CN102645490A - Frequency-adjustable longitudinal modal magnetostriction sensor - Google Patents

Abstract

A frequency-tunable longitudinal mode magnetostrictive sensor, which includes a permanent magnet magnetic circuit, a flexible printed excitation coil, a flexible printed induction coil, and a connector, can excite a longitudinal mode in a cylindrical ferromagnetic material waveguide. State-of-the-art ultrasonic guided waves are used to detect defects. The flexible printed excitation coil can adjust the overall bias magnetic field strength on the basis of the bias magnetic field provided by the permanent magnet magnetic circuit, so that the waveguide material can reach the best magnetization state; the flexible printed induction coil can be rolled into a cylindrical shape and connected by a connector After tightening and tightening, it is installed on the surface of a steel rod or a steel cable, in which it excites and receives longitudinal mode ultrasonic guided waves; by changing the connection mode of each coil end in the flexible printing induction coil, the frequency characteristic parameters of the sensor can be changed, The adjustment of the center frequency is realized, thereby expanding the working frequency band range of the single longitudinal mode magnetostrictive sensor.

Description

A Frequency Adjustable Longitudinal Mode Magnetostrictive Sensor

technical field

The invention is a longitudinal mode magnetostrictive sensor with an adjustable central frequency, which belongs to the technical field of electromagnetic acoustic sensors, and is suitable for being installed on cylindrical ferromagnetic material waveguides such as steel rods and steel cables.

Background technique

When the magnetostrictive sensor detects defects in waveguides such as steel rods and steel cables, it is necessary to select sensors with different frequencies according to the actual detection conditions: when a long detection distance is required, a low-frequency sensor is generally selected; when a high detection accuracy is required, a high frequency sensor is generally selected. frequency sensor. When a single sensor has only a single center frequency, if it is necessary to use different frequency bands to detect the same waveguide, it is necessary to manufacture multiple sensors with different center frequencies and to replace them several times during detection. In addition, when the sensor uses a fixed permanent magnet magnetic circuit, if the measured waveguide material and size change, it is difficult for the material to maintain the optimal magnetization state. Therefore, it is necessary to develop a single sensor with adjustable center frequency and adjustable static bias magnetic field to meet the requirements of actual detection.

Contents of the invention

The purpose of the present invention is to realize a single longitudinal mode magnetostrictive sensor with adjustable center frequency, so that it can excite longitudinal mode ultrasonic guided waves in cylindrical ferromagnetic material waveguides such as steel rods and steel cables, and The strength of the static bias magnetic field provided by the sensor can be controlled to accommodate changes in waveguide material and dimensions to ensure optimal magnetization of the material.

In order to achieve the above object, the present invention adopts the following technical solutions. The frequency adjustable longitudinal mode magnetostrictive sensor includes a permanent magnet magnetic circuit composed of a semicircular iron ring 1 , a yoke 3 , a permanent magnet 7 and a saddle piece 8 , and a flexible printed excitation coil 4 and a flexible printed induction coil 5 . The inner diameter of the circular hole formed by the semicircular iron ring 1 is larger than the outer diameter of the cylindrical ferromagnetic material waveguide 2 . The two yokes 3 are located on both sides of the cylindrical ferromagnetic material waveguide 2 and are parallel to the axial direction of the cylindrical ferromagnetic material waveguide 2 . The two ends of the yoke 3 are respectively lapped on the ring composed of two semicircular iron rings 1 through the permanent magnet 7 and the saddle piece 8; The yoke iron 3, the permanent magnet 7, the semicircular iron ring 1 and the saddle piece 8 form a unilateral magnetic circuit; the flexible printed excitation coil 4 and the flexible printed induction coil 5 are crimped once and then buckled with the respective welded connectors 6 Installed on the cylindrical ferromagnetic material waveguide 2 after being closed and locked; the flexible printed excitation coil 4 and the flexible printed induction coil 5 keep the same axial geometric center position, and the axial length of the flexible printed excitation coil 4 is greater than that of the flexible printed induction coil 5 The axial length is more than 2 times; the flexible printing excitation coil 4 is located outside the flexible printing induction coil 5,

