CN103837606B - The method that the electromagnet ultrasonic changer of polyphase structure and ultrasonic high-efficiency excite - Google Patents

Abstract

The method that the present invention relates to the electromagnet ultrasonic changer of a kind of polyphase structure and utilize it to carry out ultrasonic high-efficiency and excite. The wherein design of EMAT drive coil, adopt multiple broken line winding, to improve the space density of ultrasonic excitation, broken line winding is made up of multilayer inflection coil, being combined in space and phase place the electric current excitation staggered, dislocation relation and excitation phase coincide, and can increase the a.t. in effective excitation area, improve ultrasonic intensity, it is achieved hyperacoustic efficient excitation and unidirectional emission. In the present invention, permanent magnet magnetizing direction is that level magnetizes, and being applicable to analyte is ferromagnetic substance, based on the electromagnetic acoustic nondestructive testing of magnetostrictive effect principle.

Description

Electromagnetic ultrasonic transducer with multi-phase structure and method for efficient excitation of ultrasonic waves

technical field

The invention relates to electromagnetic ultrasonic non-destructive testing, in particular to an electromagnetic ultrasonic transducer with a multi-phase structure.

Background technique

During the operation of natural gas pipelines, there will be defects such as corrosion and cracks, which seriously affect the safe operation of the pipelines, so the pipelines must be inspected to evaluate their safety. The detection of corrosion defects mainly uses magnetic flux leakage technology, while the detection of cracks generally uses ultrasonic testing technology. Piezoelectric ultrasonic detection requires a coupling medium, which is difficult to apply to the online detection of natural gas pipelines.

Electromagnetic ultrasonic is a new technology in the field of non-destructive testing. It is attracting more and more attention due to its advantages of high precision, no need for couplant, non-contact, suitable for high temperature detection, mobile detection, and easy excitation of various ultrasonic patterns. and attention.

However, its limitation is that the amount of detected surface defect information that can be extracted is discrete, and it is difficult to locate the defect position on the surface and inside of the plate and estimate its damage; especially its energy conversion efficiency is low, and high-power pulse current is required to excite , limiting the application of this technique.

In order to improve the energy conversion efficiency of an electromagnetic ultrasonic transducer, the invention provides an EMAT with a multi-phase structure and a method for efficiently exciting ultrasonic waves using it.

Contents of the invention

The main technical problem to be solved by the present invention is to provide an electromagnetic ultrasonic transducer with a multi-phase structure, which can improve the energy conversion efficiency of the electromagnetic ultrasonic transducer and realize efficient excitation of ultrasonic waves.

The secondary technical problem to be solved by the present invention is to provide a method for ultrasonic excitation using the above-mentioned electromagnetic ultrasonic transducer.

In order to solve the above-mentioned technical problems, the present invention provides an electromagnetic ultrasonic transducer with a multi-phase structure, comprising: a permanent magnet, a multi-phase EMAT coil, a measured ferromagnetic material, a signal source, and a multi-phase drive circuit; The permanent magnet is placed above the tested ferromagnetic material to magnetize the tested ferromagnetic material and provide a bias magnetic field in the horizontal direction;

The polyphase EMAT coil is composed of n zigzag windings, n>1; and placed on the surface of the tested ferromagnetic material to increase the space density of ultrasonic excitation; EMAT coil plane;

The folded wire winding is composed of m layers of folded coils, m>1; the folded coil adopts an S-shaped folded wiring mode, and ensures that the currents of the corresponding positions of each layer are in the same direction, and the folded coils of each layer pass through the interlayer Through-hole electrical connection;

The spacing p=nxl between adjacent traces in the folded coil; the spacing p is determined by the speed C and frequency f of the excited ultrasonic wave propagating in the tested ferromagnetic material, and its mathematical relationship is p =C/2f;

The signal source generates a periodic signal S of frequency f, and generates an output of the same-frequency periodic signal S[i] whose initial phase is iπ/n by phase shifting, 1≤i≤n; the same-frequency periodic signal S[i] is passed through After the multi-phase drive circuit is excited, the n zigzag windings are sequentially connected, so that the excitation current phase differences in adjacent zigzag windings are all π/n.

A method for efficiently exciting ultrasonic waves using the above-mentioned electromagnetic ultrasonic transducer with a multi-phase structure, the specific steps are:

1) the permanent magnet and the measured ferromagnetic material are arranged according to the above-mentioned spatial relationship, and the measured ferromagnetic material is magnetized in the horizontal direction to form a horizontal bias magnetic field;

2) Place the multiphase EMAT coil within the range of the horizontal bias magnetic field, and place it directly above the surface of the ferromagnetic material to be tested according to a certain lift-off value. Wherein, the routing direction of the broken wire winding in the multi-phase EMAT coil is kept perpendicular to the horizontal bias magnetic field;

3) The periodic signal S with frequency f is excited by the signal source, and n periodic signals S[i] of the same frequency are generated through phase shifting, 1≤i≤n; the phase difference between adjacent signals is π/n;

4) Connecting the n same-frequency periodic signals S[i] to corresponding multi-phase drive circuits respectively to form n same-frequency excitation outputs with equal phase differences;

5) according to the phase difference of the same-frequency excitation, the n excitation output ends of the multiphase drive circuit are electrically connected to the n zigzag windings in the multiphase EMAT coil in turn;

6) Under the excitation of the multi-phase EMAT coil, the measured ferromagnetic material particles generate mechanical vibrations of corresponding frequencies, and form ultrasonic waves of frequency f; the ultrasonic waves are parallel to the bias magnetic field, and the excitation currents along each broken line winding The direction of phase increase is unidirectional.

