CN112147235A - An electromagnetic ultrasonic excitation device for pipeline guided wave mixing detection - Google Patents

Abstract

The invention relates to an electromagnetic ultrasonic excitation device for pipeline guided wave mixing detection. The device includes a double-layer flexible printed circuit board and a sheet-shaped rubber NdFeB magnet made by flexible plate-making technology. The back-folded multi-cluster coils printed on the bottom layer and the top layer have different spacings between adjacent cluster lines, and the centers of the top layer and bottom layer coils are in the same position; the double-layer flexible printed circuit board is pasted on one side of the sheet rubber NdFeB magnet. A two-layer flexible printed circuit board is located between the magnet and the outer surface of the DUT. The device is easy to install and disassemble, has a simple and compact structure, is small in size, and has flexibility, can adapt to curved surfaces and narrow environments, and can effectively detect and locate micro-cracks in pipes.

Description

An electromagnetic ultrasonic excitation device for pipeline guided wave mixing detection

technical field

The invention belongs to the field of electromagnetic ultrasonic detection, in particular to an electromagnetic ultrasonic excitation device used for pipeline guided wave mixing detection.

Background technique

As an important branch in the field of non-destructive testing, ultrasonic guided wave testing technology has been widely used in the field of non-destructive testing of pipelines in recent years. Detecting and locating micro-cracks in pipelines can effectively avoid potential safety hazards caused by damage expansion. However, the traditional ultrasonic nondestructive testing technology is to use the linear features such as reflection and scattering of sound waves to detect defects during the ultrasonic propagation process. Small defects can be effectively detected. In order to effectively detect pipeline micro-cracks, nonlinear ultrasonic testing technology can be used. Non-linear ultrasonic testing technology can essentially reflect the influence of small defects in materials on the ultrasonic propagation process, and can detect small defects that cannot be detected by traditional ultrasonic testing.

Since nonlinear distortions inevitably occur in transmit/receive systems such as amplifiers, transducers, and coupling media, in practice, the nonlinear high-harmonic method will give false alarms due to nonlinearities caused by the test system And other issues. To overcome these limitations, nonlinear ultrasonic mixing detection techniques can be employed, which are based on the fact that when two waves meet in a nonlinear region containing nonlinear sources such as closed cracks, an interaction occurs, and the New frequency components are observed in the frequency domain. In this way, the detection of material damage can be realized, and the new frequency components can be analyzed correspondingly by controlling the wave mixing position, so as to realize the location of the material damage.

For nonlinear ultrasonic mixing testing on pipelines, electromagnetic ultrasonic transducers (EMAT) can be used. EMAT is a non-contact transducer that does not need to contact the tested material through a couplant, which suppresses additional nonlinearity. The coating and oil, dirt, water, oxides and paints commonly found on the surface of pipeline specimens are not sensitive, so they are suitable for ultrasonic testing of pipelines. Ultrasonic mixing detection requires two excitation transducers. Existing detection methods usually use two multi-cluster coils separated by a certain distance to excite two columns of ultrasonic waves of different frequencies respectively. This structure makes the overall transducer device longer in axial length. , the volume is larger, and the magnetic flux density varies greatly at different positions. At present, EMAT usually uses solenoid electromagnets or rigid permanent magnets to provide bias magnetic fields. Solenoid electromagnets require additional power and are complicated to install on the pipeline structure. Permanent magnets need to be fixed on the surface of the pipeline with fixing devices such as iron yokes and hinges. . Due to its large size and complicated installation, the applications of electromagnets and rigid permanent magnets in pipeline electromagnetic ultrasonic transducers are limited. Therefore, when the electromagnetic ultrasonic mixing detection technology is applied to the pipeline, the excitation device needs to be designed. In response to this demand, the present invention proposes an electromagnetic-ultrasonic mixing excitation device suitable for curved-surface pipeline specimens.

SUMMARY OF THE INVENTION

The purpose of the present invention is to design an electromagnetic ultrasonic pipeline guided wave mixing with convenient installation and disassembly, simple and compact structure, small volume, flexibility, adaptability to curved surfaces and narrow environments, and effective detection and positioning of pipeline micro-cracks. Incentive device.

