Multimodal surface sound velocity synchronous detection system and method based on laser ultrasound

Abstract

The application provides a multimodal surface sound velocity synchronous detection system based on laser ultrasound, which comprises a general control module, a laser scanning excitation module, a visual positioning module, a laser interference vibration detection module and a data backend processing module; the output ends of the general control module are connected with the input ends of the laser scanning excitation module and the laser interference vibration detection module respectively, the output end of the visual positioning module is connected with the input ends of the general control module and the data backend processing module respectively, and the output end of the laser interference vibration detection module is connected with the input end of the data backend processing module.

Description

Technical Field

[0001] This invention relates to a technique for measuring the properties of solid materials, and in particular to a multimodal surface sound velocity synchronous detection system and method based on laser ultrasound. Background Technology

[0002] Sound velocity is a core physical parameter characterizing the mechanical properties of solid materials. In the field of materials science research, by precisely measuring the sound velocity of multimodal surface acoustic waves, researchers can achieve quantitative inversion and evaluation of the elastic modulus, Poisson's ratio, residual stress field distribution, and microstructure evolution process of materials. In ultrasonic testing engineering applications, obtaining real-time and accurate sound velocity values ​​of materials is of vital importance for correcting sound path errors and significantly improving the accuracy of defect location.

[0003] Currently, traditional methods for measuring the surface sound velocity of solid materials mainly rely on piezoelectric transducers. This method achieves the excitation and reception of ultrasonic waves through physical contact between a piezoelectric probe and the sample surface. However, limited by the contact-based detection mode, this technology has the following limitations in practical applications: First, the measurement process is highly dependent on the acoustic coupling agent, making non-contact detection difficult, and its environmental adaptability is poor, with detection performance easily degraded by external operating conditions; second, the physical contact surface of the transducer is difficult to adapt to workpieces with complex geometric contours or irregular surfaces; third, the spatial positioning accuracy of the surface wave measurement point is low due to the influence of the probe's physical size. Finally, traditional transducers typically only generate a single-mode ultrasonic signal under a single excitation. To obtain multi-mode sound velocity information, repeated experiments or probe replacements are required, which not only increases operational complexity but also easily introduces large systematic errors due to differences in the consistency of experimental conditions. Summary of the Invention

[0004] The purpose of this invention is to provide a multimodal surface sound velocity synchronous detection system based on laser ultrasound, comprising a central control module, a laser scanning excitation module, a visual positioning module, a laser interferometric vibration measurement module, and a data back-end processing module; the output of the central control module is connected to the input of the laser scanning excitation module and the input of the laser interferometric vibration measurement module, respectively; the output of the visual positioning module is connected to the input of the central control module and the data back-end processing module, respectively; and the output of the laser interferometric vibration measurement module is connected to the input of the data back-end processing module.

[0005] The main control module is used to control the laser scanning excitation module to emit scanning pulses to excite the laser, and to start the laser interferometric vibration measurement module, coordinating the ultrasonic excitation of the laser scanning excitation module and the detection timing of the laser interferometric vibration measurement module;

[0006] The laser scanning excitation module is used to scan and irradiate the surface of the sample under test along a preset direction with a set step size, thereby exciting broadband multimodal surface acoustic waves on the surface of the sample under test.

[0007] The visual positioning module is used to capture the spatial coordinate changes of each scanning step and process the coordinate data and feed it back to the central control module to achieve closed-loop position calibration.

[0008] The laser interferometric vibration measurement module is used to emit probe light onto the surface of the sample to capture surface vibration signals, and to make the probe light carrying vibration information interfere with the reference light, and then output the interference signal after converting the interference signal into an electrical signal.

[0009] The data backend processing module is used to simultaneously extract multimodal surface sound velocity by identifying the characteristics of different modes of sound waves and combining the information on changes in scanning position and sound wave flight time information.

