Numerical investigation of unidirectional generation of circumferential SH waves applied to defect detection in pipe

Circumferential Shear horizontal (CSH) ultrasonic guided waves are useful for non-destructive evaluation of pipes. SH waves can be efficiently generated using a periodic permanent magnet electromagnetic acoustic transducer (PPM EMAT). Those transducers generate waves that propagate in both clockwise and counterclockwise directions, which complicates the interpretation of the received signal since the scattered waves from a potential defect can mix with direct waves generated by the transmitter. We recently presented designs of dual-PPM EMATs that generate SH waves in a single direction. In this paper, we investigate through finite element simulations how unidirectional generation can ease the signal interpretation task for the higher-order CSH1 wave mode. Results show that, due to the mode conversion and dispersion, several wavefronts can be detected, under conventional bidirectional generation, rendering signal interpretation and defect echo identification complicated, for a range of defect positions. Unidirectional generation of CSH waves proves itself to be an important feature in pipeline inspection, providing more reliable signal interpretation.