A cross-scale defect evaluation method based on biased AC magnetization modulation TMR sensor

Abstract

This application provides a cross-scale defect assessment method based on a biased AC magnetization modulation TMR sensor. The method includes a sensor system consisting of an AC coil and a magnetic core. The magnetic core is inserted into the AC coil to enhance the AC magnetic field generated by the AC coil. The system employs a TMR sensor with a push-pull Wheatstone full-bridge design. The TMR sensor is secured to a printed circuit board (PCB) with permanent magnets placed on either side of the sensor. AC and DC modulated signals are applied, and the method evaluates defects of various scales based on the different characteristics of the voltage signal output by the TMR sensor. The method verifies whether the TMR sensor's range can be expanded by increasing the AC magnetic field strength to meet higher range requirements. This cross-scale defect assessment method based on a biased AC magnetization modulation TMR sensor enables full-scale detection of defects from micron to millimeter scales by analyzing the AC waveform peak, waveform width, and valley values.

Description

Technical Field

[0001] The present application relates to the technical field of magnetic flux leakage detection sensors, and specifically to a cross-scale defect evaluation method based on a biased AC magnetization modulation TMR sensor. Background Art

[0002] Magnetic flux leakage testing (MFL) is a widely used nondestructive testing technique for ferromagnetic materials. Its core principle is based on the material's magnetic properties and consists of the following steps: First, an external magnetic field is applied to the object being tested to achieve magnetic saturation. Second, when a defect is present in the material, the magnetic permeability at the defect changes suddenly, causing magnetic flux to leak through the defect and form a detectable leakage magnetic field. A magnetic sensor is used to capture the leakage magnetic field signal, and by analyzing the signal's amplitude, gradient, and spectrum, the defect's location, size, and type can be determined. Based on the magnetization method, MFL testing methods can be categorized as DC magnetization and AC magnetization. DC magnetization applies a constant magnetic field to achieve magnetic saturation in the object being tested. When a defect is present, the magnetic permeability of the defect area changes, causing magnetic flux to leak to the surface, forming a leakage magnetic field. This method, which often uses permanent magnets or DC electromagnets as the excitation source, offers strong signal stability and a high signal-to-noise ratio, making it suitable for detecting deeper defects.

[0003] However, due to limitations in sensor performance and the skin effect, the detection sensitivity of tiny defects is insufficient, easily leading to missed detections. Traditional DC or AC magnetization methods cannot simultaneously detect both millimeter- and micron-scale defects, limiting the detection range. Existing signal processing methods are overly simplistic, typically relying solely on the peak value or integral value of the signal, while ignoring the details of the time and frequency domains. Power frequency interference and broadband noise generated by motor equipment can drown out defect signals. Furthermore, mechanical vibrations caused by relative motion between the sensor and the workpiece can cause the magnetic induction signal baseline to drift. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present application provides a cross-scale defect evaluation method based on a biased AC magnetization modulation TMR sensor, which solves the problem of being unable to simultaneously detect tiny defects and large-scale defects, and the problem that power frequency interference and broadband noise generated by motor equipment will drown out the defect signal and cause the magnetic induction signal baseline drift.

[0005] To achieve the above objectives, the present application is implemented through the following technical solutions: a cross-scale defect evaluation method based on a biased AC magnetization modulation TMR sensor, comprising the following steps:

[0006] a. Using a TMR sensor system comprising an AC coil and a magnetic core, inserting the magnetic core into the AC coil to enhance the alternating magnetic field generated by the AC coil;

[0007] b. Using TMR sensor, using push-pull Wheatstone full bridge design, providing differential voltage output, with Wide dynamic range and good temperature stability;

[0008] c. Fix the TMR sensor to the PCB and use a pad to maintain a certain gap between the TMR sensor and the surface of the test piece.

[0009] d. Place permanent magnets on both sides of the TMR sensor to stabilize the sensor and prevent shaking during measurement that could affect the signal.

