JP2965784B2 - Electromagnetic ultrasonic transducer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to non-destructive and non-contact metal defect detection, measurement of thickness, sound velocity, thickness resonance frequency, stress, etc. using electromagnetic ultrasonic waves, and deep drawing of thin metal sheets. The present invention relates to an electromagnetic ultrasonic transducer for measuring properties and the like.

[0002]

2. Description of the Related Art An electromagnetic ultrasonic transducer is capable of generating ultrasonic waves in a metal to be measured in a non-contact manner and detecting ultrasonic waves in the metal to be measured by using an electromagnetic force. Depending on the type of magnets and coils that constitute the transducer, longitudinal waves, transverse waves, plate waves, surface waves, etc. can be generated and detected, and are used to measure various physical properties of metals (Kawashima, "Electromagnetic ultrasonic transducers and applications," Applied Physics, 52-12 (1983), etc.).

Generally, in the measurement using such an electromagnetic ultrasonic transducer, if the electromagnetic ultrasonic transducer is arranged in a non-contact manner with the metal to be measured, a lot of noise is generated, which hinders the measurement. Most of this noise can be removed by short-circuiting the metal to be measured and the transmitting and receiving coils of the electromagnetic ultrasonic transducer to make it conductive. By the way, when the metal to be measured is measured in a stationary state with respect to the electromagnetic ultrasonic transducer, it is not possible to make the conductive state by short-circuiting the transmitting coil of the electromagnetic ultrasonic transducer and the receiving coil and the metal as described above. Although it is easy, when the metal to be measured is relatively moving with respect to the electromagnetic ultrasonic transducer, an appropriate short circuit is provided between the metal to be measured and the transmitting and receiving coils of the electromagnetic ultrasonic transducer. There was no way. For example, as a method, the conductive roll is brought into contact with the metal to be measured, and the metal surface to be measured and the electromagnetic ultrasonic transducer are transmitted and received by electrically connecting the roll surface, the roll bearing and the shaft, and the coil. A method of short-circuiting between the coil and the coil is conceivable, but there are problems such as abrasion of the roll and a problem that the surface of the metal to be measured is easily damaged. Thus, when the metal to be measured is relatively moving with respect to the electromagnetic ultrasonic transducer, measurement in a noisy state must be performed.

[0004]

In the measurement using a conventional electromagnetic ultrasonic transducer, when the metal to be measured and the electromagnetic ultrasonic transducer are arranged in a completely non-contact state, the metal to be measured is In addition, there is a problem that a large amount of electromagnetic ultrasonic noise is generated due to the fact that the electric potential between the transmitting and receiving coils of the electromagnetic ultrasonic transducer does not become the same as that of the coil, which causes an obstacle to measurement. SUMMARY OF THE INVENTION It is an object of the present invention to provide an electromagnetic ultrasonic transducer capable of reducing noise generated during measurement in a non-contact state of metal.

[0005]

The present invention SUMMARY OF THE INVENTION In order to achieve the above object, the electromagnetic ultrasonic transducers for measuring without contact the metal, between the measured metal, eddy current
When placing metal foil with cuts to prevent occurrence
The gist of the invention is an electromagnetic ultrasonic transducer characterized by being electrically connected to a coil of the transducer.

[0006]

By arranging a metal foil having the same potential as the coil between the metal to be measured and the transmitting and receiving coils of the electromagnetic ultrasonic transducer, the metal foil reduces external noise such as the metal to be measured. It absorbs and stably generates ultrasonic waves in the metal to be measured, and can stably detect the ultrasonic waves in the metal, thereby reducing noise in measurement using electromagnetic ultrasonic waves. The metal foil is a nonmagnetic material having a low magnetic permeability, and a material having a relatively low conductivity is suitable. This is because the magnetic field from the transducer is not interrupted by the metal foil as much as possible, and an eddy current is generated in the metal foil, and the power exchanged between the transducer and the metal under test during transmission and reception is reduced. This is in order to avoid being deprived as much as possible.

[0007] Furthermore, if a cut such as a radial line is formed in the metal foil, eddy currents are less likely to be generated in the metal foil, and the transmitter and the receiver are exchanged between the transducer and the metal to be measured during transmission and reception. Since a portion of the power is not lost, more efficient measurement can be performed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described in detail with reference to FIG. The electromagnetic ultrasonic transducer 1 is connected to the metal 5 to be measured.
On the other hand, in an electromagnetic ultrasonic measurement system for generating and detecting electromagnetic ultrasonic waves inside and on the surface of the metal 5 to be measured in an electrically non-contact state, the surface of the metal 5 to be measured and the electromagnetic ultrasonic transducer 1 A metal foil 4 is disposed between the transmitting and receiving coils 3 in parallel with the surface of the metal 5 to be measured, and the same potential is applied between the metal foil and the transmitting and receiving coils.

The electromagnetic ultrasonic transducer 1 comprises a magnet 2 for generating a magnetic field in the metal 5 to be measured, and a transmitting coil and a receiving coil 3 for generating and detecting an eddy current. Electromagnetic ultrasonic transducers include
There is a coil having only one of the coil and the receiving coil and used only for transmission and reception, and a coil having one coil for both transmission and reception and performing both transmission and reception. There are types that generate waves in various modes such as a plate wave and a surface wave.

