A Novel Conductivity Measurement Method for Non-Magnetic Materials Based on Sweep-Frequency Eddy Current Method

Metallic plates are widely used in a variety of industrial applications, from which conductivity is a key parameter related to the quality of metals. In order to accurately measure the conductivity, this article proposes a novel eddy current method based on sweep-frequency strategy. First, a simplified theoretical model for conductivity measurement is derived from the classical Dodd and Deeds analytical solution. Based on the analytical solution, the real and imaginary parts of the mutual inductance signal have an intersection in the frequency domain. According to mathematical derivation, the corresponding frequency (crossover frequency) of the intersection is inversely proportional to the conductivity of the sample. Moreover, the liftoff compensation method is proposed to reduce the effect of liftoff variation. Experiments have been carried out for samples with different conductivities, ranging from 0.5 to 58 MS/m, to verify the proposed method. The results show that the average error of the conductivity estimation with the proposed approach can be controlled within 1.1%, and the liftoff compensation method can significantly reduce the conductivity estimation error.