Effects of relative motion on a Rayleigh wave electromagnetic acoustic transducer operating on aluminium

Electromagnetic acoustic transducers (EMATs) generate and receive ultrasonic waves without mechanical coupling. Because of this, it is often claimed that EMATs are suitable for use in high-speed scanning and inspection. In this paper, simulations are used to show the effect of electromagnetic changes caused by a relative velocity between a Rayleigh wave EMAT and an aluminium sample on the efficiency of Rayleigh wave generation. It is shown that, when a relative velocity is present, eddy currents are generated within the inspection sample, leading to a distortion in the magnetic field produced by the EMAT and, therefore, the Lorentz force distributions within the sample. These changes cause the efficiency of Rayleigh wave generation to differ between the leading and trailing directions. The trailing edge shows an uninterrupted increase in the efficiency of Rayleigh wave generation with velocity, while the leading edge shows an initial decrease before reversing and becoming more efficient as the velocity increases.