[0010] Further, electromagnetic ultrasonic transducers are used at frequencies of about several hundred kHz to 100 MHz, and include those using pulsed ultrasonic waves, those using continuous waves, those generating standing waves in the metal to be measured, and the like. Yes, it is used for the purpose of detecting defects in the metal to be measured, measuring the speed of sound, measuring the thickness, measuring the resonance frequency, measuring the material, measuring stress, and the like. Among these, those that generate a standing wave are used when the metal to be measured has a plate shape of about 0.1 to 10 mm, and generate ultrasonic waves of each frequency traveling in the thickness direction of the plate as a continuous wave,
When an ultrasonic wave of a specific frequency is generated, a phenomenon in which resonance occurs in the thickness direction is captured and used. The electromagnetic ultrasonic transducer 1 may be measured by bringing it into contact with the metal 5 to be measured, but it can also be placed in a non-contact manner, and the gap between them is usually about 10 mm or less.

As the metal 5 to be measured, iron, stainless steel,
Regardless of iron, non-ferrous metal such as aluminum, titanium, copper, etc.
In addition, various alloys and those having plating, coating, rust, etc. on the surface can be used.

As the metal foil 4, a nonmagnetic material having a relatively low conductivity is suitable. For example, austenitic stainless steel, titanium, manganin, constantan, evanome, invar, platinum and the like can be used. The same effect can be obtained by using a conductive film instead of the foil. The thickness of the metal foil 4 is approximately 1 to 100 μm,
For example, a 30 μm austenitic stainless steel has an effect of reducing noise at a frequency of about 100 kHz to 50 MHz. The metal foil 4 is disposed between the transmitting coil / receiving coil and the metal 5 to be measured in parallel with the surface of the metal 5 to be measured, but the distance between the metal foil 4 and the transmitting coil / receiving coil 3 is arbitrary, The metal foil 4 may be arranged so as to be in contact with the transmitting / receiving coil 3. Further, the size may be equal to or larger than the size of the transmitting coil / receiving coil 3.

Further, when an eddy current is generated in the metal foil 4, when transmitting and receiving, the transducer and the metal 5 to be measured
Since a part of the power exchanged between them is taken away and the signal sensitivity is reduced, it is desirable to minimize the eddy current generated in the metal foil 4 as much as possible. For this purpose, if radial cuts are made in the metal foil 4 as shown in FIG. 2 or a large number of parallel cuts are made in the metal foil 4 as shown in FIG. It is less likely to occur, and more efficient measurement can be performed. Further, in the embodiments, the present invention is effective even if the metal surface to be measured is not a flat surface but a curved surface.

Finally, a measurement result of an ultrasonic spectrum when measuring a frequency at which a longitudinal wave of an ultrasonic wave propagating in the thickness direction of the cold-rolled steel sheet causes resonance in the thickness direction is shown.
First, FIG. 4 shows the result of the measurement by the conventional method without implementing the noise reduction measure of the present invention, and FIG. 5 shows the result of performing the noise reduction measure using the metal foil of the present invention. Is shown. 4 and 5, the horizontal axis represents frequency, and the vertical axis represents power spectrum. In this measurement example, the measurement result in the case where the present invention is implemented is, as compared with the conventional measurement result, the noise level is changed from -66 dB to -84 dB,
It is about 18 dB lower. Further, since the peak level of the resonance frequency is -45 dB, which is not changed, the signal-to-noise ratio is improved by 18 dB by implementing the present invention.

[0015]

According to the present invention, non-destructive and non-destructive
Significantly reduces electromagnetic ultrasonic signal noise when performing non-contact metal defect detection, measurement of thickness, sound velocity, thickness resonance frequency, stress, etc., and measurement of deep drawability of thin metal sheets. To be able to

[Brief description of the drawings]

FIG. 1 is an electromagnetic ultrasonic transducer having a metal foil disposed thereon.

FIG. 2 is a metal foil with radial cuts.

FIG. 3 is a metal foil cut in parallel.

FIG. 4 shows a measurement example when the present invention is not performed.

FIG. 5 is a measurement example when the present invention is implemented.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electromagnetic ultrasonic transducer 2 Magnet coil 3 Transmitting / receiving coil 4 Metal foil 5 Metal under test 6 Power supply for magnet 7 Signal processing device

────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Katsuhiro Kawashima 5-10-1 Fuchinobe, Sagamihara-shi, Kanagawa Prefecture Nippon Steel Corporation Electronics Research Laboratory (56) References JP-A-2-96607 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 29/00-29/28

Claims (1)

(57) [Claims] 1. An electromagnetic ultrasonic transducer for measuring a metal in a non-contact manner, wherein an eddy current of an eddy current flows between the metal and a metal to be measured .
When placing metal foil with cuts to prevent occurrence
Moni, electromagnetic ultrasonic transducers, characterized in that the conductive coil of the transducer.