| 摘要 |
PURPOSE:To take an accurate measurement in a material to be inspected by providing a conductive thin plate which is insulated acoustically from the side of a magnet between the magnet and a transmitting and receiving coil, and easily removing unnecessary echoes on the magnet side. CONSTITUTION:The transmitting and receiving coil 3, etc., are provided between the material 1 to be inspected and magnet 2. The conductive thin plate 7 is provided between the magnet 2 and coil 3 while insulated acoustically from the side of the magnet 2. Then when a high frequency alternating current I is supplied to the coil 3, an eddy current J is generated at the surface part of the material 1 to be inspected. Then, vibrations F occur as shown by an arrow owing to a Lorentz force generated through the mutual operation between the eddy current J and a magnetic field B established by the magnet 2 at right angles to the material 1 to be inspected, and the vibrations F are propagated as an ultrasonic wave. This ultrasonic wave is received in the opposite process. An eddy current flows to a thin plate 7 as well by the current I. Consequently, no eddy current flows to the magnet 2. The eddy current in the thin plate 7 also generates an ultrasonic wave, but this ultrasonic wave is reflected repeatedly between the top and reverse surfaces of the thin plate 7 and attenuated. Thus, unnecessary echoes are removable.
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