Defect size evaluation system based on electromagnetic ultrasonic echo and evaluation method thereof

Abstract

The invention provides a defect size evaluation system and method based on electromagnetic ultrasonic echoes, and the system comprises an excitation signal transmitting module, an echo signal receiving module, a short-time Fourier transform module, and a defect size evaluation module. Wherein the excitation signal sending module is used for sending a body wave excitation signal to a to-be-tested product so as to generate an ultrasonic vibration signal in the to-be-tested product; under the action of a defect to be detected in the product to be detected, the ultrasonic vibration signal forms an ultrasonic echo signal; the echo signal receiving module is used for receiving the ultrasonic echo signal and generating an echo voltage signal; the short-time Fourier transform module is used for performing short-time Fourier transform on the echo voltage signal to form an echo local frequency spectrum; and the defect size evaluation module is used for analyzing the echo local frequency spectrum to determine the defect size of the defect to be detected. The problem that the defect size in the metal plate cannot be effectively recognized can be solved.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing (NDT) technology, and more specifically, to a defect size assessment system and method based on electromagnetic ultrasonic echo. Background Technology

[0002] With the continuous development of the social economy, the demand for metal sheets such as aluminum plates and steel plates in various industries is increasing day by day. Metal sheets (including aluminum plates and steel plates) play a vital role in many fields due to their lightweight, high strength, good thermal conductivity and excellent corrosion resistance, especially in the manufacturing industries such as aviation, automobiles and ships.

[0003] Specifically, in aerospace applications, sheet metal (especially aluminum) can withstand long-term harsh environmental challenges, thus improving mission reliability and economy; in automobile manufacturing, sheet metal (especially aluminum) is lightweight and high-strength, thus significantly reducing vehicle weight, improving fuel efficiency and reducing emissions; in shipbuilding, sheet metal (especially aluminum) is corrosion-resistant and high-strength, making it an ideal material for marine environments.

[0004] Currently, die-cast metal sheets (including aluminum sheets, steel sheets, etc.) have become key materials in various industrial fields, possessing extremely broad development prospects and application value. The entire process of production and application of die-cast metal sheets mainly includes production and processing, mass production, actual use, storage, and transportation; however, these stages may lead to various internal defects in the metal sheets, such as cracks and holes, due to process limitations, external pressure and impact, and electrochemical corrosion.

[0005] In actual use, if the size of defects (especially micro-defects) inside the metal sheet is not effectively identified in the early stage, it will lead to misjudgment of quality assessment and handling strategies, which in turn will cause problems such as deviation in safety margin assessment, distortion of life prediction and difficulty in traceability and location.

[0006] Therefore, there is an urgent need for a solution that can effectively identify the size of micro-defects inside metal sheets. Summary of the Invention

[0007] In view of the above problems, the purpose of this invention is to provide a defect size assessment system and method based on electromagnetic ultrasonic echo, so as to solve the problem that the defect size inside metal plates cannot be effectively identified.

[0008] The defect size assessment system based on electromagnetic ultrasonic echo provided by this invention includes an excitation signal transmission module, an echo signal reception module, a short-time Fourier transform module, and a defect size assessment module; wherein, The excitation signal transmitting module is used to send a body wave excitation signal to the product under test in order to generate an ultrasonic vibration signal within the product under test; Under the influence of the defect to be tested within the product under test, the ultrasonic vibration signal generates an ultrasonic echo signal; The echo signal receiving module is used to receive the ultrasonic echo signal and generate an echo voltage signal; The short-time Fourier transform module is used to perform a short-time Fourier transform on the echo voltage signal to form the local spectrum of the echo. The defect size assessment module is used to analyze the local spectrum of the echo to determine the defect size of the defect to be tested.

[0009] Alternatively, the defect size evaluation module may include a peak value determination unit, a ratio calculation unit, and a defect size determination unit; wherein, The peak value determination unit is used to determine the main lobe peak value and the side lobe peak value under the local spectrum of the echo. The ratio calculation unit is used to calculate the peak ratio of the main lobe peak value to the side lobe peak value; The defect size determination unit is used to input the peak ratio into a preset fitted quantitative relationship curve to obtain the defect size of the defect to be tested.

[0010] Furthermore, an optional solution is that the defect size assessment system based on electromagnetic ultrasonic echo provided by the present invention further includes a defect location determination module; wherein, The defect location determination module is used to determine the defect location of the defect to be tested based on the echo voltage signal; and... The short-time Fourier transform module is used to perform a short-time Fourier transform on the local signal in the echo voltage signal corresponding to the defect location, so as to form the local spectrum of the echo.

