A multi-point excitation laser-ultrasonic non-destructive testing device and method

Abstract

This invention discloses a multi-point excitation laser ultrasonic nondestructive testing device and method. The invention includes a laser ultrasonic excitation system, an ultrasonic signal detection system, a computer control and processing system, and a two-dimensional scanning system. The laser ultrasonic excitation system splits a single-point pulsed laser into multi-point excitation lasers via optical fiber, achieving multi-point excitation of ultrasonic signals. The ultrasonic signal detection system detects, preprocesses, and collects multiple ultrasonic signals containing information about the sample under test. The computer control and processing system controls the start and stop of the laser ultrasonic excitation system, the working state of the ultrasonic signal detection system, and the movement of the two-dimensional scanning system. By processing the ultrasonic signals, the material property parameters of the sample under test are obtained. This method simultaneously excites ultrasonic waves on the sample surface using multi-point lasers and detects and collects the ultrasonic signals, enabling the analysis and determination of basic material property parameters such as sample thickness, Poisson's ratio, and wave velocity without prior knowledge.

Description

Technical Field

[0001] This invention relates to the field of laser ultrasonic nondestructive testing technology, specifically to a laser ultrasonic nondestructive testing device and method based on multi-point excitation. This invention utilizes laser pulses to form different forms of spatial array excitation on the surface of the sample under test, including single-point excitation, four-point array excitation, sixteen-point array excitation, and other multi-point array excitation methods. The spatial distribution of the excitation laser is controlled to optimize the ultrasonic wave propagation mode.

[0002] By combining a single-point non-contact ultrasonic signal receiving method, the response signals after the interaction of ultrasonic waves generated by multiple excitation sources are collected, processed, and analyzed. This allows for the detection and characterization of material properties of the sample under test without prior knowledge. This invention is applicable to non-contact material performance evaluation and non-destructive testing of metal sheets and other isotropic solid structures. Background Technology

[0003] Laser ultrasonic testing technology is a non-contact, non-destructive testing method that uses pulsed lasers to excite ultrasonic waves and receives the ultrasonic response signals using optical or non-optical methods. It has significant advantages such as no need for coupling agents, no probe wear, wide frequency response bandwidth, and high spatial resolution.

[0004] Compared to traditional contact ultrasonic testing, this technology fundamentally eliminates the interference of coupling agent state and contact pressure changes on the stability of the detection signal. Therefore, it is particularly suitable for in-service testing in harsh conditions such as high-temperature environments, high-speed moving components, strong radiation exposure, and confined or inaccessible spaces. Meanwhile, laser ultrasonic testing exhibits excellent geometric adaptability to complex curved surfaces, thin-walled structures, and micro-sized devices, enabling efficient and rapid characterization of internal material defects, surface conditions, and near-surface mechanical properties. It has become an important development direction in the field of advanced nondestructive testing.

[0005] In recent years, laser ultrasonic testing technology has been widely used in material composition analysis, defect identification and quantification, evaluation of mechanical properties such as elastic constants and strength, monitoring of service damage evolution, and real-time tracking of phase transformation processes.

[0006] In typical application scenarios such as key structures of aerospace vehicles, pressure-bearing components of nuclear energy equipment, lightweight automotive parts, and advanced electronic packaging interconnect structures, the use of laser ultrasound for online and real-time detection not only helps to improve product quality and service safety, but also provides effective data support for process parameter optimization, manufacturing cost control, and material utilization improvement.

[0007] With the continuous advancement of high-performance materials and intelligent manufacturing technologies, the industry's demand for rapid, accurate, and non-contact measurement capabilities of material property parameters is becoming increasingly urgent, further promoting the research and application of laser ultrasonic testing technology and related equipment.

[0008] Existing single-point excitation laser ultrasonic testing methods, when measuring basic material properties, mostly employ pulse-echo or transmission methods, relying primarily on bulk wave propagation time for parameter inversion. These methods typically require prior knowledge of the longitudinal or transverse wave velocities in the material to further calculate parameters such as sample thickness and Poisson's ratio; or they require known sample thickness to inversely deduce the sound velocity and other mechanical parameters. Therefore, when the sound velocity and thickness of the sample are unknown, traditional methods often struggle to achieve simultaneous multi-parameter measurements, significantly limiting their application, especially for the rapid characterization of unknown materials or in-service components.

[0009] To overcome the aforementioned shortcomings, the multi-point excitation laser ultrasonic testing method constructs a spatially periodically distributed excitation array. Utilizing the coherent superposition effect between excitation sources, it selectively excites surface wave and guided wave zero-group velocity resonance modes. Combined with single-point non-contact reception and spectral analysis techniques, it can simultaneously obtain fundamental characteristic parameters of the material, such as longitudinal and transverse wave velocities, Poisson's ratio, and thickness, without prior knowledge of the material's sound velocity or sample thickness. This testing device and method not only broaden the applicability of laser ultrasonic non-destructive testing but also provide a new technical means for performance evaluation and condition monitoring of unknown materials and complex structures, demonstrating significant engineering application prospects and widespread value. Summary of the Invention

[0010] The purpose of this invention is to provide a multi-point excitation laser ultrasonic non-destructive testing device and method, which can realize the function of detecting the material characteristic parameters of the sample by multi-point excitation and single-point detection.

