Differential Frequency Selective Surface Sensor for Polymeric Coating Damage Detection Using Electromagnetically Shielded Reference Resonator

Detecting coating damage in dynamic environments remain an unaddressed challenge for Frequency Selective Surface (FSS)-based sensors, which struggle to differentiate coating wear from environmental noises, affecting sensing reliability. This work presents a differential FSS sensor using a bi-layered resonator architecture, designed to distinguish sensor responses due to coating damage, from environmental impact. The differential FSS comprises a sensing and a reference FSS, operating at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sim 3 \text{GHz}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sim 5 \text{GHz}$</tex>, respectively, with the sensing FSS optimized for sensitivity to coating damage and reference FSS optimized to minimize dielectric interaction while providing environmental compensation. The developed differential FSS was tested by the wear of a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$240 \mu ~\mathrm{m}$</tex> PVC coating, resulting in a resonant frequency increase of 201 MHz in the sensing FSS, averaging <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sim 67 \text{MHz} / 80\ \mu \mathrm{m}$</tex> of wear, while the reference FSS exhibited <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sim 5 \text{MHz}$</tex> variation. The results demonstrate the sensor's potential for marine, and energy applications in harsh environments.