The flexible printed induction coil 5 is printed with 2N sections of copper coil 9 with consistent wiring. After the connector 6 is fastened and locked, the flexible printed induction coil 5 forms a solenoid coil with 2N sections coaxial with the cylindrical ferromagnetic material waveguide 2 . Each segment of the solenoid includes two connection ports 11, and a total of 4N ports are printed and arranged on the flexible substrate 10, where N is a natural number.

By connecting 4N interfaces in different ways, it is possible to control the winding direction of 2N sections of solenoids, forming n sections of equal-spaced solenoids wound alternately in forward and reverse directions, and finally realizing the control of the center frequency of the sensor , where n is a natural number divisible by 2N, and N is a natural number.

The permanent magnet magnetic circuit mainly provides the static bias magnetic field for magnetizing the cylindrical ferromagnetic material waveguide 2. When the material and size of the cylindrical ferromagnetic material waveguide 2 change, the optimal static bias magnetic field strength is different. Therefore, it is necessary to adjust the strength of the static bias magnetic field according to the actual detection conditions. For this purpose, the flexible printed excitation coil is designed, and the size and direction of the direct current are controlled to increase or decrease the static bias magnetic field formed on the basis of the permanent magnet magnetic circuit. Reduce the strength of the bias magnetic field.

The even-numbered solenoid coils wound in the same direction in the flexible induction coil can be divided into coil groups with equal length intervals, the number of coil groups is a natural number divisible by the number of flexible induction coils, and the number of coil groups × each group Including the number of flexible printed coil segments = the total number of flexible printed induction coil segments, the frequency characteristic parameters of the flexible induction coil are adjusted by adjusting the connection mode of all the connection ports of the flexible coil that are twice the number of flexible induction coil segments. The connection port is at one end of the flexible substrate 10 , so that the inner coils of each group can be wound in the same direction, and the coil groups can be wound alternately in forward and reverse directions.

The present invention can obtain following beneficial effect:

The present invention adopts the above technical scheme, so that the single flexible longitudinal mode magnetostrictive sensor can realize the adjustment of the center frequency, expand the working frequency band unit of the single magnetostrictive sensor, and adjust the best for the change of the measured waveguide material and the size change The static bias field strength required for magnetization to optimize sensor performance.

Description of drawings

Fig. 1 overall installation diagram of the present invention;

Fig. 2 Schematic diagram of flexible printing induction coil;

Fig. 3 The connection mode of the flexible printing induction coil port when the frequency characteristic parameter is L;

Fig. 4 The port connection mode of the flexible printing induction coil when the frequency characteristic parameter is L/2;

Fig. 5 The port connection mode of the flexible printing induction coil when the frequency characteristic parameter is L/n;

Fig. 6 is the wavelength-frequency dispersion curve of the L(0,1) mode in a 6.3mm steel rod;

Figure 7: When the single sensor works at a center frequency of 64KHz, the experimental signal in a steel rod with a diameter of 6.3mm;

Center frequency when the characteristic parameter D=40mm of Fig. 8;

Figure 9 is the experimental signal in a steel rod with a diameter of 6.3mm when the single sensor works at a center frequency of 130KHz;

Center frequency when the characteristic parameter D=20mm in Fig. 10;

Figure 11: When the single sensor works at the center frequency of 240KHz, the experimental signal in the steel rod with a diameter of 6.3mm;

Figure 12 The center frequency when the characteristic parameter D=10mm.

