Influence of Angled Horizontal Magnetic Field on Guided-Wave Type Transition for EMAT

Electromagnetic acoustic transducers (EMATs) have been applied to generate guided waves. The type of guided waves in steel plates is transformed as the bias angle of horizontal magnetic field varies. A simple analytical model to predict three transduction mechanisms including Lorentz, magnetization and magnetostriction force has been put forward in this paper. Three coefficients were determined to explain the effect. The experiments on single-coil EMAT presented the echo amplitude distribution of SH guided waves and Lamb waves. It shows that 40° and 70° are the type transition angles. The most efficient generation angle for Lamb waves is 90°, but that for SH guided waves is dependent on the field magnitude.