Calculation of the response of electromagnetic acoustic transducers to broadband acoustic transients

Summary form only given. Electromagnetic acoustic transducers (EMATs) operate via a Lorentz force interaction between an acoustic wave and a static magnetic field. This generates eddy currents which can be detected by a suitably orientated coil. A Nd:YAG laser with a risetime of 10 μs is used to generate line or point ultrasonic sources with normal drive and approximately Heaviside time dependence. Solutions for these ultrasonic sources give the surface displacement. In order to calculate the response of the EMATs to these displacements, the authors convolve with an appropriate time function and differentiate to give velocity. This is easiest on epicentre (on the opposite face vertically below the source) where the waves approximate to plane waves and phase differences across the face of the EMAT can be ignored. The waveform can be calculated by convolving with a Gaussian time function appropriate to the band width of the EMAT/amplifier combination