Energy-gathered fiber bragg grating acoustic emission sensor

Abstract

The invention relates to the technical field of fiber bragg grating sensors, and discloses an energy-gathered fiber bragg grating acoustic emission sensor, which is characterized in that an acoustic black hole structure is centrally mounted in a cylindrical cavity in an outer shell by adopting a positioning and fixing assembly; the shell top cover is fixed at the top of the shell body; the shell top cover is used for pressing and fixing the pressing sheets into the corresponding pressing plate grooves; the fiber bragg grating penetrates through the through hole in the shell wall of the outer shell and is located in the first semi-circular groove and the second semi-circular groove, and the second semi-circular groove is located in the middle of the fiber bragg grating in the length direction. A fiber bragg grating sensor structure based on transverse force is adopted, a signal loading point is located in the middle of the length of the fiber bragg grating, and the sensitivity of acoustic emission signal detection is improved. The acoustic black hole structure is adopted, acoustic emission signal energy is gathered at the top end of the acoustic black hole structure, maximum deformation is generated, the signal receiving strength of the fiber bragg grating is improved, the acoustic emission signal amplitude is enhanced, and then the detection sensitivity and accuracy are improved.

Description

Technical Field

[0001] The invention relates to the technical field of fiber grating sensors, in particular to an energy-focusing fiber grating acoustic emission sensor. Background Art

[0002] Acoustic Emission (AE) refers to the internal stress concentration of a material or structure when it is subjected to external forces or undergoes slight changes or damage internally. When the stress exceeds the material's bearing capacity, tiny crack extension, phase change, plastic deformation and other phenomena will occur. These processes will release energy and generate elastic waves. Acoustic emission technology is a non-destructive testing method that evaluates the integrity of a material or structure by capturing the sound waves generated by tiny damage inside the material. Its advantages are high sensitivity, strong real-time performance, and a wide range of applications. It can detect material defects early and is suitable for a variety of materials such as metals and composite materials. Acoustic emission technology has a wide range of applications in aerospace, petrochemical, electric power, bridges and other fields, such as detecting fatigue cracks in aircraft fuselages, pipeline corrosion, welding defects, etc., providing a reliable technical means to ensure the safe operation of equipment.

[0003] Fiber Bragg grating sensor is a high-performance fiber optic sensor based on the fiber Bragg grating (FBG) principle. It has many advantages such as anti-electromagnetic interference, corrosion resistance, high temperature resistance, small size, light weight, high sensitivity, wide measurement range, fatigue resistance, good long-term stability, multi-parameter measurement, radiation resistance, safety and reliability, strong multiplexing capability, and long transmission distance. The patent "A method of changing the strain of a rope using transverse force and its application in fiber Bragg grating accelerometer (ZL201310415482.2)" and the paper "K.Li, et.al. Very sensitive fiber Bragg grating accelerometer using transverse forces with an easy over-range protection and low cross axial sensitivity. Applied Optics, vol.52, no.25, pp.6401-6410, 2013." analyze the working principle and characteristics of fiber Bragg grating accelerometer based on transverse force in detail. Compared with fiber Bragg grating sensor based on axial force, it has the advantages of small size, high sensitivity, and low cross sensitivity.

[0004] The existing fiber Bragg grating acoustic emission sensor is to directly stick the sensitive part of the grating on the surface of the test piece, which has low sensitivity. The energy of the acoustic emission signal itself is low and easy to attenuate, so a more sensitive detection scheme is needed to collect the acoustic emission signal. To this end, we have launched a focused fiber Bragg grating acoustic emission sensor. Summary of the invention

[0005] The object of the present invention is to provide an energy-focusing fiber grating acoustic emission sensor to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A focused fiber Bragg grating acoustic emission sensor comprises a housing top cover, a fiber Bragg grating, an outer housing, an acoustic black hole structure and a pressing sheet, wherein the acoustic black hole structure is centrally mounted in a cylindrical cavity inside the outer housing by a positioning and fixing assembly;

[0008] The top shell wall of the outer shell is provided with two symmetrically distributed first fixing screw holes and two symmetrically distributed pressure plate grooves, the bottom of the top fixing bolt on the outer shell top cover is screwed into the corresponding first fixing screw hole, the outer shell top cover is fixed to the top of the outer shell, and the outer shell top cover presses the pressing sheet into the corresponding pressure plate groove;

[0009] The fiber grating passes through the through hole on the shell wall of the outer shell and is located in the first semicircular groove at the bottom of the pressure plate groove and the second semicircular groove at the top of the acoustic black hole structure, and the second semicircular groove is located in the middle position of the fiber grating length direction.