[0011] To achieve the above objectives, the present invention provides a multi-point excited laser ultrasonic nondestructive testing device, comprising a laser ultrasonic excitation system, an ultrasonic signal detection system, a computer control and processing system, and a two-dimensional scanning system, wherein:

[0012] The laser ultrasonic excitation system divides a single-point pulse laser into a multi-point excitation laser through an optical fiber. The array of multi-point excitation lasers simultaneously excites multiple ultrasonic signals on the sample surface, thus achieving multi-point excitation.

[0013] The ultrasonic signal detection system enables the detection, preprocessing, and collection of multiple ultrasonic signals containing test information of the sample;

[0014] The computer control and processing system controls the start and stop of the laser ultrasonic excitation system, controls the working status of the ultrasonic signal detection system, and controls the movement of the two-dimensional scanning system. By processing the ultrasonic signals, the material property parameters of the sample under test are obtained.

[0015] The two-dimensional scanning system consists of a two-dimensional scanning platform, a two-dimensional scanning platform driver, and a scanning controller, and achieves scanning imaging by moving the sample.

[0016] Furthermore, the laser ultrasonic excitation system includes a picosecond pulse laser, a focusing lens I, a beam splitter fiber, a fiber optic clamp, a polarizing beam splitter I, a quarter-wave plate I, a sleeve lens, and an objective lens.

[0017] A single laser beam emitted from a picosecond pulse laser is split into multiple laser beams by focusing lens I and a beam-splitting fiber. Fiber optic clamps control the relative positions of these multiple laser beams, resulting in a square array distribution. The combination of polarizing beam splitter I and quarter-wave plate I ensures that the direction of the multiple laser beams is limited to the sample, but the laser reflected from the sample does not return to the picosecond pulse laser, thus avoiding impact on laser performance. The multiple laser beams, after passing through the combination of polarizing beam splitter I and quarter-wave plate I, directly enter a sleeve lens, which transforms the active source of the multiple laser beams into an infinity source. The objective lens scales down the square array distribution of the multiple laser beams into an even smaller square array distribution before striking the sample surface, simultaneously exciting a superimposed signal of multiple ultrasonic signals on the sample surface.

[0018] Furthermore, the ultrasonic signal detection system includes a continuous probe laser, an optical fiber, a polarizing beam splitter II, a quarter-wave plate II, a focusing lens II, a Fabry-Perot interferometer cavity, a focusing lens III, a magnifying photodetector, a bandpass filter, an amplifier, and an oscilloscope.

[0019] A continuous probe laser emits a continuous probe laser, which is connected to a fiber optic clamp in a laser ultrasonic excitation system via an optical fiber. The fiber optic clamp controls the probe laser to be positioned at the center of the square array of excitation lasers. The probe laser reflected from the sample surface passes through a quarter-wave plate I, a polarizing beam splitter I, a polarizing beam splitter II, a quarter-wave plate II, a focusing lens II, and reaches a Fabry-Perot interferometer cavity. The probe laser reflected from the Fabry-Perot interferometer cavity then passes through a quarter-wave plate II, a polarizing beam splitter II, a focusing lens III, and reaches a magnified photodetector for reception. The received signal is preprocessed by a bandpass filter and an amplifier, and then collected by an oscilloscope.

[0020] Furthermore, the main functions of the computer control and processing system are to control the start and stop of the laser ultrasonic excitation system, control the start and stop of the pulsed laser through computer software, set the pulse energy and repetition frequency of the pulsed laser, and monitor the working status of the pulsed laser; control the on-cavity voltage of the Fabry-Perot interferometer cavity through a PID control program, so that the working state of the ultrasonic signal detection system is in a sensitive state; control the movement of the scanning platform in the two-dimensional scanning system through a motion control program; and obtain the material property parameters of the sample under test by processing the ultrasonic signal.

[0021] Furthermore, the two-dimensional scanning system includes a two-dimensional scanning platform, a two-dimensional scanning platform driver, and a scanning controller. The scanning controller is connected to a computer control and processing system.

[0022] The computer control and processing system controls the two-dimensional scanning platform driver through the motion control program, and further controls the scanning speed and scanning range of the two-dimensional scanning platform.

