A high spatial resolution magnetic Barkhausen noise (MBN) sensor and measurement method

Abstract

The present invention discloses a high spatial resolution magnetic Barkhausen noise (MBN) sensor and measurement method, which belongs to the field of micromagnetic non-destructive testing technology. The magnetic Barkhausen noise (MBN) non-destructive testing method is adopted to avoid destructive operations such as grinding and polishing the material surface and pickling, thereby realizing the measurement of the material grain boundary position and grain boundary inclination angle. First, through an innovative horseshoe-shaped yoke design, by optimizing the yoke structure and precisely processing its tip air gap, the preparation of a high spatial resolution MBN sensor is realized. Then, by utilizing the difference between the grain boundary position of ferromagnetic materials and the magnetic signals inside the grains, through plane scanning and eigenvalue extraction, it is possible to accurately distinguish between the interior of the grains and the grain boundary area, and realize the positioning of the grain boundary position. At the same time, a magnetic field rotation method is introduced to accurately measure the inclination angle of the grain boundary by comparing and analyzing the MBN signals under different magnetic field directions. The device and method effectively improve the measurement efficiency of microstructures such as grain boundaries of ferromagnetic materials.

Description

Technical Field

[0001] This application relates to the field of micromagnetic nondestructive testing technology, and more particularly to a method and apparatus for measuring the position and tilt angle of grain boundaries in ferromagnetic materials. The method, based on magnetic Barkhausen noise detection technology, does not require surface treatment of the material and enables the location of grain boundaries and detection of their tilt angles. Background Art

[0002] The importance of ferromagnetic materials. Grain boundaries, as key microstructural defects in materials, significantly affect the magnetic and mechanical properties of materials. Traditional methods of detecting grain boundary information include metallographic microscopes, magneto-optical Kerr microscopes, transmission electron microscopes, etc., but these methods all require grinding, polishing, and even pickling of the surface, which is a cumbersome process and a lossy measurement method. Magnetic Barkhausen noise (MBN) has been proven to be an effective detection method for the microstructure of ferromagnetic materials. It has the advantages of non-destructive testing and rapid detection, and is therefore widely used in the detection of ferromagnetic material properties.

[0003] However, traditional MBN sensors have poor spatial resolution, often on the millimeter scale. Common ferromagnetic materials such as steel have grain sizes on the micrometer scale, so traditional MBN sensors cannot accurately measure grain boundary information (including position and tilt angle) in ferromagnetic materials. Summary of the Invention

[0004] Based on the above, the purpose of the present invention is to provide a high spatial resolution MBN detection method, which combines plane scanning and magnetic field rotation methods to achieve non-destructive detection of grain boundary positions and tilt angles of ferromagnetic materials.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A nondestructive testing method for the position and tilt angle of grain boundaries in ferromagnetic materials is characterized by the design of a high-spatial-resolution MBN sensor. This method uses a planar scanning method to detect MBN patterns line by line and point by point, selecting appropriate magnetic features to ultimately achieve planar magnetic imaging of the material. Based on the difference in magnetic signals between grain boundaries and those within the grains, the magnetic imaging results are used to accurately identify the position of grain boundaries. The invention also incorporates a magnetic field rotation mechanism. By comparing and analyzing the measurement results at the grain boundaries after magnetic field rotation with the data within the grains, the tilt angle of the grain boundaries can be accurately measured.

[0007] The high spatial resolution MBN sensor adopts a horseshoe-shaped magnetic yoke design and precisely processes the tip air gap that determines the spatial resolution, achieving an air gap size of the micron level.

[0008] The method for detecting the grain boundaries and the grain boundary tilt angles of ferromagnetic materials is as follows:

[0009] 1) Use a function generator to generate a 10Hz to 100Hz sinusoidal signal, which is then processed by a power amplifier and fed into the excitation yoke to perform AC magnetization on the test piece.