For achieving the above object, the technical scheme adopted in the present invention is:

An electromagnetic ultrasonic excitation device for pipeline guided wave mixing detection, comprising a double-layer circuit board made by flexible plate-making technology, a sheet rubber NdFeB magnet, and a double-layer flexible printed circuit board printed on the bottom layer and the top layer. The distance between the adjacent cluster lines of the back-folded multi-cluster coils is different, and the top and bottom coil centers are in the same position; the double-layer flexible printed circuit board is pasted on one side of the sheet rubber NdFeB magnet, and the double-layer flexible printed circuit board is located at the detection time. Between the magnet and the outer surface of the test piece to be tested.

The sheet-shaped rubber NdFeB magnet is a flexible sheet-shaped permanent magnet material that uses rubber as a binder, NdFeB powder as a filler and is magnetized in the thickness direction. The upper surface has a single polarity and the lower surface has a single polarity. It can provide magnetic induction along the radial direction of the pipe when it is bonded to the flexible printed circuit board and wrapped around the pipe. The axial width of the magnet is larger than the width of the double-layer flexible printed circuit board, so that the coil on the circuit board is completely placed in the magnetic field. size.

The direction of current passing between adjacent clusters of each layer of the double-layer flexible printed circuit board is opposite, the top coil and the bottom coil are respectively fed with excitation current signals of different frequencies, and the distance between adjacent clusters of each layer of coils is the same as that at the corresponding excitation frequency. Half of the modal guided wave wavelength λ is required.

The detection process of the present invention is:

According to the dispersion curve of the tested piece, a certain modal guided wave of the tested piece is selected as the excitation signal: the longitudinal modal guided wave has multi-modal and dispersion characteristics. There are L(0,1) and L(0,2) modes coexisting in the frequency band. At the same frequency, the transducer will excite these two wave modes at the same time. Depending on the specific pipeline dispersion curve, a certain mode is determined as the desired mode. Modal required. When the vibration excited by a cluster coil propagates to a distance of λ/2 at the phase velocity c _p , it can constructively interfere with the vibration of the same direction particle caused by the adjacent cluster coil, so that the required modal guided wave intensity increases , and suppress other modal guided waves.

When testing, the flexible printed circuit board is pasted on one side of the sheet rubber NdFeB magnet, and wrapped around the test piece in the form of multi-cluster coils unfolding in the circumferential direction. The flexible printed circuit board is located between the magnet and the outer surface of the pipe. During the period, alternating currents of different frequencies are respectively fed into the top and bottom layers at intervals of time. The alternating current induces eddy currents in the specimen and generates alternating Loran under the bias magnetic field provided by the rubber NdFeB magnets. This force induces particle vibration, and the vibration propagates along the axis of the pipeline in the form of longitudinal guided waves, resulting in two columns of guided waves;

The current passed into the coil is a sinusoidal pulse signal. The top coil is fed with an excitation current of frequency f ₁ , the bottom coil is fed with an excitation current of frequency f ₂ , and the group velocities of the guided waves excited by the two-layer coils are c ₁ respectively. and c ₂ , the group velocity is the velocity of the envelope propagation of the wave. According to the group velocity, the two waves can reach a certain position of the pipeline at the same time by controlling the time difference of the excitation current in the two layers of coils.

If there are no micro-cracks in the pipeline, there will be no nonlinear components of sum and difference frequencies; if there are micro-cracks, the sum and difference components of the two fundamental frequencies will appear. When the two waves arrive at the same time At the position of the micro-crack, the amplitudes of the sum-frequency and difference-frequency components are the largest at this time, according to which, the detection and positioning of the micro-crack can be completed.

Compared with the prior art, the present invention has the following advantages and outstanding effects:

1) In the present invention, the two fundamental frequency signals required for the nonlinear detection of ultrasonic mixing are respectively excited by the coils on the top layer and the bottom layer. Compared with the dual-excitation transducer mixing detection method placed in parallel, the axial length is very small, It is beneficial to the miniaturization of the frequency mixing excitation device, and the difference in magnetic flux density between different cluster positions of the coil is small in the area below the magnet. The ultrasonic mixing nonlinear detection can effectively detect micro-cracks, and is not sensitive to the nonlinearity of the system. The mixing technology can also scan the area by using different delays to control the position where the two waves are mixed. The installation and disassembly of the present invention It is more convenient, and has better control over the volume of the transducer, has the advantages of ultrasonic mixing detection, and has better control over its shortcomings.

