frequency of the piezoelectric element, the peak frequency can also be adjusted to be within the frequency range of the sensor. For the acoustic emission signal in the middle of the sensor, the Fresnel lens uses the difference in sound velocity between the transmission region and the phase inversion region to produce a phase difference of the acoustic emission wave, so that the acoustic emission wave energy is superimposed and enhanced at the lower surface of the piezoelectric element. The circular truncated cone piezoelectric element limits the size of the lower surface, and thus limits the lateral displacement of the piezoelectric element caused by the acoustic emission wave. Since the total displacement is constant, the displacement of the piezoelectric element in the longitudinal direction is larger, and the electromechanical conversion efficiency is improved. Therefore, when the environmental noise is large, the present application significantly improves the response capability of the sensor to the acoustic emission source, the amplitude of the received signal, and the signal-to-noise ratio.

[0020] By adjusting the axial distance between the annular pair, the present application can adjust the high-frequency or low-frequency acoustic emission signal to be near the resonant frequency of the piezoelectric element, so as to realize better response of the sensor to the acoustic emission source. At the same time, the Fresnel lens is used to superimpose and enhance the acoustic emission wave energy at the lower surface of the piezoelectric element, and the circular truncated cone piezoelectric element is designed to increase the displacement of the piezoelectric element affected by the acoustic emission wave, so as to realize high response of the sensor to the acoustic emission source. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a schematic perspective view of a high-response acoustic emission sensor based on an acoustic structure according to the present application; Figure 2 is a schematic main view of a high-response acoustic emission sensor based on an acoustic structure according to the present application; Figure 3 is a schematic perspective view of a high-response acoustic emission sensor based on an acoustic structure according to the present application (housing perspective); Figure 4 is a schematic view of an acoustic emission signal amplification; Figure 5 is a schematic perspective view of a housing; Figure 6 is a schematic perspective view of an acoustic structure cavity; Figure 7 is a schematic perspective view of a first Fresnel lens; Figure 8 is a schematic perspective view of a second Fresnel lens.

[0022] In the figure: 1, housing; 11, clamping platform; 2, acoustic structure cavity; 21, mounting plate; 22, first circular ring; 23, tenon; 3, Fresnel lens; 31, circular groove; 32, phase inversion zone; 33, transmission zone; 34, limiting clamping groove; 4, circular truncated piezoelectric element; 5, connector; 6, distance adjusting bolt; 7, second circular ring. DETAILED DESCRIPTION

[0023] DETAILED DESCRIPTION Figures 1-8 It is necessary to describe the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0024] It should be noted that the descriptions of "front", "back", "left", "right", "inner", "outer", "left side", "right side", "upper", "lower", "top", "bottom" and the like in the present application are defined based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the described structure must be constructed and operated in a particular orientation, therefore, it cannot be understood as a limitation on the present application. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0025] In the description of the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral connection; it can be directly connected, or indirectly connected through an intermediate medium, it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0026] A high-response acoustic emission sensor based on acoustic structure, comprising a shell 1, an acoustic structure cavity 2, a Fresnel lens 3, a circular truncated cone piezoelectric element 4, a connector 5 and a distance adjusting bolt 6, wherein the shell 1 is fixedly buckled on the Fresnel lens 3, the acoustic structure cavity 2 comprises a mounting plate 21 and at least one first circular ring 22 fixedly arranged on the lower end surface of the mounting plate 21, when the number of the first circular ring 22 is multiple, the diameters of the multiple first circular rings 22 are different and arranged coaxially from inside to outside, The Fresnel lens 3 is in a barrel structure, and a plurality of annular grooves 31 are arranged coaxially on the bottom end of the Fresnel lens 3, and the annular grooves 31 are filled with phase inversion material, so that a phase inversion area 32 is formed in the annular grooves 31, and the structure of the Fresnel lens 3 except the phase inversion area 32 is a transmission area 33, At least one second circular ring 7 is fixedly arranged in the barrel structure of the Fresnel lens 3, and the second circular ring 7 is arranged radially staggered with the first circular ring 22, when the number of the second circular ring 7 is multiple, the diameters of the multiple second circular rings 7 are different and arranged coaxially from inside to outside, The circular truncated cone piezoelectric element 4 is coaxially mounted on the Fresnel lens 3 inside the innermost second circular ring 7, The distance adjusting bolt 6 is sequentially threaded on the shell 1 and the mounting plate 21 from top to bottom, and the axial distance between the acoustic structure cavity 2 and the Fresnel lens 3 is adjusted by the distance adjusting bolt 6, The connection between the circular truncated cone piezoelectric element 4 and the external equipment is realized by the connector 5.

