Meander Line Coil EMAT Based on Spatial Pulse Compression for Rayleigh Waves

Electromagnetic acoustic transducer (EMAT) has been applied to generate Rayleigh waves, for evaluating the surface and near-surface quality of a sample. The main disadvantages of EMAT are their low coupling efficiency and signal to noise ratio (SNR). Pulse compression technology is adopted to improve SNR, which designing a designed excitation waveform and corresponding a matched filter. This paper presents new methods, called linear wavelength modulation (LWM) and nonlinear wavelength modulation (NLWM), to design Rayleigh wave EMAT. Different from traditional structure, it used non-equidistant meander line coils, which based on spatial pulse compression. A finite element model is established to prove the new structure can excite wave packets with designed spatial wavelength distribution. The feasibility of spatial pulse compression and the effectiveness of the new method are proved by the simulation and experiments.