A laser-ultrasonic non-destructive testing system
Patent Information
- Application Number
- CN202611218919.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-12
- Publication Date
- 2026-10-27
AI Technical Summary
由于箔材极薄、层数多，传统接触式超声检测易造成薄箔形变损伤，耦合剂易污染极片；射线检测对层间虚焊、脱层等面积型缺陷检出率低；涡流检测仅能评估表面状态，无法反映深层焊接质量
[0026]完全非接触、无需耦合剂：采用脉冲激光激励超声波、连续探测激光接收超声信号，全过程无需液体或固体耦合剂，避免了耦合剂对工件（特别是电池极耳薄箔材）的污染或损伤，也适用于高温、高压或禁止接触液体的检测环境。
Smart Images
Figure CN122983209A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of nondestructive testing technology, and in particular to a laser ultrasonic nondestructive testing system. Background Technology
[0002] Conventional nondestructive testing techniques (such as ultrasonic testing, radiographic testing, and eddy current testing) have been widely used in many industrial fields, but they still have limitations in certain special engineering situations. For example, in in-service testing under high temperature, high pressure, high corrosion, and high radiation environments, and in situations where the use of liquid coupling agents is not allowed, traditional ultrasonic testing cannot be applied because it requires coupling agents; radiographic testing has radiation protection requirements and is not sensitive to area defects; eddy current testing is only suitable for conductive materials and is sensitive to near-surface defects.
[0003] Laser ultrasonic testing, as a novel non-destructive testing method, utilizes pulsed lasers to generate ultrasonic waves within the workpiece being tested, and employs another laser beam to detect the propagation of these waves, thereby acquiring information about internal defects. This technology eliminates the need for liquid coupling agents, enabling long-distance, non-contact testing and meeting the non-destructive testing requirements of workpieces subjected to high temperatures, high pressures, and those that cannot come into contact with liquids. However, existing laser ultrasonic receiving solutions generally suffer from insufficient sensitivity to weak vibrations, poor environmental immunity, and insufficient long-term operational stability. Furthermore, the testing effectiveness for ultra-thin, multi-layered structures still needs improvement.
[0004] In the field of new energy power battery manufacturing, electrode tab welding (including ultrasonic welding and laser welding) is a key process in battery assembly. Typically, 40 to 80 layers of extremely thin metal foil (approximately 4 μm thick for copper foil and 12 μm thick for aluminum foil) need to be welded to the electrode post or adapter plate. Due to the extremely thin foil and numerous layers, traditional contact ultrasonic testing easily causes deformation damage to the thin foil, and coupling agent easily contaminates the electrode sheet; X-ray testing has a low detection rate for area-type defects such as interlayer cold solder joints and delamination; eddy current testing can only assess the surface condition and cannot reflect the quality of deep welds. Therefore, there is an urgent need for a non-contact non-destructive testing method with high sensitivity and high stability to conduct online or offline inspection of welding quality. Developing a laser ultrasonic non-destructive testing system for battery electrode tab welding has significant engineering application value. Summary of the Invention
[0005] This invention addresses the technical problem that conventional non-destructive testing techniques are difficult to apply in non-contact, high-temperature, or coupling agent-prohibited situations. It proposes a laser ultrasonic non-destructive testing system, which uses a low-frequency pulsed laser to non-contactly excite ultrasonic waves and uses a continuous probe laser to demodulate the Doppler frequency shift signal caused by the ultrasonic waves via a Fabry-Perot interferometer. Combined with cavity length closed-loop control and polarization-separated light and light path design, it achieves non-contact, high-precision, and high-stability ultrasonic testing of workpieces.
[0006] To solve the technical problem, the technical solution of the present invention is as follows:
[0007] A laser ultrasonic nondestructive testing system includes a laser ultrasonic excitation module, a continuous light detection and beam splitting module, a Fabry-Perot interferometry demodulation and cavity length closed-loop control module, and a signal acquisition and processing module.
[0008] The laser ultrasonic excitation module includes a pulsed laser controller, a pulsed laser, a collimating lens, a third polarizing beam splitter, a half-wave plate, and a focusing lens. The pulsed laser controller is used to output a pulse signal to the pulsed laser, and the pulsed laser is used to output excitation light. The excitation light passes through the collimating lens, the third polarizing beam splitter, the half-wave plate, and the focusing lens in sequence before irradiating the surface of the sample to be tested, so as to excite ultrasonic vibration in the sample to be tested.
