Influence of Core and Shield of Coil on Skin Depth in Eddy Current Testing

Abstract

ABSTRACT In eddy current (EC) nondestructive testing, coil is usually wound on core or covered by shield to improve the sensitivity of defect detection and ability of anti-interference of the probe. However, when core or shield is used, the magnetic field will be redistributed, resulting in a change in the speed of EC attenuation in the depth direction. The purpose of this paper is to reveal the influence of core and shield on skin depth of EC. The results of the finite element analysis show that applying core or shield on coil results in smaller skin depth and the skin depth decreases as the core or shield approaches the test sample. In addition, when both core and shield are used, the reduction of skin depth is minimal if both core and shield are ferromagnetic. The simulation results are verified by experiment.