Compared with the prior art, the present invention has the following beneficial effects:

The invention combines the EAMT coil with multi-phase structure and multi-phase excitation current, and realizes the high-efficiency excitation and unidirectional emission of ultrasonic waves by improving the spatial density, spatial intensity and spatial directivity of ultrasonic excitation.

Description of drawings

Fig. 1 is the schematic structural diagram of the electromagnetic ultrasonic transducer of polyphase structure in the preferred embodiment of the present invention;

Fig. 2 is a schematic diagram of the direction of the isolated broken line winding in the preferred embodiment of the present invention;

Fig. 3 is the three-phase EMAT coil schematic diagram under three-phase excitation in the preferred embodiment of the present invention;

Fig. 4 is a side sectional view of an electromagnetic ultrasonic transducer under three-phase excitation in a preferred embodiment of the present invention;

detailed description

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

With reference to Fig. 1-4, the electromagnetic ultrasonic transducer of a kind of polyphase structure comprises: permanent magnet 10, polyphase EMAT coil 11, measured ferromagnetic material 12, signal source, polyphase driving circuit constitute; The magnet 10 is placed above the ferromagnetic material 12 to be tested, magnetizes the ferromagnetic material 12 to be tested, and provides a bias magnetic field in the horizontal direction;

The multi-phase EMAT coil is composed of n zigzag windings, n>1; preferably 3 phases in this embodiment, i.e. n=3; and placed on the surface of the tested ferromagnetic material to increase the space density of ultrasonic excitation ; The equidistant distance l between the folded wire windings is distributed on the plane of the EMAT coil;

The folded wire winding is composed of m layers of folded coils, m>1; the folded coil adopts an S-shaped folded wiring mode, and ensures that the currents of the corresponding positions of each layer are in the same direction, and the folded coils of each layer pass through the interlayer Through-hole electrical connection;

The spacing p=nxl between adjacent traces in the folded coil; the spacing p is determined by the speed C and frequency f of the excited ultrasonic wave propagating in the tested ferromagnetic material, and its mathematical relationship is p =C/2f;

For 3-phase EMAT coils, there is 3xl=C/2f, that is, l=C/6f.

The multi-phase EMAT coil 11 will be described below with the PCB double-layer board (m=2) as the carrier, in conjunction with FIGS. 2 and 3 :

The dark line segment in the figure represents the line segment of the broken line coil located on the upper layer of the PCB, the light line segment represents the line segment of the line coil located on the lower layer of the PCB board, and the dark circle drawn at the junction of the dark line segment and the light line segment represents The interlayer vias are used to electrically connect the wiring segments of the upper folded coils to the lower folded coils, so that the upper/lower excitation current flows to the lower/upper layers through the interlayer vias.

As shown in Fig. 2, the current direction of the isolated zigzag winding is described first (n=1). The line segment thickness and labels in the figure are used to assist in explaining the current path.

The excitation current starts from the middle label 0 end of the upper layer of the PCB board, passes through the upper layer wiring (dark thick line segment) to the interlayer via hole 1, and connects through the interlayer via hole, the excitation current flows into the lower layer of the PCB board, and the lower layer wiring (shallow line) thick line) to interlayer via hole 2, the excitation current flows into the upper layer of the PCB through the interlayer via hole. In the same manner, the excitation current is switched between the upper and lower layers of the PCB, and the current flows to the interlayer via hole 3 .

When the excitation current flows to the right end of Figure 2, the excitation current turns back to the left of Figure 2, and the broken line winding line segment between the interlayer via hole 2 and the interlayer via hole 3 is located on the upper layer of the PCB, while the interlayer via hole The broken line winding segment between 4 and the interlayer via hole 5 is located on the lower layer of the PCB. The excitation currents of the corresponding positions on the two layers are in the same direction. In a similar manner, the excitation current flows through the interlayer via hole 6 and returns to the terminal marked 7 . Form the broken line winding circuit 0-1-2-3-4-5-6-7.

As shown in Figure 3, the isolated broken-line winding in Figure 1 is shifted to the right of the figure by 1/6 of the ultrasonic wavelength distance to become the second phase broken-line winding, and then the second phase broken-line winding is shifted to the right of the figure by 1/6 The distance between the ultrasonic wavelengths forms an EMAT coil with a three-phase structure.

After the translation of the isolated broken-line windings, the broken-line coils are evenly distributed on the PCB, which is beneficial to improve the space density of ultrasonic excitation. In this embodiment, the crossing wire segments at any position are in different layers; and the excitation currents of the wires at corresponding positions on the upper and lower layers can be kept in the same direction, which is beneficial to increase the ampere-turns of excitation and improve the spatial intensity of ultrasonic excitation.