[0010] Furthermore, the overall control module includes a timing controller and an electromechanical controller; the electromechanical controller drives the laser scanning excitation module to perform step scanning according to the instructions of the timing controller, and compensates the deflection angle of the galvanometer in the laser scanning excitation module in real time according to the coordinate information fed back by the visual positioning module.

[0011] Furthermore, the laser scanning excitation module includes a pulsed laser, an isolator, a first dichroic mirror, a second dichroic mirror, a galvanometer, and a field mirror. The pulsed laser emits an excitation laser beam, which is transmitted through the isolator, the first dichroic mirror, and the second dichroic mirror to the galvanometer. The galvanometer receives a control signal from the main control module and deflects the beam to change the reflection angle, so that the laser beam is vertically focused by the field mirror to a designated position on the surface of the sample to be tested, forming a scanning excitation source that steps along a fixed direction.

[0012] Furthermore, the visual positioning module includes an auxiliary continuous laser, a camera, and a coordinate calibration module. The auxiliary beam emitted from the auxiliary continuous laser is reflected by a first dichroic mirror to a second dichroic mirror and combined with the excitation beam. Then, it is reflected by a galvanometer and a field mirror onto the sample surface along with ambient light within the field of view. After passing through the field mirror and the galvanometer, it is reflected by the second dichroic mirror to the photosensitive surface of the camera. The camera acquires a coaxial image containing the spot of the auxiliary beam and the ambient light. The coordinate calibration module is used to identify the pixel coordinates of the spot in the image and convert them into physical space coordinate information, which is then output to the main control module and the data back-end processing module.

[0013] Furthermore, the laser interferometric vibration measurement module includes a laser interferometer and a probe; the laser interferometer receives the control signal from the main control module and emits a probe laser, which is focused onto the surface of the sample to be tested by the probe. The probe light carrying the vibration information of the sample surface is reflected back to the probe and collected by the laser interferometer, generating an interference signal inside the laser interferometer and outputting an electrical signal to the data back-end processing module.

[0014] Furthermore, the data back-end processing module includes an analog-to-digital converter and a computer; the analog-to-digital converter converts the analog electrical signals collected by the laser interferometric vibration measurement module into digital signals and transmits them to the computer; the computer identifies the characteristics of different modes of sound waves, analyzes the relationship between spatial coordinate changes and flight time, and simultaneously extracts multimodal sound velocity information.

[0015] This invention also provides a method for synchronous detection of multimodal surface sound velocity based on laser ultrasound, comprising:

[0016] Step S100: Fix the sample to be tested, install the laser scanning excitation module, and complete the optical path alignment; start the main control module to perform zero-point reset of the galvanometer in the laser scanning excitation module; turn on the auxiliary continuous laser to perform boundary calibration field of view with the preset effective scanning range; adjust the laser interferometric vibration measurement module so that the detection spot falls within the effective scanning range.

[0017] Step S200: The master control module drives the galvanometer to control the auxiliary indicator light to perform array scanning within the effective field of view. The visual positioning module acquires the pixel center coordinates of each scanning position in the image coordinate system. Based on the mapping relationship between the deflection voltage of the galvanometer and the corresponding pixel coordinates, a transformation matrix is ​​used to map it to the physical space coordinate system; the position of the probe spot in the image is captured, and its physical space coordinates are calculated. ), and use it as the geometric reference origin for the acoustic wave scan;

[0018] Step S300: Based on the material properties of the sample to be tested and the testing requirements, a linear scanning path is set in the main control module; this path is based on the coordinates of the detection point (x... det, y det Using ) as the reference point, set the starting scan distance d. start Step interval d step The total number of scanning points N is determined; the main control module starts the laser interferometric vibration measurement module and the analog-to-digital converter to start real-time acquisition of the vibration waveform of the sample surface at the detection points, and then starts the laser scanning excitation module to start scanning along the preset path to obtain a spatiotemporal two-dimensional data matrix S(t,d) composed of N surface ultrasonic waveforms, where d is the scanning distance and t is the arrival time of the scan.

