Electromagnetic generation of electronically steered ultrasonic bulk waves

Abstract
The frequency dependence of the propagation direction of ultrasonic shear and longitudinal waves generated by a meander‐line electromagnetic transducer (EMAT) at MHz frequencies has been determined. The results are found to agree well with theory and demonstrate that electronic beam steering is possible using EMAT’s. The relative efficiency of generation in aluminum was also studied and, for a specific meander‐line geometry with a permanent magnet providing the necessary static magnetic field, it was found to be relatively flat versus frequency. Efficiency for shear‐wave generation (frequency range, 5–9 MHz) was about 4 dB per conversion less than the Rayleigh‐wave generation efficiency at 4.6 MHz, and for longitudinal waves (frequency range, 10–24 MHz) about 10 dB less.

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