[0009] The continuous light detection and beam splitting module includes a continuous detection laser, a collimator, a beam splitter, a reflector, a first polarizing beam splitter, a quarter-wave plate, a lens, and a second polarizing beam splitter. The continuous detection laser is used to output continuous detection light. The continuous detection light is collimated by the collimator and then incident on the beam splitter, where it is split into path 1 reflected light and path 2 transmitted light.
[0010] The reflected light from path 1 is reflected by the mirror and then incident on the second polarizing beam splitter. The mirror is mounted on a rotating stage, which is connected to a host computer. The host computer controls the rotation of the mirror to switch the optical path connection state between the reflected light from path 1 and the second polarizing beam splitter.
[0011] The transmitted light from path 2 passes through the first polarizing beam splitter, the quarter-wave plate, and the lens before illuminating the surface of the sample under test. The ultrasonic vibration of the sample surface modulates the return scattered light from path 2, causing the return scattered light to carry ultrasonic vibration information. The return scattered light then passes through the lens, the quarter-wave plate, and the first polarizing beam splitter before entering the second polarizing beam splitter.
[0012] The Fabry-Perot interferometer demodulation and cavity length closed-loop control module includes a Fabry-Perot interferometer, a photodetector, an FP driving circuit, and a piezoelectric ceramic; the second polarizing beam splitter is used to receive the reflected light from path 1 and the returned scattered light at different working stages, and guide the reflected light from path 1 or the returned scattered light to the Fabry-Perot interferometer.
[0013] The Fabry-Perot interferometer operates in the linear slope region of its transmission spectrum and uses an edge detection method to demodulate the ultrasonic vibration information carried by the returned scattered light, so as to convert the optical frequency change caused by the ultrasonic vibration into an optical intensity change signal; the photodetector is used to receive the output light of the Fabry-Perot interferometer and convert the output light into an electrical signal.
[0014] The output terminal of the photodetector is connected to the data acquisition card and the FP driving circuit respectively, and is used to output a detection signal to the data acquisition card and a feedback signal to the FP driving circuit. The FP driving circuit outputs a piezoelectric driving signal according to the feedback signal, and drives the piezoelectric ceramic to adjust the cavity length of the Fabry-Perot interferometer, so that the Fabry-Perot interferometer maintains a stable working state.
[0015] The signal acquisition and processing module includes a data acquisition card, a computer, and laser ultrasound analysis software; the pulsed laser controller is connected to the data acquisition card and is used to output a reference signal to the data acquisition card; the data acquisition card is used to receive the reference signal and the detection signal, and uses the reference signal as a synchronization reference for the acquisition of the detection signal; the computer is used to process and store the data acquired by the data acquisition card, and the laser ultrasound analysis software is used to perform laser ultrasound analysis on the acquired data.
[0016] Furthermore, the excitation light output by the pulsed laser is 1064nm pulsed light, and the continuous probe light output by the continuous probe laser is 532nm continuous light.
[0017] Furthermore, the third polarizing beam splitter and the half-wave plate are disposed in the excitation optical path between the pulsed laser and the focusing lens, and are used to adjust the polarization state of the excitation light and / or the excitation light energy incident on the surface of the sample to be tested.
[0018] Furthermore, the transmitted light from path 2 and the return scattered light returning from the surface of the sample under test pass through the quarter-wave plate twice during their round-trip propagation, causing the return scattered light returning to the first polarizing beam splitter to rotate 90° relative to the polarization direction of the transmitted light from path 2 incident on the quarter-wave plate, thereby guiding it through the first polarizing beam splitter to the second polarizing beam splitter.
[0019] Furthermore, during the calibration phase, the reflected light from path 1 enters the second polarizing beam splitter and is output to the photodetector via the Fabry-Perot interferometer. The photodetector outputs a signal to obtain the stable operating point of the Fabry-Perot interferometer. During the detection phase, the reflector is rotated by the rotating stage, causing the reflected light from path 1 to no longer enter the second polarizing beam splitter. The returned scattered light enters the Fabry-Perot interferometer, and the photodetector outputs a detection signal.
[0020] Furthermore, the Fabry-Perot interferometer utilizes the linear slope of its transmission spectrum to convert the Doppler frequency shift information caused by the ultrasonic vibration of the sample surface in the returned scattered light into a corresponding light intensity change signal.
[0021] Furthermore, during the detection phase, when the operating point of the Fabry-Perot interferometer changes, the FP driving circuit drives the piezoelectric ceramic to perform periodic scanning motion to change the cavity length of the Fabry-Perot interferometer and redetermine the stable operating point based on the output signal of the photodetector.
