Metrological characterization of an ECT method for thickness estimation based on dimensional analysis

The thickness estimation of conductive plates is a crucial task in several application fields. Methods based on Eddy Current Testing (ECT) for thickness measurement involve several variables such as frequency, electrical conductivity, lift-off and probe geometry. The ECT thickness estimation depends on the quality of these variables knowledge and, typically, is based on time-consuming approaches that, needing multiple frequency measurements, deeply reduce their application in industrial scenarios. This paper focuses on the metrological characterization of a method previously developed by the authors and based on the application of the Buckingham's $\pi$ theorem to ECT for the simultaneous dual estimation of the thickness and electrical conductivity of conductive plates. In particular, the performance of the method was experimentally analyzed with respect to the stimulus ECT frequencies and to the features used for the estimation process of unknown thicknesses. The results showed the presence of an optimal set of frequencies in which the method can be applied using a single-frequency approach with good performance that, using the best feature for the thickness estimation, gives rise to a mean absolute relative error lower than 1.09%. The presented analysis opens the potentiality of the method to new performance challenges by adopting data fusion and double-frequencies techniques.