[0010] e. Applying AC and DC modulation signals as the total magnetic field, where the total magnetic field is a combination of the AC magnetic field and the DC magnetic field;

[0011] f. Evaluate defects of various scales through different signal characteristics. That is, based on the different stages of the TMR sensor output signal, such as signal amplitude changes, signal frequency response, and signal width changes, the different characteristics of defects from micro defects to large defects are evaluated, thereby achieving cross-scale defect detection (micro defects are defined as defects less than 1 mm, and large defects are defined as defects greater than or equal to 1 mm);

[0012] g. Verify whether the TMR sensor range can be expanded by increasing the AC magnetic field strength to meet higher range requirements. The specific steps are as follows:

[0013] i. Increase the magnetizing current from 0A to 30A and record the output voltage of the TMR sensor;

[0014] ii. Place a Tesla meter at the same location as the TMR sensor and measure the magnetic field strength corresponding to the magnetizing current;

[0015] iii. Divide the TMR sensor output into four stages;

[0016] iv. The voltage signal output by the TMR sensor is amplified, filtered, and differentially processed by a signal processing device. The subsequent signal is transmitted to a computer for display or the data is exported in software for further processing.

[0017] Preferably, the sensor system is based on the tunnel magnetoresistance effect. The sensor system consists of a reference layer with a fixed magnetization direction, a free layer that changes with the total magnetic field, and an insulating layer in the middle. The high-sensitivity conversion of magnetic field to resistance is achieved through the quantum tunneling effect: when the magnetization directions of the two ferromagnetic layers are parallel, the resistance is lowest, and when they are antiparallel, the resistance is highest. The total magnetic field changes the magnetization direction of the free layer to cause continuous changes in resistance. The sensor system uses a Wheatstone full-bridge design to convert resistance changes into differential voltage signals, the preamplifier amplifies weak signals, the filter circuit eliminates high-frequency noise, and then digitally processes the analog signal into a digital signal, which is transmitted to the processor through the SPI / I2C interface. The magnetic core is a permanent magnet, and the outer diameter of the AC coil is 14 mm and the inner diameter is 8 mm.

[0018] Preferably, defects of various scales are evaluated by different features of the voltage signal output by the TMR sensor, wherein the different features include amplitude, frequency and width.

[0019] Preferably, the amplitude change of the TMR sensor output signal is used to characterize tiny defects, and the width change of the TMR sensor output signal is used to characterize large-scale defects. The combination of the two realizes high-precision detection of cross-scale defects.

[0020] Preferably, the total magnetic field is Bsen, the AC magnetic field is Bac, and the DC magnetic field is Bdc.

[0021] Preferably, the TMR sensor is a TMR2905 sensor.

[0022] Preferably, the total magnetic field is specifically:

[0023]

[0024] in represents the frequency of alternating current, t represents the unit time, and Represent the amplitudes of the AC magnetic field and the DC magnetic field respectively; the working state of the TMR sensor is adjusted by adjusting the intensity and frequency of the AC magnetic field to detect defects of different scales.

[0025] Preferably, the first stage of the TMR sensor output is that the magnetizing coil generates a magnetic field and adds an AC / DC modulation field whose amplitude is weaker than the bias magnet magnetic field and is in the reverse saturation region;

[0026] The second stage of TMR sensor output is that the TMR sensor output peak value gradually increases;

[0027] The third stage of TMR sensor output is the increase in the width of the TMR sensor output waveform;

[0028] The fourth stage of the TMR sensor output is that the TMR sensor output valley value gradually decreases.

[0029] Preferably, the distance between the permanent magnets on both sides of the TMR sensor is 5 mm to 10 mm. By adjusting this distance, the magnetic field distribution is optimized to ensure that the background magnetic field in the TMR sensor area is close to zero, thereby effectively reducing background interference and enhancing the accuracy and stability of defect detection.

[0030] Preferably, the dimensions of the permanent magnet are 8 mm in diameter, 15 mm in height, and the magnetic field strength of the permanent magnet is 1.2 T.

[0031] Preferably, the frequency range of the AC magnetic field is 100 Hz to 10 kHz, the amplitude adjustment range is 0.5 T to 1.5 T, and the intensity range of the DC magnetic field is 0.2 T to 1.0 T.

[0032] This application provides a cross-scale defect assessment method based on a biased AC magnetization modulation TMR sensor, which has the following beneficial effects:

[0033] This cross-scale defect assessment method, based on a biased AC magnetization-modulated TMR sensor, enables full-scale detection of defects from micrometer to millimeter levels by analyzing the peak, waveform width, and valley values ​​of the TMR sensor's output voltage signal. This full-scale detection capability enables the TMR sensor to simultaneously cover high sensitivity and a wide measurement range, meeting the accuracy and efficiency requirements of practical inspections. Through the coordinated modulation of AC and DC magnetic fields, the TMR sensor's measurement range is extended from ±10 Gs to ±300 Gs, covering the full range of weak to strong magnetic leakage.