[0022] Furthermore, the photodetector is a single photodetector, and its output terminal is connected to the data acquisition card and the FP driving circuit respectively, outputting detection signals to the data acquisition card and feedback signals to the FP driving circuit respectively.
[0023] Furthermore, the pulsed laser controller is configured to synchronously generate the pulse signal and the reference signal to achieve timing synchronization between pulsed laser excitation and detection signal acquisition.
[0024] Furthermore, the sample to be tested is a power battery tab welding structure, which includes a tab welding area formed by welding multiple layers of copper foil or multiple layers of aluminum foil; the laser ultrasonic analysis software is used to obtain the welding quality detection result of the tab welding area based on the detection signal.
[0025] This application has the following advantages:
[0026] Completely non-contact and without coupling agent: The ultrasonic wave is excited by a pulsed laser and the ultrasonic signal is received by a continuous detection laser. The entire process does not require liquid or solid coupling agents, which avoids contamination or damage to the workpiece (especially the thin foil material of the battery tabs) by the coupling agent. It is also suitable for detection environments with high temperature, high pressure or where contact with liquid is prohibited.
[0027] High detection accuracy and high sensitivity: By modulating the Doppler frequency shift effect of the probe laser with ultrasound, and operating the Fabry-Perot interferometer in the linear slope region of the transmission spectrum, high-resolution demodulation is performed by edge detection, which can effectively extract weak ultrasonic signals and achieve sensitive detection of internal defects (such as poor soldering, delamination, pores, etc.) in extremely thin foil materials (4μm copper foil, 12μm aluminum foil) and multilayer structures (40~80 layers).
[0028] High system stability: By forming a closed-loop feedback control with a single photodetector and FP drive circuit, the cavity length of the Fabry-Perot interferometer is adjusted in real time, so that the interferometer is always locked at the linear operating point of the transmission spectrum. This can effectively compensate for cavity length drift caused by environmental disturbances and ensure detection accuracy and signal stability.
[0029] Strong anti-interference capability of optical path: The polarization separation design of the light receiving and receiving path, which combines a polarization beam splitter and a quarter-wave plate, can effectively suppress back light stray light and background noise, improve the receiving efficiency and signal-to-noise ratio of scattered light signals, and adapt to the test workpieces with different surface conditions.
[0030] The laser parameters are highly adaptable: the excitation laser adopts a low-frequency, low-energy, and narrow-pulse-width parameter design (repetition frequency ≤ 2kHz, single-pulse energy ≤ 100μJ, pulse width ≤ 1ns), which can be optimized for thin material scenarios such as electrode welding, ensuring the ultrasonic excitation effect while avoiding thermal damage to the workpiece.
[0031] Easy to integrate with automation: The system uses host computer software to uniformly control laser excitation, signal reception and data acquisition. The process is simple and controllable, and it can be integrated with production lines, robotic arms or displacement platforms to achieve online automatic detection. Attached Figure Description
[0032] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0033] Figure 1 This is a schematic diagram of the overall structure of the laser ultrasonic nondestructive testing system proposed in the embodiments of this application;
[0034] Figure 2 This is the optical path diagram for the calibration stage proposed in the embodiments of this application;
[0035] Figure 3 This is the optical path diagram for the detection stage proposed in the embodiments of this application;
[0036] Figure 4This is a flowchart illustrating the workflow of the laser ultrasonic nondestructive testing system proposed in this application.
[0037] Figure 5 This is a schematic diagram of the structure and working state of the reflector M1 and the rotary table proposed in the embodiments of this application;
[0038] Figure 6 This is a schematic diagram of the periodic scanning control and operating point maintenance of the Fabry-Perot interferometer proposed in the embodiments of this application. Detailed Implementation
[0039] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0040] Example 1:
[0041] like Figures 1 to 6 As shown, this embodiment provides a laser ultrasonic non-destructive testing system, which is particularly suitable for post-weld non-contact non-destructive testing of the electrode tab welding area of a power battery.
[0042] The sample to be tested can be a power battery electrode welding structure, which includes an electrode welding area formed by welding multiple layers of copper foil or multiple layers of aluminum foil, for example, a welding structure formed by welding 40 to 80 layers of metal foil to an electrode post or adapter piece. Since the electrode foil material is relatively thin and the welding area is not suitable for contact testing, this embodiment uses a pulsed laser to excite ultrasonic waves in the sample to be tested, and a continuous probe laser combined with a Fabry-Perot interferometer is used to detect and demodulate the optical signal modulated by the ultrasonic vibration, thereby achieving non-contact, non-destructive testing of the sample to be tested.
