Microcrack detection method, device and preparation method

Abstract

The present invention relates to the field of microcrack detection technology, and specifically to a microcrack detection method, device, and preparation method, comprising: constructing a microcrack detection system, and calculating the transverse and longitudinal wave propagation time difference based on the sound velocity of the solid material being tested and the estimated defect position, and applying a delay to the excitation signal through an FPGA controller; synchronously triggering the transverse and longitudinal wave emission of the microcrack detection system so that transverse and longitudinal waves of different frequencies, which have been delayed and controlled, simultaneously enter the solid material being tested. When the transverse and longitudinal waves simultaneously act on the microcrack defects of the solid material being tested, a mixing effect is generated based on the nonlinear characteristics of the solid material being tested, generating a difference frequency component; and capturing and analyzing the difference frequency echo signal to complete microcrack detection of the solid material being tested. The application of the present invention can achieve high-precision time delay control and high signal-to-noise ratio mixing echo capture, and effectively improve the detection rate.

Description

Technical Field

[0001] The present invention relates to the technical field of microcrack detection, and in particular to a microcrack detection method, device and preparation method. Background Art

[0002] Lithium niobate (LN) crystals are widely used in ultrasonic transducer design due to their excellent piezoelectric properties and high-temperature stability. Traditional ultrasonic testing technologies mostly use single-mode probes (transverse waves or longitudinal waves), which transmit single-frequency sound wave signals and rely on the amplitude attenuation or time delay changes of the reflected echo to determine the presence of defects. However, the detection of microcracks in solid materials faces challenges: transverse waves are sensitive to surface defects but have limited penetration depth, while longitudinal waves have strong penetration but insufficient resolution for tiny cracks. In addition, traditional analysis methods based on amplitude or time delay changes are easily affected by noise and material inhomogeneity. Not only is the detection sensitivity limited, but the determination of early cracks is particularly difficult. Due to the lack of adaptive delay and real-time difference frequency extraction mechanisms, it is difficult to use them across different materials, and detection stability and accuracy are also difficult to guarantee. Summary of the Invention

[0003] The purpose of the present invention is to provide a microcrack detection method, device and preparation method, which realizes high-precision delay control and high signal-to-noise ratio mixed frequency echo capture through LN transverse and longitudinal wave dual-mode microprobe and adaptive difference frequency detection, and effectively improves the detection rate.

[0004] The present invention is achieved through the following technical solutions:

[0005] A microcrack detection method, the method comprising the steps of:

[0006] Build a microcrack detection system and set the parameters of the excitation signal of the microcrack detection system. Based on the sound velocity of the solid material being tested and the estimated defect location, calculate the propagation time difference between the transverse and longitudinal waves, and apply a delay to the excitation signal through the FPGA controller.

[0007] The transverse and longitudinal waves of the microcrack detection system are synchronously triggered, so that the transverse and longitudinal waves of different frequencies, which have been delayed and controlled, enter the solid material under test at the same time. When the transverse and longitudinal waves act on the microcrack defects of the solid material under test at the same time, a mixing effect is generated based on the nonlinear characteristics of the solid material under test, generating a difference frequency component;

[0008] The difference frequency echo signal is captured and analyzed, and the micro crack detection of the solid material under test is completed based on the analysis results of the difference frequency echo signal.

[0009] Optionally, the microcrack detection system specifically comprises: a microcrack detection device, an excitation signal generator and a host computer control system, and a data acquisition card connected in sequence; the receiving end of the microcrack detection device is connected to the data acquisition card, and the data acquisition card is connected to the host computer control system;

[0010] The microcrack detection device is specifically an LN transverse and longitudinal wave dual-mode microprobe, which is used to convert electrical signals into ultrasonic waves and simultaneously capture the echo signals reflected by the solid material being tested;

[0011] The excitation signal generator is used to receive the frequency and delay parameters transmitted by the host control system and simultaneously generate two electric pulse signals, including an X channel: a shear wave excitation signal and a Z channel: a longitudinal wave excitation signal;

[0012] The data acquisition card is used to convert the echo signal into a digital signal at a set sampling rate;

[0013] The host computer control system is used to control the various components of the microcrack detection system through the FPGA / PCIe interface, coordinate the timing of the microcrack detection system, and run the corresponding algorithm to perform data processing and visualization;

[0014] The microcrack detection system is preset with signal transmission logic and signal echo logic.

[0015] Optionally, the signal transmission logic is specifically:

[0016] Input the type of solid material to be measured in the host computer control system and load the pre-stored sound velocity of the solid material to be measured;

[0017] Calculate the time difference between the transverse and longitudinal waves, and the host computer control system uses the time difference between the transverse and longitudinal waves as the delay, and writes it to the excitation signal generator through the FPGA controller;

[0018] The FPGA controller sends a synchronous trigger pulse to the excitation signal generator, which outputs two electrical pulse signals: X channel: immediately emits a shear wave excitation signal, and Z channel: emits a longitudinal wave excitation signal based on a delay;

[0019] The microcrack detection device converts electrical signals into ultrasonic waves and transmits them into the solid material being tested. After the transverse and longitudinal waves are compensated for the propagation path, they arrive at the preset depth of the solid material being tested at the same time. Under the action of the transverse and longitudinal waves, the microcracks produce a nonlinear mixing effect and generate a difference frequency component.

[0020] Optionally, the signal echo logic is specifically as follows:

[0021] The micro-crack detection device acquires the echo signal of the difference frequency component, and the data acquisition card converts the difference frequency echo signal from an analog signal to a digital signal at a set acquisition rate;

[0022] Perform fundamental component analysis on the difference frequency echo digital signal to obtain the shear wave fundamental amplitude;

[0023] The difference frequency echo digital signal is subjected to bandpass filtering, Hilbert transform and envelope detection in sequence to obtain the envelope sequence of the difference frequency echo digital signal. Within the preset theoretical arrival time window, the envelope sequence is subjected to peak detection to obtain the difference frequency peak value.

[0024] The nonlinear coefficient of the solid material being tested is obtained by combining the shear wave fundamental amplitude and the difference frequency peak value.

[0025] The nonlinear coefficient of the solid material being tested is verified to obtain the microcrack detection result of the solid material being tested.

[0026] Optionally, after the microcrack detection device obtains the echo signal of the difference frequency component, it also includes: amplifying the echo signal of the difference frequency component, and performing anti-aliasing filtering on the echo signal of the difference frequency component to obtain a preprocessed difference frequency component echo signal.

[0027] A microcrack detection device comprises: a substrate; a conductive adhesive layer disposed on the substrate; an LN material layer disposed on the conductive adhesive layer, the LN material layer comprising a first piezoelectric unit for exciting shear mode shear waves and a second piezoelectric unit for exciting stretch mode longitudinal waves; a matching layer disposed on the first and second piezoelectric units; an upper electrode and a lower electrode disposed on the first piezoelectric unit, wherein an electric field is formed between the upper and lower electrodes for exciting shear mode shear waves; and a positive electrode and a negative electrode disposed on the second piezoelectric unit, wherein an electric field is formed between the positive and negative electrodes for exciting stretch mode longitudinal waves.

[0028] A method for preparing a microcrack detection device, the method comprising the steps of:

[0029] In a molten environment, lithium niobate crystals are grown with air, and the diameter of the lithium niobate crystals is kept constant during the growth process;

[0030] Cutting the grown lithium niobate single crystal rod along the X-axis to obtain an x-cut LN wafer;

[0031] Deposit metal layers on the front and back of the x-cut LN wafer in sequence, and add scribe marks on the back. After dicing, the LN transverse and longitudinal wave integrated device substrate is obtained;

[0032] The front metal layer of the substrate for preparing the LN transverse and longitudinal wave integrated device is patterned and etched, and the back metal layer of the substrate for preparing the LN transverse and longitudinal wave integrated device in the telescopic working mode is deeply etched to obtain the longitudinal wave device part;

[0033] The front metal layer of the substrate for the LN transverse and longitudinal wave integrated device is deeply etched to obtain the transverse wave device part. An isolation trench is formed between the transverse wave device part and the longitudinal wave device part to constitute the LN transverse and longitudinal wave integrated device. The prepared LN transverse and longitudinal wave integrated devices are arrayed to complete the preparation of the LN transverse and longitudinal wave dual-mode microprobe.

