| 摘要 |
PURPOSE:To reduce blind sectors by improving the shape and arrangement of transmitting coils and receiving coils. CONSTITUTION:An electromagnetic sound transducer in which transmitting coils 4 are placed in the clearance between a central magnetic pole 3a and outer peripheral pole 3b of a coil 1 and two receiving coils 51, 52 are arranged concentrically in the clearance is placed oppositely to an object to be tested. When a high-frequency current is applied to the transmitting coil 4, an eddy current is generated, and a ultrasonic wave that propagates in the direction perpendicular to the surface of the object to be tested is generated. At this time, the high frequency current applied to the transmitting coil 4 is induced by the coils 51, 52 for split reception, and generates a voltage. As the coils 51, 52 for split reception are reverse in the direction of winding and connected in series, the induced voltage is canceled. Consequently, the induced voltage is not generated in the terminals of the receiving coils 51, 52 and blind sectors are elminated. |