[0043] The laser ultrasonic nondestructive testing system in this embodiment includes a laser ultrasonic excitation module, a continuous light detection and beam splitting module, a Fabry-Perot interferometry demodulation and cavity length closed-loop control module, and a signal acquisition and processing module.
[0044] 1. Laser-ultrasonic excitation module
[0045] The laser-ultrasonic excitation module includes a pulsed laser controller, a pulsed laser, a collimating lens, a third polarizing beam splitter, a half-wave plate, and a focusing lens.
[0046] The pulsed laser controller outputs pulse control signals to the pulsed laser and a synchronization reference signal to the data acquisition card. The pulsed laser outputs pulsed excitation light. Preferably, the pulsed laser outputs pulsed laser light with a wavelength of 1064 nm, a repetition frequency not exceeding 2 kHz, a single pulse energy not exceeding 100 μJ, and a pulse width not exceeding 1 ns.
[0047] The pulsed excitation light passes sequentially along the excitation optical path through the collimating lens, the third polarizing beam splitter, the half-wave plate, and the focusing lens. The collimating lens collimates the pulsed excitation light; the third polarizing beam splitter and the half-wave plate adjust the polarization state and / or incident energy of the pulsed excitation light; and the focusing lens converges the pulsed excitation light onto the test area of the sample. Preferably, the diameter of the light spot after the pulsed excitation light is converged onto the surface of the sample by the focusing lens is no greater than 0.5 mm.
[0048] The focused pulsed excitation light acts on the surface or near-surface of the sample under test, exciting ultrasonic waves inside the sample through transient thermoelastic effects. By using low-frequency, low-energy, and short-pulse-width pulsed lasers, the thermal impact and damage risk of laser action on the surface of the tab-thin metal foil can be reduced while obtaining ultrasonic excitation signals.
[0049] 2. Continuous light detection and beam splitting module
[0050] The continuous light detection and beam splitting module includes a continuous detection laser, a collimator, a beam splitter, a reflector M1, a first polarizing beam splitter PBS1, a quarter-wave plate, a lens, and a second polarizing beam splitter PBS2.
[0051] The continuous probe laser is used to output continuous probe light. Preferably, the continuous probe laser is a continuous wave single-frequency laser with an output wavelength of 532 nm. After being collimated by the collimator, the continuous probe light is incident on the beam splitter, and is split into path 1 reflected light and path 2 transmitted light by the beam splitter.
[0052] Path 1 serves as the calibration optical path for the Fabry-Perot interferometer. The reflected light from Path 1 is reflected by mirror M1 and then incident on the second polarizing beam splitter PBS2, which guides it to the Fabry-Perot interferometer.
[0053] The reflector M1 is mounted on a rotating platform, which is connected to a host computer via a control circuit. The host computer can control the rotation angle of the rotating platform through the control circuit, thereby rotating the reflector M1 and changing the propagation direction of the reflected light from path 1, thus controlling whether the reflected light from path 1 enters the second polarizing beam splitter PBS2.
[0054] Path 2 serves as the detection optical path. The transmitted light from path 2 passes sequentially through the first polarizing beam splitter PBS1, a quarter-wave plate, and a lens before illuminating the surface of the sample to be tested, forming a detection spot on the sample surface. The detection spot and the excitation spot formed by the pulsed excitation light can be positioned within the corresponding detection area of the sample to be tested, depending on the specific detection method.
[0055] When the ultrasonic waves excited by the pulsed excitation light propagate in the sample and cause minute vibrations on the surface of the sample, the minute vibrations modulate the continuous probe light irradiating the sample surface, so that the scattered light returning from the sample surface carries optical frequency change information corresponding to the ultrasonic vibrations.
[0056] The returned scattered light passes sequentially through the lens and quarter-wave plate along the return optical path and returns to the first polarizing beam splitter PBS1. Because the transmitted light from path 2 and its returned scattered light pass through the quarter-wave plate twice during their round-trip propagation, the polarization state of the returned scattered light relative to the incident probe light changes. This causes the returned scattered light to be guided through the first polarizing beam splitter PBS1 to the second polarizing beam splitter PBS2, and further into the Fabry-Perot interferometer.
[0057] The polarization-transmitting optical path formed by the first polarization beam splitter PBS1 and the quarter-wave plate can realize the separation of the incident probe light and the returned scattered light, and help reduce the influence of return stray light on the detection signal.