[0011] Furthermore, an optional solution is that the defect size assessment system based on electromagnetic ultrasonic echo provided by this invention also includes a signal processing module; wherein, The signal processing module is used to amplify and filter the echo voltage signal, and send the processed echo voltage signal to the defect location determination module.

[0012] Furthermore, an optional solution is that the defect size assessment system based on electromagnetic ultrasonic echo provided by the present invention further includes a defect type determination module, which comprises a displacement amplitude determination unit and a defect type determination unit; wherein, The displacement amplitude determination unit is used to determine the displacement amplitude of the main lobe and side lobes under the local spectrum of the echo; The defect type determination unit is used to determine the defect type of the defect to be tested based on the displacement amplitude of the main lobe and the side lobe.

[0013] Alternatively, the excitation signal transmitting module may include an electromagnetic ultrasonic transducer; wherein, The electromagnetic ultrasonic transducer is used to send the body wave excitation signal to the product under test.

[0014] Alternatively, the body wave excitation signal may include a weighted Hanning window cosine function signal.

[0015] Alternatively, the electromagnetic ultrasonic transducer may be equipped with a probe; and, The probe is a miniature spiral probe.

[0016] On the other hand, the present invention also provides a defect size assessment method based on electromagnetic ultrasonic echo, which assesses the defect type based on the aforementioned electromagnetic ultrasonic echo defect type assessment system; including: The excitation signal transmission module sends a body wave excitation signal to the product under test to generate an ultrasonic vibration signal within the product under test. Under the influence of the defect to be tested within the product under test, the ultrasonic vibration signal generates an ultrasonic echo signal; The echo signal receiving module receives the ultrasonic echo signal and generates an echo voltage signal; The echo voltage signal is subjected to short-time Fourier transform based on the short-time Fourier transform module to form the local spectrum of the echo. The defect size of the defect under test is determined by analyzing the local spectrum of the echo based on the defect size assessment module.

[0017] Alternatively, the defect size assessment module may analyze the local spectrum of the echo to determine the defect size of the defect under test, including: The peak value of the main lobe and the peak value of the side lobe under the local spectrum of the echo are determined based on the peak value determination unit. The peak ratio of the main lobe peak value to the side lobe peak value is calculated based on the ratio calculation unit; The peak ratio is input to a preset fitted quantitative relationship curve based on the defect size determination unit to obtain the defect size of the defect to be tested.

[0018] Compared with the prior art, the defect size assessment system and method based on electromagnetic ultrasonic echo provided by the present invention have the following advantages: By sending a bulk wave excitation signal to the product under test, an ultrasonic vibration signal is generated within the product, thereby forming an ultrasonic echo signal. An echo voltage signal is generated based on the ultrasonic echo signal, and then a short-time Fourier transform is performed on the echo voltage signal to form the local echo spectrum. Finally, the local echo spectrum is analyzed to accurately determine the defect size of the defect under test. In addition, the defect size assessment system based on electromagnetic ultrasonic echo provided by this invention has a simple structure and low manufacturing cost.

[0019] To achieve the foregoing and related objectives, one or more aspects of the invention include the features which will be described in detail below and specifically pointed out in the claims. The following description and accompanying drawings illustrate certain exemplary aspects of the invention. However, these aspects indicate only a few of the various ways in which the principles of the invention can be used. Furthermore, the invention is intended to include all such aspects and their equivalents. Attached Figure Description

[0020] Other objects and results of the invention will become more apparent and readily understood with reference to the following description taken in conjunction with the accompanying drawings and the contents of the claims, and with a more complete understanding of the invention. In the drawings: Figure 1 A schematic diagram illustrating the working principle of existing EMAT technology; Figure 2 This is an overall architecture diagram of a defect size assessment system based on electromagnetic ultrasonic echo provided according to an embodiment of the present invention; Figure 3 A comparison diagram of the local time-domain spectrum and local frequency-domain spectrum of the echo of a defect with a size of 1mm-6mm according to an embodiment of the present invention; Figure 4 A preset fitted quantitative relationship curve is provided for the embodiments of the present invention; Figure 5 This is a flowchart of a defect size assessment method based on electromagnetic ultrasonic echo provided according to an embodiment of the present invention. Detailed Implementation

[0021] In the following description, numerous specific details are set forth for illustrative purposes and to provide a thorough understanding of one or more embodiments. However, it will be apparent that these embodiments may also be implemented without these specific details. In other instances, well-known structures and devices are shown in block diagram form for ease of description of one or more embodiments.