[0019] Step S400: The computer performs time-frequency analysis on the acquired two-dimensional data matrix, identifying and distinguishing at least one of Rayleigh waves, Lamb waves, and longitudinal waves in the signal; for each identified mode, its arrival time t at different scanning distances d is extracted, and linear fitting is performed on multiple sets of data points. The slope of the fitted line is the surface sound velocity V of that mode on the current material surface.

[0020] ,

[0021] Where Δd represents the change in scanning distance and Δt represents the change in arrival time; finally, the sound velocity measurement results of multiple modes are output synchronously.

[0022] Furthermore, in step S300, at each scanning position, the visual positioning module verifies the physical coordinates in real time by capturing the auxiliary indicator light spot; if the position deviation exceeds a preset threshold, the central control module uses a transformation matrix to perform closed-loop correction on the galvanometer control voltage to ensure the step interval d. step Physical precision.

[0023] Compared with the prior art, the significant advantages of this invention are: (1) This invention uses laser as the excitation source of ultrasound, which can simultaneously excite broadband multimodal signals, so that the system can simultaneously measure the surface sound velocity of multimodal components, avoiding the system error introduced by the separate measurement; (2) This invention uses a visual positioning module with a galvanometer field mirror to achieve high-precision closed-loop positioning and scanning of the excitation source, which has the significant advantages of high precision and high spatial resolution measurement, and high sound velocity measurement accuracy; (3) This invention uses an optical ultrasonic detection method, which has high spatial resolution and improves the sound velocity measurement accuracy; (4) This invention uses a fully optical excitation detection method, which has a wide range of applications and is suitable for sound velocity detection in extreme working conditions such as high-temperature workpieces and complex components. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the system of the present invention.

[0025] Figure 2 This is a schematic diagram of the scanning path and spot distribution for sample scanning according to the present invention.

[0026] Figure 3 This is a schematic diagram showing the relative positions of the probe spot emitted by the laser interferometric vibration measurement module and the scanning excitation spot emitted by the laser scanning excitation module, as well as the scanning path of the excitation spot.

[0027] Figure 4 The graph shows the multi-step signals acquired by the laser interferometric vibration measurement module in this invention, as well as the distance-time fitting curves of the surface wave and longitudinal wave of the aluminum block and the sound velocity measurement results.

[0028] The attached figures are labeled as follows: main control module 10, timing controller 101, electromechanical controller 102, laser scanning excitation module 20, pulsed laser 201, isolator 202, first dichroic mirror 203, second dichroic mirror 204, galvanometer 205, field mirror 206, visual positioning module 30, auxiliary continuous laser 301, camera 302, laser interferometric vibration measurement module 40, laser interferometer 401, probe 402, data back-end processing module 50, analog-to-digital converter 501, computer 502, detection laser spot 601, excitation laser spot 602, linear scanning trajectory 603, and calibration field of view 604. Detailed Implementation

[0029] This embodiment uses the synchronous measurement of multimodal sound velocity on the surface of a 5cm thick aluminum block as an example. Figure 1 As shown in the figure, this embodiment proposes a multimodal surface sound velocity synchronous detection system based on laser ultrasound. The system includes a central control module 10, a laser scanning excitation module 20, a visual positioning module 30, a laser interferometric vibration measurement module 40, and a data back-end processing module 50.

[0030] The output of the main control module 10 is connected to the input of the laser scanning excitation module 20 and the input of the laser interferometric vibration measurement module 40. The output of the visual positioning module 30 is connected to the input of the main control module 10 and the data back-end processing module 50. The output of the laser interferometric vibration measurement module 40 is connected to the input of the data back-end processing module 50.

[0031] The main control module 10 includes a timing controller 101 and an electromechanical controller 102. The electromechanical controller 102 drives the laser scanning excitation module 20 to perform step scanning according to the instructions of the timing controller 101, and compensates the deflection angle of the scanning mechanism in real time according to the coordinate information fed back by the vision positioning module 30.

