Microwave Detection of Rust Under Paint and Composite Laminates

Accurate, reliable, and early detection of rust/corrosion under paint and laminate composites in many industrial and military applications is of great concern and interest. Although there are several methods for detecting rust under paint, they all have their respective limitations. Microwave nondestructive and noncontact inspection techniques are well suited for the early and reliable detection of rust under various paints and composite laminates. In this paper, the potential of utilizing open-ended rectangular waveguide sensors for detecting rust under paint and laminate composites is investigated theoretically and experimentally. An electromagnetic model describing the interaction of microwave signals radiating from an open-ended rectangular waveguide with a stratified dielectric structure is used to model the presence of rust under paint and a composite laminate coating. For the experimental investigations, we used a rusted steel specimen that was painted over by common spray paint to as much as ten coats of paint. These experiments are conducted at 24 and 10 GHz. The issue of detecting rust unambiguously while a certain paint thickness variation may exist is also addressed.