[0034] A DC bias magnetic field is used to offset background magnetic fields, and the magnet spacing is adjusted to keep the background magnetic field near zero in the TMR sensor area. This effectively eliminates background interference while preserving the defect leakage magnetic field signal, significantly improving detection accuracy and stability, especially in complex industrial environments. The sensor is also adaptable to a wide variety of industrial components and can accurately detect defects in new components. This optimized design enhances the TMR sensor's versatility, enabling reliable detection results across a wide range of complex defect morphologies and materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the waveforms of the initial state, small defects, and large-scale defects of the magnetic flux leakage detection in this application;

[0036] Figure 2 This is a schematic diagram of the corresponding relationship between the TMR sensor output and the total magnetic field in the first stage of this application;

[0037] Figure 3 This is a schematic diagram of the corresponding relationship between the TMR sensor output and the total magnetic field in the second stage of this application;

[0038] Figure 4 This is a schematic diagram of the corresponding relationship between the TMR sensor output and the total magnetic field in the third stage of this application;

[0039] Figure 5 This is the metallographic diagram of the crack of the weld fatigue bending test piece No. 2051 of this application;

[0040] Figure 6 Metallographic diagram of crack in weld fatigue bending test piece No. 2631 of this application;

[0041] Figure 7 This is the metallographic diagram of the crack of the weld fatigue bending test piece of this application number 2052;

[0042] Figure 8 This is the metallographic diagram of the crack of the weld fatigue bending test piece No. 2055 of this application;

[0043] Figure 9 This is a schematic diagram of the results of TMR2901 under fatigue crack detection of different sizes in this application;

[0044] Figure 10 This is a schematic diagram of the results of the HQ0811 Hall element under fatigue crack detection of different sizes in this application;

[0045] Figure 11 This is the result of the inner surface defect detection of 5mm thick steel plate in this application;

[0046] Figure 12 This is the result of the inner surface defect detection of 10 mm thick steel plate in this application. DETAILED DESCRIPTION

[0047] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0048] Example 1

[0049] like Figures 1-8 As shown, the embodiment of the present application provides a cross-scale defect evaluation method based on a biased AC magnetization modulation TMR sensor, comprising the following steps:

[0050] a. A sensor system consisting of an AC coil and a magnetic core is based on the tunnel magnetoresistance effect. The sensor system consists of a reference layer with a fixed magnetization direction, a free layer that varies with the total magnetic field, and an intermediate insulating layer. The quantum tunneling effect achieves highly sensitive magnetic field-resistance conversion: Resistance is lowest when the magnetization directions of the two ferromagnetic layers are parallel, and highest when they are antiparallel. The total magnetic field changes the magnetization direction of the free layer, causing a continuous change in resistance. The sensor system uses a Wheatstone full-bridge design to convert resistance changes into differential voltage signals. A preamplifier amplifies weak signals, and a filter circuit eliminates high-frequency noise. Digital processing converts the analog signal into a digital signal, which is then transmitted to a processor via an SPI / I2C interface. A permanent magnet is used as the magnetic core, which is inserted into the AC coil to enhance the alternating magnetic field generated by the coil. The AC coil has an outer diameter of 14 mm and an inner diameter of 8 mm. Defects in the test piece can be effectively scanned by the TMR sensor, enabling efficient defect detection.

[0051] b. If Figure 1 As shown, it adopts TMR sensor and uses push-pull Wheatstone full bridge design to provide differential voltage output. The TMR sensor has a wide dynamic range and good temperature stability. The output signal of the TMR sensor includes three characteristics: amplitude, frequency and width. The amplitude change of the TMR sensor output signal is used to characterize small defects, and the width change of the TMR sensor output signal is used to characterize large-scale defects. Figure 1 The signal output diagram is for detecting the initial state, tiny defects, and large-scale defects in sequence. The combination of the two realizes high-precision detection of cross-scale defects. The TMR sensor is the TMR2905 sensor, and the TMR sensor is powered by a 5V DC power supply.

[0052] c. Fix the TMR sensor to the PCB and use a backing plate to maintain a 0.2mm gap between the TMR sensor and the surface of the test piece.

[0053] d. Permanent magnets are placed on both sides of the TMR sensor to stabilize the sensor and prevent shaking during measurement that could affect the signal. The spacing between the permanent magnets is 5 mm to 10 mm. By adjusting this spacing, the magnetic field distribution is optimized to ensure that the background magnetic field in the TMR sensor area is close to zero, effectively reducing background interference and enhancing the accuracy and stability of defect detection. The permanent magnets are 8 mm in diameter and 15 mm in height, with a magnetic field strength of 1.2 T, which ensures a stable magnetic field within the TMR sensor's operating area to meet the requirements of defect detection.

[0054] e. If Figure 2 , Figure 3 , Figure 4As shown, AC and DC modulation signals are applied as the total magnetic field. The total magnetic field is a combination of the AC magnetic field and the DC magnetic field. The total magnetic field is Bsen, the AC magnetic field is Bac, and the DC magnetic field is Bdc. The total magnetic field is specifically:

[0055]

[0056] in represents the frequency of alternating current, t represents the unit time, and The AC and DC magnetic fields represent the amplitudes, respectively. Adjusting the AC magnetic field's intensity and frequency allows the TMR sensor to detect defects of varying sizes. The magnetic field's intensity and frequency can be flexibly adjusted, enabling comprehensive detection of defects from tiny to large.

[0057] in:

[0058] For tiny defects, ensure that the TMR sensor can accurately detect very weak magnetic leakage signals.

[0059] Magnetic field strength adjustment: The magnetic field strength is maintained at 0.8 T by adjusting the distance between the permanent magnets.

[0060] By adjusting the spacing of the permanent magnets, the influence of the background magnetic field can be effectively reduced, thereby enhancing the signal of tiny defects.

[0061] Frequency adjustment: The frequency is 1 kHz. A lower frequency helps capture subtle changes caused by small defects, thereby avoiding oversaturation of the signal.

[0062] Specific operation: The applied AC / DC modulation signals make the total magnetic field contain 0.8 T AC and DC magnetic fields. By adjusting the magnetic field strength and frequency, the leakage magnetic signals of tiny defects can be effectively captured under low magnetic fields.

[0063] Adjusting the magnetic field strength for large defects: When detecting large defects, increase the magnetic field strength of the permanent magnet to 1.5 T to ensure a strong enough magnetic field response to large defects. By increasing the magnetic field strength, a larger defect area can be covered and the leakage magnetic signal is strong enough to be distinguished from background noise.

[0064] Frequency Adjustment: For large defects, using a higher frequency AC magnetic field helps improve signal response speed and avoid background noise interference. The frequency can be adjusted up to 10 kHz. High-frequency AC magnetic fields can more effectively detect changes in magnetic flux leakage caused by large defects and improve detection accuracy.

[0065] Specific operation: The applied AC and DC modulation signals ensure that the total magnetic field contains AC and DC magnetic fields of 1.5 T. By adjusting the AC magnetic field strength to a higher value and the frequency to 10 kHz, the leakage magnetic signals of large-scale defects can be effectively captured and analyzed.

[0066] f. Verify whether the TMR sensor range can be expanded by increasing the AC magnetic field strength to meet the requirements of a higher range environment. The specific steps are as follows:

[0067] i. Increase the magnetizing current from 0A to 30A and record the output voltage of the TMR sensor.

[0068] ii. Place a Tesla meter at the same location as the TMR sensor and measure the magnetic field strength corresponding to the magnetizing current.

[0069] iii. The TMR sensor output is divided into four stages. The first stage of the TMR sensor output is that the magnetizing coil generates a magnetic field and adds an AC / DC modulation field whose amplitude is weaker than the bias magnet magnetic field and is in the reverse saturation region.

[0070] The second stage of the TMR sensor output is that the TMR sensor output peak value gradually increases.

[0071] The third stage of the TMR sensor output is that the width of the TMR sensor output waveform increases.

[0072] The fourth stage of the TMR sensor output is that the TMR sensor output valley value gradually decreases.

[0073] iv. The voltage signal output by the TMR sensor is amplified, filtered, and differentially processed by the signal processing device, and the subsequent signal is transmitted to the computer for display.

[0074] When performing step f, this embodiment performs the following verification experiment (such as Figure 5 , Figure 6 , Figure 7 , Figure 8 ):

[0075] Experiment 1: When testing a 10mm thick steel plate, the AC magnetic field strength was increased to 1.2T by adjusting the magnetizing current. It was found that the TMR sensor was able to effectively detect deeper defects, and the output signal could accurately correspond to the defect location, significantly improving the depth and accuracy of detection.

[0076] Experiment 2: When inspecting larger weld defects, increasing the magnetic field strength to 1.5 T allows the TMR sensor to cover a wider area and accurately identify larger magnetic flux leakage signals, thereby expanding the detection range and improving the TMR sensor's range capability to meet detection needs with higher range requirements.

[0077] Examples of situations where the TMR sensor range cannot be extended by increasing the AC magnetic field strength:

[0078] Experiment 3: When operating at high frequencies, if the magnetic field strength is too strong, the TMR sensor may enter saturation, resulting in distortion of the magnetic flux leakage signal and inability to effectively detect small defects. Even when the magnetic field strength was increased to 2 T, the output signal plateaued, failing to provide any useful detection information. Increasing the magnetic field strength in this case would actually limit the TMR sensor's sensitivity, preventing further improvement in detection accuracy.

[0079] Experiment 4: In a high-temperature environment, magnetic field strengths exceeding 1.5 T may cause demagnetization of the TMR sensor element material or increase heat loss, resulting in the TMR sensor's inability to effectively respond to high-intensity magnetic fields, ultimately affecting measurement range expansion and signal stability.

[0080] Comparative Example

[0081] like Figure 9 、 Figure 10 As shown, the embodiment of the present application provides a cross-scale defect evaluation method based on a biased AC magnetization modulation TMR sensor, comprising the following steps:

[0082] a. A sensor system consisting of an AC coil and a magnetic core is used. The magnetic core is inserted into the AC coil to enhance the alternating magnetic field generated by the AC coil. The magnetic core is a permanent magnet. The AC coil has an outer diameter of 14 mm and an inner diameter of 8 mm. Defects in the test piece can be effectively scanned by the TMR sensor, enabling efficient defect detection.

[0083] b. Using TMR sensor, using push-pull Wheatstone full bridge design, providing differential voltage output, with The TMR sensor has a wide dynamic range and good temperature stability. The different characteristics of the voltage signal output by the TMR sensor are used to evaluate defects of various scales. The different characteristics include amplitude, frequency and width. The amplitude change of the TMR sensor output signal is used to characterize small defects, and the width change of the TMR sensor output signal is used to characterize large-scale defects. The combination of the two realizes high-precision detection of cross-scale defects. The TMR sensor uses the TMR2901 sensor and the HQ0811 Hall element to detect fatigue cracks. The TMR sensor is powered by a 5V DC power supply.

[0084] c. Fix the TMR sensor to the PCB and use a backing plate to maintain a 0.2mm gap between the TMR sensor and the surface of the test piece.

[0085] d. Place permanent magnets on both sides of the TMR sensor to stabilize the sensor and prevent shaking during measurement that could affect the signal.

[0086] e. Apply AC / DC modulation signals as the total magnetic field. The total magnetic field is the combination of the AC magnetic field and the DC magnetic field. The total magnetic field is Bsen, the AC magnetic field is Bac, and the DC magnetic field is Bdc. The total magnetic field is specifically:

[0087]

[0088] in represents the frequency of alternating current, t represents the unit time, and Represents the amplitude of the AC magnetic field and the DC magnetic field respectively. By adjusting the intensity and frequency of the AC magnetic field, the working state of the TMR sensor is adjusted to detect defects of different scales. The intensity and frequency of the magnetic field can be flexibly adjusted to achieve comprehensive detection of defects from tiny to large scale.

[0089] f. Evaluate defects of various scales through different signal characteristics. Specifically, based on the different stages of the TMR sensor output signal, such as signal amplitude changes, signal frequency response, and signal width changes, the different characteristics of defects from tiny to large scales are evaluated, thereby achieving cross-scale defect detection.

[0090] In this embodiment, the detection results of the TMR2901 sensor are as follows Figure 9 As shown, due to the large background magnetic field, the TMR2901 sensor has been saturated and cannot perform the detection under the weak background magnetic field. The output is all saturated values. However, the linear range of the HQ0811 Hall element is large, and the detection results are as follows: Figure 10 shown.

[0091] Experimental Example 1

[0092] The present invention provides a cross-scale defect assessment method based on a biased AC magnetization modulation TMR sensor, comprising the following steps:

[0093] a. A TMR sensor system consisting of an AC coil and a magnetic core is used. The magnetic core is inserted into the AC coil to enhance the alternating magnetic field generated by the AC coil. The magnetic core is a permanent magnet. The AC coil has an outer diameter of 14 mm and an inner diameter of 8 mm. Defects in the test piece can be effectively scanned by the TMR sensor, enabling efficient defect detection.

[0094] b. Using TMR sensor, using push-pull Wheatstone full bridge design, providing differential voltage output, with The system has a wide dynamic range and good temperature stability. Defects of various scales are evaluated through the different characteristics of the voltage signal output by the TMR sensor. These characteristics include amplitude, frequency, and width. The amplitude change of the TMR sensor output signal is used to characterize tiny defects, while the width change of the TMR sensor output signal is used to characterize large-scale defects. The combination of the two enables high-precision detection of defects across scales. The TMR sensor is a TMR2905 sensor, and the TMR sensor is powered by a 5V DC power supply.

[0095] c. Secure the TMR sensor to the PCB and use a backing plate to maintain a 0.2mm gap between the TMR sensor and the surface of the test piece. The test piece used is a 5mm thick sample with surface defects of 0.25mm, 0.5mm, 0.75mm, 1mm, 1.25mm, 1.5mm, and 2.0mm.

[0096] d. Place permanent magnets on both sides of the TMR sensor to stabilize the sensor and prevent shaking during measurement that could affect the signal.

[0097] e. Apply AC / DC modulation signals as the total magnetic field. The total magnetic field is the combination of the AC magnetic field and the DC magnetic field. The total magnetic field is Bsen, the AC magnetic field is Bac, and the DC magnetic field is Bdc. The total magnetic field is specifically:

[0098]

[0099] in represents the frequency of alternating current, t represents the unit time, and Represents the amplitude of the AC magnetic field and the DC magnetic field respectively. By adjusting the intensity and frequency of the AC magnetic field, the working state of the TMR sensor is adjusted to detect defects of different scales. The intensity and frequency of the magnetic field can be flexibly adjusted to achieve comprehensive detection of defects from tiny to large scale.

[0100] f. Evaluate defects of various scales through different signal characteristics. Specifically, based on the different stages of the TMR sensor output signal, such as signal amplitude changes, signal frequency response, and signal width changes, the different characteristics of defects from small to large scales are evaluated, thereby achieving cross-scale defect detection;

[0101] iv. The voltage signal output by the TMR sensor is amplified, filtered and differentially processed by the signal processing device, and the subsequent signal is transmitted to the computer for display. The detection results of different defect sizes are as follows Figure 11 shown.

[0102] Experimental Example 2

[0103] Different from the experimental example 1, the test pieces in this example are 10mm thick samples with defects of 0.25mm, 0.5mm, 0.75mm, 1mm, 1.25mm, 1.5mm and 2.0mm, respectively. The magnetizing current is adjusted to 4.3A. The test results of different defect sizes are shown in the figure below. Figure 12 shown.

[0104] Results display: The detection results of different defect sizes are as follows: Figure 12 As shown. Figure 12 In the figure, it can be seen that as the defect size increases, the amplitude and width of the TMR sensor output signal change significantly. Specifically:

[0105] For tiny defects (such as 0.25mm and 0.5mm), the signal amplitude output by the TMR sensor is small and the width is also narrow.

[0106] For large-scale defects (such as 1mm, 1.5mm and 2.0mm), the signal amplitude is larger and the width is also significantly increased.

[0107] Especially when the defect size is larger than 1mm, the change in the output signal is more significant, and the presence of the defect can be easily distinguished from the background noise. Therefore, micro defects are defined as defects less than 1mm, and large defects are defined as defects greater than or equal to 1mm.