[0058] In this embodiment, the calibration optical path of path 1 and the detection optical path of path 2 operate in a time-division multiplexing mode. During the Fabry-Perot interferometer calibration phase, the reflected light from path 1 enters the Fabry-Perot interferometer via mirror M1 and the second polarizing beam splitter PBS2 to determine the stable operating point of the Fabry-Perot interferometer. After calibration, the host computer controls the rotary stage to rotate mirror M1, changing the propagation direction of the reflected light from path 1, thus preventing the reflected light from entering the second polarizing beam splitter PBS2 and the Fabry-Perot interferometer. Subsequently, the system enters the detection phase, where the return scattered light from path 2 enters the Fabry-Perot interferometer for detection via the second polarizing beam splitter PBS2.
[0059] Therefore, the reflected light from path 1 and the returned scattered light from path 2 enter the second polarizing beam splitter PBS2 and the Fabry-Perot interferometer at different working stages, respectively, instead of simultaneously entering the Fabry-Perot interferometer as detection light.
[0060] 3. Fabry-Perot interferometry demodulation and cavity length closed-loop control module
[0061] The Fabry-Perot interferometry demodulation and cavity length closed-loop control module includes a Fabry-Perot interferometer, a photodetector, an FP drive circuit, and a piezoelectric ceramic PZT for adjusting the cavity length of the Fabry-Perot interferometer.
[0062] The second polarizing beam splitter PBS2 is used to guide the reflected light from path 1 or the return scattered light from path 2 to the Fabry-Perot interferometer at different working stages.
[0063] The Fabry-Perot interferometer utilizes the linear slope region of its transmission spectrum to demodulate optical frequency variations. When reflected light carrying ultrasonic vibration information enters the Fabry-Perot interferometer, the interferometer employs an edge detection method to convert the frequency changes of the reflected light caused by ultrasonic vibrations on the surface of the sample into corresponding light intensity change signals.
[0064] The photodetector is located at the output end of the Fabry-Perot interferometer and is used to receive the optical signal output by the Fabry-Perot interferometer and convert it into an electrical signal.
[0065] This embodiment employs a single photodetector. The output of the single photodetector is connected to both the FP driving circuit and the data acquisition card. During the acquisition of the Fabry-Perot interferometer's operating point, the output signal of the photodetector serves as the basis for determining the Fabry-Perot interferometer's operating state; during laser ultrasonic testing, the electrical signal containing ultrasonic information output by the photodetector is used as the detection signal input to the data acquisition card.
[0066] The FP driving circuit is connected to the piezoelectric ceramic PZT. By applying a driving signal to the piezoelectric ceramic PZT, the FP driving circuit causes the piezoelectric ceramic PZT to produce a corresponding displacement, thereby changing the cavity length of the Fabry-Perot interferometer. Therefore, the object adjusted by the FP driving circuit and the piezoelectric ceramic PZT is the cavity length of the Fabry-Perot interferometer.
[0067] During the system calibration phase, the reflected light from path 1 enters the Fabry-Perot interferometer via the second polarizing beam splitter PBS2, where a photodetector detects the output light signal. The FP drive circuit drives the piezoelectric ceramic PZT to adjust the cavity length of the Fabry-Perot interferometer and determines its operating state based on the photodetector's output signal. Once the photodetector's output signal indicates that the Fabry-Perot interferometer has reached the predetermined stable operating point, the calibration process corresponding to path 1 is completed.
[0068] After calibration, the host computer controls the rotary table to rotate via the control circuit, so that the reflector M1 is rotated to a position where the reflected light from path 1 no longer enters the second polarizing beam splitter PBS2, thereby stopping the calibration light from path 1 from entering the Fabry-Perot interferometer, and the system switches to the path 2 detection state.
[0069] During the detection phase, the reflected light from the surface of the sample enters the Fabry-Perot interferometer via the first polarizing beam splitter PBS1 and the second polarizing beam splitter PBS2. The Fabry-Perot interferometer converts the frequency variation carried by the reflected light into a light intensity variation, and the photodetector then converts this light intensity variation into a corresponding electrical signal.
[0070] During the detection process, to reduce the impact of environmental changes and other factors on the operating point variations of the Fabry-Perot interferometer on the detection results, the FP driving circuit drives the piezoelectric ceramic PZT to perform periodic scanning. This causes the piezoelectric ceramic PZT to periodically adjust the cavity length of the Fabry-Perot interferometer, and the stable operating point of the Fabry-Perot interferometer is re-acquired based on the signal output by the photodetector during the scanning process. By readjusting the cavity length of the Fabry-Perot interferometer, it is brought back to a working state suitable for edge detection and demodulation.
