Nondestructive inspection of structures is important for ensuring the safety of the social infrastructure. Among them, the ultrasonic inspection method plays a role as a major technology. However, when examining a huge structure, the inspection time tends to be very long. Therefore, a system for transmitting and receiving ultrasonic waves in all directions from the ultrasonic sensor has been constructed. Several types of ultrasonic sensors using this concept have already been devised, but since the ultrasonic energy is dispersed in all directions, there is a problem that a sufficient detection performance cannot be ensured, especially when the thickness of the material to be inspected becomes thick. Therefore, we developed a highly sensitive omnidirectional ultrasonic sensor utilizing the resonance phenomenon of the ultrasonic wave propa-gating in the thickness direction. The omnidirectional ultrasonic system also consists of an electromagnetic ultrasonic transducer (EMAT) using a circular magnet. It is possible to inspect the plate thickness from 0.3 mm to 10 mm and the inspection range of the diameter of 300 mm around the sensor by the developed system. It is indicated that the developed system allows the high-speed inspection of huge structures.
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