Detecting surface features on conducting specimens through an insulation layer using a capacitive imaging technique

This paper describes the application of the capacitive imaging (CI) technique to the detection of surface features on conducting specimens. The fundamental theory of the CI technique was briefly described. Comparison was made between the CI technique and the eddy current approach. A two-dimensional finite-element method was employed to model the electric field distribution from the CI probe, and how it interacts with conducting specimens through an insulation layer. Experiments using prototype CI probes were carried out. Effects of electrical conditions of the conducting specimen, lift-off distances and thicknesses of insulation between the CI probe and the conducting specimen were studied. The proof-of-concept results indicated that the CI technique is sensitive to surface features on conducting specimens through a significant air gap and/or insulation layer, thus could be used to detect Corrosion Under Insulation (CUI).