Pulse electromagnetic-ultrasonic composite ferromagnetic material structure defect detection probe, system and method

Abstract

The invention provides a pulse electromagnetic-ultrasonic composite ferromagnetic material structure defect detection probe, system and method. The probe comprises a core winding coil, a magnetic core, an inflection-shaped coil, a metal top cover, a fastening bolt, a metal shell, a ceramic chip, a transparent film, a patch cord and an adapter; the system comprises a probe, a signal generation device, a power amplifier, a long pulse current source, a filter, a pre-amplifier, a signal acquisition device and a computer, and the specific working method comprises the steps that the signal generator generates trigger signals T1 and T2 respectively, and current signals P1 and P2 are generated through the long pulse current source and the power amplifier and transmitted to the probe; a pulse electromagnetic-ultrasonic signal is generated based on an electromagnet and a dictionary stretching effect, a receiving coil in an inflection coil is used for capturing a pulse electromagnetic signal and an ultrasonic echo signal, and finally data extraction and analysis are performed to determine whether a defect exists or not. According to the invention, composite detection of pulse electromagnetic and electromagnetic ultrasonic technologies is realized, detection methods can be switched according to detection scenes and requirements, and the method has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology, specifically to a pulsed electromagnetic-ultrasound composite probe, system, and method for detecting structural defects in ferromagnetic materials. Background Technology

[0002] For defect detection methods in ferromagnetic material structures, common non-destructive testing (NDT) methods such as magnetic particle testing, X-ray inspection, and eddy current testing generally suffer from drawbacks such as low detection efficiency and limited detection range. Electromagnetic ultrasonic testing utilizes the principle of electromagnetic induction, exciting ultrasonic waves through the Lorentz force or magnetostriction effect. Ultrasonic waves are elastic waves; during propagation, they are reflected when encountering defects or material boundaries. The reflected waves propagate to the probe, converting the mechanical signal into an electrical signal, thus enabling rapid detection of large-area defects on the specimen surface. However, while electromagnetic ultrasonic testing offers advantages such as high detection speed and efficiency, it suffers from a near-field blind zone, limiting its application and making detection in areas close to the probe often difficult.

[0003] Pulsed electromagnetic testing (PET), as an important branch of electromagnetic nondestructive testing (NDT) technology, offers several significant advantages over traditional NDT methods (such as conventional eddy current testing, ultrasonic testing, and radiographic testing). These advantages include wide-spectrum excitation, enabling the detection of multiple depths and defect types; the elimination of coupling agents, allowing adaptation to complex surfaces and harsh environments; and high testing speed, suitable for batch or online inspections. Pulsed electromagnetic testing has demonstrated outstanding performance in complex operating conditions and high-quality inspection scenarios. However, PLT has relatively low efficiency for large-area, wide-range inspections, often requiring specialized scanning mechanisms, which significantly increases the complexity of the inspection process. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention aims to provide a pulsed electromagnetic-ultrasound composite ferromagnetic material structural defect detection probe, system, and method. The probe has a compact and flexible structure, requires no coupling agent, and the proposed system can be used for both pulsed electromagnetic detection and electromagnetic ultrasonic detection, achieving dual-purpose functionality. The detection method can be adjusted for different application scenarios. For example, pulsed electromagnetic detection can be used for near-field, near-surface defect detection, while electromagnetic ultrasonic detection can be used for far-field, long-distance detection. The two methods complement each other, achieving high-efficiency and full-coverage detection.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A pulsed electromagnetic-ultrasound composite ferromagnetic material structural defect detection probe includes a core coil 1, a magnetic core 2, a folded coil 3, a metal top cover 4, fastening bolts 5, a metal shell 6, a ceramic sheet 7, a transparent film 8, an adapter cable 9, and an adapter interface 10. The core coil 1 has a multi-turn structure and is wound around the magnetic core 2. Both are embedded inside the metal shell 6 and clamped by the metal top cover 4 and the metal shell 6 through the fastening bolts 5. The ceramic sheet 7 is located directly below the magnetic core 2, and the folded coil 3 is located directly below the ceramic sheet 7 and is bonded to the lower surface of the ceramic sheet 7. The transparent film 8 is located below the folded coil 3 and serves a protective function. The adapter cable 9 is located inside the detection probe. One end of the adapter cable 9 is connected to the adapter interface 10, and the other end is connected to the core coil 1 and the folded coil 3 respectively. The adapter interface 10 is fixed to the outside of the metal shell 6.

