| 摘要 |
PROBLEM TO BE SOLVED: To measure the thickness even of a thin specimen or the position and the size of a defect in the vicinity of the surface of a specimen accurately, by arranging a permanent magnet on a receiving coil, laminating a dummy coil and a dummy plate thereon and arranging a phase shifter, an amplifier and a subtractor thereon. SOLUTION: A transmitter 21 generates an exciting current, which is outputted to a transmission coil 3. The current flowing through the transmission coil 3 induces an eddy current in a specimen and a Lorentz force is generated through interaction with the field of a permanent magnet 2a. Consequently, an ultrasonic wave is generated directly in the specimen, transmitted in the direction of thickness and reflected on the bottom face before being detected by a receiving coil 4. On the other hand, a voltage is induced on the receiving coil 4 side. When the specimen is sufficiently thin, the induction signal generates a bottom face reflection echo in a dead band region. Effect of the exciting current is eliminated on the transmission side by a dummy coil 11, a dummy plate 12, a phase shifter and a subtractor 15 and a signal containing only the bottom face reflection echo is outputted from the subtractor 15 and presented on a display 24 through a main amplifier 22 and a signal processing section 23. |
