A capacitive probe for quantitative nondestructive evaluation of wiring insulation

A capacitive probe has been developed for quantitative evaluation of wiring insulation permittivity. The probe consists of two patch electrodes that conform to the curvature of the wire under test. A numerical model is utilized for inverse determination of insulation complex permittivity from measured probe response. Experimental studies on thermally and hydrolytically degraded wire samples show that the resulting permittivity change of the insulation is successfully detected using the described capacitive probe, for the wire type MIL-W-81381/12, which is predominantly Kapton®Kapton® coated. Changes in the permittivity of the wiring insulation, detected by the capacitive probe, are shown to be in accordance with the results of research conducted previously on Kapton®Kapton® film samples degraded by thermal and hydrolytic exposure. Thus, the feasibility of assessing wiring insulation degradation status by quantitative capacitive techniques is demonstrated, which is of particular interest to the aerospace industry.