Estimation of Thickness and Radius of Hollow Metallic Spheres With a Simplified Forward Model

The measurement of metallic spherical objects in various industrial applications has a significant role in guaranteeing safety and product quality, which can be realized by the eddy-current testing (ECT) technique without contact. In this study, for the measurement of thickness and radius of nonmagnetic spherical shells, the original analytical model is simplified according to the asymptotic forms of the modified spherical Bessel functions. The simplified model contains only elementary functions, and can therefore accelerates the sphere property estimation by employing the optimization approach based on the Newton–Raphson method. In numerical simulation and experimental study, the proposed method can provide accurate spherical shell radii with less computational time compared with the original analytical model.