[0027] The second circular ring 7 is arranged radially staggered with the first circular ring 22, forming a Z-shaped gap. The number of the first circular ring 22 and the second circular ring 7 is not limited, preferably one or two, too many will result in large sensor volume and large signal attenuation, the number depends on the degree of frequency adjustment. When the number of the first circular ring 22 and the second circular ring 7 is two, the two first circular rings 22 and the two second circular rings 7 are arranged radially staggered.

[0028] One end of the annular groove 31 provided on the Fresnel lens 3 is in contact with the measured member.

[0029] The Fresnel lens 3 enhances the fault acoustic emission signal; Fresnel lens 3 is located at the bottom of the sensor, which is used to focus the acoustic emission wave on the lower surface of the circular truncated piezoelectric element 4; the circular truncated piezoelectric element 4 is used to realize the electromechanical conversion; the connector 5 connects the inside and outside of the sensor, which is used for connection with external equipment. The adjusting bolt 6 is used to adjust the axial distance between the acoustic structure cavity 2 and the Fresnel lens 3, thereby controlling the size of the Z-shaped bending path.

[0030] Compared with the traditional acoustic emission sensor, the present application is based on the acoustic structure cavity 2, and the annular pair formed by the first circular ring 22 and the second circular ring 7 forms one or more continuous Z-shaped structure to amplify the amplitude of the sound signal. Since the acoustic emission signal is not always vertically incident on the lower surface of the acoustic emission sensor, the Z-shaped structure forces the acoustic emission signal incident on both ends to pass along the bending path, and the increased path length can reduce the peak frequency of the acoustic signal, and changing the length of the Z-shaped path can gradually adjust the peak frequency of the incident acoustic emission signal, and the acoustic emission signal outside the resonance frequency of the piezoelectric element can also be adjusted to the sensor frequency band range. For the acoustic emission signal in the middle of the sensor, the Fresnel lens 3 uses the difference in sound speed between the transmission area 33 and the phase inversion area 32 material to generate a phase difference of the acoustic emission wave, so that the acoustic emission wave energy is superimposed and enhanced at the lower surface of the piezoelectric element. The circular truncated piezoelectric element 4 limits the size of the lower surface, thereby limiting the lateral displacement of the lower surface of the piezoelectric element caused by the acoustic emission wave, and the total displacement is constant, so the displacement of the piezoelectric element in the longitudinal direction is larger, thereby improving the electromechanical conversion efficiency. Therefore, when the environmental noise is large, the present application significantly improves the response ability of the sensor to the acoustic emission source, the amplitude of the received signal and the signal-to-noise ratio for the same acoustic emission source.

[0031] In actual acoustic emission fault monitoring, the source of the acoustic emission signal is various, and the peak frequency of the acoustic emission signal is different for different damages or other acoustic emission sources. Taking the acoustic emission signal frequency of common metal as an example, the frequency range is 100kHz~200kHz, so the resonance frequency of the sensor piezoelectric element is often set to be near 150kHz, which reduces the response effect of the sensor to the acoustic emission signal with low frequency such as 120kHz or high frequency such as 180kHz. The present application can adjust the high frequency or low frequency acoustic emission signal to the resonance frequency of the piezoelectric element by adjusting the axial distance between the annular pair, so as to realize better response of the sensor to the acoustic emission source, and use the Fresnel lens 3 to superimpose and enhance the acoustic emission wave energy at the lower surface of the piezoelectric element, and design the circular truncated piezoelectric element 4 to increase the displacement of the piezoelectric element affected by the acoustic emission wave, thereby realizing high response of the sensor to the acoustic emission source.

