JPH0348109A - Electromagnetic acoustic transducer - Google Patents

Abstract

PURPOSE:To detect and measure a damage with high sensitivity and high resolution by generating electromagnetic acoustic waves of transverse waves formed in a spherical shape and having the collecting effect of a magnetic flux. CONSTITUTION:A transmission coil 8 and a receiving coil 9 are printed concentrically on a film base so that the winding direction of the coils adjacent to each other on a plane are opposed. When the acoustic wave from each group of coil has a wavelength lambda, a transverse spherial wavy is formed by Fresnel zones having radii differently by lambda/2. When checking, a magnetic field is generated between a material 1 to be checked an permanent magnets 6,7. Then, a pulse signal is impressed to the coil 8, so that the magnetic flux is collected at a predetermined position in the material 1. The electromagnetic acoustic waves from the coil 8 are current-converted and reach the coil 9. The time necessary for the transmission/receipt of the acoustic eaves is detected. While the phase of the incident waves is changed, the acoustic waves are transmitted and received in the same manner as above. Accordingly, the damage and thickness of the material 1 are detected and measured from the time difference in the transmission/receipt of the acoustic waves and amplitude.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to EMAT (Electro-Technology Testing System), which conducts inspections such as flaw detection and wall thickness measurement of conductive materials such as steel, aluminum, and copper.
magnetic acoustic transdu
cer), relating to electromagnetic ultrasound probes.

[Conventional technology]

When inspecting a specimen using an electromagnetic ultrasound probe (EMAT), first a pulsed current is applied to a coil placed opposite the specimen in a static magnetic field generated by a magnet.
The interaction between the eddy current generated by this and the static magnetic field (Lorentz force) generates ultrasonic waves. Then, eddy currents induced by the ultrasonic vibrations on the material surface and the static magnetic field generated by the ultrasonic waves are detected. Furthermore, the time between transmission and reception is measured, and flaw detection and wall thickness measurement are performed based on the vibration and time difference.

Electromagnetic ultrasonic probes are capable of transmitting and detecting ultrasonic waves without coming into contact with the material to be inspected, so they can be used to measure the thickness of rough surfaces, hot materials, and internal materials with poor contact conditions. Applicable to defect inspection. It is also possible to detect flaws and measure wall thickness from the paint on oil tank bottom plates, etc. Furthermore, by changing the direction of the static magnetic field and the shape of the coil, longitudinal waves, transverse waves 1
It has the advantage of being able to transmit and receive electromagnetic ultrasonic waves of various wave modes (modes) such as surface waves.

Such an electromagnetic ultrasonic probe is a wall thickness measuring meter for hot seamless steel pipes (r Tetsu to Hagane 1 No. 9, reprint, 1984. PP, 147-154) developed by the present inventors. Also, a needle for measuring the solidification thickness of continuously cast steel slabs (r Steel Research 1 No. 310,
1982. PP, 374-387).

Furthermore, Japanese Patent Application Laid-Open No. 58-5089 proposes an electromagnetic ultrasonic probe that efficiently emits ultrasonic waves around the entire circumference of a tube using a plate wave having a transverse wave component perpendicular to the inner surface of the tube.

In addition, the influence of electromagnetic coupling is removed with a compensation coil,
An electromagnetic ultrasonic probe that reduces the dead zone was published in Japanese Patent Application Laid-open No. 57-2.
It is disclosed in Japanese Patent No. 08451. Also, JP-A-57-
No. 203949 and Japanese Unexamined Patent Publication No. 57-203950 attempt to improve performance such as transmission/reception efficiency and sensitivity by using an electromagnetic ultrasonic probe having a structure that improves the static magnetic field strength.

[Problem to be solved by the invention]

By the way, in order to perform flaw detection and measurement using an electromagnetic ultrasonic probe with even higher sensitivity and resolution, the curvature of the material surface is used to generate a cylindrical wavefront, and the wave focusing effect is used. Method of flaw detection and measurement (1977Br1tish
Journal of NDT, P178-184)
Furthermore, a surface wave electromagnetic ultrasonic probe (Japanese Unexamined Patent Application Publication No. 106086/1986) has been proposed in which the transmitter/receiver coil is formed into a curved surface.

