A Method of Rayleigh Wave Combined With Coil Spatial Pulse Compression Technique for Crack Defects Detection

Rayleigh wave methods utilizing electromagnetic acoustic transducers (EMATs) are widely used to detect a crack defect on the metal surface due to the merits of high sensitivity and long detection distance. However, the current EMATs for Rayleigh wave have low energy conversion efficiency and usually produce a wide echo-wave packet, reducing the spatial resolution and signal-to-noise ratio (SNR) of detection signals. To address the issues, the coil spatial pulse compression technique (CSPCT) is proposed to improve the physical structure of EMATs. First, a comprehensive analysis of the coil design is given to realize spatial phase encoding pulse compression. Second, the influence of the key parameters of EMATs on the pulse compression effect is studied. Finally, the crack detection experiment is conducted on an aluminum plate to verify the performance improvement of the designed EMAT. Compared to existing EMATs, our designed EMATs reduce the width of the main lobes and enhance the amplitude of the echo-wave signals. Results indicated that the spatial resolution was improved by up to 72% with an increase of 0.72 dB in SNR. In comparison to the existing time-domain pulse compression technique (PCT), the CSPCT requires no complex hardware and software tools, which has the merits of low cost and fast response. This work expands the application boundary of EMAT systems.