[0032] The shell 1 is used to protect the internal elements of the sensor from adverse environmental factors and effectively block external electromagnetic interference, and the shell 1 and the Fresnel lens 3 are connected in an interference fit manner.

[0033] The top of the shell 1 is provided with a first mounting hole for mounting the distance adjusting bolt 6, and the distance adjusting bolt 6 is coaxially arranged with the acoustic structure cavity 2. The upper part of the shell 1 is provided with a second mounting hole for mounting the connector 5.

[0034] The transmission zone 33 in the Fresnel lens 3 and the phase inversion zone 32 adopt materials with similar acoustic impedance, and the acoustic speed in the materials needs to have a certain difference.

[0035] When the number of the first annular ring 22 and the second annular ring 7 is multiple, the spacing between each adjacent first annular ring 22 and second annular ring 7 is the same.

[0036] The upper surface diameter of the circular truncated cone piezoelectric element 4 is larger than the lower surface diameter, and the material is PZT-5. In this way, PZT-5 is lead zirconate titanate piezoelectric ceramic, which has larger electromechanical coupling coefficient and piezoelectric strain constant than piezoelectric polymer. The upper surface of the circular truncated cone piezoelectric element 4 is positive, and the lower surface is negative.

[0037] The shell 1 is a barrel-shaped structure. In order to better realize the interference fit between the shell 1 and the Fresnel lens 3, the inner wall of the opening end of the shell 1 is processed with a clamping table 11 along the circumference, and the upper end of the Fresnel lens 3 is clamped in the clamping table 11.

[0038] The mounting plate 21 is provided with a threaded hole, the lower end of the distance adjusting bolt 6 is screwed with the mounting plate 21, the upper inner wall of the Fresnel lens 3 is processed with a limiting clamping groove 34, and the outer wall of the outermost first annular ring 22 in the acoustic structure cavity 2 is processed with a tenon 23 matched with the limiting clamping groove 34. In this way, through the cooperation of the tenon 23 and the limiting clamping groove 34, the circumferential limiting of the acoustic structure cavity 2 is realized, so that the acoustic structure cavity 2 only retains the longitudinal degree of freedom, that is, when the distance adjusting bolt 6 rotates, it can only drive the acoustic structure cavity 2 to move in the up-down direction. The number of limiting clamping grooves 34 and the number of tenons 23 are preferably two, and are arranged to further ensure the circumferential limiting effect.

[0039] The mounting plate 21 is provided with a wire hole. In this way, the wire passes through the wire hole, which is convenient for connecting the connector 5 and the circular truncated cone piezoelectric element 4 through the wire.

[0040] The thickness of the first annular ring 22 and the second annular ring 7 is the same, and the minimum thickness is 1mm, and the maximum thickness is half of the spacing between the adjacent first annular ring 22 and the second annular ring 7. In this way, it is beneficial to the propagation of acoustic emission wave along the specified zigzag path, and the energy attenuation caused by the additional propagation path is minimized.

[0041] The material of the transmission area 33 of the Fresnel lens 3 is copper, and the material of the phase inversion area 32 is aluminum oxide. In this way, the difference in sound speed between the two materials can cause the phase change of the acoustic emission wave incident into the phase inversion area, the close acoustic impedance of the two materials can reduce the energy loss of the acoustic emission wave when it is incident from the phase inversion area into the transmission area, and finally the constructive interference in the focusing area can improve the focusing effect.

[0042] The first circular ring 22 and the second circular ring 7 are made of the same material, which is aluminum.