[0071] Therefore, the acquisition of the stable operating point in this embodiment includes both the calibration performed using path 1 before the detection begins and the periodic scanning of the Fabry-Perot interferometer cavity length by driving the piezoelectric ceramic PZT through the FP driving circuit during the detection phase, and re-acquiring the stable operating point based on the output signal of a single photodetector.
[0072] 4. Signal Acquisition and Processing Module
[0073] The signal acquisition and processing module includes a data acquisition card, a computer, and laser ultrasound analysis software.
[0074] The data acquisition card is connected to the pulsed laser controller, the photodetector, and the computer, respectively.
[0075] The pulsed laser controller outputs a pulse control signal to the pulsed laser while simultaneously outputting a synchronization reference signal to the data acquisition card. The data acquisition card uses this synchronization reference signal as the time reference for acquiring detection signals, thereby achieving time synchronization between pulsed laser excitation and laser ultrasonic detection signal acquisition.
[0076] During the detection process, the photodetector converts the light intensity change signal output by the Fabry-Perot interferometer into an electrical signal, and inputs this electrical signal as a detection signal into the data acquisition card. The data acquisition card acquires the detection signal according to the synchronization reference signal, thereby obtaining the laser ultrasonic response signal corresponding to the detection position of the sample under test.
[0077] The data acquisition card transmits the acquired data to the computer, where it performs signal processing and data storage. The laser ultrasonic analysis software can perform time-domain, frequency-domain, and / or time-frequency analysis on the acquired laser ultrasonic signals, and can extract features such as amplitude, time delay, and spectrum of the ultrasonic signals for analysis of the welding quality of the area under test.
[0078] For the welding structure of the power battery tabs, the welding status of the tab welding area can be analyzed based on the obtained laser ultrasonic detection signal, thereby providing a basis for judging welding quality problems such as incomplete welding, poor welding, uneven welding and / or abnormal interlayer bonding.
[0079] 5. Working process of this embodiment
[0080] When the laser ultrasonic nondestructive testing system of this embodiment is working, the working point calibration of the Fabry-Perot interferometer is first performed.
[0081] The continuous probe laser outputs continuous probe light, which is collimated by a collimator and then split into path 1 reflected light and path 2 transmitted light by a beam splitter. During the calibration phase, the host computer controls the rotary stage to position the reflector M1 mounted on the stage so that it can guide the path 1 reflected light to the second polarizing beam splitter PBS2. The path 1 reflected light is reflected by the reflector M1 and enters the second polarizing beam splitter PBS2, which then guides it to the Fabry-Perot interferometer.
[0082] The reflected light from path 1 is received by a single photodetector after passing through the Fabry-Perot interferometer. The FP drive circuit drives the piezoelectric ceramic PZT to adjust the cavity length of the Fabry-Perot interferometer based on the signal output from the photodetector, and uses the output signal of the photodetector as the basis for determining the operating state of the Fabry-Perot interferometer. Once the Fabry-Perot interferometer is determined to have reached a stable operating point, calibration is completed.
[0083] After calibration, the host computer controls the rotating stage to rotate via the control circuit, causing the reflector M1 to change its angle. This alters the propagation direction of the reflected light from path 1 and prevents it from entering the second polarizing beam splitter PBS2 and the Fabry-Perot interferometer. At this point, the calibration optical path for path 1 exits, and the system switches from the calibration phase to the detection phase.
[0084] During formal testing, the pulsed laser controller outputs a pulse control signal to the pulsed laser, causing the pulsed laser to output pulsed excitation light. The pulsed excitation light passes sequentially through a collimating lens, a third polarizing beam splitter, a half-wave plate, and a focusing lens before acting on the surface of the sample under test, thus exciting ultrasonic waves within the sample.
[0085] Meanwhile, the transmitted light from path 2 of the continuous probe laser passes sequentially through the first polarizing beam splitter PBS1, a quarter-wave plate, and a lens before illuminating the surface of the sample to be tested.
[0086] When the ultrasonic wave propagates and causes a tiny vibration on the surface of the sample to be tested, the tiny vibration modulates the return scattered light of the probe light in path 2, so that the return scattered light carries optical frequency change information corresponding to the ultrasonic vibration.