[0010] Preferably, the outer shell is a cylindrical structure, with an outer diameter of 18.4 mm and a height of 16 mm; an inner diameter of the cylindrical cavity of 10.4 mm and a height of 13 mm; and a bottom thickness of 3 mm.

[0011] Preferably, a second fixing screw hole is provided at the center of the bottom of the outer shell;

[0012] The positioning and fixing assembly includes a round pin column arranged at equal intervals with the second fixing screw hole as the center at the bottom of the cylindrical cavity, a round pin groove arranged at the bottom of the acoustic black hole structure 4, and a bottom fixing bolt arranged in the second fixing screw hole;

[0013] The top of the round pin column is inserted into the corresponding round pin groove, and the top of the bottom fixing bolt is screwed into the middle fixing screw hole in the middle of the bottom of the acoustic black hole structure.

[0014] Preferably, the acoustic black hole structure is a wedge-shaped structure whose size gradually decreases from the bottom to the top, and the outer diameter of the bottom of the acoustic black hole structure is consistent with the inner diameter of the cylindrical cavity.

[0015] Preferably, the first fixing screw holes and the pressure plate grooves are evenly spaced and distributed on the top wall of the outer shell;

[0016] The top cover of the housing is provided with a third fixing screw hole for passing a top fixing bolt.

[0017] Preferably, the outer diameter of the outer shell top cover is the same as that of the outer shell body, and an annular raised seat is provided on the outer side of the top of the cylindrical cavity, and the annular raised seat is inserted into the annular groove at the bottom of the outer shell top cover.

[0018] Preferably, a third semicircular groove is further provided at the bottom of the pressing sheet. The third semicircular groove is located directly above the first semicircular groove. The radius of the third semicircular groove is 0.125 mm and is used to reinforce the optical fiber Bragg grating.

[0019] Preferably, during installation, the fiber grating needs to be pre-pulled to both ends for a certain distance, and then the fiber grating is fixed in the pressing plate groove and the second semicircular groove using epoxy resin glue.

[0020] Preferably, the diameter of the through hole is 0.25 mm, the first semicircular groove and the second semicircular groove are coaxial with the through hole and have the same radius, and the diameter of the fiber grating is 0.125 mm and the length is 10 mm.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention adopts a fiber Bragg grating sensor structure based on lateral force, the signal loading point is located in the middle of the fiber Bragg grating length, the sensitivity of acoustic emission signal detection is improved, and an acoustic black hole structure is adopted to make the energy of the acoustic emission signal concentrate at the top of the acoustic black hole structure, so that it produces maximum deformation, thereby improving the intensity of the fiber Bragg grating receiving signal, enhancing the amplitude of the acoustic emission signal, and thus improving the sensitivity and accuracy of detection; the overall compact design is adopted, the size is smaller at the same sensitivity, and the scene adaptability is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the overall decomposition structure of the present invention;

[0023] Figure 2 It is a schematic diagram of the three-dimensional structure of the housing top cover of the present invention;

[0024] Figure 3 It is a schematic diagram of the three-dimensional structure of the tablet of the present invention;

[0025] Figure 4 It is a schematic diagram of the three-dimensional structure of the acoustic black hole structure of the present invention;

[0026] Figure 5 It is a schematic diagram of a first three-dimensional structure of the outer shell of the present invention;

[0027] Figure 6 It is a second three-dimensional structural schematic diagram of the outer shell of the present invention;

[0028] Figure 7 It is a schematic cross-sectional structural diagram of the outer shell of the present invention;

[0029] Figure 8 It is a schematic diagram of the three-dimensional structure after the overall assembly of the present invention;

[0030] Fig. 9 It is a schematic cross-sectional view of the structure of the present invention after overall assembly;

[0031] Fig.10 It is a schematic diagram of the three-dimensional structure after the fiber Bragg grating, outer shell and acoustic black hole structure of the present invention are assembled.

[0032] In the figure: 1. outer shell top cover; 101. third fixing screw hole; 102. annular groove; 2. optical fiber Bragg grating; 3. outer shell; 301. second fixing screw hole; 302. first fixing screw hole; 303. pressure plate groove; 304. round pin column; 305. through hole; 306. first semicircular groove; 307. annular raised seat; 308. cylindrical cavity; 4. acoustic black hole structure; 401. middle fixing screw hole; 402. round pin groove; 403. second semicircular groove; 5. pressing plate; 501. third semicircular groove; 6. top fixing bolt; 7. bottom fixing bolt. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Example:

[0035] See also Figure 1-10 , the present invention provides a technical solution:

[0036] A focused fiber Bragg grating acoustic emission sensor can realize efficient collection of acoustic emission signals, comprising a housing top cover 1, a fiber Bragg grating 2, an outer housing 3, an acoustic black hole structure 4 and a pressing sheet 5;

[0037] The outer shell 3 is a cylindrical structure, with an outer diameter of 18.4 mm and a height of 16 mm; the inner diameter of the cylindrical cavity 308 is 10.4 mm and a height of 13 mm; and the bottom thickness of the outer shell 3 is 3 mm.

