Measurement of Coating Thickness and Loading Using Concentric Fringing Electric Field Sensors

Multilayer coating stack-up on an aircraft is a primary defense against corrosion, abrasion, and degradation. The correct coating thickness on an aircraft cannot only provide better protection against environmental impact during flight, but also minimize the reflected electromagnetic signature. Instrumentation to estimate the characteristics of an aircraft's coating stack-up can help to minimize or eliminate the need for coating stripping and reapplying during manufacturing and regular maintenance. This paper investigates the feasibility of using a customized 4 mm penetration depth concentric fringing electric field sensor and a dielectric spectroscopy meter to independently and simultaneously measure the functional coating layer thickness and the coating loading (percentage of silicone with iron oxide filler) on an aircraft. The results show that the sensor capacitance is more sensitive to the variation in coating loading than in coating thickness. Furthermore, this paper demonstrates that the functional coating layer loading and thickness measurement algorithm has been used to successfully estimate the functional coating layer thickness and loading on an aircraft. The currently achievable measurement accuracy for the functional coating layer thickness is similar to 0.1 mm, and the coating loading is similar to 1.5%.