An innovative exciting coil design for magneto-optic imaging in nondestructive evaluation

The laser-based magneto-optic microscopy (LMOM) system is based on eddy current technology and its image quality mainly depends on the incentive effects, where the excitation coil is widely adopted as an incentive device by placing it above the inspecting surface of the specimen. This paper proposed an innovative excitation coil design, which can generate a region of linear eddy current distribution in the specimen and consequently make the uniformly induced magnetic field possible and parallel to the surface in defect-free geometry. The sensitivity of defect imaging will be greatly enhanced since the detected normal magnetic field is only determined by the discontinuities and decoupled with the induced main field. A single rectangular coil and the cross placed coils are studied in this paper and simulation results of the new design were compared with the traditional coil design results, which clearly validated its advantages and demonstrated the potential of the new set up of LMOM to achieve better image resolution and contrast.