[0034] Optionally, after cutting the grown lithium niobate single crystal rod along the X-axis, the method further includes grinding and polishing the cut lithium niobate wafer to obtain an x-cut LN wafer.

[0035] Optionally, the growing of lithium niobate crystals in air is specifically: growing the lithium niobate crystals by a Czochralski method.

[0036] Optionally, the metal layer is deposited on the front side and the back side of the x-cut LN wafer in sequence, and both the front side metal layer deposition and the back side metal layer deposition are performed by magnetron sputtering.

[0037] The technical solution of the present invention has at least the following advantages and beneficial effects:

[0038] The present invention prepares an LN transverse and longitudinal wave dual-mode microprobe and uses FPGA to achieve high-precision delay control of the excitation signal, so that transverse and longitudinal waves of different frequencies can reach the defect at the same time and produce a strong mixing effect. The large dynamic range detection circuit combined with adaptive filtering and phase-locked amplification method can effectively capture microvolt-level difference frequency echoes and significantly improve the signal-to-noise ratio, with a detection rate of more than 95% for microcracks. In addition, the present invention designs the excitation waveform through parameterization of material sound velocity and defect depth, which can achieve automatic matching in a variety of metals and composite materials, significantly shortening the detection cycle and operation and maintenance costs, and realizing an integrated hardware solution for dual-mode detection and real-time difference frequency analysis, providing high-sensitivity and high-efficiency non-destructive detection capabilities for microcracks, meeting the reliability requirements of harsh industrial scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic flow chart of the microcrack detection method provided by the present invention;

[0040] Figure 2 Schematic diagram of the LN shearing working mode provided by the present invention;

[0041] Figure 3 A schematic diagram of the LN telescopic working mode provided by the present invention;

[0042] Figure 4 Schematic diagram of the basic structure of the LN transverse and longitudinal wave dual-mode microprobe provided by the present invention;

[0043] Figure 5Schematic diagram of nonlinear detection of microcracks using the LN transverse and longitudinal wave dual-mode microprobe provided by the present invention. DETAILED DESCRIPTION

[0044] Reference Figure 1 As shown, in one embodiment, the present invention provides a microcrack detection method, the method comprising the steps of:

[0045] A microcrack detection system was constructed based on an LN transverse and longitudinal wave dual-mode microprobe. The excitation signal parameters of the microcrack detection system were set. The propagation time difference between the transverse and longitudinal waves was calculated based on the sound velocity of the solid material being tested and the estimated defect location. A delay was then applied to the excitation signal using an FPGA controller.

[0046] The transverse and longitudinal waves of the microcrack detection system are synchronously triggered, so that the transverse and longitudinal waves of different frequencies, which have been delayed and controlled, enter the solid material under test at the same time. When the transverse and longitudinal waves act on the microcrack defects of the solid material under test at the same time, a mixing effect is generated based on the nonlinear characteristics of the solid material under test, generating a difference frequency component;

[0047] The difference frequency echo signal is captured and analyzed, and the micro crack detection of the solid material under test is completed based on the analysis results of the difference frequency echo signal.

[0048] Specifically, nonlinear ultrasonic detection technology utilizes the nonlinear effect produced by the interaction of limited-amplitude transverse and longitudinal dual-mode acoustic waves with micro-defects when propagating in the specimen to achieve the detection of micro-defects and the evaluation of material properties. When the transverse and longitudinal dual-mode signal propagates in a solid material, the inherent nonlinearity of the material and the nonlinearity caused by damage interact with it, causing the detection sound wave signal to be distorted, generating second-order, third-order and higher-order harmonic frequency components. These high-order harmonic signals contain rich information about the micro-defects inside the specimen. By analyzing the characteristics of the high-order harmonic signals, the detection of micro-defects inside the specimen can be achieved. In this embodiment, this embodiment combines the LN transverse and longitudinal dual-mode probe with a nonlinear ultrasonic detection algorithm. By enhancing the signal through the nonlinear effect, tiny defects or changes inside the solid material can be detected. The schematic diagram of nonlinear detection is shown in the figure. Figure 5 Specifically, by adjusting the delay time of the applied voltage excitation signal, the transmitted transverse and longitudinal waves of different frequencies reach the microcracks simultaneously, interacting with the microcracks to generate nonlinear components. By analyzing the difference frequency echo signal, extremely small defects inside the solid can be detected.

[0049] In a specific implementation of the above embodiment, the microcrack detection system based on the LN transverse and longitudinal wave dual-mode microprobe is constructed, which specifically includes: an LN transverse and longitudinal wave dual-mode microprobe, an excitation signal generator, a host computer control system, and a data acquisition card connected in sequence; the receiving end of the LN transverse and longitudinal wave dual-mode microprobe is connected to the data acquisition card, and the data acquisition card is connected to the host computer control system;

[0050] The LN transverse and longitudinal wave dual-mode microprobe converts electrical signals into ultrasonic waves and simultaneously captures the echo signals reflected by the solid material being tested;

[0051] The excitation signal generator receives the frequency and delay parameters transmitted by the host control system and simultaneously generates two electric pulse signals, including an X channel: a shear wave excitation signal and a Z channel: a longitudinal wave excitation signal;

[0052] The data acquisition card converts the echo signal into a digital signal at a set sampling rate;

[0053] The host computer control system controls the various components in the microcrack detection system through the FPGA / PCIe interface, coordinates the timing of the microcrack detection system, and runs the corresponding algorithm to perform data processing and visualization.

[0054] Specifically, the microcrack detection system is preset with signal transmission logic and signal echo logic.

[0055] The signal transmission logic is specifically as follows:

[0056] Input the type of solid material to be measured in the host computer control system and load the pre-stored sound velocity of the solid material to be measured;

[0057] Calculate the time difference between the transverse and longitudinal waves, and the host computer control system uses the time difference between the transverse and longitudinal waves as the delay, and writes it to the excitation signal generator through the FPGA controller;

[0058] The FPGA controller sends a synchronous trigger pulse to the excitation signal generator, which outputs two electrical pulse signals: X channel: immediately emits a shear wave excitation signal, and Z channel: emits a longitudinal wave excitation signal based on a delay;

[0059] The LN transverse and longitudinal wave dual-mode microprobe converts electrical signals into ultrasonic waves and transmits them into the solid material being tested. After the propagation path is compensated, the transverse and longitudinal waves arrive at the preset depth of the solid material being tested at the same time. Under the action of the transverse and longitudinal waves, the microcracks produce a nonlinear mixing effect and generate a difference frequency component.

[0060] In the specific implementation, the present embodiment first inputs the type of solid material to be tested (such as 304 stainless steel) into the host computer control system, and sets the detection depth (such as d=8mm) and the pre-stored sound velocity parameters (transverse wave 3,200m / s, longitudinal wave 5,900m / s), and through To solve for the delay time, the host control system writes the delay parameters to the excitation signal generator via the FPGA controller. The FPGA controller then sends a synchronous trigger pulse to the excitation signal generator, which then outputs two signals: the X-channel, which immediately transmits a 2MHz shear wave excitation signal; and the Z-channel, which transmits a 2.5MHz longitudinal wave excitation signal after a 0.98μs delay. The probe converts the electrical signal into ultrasonic waves, which are then transmitted into the solid material being measured. After propagation path compensation, the shear and longitudinal waves arrive simultaneously at a preset depth (e.g., 8mm). The dual-mode ultrasonic wave generates nonlinear mixing in the microcracks, generating a 0.5MHz difference frequency signal.