[0023] Furthermore, the aforementioned beam-splitting fiber couples the spatial laser emitted from the picosecond pulse laser into a single-beam end of the beam-splitting fiber via a focusing lens. The spatial laser at the single-beam end is then split into 4, 16, or even more beams by the beam-splitting fiber before being emitted. fiber bundle, (Greater than or equal to 1), the outer diameter of each fiber at the multi-bundle end of the split fiber matches the diameter of the array of circular holes in the center of the fiber clamp.

[0024] Furthermore, the fiber optic clamp is made of resin board with an array of circular holes in the center. The diameter of the circular holes matches the outer diameter of the fiber optic cable. The central circular hole of the fiber optic clamp is the fixed position of the probe fiber, and the surrounding array of circular holes is the fixed position of the excitation fiber. The four corners of the fiber optic clamp are provided with mounting holes, and it is installed into the optical cage system through an adapter.

[0025] Furthermore, the fiber optic clamp adapter allows the fiber optic clamp to be directly connected to the adapter, and the adapter can be directly connected to the optical cage system.

[0026] Furthermore, the two-dimensional scanning platform consists of a servo motor and a grating ruler. The servo motor is connected to the moving parts of the platform and to the two-dimensional scanning platform driver. The grating ruler is set in the direction of platform movement and is connected to the two-dimensional scanning platform driver. The two-dimensional scanning platform driver is connected to the scanning controller and receives control from the scanning controller. Closed-loop control is adopted to achieve high-precision two-degree-of-freedom movement.

[0027] Based on the aforementioned multi-point excitation laser ultrasonic nondestructive testing device, the present invention also provides a multi-point excitation laser ultrasonic nondestructive testing method, comprising the following steps:

[0028] S1. Fix the sample on the two-dimensional scanning platform;

[0029] S2. Set the motion trajectory of the two-dimensional scanning platform in the specified area in the computer control and processing system, set the laser parameters, and turn on the pulsed laser.

[0030] S3. Emit an excitation laser to generate an ultrasonic signal on the sample surface, and collect the ultrasonic signal using an ultrasonic signal detection system. If the ultrasonic signal intensity is lower than the set threshold, adjust the parameters of the picosecond pulse laser and repeat the experiment.

[0031] S4. Process the collected ultrasonic signals and calculate the basic material properties of the sample, such as thickness, Poisson's ratio, and wave velocity, using the ultrasonic parameter inversion method based on zero group velocity resonance.

[0032] S5. Set the motion trajectory of the 2D scanning platform and complete the detection of all areas.

[0033] Furthermore, in the multi-point excitation laser ultrasonic nondestructive testing method, the simultaneous excitation of multiple points causes the generated ultrasonic signals to superimpose, resulting in a zero group velocity resonance phenomenon with a stronger resonance amplitude. By processing the ultrasonic signals, the material characteristic parameters of the sample are obtained.

[0034] The advantages of this invention over the prior art are as follows: First: Achieve synchronous representation of multiple parameters without prior knowledge.

[0035] Traditional single-point laser ultrasonic testing relies on the propagation time of volume waves to perform parameter inversion, which cannot be decoupled for measurement when the sound velocity and thickness of the material are unknown.

[0036] This invention employs a multi-point array excitation method, utilizing the superimposed ultrasonic fields generated by spatially periodically distributed excitation sources to form a zero-group velocity resonance enhancement effect. Combined with single-point non-contact reception and spectrum analysis, it can simultaneously invert basic characteristic parameters such as longitudinal wave velocity, transverse wave velocity, Poisson's ratio, and thickness without prior knowledge of the sound velocity or thickness, effectively overcoming the parameter coupling limitations of traditional methods.

[0037] Second: The detection mode is flexible and adjustable, and has strong applicability.

[0038] This invention can switch between single-point, four-point, and sixteen-point array modes through optical path control.

[0039] The single-point mode is suitable for routine benchmark scanning, while the four-point and sixteen-point array modes can improve excitation energy and spectral signal-to-noise ratio, meeting the diverse needs of different detection objects, from thin plate materials to high-attenuation components.

[0040] Third: Significantly enhances the zero-group velocity resonance amplitude, broadening the scope of engineering applications.

[0041] This invention utilizes the ultrasonic superposition effect generated by the excitation source to effectively enhance the amplitude of the zero-group velocity resonance frequency response signal compared to traditional excitation methods. This improves the accuracy and repeatability of resonance feature extraction and enables stable operation in complex environments, providing reliable technical support for practical engineering applications such as online monitoring of plate thickness, material quality evaluation, and coating quality inspection. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the device system structure according to an embodiment of the present invention.

[0043] Figure 2 This is a schematic diagram of a laser ultrasonic excitation system according to an embodiment of the present invention.

[0044] Figure 3 This is a schematic diagram of an optical fiber clamp according to an embodiment of the present invention.

[0045] Figure 4 This is a schematic diagram of an optical fiber clamp adapter according to an embodiment of the present invention.