However, with the above method, it is not possible to form and focus volume waves such as longitudinal waves and transverse waves on a spherical or cylindrical surface, which is essential for flaw detection inside the material and thickness measurement of materials with large thickness changes. There has been a problem in that electromagnetic ultrasonic flaw detection or measurement using volume waves cannot be performed with sufficient sensitivity and high performance.

The present inventor conducted various experiments and research to solve the above-mentioned problems, and found that the transmitter/receiver coil is wound by winding adjacent windings or winding groups on a plane at a pitch that can form a Fresnel zone. It was discovered that by creating a structure in which the directions are opposite to each other, transverse waves, which are volume waves, can be generated and focused in a spherical shape, and the static magnetic field strength can be increased, resulting in high sensitivity. .

The present invention was made based on this knowledge, and by generating transverse electromagnetic ultrasonic waves formed in a spherical shape and having a focusing effect, flaw detection can be performed with higher sensitivity and higher resolution than in the past. The object of the present invention is to provide an electromagnetic ultrasonic probe that generates transverse waves for measurement.

[Means to solve the problem]

The electromagnetic ultrasonic probe according to the present invention is an electromagnetic ultrasonic probe that receives ultrasonic waves generated in a test material by the interaction of an eddy current and a static magnetic field by the reverse action of the test material. A magnet that has both N and S magnetic pole faces facing the material and generates the static magnetic field, and a pitch that is arranged between both the magnetic pole faces and the surface of the material to be inspected and that can form a Fresnel zone. The ultrasonic transmitting coil and the receiving coil are formed such that the winding directions of adjacent windings or winding groups are opposite to each other on a plane.

[Effect]

In the electromagnetic ultrasound probe of the present invention, the ultrasonic waves generated from each winding or winding group of the transmitting coil due to the interaction are ultrasonic waves emitted from adjacent windings or winding groups, and the phase difference between them is π. Each wave is a different transverse wave and is focused at a predetermined focusing position determined by the winding shape of the coil. Also, due to this reverse action, the spherical wave is converted into a current, which is received by each winding or winding group of the receiving coil. This makes it possible to perform flaw detection or wall thickness measurement using the focusing effect of transverse waves.

[Examples] Hereinafter, the present invention will be specifically explained based on drawings showing examples thereof. FIG. 1 is a schematic vertical sectional view showing the structure of the electromagnetic ultrasound probe of the present invention.

The electromagnetic ultrasonic probe according to the present invention includes magnets 6 and 7, each of which has a lower magnetic pole face facing a material 1 to be inspected, with its lower magnetic pole face being substantially parallel to the material 1 to be inspected. and the magnet 6
．． 7, each of the lower pole surfaces 6a.

A transmitting coil 8 and a receiving coil 9 are provided in parallel with 7a, respectively, and are stacked in the thickness direction between the magnets 6, 7 and the specimen 1.

The magnets 6 and 7 are two permanent magnets in the shape of a rectangular bar, and are constructed in such a manner that the former's N pole (positive pole) and the latter's S pole (negative pole) are adjacent to each other in the same plane. It is.

Moreover, the transmitting coil 8. The receiving coil 9 is a printed coil printed on a film stand made of glass fiber reinforced plastic, and the transmitting coil 8 is placed opposite the magnetic pole surfaces 6a and 7a. It has a configuration in which the receiving coils 9 are stacked in this order or vice versa.

A magnet 6.7 and a transmitting/receiving coil 8 having the configuration as described above.
．． 9 is housed in a case consisting of a flat plate-shaped lid 2 that can be opened and closed, and a rectangular cylindrical case main body 5 having a top surface 3 facing substantially parallel to the lid 2.

Specifically, the magnets 6.7 are placed in the center of the back surface of the top surface 3, and the magnetic pole faces 6a, ? A is fixed to the back surface of the lid 2 in a manner substantially parallel to and opposed to the back surface of the lid 2, and the transmitter/receive coils 8.9 are arranged in a stacked manner as described above at the center of the back surface of the lid 2.