[0108] Although the embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A cross-scale defect evaluation method based on a biased AC magnetization modulation TMR sensor, characterized in that: The following steps are involved: a. Using a sensor system comprising an AC coil and a magnetic core, inserting the magnetic core into the AC coil to enhance the alternating magnetic field generated by the AC coil; b. Using TMR sensor, using push-pull Wheatstone full bridge design, providing differential voltage output, with Wide dynamic range; c. Fix the TMR sensor to the PCB and use a pad to maintain a certain gap between the TMR sensor and the surface of the test piece. d. Place permanent magnets on both sides of the TMR sensor to stabilize the sensor. e. Applying AC and DC modulation signals as the total magnetic field, where the total magnetic field is a combination of the AC magnetic field and the DC magnetic field; f. Evaluate defects of various scales through the different characteristics of the voltage signal output by the TMR sensor; g. Verify whether the TMR sensor range can be expanded by increasing the AC magnetic field strength to meet higher range requirements. The specific steps are as follows: i. Increase the magnetizing current from 0A to 30A and record the output voltage of the TMR sensor; ii. Place a Tesla meter at the same location as the TMR sensor and measure the magnetic field strength corresponding to the magnetizing current; iii. Divide the TMR sensor output into four stages; iv. The voltage signal output by the TMR sensor is amplified, filtered, and differentially processed by a signal processing device. The subsequent signal is transmitted to a computer for display or the data is exported in software for further processing.

2. The cross-scale defect assessment method based on a biased AC magnetization modulation TMR sensor according to claim 1, characterized in that: The sensor system consists of a reference layer with a fixed magnetization direction, a free layer that changes with the total magnetic field, and an insulating layer in the middle. The sensor system uses a Wheatstone full-bridge design to convert resistance changes into differential voltage signals. The magnetic core is a permanent magnet, and the outer diameter of the AC coil is 14mm and the inner diameter is 8mm.

3. The cross-scale defect assessment method based on a biased AC magnetization modulation TMR sensor according to claim 1, characterized in that: Defects of various scales are evaluated through different features of the voltage signal output by the TMR sensor, where the different features include amplitude, frequency and width.

4. The cross-scale defect assessment method based on a biased AC magnetization modulation TMR sensor according to claim 3, characterized in that: The amplitude change of the voltage signal output by the TMR sensor is used to characterize tiny defects, while the width change of the voltage signal output by the TMR sensor is used to characterize large-scale defects.

5. The cross-scale defect assessment method based on a biased AC magnetization modulation TMR sensor according to claim 1, characterized in that: The TMR sensor is a TMR2905 sensor.

6. The cross-scale defect assessment method based on a biased AC magnetization modulation TMR sensor according to claim 5, characterized in that: The total magnetic field is Bsen, the AC magnetic field is Bac, and the DC magnetic field is Bdc. The total magnetic field Bsen is specifically: in represents the frequency of alternating current, t represents the unit time, and Represent the amplitudes of the AC magnetic field and the DC magnetic field respectively; the working state of the TMR sensor is adjusted by adjusting the intensity and frequency of the AC magnetic field to detect defects of different scales.

7. The cross-scale defect assessment method based on a biased AC magnetization modulation TMR sensor according to claim 1, characterized in that: The first stage of the TMR sensor output is when the magnetizing coil generates a magnetic field and adds an AC / DC modulation field whose amplitude is weaker than the bias magnet field and is in the reverse saturation region; The second stage of TMR sensor output is that the TMR sensor output peak value gradually increases; The third stage of TMR sensor output is the increase in the width of the TMR sensor output waveform; The fourth stage of the TMR sensor output is that the TMR sensor output valley value gradually decreases.

8. The cross-scale defect assessment method based on a biased AC magnetization modulation TMR sensor according to claim 1, characterized in that: The permanent magnets on either side of the TMR sensor are spaced 5 mm to 10 mm apart.

9. The cross-scale defect assessment method based on a biased AC magnetization modulation TMR sensor according to claim 2, characterized in that: The dimensions of the permanent magnet are 8 mm in diameter, 15 mm in height, and the magnetic field strength of the permanent magnet is 1.2 T.

10. The cross-scale defect assessment method based on a biased AC magnetization modulation TMR sensor according to claim 1, characterized in that: The frequency range of the AC magnetic field is 100 Hz to 10 kHz, the amplitude adjustment range is 0.5 T to 1.5 T, and the intensity range of the DC magnetic field is 0.2 T to 1.0 T.

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