A Novel Measurement Method of Conductivity and Radius for Nonmagnetic Metallic Rod

The parameter coupling affects the measurement accuracy in eddy current testing (ECT). In this article, we have developed a decoupling method to simultaneously measure conductivity and radius for nonmagnetic metallic rods using a sweep frequency strategy. First, the crossover frequency (i.e., the frequency corresponding to the intersection of real and imaginary parts of mutual inductance) is derived to proportional to the reciprocal of conductivity in line with the proposed simplified Dodd-Deeds analytical solution. Meanwhile, the slope of the linear fitting function can be expressed as a power function of metallic rod diameter, and the corresponding coefficient of power function is associated with the coil size. Hence, a sensor composed of two absolute coils with different sizes is designed to simultaneously measure the conductivity and diameter. According to the relationship between the crossover frequency and parameters of the metallic rod, the conductivity and diameter can be reconstructed from the response signals of two absolute coils with different sizes. Finally, the proposed rod conductivity and diameter measurement method has been validated by experiments, which demonstrates the proposed methodology is feasible and effective.