Development of point-focusing EMATs with large incident angles beyond conventional design limitation

Abstract Shear-vertical-wave (SV-wave) point-focusing electromagnetic acoustic transducer (PF-EMAT) enables non-contact, high-sensitivity ultrasonic inspection. However, conventional designs limit the incident angle to approximately 40°, since exceeding this angle results in a substantial degradation of the SV-wave excitation efficiency. To expand the range of applications, larger incident angles are required. In this study, we developed PF-EMATs capable of operating beyond this limit by exciting line sources oscillating normal to the specimen surface. Experiments on aluminum alloy plates demonstrated that the new design successfully achieved point focusing of SV waves at incident angles of approximately 45°–60°. Furthermore, the performance was comparable to that of conventional PF-EMAT in terms of signal strength, defect detection sensitivity, and spatial resolution. The displacement amplitude at the focal point reached 3.5 nm peak-to-peak, and slit detection tests clearly identified defects as small as 0.5 mm depth with signal-to-noise ratio exceeding 22.