Analytical model and optimal focal position selection for oblique point-focusing shear horizontal guided wave EMAT

Abstract As an important application in nondestructive testing (NDT) technology, ultrasonic guided wave testing is widely used in the detection of defects in metal plates, pipes, and bridges. In the detection of defects in metal plates, electromagnetic acoustic transducers (EMATs) can easily excite shear horizontal (SH) guided waves, and a couplant is not required, in contrast to piezoelectric ultrasonic transducers. However, the low energy conversion efficiency of an EMAT has always been its main drawback. Therefore, in this work, we propose a new oblique point-focusing SH (OPFSH) EMAT configuration and obtain two analytical models for both continuous sine pulses and burst signals. The proposed transducer can achieve high-sensitivity detection of defects in the focal area. Moreover, the influence of the focal position on the signal intensity is also studied, and an optimal focal position selection method is demonstrated through simulation and experimental methods. By performing finite element calculations of the wave fields at different focal positions, we find that the optimal focal points are approximately distributed along a line. Therefore, the optimal focal position should be selected carefully to achieve the best OPFSH-EMAT focusing performance.