With further reference to Figure 4, a method for efficiently exciting ultrasonic waves using an electromagnetic ultrasonic transducer with a multi-phase structure:

The permanent magnet 10 and the tested ferromagnetic material 12 are arranged according to the spatial relationship shown in FIG. 4 , and the tested ferromagnetic material 12 is magnetized in the horizontal direction to form a horizontal bias magnetic field.

Place the multiphase EMAT coil 11 within the range of the horizontal bias magnetic field, and place it directly above the surface of the ferromagnetic material 12 to be tested according to the lift-off value of 1 mm. Wherein, the routing direction of the zigzag winding in the multiphase EMAT coil 11 is kept perpendicular to the bias magnetic field.

The direction of excitation current at the cross-section has two directions: inward (indicated by ×) perpendicular to the plane of paper and outward (indicated by *) perpendicular to the plane of paper. Viewed from left to right in Figure 4, the direction of the excitation current passes through the paper in sequence, appearing in the upper layer-lower layer-upper layer corresponding wire segment represented by dark color, and then returns to the left through the lower layer-upper layer-lower layer path represented by light color. The windings of different phases and the exciting currents are distinguished by different shapes, which are circle, square and triangle.

The graph in FIG. 4 shows the relationship between time (set as x-axis) and particle position or current (set as y-axis). Along the x-axis, the excitation current of any phase broken-line winding at the corresponding position can be observed as a function of time. Along the y-axis, the phase relationship of the excitation current on the zigzag windings of each phase at any moment can be observed, as well as the particle vibration of the measured ferromagnetic material at each corresponding position.

The three same-frequency periodic signals excited by the signal source respectively form three same-frequency excitation outputs with equal phase differences. The excitation output terminals of the three-phase drive circuit are electrically connected with the three zigzag windings in the EMAT coil in turn. Taking the position of the middle section of the three-phase EMAT coil windings to observe, the phase relationship of the three-phase excitation current is shown in the coordinate diagram in Figure 4.

Under the excitation of the EMAT coil, the measured ferromagnetic material particles generate mechanical vibrations of corresponding frequencies, and form ultrasonic waves of frequency f. This ultrasonic wave is parallel to the bias magnetic field and propagates in the horizontal direction.

Analyzing the propagation process of each phase of ultrasonic waves to the right, the mechanical vibration of the corresponding frequency generated by the measured ferromagnetic material particles is in the same phase as the excitation current at this position in terms of frequency and phase (that is, the ultrasonic waves are superimposed on each other in the same phase during the process of propagating to the right. ), the ultrasonic intensity in this direction is effectively improved. Similarly, the process of ultrasonic waves propagating to the left side of each phase is analyzed. The phases of the ultrasonic waves excited by the three-phase currents are different, and the superposition result is zero, that is, the excited ultrasonic waves cancel each other out in the process of propagating to the left. Therefore, the EMAT with multi-phase structure can realize the unidirectional emission of ultrasonic waves.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present invention can easily think of changes or Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (1)

1. The method of efficient ultrasonic excitation, the specific steps are: 1) Place the permanent magnet above the ferromagnetic material to be tested, and magnetize the ferromagnetic material in the horizontal direction to form a horizontal bias magnetic field; 2) The multiphase EMAT coil is placed within the range of the horizontal bias magnetic field, and placed directly above the surface of the ferromagnetic material to be tested according to a certain lift-off value, so as to increase the spatial density of ultrasonic excitation; wherein, the multiphase EMAT The coil is composed of n folded wire windings, n>1; and placed on the surface of the tested ferromagnetic material to increase the space density of ultrasonic excitation; the equal distance l between the folded wire windings is distributed on the plane of the EMAT coil; The zigzag winding is composed of m layers of zigzag coils, m>1; the zigzag coils adopt an S-type zigzag wiring mode, and ensure that the currents of the corresponding positions of each layer are in the same direction, and the zigzag coils of each layer pass through the interlayer The hole is electrically connected; the spacing p=nxl between adjacent traces in the folded coil; the spacing p is determined by the speed C and frequency f of the excited ultrasonic wave propagating in the tested ferromagnetic material, and its The mathematical relationship is p=C/2f; 3) The periodic signal S with frequency f is excited by the signal source, and n periodic signals S[i] of the same frequency are generated through phase shifting, 1≤i≤n; the phase difference between adjacent signals is π/n; 4) Connecting the n same-frequency periodic signals S[i] to corresponding multi-phase drive circuits respectively to form n same-frequency excitation outputs with equal phase differences; 5) according to the phase difference of the same-frequency excitation, the n excitation output ends of the multiphase drive circuit are electrically connected to the n zigzag windings in the multiphase EMAT coil in turn; 6) Under the excitation of the multi-phase EMAT coil, the measured ferromagnetic material particles generate mechanical vibrations of corresponding frequencies, and form ultrasonic waves of frequency f; the ultrasonic waves are parallel to the bias magnetic field, and the excitation currents along each broken line winding The direction of phase increase is unidirectional.