A residual thickness measurement method for corroded steel plates using ultrasonic waves is presented. A shear horizontal (SH) plate wave is transmitted in a steel plate by an SH array transducer, and the echo received due to reflection that occurred because of the cutoff phenomena of the plate wave is used. Furthermore, the configuration of the SH array transducer suitable for the measurement method is studied. It is shown that not only the sensitivity itself but also the sensitivity variation among array elements can be improved by ditching grooves on the surface of the protection plate of the transducer, which provides pressure concentration points on the surface. Experiments are performed to verify the method using the SH array transducer with grooves. The residual thickness obtained by the method agrees well with the actual size of the steel plate.
