Non-Destructive Measurements of Multi-Layer Coatings Using Spatially Modulated Dielectrometry

Existing field-compatible coating thickness measurement systems are not capable of advanced material coating characterization. With rapidly rising percentages of advanced composite materials used in manufacturing military and civil aircraft, many of these systems, including magnetic and simple capacitance meters, are becoming obsolete. Illionix, LLC proposes to develop an advanced coating evaluation system based on spatially modulated dielectrometry. The expected outcome of this project is a highly versatile hand-held instrument capable of non-contact in-process evaluation of advanced multi-layer coating systems. Information provided by spatially modulated dielectrometry sensors for each individual layer in a coating stack-up will include layer thickness, degree of cure, and an estimate of post-cure complex dielectric permittivity. In Phase I, the effort will be aimed at evaluating the sensor system using laboratory-prepared two-layer coating system samples of various thicknesses and degrees of cure consisting of polyurethane primer (BMS 10-72) and topcoat (MIL-C-85285C) spray-painted onto a composite substrate (BSM 8-276). In Phase II, a hand-held prototype will be developed with a property estimation algorithm that will be further expanded to cover an arbitrary number of layers and a range of sample temperatures. Calibration curves for a range of military and commercial aircraft coating materials and substrates will be developed. BENEFIT: The main benefit of developing and integrating the proposed spatially modulated dielectrometry coating evaluation system into the initial and refurbishment aircraft coating processes is the added capability to measure the coating system properties in-process, while the coatings are not completely cured. This capability will help to avoid the very laborious, expensive, and environmentally damaging process of coating stripping and subsequent repainting. The proposed sensor system has a number of potential commercial applications outside of the aerospace industry. Some of the identified applications include sensor automation of the painting process of naval ship hulls, industrial painting quality control systems for automotive industry, and a number of possible applications that would benefit from the proposed sensor’s ability to monitor the curing process as well as spatial profiles of dielectric properties non-invasively.