In the figure: 1. Semicircular iron ring, 2. Cylindrical ferromagnetic material waveguide, 3. Yoke iron, 4. Flexible printing excitation coil, 5. Flexible printing induction coil, 6. Connector, 7. Permanent magnet, 8. Saddle sheet, 9, copper coil, 10, flexible substrate, 11, connection port.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment the present invention will be further described:

As shown in Figure 1, the frequency-adjustable longitudinal mode magnetostrictive sensor consists of a permanent magnet magnetic circuit, a flexible printed excitation coil 4 and a flexible printed induction coil 5 . The flexible printing induction coil 5 includes 2N (N is a natural number) segments, and the length of the flexible printing induction coil 5 is greater than the axial circumference of the tested cylindrical ferromagnetic material waveguide. The permanent magnet magnetic circuit is mounted on the cylindrical ferromagnetic material waveguide 2 in a non-contact manner after fastening two semicircular iron rings, and the permanent magnet magnetic circuit can be disassembled from the cylindrical ferromagnetic material waveguide 2 by separating the two semicircular iron rings Both the flexible printed excitation coil 4 and the flexible printed induction coil 5 are flexible and can be rolled into a cylindrical shape, pasted on the surface of the cylindrical ferromagnetic material waveguide 2, and mounted on the cylindrical ferromagnetic material waveguide 2 after being fastened by the connector , after unlocking the connector, it can be disassembled from the cylindrical ferromagnetic material waveguide 2 . Therefore, the entire frequency-adjustable flexible longitudinal mode magnetostrictive sensor is easy to assemble and disassemble, and is suitable for practical engineering detection.

In order to control the center frequency f of the longitudinal mode magnetostrictive sensor, it is necessary to divide the 2N (N is a natural number) segments of co-winding solenoids contained in the flexible printing induction coil 5 with an axial length of L into n(n It is a natural number divisible by 2N) groups of equally spaced coils. In each group of coils, the coils of each segment are still wound in the same direction, but the adjacent two groups of coils must be alternately wound in positive and negative directions.

The axial length of each group of coils is L/n, which is called the frequency characteristic parameter D (as shown in Figure 2). When n (n is a natural number divisible by 2N) takes different values, the frequency characteristic parameter of the flexible printing induction coil 5 D takes different values. As group number n=1 in Fig. 3, then its frequency characteristic parameter is L; Group number n=2 among Fig. 4, then its frequency characteristic parameter is L/2; Group number among Fig. 5 is n, then its The frequency characteristic parameter is L/n.

After the frequency characteristic parameter D of the flexible printing induction coil 5 is determined, by calculating the dispersion curve of the wavelength (λ) and frequency (f) of the longitudinal mode in the cylindrical ferromagnetic material waveguide 2, let D=L/n=λ /2, the frequency f corresponding to the frequency characteristic parameter D can be determined, which is called the center frequency of the flexible printing induction coil 5 under the control of the frequency characteristic parameter D.

In order to verify the frequency-adjustable function of the single magnetostrictive sensor, a coil with an axial length of 40mm and divided into 2N=4 groups is used for the test. According to the above-mentioned coil division method, there are three division methods corresponding to n=1, n=2 and n=4. Using the above-mentioned interface connection method (Fig. 3, 4, 5), the frequency characteristic parameters corresponding to the three methods are D=40mm, D=20mm and D=10mm respectively. Figure 6 is the wavelength-frequency dispersion curve of the L(0,1) mode in a steel rod with a diameter of 6.3mm. The frequency characteristic parameters D=40mm, D=20mm and D=10mm respectively control the center frequency to be about f=64kHz , f=130kHz and f=240kHz.

