Conductivity estimation of non-magnetic materials using eddy current method

Titanium and stainless steel are widely used in industries due to their advantages of high strength and good corrosion resistance. Such materials have common electromagnetic features–with a relatively low conductivity ～10⁵ − 10⁶ S/m and a relative permeability of 1. In terms of structure health monitoring, conductivity is an important physical parameter of metal materials, which is closely related to its purity, heat treatment state, internal stress state, hardness and temperature. Therefore, accurate and efficient conductivity estimation of such metals is extremely important to ensure product quality and normal operation of equipment. This paper presents an efficient conductivity estimation method of metals based on eddy current testing. The sensors used are with two coaxially cylindrical coils acting as transmitting coil and receiving coil respectively. According to the characteristics of low-conductivity and sensor configuration, a simplified theoretical model derived from the classic Dodd–Deeds theory is proposed. Moreover, the finite element method (FEM) simulation and experiments are carried out to verify the proposed model. The experiments are carried out on stainless steel 316 and different Titanium alloys with a commercial impedance analyzer, and the results indicate that the average relative measurement error is less than 2.8%.