Analysis of Eddy Current Probe Signal Model for Structural Monitoring of Aircraft Materials

We develop a physico-mathematical model of the “eddy current probe – test object” (ECP–TO) system that analytically describes current dynamics in coupled probe circuits while accounting for key physical and electrical parameters. The model, derived from the characteristic equation of transformer-type configurations for nonmagnetic and magnetic targets, explains when the measured response is harmonic or damped harmonic as a function of excitation mode and system parameters, thereby revealing additional informative features for material evaluation. We validate the model numerically using finite element (FEM) simulations (COMSOL, Magnetic Fields, frequency domain) and introduce a digital signal-processing workflow that extracts instantaneous amplitude- and phase-time characteristics during scanning. Experiments on aluminum alloy specimens demonstrate sensitivity to small conductivity variations and identify optimal excitation frequencies for reliable subsurface defect detection; in the tested configuration, an “infinitely deep crack” was detectable to 15.3 mm at 50 Hz. The combined analytical–numerical–experimental approach supports sensitivity-driven ECP design, accelerates inspection parameter selection, and facilitates integration with structural health monitoring (SHM) systems for aerospace structures.