[0032] The laser scanning excitation module 20 includes a pulsed laser 201, an isolator 202, a first dichroic mirror 203, a second dichroic mirror 204, a galvanometer 205, and a field mirror 206.

[0033] The pulsed laser 201 is preferably an Nd:YAG laser with a wavelength of 1064 nm, a single pulse energy of 1 mJ, and a pulse width of 20 ns. The pulsed laser irradiates the surface of the sample material under test, causing the sample surface to absorb the laser energy and undergo thermal expansion, thus exciting thermoelastic acoustic waves. Those skilled in the art should understand that the above laser parameters can be adjusted within a certain range according to the damage threshold of the material under test and the required detection sensitivity, and are not limited to the values ​​given in this embodiment. In this embodiment, the sample under test is an aluminum block with a relatively large thickness, and the focus is on detecting longitudinal waves and surface waves.

[0034] The first dichroic mirror 203 and the second dichroic mirror 204 are preferably long-pass dichroic mirrors with a starting wavelength of 805 nm. These dichroic mirrors are capable of combining a 1064 nm excited laser beam with visible light. Those skilled in the art should understand that, depending on the wavelength of the pulsed laser 201 and the auxiliary indicator laser used, dichroic mirrors with different starting wavelengths should be employed, and the selection is not limited to the devices given in this embodiment.

[0035] The visual positioning module 30 includes an auxiliary continuous laser 301, a camera 302, and a coordinate calibration module. The beam emitted from the auxiliary continuous laser 301 is reflected by a first dichroic mirror 203 to a second dichroic mirror 204 where it is combined with the excitation beam. Subsequently, it is reflected along with ambient light from the sample surface by a galvanometer 205 and a field lens 206. After passing through the field lens 206 and galvanometer 205, it is reflected again by the second dichroic mirror 204 to the photosensitive surface of the camera 302. The camera 302 acquires a coaxial image containing the auxiliary laser beam spot and ambient light. The coordinate calibration module identifies the pixel coordinates of the spot in the image and converts them into physical space coordinate information, which is then output to the main control module 10 and the data back-end processing module 50.

[0036] The auxiliary continuous laser 301 is preferably a 520nm semiconductor continuous laser, which can be combined with the excitation laser and ultimately incident on the photosensitive surface of the camera 302 along with ambient natural light. Those skilled in the art should understand that, based on the wavelength difference between the pulsed laser 201 and the probe laser of the laser interferometer 401, the wavelength of the auxiliary continuous laser 301 can also be preferably 635nm or other visible light bands to avoid spectral interference between the auxiliary laser and the probe light.

[0037] The laser interferometric vibration measurement module 40 includes a laser interferometer 401 and a probe 402. The laser interferometer 401 is preferably a Sagnac interferometer. Upon receiving a control signal from the main control module, the laser interferometer 401 emits a probe laser. This probe laser is focused onto the surface of the sample under test by the probe 402. The probe light, carrying vibration information from the sample surface, is reflected back to the probe 402 and collected by the laser interferometer 401. An interference signal is generated within the laser interferometer 401, and an electrical signal is output to the data back-end processing module 50.

[0038] The data back-end processing module 50 includes an analog-to-digital converter 501 and a computer 502. The analog-to-digital converter 501 converts the analog electrical signals collected by the laser interferometric vibration measurement module 40 into digital signals and transmits them to the computer 502. The computer 502 identifies the characteristics of different modes of sound waves, analyzes the relationship between spatial coordinate changes and flight time, and simultaneously extracts multimodal sound velocity information.

