Preliminary Study on Multi-Parameter Estimation in Single-Frequency Eddy Current Testing via Dimensionless Analysis and Scaled Probes

This paper investigates a single-frequency Eddy Current Testing (ECT) approach for the simultaneous estimation of lift-off, electrical conductivity, and thickness in conductive plates. The method is based on dimensional analysis and employs two geometrically scaled coaxial probes to extract complementary information at a single excitation frequency. By reformulating the problem through Buckingham's π-theorem, impedance responses are represented in a reduced dimensionless space, enabling a twostep inversion strategy. The smaller coil operates under semiinfinite conditions to estimate lift-off and conductivity, while the larger coil enables thickness estimation and conductivity refinement. Numerical validation on five representative case studies shows relative errors below 2% in noise-free conditions and satisfactory robustness up to 1% Gaussian noise. The results confirm the effectiveness of the proposed dimensionless singlefrequency framework for multi-parameter ECT characterization.