Alignment precision enhancement of side-shifted dual periodic permanent magnets array with an enclosed-case electromagnetic acoustic transducer

Shear horizontal ultrasonic guided waves are widely used in non-destructive testing and can be generated, without requiring contact with the medium under test, through periodic permanent magnets electromagnetic acoustic transducers (PPM EMATs). PPM EMATs generate both forward and backward propagating waves, which may be undesirable. Recently, we presented a non-conventional PPM-like EMAT transducer that generated waves mainly in one direction, the so-called side-shifted dual-PPM EMAT. The construction of this device, however, should be conducted with fine precision in order to avoid misalignment of its main pairs, which can hinder its unidirectional capability. In this paper, we present a robust misalignment-free enclosed-case side-shifted dual-PPM EMAT. The performance of the device was experimentally evaluated by its radiation pattern and showed similar performance to the hand-aligned device, when carefully mounted, without the need for fine manual alignment. In addition, the capacity of unidirectional generation of SH waves in plates was further experimentally illustrated. The designed unidirectional SH wave transducer can be readily used without any fine manual adjustment.