Single-body longitudinal mode magnetostrictive sensors with coil frequency characteristic parameters of D=40mm, D=20mm and D=10mm were tested sequentially in a steel rod with a diameter of 6.3mm and a length of 2.0m. The single longitudinal mode magnetostrictive sensor is installed at a distance of 0.5m from the left end of the steel rod, and there is an artificial cut groove with an axial length of 2mm and a depth of 2mm at a distance of 0.5m from the right end of the steel rod. Figures 7, 9 and 11 respectively correspond to the test signals when the frequency characteristic parameters are D=40mm, D=20mm and D=10mm. Select the right end face echoes in Figures 7, 9 and 11, and calculate their spectrum diagrams respectively. It can be seen that when the frequency characteristic parameters are D=40mm, D=20mm and D=10mm, the frequencies are shown in Figures 8, 10 and 12 ; The longitudinal mode magnetostrictive sensor can work at f=64kHz, f=130kHz and f=240kHz, thereby expanding the working frequency band range of the single longitudinal mode magnetostrictive sensor.

The flexible printed excitation coil 4 included in the frequency-adjustable longitudinal mode magnetostrictive sensor is a solenoid coil wound in the same direction, and a direct current is passed into it to form a static bias magnetic field inside it, and it is magnetically connected with a permanent magnet. The static bias magnetic field formed by the circuit is superimposed to magnetize the cylindrical ferromagnetic material waveguide 2. When the magnetostriction coefficient of the material corresponding to the magnetic field strength is the largest, the best magnetization state is reached, which can improve the magnetostrictive sensor in the cylindrical ferromagnetic waveguide. The ability to excite and receive ultrasonic guided waves in the magnetic material waveguide 2. When the material and size of the cylindrical ferromagnetic material waveguide 2 change, the static bias magnetic field intensity corresponding to the best magnetization state changes. When the magnitude and direction of the direct current fed into the flexible printing excitation coil 4 are controlled, the magnitude and magnitude of the superimposed static bias magnetic field can be controlled to maintain the performance of the magnetostrictive sensor to excite and receive ultrasonic guided waves.

Claims (2)

1. A frequency-adjustable longitudinal mode magnetostrictive sensor, including a permanent magnet magnetic circuit composed of a semicircular iron ring (1), a yoke (3), a permanent magnet (7) and a saddle piece (8) and a piece of flexible A printed excitation coil (4) and a piece of flexible printed induction coil (5); it is characterized in that: two yokes (3) are located on both sides of the cylindrical ferromagnetic material waveguide (2), parallel to the cylindrical ferromagnetic material waveguide ( 2) in the direction of the axis; the two ends of the yoke (3) are lapped on the outside of the ring composed of two semicircular iron rings (1) through the permanent magnet (7) and the saddle piece (8); the cylindrical ferromagnetic material The two ends of the waveguide (2) are framed in the ring formed by the semicircular iron ring (1); the inner diameter of the ring formed by the semicircular iron ring (1) is larger than the outer diameter of the cylindrical ferromagnetic material waveguide (2) ; The yoke (3), the permanent magnet (7), the semicircular iron ring (1) and the saddle piece (8) form a unilateral magnetic circuit; the flexible printing excitation coil (4) and the flexible printing induction coil (5) are crimped once and then passed through After fastening and locking with the respective welded connectors (6), they are installed on the cylindrical ferromagnetic material waveguide (2); the flexible printing excitation coil (4) and the flexible printing induction coil (5) keep the axial geometric center position consistent, In addition, the axial length of the flexible printing excitation coil (4) is more than twice the axial length of the flexible printing induction coil (5); the flexible printing excitation coil (4) is located outside the flexible printing induction coil (5); The flexible printed induction coil (5) is printed with 2N sections of copper coil (9) with consistent wiring, and after the connector (6) is fastened and locked, the flexible printed induction coil (5) forms a 2N section and a cylindrical ferromagnetic material waveguide (2) Coaxial solenoid coils. Each segment of the solenoid includes two connection ports (11), and a total of 4N interfaces are printed and arranged on the flexible substrate (10), wherein N is a natural number. 2. The frequency adjustable longitudinal mode magnetostrictive sensor according to claim 1, characterized in that: the cylindrical ferromagnetic material waveguide (2) is a steel rod or a steel cable.

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