Eddy current evaluation of air–gaps in aeronautical multilayered assemblies using a multi-frequency behavioral model

This paper reports on the estimation of the air–gap thickness between parts in an aeronautical multilayered metallic assembly, by the means of the eddy current method. A behavioral multi-frequency modeling of the interactions between the used cup core sensor and the multilayered structure was developed thanks to the analysis of experimental data, completed with finite element electromagnetic computations. The elaborated model was used to estimate the air–gap thickness (in the range of 0–500 μm) of a multilayered structure featured by a metallic coating of known thickness (1.5 mm) and a distant metallic layer of unknown thickness (in the range 1.5–3.5 mm). The obtained estimation error is smaller than a few percents, either for simulated or experimental data.