Characterizing Halbach EMAT Configurations for SH0 Ultrasonic Waves

Electromagnetic acoustic transducers (EMATs) can efficiently generate the shear horizontal (SH) guided wave modes. In this article, the Halbach magnet array pattern is explored as an alternate to the conventional periodic permanent magnet (PPM) structure. The magnetic field strength of a Halbach array is significantly higher on one side of the structure while it is weak on the opposite side of the array. This magnetic field distribution enables Halbach EMATs to generate ultrasonic waves with relatively large amplitude. To observe this phenomenon, this study compares the amplitude generated from multiple single-row Halbach EMATs with single-row PPM EMAT configurations using finite-element-based simulation models for SH0 ultrasonic wave generation. This article then presents the ultrasonic wave fields generated by various double-row Halbach EMAT configurations using finite-element-based simulation models and experimentally validated for guided fundamental SH0 mode generated in an aluminum plate specimen. It is observed that distinct ultrasonic guided wave beam patterns be associated and predicted for different double-row Halbach EMAT configurations.