[0039] like Figure 2 As shown in the figure, this embodiment employs the scanning method illustrated. The border in the figure represents the calibration field of view 604 of the auxiliary continuous laser 301, i.e., the linear response range of the galvanometer 205 and field mirror 206 system. The black dots in the figure represent the probe laser spot 601, and the white dots represent the position of each step of the excitation laser spot 602. The linear scanning trajectory 603 starts from the position of the probe laser spot 601 and extends in a straight line along a set direction. The visual positioning module 30 performs closed-loop correction on each excitation point to ensure that the excitation laser spot strictly follows the preset step interval d. stepThe probe spot moves away from the detector, thus eliminating displacement errors caused by scanning nonlinearity.

[0040] like Figure 3 As shown in the figure, this embodiment proposes a multimodal surface sound velocity synchronous detection method based on laser ultrasound, including the following steps:

[0041] Step S10, System Initialization: Fix the sample to be tested, install the laser scanning excitation module 20, and complete the optical path alignment; start the main control module 10 to perform zero-point reset of the galvanometer 205 in the laser scanning excitation module 20. Turn on the auxiliary continuous laser 301 to perform boundary calibration field of view with the preset effective scanning range; adjust the laser interferometric vibration module 40 to make the detection spot fall within the effective scanning range.

[0042] Step S20, Coordinate Mapping Calibration: The master control module drives the galvanometer 205 to control the auxiliary indicator light to perform array scanning within the effective field of view. The visual positioning module 30 acquires the pixel center coordinates (u) of each scanning position in the image coordinate system. i ,v i Based on the mapping relationship between the deflection voltage of the galvanometer 205 and the corresponding pixel coordinates, a transformation matrix is ​​used to map it to the physical space coordinate system; the position of the probe spot in the image is captured, and its physical space coordinates (x, y, y) are calculated. det, y det ), which is used as the geometric reference origin for acoustic wave scanning.

[0043] Step S30, Linear Scan: Based on the material properties of the sample and the testing requirements, a linear scan path is set in the central control module. This path is based on the coordinates of the detection point (x...). det, y det Using ) as the reference point, set the starting scan distance d. start Step interval d step The total number of scan points N is determined. The main control module activates the laser interferometric vibration measurement module 40 and the analog-to-digital converter 501 to begin real-time acquisition of the vibration waveform of the sample surface at the detection points. Subsequently, the laser scanning excitation module 20 is activated to begin scanning along a preset path. At each scan position, the visual positioning module 30 verifies the physical coordinates in real time by capturing the auxiliary indicator light spot. If the position deviation exceeds a preset threshold, the main control module uses a transformation matrix to perform closed-loop correction on the control voltage of the galvanometer 205 to ensure the step interval d. step The physical precision. Repeat the above process until N scans are completed, obtaining the result from... A two-dimensional spatiotemporal data matrix S(t,d) composed of ultrasonic waves.

[0044] Step S40, Multimodal sound velocity synchronous extraction: Computer 502 performs digital filtering and averaging on the acquired two-dimensional data matrix to improve the signal-to-noise ratio; performs time-frequency analysis on the scanned signal to identify and distinguish at least one of Rayleigh waves, Lamb waves, and longitudinal waves; for each identified mode, extracts its arrival time t at different scanning distances d, performs linear fitting on multiple sets of data points, and the slope of the fitted line is the surface sound velocity V of that mode on the current material surface:

[0045] ,

[0046] Where Δd represents the change in scanning distance and Δt represents the change in arrival time; finally, the sound velocity measurement results of multiple modes are output synchronously.

[0047] like Figure 4 As shown, in this embodiment, the surface wave velocity in the aluminum block was measured to be 2727.60 m / s, and the longitudinal wave velocity was 5726.05 m / s. The nominal surface wave velocity of the measured aluminum block is approximately 2890 m / s, and the longitudinal wave velocity is approximately 6170 m / s. The error rate remained within 10%, and the errors mainly originated from minor errors in galvanometer positioning and minor interferences from sample surface roughness and environmental vibrations on the interferometer. Within the allowable error range, it can be considered that the system fully verifies the high accuracy and reliability of the system of the present invention in the synchronous extraction of multimodal sound velocities. The determination coefficient R of the linear fitting in this embodiment is... 2 The result, exceeding 0.99, verifies the high stability of this detection system and method.