2) The present invention is designed for the curved surface of the pipeline. The sheet rubber NdFeB magnet has the characteristics of lightness, thinness and flexibility. Compared with the rigid permanent magnet, it can be covered on the surface of the pipeline without heavy fasteners, and the surface does not need to be polished. After processing, it can fit well with specimens of various pipe diameters. In addition, the flexible design of the magnet and the circuit board enables it to fit well on any piece to be tested. It can wrap the side of the pipe in the circumferential direction, or wrap the non-closed curved surface in the circumferential direction.

3) The distance between adjacent clusters of the turn-back multi-cluster coil is equal to the half wavelength of the required modal guided wave at the excitation frequency, which can improve the vibration intensity of the required modal guided wave at the excitation frequency of each coil, and suppress the generation of other modes, so that the The mixing wave signal reception effect is better; the folded-back multi-cluster coil is made by a flexible printed circuit board, which is low in cost compared with winding wires, and it is easy to accurately control the spacing between adjacent clusters of the coil. It can be attached to the surface of the pipe with the rubber permanent magnet, which is convenient for installation and disassembly.

4) The total thickness of the double-layer flexible printed circuit board used is 0.13mm+/-0.03mm, which is thinner than the general double-layer PCB version, the coil lift-off distance is short, the excitation effect is better, and the distance between the bottom layer and the top layer is very small, Therefore, the excitation effect of the coils located in each layer is similar.

Description of drawings

1 is a schematic structural diagram of an electromagnetic ultrasonic excitation device used for pipeline guided wave mixing detection installed on a pipeline according to the present invention;

2 is a schematic diagram of the excitation process principle of the electromagnetic ultrasonic excitation device used for pipeline guided wave mixing detection according to the present invention;

3 is a schematic diagram of an open state of the double-layer flexible printed circuit board of the present invention;

Figure 4 shows the phase velocity and group velocity dispersion curves of the longitudinal modal guided wave of an aluminum alloy pipe with an outer diameter of 45mm and a wall thickness of 1mm;

Figure 5 shows the received signal when the excitation frequency is 900kHz and 1300kHz;

6 is a frequency domain diagram of a received signal;

7 is a schematic diagram of the device of the present invention applied to a non-closed curved surface test piece;

In the figure, 1 is a magnet, 2 is a double-layer flexible printed circuit board, and 3 is a test piece.

Detailed ways

The present invention is further explained below with reference to the embodiments and accompanying drawings, but this is not intended to limit the protection scope of the present application.

As shown in Figure 1, the electromagnetic ultrasonic excitation device for pipeline guided wave mixing detection of the present invention is applied to pipeline guided wave mixing detection. Layer flexible printed circuit board 2 is formed; when testing, the double-layer flexible printed circuit board is pasted on one side of the sheet rubber NdFeB magnet, and the whole is covered on the outer surface of the pipeline test piece 3 to be tested, so that the double-layer flexible printed circuit board is printed The multi-cluster coils of the circuit board are extended in the circumferential direction, and the axial width of the magnet is larger than the width of the double-layer flexible printed circuit board, so that the coils on the double-layer flexible printed circuit board are completely placed in the magnetic field. The coils are in the form of foldback multi-cluster coils, and the center positions of the foldback coils on the top layer and the bottom layer are the same, that is, when the two layers of coils are open, they are coaxial, and the overall width of the two layers of coils can be different, but when the upper and lower layers are printed on the circuit board, the axis Aligned, that is, the same center position. The top coil and the bottom coil are respectively fed with alternating currents of different frequencies, and two columns of longitudinal guided waves are excited by the dual output channels and output delay function of the excitation source. By controlling the time difference between the excitation currents in the two-layer coils, the two waves can reach a certain position of the pipeline at the same time. A series of delays are used to control the mixing position of the two waves, and the amplitudes of the sum frequency and difference frequency components can be observed to determine the Scan the area.

