A Novel Magnetic Field Gradient-Enhanced Excitation Source for Motion-Induced Eddy Current Testing

As production speeds continue to increase, accurately measuring defects during the high-speed motion of samples becomes of significant practical importance. Motion-induced eddy current (MIEC) is a nondestructive testing method well-suited for detecting defects in high-speed moving samples. Existing studies typically employ permanent magnets or coils as excitation sources, without addressing the impact of the central magnetic field and magnetic field gradient of the excitation source on the generated MIEC signals. This study analyzes, both theoretically and through simulations, the influence of the central magnetic field and magnetic field gradient on MIEC signals. Based on these findings, a new excitation source structure is designed, and an improved multi-objective RIME optimization algorithm is proposed to optimize the shape of the magnetic yoke surrounding the permanent magnet. Numerical simulations demonstrate that the optimized excitation source structure significantly enhances the amplitude of defect signals, across various sample motion speeds. Finally, an experimental setup is constructed to validate the results. The experimental results indicate that the optimized excitation source structure effectively enhances the MIEC signal amplitude for five different slot-shaped defects ranging from 0.5 mm to 2.5 mm in length on the aluminum disk, with a minimum amplitude increase of 52% and a maximum of 74.1%.