JPH041497Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an electromagnetic ultrasonic transducer that is inserted into a pipe-like structure such as a thin tube and performs ultrasonic flaw detection by emitting ultrasonic waves. Conventional equipment for ultrasonic flaw detection inside thin tubes has a structure that detects flaws by emitting ultrasonic waves only on a part of the surface inside the tube.To detect flaws on the entire surface inside the tube, either the tube or the transducer must be rotated. The operation is extremely complicated, and simplification has been desired.

This invention was made to eliminate the above-mentioned drawbacks, and by simultaneously generating ultrasonic waves (SH waves) on the entire circumferential wall of the capillary, it is possible to efficiently transmit ultrasonic waves to the entire circumferential wall of the capillary without rotating the tubule, etc. The present invention aims to provide an electromagnetic acoustic transducer that can generate

First, a conventional device will be explained with reference to FIGS. 1 and 2.

As an electromagnetic acoustic transducer (hereinafter abbreviated as EMAT) that is inserted into a thin tube to perform ultrasonic flaw detection, one having the structure shown in FIG. 1 is conventionally known. That is, 1 in the figure is a permanent magnet arranged so that the upper and lower polarities are opposite to each other, and a coil 2 is wound around this permanent magnet 1 so that, for example, five permanent magnets form one unit. By EMAT3
is configured. In addition, 4 in the figure is EMAT3
is the thin tube into which it is inserted. The operation of such EMAT will be explained with reference to FIG. When a high frequency current is passed through the coil 2 of the EMAT 3, an eddy current I is generated in the thin tube 4 in contact with the coil 2. On the other hand, a perpendicular and periodically changing magnetic flux B is applied from the permanent magnet 1 to the inner surface of the thin tube 4, and Lorentz force F is generated by interaction with the eddy current I. This Lorentz force F changes at the same period as the magnetic flux period, and this force F generates ultrasonic waves (plate waves) called SH waves in the thin tube 4. Note that the ultrasonic waves are detected by converting them into electrical signals in a process reverse to that described above.

However, in the case of EMAT3 mentioned above,
Since the structure is such that ultrasonic waves are generated only on a part of the circumference of the thin tube 4 where the coil 2 is located, in order to detect flaws on the entire surface of the thin tube 4, either the thin tube or the EMAT 3 must be rotated. Flaw detection operations become complicated. Also, due to the shape of the permanent magnet 1, the coil 2
A portion where the surface of the ultrasonic wave is separated from the inner surface of the thin tube 4 inevitably occurs, and in this portion, the efficiency of ultrasonic wave generation is poor and the sensitivity is low.

The present invention was devised in order to improve these problems, and consists of a cylindrical core with a center hole and a plurality of magnets, alternately arranged so that the poles of the magnets are the same across the core. A group of arranged magnets, a coil wound in a toroidal shape through these center holes, a conductor core passed through the center hole, and both ends of the conductor core are electrically short-circuited to the inner surface of the tube to be ultrasonically tested. The present invention relates to an electromagnetic ultrasonic transducer characterized by comprising a conductor disk and a conductor ring that is in close contact with the inner surface of the tube.

Next, an embodiment of the electromagnetic ultrasonic transducer (EMAT) of the present invention will be described with reference to FIGS. 3 to 7.

A perspective view of the EMAT for small tubes is shown in Figure 3. The cross-sectional structures of the magnet 1 and the core 2 are as shown in FIG. 4, with the same poles facing each other with the core in between. The core rod 4, disk 5, and ring 6 are all made of metal with high conductivity, and are electrically connected as shown in FIG. Further, the ring 6 has a structure in which the ring 6 is pressed into the thin tube when inserted into the thin tube like a piston ring, and the thin tube is electrically connected to the core rod 4, the disk 5, and the ring 6. The entire cross section is the 6th
As shown in the figure. The coil 3 is wound toroidally around the magnet 1 and the core 2 through a hole in the center, as shown in FIGS. 4 and 3.

Next, we will explain the mechanism by which EMAT generates ultrasonic waves. Figure 7 shows the state when the EMAT is inserted into the thin tube and a high frequency current is passed through the coil 3.

The thin tube 10, the ring 6, the disc 5, and the core rod 4 together serve as one coil of a toroidal core composed of a cylindrical core 2 and a magnet 1, and the coil 3 is also a toroidal core. The coil has n turns, and the whole has a transformer structure.

Therefore, when a high frequency current 20 is passed through the coil 3, a magnetic field is generated in a direction perpendicular to the plane of the paper of FIG. 7, and a current 21 is induced in the path shown by the broken line due to electromagnetic induction.

This current 21 is n times the current flowing through the coil 3 in an ideal state, assuming that the number of turns of the coil 3 is n. Letting this be J, J flows in the axial direction of the capillary. On the other hand, the magnetic field generated by the magnet 1 and the core 2 is generated in the radial direction B of the tubule in the tubule wall near the core.
Its direction is reversed at the pitch T, and a force F is generated by interaction with the above-mentioned current J. This force is perpendicular to the plane of the paper and its direction is reversed at the T pitch. The direction of this force matches the vibration direction of the SH wave with a period of 2T, and generates an SH wave. Detection of ultrasonic waves can be performed by the reverse mechanism.

According to the electromagnetic ultrasonic transducer of the present invention described above, the structure is axially symmetrical, and SH waves are generated on the entire surface of the capillary wall, and this wave propagates in the axial direction, causing defects around the circumference. No matter where it is located on the top, a reflected wave is generated and can be detected. accordingly
There is no need to rotate EMAT. In addition, the current generated in the thin tube is n times the current in the coil 3,
Because it can generate high-level ultrasonic waves,
Defect detectability is improved.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the overall appearance of a conventional electromagnetic ultrasonic transducer, Fig. 2 is an explanatory diagram of the internal functions of the conventional transducer, and Fig. 3 is an electromagnetic ultrasonic transducer according to the present invention. FIG. 4 is a cross-sectional structural diagram of the magnet of the present invention; FIG. 5 is a central cross-sectional view of the conductor core, conductor disk, and conductor ring of the transducer of the present invention; FIG. 6 is an overall sectional view showing the magnet, coil, core rod, disk, and ring of the transducer of the present invention, and FIG. 7 is a state explanatory diagram illustrating the function of ultrasonic wave generation according to the present invention. 1...Magnet, 2...Core, 3...Coil, 4...
...Conductor core rod, 5...Conductor disk, 6...Conductor disk.

Claims (1)

[Scope of utility model registration request] A group of magnets in which a plurality of cylindrical cores and magnets each having a center hole are alternately arranged so that the poles of the magnets are the same across the core, and a coil is wound in a toroidal shape through these center holes. Equipped with a conductor core passed through the center hole, a conductor disk for electrically short-circuiting both ends of the conductor core with the inner surface of the tube to be ultrasonically tested, and a conductor ring that closely contacts the inner surface of the tube. An electromagnetic ultrasonic transducer featuring: