A model-based approach for inspection of aeronautical multi-layered structures by eddy currents

Abstract

Purpose The purpose of this paper is to propose an approach, which is easy to implement, for estimating the thickness of the air layer that may separate metallic parts in some aeronautical assemblies, by using the eddy current method. Design/methodology/approach Based on an experimental study of the coupling of a magnetic cup core coil sensor with a metallic layered structure (consisting of first metal layer/air layer/second metal layer), which is confirmed by finite element modelling simulations, an inversion technique relying on a polynomial forward model of the coupling is proposed to estimate the air layer thickness. The least squares and the nonnegative least squares algorithms are applied and analysed to obtain the estimation results. Findings The choice of an appropriate inversion technique to optimize the estimation results is dependent on the signal-to-noise ratio of measured data. The obtained estimation error is smaller than a few percent, for both simulated and experimental data. The proposed approach can be used to estimate both the air layer thickness and the second metal layer thickness simultaneously/separately. Originality/value This model-based approach is easy to implement and available to all types of eddy current sensors.

Locating complex eigenvalues for analytical eddy-current models used to detect flaws

“…The approaches based on the Cauchy argument principle are reliable but they require a long time for calculations. This makes it impossible to effectively use such solutions in many applications, such as measurements carried out in real-time or multi-frequency eddy current testing (Cung et al, 2019). The classic approach, in turn, though being considerably faster, does not guarantee the correct computation of all eigenvalues and requires the performance of additional iterations because of the possibility of obtaining the same root for several different initial points.…”