[0006] Preferably, the core coil 1 and the folded coil 3 are made of high-temperature resistant enameled copper wire. The folded coil 3 is a double-layer coil, with one layer used to excite ultrasonic waves (as the transmitting coil) and the other layer used to receive ultrasonic signals (as the receiving coil). The transmitting and receiving coils are functionally independent, have strong anti-interference capabilities, and help improve the signal-to-noise ratio.

[0007] Preferably, the metal top cover 4 and the metal shell 6 are 3D printed and made of lightweight aluminum alloy, which has good corrosion resistance and heat dissipation; the two are connected by fastening bolts 5 to ensure structural stability and reliability.

[0008] Preferably, the magnetic core 2 is made of a high-permeability material, which can reduce leakage magnetic loss and improve energy utilization efficiency. The material's interior is used to transmit magnetic field lines, and the core coil 1 is spirally wound on its outer surface. The two together form an electromagnet. Under the same conditions, the more turns the coil has, the stronger the magnetism.

[0009] Preferably, the folded coil 3 is U-shaped, fabricated using flexible printed circuit technology, and consists of straight segments and curved segments, wherein the spacing between adjacent straight segments is half the wavelength of the ultrasonic wave. λ An odd multiple of 2 helps ultrasound achieve constructive interference in the propagation direction, increasing the intensity of the ultrasound signal. The coil width is smaller than the width of the magnetic core 2, ensuring that the magnetic core completely covers the coil, maximizing the use of the "effective magnetic field", and enhancing the concentration of the magnetic field to improve the intensity of the ultrasound signal.

[0010] Preferably, at least three adapter ports 10 are provided for connection to the long pulse current source 20, the power amplifier 19, and the filter 21, respectively, wherein the adapter cable 9 is a cable with electromagnetic shielding effect.

[0011] A pulsed electromagnetic-ultrasonic composite ferromagnetic material structural defect detection system is disclosed. The system includes a detection probe, a signal generating device 18, a power amplifier 19, a long pulse current source 20, a filter 21, a preamplifier 22, a signal acquisition device 23, and a computer 24. The signal generating device 18 is connected to the power amplifier 19 and the long pulse current source 20 via cables. The power amplifier 19 is connected to the folded coil 3 of the detection probe via a cable. The long pulse current source 20 is connected to the core coil 1 of the detection probe via a cable. The input channel of the filter 21 is connected to the duplexer in the power amplifier 19 or the receiving coil in the folded coil 3. The output channel of the filter 21 is connected to the input channel of the preamplifier 22. The amplified output channel of the preamplifier 22 is connected to the signal acquisition device 23. The input channel of the signal acquisition device 23 is connected to the folded coil 3 of the detection probe. The output channel of the signal acquisition device 23 is connected to the computer 24 via a cable for transmitting and storing signals.