[0043] The shell 1 is made of stainless steel. In this way, the stainless steel has high mechanical strength, impact resistance, corrosion resistance, and good electromagnetic shielding performance, can meet the long-term use of the sensor, effectively block external electromagnetic interference, ensure stable signal transmission of the sensor, and further protect the internal elements from the influence of the external harmful environment. Specifically, 304 stainless steel can be used.

[0044] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can make equivalent replacements or changes within the technical range disclosed by the present application according to the technical solution and the inventive concept of the present application, which should be covered within the protection scope of the present application.

Claims

1. A high-response acoustic emission sensor based on an acoustic structure, characterized in that: The system includes a housing (1), an acoustic structural cavity (2), a Fresnel lens (3), a frustum-shaped piezoelectric element (4), a connector (5), and an adjusting bolt (6). The housing (1) is fixedly fastened to the Fresnel lens (3). The acoustic structural cavity (2) includes a mounting plate (21) and at least one first ring (22) fixed to the lower end face of the mounting plate (21). When there are multiple first rings (22), the diameters of the multiple first rings (22) are different and they are arranged coaxially from the inside to the outside. The Fresnel lens (3) has a barrel-shaped structure and several coaxially distributed annular grooves (31) are provided at its bottom. The annular grooves (31) are filled with phase reversal material, so that a phase reversal region (32) is formed in the annular grooves (31). The Fresnel lens (3) structure other than the phase reversal region (32) serves as the transmission region (33). The Fresnel lens (3) has at least one second ring (7) fixed inside its barrel-shaped structure, and the second ring (7) is radially offset from the first ring (22). When there are multiple second rings (7), the diameters of the multiple second rings (7) are different and they are arranged coaxially from the inside to the outside. The frustum-shaped piezoelectric element (4) is coaxially mounted on the Fresnel lens (3) inside the innermost second ring (7). Adjusting bolts (6) are sequentially installed from top to bottom on the outer shell (1) and the mounting plate (21). The axial distance between the acoustic cavity (2) and the Fresnel lens (3) is adjusted by adjusting bolts (6). The frustum-shaped piezoelectric element (4) is connected to an external device via a connector (5).

2. The high-response acoustic emission sensor based on acoustic structure according to claim 1, characterized in that: When there are multiple first rings (22) and second rings (7), the spacing between each adjacent first ring (22) and second ring (7) is the same.

3. The high-response acoustic emission sensor based on acoustic structure according to claim 1, characterized in that: The upper surface diameter of the frustum-shaped piezoelectric element (4) is larger than the lower surface diameter, and its material is PZT-5.

4. A high-response acoustic emission sensor based on an acoustic structure according to claim 1, characterized in that: The outer shell (1) is a cylindrical structure.

5. A high-response acoustic emission sensor based on an acoustic structure according to claim 1, characterized in that: The mounting plate (21) has a threaded through hole. The lower end of the adjusting bolt (6) is threaded to the mounting plate (21) through the threaded hole. The upper inner wall of the Fresnel lens (3) is machined with a limiting groove (34). The outermost first ring (22) in the acoustic structure cavity (2) has a tenon (23) that mates with the limiting groove (34).

6. A high-response acoustic emission sensor based on an acoustic structure according to claim 1, characterized in that: The mounting plate (21) has wire holes.

7. A high-response acoustic emission sensor based on an acoustic structure according to claim 1, characterized in that: The first ring (22) and the second ring (7) have the same thickness, with a minimum thickness of 1 mm and a maximum thickness of half the distance between adjacent first rings (22) and second rings (7).

8. A high-response acoustic emission sensor based on an acoustic structure according to claim 1, characterized in that: The transmission region (33) of the Fresnel lens (3) is made of copper, and the phase reversal region (32) is made of aluminum oxide.

9. A high-response acoustic emission sensor based on an acoustic structure according to claim 1, characterized in that: The first ring (22) and the second ring (7) are made of the same material, aluminum.

10. A high-response acoustic emission sensor based on an acoustic structure according to claim 1, characterized in that: The outer shell (1) is made of stainless steel.

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