Nonequal Spacing Interval Meander-Line-Coil EMAT for Signal Amplitude Enhancement of Rayleigh Wave

As a type of nondestructive testing transducer, electromagnetic acoustic transducers (EMATs) are widely applied in industries for evaluation and detection of metals. To improve the poor conversion efficiency of Rayleigh wave EMATs, a new design of nonequal spacing interval meander-line-coil (MLC) EMAT is proposed in this article. The eddy current at the specimen surface generated by new EMAT is much larger than that of the original one. In addition, the magnetic field at the positions of enhanced eddy current significantly promotes the generation of Rayleigh waves. However, the individual Rayleigh waves generated by the conductors in new EMAT are out of phase, which leads to nonconstructive interference. The resultant amplitude is not simply the addition of amplitudes of these individual Rayleigh waves for the phase difference must be considered. A mathematical model is established to express the interference process of the Rayleigh waves generated by the original EMAT and new EMAT. The results of qualitative analysis show that compared with the Rayleigh waves generated by the original EMAT, the Rayleigh waves generated by the differently distributed conductors in the new EMAT are more favorable for improving the conversion efficiency. Simulation and experimental results validate that the loss of conversion efficiency due to nonconstructive interference is outweighed by the improvement of the amplitude of Rayleigh waves generated by the new EMAT. Moreover, the conversion efficiency of the new EMAT is increased by about 50%.