As shown in FIG. 2 , it is a schematic diagram of the excitation principle of the electromagnetic ultrasonic excitation device for pipeline guided wave mixing detection according to the present invention. The coils printed on the bottom layer and the top layer of the double-layer circuit board are respectively supplied with high-frequency and high-power excitation currents J _m1 and J _m2 , wherein the frequency of J _m1 is higher. As shown in (a) in Figure 2, the current J _m1 is first excited, and the eddy current J _e1 is induced in the skin depth of the pipeline. The eddy current will be affected by the Lorentz force under the action of the magnetic field, causing the high-frequency vibration of the surface particles to generate a series of Longitudinal guided waves. As shown in (b) in Figure 2, after a period of time delay, the current J _m2 is excited, and the eddy current J _e2 is induced. Similarly, the second row of longitudinal guided waves will be obtained. The second row of longitudinal guided waves will be at a certain position with the first row of longitudinal guided waves. When they meet, the position of the wave mixing is controlled by controlling the time difference between the excitation currents J _m1 and J _m2 of the two sets of coils.

The structure of the double-layer flexible printed circuit board is shown in Figure 3. In the figure, the double-layer flexible printed circuit board as a whole is 4, the back-folded coil printed on the bottom layer, that is, the bottom coil is 5, and the back-folded coil printed on the top layer, that is, the top coil is 6. , the adjacent cluster spacing of each layer of coils is half of the required modal guided wave wavelength λ at the corresponding excitation frequency, that is, _cp /2f, where _cp is the phase velocity of the guided wave, and f is the frequency of the guided wave. The top and bottom coils have unequal spacing between adjacent clusters.

As shown in FIG. 7 , the test piece is a semicircular tube wall test piece, such as 2 is a double-layer flexible printed circuit board, and 3 is a test piece.

Example:

Take the detection of microcracks in 6061 aluminum alloy pipes with an outer diameter of 45mm and a wall thickness of 1mm as an example.

Figure 4 shows the phase velocity and group velocity dispersion curves of the longitudinal modal guided waves of a 6061 aluminum alloy pipe with an outer diameter of 45mm and a wall thickness of 1mm. According to the dispersion curve of the pipeline, the L(0,2) mode guided wave has almost non-dispersive characteristics at lower frequencies, which makes the interpretation of the signal easier, and its propagation speed is fast and easy to distinguish from other modes. Therefore, the L(0,2) modal guided wave is used as the excitation signal. According to the dispersion curve, the phase velocity of the L(0,2) mode guided wave at 0.9MHz is 5288m/s, so its wavelength λ1 is _5.876mm , the half wavelength is 2.938mm, and the L(0,2) at 1.3MHz The phase velocity of the modal guided wave is 5192 m/s, the wavelength λ ₂ is 3.994 mm, and the half wavelength is 1.997 mm. The spacing between adjacent cluster lines of the top coil of the double-layer flexible printed circuit board is 2.938mm, and the spacing between adjacent cluster lines of the bottom coil is 1.997mm, both of which are 12-cluster coils. It can be considered as a circle around the pipe after connecting the details. For a strong excitation effect, the top coil is connected to a 0.9MHz excitation signal, and the bottom coil is connected to a 1.3MHz excitation signal.

The double layer flexible printed circuit board uses 0.5OZ copper cladding, the total thickness of this laminated structure is 0.13mm+/-0.03mm, and the distance between the top layer and the bottom layer is about 0.074mm. The thickness of the sheet rubber NdFeB magnet is 5mm, the width is 50mm, the length is 140mm, the lower surface is N pole, and the residual magnetic flux density is 800mT.

During detection, the center position of the printed coil on the double-layer flexible printed circuit board is set to 0, and the position of the ultrasonic receiving probe is set to 300mm. There is a microcrack somewhere between the excitation device and the receiving probe. According to the group velocity dispersion curve, the group velocity of the L(0,2) mode guided wave at 1.3MHz is 4799m/s, and the group velocity of the L(0,2) mode guided wave at 0.9MHz is 5139m/s, so There is no delay for the excitation signal of the bottom coil, and the delay time of the excitation signal of the top coil is t. The maximum delay is the delay when the two waves meet at the receiving probe position. According to the calculation, the maximum delay is 4.1 microseconds. For damage location, different delays from 0 to 4.1 microseconds are used to scan the area. The smaller the scan time step used, the higher the location accuracy. In the experiment, the scan was performed with a time step of 0.455 microseconds, the number of scans was 10, and the error was ±16.7mm. The fifth scan in the experiment, that is, when the delay time t was 2.275 microseconds, the sum frequency and difference frequency The sum of the magnitudes of the components is the largest. After calculation, it can be known that the position of the micro-crack is at 167mm±16.7mm. After the actual measurement, the crack is at 163mm, which is within the design error range. Figure 5 shows the received signal when the delay time t is 2.275 microseconds, and the time includes the propagation time of the wave in the ultrasonic receiving probe (the ultrasonic receiving probe does not belong to the excitation device of the present application, but belongs to an external device). Figure 6 is the frequency domain diagram after Fourier transform of the received signal, in which 7 and 8 are the 0.9MHz and 1.3MHz fundamental frequency components, 9 is the difference frequency component of the two fundamental frequencies, and 10 is the two fundamental frequencies. and frequency components. The above examples prove that the present invention can complete the detection and localization of micro-cracks.

