Development of shear-vertical-wave point-focusing electromagnetic acoustic transducer

Abstract

A shear-vertical-wave point-focusing electromagnetic acoustic transducer is developed for the purpose of detecting stress corrosion cracking in stainless steel. The transducer is composed of a permanent magnet and two identical concentric meander-line coils, one for the transmitter and the other for the receiver, and the shear-vertical waves are excited and detected by the Lorentz force mechanism. The meander-line coils are designed so that the phases of all the excited shear-vertical waves are focused in phase at a focal point. The focal area is evaluated experimentally, and it is confirmed that the developed transducer is capable of detecting slit defects deeper than 0.05mm at the bottom surface of a stainless-steel plate 20mm thick.