Inversion of Eddy Current Data for Conductive Films and Coatings Thickness and Conductivity Measurement

Abstract

Eddy current testing is currently used to determine the physical characteristics of a conductive specimen and to detect defects by measurements of electrical impedance of an eddy current probe. In this study we developed two systems of coils allowing to determine properties of conductive coatings and foils. A probe contained two plane rectangular coils connected in series and separated by a fixed distance. A coated plate or a foil was placed between the coils and the coil impedance was measured using a digital impedancemeter. The discussed probe had a large length-to-width ratio and was modeled using the simple two-conductor line model, which express solutions in terms of the integrals containing no Bessel but, only common trigonometric functions, which considerably reduces the inversion time. The method allows reproducible measurements on coated conductive sheets. Aluminum 15–45 μm layers have been measured on steel and stainless steel substrates.