Optimization of Narrow-magnet EMAT for Lamb Waves with Low Distortion

Compared to traditional electromagnetic acoustic transducer (EMAT), the narrow-magnet EMAT extends its meander conductors to the edges and outside of the magnet, hence a wider area of the magnetic field can be used to excite stronger ultrasound waves. Because of the magnetic field inhomogeneity, the classical half-wavelength spacing rule is not suitable for the coil used in the narrow-magnet EMAT. Otherwise, obvious waveform distortions will appear. In this work, the coil conductor spacing correction methodology proposed in previous works is testified for Lamb wave excitations, and a simpler wavelength-based adjustment approach is proposed, where waveforms of low distortions can be obtained. Both approaches are evaluated in simulation and practical experiments, where the Lamb wave amplitude enhancement brought by the coil conductor spacing correction method is more than 157.41%, and the improvement achieved by the proposed wavelength adjustment concept is above 179.34%.