[0046] Figure 5 This is a schematic diagram of an ultrasonic signal detection system according to an embodiment of the present invention.

[0047] Figure 6 This is an optical path diagram of the Fabry-Perot interferometer cavity according to an embodiment of the present invention.

[0048] Figure 7 This is a schematic diagram of the optical path for multi-point excitation laser ultrasonic detection according to an embodiment of the present invention.

[0049] Figure 8 This is a flowchart of the detection steps according to an embodiment of the present invention.

[0050] Figures 9-12 This is the result of ultrasound signal analysis according to one embodiment of the present invention. Detailed Implementation

[0051] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention. The invention will be specifically described below with reference to the accompanying drawings and embodiments.

[0052] like Figure 1 The diagram shown is a schematic diagram of the device system structure according to an embodiment of the present invention.

[0053] It includes a laser ultrasonic excitation system, an ultrasonic signal detection system, a computer control and processing system, and a two-dimensional scanning system.

[0054] The system comprises: a laser ultrasonic excitation system that splits a single-point pulsed laser into multi-point excitation lasers via optical fiber; and an array of these multi-point excitation lasers simultaneously generate multiple ultrasonic signals on the sample surface, achieving multi-point excitation. An ultrasonic signal detection system detects, preprocesses, and collects these multiple ultrasonic signals containing the sample's test information. A computer control and processing system controls the start and stop of the laser ultrasonic excitation system, the operating state of the ultrasonic signal detection system, and the movement of the two-dimensional scanning system. By processing the ultrasonic signals, the material property parameters of the sample are obtained. The two-dimensional scanning system consists of a two-dimensional scanning platform, a two-dimensional scanning platform driver, and a scanning controller, achieving scanning imaging through sample movement.

[0055] like Figure 2 The diagram shown is a schematic diagram of a laser ultrasonic excitation system according to an embodiment of the present invention.

[0056] A picosecond pulsed laser emits an excitation laser beam, which is focused by a focusing lens, reducing the laser spot size and efficiently coupling it into a beam-splitting fiber. The beam-splitting fiber distributes the single laser beam into multiple output lasers, transforming the excitation from single-point excitation to multi-point array excitation. The multi-beam ends of the beam-splitting fiber are fixed to fiber optic clamps. By constraining and adjusting the positions of each output port, multiple output beams are arranged in a preset spatial pattern to form an array excitation laser, thereby achieving synchronous excitation of multiple regions on the sample surface. The array excitation laser sequentially passes through a polarizing beam splitter I, a quarter-wave plate I, a sleeve lens, and an objective lens, generating ultrasonic signals on the sample surface.

[0057] The polarizing beam splitter I is used to transmit the excitation laser with a specific polarization direction and separate the returning light, isolating the excitation optical path from the subsequent detection optical path and preventing reflected light from entering the laser. The quarter-wave plate I is used to change the polarization state of the laser. When the linearly polarized laser passes through the quarter-wave plate I, it becomes circularly polarized light. When the laser is reflected from the sample surface and passes through the quarter-wave plate I again, its polarization direction is further rotated, causing the polarization direction of the returning laser to differ from that of the incident laser. This prevents the returning light from passing through the polarizing beam splitter I along the original optical path and entering the picosecond pulse laser, effectively avoiding damage to the internal optical components of the laser caused by reflected laser light.

[0058] The sleeve lens is used for relay transmission and beam adjustment of the array-excited laser. By changing the beam propagation characteristics, it allows the array beam to enter the objective lens with a suitable size and divergence angle. The objective lens is used to further focus the array-excited laser, increase the laser energy density, and allow multiple focused beams to act on the sample surface according to a predetermined array distribution.

[0059] like Figure 3 The diagram shown is a schematic diagram of an optical fiber clamp according to an embodiment of the present invention.

[0060] The circular holes arranged in the central square array are the fixed positions for the multi-beam ends of the split fiber, and the central circular hole is the fixed position for the fiber output port of the continuous laser in the detection module. The circular holes at the four corners are used to connect the fiber clamps and clamp adapters. The diameter of the circular holes at the fiber port fixing positions matches the outer diameter of the fiber, and the diameter of the circular holes connecting the fiber clamps and adapters matches the outer diameter of the fiber. The left figure is a schematic diagram of a four-point excitation fiber clamp, and the right figure is a schematic diagram of a sixteen-point excitation fiber clamp.

[0061] like Figure 4 The diagram shown is a schematic of an optical fiber clamp adapter according to an embodiment of the present invention.

[0062] The four internal circular holes connect to the fiber optic clamps, and the four corner circular holes are used to connect the adapter to the optical cage system. The diameter of the four corner circular holes matches the outer diameter of the optical connecting rod.

[0063] like Figure 5 The diagram shown is a schematic diagram of an ultrasonic signal detection system according to an embodiment of the present invention.

