Study on weld inspection using HC-PPM EMAT based on multi-region spatial magnetic field superposition

Abstract The detection of pipeline weld defects is a crucial step in ensuring the safety and reliability of engineering structures. Electromagnetic ultrasound is an effective method for non-destructive testing of pipeline welds. However, traditional electromagnetic acoustic transducers suffer from low transduction efficiency and insensitivity in detecting weld defects. Based on the spatial superposition principle of magnetic fields in wire loops derived from the Biot–Savart law, this study establishes a theoretical model for multi-region spatial magnetic field superposition of H-shaped coil. This model reveals the positive correlation between magnetic induction intensity and displacement fluctuation, and clarifies the mechanism of gradient-enhanced coupling formed in the central region through magnetic field superposition. Based on this theory, a novel H-shaped coil periodic permanent magnet electromagnetic acoustic transducer (HC-PPM EMAT) structure is proposed, which achieves directional energy concentration through multi-region spatial magnetic field matching design. The study aims to improve weld inspection performance by optimizing the coil configuration and structural parameters, and conducts systematic simulation analysis and experimental validation of the designed HC-PPM EMAT. The results show that the proposed HC-PPM EMAT can effectively excite circumferential shear horizontal (CSH) guided waves. Compared with traditional PPM EMAT structures, the transduction efficiency is increased by 60.3%, and the signal-to-noise ratio of detection echoes is improved by 48.9%, significantly enhancing both transduction efficiency and sensitivity in weld defect detection, thus providing a new structure for effectively exciting CSH guided waves and detecting weld defects.