Increase of efficiency of magnetostriction SH-wave electromagnetic acoustic transducer by angled bias field: Piezomagnetic theory and measurement

The increase of the coupling efficiency of a magnetostriction shear-horizontal (SH)-wave electromagnetic acoustic transducer (EMAT) has been achieved by applying an angled bias magnetic field. A generalized model involving piezomagnetic theory is presented to explain the physical principle of the EMAT. It indicates a dominant contribution of the piezomagnetic coefficient e(6x)((MS)) and predicts an efficient generation of the SH waves with an angled bias magnetic field. Dependences of the SH-wave amplitude on the magnitude and direction of the bias field were measured, which showed good agreement with those of the coefficient e(6x)((MS)). The most efficient generation was accomplished with a 45 angled bias field. The amplitude gain was 250%.