[0012] The method for detecting defects in ferromagnetic material structures using a pulsed electromagnetic-ultrasound composite system includes a pulsed electromagnetic detection method suitable for near-field, near-surface detection and an electromagnetic ultrasonic detection method suitable for far-field, long-distance detection. The electromagnetic ultrasonic detection method includes the following steps: S1. A first trigger signal T1 and a second trigger signal T2 are generated using a signal generating device 18. The first trigger signal T1 is transmitted to a long pulse current source 20 via a wire to trigger the long pulse current source to generate a long pulse current signal P1. The second trigger signal T2 is transmitted to a power amplifier 19 via a wire to generate a high-frequency excitation current signal P2. S2. The long pulse current signal P1 and the high frequency excitation current signal P2 are transmitted to the detection probe, and then transmitted to the core coil 1 and the folded coil 3 through the adapter 10 of the detection probe, respectively, to generate a static bias magnetic field 12 and a dynamic magnetic field 14 on the surface of the ferromagnetic material specimen for a period of time. Under the coupling of the two magnetic fields, the surface ultrasonic waves 15 are excited based on the magnetostrictive effect. S3. When the surface ultrasonic wave 15 encounters a defect or end face, it generates a reflected wave 16. When the reflected wave returns to the detection probe, it is converted into an electrical signal of the receiving coil in the folded coil 3 through the magnetostriction inverse effect. The electrical signal of the receiving coil in the folded coil 3 is transmitted to the signal acquisition device 23 for acquisition after passing through the filter 21 and the preamplifier 22. Finally, it is displayed and stored in the computer 24. S4. Computer 24 displays the received coil electrical signal diagram of the folded coil 3 after filtering and amplification. Since the end face of the ferromagnetic material specimen will reflect the surface ultrasonic waves 15, the end face echo with a large signal amplitude can be seen in the signal diagram. If there is a defect, since the distance between the defect and the detection probe is less than the distance between the far end face of the ferromagnetic material specimen and the detection probe, the defect echo in the signal diagram will precede the far end face echo in time. Then, the ultrasonic wave propagation distance is calculated based on the ultrasonic wave velocity and the time when the defect echo appears. Half of the ultrasonic wave propagation distance is recorded as the distance between the defect and the detection probe, thus detecting the defect. Otherwise, the defect is not detected. The pulse electromagnetic detection method includes the following steps: S1. A first trigger signal T1 is generated using the signal generating device 18. The first trigger signal T1 is transmitted to the long pulse current source 20 via a wire to trigger the long pulse current source to generate a long pulse current signal P1. S2. The long pulse current signal P1 is transmitted to the core coil 1 through the adapter 10 of the detection probe. Due to the principle of electromagnetic induction, a static bias magnetic field 12 is generated on the surface of the ferromagnetic material specimen for a period of time, thereby magnetizing the near surface of the ferromagnetic material specimen. S3. When the static bias magnetic field 12 encounters a defect near the surface of the ferromagnetic material specimen, a leakage magnetic field will be generated. Due to the leakage magnetic field, the magnetic flux passing through the folded coil 3 changes, causing the electrical signal of the receiving coil in the folded coil 3 to be distorted. The distorted signal is transmitted to the signal acquisition device 23 through the wire to complete the acquisition, and then transmitted to the computer 24 for display. S4. Finally, determine whether there is a defect. First, use steps S1-S3 to obtain the electrical signal of the receiving coil in the folded coil 3 when the ferromagnetic material specimen is defect-free. Record this as the original signal. Then, perform differential analysis between the signal obtained in steps S1-S3 and the original signal and extract the amplitude. If there is a defect, that is, a leakage magnetic field caused by the defect exists, the leakage magnetic field will increase the magnetic flux passing through the folded coil 3, and the amplitude of the distorted signal will be greater than the amplitude of the original signal. When the amplitude of the differential signal is much greater than the system noise, it is determined that there is a defect directly below the detection probe. Otherwise, there is no defect.

[0013] Compared with the prior art, the present invention has at least the following beneficial effects: (1) Existing sensors are bulky and lack flexible detection capabilities. However, the sensor of this invention is based on an electromagnet architecture, which eliminates the limitation of fixed magnetic field strength of traditional permanent magnet probes. It controls the input voltage and thus changes the magnetic field strength, making it more adaptable. Furthermore, the detection probe of this invention is integrated and fixed with bolts, making the structure reliable and durable.

[0014] (2) Existing technologies have limited methods for detecting structural defects in ferromagnetic materials and have poor adaptability. Since this invention is a composite method that includes pulsed electromagnetic detection and electromagnetic ultrasonic detection, the detection method can be switched according to the detection scenario and requirements. Pulsed electromagnetic detection is suitable for near-field and near-surface detection and is less affected by surface interference. Electromagnetic ultrasonic detection is suitable for far-field and long-distance detection, with fast detection speed and wide detection range. The two methods complement each other and make up for the shortcomings of electromagnetic ultrasonic detection being undetectable in the near field and pulsed electromagnetic detection being slow, thus expanding the detection range. Attached Figure Description

[0015] Figure 1 This invention provides a schematic diagram of the structure and working system of a pulsed electromagnetic-ultrasound composite ferromagnetic material structural defect detection probe.

