Enhancing Shear Horizontal Wave Generation With a Multilayer Coil Electromagnetic Acoustic Transducer

The electromagnetic acoustic transducer (EMAT) offers a promising solution for noncontact inspection in the field of nondestructive testing (NDT), allowing the generation of shear horizontal (SH) guided waves in plate-like conductive structures. The fundamental mode of SH wave is particularly effective in NDT applications due to its nondispersive characteristics. In this study, we propose a new EMAT designed specifically for the generation of SH-guided waves, inspired by and improved from the original chevron EMAT design, which focused on using two distinct chevron coils to address side lobes. However, it’s observed that widening the gap between these coils leads to increased cycle numbers. This study presents a novel strategy employing overlapped multilayer coils to generate a coherent waveform and enhance spatial resolution in inspections. The proposed EMAT utilizes a multilayer coil combined with periodic permanent magnets (PPMs), enabling a reduction in size without sacrificing output response and enhancing signal waveform compared to the original chevron EMAT. Numerical simulations have been conducted to explain the functionality of the proposed EMAT, and the results have been validated through experimental testing.