[0022] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] Before introducing the defect size assessment system and method based on electromagnetic ultrasonic echo provided by this invention, it is necessary to first explain the existing non-destructive testing methods for metal sheets (used to detect internal defects in metal sheets). Currently, common non-destructive testing methods mainly include ultrasonic testing (UT), eddy current testing (ECT), magnetic flux leakage testing (MFLT), and radiographic testing (RT). Among them, eddy current testing can detect very small internal defects such as cracks, but due to the skin effect, eddy current testing is mainly used for surface and near-surface defects and cannot detect deep defects. Magnetic flux leakage testing is relatively more convenient to operate and is suitable for testing large-area steel pipes, tanks, and other large structures, but it cannot test non-ferromagnetic materials. Radiographic testing has high resolution and is applicable to a wide range of materials, but the testing cost is high and it is not convenient to carry or conduct on-site testing.

[0024] Among all non-destructive testing methods, electromagnetic ultrasonic testing (EMAT) technology has the widest application range. Due to its high efficiency, safety, and convenience, EMAT is widely used both domestically and internationally, and is currently the fastest-growing and most frequently used non-destructive testing technology. Its main advantages include: strong applicability to various objects, large detection depth, accurate defect location, high sensitivity, fast detection speed, and harmlessness to the human body, making it very suitable for direct field use. These advantages make ultrasonic testing a highly valuable and promising testing technology.

[0025] The working principle of existing electromagnetic ultrasonic testing technology is detailed below. Electromagnetic ultrasonic testing technology essentially uses the principle of electromagnetic coupling, which involves the coupling of three physical fields: electromagnetism, acoustics, and solid mechanics. EMAT differs significantly from traditional piezoelectric ultrasonic testing. In piezoelectric ultrasonic applications, piezoelectric materials are used as sensors or transmitters. When a voltage is applied to the piezoelectric material, it generates mechanical vibrations, which propagate as ultrasonic waves. When these ultrasonic vibrations strike the piezoelectric material, they generate electrical signals. This process requires contact with the object being tested or the transmission of ultrasonic waves through a coupling agent (water or gel). EMAT, however, operates on the principle of electromagnetic induction, eliminating the need for a medium. It utilizes the interaction between the magnetic field generated by the alternating current through a coil and the magnetism within the metal material to produce ultrasonic signals. This method allows for the generation and reception of ultrasonic waves on or inside metal surfaces without the need for a coupling agent.

[0026] The transduction mechanism of EMAT is divided into Lorentz force, magnetization force and magnetostriction mechanism. In non-ferromagnetic materials, due to their difficulty in being magnetized, it is more appropriate to use EMAT based on Lorentz force to generate ultrasonic signals. In ferromagnetic materials, the excitation of ultrasonic signals is mainly caused by the combined action of magnetization force and magnetostriction force, so it is more appropriate to use EMAT based on magnetostriction mechanism.

[0027] Furthermore, when a conductor (such as a metal) moves in a magnetic field, or when the magnetic field changes within a conductor, a Lorentz force is generated. In EMAT technology, an alternating current generated by a coil excites a changing magnetic field. When this magnetic field interacts with the induced current on the metal surface, the resulting Lorentz force excites ultrasonic waves within the material. Because this mechanism relies on the interaction between current and magnetic field, it is effective for both non-magnetic and magnetic materials. The magnetization mechanism involves changes in the magnetization state of a magnetic material, leading to the generation of internal forces. In EMAT technology, a changing magnetic field can alter the magnetization state of a material, thereby generating a magnetization force. The generation of this magnetization force depends on the material's magnetism; therefore, this mechanism is primarily applicable to magnetic materials. Magnetostriction describes the deformation behavior of magnetic materials under the influence of an external magnetic field. The mechanical stress generated by this deformation can excite ultrasonic waves within the material.

[0028] The working principle of EMAT technology is as follows: Figure 1 As shown, combined with Figure 1 It can be known that: The magnitude of the Lorentz force can be calculated using Maxwell's equations, and its expression is as follows: (2-1) (2-2) (2-3) (2-4) in The magnetic field strength is expressed in units of 1 / 2 Ω. ; The current density of the excitation coil, in units of ; The density of displacement current, in units of ; The electric field strength is expressed in units of 1 / 2 Ω. ; Magnetic flux density, unit: ; Free charge volume density, in units of .

[0029] At this time, the magnetic induction intensity generated by the permanent magnet is: (2-5) in, The magnetic permeability of the tested component is given.

[0030] Since there is no displacement current inside the specimen, When the value is 0, equation (2-1) can be written as: (2-6) Furthermore, the magnetic flux density in the test piece is: (2-7) Therefore, conductivity can be used to... Calculate the induced eddy current intensity and current density for: (2-8) (2-9) The Lorentz force experienced by a single particle within the specimen for: (2-10) The total Lorentz force on the specimen can be obtained by adding the individual forces together. The total Lorentz force on the specimen is: (2-11) When testing non-ferromagnetic materials, only the influence of the Lorentz force inside the specimen needs to be considered. Furthermore, since the products to be tested in this invention are mainly die-cast aluminum plates, there is no need to consider magnetization force and magnetostrictive force.

[0031] Furthermore, for electromagnetic ultrasonic testing technology, existing methods for extracting defect dimensions such as width and length are based on defect size estimation methods using the echo amplitude ratio. Specifically, when a guided wave encounters a defect during propagation, the scattered and reflected energy is related to the defect's geometric dimensions. The wider the defect, the stronger the echo energy, while the bottom echo energy is correspondingly attenuated. By fitting the amplitude ratio of these two factors, a functional relationship between defect size and amplitude ratio can be established. Therefore, existing methods typically use the ratio of defect echo amplitude to bottom echo amplitude to reflect the defect size.

[0032] Specifically, when ultrasonic waves propagate through a test specimen, if defects such as cracks, holes, or corrosion exist along their path, the ultrasonic energy will be reflected and scattered at the defect interface, causing some energy to return and form a defect echo signal. Simultaneously, some ultrasonic energy continues to propagate and reaches the bottom surface of the specimen, then reflects back to form a bottom surface echo signal. As the defect width increases, the reflection and scattering effects intensify, and the amplitude of the defect echo signal increases accordingly, while the energy transmitted to the bottom surface decreases, resulting in a weakening of the bottom surface echo amplitude. By measuring and calculating the amplitude ratio of the defect echo to the bottom surface echo, a quantitative index closely related to the defect's geometric width can be obtained. Furthermore, research shows that the amplitude ratio of the defect echo to the bottom surface echo often exhibits a relatively stable monotonic relationship with the defect size (such as the defect width). Therefore, a functional relationship between the defect size and the amplitude ratio can be established through experimental calibration or mathematical fitting for defect size characterization.

[0033] However, the existing defect size estimation methods based on the echo amplitude ratio of defect echo to bottom surface echo also have certain shortcomings. When the defect is deep or the defect size is small, the defect echo is often confused with the noise signal, resulting in poor detection accuracy and difficulty in accurately extracting amplitude features. As a result, the existing defect size estimation methods based on echo amplitude ratio have insufficient detection accuracy for micro-defects or deep defects.

[0034] To address the problem that existing electromagnetic ultrasonic testing techniques lack sufficient accuracy in estimating the size of micro-defects or deep defects, this invention provides a novel defect size assessment system based on electromagnetic ultrasonic echoes. The specific architecture of the defect size assessment system based on electromagnetic ultrasonic echoes provided by this invention is described in detail below.

[0035] Figure 1 The overall architecture of a defect size assessment system based on electromagnetic ultrasonic echo provided according to an embodiment of the present invention is shown. Figure 2 The simulation detection principle of the defect size assessment system based on electromagnetic ultrasonic echo provided by the present invention is illustrated for different types of defects. Figure 3The diagram illustrates the spectrum generated by the electromagnetic ultrasonic echo-based defect size assessment system according to an embodiment of the present invention for a vertical defect. Figure 4 The spectrum generated by the electromagnetic ultrasonic echo-based defect size assessment system according to an embodiment of the present invention for transverse defects is shown.

[0036] Combination Figures 1 to 4 The present invention provides a defect size assessment system based on electromagnetic ultrasonic echo, comprising an excitation signal transmission module, an echo signal receiving module, a short-time Fourier transform module, and a defect size assessment module. The excitation signal transmission module transmits a bulk wave excitation signal (excitation magnetic field) to the product under test (metal sheet, especially die-cast aluminum sheet). Under the influence of the bulk wave excitation signal, the product under test generates an ultrasonic vibration signal within it. The ultrasonic vibration signal propagates within the product under test and forms an ultrasonic echo signal based on the defect within the product. The echo signal receiving module receives the ultrasonic echo signal and generates an echo voltage signal based on it. The short-time Fourier transform module performs a short-time Fourier transform on the echo voltage signal to form a local echo spectrum. The defect size assessment module analyzes the local echo spectrum to determine the defect size of the defect under test.

[0037] It should be noted that the body wave excitation signal sent by the excitation signal sending module to the product under test is a body wave high-frequency excitation magnetic field. The body wave high-frequency excitation magnetic field will generate eddy currents inside the product under test. Under the action of the external magnetic field of the excitation signal sending module, the eddy currents will be subjected to mechanical action and generate high-frequency vibration, thereby generating ultrasonic vibration signals (ultrasound).

[0038] It should be further explained that when there is no defect inside the product under test, the ultrasonic vibration signal enters the product under test and is reflected back from the bottom of the product under test; when there is a defect inside the product under test, part of the ultrasonic vibration signal will be reflected from the defect cross-section, and the remaining ultrasonic vibration signal will be reflected from the bottom of the product under test; when the echo signal receiving module with scanning function is directly above the defect, the ultrasonic echo signal reflected back from the defect can be obtained.

[0039] When the probe is positioned above the defect during scanning, the acquired ultrasonic echo signal contains obvious defect reflection echoes. To quantitatively analyze this ultrasonic echo signal, a short-time Fourier transform (STFT) can be used to convert the time-domain signal of the ultrasonic echo signal to the frequency domain, obtaining local spectrum diagrams of the ultrasonic echo signal at different frequencies. Abrupt changes caused by defect edges and sharp corners can lead to sharp changes in the time-domain waveform of the scattered wave (e.g., sudden amplitude jumps or abrupt phase changes), increasing its high-frequency components. When the defect width is small, the ultrasonic echo signal reflected from the defect is also small. In this case, the characteristic parameters reflecting the defect characteristics (i.e., the peak ratio of the sidelobe peak to the main lobe peak) can be extracted by analyzing the sidelobe peaks and main lobe peaks in the local spectrum diagram and calculating their peak-to-peak ratio. In practical design, taking defects ranging from 1mm to 6mm in size as an example, the local time-domain spectrum and local frequency-domain spectrum of the ultrasonic echo signal for defects of various sizes can be determined first (e.g.,...). Figure 3 (As shown), then the peak ratio of the sidelobe peak value to the main lobe peak value under different defect sizes is calculated. Subsequently, the discrete points of the peak ratio obtained under different defect sizes are fitted to establish a quantitative relationship between the defect size (width) and the peak ratio (of the main lobe peak value and the sidelobe peak value). Through this quantitative relationship, the fitted quantitative relationship curve can be simulated (as shown). Figure 4 (as shown in the figure) (i.e., the preset fitted quantitative relationship curve).

[0040] The fitted quantitative relationship curve can be used to characterize the quantitative relationship between the actual size of the defect and the peak ratio. Subsequently, based on the preset fitted quantitative relationship curve, the specific size of other defects to be tested can be accurately determined by the peak ratio of the main lobe peak value to the side lobe peak value, thus providing a basis for the quantitative evaluation of defect size.

[0041] Furthermore, in practical use, the defect size assessment module may include a peak value determination unit, a ratio calculation unit, and a defect size determination unit; wherein, the peak value determination unit is used to determine the main lobe peak value and the side lobe peak value under the local spectrum of the echo; the ratio calculation unit is used to calculate the peak value ratio of the main lobe peak value and the side lobe peak value; and the defect size determination unit is used to input the peak value ratio into a preset fitted quantitative relationship curve to obtain the specific defect size of the defect to be tested.

[0042] In a specific embodiment of the present invention, to realize the design of the excitation signal transmission module, the excitation signal transmission module may include an electromagnetic ultrasonic transducer, which is used to send a bulk wave excitation signal to the product under test. Further, the electromagnetic ultrasonic transducer is equipped with a miniature spiral probe, which is used to scan the product under test. An excitation coil and a permanent magnet are disposed within the miniature spiral probe; wherein, the excitation coil is used to generate a bulk wave excitation signal, which generates eddy currents within the product under test. These eddy currents, based on the external magnetic field generated by the permanent magnet, form an ultrasonic vibration signal within the product under test.

[0043] It should be noted that the specific parameters of the excitation coil can be determined through simulation design. For example, in the simulation design, the width of the crack defect can be preset to a fixed value of 2mm, while keeping the size of the permanent magnet, the lift-off (lift-off height) of the excitation coil, and the frequency and intensity of the body wave excitation signal unchanged. The probe is designed as a spiral with an inner diameter of 1mm. In the parametric scanning of the simulation, the wire spacing in the excitation coil is set to 0.1mm to 0.2mm, the scanning step size is 0.01mm, the number of turns of the excitation coil is set to 10 to 30 turns, the scanning step size is 1, and the line segment on the surface of the product under test below the excitation coil is taken as the observation line. The average displacement of the defect echo on the observation line is calculated. It is found that the defect echo is the largest when the wire spacing is 0.16mm and the number of turns is 15. Therefore, the wire spacing in the excitation coil of the miniature spiral probe provided by the present invention is preferably set to 0.16mm, the number of turns is preferably set to 15, and the total length is preferably set to 5.5mm.

[0044] Furthermore, it should be noted that during the propagation of ultrasonic vibration signals, different frequency components have different propagation speeds. This dispersion characteristic leads to the dispersion and accelerated attenuation of sound wave energy, which easily causes waveform distortion. To mitigate this effect, this invention preferably uses a weighted Hanning window cosine function signal as the body wave excitation signal of the electromagnetic ultrasonic transducer. The Hanning window, as a smoothing window function, can effectively control the signal bandwidth. By modulating the cosine waveform, the concentration of signal energy can be maintained, thereby reducing the diffusion of ultrasonic vibration signals and helping to reduce energy loss and signal distortion during the propagation of ultrasonic vibration signals. The excitation function of the body wave excitation signal can be expressed as: Among them, current Preferably 1A, The incentive cycle is configured to have 5 cycles. As a time variable in the incentive process, This refers to the actual excitation frequency.

[0045] In a preferred embodiment of the present invention, the defect size assessment system based on electromagnetic ultrasonic echo provided by the present invention may further include a defect location determination module; wherein, the defect location determination module is used to determine the defect location of the defect to be tested based on the echo voltage signal; and, a short-time Fourier transform module is used to perform a short-time Fourier transform on the local signal in the echo voltage signal corresponding to the defect location to form a local echo spectrum. This approach not only allows for the detection of both the location and type of the defect to be tested using the same detection system, but also enables the performance of a short-time Fourier transform on only a local signal of the echo voltage signal based on the location of the defect to be tested, thereby reducing the number of internal operation steps and further improving the overall system efficiency.

[0046] Furthermore, to improve the detection accuracy of the defect size assessment system based on electromagnetic ultrasonic echo provided by the present invention, the defect size assessment system based on electromagnetic ultrasonic echo provided by the present invention may also include a signal processing module; wherein, the signal processing module uses analog circuits to amplify, filter and demodulate the echo voltage signal, and sends the processed echo voltage signal to the defect location determination module, and the defect location determination module subsequently determines the precise location of the defect to be tested based on the processed echo voltage signal.

[0047] In one specific embodiment of the present invention, the defect location determination module may include an oscilloscope. The processed echo voltage signal is input to the oscilloscope for display, and the changes in the echo signal are observed. If a defect echo appears during the probe scanning process, and the amplitude of the defect echo changes from high to low and then back to high within a specific scanning area, the lowest point is the center point of the defect during the scanning process. It is determined that the defect exists directly below the probe. The defect depth can then be calculated by the time difference between the excitation and the defect echo. After determining the defect depth, the specific location of the defect can be determined.

[0048] It should be noted that, in order to enable the echo signal receiving module to receive ultrasonic echo signals and generate echo voltage signals, the echo signal receiving module may also include the aforementioned electromagnetic ultrasonic transducer (which may share the same electromagnetic ultrasonic transducer with the excitation signal sending module); wherein, the excitation coil in the electromagnetic ultrasonic transducer may also serve as a receiving coil to receive ultrasonic echo signals and generate induced electromotive force within it, thereby forming an echo voltage signal.

[0049] Furthermore, to achieve accurate analysis of the defect type under test by the defect size assessment module, the defect size assessment system based on electromagnetic ultrasonic echo provided by this invention may also include a defect type determination module. This defect type determination module may include a displacement amplitude determination unit and a defect type determination unit. The displacement amplitude determination unit is used to determine the displacement amplitude of the main lobe and side lobes under the local spectrum of the echo. The defect type determination unit is used to determine the defect type of the defect under test based on the displacement amplitude of the main lobe and side lobes.