The transmitting coil 8 is connected to a female transmitting connector 8b provided on the N-pole side of the back surface of the lid 2, and the receiving coil 9 is connected to a female receiving connector 9b similarly provided on the negative-pole side.

Furthermore, the transmitting connector female 8b is electrically connected to the transmitting connector 8c provided on the positive side of the top surface 3, and the receiving connector female 9b is electrically connected to the receiving connector female 9c also provided on the negative side. It has become.

The transmitting connector 8c is connected to a pulse transmitting circuit (not shown), and allows a pulse current to flow through the transmitting coil 8, so that an electromagnetic ultrasonic wave composed of a Fresnel zone is incident on the test material l. On the other hand, the reception connector 9c detects the eddy current on the test material 1 induced by the electromagnetic ultrasonic waves using a reception amplifier circuit (both not shown) connected to the timekeeping circuit, and supplies the detected eddy current to the timekeeping circuit. There is.

FIG. 2 is an explanatory diagram of a Fresnel zone formed by the electromagnetic ultrasonic probe of the present invention. A in the figure is a plane on which the transmitting coil 8 or the receiving coil 9 is arranged, and the transmitting coil 8 or the receiving coil 9 is arranged so that the winding directions of adjacent winding groups a1 to a% are opposite on the plane. These are printed coils that are printed concentrically on the film stand. For example, when a pulse current is applied to the winding groups a1 to as of the transmitting coil 80 through the transmitting connector 8c, ultrasonic waves generated from the adjacent winding groups are The phase difference is π. As a result, winding groups a, ~a,
The ultrasonic waves generated from Ru. Similarly, the spherical wave of the transverse wave transmitted from point R is transmitted to the first to
When the portion corresponding to the fifth Fresnel zone is reached, an eddy current is generated, and the receiving coil 9 detects this eddy current.

In addition, by making the film base of the printed coil made of a material with low acoustic transmission such as glass fiber reinforced plastic, vibrations caused by the Lorentz force generated in the transmitting coil are prevented from propagating to the receiving coil, and the dead zone is reduced. , transmission and reception efficiency is improved.

Furthermore, when performing flaw detection using the electromagnetic ultrasonic probe of the present invention, for example, if the focusing position of the ultrasonic waves generated from the transmitting coil 8 and the focusing position of the ultrasonic waves generated from the receiving coil 9 are set to the same point. Although highly sensitive flaw detection can be performed, the sensitivity and resolution drop sharply when moving away from the vicinity of the focused position.

Therefore, by making the focusing positions of the transmitting coils 8 and 9 different in the thickness direction of the material to be inspected 1, the range of the focusing positions can be expanded, and the flaw detection range in the vicinity of the focusing positions can be expanded.

When inspecting a specimen using the electromagnetic ultrasonic probe of the present invention, a magnetic field is generated between the permanent magnet 6.7 and the specimen 1. Next, the transmission coil 8 is connected from the pulse transmission circuit through the transmission connector 8c and the transmission connector female 8b.
A pulse signal is applied to. Due to the Lorentz force generated by this, the electromagnetic ultrasonic waves are incident from the transmitting coil 8 into the test material l.The transmitting coil 8 is configured so that the phase difference between the ultrasonic waves generated from adjacent winding groups is π. As shown in Fig. 2, the ultrasonic waves generated from each winding group are formed into a spherical wave composed of the first to fifth Fresnel zones, and are transmitted to a predetermined position within the specimen l. Focus.

On the other hand, as mentioned above, the spherical electromagnetic ultrasonic waves emitted from the transmitting coil 8 are converted into electric current by electromagnetic induction and reach the receiving coil 9, which connects the receiving connector female 9b and the transmitting connector 9.
The signal is input to the reception amplifier circuit through C, and the timer circuit detects the time required for this transmission and reception. Then, by changing the phase of the electromagnetic ultrasonic waves incident on the test material 1, transmission and reception are performed in the same manner, and the test material 1 is flaw-detected based on the time difference and amplitude required for transmission and reception.