[0016] Figure 2 The image shows a bottom view of a pulsed electromagnetic-ultrasound composite ferromagnetic material structural defect detection probe provided by the present invention.

[0017] Figure 3 This is a schematic diagram illustrating the working process of a pulsed electromagnetic-ultrasound composite method for detecting structural defects in ferromagnetic materials, as provided by the present invention.

[0018] Figure 4 This invention provides a method for detecting structural defects in ferromagnetic materials using pulsed electromagnetic ultrasound, along with a probe and system, and a schematic diagram illustrating the triggering and receiving signals. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0020] like Figure 1As shown, this invention proposes a pulsed electromagnetic-ultrasound composite ferromagnetic material structural defect detection probe, which is used on ferromagnetic material specimen 11. The detection probe is encapsulated in a box shape, and the interior is a highly integrated pulsed electromagnetic-ultrasound transceiver structure. The detection probe includes a core coil 1, a magnetic core 2, a folded coil 3, a metal top cover 4, a fastening bolt 5, a metal shell 6, a ceramic plate 7, a transparent film 8, an adapter cable 9, and an adapter interface 10. The core coil 1 has a multi-turn structure and is spirally wound around the periphery of the magnetic core 2. Both are embedded inside the metal shell 6 and are clamped by the metal top cover 4 and the metal shell 6 through fastening bolts 5. The ceramic sheet 7 is located directly below the magnetic core 2, and the folded coil 3 is located directly below the ceramic sheet 7 and is bonded to the lower surface of the ceramic sheet 7. The transparent film 8 is located below the folded coil 3 and serves a protective function. The adapter cable 9 is located inside the detection probe. One end of the adapter cable 9 is connected to the adapter interface 10, and the other end is connected to the core coil 1 and the folded coil 3 respectively. The adapter interface 10 is fixed to the outside of the metal shell 6. The system includes a detection probe, a signal generating device 18, a power amplifier 19, a long pulse current source 20, a filter 21, a preamplifier 22, a signal acquisition device 23, and a computer 24. The signal generating device 18 is connected to the power amplifier 19 and the long pulse current source 20 via cables. The power amplifier 19 is connected to the folded coil 3 of the detection probe via cables. The long pulse current source 20 is connected to the core coil 1 of the detection probe via cables. The input channel of the filter 21 is connected to the duplexer in the power amplifier 19 or the receiving coil in the folded coil 3. The output channel of the filter 21 is connected to the input channel of the preamplifier 22. The amplified output channel of the preamplifier 22 is connected to the signal acquisition device 23. The input channel of the signal acquisition device 23 is connected to the folded coil 3 of the detection probe. The output channel of the signal acquisition device 23 is connected to the computer 24 via cables for transmitting and storing signals.

[0021] like Figure 2 As shown, the folded coils 3 are arranged in a "U" shape, and the whole structure can be a flexible thin film structure, which can be fabricated using flexible printed circuit technology. The center-to-center distance between adjacent coil clusters is half a wavelength. λ The current direction of adjacent folded coils must be an odd multiple of 2, the width of a single folded coil cluster must not exceed half a wavelength, and the current direction of adjacent folded coils must be opposite. The folded coil 3 is a double-layer coil, with one layer used to excite ultrasonic waves (the transmitting coil) and the other layer used to receive ultrasonic signals (the receiving coil). Three adapters 10 are provided, for connection to a pulse current source, a power amplifier, and a signal amplifier, respectively.

[0022] This invention discloses a simple, adaptable, and highly efficient pulsed electromagnetic-ultrasonic composite defect detection system for ferromagnetic materials, enabling multi-scenario applications and high-efficiency detection. The specific detection methods include pulsed electromagnetic detection and electromagnetic ultrasonic detection, with the electromagnetic ultrasonic detection method comprising the following steps: S1. A first trigger signal T1 and a second trigger signal T2 are generated using a signal generating device 18. The first trigger signal T1 is transmitted to a long pulse current source 20 via a wire to trigger the long pulse current source to generate a long pulse current signal P1. The second trigger signal T2 is transmitted to a power amplifier 19 via a wire to generate a high-frequency excitation current signal P2. S2. The long pulse current signal P1 and the high frequency excitation current signal P2 are transmitted to the detection probe, and then transmitted to the core coil 1 and the folded coil 3 through the adapter 10 of the detection probe, respectively, to generate a static bias magnetic field 12 and a dynamic magnetic field 14 on the surface of the ferromagnetic material specimen for a period of time. Under the coupling of the two magnetic fields, the surface ultrasonic waves 15 are excited based on the magnetostrictive effect. S3. When the surface ultrasonic wave 15 encounters a defect or end face, it generates a reflected wave 16. When the reflected wave returns to the detection probe, it is converted into an electrical signal of the receiving coil in the folded coil 3 through the magnetostriction inverse effect. The electrical signal of the receiving coil in the folded coil 3 is transmitted to the signal acquisition device 23 for acquisition after passing through the filter 21 and the preamplifier 22. Finally, it is displayed and stored in the computer 24. S4. Computer 24 displays the received coil electrical signal diagram of the folded coil 3 after filtering and amplification. Since the end face of the ferromagnetic material specimen will reflect the surface ultrasonic waves 15, the end face echo with a large signal amplitude can be seen in the signal diagram. If there is a defect, since the distance between the defect and the detection probe is less than the distance between the far end face of the ferromagnetic material specimen and the detection probe, the defect echo in the signal diagram will precede the far end face echo in time. Then, the ultrasonic wave propagation distance is calculated based on the ultrasonic wave velocity and the time when the defect echo appears. Half of the ultrasonic wave propagation distance is recorded as the distance between the defect and the detection probe, thus detecting the defect. Otherwise, the defect is not detected. The pulse electromagnetic detection method includes the following steps: S1. A first trigger signal T1 is generated using the signal generating device 18. The first trigger signal T1 is transmitted to the long pulse current source 20 via a wire to trigger the long pulse current source to generate a long pulse current signal P1. S2. The long pulse current signal P1 is transmitted to the core coil 1 through the adapter 10 of the detection probe. Due to the principle of electromagnetic induction, a static bias magnetic field 12 is generated on the surface of the ferromagnetic material specimen for a period of time, thereby magnetizing the near surface of the ferromagnetic material specimen. S3. When the static bias magnetic field 12 encounters a defect near the surface of the ferromagnetic material specimen, a leakage magnetic field will be generated. Due to the leakage magnetic field, the magnetic flux passing through the folded coil 3 changes, causing the electrical signal of the receiving coil in the folded coil 3 to be distorted. The distorted signal is transmitted to the signal acquisition device 23 through the wire to complete the acquisition, and then transmitted to the computer 24 for display. S4. Finally, determine whether there is a defect. First, use steps S1-S3 to obtain the electrical signal of the receiving coil in the folded coil 3 when the ferromagnetic material specimen is defect-free. Record this as the original signal. Then, perform differential analysis between the signal obtained in steps S1-S3 and the original signal and extract the amplitude. If there is a defect, that is, a leakage magnetic field caused by the defect exists, the leakage magnetic field will increase the magnetic flux passing through the folded coil 3, and the amplitude of the distorted signal will be greater than the amplitude of the original signal. When the amplitude of the differential signal is much greater than the system noise, it is determined that there is a defect directly below the detection probe. Otherwise, there is no defect.

[0023] The detection method can be switched to suit different usage scenarios and detection needs, such as Figure 3 As shown, for near-field, near-surface detection, pulsed electromagnetic detection is used to avoid the near-field blind zone of electromagnetic ultrasound; for far-field, long-distance detection, electromagnetic ultrasound detection is used, which can achieve high-efficiency, large-area, and rapid detection.

[0024] like Figure 4 As shown, the pulse waveform of the long pulse current source is approximately rectangular, and the pulse width is... t w >2L / c, where L is the length of the detection area and c is the propagation velocity of the electromagnetic ultrasonic surface wave; the high-frequency excitation current signal waveform is one or more periodic sine waves with a frequency of 1kHz~5MHz. The pulsed electromagnetic signal mainly appears in the rising and falling edges of the long pulse signal, while the electromagnetic ultrasonic signal mainly appears in the steady-state stage of the long pulse signal, thus avoiding mutual interference between the two signals to a certain extent.

Claims

1. A pulsed electromagnetic-ultrasound composite ferromagnetic material structural defect detection probe, characterized in that: The probe includes a core coil (1), a magnetic core (2), a folded coil (3), a metal top cover (4), fastening bolts (5), a metal shell (6), a ceramic plate (7), a transparent film (8), an adapter cable (9), and an adapter interface (10). The core coil (1) has a multi-turn structure and is wound around the magnetic core (2). The two are embedded inside the metal shell (6) and clamped by the metal top cover (4) and the metal shell (6) through the fastening bolts (5). The ceramic plate (7) is located directly below the magnetic core (2). The folded coil (3) is located directly below the ceramic plate (7) and is bonded to the lower surface of the ceramic plate (7). The transparent film (8) is located below the folded coil (3) and serves a protective function. The adapter cable (9) is located inside the detection probe. One end of the adapter cable (9) is connected to the adapter interface (10), and the other end is connected to the core coil (1) and the folded coil (3) respectively. The adapter interface (10) is fixed to the outside of the metal shell (6).

2. The pulsed electromagnetic-ultrasound composite ferromagnetic material structural defect detection probe according to claim 1, characterized in that: The core coil (1) and the folded coil (3) are made of high-temperature resistant enameled copper wire. The folded coil (3) is a double-layer coil, one layer of which is used to excite ultrasonic waves and is the transmitting coil, and the other layer is used to receive ultrasonic signals and is the receiving coil.

3. The pulsed electromagnetic-ultrasound composite ferromagnetic material structural defect detection probe according to claim 1, characterized in that: The metal top cover (4) and the metal shell (6) are 3D printed and made of lightweight aluminum alloy. They are connected by fastening bolts (5) to ensure structural stability and reliability.

4. The pulsed electromagnetic-ultrasound composite ferromagnetic material structural defect detection probe according to claim 1, characterized in that: The magnetic core (2) is made of a high permeability material. The material is used to transmit magnetic lines of force. The core coil (1) is spirally wound on its outer surface. The two are combined to form an electromagnet. Under the same conditions, the more turns of the coil, the stronger the magnetism.

5. The pulsed electromagnetic-ultrasound composite ferromagnetic material structural defect detection probe according to claim 1, characterized in that: The folded coil (3) is similar to a U-shape and is made using flexible printed circuit technology. It consists of straight segments and curved segments, with the spacing between adjacent straight segments being half the wavelength of the ultrasonic wave. λ The width of the coil is less than the width of the magnetic core (2) when it is an odd multiple of 2.

6. The pulsed electromagnetic-ultrasound composite ferromagnetic material structural defect detection probe according to claim 1, characterized in that: At least three adapters (10) are provided for connection to the long pulse current source (20), power amplifier (19), and filter (21), respectively. The adapter cable (9) is a cable with electromagnetic shielding effect.

7. A pulsed electromagnetic-ultrasound composite defect detection system for ferromagnetic materials, characterized in that: The system includes a detection probe as described in any one of claims 1 to 6, a signal generating device (18), a power amplifier (19), a long pulse current source (20), a filter (21), a preamplifier (22), a signal acquisition device (23), and a computer (24); the signal generating device (18) is connected to the power amplifier (19) and the long pulse current source (20) via cables, the power amplifier (19) is connected to the folded coil (3) of the detection probe via cables, and the long pulse current source (20) is connected to the winding core of the detection probe via cables. The input channel of the filter (21) is connected to the duplexer in the power amplifier (19) or the receiving coil in the folded coil (3). The output channel of the filter (21) is connected to the input channel of the preamplifier (22). The amplified output channel of the preamplifier (22) is connected to the signal acquisition device (23). The input channel of the signal acquisition device (23) is connected to the folded coil (3) of the detection probe. The output channel of the signal acquisition device (23) is connected to the computer (24) via a cable for transmitting and storing signals.