[0087] The returned scattered light passes sequentially through a lens and a quarter-wave plate along the return optical path, and is guided by the first polarizing beam splitter PBS1 to the second polarizing beam splitter PBS2, and then enters the Fabry-Perot interferometer through the second polarizing beam splitter PBS2.
[0088] The Fabry-Perot interferometer operates in the region of linear slope of its transmission spectrum and converts the optical frequency changes carried by the returned scattered light into corresponding optical intensity change signals through edge detection. A single photodetector receives the output light from the Fabry-Perot interferometer and converts it into an electrical signal, which is then input as a detection signal to the data acquisition card.
[0089] The pulsed laser controller simultaneously outputs a synchronization reference signal to the data acquisition card. The data acquisition card uses this synchronization reference signal as the time reference for acquiring the detection signal, collects the detection signal output by the photodetector, and transmits the acquired data to the computer. Laser ultrasonic analysis software analyzes the detection data to obtain the laser ultrasonic detection results corresponding to the area under test.
[0090] During the detection process, the FP driving circuit drives the piezoelectric ceramic PZT to perform scanning motion according to a set cycle, causing a corresponding change in the cavity length of the Fabry-Perot interferometer. By acquiring the signal output from a single photodetector during the scanning process, the stable operating point of the Fabry-Perot interferometer is re-determined. The cavity length of the Fabry-Perot interferometer is then readjusted using the piezoelectric ceramic PZT, restoring the Fabry-Perot interferometer to a suitable operating state for detection before continuing laser ultrasonic signal detection.
[0091] Through the above working method, the calibration light of path 1 and the detection light of path 2 enter the Fabry-Perot interferometer in a time-division manner. A single photodetector is used both to determine the working status of the Fabry-Perot interferometer during the calibration stage and to receive the laser ultrasonic signal during the detection stage. At the same time, the piezoelectric ceramic PZT is driven by the FP driving circuit to change the cavity length of the Fabry-Perot interferometer, and periodic scanning is performed during the detection process to reacquire a stable working point, which helps to reduce the impact of working point drift on the detection process.
[0092] The laser ultrasonic nondestructive testing system of this embodiment can perform laser ultrasonic testing on the welding area of the battery tabs without contacting the workpiece and without using a liquid coupling agent. Edge detection demodulation using a Fabry-Perot interferometer enables the detection of optical frequency changes caused by ultrasonic vibration. The system's operational stability during testing is improved by using path 1 to calibrate the optical path, path 2 to detect the optical path, and optical path switching via mirror M1, combined with adjustment of the Fabry-Perot interferometer cavity length using piezoelectric ceramic PZT.
[0093] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.
[0094] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.
Claims
1. A laser ultrasonic nondestructive testing system, characterized in that, It includes a laser ultrasonic excitation module, a continuous light detection and beam splitting module, a Fabry-Perot interferometry demodulation and cavity length closed-loop control module, and a signal acquisition and processing module; The laser ultrasonic excitation module includes a pulsed laser controller, a pulsed laser, a collimating lens, a third polarizing beam splitter, a half-wave plate, and a focusing lens. The pulsed laser controller is used to output a pulse signal to the pulsed laser, and the pulsed laser is used to output excitation light. The excitation light passes through the collimating lens, the third polarizing beam splitter, the half-wave plate, and the focusing lens in sequence before irradiating the surface of the sample to be tested, so as to excite ultrasonic vibration in the sample to be tested. The continuous light detection and beam splitting module includes a continuous detection laser, a collimator, a beam splitter, a reflector, a first polarizing beam splitter, a quarter-wave plate, a lens, and a second polarizing beam splitter. The continuous detection laser is used to output continuous detection light. The continuous detection light is collimated by the collimator and then incident on the beam splitter, where it is split into path 1 reflected light and path 2 transmitted light. The reflected light from path 1 is reflected by the mirror and then incident on the second polarizing beam splitter. The mirror is mounted on a rotating stage, which is connected to a host computer. The host computer controls the rotation of the mirror to switch the optical path connection state between the reflected light from path 1 and the second polarizing beam splitter. The transmitted light from path 2 passes through the first polarizing beam splitter, the quarter-wave plate, and the lens before illuminating the surface of the sample under test. The ultrasonic vibration of the sample surface modulates the return scattered light from path 2, causing the return scattered light to carry ultrasonic vibration information. The return scattered light then passes through the lens, the quarter-wave plate, and the first polarizing beam splitter before entering the second polarizing beam splitter. The Fabry-Perot interferometer demodulation and cavity length closed-loop control module includes a