Development of Wideband Pulse Compression Surface Wave EMAT

Ultrasonic surface wave electromagnetic acoustic transducers (EMATs) have been widely utilized in detecting surface defects of metal materials due to their noncontact advantages. However, the signal energy of surface wave EMAT is weak, mainly influenced by energy conversion efficiency. Increasing the number of excitation signal cycles can enhance the signal energy, but it leads to longer pulsewidth and reduced time-domain resolution. Meanwhile, most of the existing studies excite surface waves with a single frequency, and the frequency information components are limited. To overcome these issues, wideband signal is introduced into the design of surface wave EMAT and combined with pulse compression technique to obtain surface wave signals with wideband, high amplitude, and narrow pulsewidth. In this article, a new wideband pulse compression surface wave EMAT (WPCSW-EMAT) is proposed. WPCSW-EMAT replaces the single frequency signal in conventional EMAT with a linear frequency modulation (LFM) signal. Additionally, the equal meander-line coil is replaced by a variable distance meander-line coil, where the distance between adjacent wires matches the frequency change of the LFM signal. Finite element simulation results demonstrate that compared to conventional EMAT, WPCSW-EMAT can obtain pulse compression surface wave signals with wideband frequency, high amplitude, and narrow pulsewidth. The performance verification experiment and defect detection experiment of EMAT were carried out on aluminum plate samples, and the experimental results indicate that the WPCSW signal excited by WPCSW-EMAT is more suitable for nondestructive testing of metal materials.