A shear horizontal wave EMAT by using encoded Halbach magnets for improving both SNR and spatial resolution and its applications in defect detection of aluminum plates

Abstract

In industrial production, metal plates are widely used in various equipment and structures. Regular non-destructive testing of metal plates is essential for ensuring long-term operational safety and product quality. The electromagnetic acoustic transducer (EMAT) holds great potential due to its capability for non-contact detection, low surface roughness requirements, and ability to detect internal material defects. However, EMATs often face challenges such as low energy conversion efficiency, low signal-to-noise ratio (SNR) in echo signals, and limited spatial resolution. To address these challenges, this research proposes an encoded periodic permanent magnet shear horizontal wave EMAT (PPM SH EMAT) that incorporates pulse compression technology to simultaneously encode the excitation signal and the magnet configuration of the conventional PPM EMAT. Matched filtering and sidelobe suppression techniques are employed to enhance the SNR and spatial resolution of the transducer. Furthermore, by leveraging the magnetic field enhancement properties of Halbach array, the amplitude of defect signals is further boosted. Experimental results from defect detection of adjacent grooves in aluminum plates show that the proposed encoded Halbach shear horizontal wave EMAT demonstrates significant improvements in both SNR and spatial resolution.