[0038] The outer diameter of the outer shell top cover 1 is the same as that of the outer shell body 3 . An annular raised seat 307 is provided on the outer side of the top of the cylindrical cavity 308 . The annular raised seat 307 is inserted into the annular groove 102 at the bottom of the outer shell top cover 1 .

[0039] The outer shell 3 may also be in the shape of a cuboid or a cube, and the acoustic black hole structure 4 may also be in different forms such as a one-dimensional wedge-shaped structure or a two-dimensional wedge-shaped structure.

[0040] The acoustic black hole structure 4 is a wedge-shaped structure whose size gradually decreases from the bottom to the top, and the outer diameter of the bottom of the acoustic black hole structure 4 is consistent with the inner diameter of the cylindrical cavity 308.

[0041] The acoustic black hole structure 4 is centrally mounted in the cylindrical cavity 308 inside the outer shell 3 using a positioning and fixing assembly;

[0042] The acoustic black hole (ABH) structure is a new type of wave manipulation technology that can form a high energy density area by reducing the propagation speed of the wave, thereby increasing the intensity of the wave and achieving an energy concentration effect.

[0043] Here is a detailed explanation:

[0044] 1. Definition and principle:

[0045] The acoustic black hole structure is analogous to the concept of a black hole in astrophysics. It can manipulate the propagation of bending waves by changing the geometric parameters of the structure (such as the thickness of the wedge structure or the mechanical parameters of the material). Ideally, the bending wave velocity gradually decreases to zero in the acoustic black hole region, allowing the vibration energy to be efficiently concentrated and dissipated.

[0046] 2. Structure and classification:

[0047] One-dimensional acoustic black hole structure: usually a beam structure, which can form a two-dimensional acoustic black hole structure by rotating along a certain axis (such as the z-axis).

[0048] Two-dimensional acoustic black hole structure: It can be constructed by rotating the one-dimensional acoustic black hole structure or in other ways, and has more complex wave behavior.

[0049] Acoustic black hole pipe structure: Another common form of acoustic black hole structure, suitable for acoustic wave control in pipes.

[0050] 3. Functions and applications:

[0051] Vibration reduction: The most important feature of the acoustic black hole structure is the vibration reduction of bending waves. Studies have shown that the one-dimensional classical acoustic black hole structure can effectively attenuate bending waves in one direction. For two-dimensional acoustic black holes, more research is reflected in the study of local wave behavior.

[0052] Wave Control: Two-dimensional acoustic black hole structures show great potential in wave control. For example, the focusing and lensing effects of bending waves can be achieved by designing specific acoustic black hole structures.

[0053] Noise reduction: Acoustic black hole structures are also used in the field of noise reduction. By controlling the weakening of bending waves, vibration radiation noise can be affected. Experiments have shown that embedding a two-dimensional acoustic black hole into the engine casing of a car can significantly reduce the engine radiation noise.

[0054] Energy recovery: Acoustic black hole structures also have application prospects in vibration energy recovery. By designing a specific acoustic black hole structure, efficient recovery and conversion of vibration energy can be achieved.

[0055] For details, please refer to the reference “V. Denis, F. Gautier, A. Pelat, and J. Poittevin, “Measurement and modelling of the reflection coefficient of an acoustic blackhole termination,” J. Sound Vib., vol. 349, pp. 67–79, Aug. 2015, doi: 10.1016 / j.jsv.2015.03.043.”

[0056] A second fixing screw hole 301 is provided at the center of the bottom of the outer shell 3;

[0057] The positioning and fixing assembly includes a round pin 304 arranged at equal intervals with the second fixing screw hole 301 as the center at the bottom of the cylindrical cavity 308, a round pin groove 402 arranged at the bottom of the acoustic black hole structure 4, and a bottom fixing bolt 7 arranged in the second fixing screw hole 301;

[0058] The top of the round pin 304 is inserted into the corresponding round pin groove 402 , and the top of the bottom fixing bolt 7 is screwed into the middle fixing screw hole 401 in the middle of the bottom of the acoustic black hole structure 4 .

[0059] Two symmetrically distributed first fixing screw holes 302 and two symmetrically distributed pressure plate grooves 303 are provided on the top shell wall of the outer shell 3. The first fixing screw holes 302 and the pressure plate grooves 303 are evenly distributed on the top shell wall of the outer shell 3.

[0060] A third fixing screw hole 101 is provided on the outer shell top cover 1 for passing the top fixing bolt 6. The bottom of the top fixing bolt 6 on the outer shell top cover 1 is screwed into the corresponding first fixing screw hole 302 to fix the outer shell top cover 1 on the top of the outer shell body 3. The outer shell top cover 1 presses the pressing sheet 5 into the corresponding pressing plate groove 303. A third semicircular groove 501 is also provided at the bottom of the pressing sheet 5. The third semicircular groove 501 is located directly above the first semicircular groove 306. The radius of the third semicircular groove 501 is 0.125 mm, which is used to reinforce the optical fiber Bragg grating 2.

[0061] The fiber Bragg grating 2 passes through the through hole 305 on the shell wall of the outer shell 3 and is located in the first semicircular groove 306 at the bottom of the pressure plate groove 303 and the second semicircular groove 403 at the top of the acoustic black hole structure 4, and the second semicircular groove 403 is located in the middle position of the length direction of the fiber Bragg grating 2;

[0062] During installation, the FBG 2 needs to be pre-pulled to both ends for a certain distance, and then the FBG 2 is fixed in the pressing plate groove 303 and the second semicircular groove 403 by using epoxy resin glue.

[0063] The diameter of the through hole 305 is 0.25 mm. After the fiber Bragg grating 2 is installed, the first semicircular groove 306 and the second semicircular groove 403 are coaxial with the through hole 305 and have the same radius. The diameter of the fiber Bragg grating 2 is 0.125 mm and the length is 10 mm.

[0064] A second fixing screw hole 301 and four round pins 304 for coordination and limiting arranged at equal intervals with the second fixing screw hole 301 as the center are provided at the center of the bottom of the outer shell 3. The round pins 304 are adapted to the round pin grooves 402 of the acoustic black hole structure 4.

[0065] Two symmetrically distributed first fixing screw holes 302 and two symmetrically distributed pressure plate grooves 303 are provided on the top shell wall of the outer shell 3. The first fixing screw holes 302 and the pressure plate grooves 303 are evenly distributed on the top shell wall of the outer shell 3.

[0066] A through hole 305 is formed on the upper part of the outer shell 3 and has a diameter of 0.25 mm for passing the fiber grating 2 . A first semicircular groove 306 is formed in the pressure plate groove 303 and is coaxial with the through hole 305 and has the same radius.

[0067] The acoustic black hole structure 4 is installed in the outer shell 3. The center position of the bottom of the acoustic black hole structure 4 is provided with a middle fixing screw hole 401 and four circular pin grooves 402 for coordination and limiting arranged at equal intervals with the middle fixing screw hole 401 as the center. The top of the acoustic black hole structure 4 is provided with a second semicircular groove 403 adapted to the optical fiber Bragg grating 2. The radius of the second semicircular groove 403 is the same as that of the through hole 305, which is 0.125 mm. After the acoustic black hole structure 4 is installed in the outer shell 3, the second semicircular groove 403 on the top of the acoustic black hole structure 4 is coaxial with the through hole 305.

[0068] The fiber Bragg grating 2 has a diameter of 0.125 mm and a length of 10 mm. The fiber Bragg grating 2 passes through the through hole 305 and is located in the second semicircular groove 403 of the fiber Bragg grating 2 in the pressure plate groove 303 and the top of the acoustic black hole structure 4, and the second semicircular groove 403 is located in the middle position of the length direction of the fiber Bragg grating 2.

[0069] During installation, the fiber Bragg grating 2 has a certain pre-tension, and the fiber Bragg grating 2 is fixed at the two pressing plate grooves 303 and the top position of the acoustic black hole structure 4 by using epoxy resin glue.

[0070] The "pre-tension" refers to an initial tension applied to both ends of the fiber Bragg grating 2 during the manufacturing or installation process of the fiber Bragg grating 2. This pre-tension can have a certain impact on the performance of the fiber Bragg grating 2, as explained below:

[0071] 1. The role of pre-tensioning:

[0072] Influence on writing speed: When manufacturing a fiber Bragg grating 2, the magnitude of the pre-tension can affect the writing speed of the grating. Experiments show that the greater the pre-tension, the faster the writing speed of the grating is generally.

[0073] Influence on grating characteristics: The pre-tension force will also affect the central wavelength, reflectivity, bandwidth and other characteristics of the written fiber grating 2. For example, the greater the pre-tension force, the smaller the central wavelength of the written fiber grating 2, the higher the reflectivity, and the larger the bandwidth.