Fabry-Perot interferometer, a photodetector, an FP driving circuit, and a piezoelectric ceramic; the second polarizing beam splitter is used to receive the reflected light from path 1 and the returned scattered light at different working stages, and guide the reflected light from path 1 or the returned scattered light to the Fabry-Perot interferometer. The Fabry-Perot interferometer operates in the linear slope region of its transmission spectrum and uses an edge detection method to demodulate the ultrasonic vibration information carried by the returned scattered light, so as to convert the optical frequency change caused by the ultrasonic vibration into an optical intensity change signal; the photodetector is used to receive the output light of the Fabry-Perot interferometer and convert the output light into an electrical signal. The output terminal of the photodetector is connected to the data acquisition card and the FP driving circuit respectively, and is used to output a detection signal to the data acquisition card and a feedback signal to the FP driving circuit. The FP driving circuit outputs a piezoelectric driving signal according to the feedback signal, and drives the piezoelectric ceramic to adjust the cavity length of the Fabry-Perot interferometer, so that the Fabry-Perot interferometer maintains a stable working state. The signal acquisition and processing module includes a data acquisition card, a computer, and laser ultrasound analysis software; the pulsed laser controller is connected to the data acquisition card and is used to output a reference signal to the data acquisition card; the data acquisition card is used to receive the reference signal and the detection signal, and uses the reference signal as a synchronization reference for the acquisition of the detection signal; the computer is used to process and store the data acquired by the data acquisition card, and the laser ultrasound analysis software is used to perform laser ultrasound analysis on the acquired data.
2. The laser ultrasonic nondestructive testing system according to claim 1, characterized in that, The pulsed laser outputs 1064nm pulsed light, and the continuous probe laser outputs 532nm continuous light.
3. The laser ultrasonic nondestructive testing system according to claim 1, characterized in that, The third polarizing beam splitter and the half-wave plate are disposed in the excitation optical path between the pulsed laser and the focusing lens, and are used to adjust the polarization state of the excitation light and / or the excitation light energy incident on the surface of the sample to be tested.
4. The laser ultrasonic nondestructive testing system according to claim 1, characterized in that, The transmitted light from path 2 and the return scattered light returning from the surface of the sample under test pass through the quarter-wave plate twice during their round-trip propagation. This causes the return scattered light returning to the first polarizing beam splitter to rotate 90° relative to the polarization direction of the transmitted light from path 2 before it is incident on the quarter-wave plate, thereby guiding it through the first polarizing beam splitter to the second polarizing beam splitter.
5. The laser ultrasonic nondestructive testing system according to claim 1, characterized in that, During the calibration phase, the reflected light from path 1 enters the second polarizing beam splitter and is output to the photodetector via the Fabry-Perot interferometer. The output signal of the photodetector is used to obtain the stable operating point of the Fabry-Perot interferometer. During the detection phase, the reflector is driven to rotate by the rotary table, so that the reflected light from path 1 no longer enters the second polarizing beam splitter, and the returned scattered light enters the Fabry-Perot interferometer, and the photodetector outputs a detection signal.
6. The laser ultrasonic nondestructive testing system according to claim 1, characterized in that, The Fabry-Perot interferometer uses the linear slope of its transmission spectrum to convert the Doppler frequency shift information caused by ultrasonic vibration of the sample surface in the returned scattered light into a corresponding light intensity change signal.
7. The laser ultrasonic nondestructive testing system according to claim 1, characterized in that, During the detection phase, when the operating point of the Fabry-Perot interferometer changes, the FP driving circuit drives the piezoelectric ceramic to perform periodic scanning motion to change the cavity length of the Fabry-Perot interferometer and redetermine the stable operating point based on the output signal of the photodetector.
8. The laser ultrasonic nondestructive testing system according to claim 1, characterized in that, The photodetector is a single photodetector, and its output terminal is connected to the data acquisition card and the FP driving circuit respectively. It outputs detection signals to the data acquisition card and feedback signals to the FP driving circuit respectively.
9. The laser ultrasonic nondestructive testing system according to claim 1, characterized in that, The pulsed laser controller is configured to synchronously generate the pulse signal and the reference signal to achieve timing synchronization between pulsed laser excitation and detection signal acquisition.
10. The laser ultrasonic nondestructive testing system according to claim 1, characterized in that, The sample to be tested is a power battery tab welding structure, which includes a tab welding area formed by welding multiple layers of copper foil or multiple layers of aluminum foil; the laser ultrasonic analysis software is used to obtain the welding quality test result of the tab welding area based on the detection signal.