A Simple Coil Design Scheme of Narrow-Magnet EMAT for Correction of Waveform Distortion

Electromagnetic acoustic transducer (EMAT) using a narrow magnet has higher excitation efficiency than the traditional solutions because it uses a larger area of coils spreading from the center area underneath the magnet to its edges. Meanwhile, due to the significant difference in the center-to-edge magnetic field direction below the magnet, narrow-magnet EMAT coils based on the classical half-wavelength conductor spacing rule face serious waveform distortions. To overcome this problem, a simple coil design scheme is proposed in this work, and the constant conductor spacing is carefully modified. Hence, the acoustic waves are efficiently excited with much less distortions than the classical designs. This new approach does not require additional coil turns, nor combinations of different conductor-spacing values among the coil tracks. According to the experimental analyses on aluminum plates, the Rayleigh waves excited by the proposed solution have an amplitude enhancement of 119.30% than the traditional ones; the frequency shift is decreased from 7.52% to 0.46%.