Development of an Electromagnetic Acoustic Transducer that can Alternately Drive the Lamb Wave and Shear Horizontal Plate Wave

The Lamb wave is often utilized for the inspection of thin metal plates using a wheel-type probe with piezoelectric oscillators is used as the sensor. The Lamb wave is too sensitive to the conditions of the surface, although it has a high ability for defect detection. On the other hand, a shear horizontal (SH) plate wave is not very sensitive to surface conditions, although it has a low ability for defect detection. They have different characteristics for defect detection. It may then be desirable if both ultrasonic waves could be used by the same transducer; however, it is difficult to generate both ultrasonic modes using a wheel-type transducer. We attempted to generate both ultrasonic modes using an electromagnetic acoustic transducer (EMAT). We then confirmed the basic structure and the fundamental drive conditions. We also observed that the basic characteristics for defect detection different between both ultrasonic modes.