[0048] The system involved in this embodiment has extremely strong adaptability to component thickness. When the sample to be tested is changed from a thick block to a thin plate structure (such as a metal plate with a thickness on the order of millimeters), due to the change in the boundary conditions for sound wave propagation, the broadband ultrasonic waves excited by the system interfere within the plate, thus converting into Lamb waves. At this time, the data back-end processing module 50 performs a two-dimensional Fourier transform on the acquired spatiotemporal two-dimensional data matrix S(t,d), etc. Time-frequency domain analysis can effectively decouple and extract the dispersion characteristics of the symmetric mode S0 and the asymmetric mode A0 of the Lamb wave, thereby simultaneously measuring the sound velocity of different modes. This fully demonstrates the versatility of this invention in multimodal nondestructive testing of various structural components.

Claims

1. A multimodal surface sound velocity synchronous detection system based on laser ultrasound, characterized in that, It includes a central control module (10), a laser scanning excitation module (20), a visual positioning module (30), a laser interferometric vibration measurement module (40), and a data back-end processing module (50); the output of the central control module (10) is connected to the input of the laser scanning excitation module (20) and the input of the laser interferometric vibration measurement module (40), the output of the visual positioning module (30) is connected to the input of the central control module (10) and the data back-end processing module (50), and the output of the laser interferometric vibration measurement module (40) is connected to the input of the data back-end processing module (50); The main control module (10) is used to control the laser scanning excitation module (20) to emit scanning pulses to excite the laser, and to start the laser interferometric vibration measurement module (40), coordinating the ultrasonic excitation of the laser scanning excitation module (20) and the detection timing of the laser interferometric vibration measurement module (40); The laser scanning excitation module (20) is used to scan and irradiate the surface of the sample under test along a preset direction with a set step size, thereby exciting broadband multimodal surface acoustic waves on the surface of the sample under test. The visual positioning module (30) is used to capture the spatial coordinate changes of each scanning step and process the coordinate data and feed it back to the main control module (10) to achieve position closed-loop calibration. The laser interferometric vibration module (40) is used to emit probe light to the surface of the sample to be tested to capture surface vibration signals, and to make the probe light carrying vibration information form an interference signal with the reference light, and then output the interference signal after converting it into an electrical signal. The data back-end processing module (50) is used to extract multimodal surface sound velocity by recognizing the characteristics of different modal acoustic waves and combining the information on the change of scanning position and the time of flight of the sound waves. The main control module (10) includes a timing controller (101) and an electromechanical controller (102); the electromechanical controller (102) drives the laser scanning excitation module (20) to perform step scanning according to the instructions of the timing controller (101), and compensates the deflection angle of the galvanometer (205) in the laser scanning excitation module (20) in real time according to the coordinate information fed back by the visual positioning module (30); The visual positioning module (30) includes an auxiliary continuous laser (301), a camera (302), and a coordinate calibration module; The auxiliary beam emitted from the auxiliary continuous laser (301) is reflected by the first dichroic mirror (203) to the second dichroic mirror (204) and combined with the excitation beam. Then, it is reflected by the galvanometer (205) and the field mirror (206) on the sample surface along with the ambient light in the field of view. After passing through the field mirror (206) and the galvanometer (205), it is reflected by the second dichroic mirror (204) to the photosensitive surface of the camera (302). The camera (302) acquires a coaxial image containing the spot of the auxiliary beam and the ambient light. The coordinate calibration module is used to identify the pixel coordinates of the spot in the image and convert them into physical space coordinate information, which is then output to the main control module (10) and the data back-end processing module (50).