What is not described in the present invention applies to the prior art.

Claims (7)

1. an electromagnetic ultrasonic excitation device for pipeline guided wave mixing detection, characterized in that the device comprises a double-layer flexible printed circuit board and a sheet rubber NdFeB magnet made by flexographic plate-making technology, and the double-layer flexible printing The back-folded multi-cluster coils printed on the bottom and top layers of the circuit board have different spacings between adjacent cluster lines, and the top and bottom coil centers are in the same position; the double-layer flexible printed circuit board is pasted on one side of the sheet rubber NdFeB magnet , the double-layer flexible printed circuit board is located between the magnet and the outer surface of the test piece during detection. 2 . The device according to claim 1 , wherein the sheet-like rubber NdFeB magnet is a flexible sheet-like permanent magnet with rubber as a binder and NdFeB powder as a filler and magnetized in the thickness direction. 3 . Material. 3 . The device according to claim 1 , wherein the width of the magnet in the axial direction is larger than the width of the double-layer flexible printed circuit board, so that the coils on the double-layer flexible printed circuit board are completely placed in the magnetic field. 4 . 4. The device according to claim 1, wherein the direction of current passing between adjacent clusters of each layer of coils of the double-layer flexible printed circuit board is opposite, and the top coil and the bottom coil are respectively connected to excitation current signals of different frequencies, The spacing between adjacent clusters of each layer of coils is half of the required modal guided wave wavelength λ at the corresponding excitation frequency. 5 . The device according to claim 1 , wherein the total thickness of the double-layer flexible printed circuit board is 0.13mm+/-0.03mm; the distance between the top coil and the bottom coil is 0.074mm. 6 . 6 . The device according to claim 1 , wherein the detection process is: obtaining the frequency dispersion characteristics of the test piece, determining that a certain longitudinal mode of the test piece to be tested is the required mode, and according to the test piece. 7 . The dispersion curve of the component selects a certain modal guided wave of the current tested component as the excitation signal; When testing, the double-layer flexible printed circuit board is pasted on one side of the sheet rubber NdFeB magnet, and wrapped around the test piece in the form of multi-cluster coils unfolding in the circumferential direction. The flexible printed circuit board is located between the magnet and the test piece. Between the outer surfaces of the specimens, alternating currents of different frequencies are respectively fed into the top and bottom folded coils for a period of time. The variable Lorentz force causes particle vibration, and the vibration will propagate along the pipe axis in the form of longitudinal guided waves, thereby generating two columns of guided waves; The current passed into the coil is a sinusoidal pulse signal. The top coil is fed with an excitation current of frequency f ₁ , the bottom coil is fed with an excitation current of frequency f ₂ , and the group velocities of the guided waves excited by the two-layer coils are c ₁ respectively. and c ₂ , according to the group velocity, set the time difference of the excitation current in the two layers of coils, and make the two waves reach a certain position of the pipeline at the same time under this time difference; If there are no micro-cracks in the pipeline, there will be no nonlinear components of sum and difference frequencies; if there are micro-cracks, the sum and difference components of the two fundamental frequencies will appear. When the two waves arrive at the same time At the position of the micro-crack, the amplitudes of the sum-frequency and difference-frequency components are the largest at this time, according to which, the detection and positioning of the micro-crack can be completed. 7 . The device according to claim 1 , wherein the tested piece is a pipe, a non-closed curved surface. 8 .

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