[0061] The signal echo logic is specifically as follows:

[0062] The LN transverse and longitudinal wave dual-mode microprobe acquires the echo signal of the difference frequency component, and the data acquisition card converts the difference frequency echo signal from an analog signal to a digital signal at a set acquisition rate;

[0063] Perform fundamental component analysis on the difference frequency echo digital signal to obtain the shear wave fundamental amplitude;

[0064] The difference frequency echo digital signal is subjected to bandpass filtering, Hilbert transform and envelope detection in sequence to obtain the envelope sequence of the difference frequency echo digital signal. Within the preset theoretical arrival time window, the envelope sequence is subjected to peak detection to obtain the difference frequency peak value.

[0065] The nonlinear coefficient of the solid material being tested is obtained by combining the shear wave fundamental amplitude and the difference frequency peak value.

[0066] The nonlinear coefficient of the solid material being tested is verified to obtain the microcrack detection result of the solid material being tested.

[0067] In specific implementation, a 0.4-0.6MHz digital bandpass filter is applied to the digitized original signal, and the filtered signal is orthogonally demodulated to generate an analytical signal, where the real part of the analytical signal is the original signal, and the imaginary part is the component of the signal after 90 degrees of phase shift. The modulus value of the analytical signal is taken to obtain a time domain amplitude envelope sequence, which reflects the intensity change of the difference frequency signal. The maximum value of the envelope sequence is searched within the theoretical echo arrival time window (such as the 10 microsecond interval) and recorded as the difference frequency peak. This value represents the intensity of the nonlinear effect caused by the defect. The original digital signal is simultaneously input into two independent filters: one uses a filter with a center frequency of 2MHz and a bandwidth of ±5% to extract the shear wave fundamental component; the other uses a filter with a center frequency of 2.5MHz and a bandwidth of ±5% to extract the longitudinal wave fundamental component. The absolute values ​​of the two filtered signals are taken respectively, and the average amplitude is calculated within 20 cycles. At the same time, the ratio of the two fundamental wave amplitudes is calculated to monitor the uniformity of the material. The nonlinear coefficient is obtained by dividing the difference frequency peak by the square of the shear wave fundamental wave amplitude and multiplying it by 100%. The difference between the nonlinear coefficient and the preset threshold is used to determine whether microcracks exist in the solid material being tested.

[0068] More specifically, after the LN transverse and longitudinal wave dual-mode microprobe obtains the echo signal of the difference frequency component, it also includes: amplifying the echo signal of the difference frequency component, and performing anti-aliasing filtering on the echo signal of the difference frequency component to obtain the preprocessed difference frequency component echo signal.

[0069] In this embodiment, the specific process of preparing the LN transverse and longitudinal wave dual-mode microprobe is as follows:

[0070] In a molten environment, lithium niobate crystals are grown with air, and the diameter of the lithium niobate crystals is kept constant during the growth process;

[0071] Cutting the grown lithium niobate single crystal rod along the X-axis to obtain an x-cut LN wafer;

[0072] Sequentially deposit metal layers on the front and back of the x-cut LN wafer, then add scribe marks and scribing on the back to prepare the substrate for the LN transverse and longitudinal wave integrated device.

[0073] The LN transverse and longitudinal wave integrated device substrate is prepared for front-side metal etching and patterning (the transverse wave device and longitudinal wave device have specific sizes, and the two parts can be distinguished after metal patterning), and then a back-cavity deep etching process is performed to obtain the LN thin film PMUT longitudinal wave device part;

[0074] The LN is deeply etched on the front to form a shear wave device, while simultaneously creating an isolation trench between the LN and longitudinal wave devices, thereby forming an LN integrated transverse and longitudinal wave device. The completed LN integrated transverse and longitudinal wave devices are then arrayed to complete the fabrication of an LN transverse and longitudinal wave dual-mode microprobe.

[0075] Specifically, the telescopic operating mode refers to a longitudinal wave device. Patterning the metal layer on the front side of the substrate results in a transverse and longitudinal wave device electrode arrangement, where both the electric field direction and the LN polarization direction of the longitudinal wave device are along the x-direction, representing the telescopic mode. Furthermore, this embodiment utilizes the Czochralski method to grow lithium niobate single crystals. Only after the lithium niobate single crystal rods are grown can they be cut along the x-axis to produce X-cut LN wafers.

[0076] In specific implementation, lithium niobate is a commonly used piezoelectric material with excellent piezoelectric properties and high electromechanical coupling coefficient. Among the piezoelectric coefficients of lithium niobate, the shear coefficient describes the shear strain generated by the material under the action of the electric field due to the piezoelectric effect, which in turn generates zero-order horizontal shear waves on the waveguide surface. Specifically, applying an electric field along the z-axis will cause shear deformation in the x-axis and y-axis directions, such as Figure 2 As shown. This characteristic determines that it can generate and receive shear waves under the excitation of the shear mode. The piezoelectric coefficient of the LN material reflects the stretching strain generated by the piezoelectric effect in the X-axis direction of the LN crystal system under the action of the electric field. Specifically, applying an electric field along the x-axis direction will cause stretching deformation in the z-axis direction. Figure 3 This characteristic determines that it can generate and receive longitudinal waves in telescopic working mode.

[0077] Furthermore, single-crystal lithium niobate has high mechanical quality factors (Qm) and electrical quality factors (Qc), resulting in minimal mechanical and electrical energy losses. In shear vibration mode, it exhibits a high material electromechanical coupling coefficient, leading to higher energy conversion efficiency. Single-crystal lithium niobate exhibits strong anisotropy, and material parameters such as the piezoelectric coefficient, which is related to the piezoelectric effect, are closely related to the shear shape of the single-crystal lithium niobate. The main shear properties of single-crystal lithium niobate are shown in Table 1.

[0078] Table 1

[0079]

[0080] After analyzing the requirements for the use of piezoelectric vibrators and the piezoelectric characteristics of each cut type, lithium niobate x-cut wafers were finally selected as the best choice. In order to obtain a transverse and longitudinal wave dual-mode probe, the x-cut LN was divided into two regions and different electric field excitations were applied to each region, so that it can work in thickness shear mode and thickness stretch mode respectively. In this way, shear waves can be excited by the shear mode, and longitudinal waves can be excited by the stretch mode, thus realizing a transverse and longitudinal wave dual-mode probe. The basic structure of the LN transverse and longitudinal wave dual-mode probe is as follows: Figure 4 shown.

[0081] Based on the above, this embodiment uses a MEMS process to fabricate an integrated LN transverse and longitudinal wave device. First, lithium niobate crystals are grown and cut to produce x-cut LN wafers. This technology utilizes the commonly used melt growth method, the Czochralski method, to directly grow lithium niobate crystals in air. The lithium niobate crystals are pulled in the x-direction, maintaining a constant diameter during growth. Next, the grown lithium niobate single crystal rods are sliced ​​using an x-cut method to produce x-cut LN wafers. After the wafers are cut, they undergo subsequent grinding and polishing to ensure surface flatness and roughness. The prepared x-cut LN wafers are sequentially subjected to front-side metal deposition, etching, back-side metal deposition, and dicing to obtain the substrate for the LN integrated transverse and longitudinal wave device. First, a metal layer is deposited on the front side of the LN using magnetron sputtering. Second, the front metal is patterned using etching. Then, the same metal layer is deposited on the back side of the LN using magnetron sputtering. Finally, mechanical dicing is performed to obtain the substrate for the LN integrated transverse and longitudinal wave device. Next, the prepared substrate is patterned on the front side by etching, retaining the upper electrode of the shear wave device and the positive and negative electrodes on the upper surface of the longitudinal wave device. The LN in the telescopic operating mode is then deeply etched from the back side to obtain an LN thin-film PMUT with a back cavity structure. Finally, the LN is deeply etched from the front side to obtain the shear wave device, while forming an isolation trench between it and the longitudinal wave device, completing the fabrication of the LN transverse and longitudinal wave integrated device. Based on the fabrication of the LN transverse and longitudinal wave integrated device, the LN transverse and longitudinal wave integrated array is fabricated.