[0064] The selected continuous probe laser is an optical fiber output laser. The continuous probe laser emits a probe laser, and the optical fiber of the output laser is directly fixed at the corresponding position of the optical fiber clamp. The probe laser passes through polarizing beam splitter I, quarter-wave plate I, sleeve lens, and objective lens. On the surface of the sample, the ultrasonic signal generated by array excitation is modulated and reflected, and then passes through objective lens, sleeve lens, quarter-wave plate I, and polarizing beam splitter I.

[0065] Because the reflected probe laser passes through quarter-wave plate I twice, its polarization state changes, causing the polarization direction of the returning light to be different from that of the incident light. Therefore, the reflected probe laser cannot return to the continuous probe laser along the original path. Instead, it undergoes polarization separation at polarization beam splitter I and enters the subsequent signal processing optical path. It then passes through polarization beam splitter II, quarter-wave plate II, and focusing lens II before entering the Fabry-Perot interferometer cavity, thus avoiding interference or damage to the continuous probe laser caused by the reflected light.

[0066] After the probe laser enters the Fabry-Perot interferometer cavity, it undergoes multiple reflections and interferences between two reflecting surfaces inside the cavity. The phase change of the probe laser caused by the ultrasonic signal is converted into a change in the intensity of the interference light, thus achieving optical demodulation of the ultrasonic signal.

[0067] After the interference output light carrying ultrasonic information exits the interference cavity, it passes through quarter-wave plate II again. Due to the two passes through quarter-wave plate II, its polarization state changes, so the output light cannot return to polarization beam splitter I along the original path through polarization beam splitter II. Instead, it passes through focusing lens III and enters the magnified photodetector to collect the detection laser signal containing ultrasonic signal.

[0068] The amplified photodetector converts the optical signal containing ultrasonic information into an electrical signal and initially amplifies the weak signal to improve signal detection sensitivity. The signal collected by the amplified photodetector is then passed through a bandpass filter for frequency band selection to filter out non-target frequency noise. Subsequently, the signal amplitude is enhanced by an amplifier, and finally input into an oscilloscope for acquisition and display, realizing the detection and analysis of laser ultrasonic signals.

[0069] like Figure 6 The diagram shown is an optical path diagram inside a Fabry-Perot interferometer cavity according to an embodiment of the present invention.

[0070] The Fabry-Perot interferometer cavity consists of two spherical mirrors (M1 and M2) with the same radius. The concave surfaces of the two mirrors face each other and are arranged along the same optical axis to form a stable optical resonator structure.

[0071] When the laser beam enters from position 3, it undergoes four reflections and then exits from position 3 again, continuously repeating this process. During this cycle, the outgoing light beams on different propagation paths within the cavity superimpose, forming multiple coherent beams that overlap at position 1, thereby enhancing the intensity of the outgoing beam at that position. Simultaneously, other outgoing beams are formed at positions 2, 3, and 4. Positions 1 and 2 are transmitted light, while positions 3 and 4 are reflected light. This invention selects reflected light for ultrasonic detection. Since the reflected light carries phase modulation information caused by the ultrasonic signal within the Fabry-Perot interferometer cavity, by collecting and analyzing the reflected output light, the phase change of the probe laser caused by ultrasonic vibration on the sample surface can be converted into a detectable change in light intensity, achieving high-sensitivity detection of the ultrasonic signal.

[0072] like Figure 7 The diagram shown is a schematic of the optical path for multi-point excitation laser ultrasonic detection according to an embodiment of the present invention.

[0073] In the excitation optical path, the lasers emitted by the picosecond pulse laser and the continuous probe laser are coupled to the splitting fiber and the optical fiber, respectively, and the other ends of the splitting fiber and the optical fiber are fixed to... Figure 3 In the fiber optic fixture shown, a square array is formed, with the probe laser at the center and the excitation laser around the perimeter. The laser beam then passes through optical elements in the excitation path, including a quarter-wave plate I, a polarizing beam splitter I, a sleeve lens, and an objective lens, before striking the sample. After reflection, the laser beam enters the probe path and interferes in the Fabry-Perot interferometer cavity. The interference signal is reflected from the cavity and carries an ultrasonic signal generated by multiple excitation points. This signal is received by a magnified photodetector, pre-processed by a bandpass filter and amplifier, and then enters an oscilloscope. Finally, the signal is imported into a computer-controlled processing system for thorough analysis.

[0074] like Figure 8 The diagram shown is a flowchart of the detection steps according to an embodiment of the present invention.

[0075] First, the sample to be tested is fixed on a two-dimensional scanning platform. The two-dimensional scanning area and scanning trajectory are set in the computer control and processing system. The excitation parameters of the pulsed laser, including laser energy, pulse width, and repetition frequency, are set according to the material type of the sample and the testing requirements. The pulsed laser is then activated to generate a laser ultrasonic signal on the surface of the sample. An ultrasonic signal detection system is used to collect the surface response signal of the sample, and the collected ultrasonic signal is transmitted to the computer control and processing system for analysis and processing.