8. The detection method of the pulsed electromagnetic-ultrasound composite ferromagnetic material structural defect detection system as described in claim 7, characterized in that, The detection methods include pulsed electromagnetic detection, suitable for near-field, near-surface detection, and electromagnetic ultrasonic detection, suitable for far-field, long-distance detection. The electromagnetic ultrasonic detection method includes the following steps: S1. A first trigger signal T1 and a second trigger signal T2 are generated using a signal generating device (18). The first trigger signal T1 is transmitted to a long pulse current source (20) via a wire to trigger the long pulse current source to generate a long pulse current signal P1. The second trigger signal T2 is transmitted to a power amplifier (19) via a wire to generate a high-frequency excitation current signal P2. S2. The long pulse current signal P1 and the high frequency excitation current signal P2 are transmitted to the detection probe, and then transmitted to the core coil (1) and the folded coil (3) respectively through the adapter (10) of the detection probe. The static bias magnetic field (12) and the dynamic magnetic field (14) are generated on the surface of the ferromagnetic material specimen for a period of time, respectively. The surface ultrasonic waves (15) are excited based on the magnetostrictive effect under the coupling of the two magnetic fields. S3. When the surface ultrasonic wave (15) encounters a defect or end face, it generates a reflected wave (16). When the reflected wave returns to the detection probe, it is converted into an electrical signal of the receiving coil in the folded coil (3) through the magnetostriction inverse effect. The electrical signal of the receiving coil in the folded coil (3) is transmitted to the signal acquisition device (23) for acquisition after passing through the filter (21) and the preamplifier (22). Finally, it is displayed and stored on the computer (24). S4. The computer (24) displays the received coil electrical signal diagram of the folded coil (3) after filtering and amplification. Since the end face of the ferromagnetic material specimen will reflect the surface ultrasonic wave (15), the end face echo with a large signal amplitude can be seen in the signal diagram. If there is a defect, since the distance between the defect and the detection probe is less than the distance between the far end face of the ferromagnetic material specimen and the detection probe, the defect echo in the signal diagram will precede the far end face echo in time. Then, the ultrasonic wave propagation distance is calculated based on the ultrasonic wave speed and the time when the defect echo appears. Half of the ultrasonic wave propagation distance is recorded as the distance between the defect and the detection probe, thus detecting the defect. Otherwise, the defect is not detected. The pulse electromagnetic detection method includes the following steps: S1. A first trigger signal T1 is generated using a signal generating device (18). The first trigger signal T1 is transmitted to a long pulse current source (20) via a wire to trigger the long pulse current source to generate a long pulse current signal P1. S2. The long pulse current signal P1 is transmitted to the core coil (1) through the adapter (10) of the detection probe. Due to the principle of electromagnetic induction, a static bias magnetic field (12) is generated on the surface of the ferromagnetic material specimen for a period of time, which then magnetizes the near surface of the ferromagnetic material specimen. S3. When the static bias magnetic field (12) encounters a defect near the surface of the ferromagnetic material specimen, a leakage magnetic field will be generated. Due to the leakage magnetic field, the magnetic flux passing through the folded coil (3) changes, causing the electrical signal of the receiving coil in the folded coil (3) to be distorted. The distorted signal is transmitted to the signal acquisition device (23) through the wire to complete the acquisition, and then transmitted to the computer (24) for display. S4. Finally, determine whether there is a defect. First, use steps S1-S3 to obtain the electrical signal of the receiving coil in the folded coil (3) when the ferromagnetic material specimen is defect-free. Record it as the original signal. Then, perform differential analysis between the signal obtained in steps S1-S3 and the original signal and extract the amplitude. If there is a defect, that is, the leakage magnetic field caused by the defect exists. Since the leakage magnetic field increases the magnetic flux passing through the folded coil (3), the amplitude of the distorted signal will be greater than the amplitude of the original signal. When the amplitude of the differential signal is much greater than the system noise, it is determined that there is a defect directly below the detection probe. Otherwise, there is no defect.

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