[0010] 2) Fix the MBN sensor to the clamping device and use a high-precision displacement device to fix the air gap of the MBN sensor to a position 0.05mm to 0.1mm from the test piece;

[0011] 3) The signal measured by the MBN sensor is filtered and amplified by hardware and then passed to the acquisition card and transmitted to the host computer;

[0012] 4) Change the measurement position and repeat steps 1) to 3) until the measurement process of the entire area to be measured including the grain boundary is completed;

[0013] 5) Rotate the excitation magnetic field and repeat steps 1) to 4);

[0014] 6) Extract characteristic values ​​from the measured MBN signal and associate them with the measurement locations. Since grain boundaries, as an important component of the microstructure, directly affect the magnetization process of the material and the characteristics of the MBN signal, there will be obvious differences in the characteristic values ​​at the grain boundaries and inside the grains.

[0015] 7) The effect of grain boundaries on micromagnetic signals is related to the angle of the magnetic field. However, commonly used ferromagnetic materials, such as grain-oriented silicon steel, are also affected by rolling stress during the production process. In order to eliminate this effect and measure the grain boundary inclination angle, it is necessary to subtract the average value of the local area inside the grain from the result measured at the grain boundary position:

[0016]

[0017] Where MBN θ MBN represents the MBN characteristic value signal after removing the rolling direction effect at the grain boundary position. gb Represents the original signal of the characteristic value measured at the same grain boundary position, MBN i Represents the MBN characteristic value signal measured inside the grain.

[0018] 8) MBN θ The grain boundary tilt angle is solved based on the principle that the characteristic value appears to be an extreme value when the magnetic field is perpendicular to the grain boundary, which corresponds to the grain boundary measurement position one by one.

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention utilizes the MBN measurement method, which does not require damage to the sample surface, and obtains information such as the position and tilt angle of the grain boundary, thereby achieving non-destructive testing of the sample.

[0021] 2. This paper proposes a high-spatial-resolution MBN sensor design approach that improves the spatial resolution of the MBN sensor by machining the air gap in the MBN sensor's magnetic yoke. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Overall schematic diagram of the sensor measurement specimen;

[0023] Figure 2 Yoke air gap size measurement diagram;

[0024] Figure 3 Schematic diagram of the sensor scanning path;

[0025] Figure 4 Schematic diagram of the sensor's two-dimensional magnetic imaging;

[0026] Figure 5 Schematic diagram of magnetic field and grain boundary tilt angle;

[0027] Figure 6 Schematic diagram of solving the grain boundary tilt angle.

[0028] In the figure: 1 - yoke 2 - coil 3 - Permalloy housing 4 - epoxy resin layer 5 - yoke air gap 6 - test piece 7 - excitation yoke 8 - excitation coil 9 - grain 1 10 - grain boundary 11 - grain 2. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings and the above embodiments. The specific implementation examples provided below are only descriptive and not restrictive, and cannot be used to limit the scope of protection of the present invention.

[0030] Figure 1The figure shows an overall schematic diagram of an MBN sensor measuring a specimen. The high-spatial-resolution MBN sensor primarily consists of a magnetic yoke, an enameled coil, a Permalloy housing, and epoxy resin. The yoke 1 is made of Permalloy and resembles a horseshoe. The size of the air gap at its tip determines the sensor's spatial resolution. Through cutting, grinding, and polishing, the air gap is adjusted to a length of 1μm to 100μm and a width of 0.1μm to 5μm. An enameled coil 2 is wound around the left side of the yoke. When magnetic field disturbances caused by microstructural changes in the material are generated, the changing magnetic field signal is converted into a voltage signal. A Permalloy housing 3 surrounds the outer surface of the yoke, minimizing the impact of external noise on the acquired signal. To reduce magnetic flux leakage during sensor operation and enhance structural stability, epoxy resin 4 is added as a filler between the horseshoe-shaped yoke and the Permalloy housing, improving the sensor's detection performance and reliability.

[0031] The size of the sensor yoke air gap 5 is measured using an optical microscope, and the results are as follows Figure 2 As shown. A function generator is used to generate a 50Hz, 1.5V sinusoidal excitation signal. After the signal is amplified by a power amplifier, it is input into the coil 8 to excite the test piece. The sensor is fixed to the clamping device and the high-precision translation stage is used to control the movement of the sensor. The measurement path is as follows Figure 3 The MBN signal collected by the sensor is bandpass filtered (10kHz to 1MHz) and then pre-amplified 1000x. The processed signal is then uploaded to the host computer via a PXIe6376 data acquisition card with a sampling rate of 2M / s. During the experiment, the measurement step size was set to 0.2mm.

[0032] The characteristic values ​​of the measured MBN signals, such as peak value and coercive force, are extracted respectively and matched with the measurement points one by one. The two-dimensional magnetic imaging is performed using data processing software. Since the grain boundary and the interior of the grain have different effects on the MBN signal, the characteristic values ​​of the MBN signal at the grain boundary will show a different trend of change from that inside the grain. The parameters closely related to the grain boundary are selected and can be used as the characteristic values ​​of grain boundary positioning, such as the MBN peak value. The schematic diagram of the two-dimensional magnetic imaging is shown as follows: Figure 4 shown.

[0033] On the basis of grain boundary positioning, a coordinate system is established with the rolling direction as the horizontal axis and the horizontal direction as the vertical axis, such as Figure 5 Taking the MBN peak as an example, the magnetic field rotation step is set to 10°, and the results at different magnetic field angles are measured, as shown in the figure below. Figure 6 As shown in (a), it can be found that the overall characteristic value shows a downward trend. By removing the influence of rolling stress on the experimental results, as shown in Figure 6 (b) shows the result. Figure 6As shown in (c), it can be found that a peak appears when the magnetic field angle is 30°. Since the MBN peak is strongest when the angle is vertical, it means that the tilt angle of the measured grain boundary is 60°.

Claims

1. A method for measuring magnetic Barkhausen noise (MBN) sensors with high spatial resolution, characterized in that: The high spatial resolution magnetic Barkhausen noise MBN sensor comprises: The magnetic yoke is a horseshoe-shaped structure made of Permalloy, and the tip air gap is precisely processed to a length of 1μm to 100μm and a width of 0.1μm to 5μm through cutting, grinding, and polishing steps to improve spatial resolution; an enameled coil, wound around the side of the magnetic yoke, for converting magnetic field disturbances generated by changes in the material's microstructure into voltage signals; Permalloy shell, wrapped around the outside of the magnetic yoke, is used to reduce the impact of external noise on the collected signal; Epoxy resin filler, set between the magnetic yoke and the Permalloy shell, reduces the magnetic leakage during the operation of the magnetic Barkhausen noise sensor (MBN sensor) and increases stability; The method for detecting grain boundaries and grain boundary inclination angles of ferromagnetic materials using the high spatial resolution magnetic Barkhausen noise (MBN) sensor comprises the following steps: a) Use a function generator to generate a 10Hz to 100Hz sinusoidal signal, amplify it through a power amplifier, and then pass it into the excitation coil to perform AC magnetization on the test piece; b) Fix the MBN sensor to the clamping device and control the end of the MBN sensor to slightly contact the test piece; use a high-precision translation stage to control the movement of the MBN sensor and perform MBN detection on the test piece point by point through plane scanning; c) The MBN sensor measurement signal is filtered and amplified by hardware and then passed to the acquisition card for transmission to the host computer; d) Change the measurement position and repeat the above measurement steps a) to c) until the entire test area including the grain boundary is measured; e) rotating the excitation magnetic field and repeating the above measurement steps a) to d); f) Extracting characteristic values ​​from the measured MBN signals and mapping the characteristic values ​​to the measurement locations, thereby distinguishing the characteristic value differences between the grain boundaries and the interior of the grains; g) MBN characteristic value signal MBN after removing the rolling direction effect by calculation θ : i=1,2,3...n Where MBN θ MBN represents the MBN characteristic value signal after removing the rolling direction effect at the grain boundary position. gb Represents the original signal of the characteristic value measured at the same grain boundary position, MBN i Represents the MBN characteristic value signal measured inside the grain; h) MBN θ The grain boundary tilt angle is solved based on the principle that the characteristic value appears to be an extreme value when the magnetic field is perpendicular to the grain boundary, which corresponds to the grain boundary measurement position one by one.

2. The method for measuring a high spatial resolution magnetic Barkhausen noise (MBN) sensor according to claim 1, characterized in that: The size of the air gap at the tip of the yoke determines the spatial resolution of the MBN sensor.

3. The method for measuring a high spatial resolution magnetic Barkhausen noise (MBN) sensor according to claim 1, wherein: By precisely machining the tip air gap size of the yoke, the spatial resolution of the MBN sensor is improved, thereby enabling simultaneous detection of the grain boundary position and grain boundary tilt angle in ferromagnetic materials.

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