Electromagnetic acoustic transducer optimisation for surface wave applications

摘要

A simplified model of surface wave generation from finite width sources is presented, and it is shown that the generated wave is given by the convolution of the spatial profile of the wave source with the temporal displacement profile of the driving function. The model is then used to analytically derive the optimum coil width for an electromagnetic acoustic transducer (EMAT) for the case of harmonic excitation. The analysis is extended to predict the optimal coil width for a pulsed coil excitation approximated by a Gaussian function, and it is shown that optimum generation is achieved for a coil width of a approximate to 4.0 delta c, where delta is the width parameter of the Gaussian excitation and c is the Rayleigh wave speed. Finite element analysis and experimental data are then presented in support of this result. A phased Rayleigh wave EMAT array concept is demonstrated as a means to improve generated signal amplitudes beyond the limit for an optimised coil suggested by the analytical and finite element models.