Dimensional analysis approach for lift-off estimation based on eddy current testing

Accurate lift-off estimation is crucial in Eddy Current Testing (ECT) for non-destructive coating thickness assessment. Traditional methods often rely on empirical calibrations, complex signal processing or multi-frequency analysis, limiting their applicability in real-time industrial environments. This paper introduces a new approach based on dimensional analysis and Buckingham's π theorem to estimate lift-off. The proposed methodology reduces the number of variables governing the problem, transforming the estimation process into a simplified physics-based model. Experimental validation was conducted on different conductive materials and lift-off conditions, demonstrating that the imaginary component and the magnitude of the analyzed dimensionless quantity provide the most accurate and repeatable estimations. The results show that the proposed approach achieves an average relative absolute error of less than 1.5%, significantly improving the robustness and repeatability of the measurements. Furthermore, the method is suitable for single-frequency operation, reducing computational complexity and enabling real-time applications in aerospace and industrial environments.