[0082] In a further implementation of this embodiment, in order to optimize the performance of the LN integrated transverse and longitudinal wave array, several different transverse and longitudinal wave array arrangements can be designed, such as transverse-longitudinal-transverse-longitudinal, transverse-transverse-longitudinal-longitudinal, transverse-longitudinal-longitudinal, transverse-transverse-longitudinal, transverse-transverse-longitudinal, etc.

[0083] In summary, this embodiment utilizes x-cut thick-cut single-crystal lithium niobate material to design and fabricate an LN transverse and longitudinal wave integrated dual-mode microprobe and its array. This technology is the first to realize a transverse and longitudinal wave integrated dual-mode microprobe, which is expected to address the problems of conventional acoustic detectors, such as a single excitation mode, large size, and poor detection performance and resolution, and fill the gap in the research of miniature transverse and longitudinal wave dual-mode microprobes at home and abroad. Compared with existing dual-mode ultrasonic probes that are simply integrated to form a common transverse wave oblique probe and a longitudinal wave straight probe, the present invention starts at the wafer level and uses processes such as magnetron sputtering, etching, metal patterning, laser deep etching, or photolithography to prepare an LN transverse and longitudinal wave integrated dual-mode probe. This probe has the advantages of miniaturization, integration, arrayability, high consistency, and easy integration with circuits.

[0084] The above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A microcrack detection method, characterized in that: The steps of the method include: A microcrack detection system was constructed, comprising an LN transverse and longitudinal wave dual-mode microprobe, an excitation signal generator, a host computer control system, and a data acquisition card. The system's excitation signal parameters were set, and the transverse and longitudinal wave propagation time differences were calculated based on the sound velocity of the solid material being tested and the estimated defect location. The excitation signal was then delayed using an FPGA controller. The transverse and longitudinal waves of the microcrack detection system are synchronously triggered, so that the transverse and longitudinal waves of different frequencies, which have been delayed and controlled, enter the solid material under test at the same time. When the transverse and longitudinal waves act on the microcrack defects of the solid material under test at the same time, a mixing effect is generated based on the nonlinear characteristics of the solid material under test, generating a difference frequency component; Capture and analyze the difference frequency echo signal, and complete the micro crack detection of the solid material under test based on the analysis results of the difference frequency echo signal; The preparation method of LN transverse and longitudinal wave dual-mode microprobe is as follows: In a molten environment, lithium niobate crystals are grown with air, and the diameter of the lithium niobate crystals is kept constant during the growth process; Cutting the grown lithium niobate single crystal rod along the X-axis to obtain an x-cut LN wafer; Deposit metal layers on the front and back of the x-cut LN wafer in sequence, and add scribe marks on the back. After dicing, the LN transverse and longitudinal wave integrated device substrate is obtained; The front metal layer of the substrate for preparing the LN transverse and longitudinal wave integrated device is patterned and etched, and the back metal layer of the substrate for preparing the LN transverse and longitudinal wave integrated device in the telescopic working mode is deeply etched to obtain the longitudinal wave device part; The front metal layer of the substrate for the LN transverse and longitudinal wave integrated device is deeply etched to obtain the transverse wave device part. An isolation trench is formed between the transverse wave device part and the longitudinal wave device part to constitute the LN transverse and longitudinal wave integrated device. The prepared LN transverse and longitudinal wave integrated devices are arrayed to complete the preparation of the LN transverse and longitudinal wave dual-mode microprobe.

2. The microcrack detection method according to claim 1, characterized in that: The microcrack detection system specifically comprises: a microcrack detection device, an excitation signal generator and a host computer control system, and a data acquisition card connected in sequence; the receiving end of the microcrack detection device is connected to the data acquisition card, and the data acquisition card is connected to the host computer control system; The microcrack detection device is specifically an LN transverse and longitudinal wave dual-mode microprobe, which is used to convert electrical signals into ultrasonic waves and simultaneously capture the echo signals reflected by the solid material being tested; The excitation signal generator is used to receive the frequency and delay parameters transmitted by the host control system and simultaneously generate two electric pulse signals, including an X channel: a shear wave excitation signal and a Z channel: a longitudinal wave excitation signal; The data acquisition card is used to convert the echo signal into a digital signal at a set sampling rate; The host computer control system is used to control the various components of the microcrack detection system through the FPGA / PCIe interface, coordinate the timing of the microcrack detection system, and run the corresponding algorithm to perform data processing and visualization; The microcrack detection system is preset with signal transmission logic and signal echo logic.

