Numerical analysis of magneto-optical eddy current imaging using FEM

Magnetic-optical film (hereafter, MO film) is a bismuth-doped iron garnet film grown on a gadolinium gallium garnet substrate by liquid phase epitaxial method. Because an MO film has physical characteristics such as Faraday rotation and magnetic anisotropy, the distribution of its external magnetic field can be visualized. The MOI (Magneto-Optic/Eddy Current Imager) was developed to detect far-side cracks and corrosions in aluminum alloy materials on an aircraft. The detection probability of 2.5mm-length cracks is 90/95% when the MO film and the induced area current are used, However, the quantitative evaluation algorithm for quantifying crack shapes and sizes has yet to be proposed. This paper investigates a quantitative evaluation algorithm for magnetic optical eddy current imaging by using the finite element analysis methods (FEM) and experimental results. The MOI including a primary induction coil was simulated by FEM software. The position, depth, shape, and the induction current frequency, lift-off were simulated and examined. A simplified quantitative evaluation algorithm for MOI is proposed by using the analysis results.