[0074] 2. Implementation method of pre-tensioning:

[0075] A common method of implementing pre-tensioning is to insert the fiber Bragg grating 2 from one side of the armored cable sleeve and pass through the fiber Bragg grating 2 fixing point when making the fiber Bragg grating sensor, so that the position of the grating reaches the preset position inside the sensor housing. Then, pre-tension the optical fiber pigtails on both sides to make the fiber Bragg grating 2 reach the required pre-tensioning amount, and fix the pigtails and the grating.

[0076] The pressing plate 5 is adapted to the pressing plate groove 303 on the outer shell 3; a third semicircular groove 501 is opened at the short center axis position of one side of the pressing plate 5, and the radius of the third semicircular groove 501 is 0.125mm, which has the same function as the through hole 305 and is used to reinforce and fix the optical fiber Bragg grating 2.

[0077] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A focused fiber Bragg grating acoustic emission sensor, comprising a housing top cover, a fiber Bragg grating, an outer housing, an acoustic black hole structure and a pressing sheet, characterized in that: The acoustic black hole structure adopts a positioning and fixing assembly to be centrally installed in a cylindrical cavity inside the outer shell; The top shell wall of the outer shell is provided with two symmetrically distributed first fixing screw holes and two symmetrically distributed pressure plate grooves, the bottom of the top fixing bolt on the outer shell top cover is screwed into the corresponding first fixing screw hole, the outer shell top cover is fixed to the top of the outer shell, and the outer shell top cover presses the pressing sheet into the corresponding pressure plate groove; The fiber grating passes through the through hole on the shell wall of the outer shell and is located in the first semicircular groove at the bottom of the pressure plate groove and the second semicircular groove at the top of the acoustic black hole structure, and the second semicircular groove is located in the middle position of the fiber grating length direction.

2. The energy-focusing fiber Bragg grating acoustic emission sensor according to claim 1, characterized in that: The outer shell is a cylindrical structure, with an outer diameter of 18.4 mm and a height of 16 mm; the inner diameter of the cylindrical cavity is 10.4 mm and the height is 13 mm; the bottom thickness of the outer shell is 3 mm.

3. The energy-focusing fiber Bragg grating acoustic emission sensor according to claim 2, characterized in that: A second fixing screw hole is provided at the center of the bottom of the outer shell; The positioning and fixing assembly includes a round pin column arranged at equal intervals with the second fixing screw hole as the center at the bottom of the cylindrical cavity, a round pin groove arranged at the bottom of the acoustic black hole structure, and a bottom fixing bolt arranged in the second fixing screw hole; The top of the round pin column is inserted into the corresponding round pin groove, and the top of the bottom fixing bolt is screwed into the middle fixing screw hole in the middle of the bottom of the acoustic black hole structure.

4. The energy-focusing fiber Bragg grating acoustic emission sensor according to claim 2, characterized in that: The acoustic black hole structure is a wedge-shaped structure whose size gradually decreases from the bottom to the top, and the outer diameter of the bottom of the acoustic black hole structure is consistent with the inner diameter of the cylindrical cavity.

5. The energy-focusing fiber Bragg grating acoustic emission sensor according to claim 1, characterized in that: The first fixing screw holes and the pressure plate grooves are distributed at equal intervals on the top wall of the outer shell; The top cover of the housing is provided with a third fixing screw hole for passing a top fixing bolt.

6. The energy-focusing fiber Bragg grating acoustic emission sensor according to claim 5, characterized in that: The outer diameter of the outer shell top cover is the same as that of the outer shell body. An annular protrusion seat is arranged on the outer side of the top of the cylindrical cavity, and the annular protrusion seat is inserted into the annular groove at the bottom of the outer shell top cover.

7. The energy-focusing fiber Bragg grating acoustic emission sensor according to claim 1, characterized in that: A third semicircular groove is also provided at the bottom of the pressing sheet. The third semicircular groove is located directly above the first semicircular groove. The radius of the third semicircular groove is 0.125 mm and is used to reinforce the optical fiber Bragg grating.

8. The energy-focusing fiber Bragg grating acoustic emission sensor according to claim 1, characterized in that: During installation, the fiber grating needs to be pre-pulled to both ends for a certain distance, and then the fiber grating is fixed in the pressure plate groove and the second semicircular groove using epoxy resin glue.

9. The energy-focusing fiber Bragg grating acoustic emission sensor according to claim 1, characterized in that: The diameter of the through hole is 0.25 mm, the first semicircular groove and the second semicircular groove are coaxial with the through hole and have the same radius, and the diameter of the fiber grating is 0.125 mm and the length is 10 mm.

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