2. The system according to claim 1, characterized in that, The laser scanning excitation module (20) includes a pulsed laser (201), an isolator (202), a first dichroic mirror (203), a second dichroic mirror (204), a galvanometer (205), and a field mirror (206). The pulsed laser (201) emits an excitation laser beam, which is transmitted through the isolator (202), the first dichroic mirror (203), and the second dichroic mirror (204) to the galvanometer (205). The galvanometer (205) receives the control signal from the main control module (10) and deflects to change the reflection angle, so that the laser beam is vertically focused by the field mirror (206) to a specified position on the surface of the sample to be tested, forming a scanning excitation source that steps along a fixed direction.

3. The system according to claim 1, characterized in that, The laser interferometric vibration measurement module (40) includes a laser interferometer (401) and a probe (402). The laser interferometer (401) receives the control signal from the main control module (10) and emits a probe laser. The probe laser is focused onto the surface of the sample to be measured by the probe (402). The probe light carrying the vibration information of the sample surface is reflected back to the probe (402) and collected by the laser interferometer (401). An interference signal is generated inside the laser interferometer (401) and an electrical signal is output to the data back-end processing module (50).

4. The system according to claim 3, characterized in that, The data back-end processing module (50) includes an analog-to-digital converter (501) and a computer (502). The analog-to-digital converter (501) converts the analog electrical signals collected by the laser interferometric vibration measurement module (40) into digital signals and transmits them to the computer (502). The computer (502) identifies the characteristics of different modes of sound waves, analyzes the relationship between spatial coordinate changes and flight time, and extracts multimodal sound speed information simultaneously.

5. A method for synchronous detection of multimodal surface sound velocity using laser ultrasound based on the system described in claim 4, characterized in that, include: Step S100: Fix the sample to be tested, install the laser scanning excitation module (20), and complete the optical path alignment; Start the main control module (10) to perform zero-point reset of the galvanometer (205) in the laser scanning excitation module (20); turn on the auxiliary continuous laser (301) to perform boundary calibration field range with the preset effective scanning range; adjust the laser interferometric vibration measurement module (40) so that the detection spot falls into the effective scanning range; In step S200, the main control module drives the galvanometer (205) to control the auxiliary indicator light to perform array scanning within the effective field of view, and the visual positioning module (30) acquires the pixel center coordinates of each scanning position in the image coordinate system. Based on the mapping relationship between the deflection voltage of the galvanometer (205) and the corresponding pixel coordinates, the transformation matrix is ​​used to map it to the physical space coordinate system; the position of the probe spot in the image is captured, and its physical space coordinates are calculated. ), and use it as the geometric reference origin for the acoustic wave scan; Step S300: Based on the material properties and testing requirements of the sample to be tested, a linear scanning path is set in the main control module (10); this path is based on the coordinates of the detection point (x... det, y det Using ) as the reference point, set the starting scan distance d. start Step interval d step The total number of scanning points N; the control module (10) starts the laser interferometric vibration measurement module (40) and the analog-to-digital converter (501) to start real-time acquisition of the vibration waveform of the sample surface in the detection point, and then starts the laser scanning excitation module (20) to start scanning along the preset path to obtain a spatiotemporal two-dimensional data matrix S(t,d) composed of N surface ultrasonic waveforms, where d is the scanning distance and t is the arrival time of the scan; Step S400: The computer (502) performs time-frequency analysis on the acquired two-dimensional data matrix, identifies and distinguishes at least one of Rayleigh waves, Lamb waves, and longitudinal waves in the signal; for each identified mode, it extracts its arrival time t at different scanning distances d, performs linear fitting on multiple sets of data points, and the slope of the fitted line is the surface sound velocity V of that mode on the current material surface. ， Where Δd represents the change in scanning distance and Δt represents the change in arrival time; finally, the sound velocity measurement results of multiple modes are output synchronously.

6. The method according to claim 5, characterized in that, In step S300, at each scanning position, the visual positioning module (30) verifies the physical coordinates in real time by capturing the auxiliary indicator light spot; if the position deviation exceeds the preset threshold, the main control module (10) uses the transformation matrix to perform closed-loop correction on the galvanometer control voltage to ensure the step interval d. step Physical precision.

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