Wall thickness measurements are taken.

[Test example]

The dimensions of the electromagnetic ultrasonic probe of the present invention and the test conditions in the test example for forming a Fresnel zone are as follows.

FIG. 3 is a plan view showing the dimensions and structure of the transmitting coil 8, and FIG. 4 is a plan view of the same (receiving coil 9). as
are perpendicular to the juxtaposition direction of each magnetic pole of the magnet 6.7, and the transmitting connector 8c side is the N pole, and the receiving connector 9c side is the S pole, so that they overlap at a position away from the vicinity of the boundary between the two magnetic poles. are arranged concentrically. Magnet 6 indicated by broken line.
The part where 7 is placed has a length of L23 and a width of WIO-.

Further, the coil wire diameter of the transmitting coil 8 shown in FIG. 3 is 0.2
The coil spacing d is 0.4, and each winding group a.

The number of turns of ~as was set to 3. The coil wire diameter of the receiving coil 9 shown in FIG. 4 is 0.1 mm, the coil spacing d is 0.2 mm, and each winding group a, ~a! The number of turns of l was 5.

Table 1 shows the Fresnel zone arrangement when 2) IHz spherical ultrasonic waves are formed with a transmitting side focusing position of 15 tm and a receiving side focusing position of 10 m5+.

Table 1 The pulse generator circuit sends a pulse signal to the transmitting coil 8 so that a burst wave (30 Apps) of 5 cycles flows.

The transmitting and receiving amplifying circuit amplifies the current that has reached the receiving coil 8 in a wide band, and then amplifies it in a bandwidth of 1 to 3 MHz.
It was amplified by 100db. As a result, the Fresnel zones were converged within the range of 7 to 17 mm, with a size of 4 degrees or less, on both the transmitting and receiving sides.

In addition, when performing flaw detection on, for example, a round bar material with the electromagnetic ultrasonic probe of the present invention, the focusing direction of the Fresnel zone is the axial direction, and the flaw detection is performed in the circumferential direction using the curvature of the material surface as before. Defects in areas where the axial and circumferential directions overlap can be detected with even higher sensitivity and resolution.

〔effect〕

As described in detail above, the electromagnetic ultrasonic probe of the present invention has a simple structure and is formed into a spherical shape, and can generate transverse electric waves having a focusing effect, making it possible to detect flaws inside the material. Highly sensitive electromagnetic ultrasonic flaw detection or measurement using volume waves, which is essential for wall thickness measurement of materials with large thickness changes.
High performance and efficient transmission and reception. Furthermore, excellent effects such as being able to easily change the focusing position and focusing range by simply changing the winding shape of the transmitter/receiver coil without changing the other configurations are achieved.

[Brief explanation of drawings]

FIG. 1 is a schematic vertical cross-sectional view of the electromagnetic ultrasound probe according to the present invention, FIG. 2 is an explanatory diagram of the Fresnel zone formed by the t-magnetic ultrasound probe of the present invention, and FIG. FIG. 4 is a plan view showing the dimensions and structure of the transmitting coil of the electromagnetic ultrasound probe of the invention, and FIG. 4 is a plan view similarly showing the dimensions and structure of the receiving coil. 6.7... Magnet 8... Transmitting coil 9... Receiving coil

Claims (1)

[Scope of Claims] 1. An electromagnetic ultrasonic probe that receives ultrasonic waves generated in a specimen material by the interaction of an eddy current and a static magnetic field, with the reverse effect thereof, which is opposed to the specimen material. a magnet having both N and S magnetic pole faces and generating the static magnetic field; and a magnet disposed between both the magnetic pole faces and the surface of the material to be inspected;
The ultrasonic transmitting coil and the receiving coil are formed such that the winding directions of adjacent windings or winding groups on a plane are opposite to each other at a pitch that can form a Fresnel zone. An electromagnetic ultrasonic probe featuring: