Oblique Point-Focusing Shear-Horizontal Guided-Wave Electromagnetic Acoustic Transducer with Variable PPM Spacing.

We realized a phase-coherent oblique point-focusing shear-horizontal (SH) guided-wave electromagnetic acoustic transducer (EMAT) composed of variable-spacing periodic permanent magnets (PPMs) and racetrack coils. For traditional focusing transducers, the necessary focal position adjustment in defect detection requires a redesign of the coil structure. More conveniently, this new transducer structure arrangement can achieve wave focusing and focal position change by rationally adjusting the layout of the periodic permanent magnet without changing the coil structure. Simulation results show that this newly designed transducer has good focusing performance: it can successfully focus the signal to a preset point, and the signal amplitude is nearly double that of the nonfocusing side. In addition, the focusing performance optimization of the transducer has been studied. The experimental results agree well with the actual location and size of a defect, which verifies the effectiveness of the newly designed focusing transducer in defect detection.