Dual-Band Frequency Selective Surface Sensor for Detection and Mapping of Coating Wear

Coating degradation on aircraft surfaces poses a critical challenge to structural integrity and operational safety, requiring precise detection of damages over large surface areas. Current non-destructive testing methods either lack the sensitivity to detect early-stage damage or are limited by slow, area-wise inspections that affect faster inspections. This work presents a multi-resonant frequency selective surface (FSS) sensor capable of localizing coating wear by correlating resonant frequency shifts with changes in coating thickness. The FSS consists of two regions with 10x10 arrays of nested square patch resonators, designed to resonate at 4.5 GHz and 5 GHz, respectively. Each region responds independently, with minimal interference, enabling precise identification of localized wear. The developed FSS is tested by the erosive wear of a 225 µm PVC coating layer by layer, resulting in resonant frequency shifts of up to 198 MHz in Region A and 231 MHz in Region B, with an average shift of 70 MHz per 75 µm of wear. With its high sensitivity, and precise localization capabilities, the developed FSS sensor system promises non-contact structural health monitoring across aerospace, automotive, and civil infrastructure applications.