Inspection of defects in conductive multi-layered structures by an eddy current scanning technique: Simulation and experiments

Multiple Material Property Characterization Using Induced Currents and Atomic Force Microscopy

“…While this appears to be a limitation of the technique, it may be useful in imaging subsurface defects or cracks that cause inhomogeneities in electrical conductivity. In fact this has been effectively used in eddy current NDE (Huang et al, 2006).…”

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

“…This requires the knowledge (for example from experimental learning) of the slope a i of the linear characteristic NID i (t) at f i and for the considered fixed values t c and t r . It is thus possible to estimate the air-gap i t according to (5).…”

“…First (case A) the sensor is assumed to be placed on the aircraft wing at a particular position where the coating and the rib thicknesses are known. As explained in section 2.2, in such a case, provided the slope a i of a linear characteristic (4) (for example previously determined by experimental learning) at a given excitation frequency f i and for the given values of t c and t r , one measurement NID i is sufficient to estimate of the air-gap according to (5).…”

“…However, as far as multilayered structures such as aeronautical assemblies are concerned, the NDE is an "ill-posed" problem the resolution of which is reputed difficult [5], among other reasons because of the incompleteness of the available EC data [6].…”

Difference in the detection limits of flaws in the depths of multi-layered and continuous aluminum plates using low-frequency eddy current testing

“…This measures the magnetic field caused by the eddy current induced by exposure to alternating magnetic fields. ECT is generally used with high-frequency magnetic fields, above kilohertz order, or search coils [1][2][3]. High-frequency magnetic fields are suitable for identifying surface defects, since skin depth d is roughly inversely proportional to the root of operation frequency f. For example, the skin depth in infinite half-space is expressed as follows:…”