3. The microcrack detection method according to claim 2, characterized in that: The signal transmission logic is specifically as follows: Input the type of solid material to be measured in the host computer control system and load the pre-stored sound velocity of the solid material to be measured; Calculate the time difference between the transverse and longitudinal waves, and the host computer control system uses the time difference between the transverse and longitudinal waves as the delay, and writes it to the excitation signal generator through the FPGA controller; The FPGA controller sends a synchronous trigger pulse to the excitation signal generator, which outputs two electrical pulse signals: X channel: immediately emits a shear wave excitation signal, and Z channel: emits a longitudinal wave excitation signal based on a delay; The microcrack detection device converts electrical signals into ultrasonic waves and transmits them into the solid material being tested. After the transverse and longitudinal waves are compensated for the propagation path, they arrive at the preset depth of the solid material being tested at the same time. Under the action of the transverse and longitudinal waves, the microcracks produce a nonlinear mixing effect and generate a difference frequency component.

4. The microcrack detection method according to claim 3, characterized in that: The signal echo logic is specifically as follows: The micro-crack detection device acquires the echo signal of the difference frequency component, and the data acquisition card converts the difference frequency echo signal from an analog signal to a digital signal at a set acquisition rate; Perform fundamental component analysis on the difference frequency echo digital signal to obtain the shear wave fundamental amplitude; The difference frequency echo digital signal is subjected to bandpass filtering, Hilbert transform and envelope detection in sequence to obtain the envelope sequence of the difference frequency echo digital signal. Within the preset theoretical arrival time window, the envelope sequence is subjected to peak detection to obtain the difference frequency peak value. The nonlinear coefficient of the solid material being tested is obtained by combining the shear wave fundamental amplitude and the difference frequency peak value. The nonlinear coefficient of the solid material being tested is verified to obtain the microcrack detection result of the solid material being tested.

5. The microcrack detection method according to claim 4, characterized in that: After obtaining the echo signal of the difference frequency component, the microcrack detection device further includes: amplifying the echo signal of the difference frequency component and performing anti-aliasing filtering on the echo signal of the difference frequency component to obtain a preprocessed difference frequency component echo signal.

6. The microcrack detection method according to claim 1, characterized in that: After the grown lithium niobate single crystal rod is cut along the X-axis, the method further includes grinding and polishing the cut lithium niobate wafer to obtain an x-cut LN wafer.

7. The microcrack detection method according to claim 6, characterized in that: The growing of lithium niobate crystals in air specifically involves growing the lithium niobate crystals by a Czochralski method.

8. The microcrack detection method according to claim 7, characterized in that: The metal layer is deposited on the front side and the back side of the x-cut LN wafer in sequence, and both the front side metal layer deposition and the back side metal layer deposition are performed by magnetron sputtering.

9. A microcrack detection device, applied to the microcrack detection method according to any one of claims 1 to 8, characterized in that: include: substrate; A conductive adhesive layer is provided on the substrate, and an LN material layer is provided on the conductive adhesive layer, wherein the LN material layer includes a first piezoelectric unit for exciting shear mode shear waves and a second piezoelectric unit for exciting telescopic mode longitudinal waves, an isolation groove is formed between the first piezoelectric unit and the second piezoelectric unit, a matching layer is provided on the first piezoelectric unit and the second piezoelectric unit, an upper electrode and a lower electrode are provided on the first piezoelectric unit, an electric field is formed between the upper electrode and the lower electrode for exciting shear mode shear waves; a positive electrode and a negative electrode are provided on the second piezoelectric unit, an electric field is formed between the positive electrode and the negative electrode for exciting telescopic mode longitudinal waves.

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