Thickness measurement of metallic plates with finite planar dimension using eddy current method

Abstract

Until now, the Dodd–Deeds model has been used to evaluate the inductance change in an air-cored sensor in the presence of an infinitely large conducting plate. In practice, it can be applied to the sample relatively larger than the radius of the sensor coil (normally >3–5 times larger), which can be regarded as a plate sample with infinite planar size. However, in various practical applications, the size of the tested sample may not satisfy this condition. In this article, a modified analytical solution based on the Dodd–Deeds model is proposed, which has introduced a new initial integration point instead of 0 for the analytical inductance of the finite-size metallic plate. Theoretical derivation has been presented for the derivation of the initial integration point. Moreover, an inversely proportional relation can be observed between the initial integration point and the radius of the test sample. The simulation and experimental measurements for the thickness of several finite-size metallic samples have been carried out for the verification of the proposed method.