[0076] The computer-controlled processing system first determines whether the signal-to-noise ratio or signal strength of the acquired signal meets the preset requirements. If the signal strength is insufficient, the pulsed laser parameters are adjusted, and laser excitation and signal acquisition are repeated until an ultrasonic signal meeting the analysis requirements is obtained. Once the signal at the current scanning position meets the requirements, feature extraction and material parameter calculation are performed on the ultrasonic signal at that position. Subsequently, it is determined whether data acquisition of all detection points within the preset scanning area has been completed. If not, the two-dimensional scanning platform is controlled to move to the next detection position, and the above detection steps are repeated. After all areas have been detected, the sample material characteristic parameters and detection results are output, and the detection process ends.

[0077] This further explains the theoretical basis for using a square dot array excitation method to generate laser ultrasonic signals and obtaining the material property parameters of the sample based on the detection signals.

[0078] This embodiment employs a two-dimensional periodic point array laser excitation method, forming multiple spatially periodically distributed laser excitation points on the surface of the sample under test. Observation of the time-domain signal clearly reveals that the detected ultrasonic signal exhibits two stages: transient response and steady-state resonance. Assume the excitation point array is evenly spaced along the x-direction, with a point spacing of [missing information]. The number of excitation points is N. After a single laser pulse is applied to the sample surface, a transient surface displacement response is generated due to the thermoelastic effect. Let the surface displacement response function generated by a single excitation point be: ; Since the laser ultrasonic propagation process follows a linear superposition relationship, the total surface displacement response generated by the periodic point array excitation is the superposition of the responses of each excitation point, that is: ; satisfy Constructive interference is generated at the wave mode, where k is the wave number and m is a positive integer. The point array can amplify the propagation speed of surface acoustic waves whose wavelength matches the period of the point array, satisfying the following condition: ; in The frequency of the surface acoustic wave is extracted from the transient response spectrum. Simultaneously, a zero-group velocity resonance mode is generated within the plate, and the dominant frequencies of the first and second zero-group velocity resonance peaks are measured. , The Poisson's ratio of the material can be determined from these two resonant frequencies: ;

[0079] in The frequency-Poisson's ratio correspondence established for Lamb wave theory. Further combining Poisson's ratio and surface acoustic wave velocity, the longitudinal wave velocity of the material can be calculated: ;

[0080] Transverse wave speed of sound: ;

[0081] The plate thickness is calculated from the resonant frequency of the first zero group velocity: ;

[0082] Therefore, parameters such as Poisson's ratio, longitudinal and transverse wave velocity, and thickness of the sample under test can be obtained through a single point array excitation and a single ultrasonic signal acquisition, providing a theoretical basis for subsequent two-dimensional scanning imaging and material performance evaluation.

[0083] like Figures 9-12 The image shows the ultrasound signal analysis results of one embodiment of the present invention.

[0084] In this embodiment, a 2mm thick 6061 aluminum alloy plate was used as the test sample. The sample was fixed on a two-dimensional scanning platform and tested at room temperature. A 1064 nm pulsed laser was used, with a pulse width of approximately 6 ns, a repetition frequency of 20 Hz, and a single pulse energy of approximately 2 mJ. All polarizing beam splitters, quarter-wave plates, sleeve lenses, and objectives in the laser ultrasonic excitation system were selected to be compatible with 1064 nm lasers. A 1550 nm continuous laser was used, and all polarizing beam splitters, quarter-wave plates, focusing lenses, and magnifying photodetectors in the ultrasonic signal detection system were selected to be compatible with 1550 nm lasers. The excitation laser, after passing through a beam-splitting fiber and fiber optic clamps, formed a square dot array excitation spot with a dot spacing of... The beam was set to 200 μm and the excitation beam was applied to the sample surface to excite surface acoustic waves and guided wave zero-group velocity resonance modes through the thermoelastic effect. 128 ultrasonic signals were continuously acquired and averaged to improve the signal-to-noise ratio. The acquired time-domain signals were then transmitted to a computer-controlled processing system for analysis.

[0085] The detected ultrasonic signal is a time-domain signal, such as... Figure 9 As shown, performing a Fourier transform on a time-domain signal can yield a signal in the frequency domain, such as... Figure 12Obvious zero-group velocity resonance peaks were observed. The frequencies of these peaks are related to material properties such as Poisson's ratio and the thickness of the sample. Among them, the dominant frequencies of the two zero-group velocity resonance peaks in the resonance spectrum are... and With frequencies of 1.43MHz and 4.66MHz respectively, a Poisson's ratio υ of 0.3394 can be obtained, representing the surface acoustic wave frequency in the transient spectrum. It is 14.496MHz.