[0050] It should be noted that the internal defects of sheet metal products under test are mainly classified into two categories: crack defects (i.e., transverse defects) and hole defects (i.e., vertical defects). Furthermore, experimental data shows that the displacement amplitudes of the main lobe and side lobe in the local echo spectrum of crack defects are significantly different from those of hole defects. Therefore, the defect type can be determined by the displacement amplitudes of the main lobe and side lobe in the local echo spectrum.

[0051] Furthermore, by performing time-domain analysis on the echo voltage signal, characteristic parameters related to defect type discrimination are extracted. Within the time period of a single echo of the defect, a short-time Fourier transform is performed on the time-domain signal (i.e., the local signal in the echo voltage signal corresponding to the defect location), yielding echo local spectra of pore defects and crack defects. Observation of the two echo local spectra reveals that when the defect is a crack defect, its echo local spectra have obvious side lobes near the main lobe at 4MHz. This is because crack defects (transverse defects) have a narrower width, and the defect edges and sharp points... The abrupt change in the collection caused by the angle leads to a sharp change in the time-domain waveform of the scattered wave (e.g., a sudden jump in amplitude or a rapid change in phase), resulting in an increase in its high-frequency components. Furthermore, since the width of crack defects (transverse defects) is relatively narrow, the ultrasonic echo signal reflected back to the echo signal receiving module from crack defects is relatively small. As a result, the side lobes on the high-frequency side of the main lobe can be significantly observed, thereby enabling the identification of crack-type defects. In contrast, in the echo local spectrum diagram of hole-type defects, no corresponding side lobes are generated on the high-frequency side of the main lobe, thereby enabling the identification of hole-type defects.

[0052] On the other hand, to further illustrate the process principle of the electromagnetic ultrasonic echo defect type assessment system provided by the present invention, the present invention also provides a defect size assessment method based on electromagnetic ultrasonic echo. Figure 5 This paper illustrates a schematic flowchart of the defect size assessment method based on electromagnetic ultrasonic echo provided by the present invention. Figure 5 As shown, the method includes: S110: The excitation signal transmission module sends a bulk wave excitation signal (excitation magnetic field) to the product under test (metal sheet, especially die-cast aluminum sheet). Under the action of the bulk wave excitation signal, the product under test will generate eddy currents inside it. The eddy currents generate ultrasonic vibration signals under the action of the external magnetic field provided by the excitation signal transmission module. S120: The ultrasonic vibration signal propagates within the product under test and forms an ultrasonic echo signal based on the defect within the product under test; S130: The receiving coil in the echo signal receiving module receives the ultrasonic echo signal, and an induced electromotive force is generated in the receiving coil to form an echo voltage signal. S140: The short-time Fourier transform module is used to perform a short-time Fourier transform on the echo voltage signal to form the local spectrum of the echo. S150: Based on the defect size assessment module, the displacement amplitude of the main lobe and side lobe in the local spectrum of the echo is analyzed to determine the defect size of the defect to be tested.

[0053] Furthermore, the local spectrum of the echo is analyzed based on the defect size assessment module to determine the defect size of the defect under test, further including: The peak value of the main lobe and the peak value of the side lobe under the local spectrum of the echo are determined based on the peak value determination unit. The peak ratio of the main lobe peak value to the side lobe peak value is calculated based on the ratio calculation unit; The peak ratio is input to a preset fitted quantitative relationship curve based on the defect size determination unit to obtain the defect size of the defect to be tested.

[0054] As can be seen from the above specific embodiments, the defect size assessment method based on electromagnetic ultrasonic echo provided by the present invention has at least the following advantages: 1. By sending a body wave excitation signal to the product under test, an ultrasonic vibration signal is generated within the product under test, which in turn forms an ultrasonic echo signal. An echo voltage signal is generated based on the ultrasonic echo signal, and then a short-time Fourier transform is performed on the echo voltage signal to form the local echo spectrum. Finally, the local echo spectrum is analyzed to accurately determine the defect type of the defect under test. 2. The defect size assessment system based on electromagnetic ultrasonic echo provided by this invention has a simple structure and low manufacturing cost; 3. By setting up a signal processing module and a defect location determination module, the location of defects inside the product under test can be accurately determined.

[0055] As per the above reference Figures 1 to 5The defect size assessment system and method based on electromagnetic ultrasonic echo according to the present invention are described by way of example. However, those skilled in the art should understand that various modifications can be made to the defect size assessment system and method based on electromagnetic ultrasonic echo proposed in the present invention without departing from the scope of the invention. Therefore, the scope of protection of the present invention should be determined by the contents of the appended claims.

Claims

1. An electromagnetic acoustic transducer based system for evaluating the size of a defect; characterized in that, The system comprises an excitation signal sending module, an echo signal receiving module, a short-time Fourier transform module, and a defect size evaluation module. The excitation signal sending module is configured to send a body wave excitation signal to a product to be tested, so as to generate an ultrasonic vibration signal in the product to be tested. The ultrasonic vibration signal forms an ultrasonic echo signal under the action of a defect to be tested in the product to be tested. The echo signal receiving module is configured to receive the ultrasonic echo signal and generate an echo voltage signal. The short-time Fourier transform module is configured to perform short-time Fourier transform on the echo voltage signal to form an echo local frequency spectrum. The defect size evaluation module is configured to analyze the echo local frequency spectrum to determine the defect size of the defect to be tested.

2. The electromagnetic acoustic echo-based defect size evaluation system of claim 1, wherein, The defect size evaluation module comprises a peak value determination unit, a ratio calculation unit, and a defect size determination unit. The peak value determination unit is configured to determine a main lobe peak value and a side lobe peak value of the echo local frequency spectrum. The ratio calculation unit is configured to calculate a peak value ratio of the main lobe peak value and the side lobe peak value. The defect size determination unit is configured to input the peak value ratio into a preset fitting quantitative relationship curve to obtain the defect size of the defect to be tested.

3. The electromagnetic acoustic echo-based defect size evaluation system of claim 1, wherein, The system further comprises a defect position determination module. The defect position determination module is configured to determine the defect position of the defect to be tested according to the echo voltage signal. The short-time Fourier transform module is configured to perform short-time Fourier transform on a local signal corresponding to the defect position in the echo voltage signal to form the echo local frequency spectrum.

4. The electromagnetic acoustic echo-based defect size evaluation system of claim 3, wherein, The system further comprises a signal processing module. The signal processing module is configured to amplify and filter the echo voltage signal and send the processed echo voltage signal to the defect position determination module.

5. The electromagnetic acoustic echo-based defect size evaluation system of claim 1, wherein, The system further comprises a defect type determination module. The defect type determination module comprises a displacement amplitude determination unit and a defect type determination unit. The displacement amplitude determination unit is configured to determine a displacement amplitude of a main lobe and a side lobe of the echo local frequency spectrum.

6. The electromagnetic acoustic echo-based defect size evaluation system of claim 1, wherein, The defect type determination unit is configured to determine the defect type of the defect to be tested according to the displacement amplitude of the main lobe and the side lobe. The excitation signal sending module comprises an electromagnetic acoustic transducer. The electromagnetic acoustic transducer is configured to send the body wave excitation signal to the product to be tested.

7. The electromagnetic acoustic echo-based defect size evaluation system of claim 6, wherein The body wave excitation signal comprises a cosine function signal of a weighted Hanning window.

8. The electromagnetic acoustic echo-based defect size evaluation system of claim 6, wherein The electromagnetic acoustic transducer is configured with a probe.

9. A method for evaluating the size of a defect based on electromagnetic acoustic echoes, characterized in that, The probe is a micro spiral probe. The electromagnetic acoustic echo-based defect type evaluation system of any one of claims 1 to 8 is used for defect type evaluation, comprising: sending a body wave excitation signal to a product to be tested based on an excitation signal sending module, so as to generate an ultrasonic vibration signal in the product to be tested; the ultrasonic vibration signal forms an ultrasonic echo signal under the action of a defect to be tested in the product to be tested; receiving the ultrasonic echo signals based on an echo signal receiving module and generating echo voltage signals; performing short-time Fourier transform on the echo voltage signals based on a short-time Fourier transform module to form echo local spectra; analyzing the echo local spectra based on a defect size evaluation module to determine the defect size of the defect under test.

10. The electromagnetic acoustic echo-based defect size evaluation method according to claim 9, wherein, The analyzing the echo local spectra based on the defect size evaluation module to determine the defect size of the defect under test comprises: determining main lobe peak values and side lobe peak values under the echo local spectra based on a peak value determination unit; calculating a peak value ratio of the main lobe peak values and the side lobe peak values based on a ratio calculation unit; inputting the peak value ratio to a preset fitting quantitative relationship curve based on a defect size determination unit to obtain the defect size of the defect under test.

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