Novel Noncontact Eddy Current Measurement of Electrical Conductivity

A new noncontact method for measuring the electrical conductivity of metals based on eddy current testing is proposed for the physics that the logarithm of phase signals of impedance change is linear to that of electrical conductivity. A finite element model for simulations was built, and the mathematical relationship between the logarithm of phase signals and that of electrical conductivity was established with linear least-squares fitting. The effects of the excitation frequency, lift-off distance, and relative permeability were investigated and analyzed. The investigations of lift-off effect enable us to reduce it by substituting the impedance of the coil at certain lift-off distance for that of the coil in air as the reference. Finally, the experimental platform was developed, and the experimental results matched well with the simulated results. The relative errors fall within 3%, which demonstrates the feasibility of the presented method for non-ferrous metals.