[0086] Transient signals such as Figure 10 The resonant peak frequency is the lowest-order guided wave zero-group velocity resonant frequency. This method equates it to the surface acoustic wave frequency. The resonant signal is as follows: Figure 11 The resonant frequency is the zero-group velocity resonant frequency of a higher-order guided wave. When a transient signal frequency peak and two resonant signal frequency peaks can be separated, information such as the Poisson's ratio, longitudinal wave velocity, and thickness of the sample can be analyzed.

[0087] In this embodiment, the excitation square array distribution interval is set. For 200 Then the surface acoustic wave velocity is The transverse wave velocity is The longitudinal wave velocity is Thickness is .

[0088] Based on the aforementioned multi-point excitation laser ultrasonic nondestructive testing device, the present invention also provides a multi-point excitation laser ultrasonic nondestructive testing method, comprising the following steps: S1. Fix the sample on the two-dimensional scanning platform.

[0089] S2. Set the motion trajectory of the two-dimensional scanning platform in the specified area in the computer control and processing system, set the laser parameters, and turn on the pulsed laser.

[0090] S3. Emit an excitation laser to generate an ultrasonic signal on the sample surface, and collect the ultrasonic signal using an ultrasonic signal detection system. If the ultrasonic signal intensity is lower than the set threshold, adjust the parameters of the picosecond pulse laser and repeat the experiment.

[0091] S4. Process the collected ultrasonic signals and calculate the basic material properties of the sample, such as thickness, Poisson's ratio, and wave velocity, using the ultrasonic parameter inversion method based on zero group velocity resonance.

[0092] S5. Set the motion trajectory of the 2D scanning platform and complete the detection of all areas.

[0093] Furthermore, in the multi-point excitation laser ultrasonic nondestructive testing method, the simultaneous excitation of multiple points causes the generated ultrasonic signals to superimpose, resulting in a zero group velocity resonance phenomenon with a stronger resonance amplitude. By processing the ultrasonic signals, the material characteristic parameters of the sample are obtained.

[0094] This application also provides an electronic device, including a processor and a memory.

[0095] The memory is used to store computer programs.

[0096] When the processor executes a program stored in the memory, it implements any of the methods described in this application.

[0097] In one possible implementation, the electronic device of this application embodiment further includes a communication interface and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus.

[0098] The communication bus mentioned in the above electronic devices can be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. This communication bus can be divided into address bus, data bus, control bus, etc.

[0099] The communication interface is used for communication between the aforementioned electronic devices and other devices.

[0100] The memory may include random access memory (RAM) or non-volatile memory (NVM), such as at least one disk storage device. Optionally, the memory may also be at least one storage device located remotely from the aforementioned processor.

[0101] The processors mentioned above can be general-purpose processors, including central processing units (CPUs), network processors (NPs), etc.; they can also be digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0102] In another embodiment provided in this application, a computer-readable storage medium is also provided, which stores a computer program that, when executed by a processor, implements any of the methods described in this application.

[0103] In another embodiment provided in this application, a computer program product containing instructions is also provided, which, when run on a computer, causes the computer to perform any of the methods described in this application.

[0104] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., solid state disk (SSD)).

[0105] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0106] The various embodiments in this specification are described in a related manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referred to each other.

[0107] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. A multi-point excitation laser ultrasonic non-destructive testing device, characterized in that, It includes a laser ultrasonic excitation system, an ultrasonic signal detection system, a computer control and processing system, and a two-dimensional scanning system, among which: The laser ultrasonic excitation system divides a single-point pulse laser into a multi-point excitation laser through an optical fiber. The array of multi-point excitation lasers simultaneously excites multiple ultrasonic signals on the sample surface, thus achieving multi-point excitation. The ultrasonic signal detection system enables the detection, preprocessing, and collection of multiple ultrasonic signals containing test information of the sample; The computer control and processing system controls the start and stop of the laser ultrasonic excitation system, controls the working status of the ultrasonic signal detection system, and controls the movement of the two-dimensional scanning system. By processing the ultrasonic signals, the material property parameters of the sample under test are obtained. The two-dimensional scanning system consists of a two-dimensional scanning platform, a two-dimensional scanning platform driver, and a scanning controller, and achieves scanning imaging by moving the sample.

2. The multi-point excitation laser ultrasonic nondestructive testing device according to claim 1, characterized in that, The laser-ultrasonic excitation system includes a picosecond pulse laser, a focusing lens I, a beam splitter fiber, a fiber optic clamp, a polarizing beam splitter I, a quarter-wave plate I, a sleeve lens, and an objective lens; The single laser beam emitted from the picosecond pulse laser is split into multiple laser beams after passing through focusing lens I and beam splitting fiber; the fiber clamp is used to control the relative positions of the multiple laser beams, so that the multiple laser beams are distributed in a square array; the combination of polarizing beam splitter I and quarter-wave plate I ensures that the direction of the multiple laser beams can only be from the picosecond pulse laser to the sample, but the laser reflected from the sample will not return to the picosecond pulse laser. Multiple laser beams, after passing through the combination of polarizing beam splitter I and quarter-wave plate I, directly enter the sleeve lens, which transforms the active source of the multiple laser beams into an infinity source. The objective lens scales down the square array distribution of multiple laser beams to a smaller square array distribution and then projects it onto the sample surface, simultaneously exciting a superimposed signal of multiple ultrasonic signals on the sample surface.

3. The multi-point excitation laser ultrasonic nondestructive testing device according to claim 1, characterized in that, The ultrasonic signal detection system includes a continuous probe laser, an optical fiber, a polarizing beam splitter II, a quarter-wave plate II, a focusing lens II, a Fabry-Perot interferometer cavity, a focusing lens III, a magnifying photodetector, a bandpass filter, an amplifier, and an oscilloscope. The continuous probe laser emits a continuous probe laser, which is connected to the fiber optic clamp in the laser ultrasonic excitation system via an optical fiber. The fiber optic clamp controls the probe laser to be located at the center of the square array distribution of the excitation laser. The probe laser reflected from the sample surface passes through a quarter-wave plate I, a polarizing beam splitter I, a polarizing beam splitter II, a quarter-wave plate II, and a focusing lens II before reaching the Fabry-Perot interferometer cavity. The probe laser reflected from the Fabry-Perot interferometer cavity then passes through a quarter-wave plate II, a polarizing beam splitter II, and a focusing lens III before reaching the magnifying photodetector for reception. The received signal is preprocessed by the bandpass filter and the amplifier, and then collected by the oscilloscope.

4. The multi-point excitation laser ultrasonic nondestructive testing device according to claim 2, characterized in that, The aforementioned beam-splitting fiber couples spatial laser light emitted from a picosecond pulsed laser into a single beam end via a focusing lens. The spatial laser light at the single beam end is then split into beams by the beam-splitting fiber. fiber bundle, The outer diameter of each fiber at the multi-bundle end of the split fiber is greater than or equal to 1, and the diameter of the array of circular holes in the center of the fiber clamp is matched.

5. The multi-point excitation laser ultrasonic nondestructive testing device according to claim 3, characterized in that, The fiber optic clamp is made of resin board with an array of circular holes in the center. The diameter of the circular holes matches the outer diameter of the fiber optic cable. The central circular hole of the fiber optic clamp is the fixed position of the probe fiber, and the surrounding array of circular holes is the fixed position of the excitation fiber. The four corners of the fiber optic clamp are provided with mounting holes, and it can be installed into the optical cage system through an adapter.

6. The multi-point excitation laser ultrasonic nondestructive testing device according to claim 3, characterized in that, The fiber optic clamp adapter allows the fiber optic clamp to be directly connected to the adapter, and the adapter can be directly connected to the optical cage system.

7. The multi-point excitation laser ultrasonic nondestructive testing device according to claim 1, characterized in that, The two-dimensional scanning platform consists of a servo motor and a grating ruler. The servo motor is connected to the moving parts of the platform and to the two-dimensional scanning platform driver. The grating ruler is set in the direction of platform movement and is connected to the two-dimensional scanning platform driver. The two-dimensional scanning platform driver is connected to the scanning controller and receives control from the scanning controller. Closed-loop control is adopted to achieve high-precision two-degree-of-freedom movement.

8. A multi-point excitation laser ultrasonic nondestructive testing method, characterized in that, This method is used to implement the system as described in claim 1, and includes the following steps: S1. Fix the sample on the two-dimensional scanning platform; S2. Set the motion trajectory of the two-dimensional scanning platform in the specified area in the computer control and processing system, set the laser parameters, and turn on the pulsed laser. S3. Emit an excitation laser to generate an ultrasonic signal on the sample surface, and collect the ultrasonic signal using an ultrasonic signal detection system. If the ultrasonic signal intensity is lower than the set threshold, adjust the parameters of the picosecond pulse laser and repeat the experiment. S4. Process the collected ultrasonic signals and calculate the basic material properties of the sample, such as thickness, Poisson's ratio, and wave velocity, using the ultrasonic parameter inversion method based on zero group velocity resonance. S5. Set the motion trajectory of the 2D scanning platform and complete the detection of all areas.

9. The multi-point excitation laser ultrasonic nondestructive testing method as described in claim 8, characterized in that, Simultaneous excitation at multiple points causes the generated ultrasonic signals to superimpose, resulting in a zero-group velocity resonance phenomenon with a stronger resonance amplitude. By processing the ultrasonic signals, the material characteristic parameters of the sample can be obtained.

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