Coating Damage Localization Using Multiresonant Noise-Compensated Split Ring Resonator Sensor

Localization of coating damage in microwave-based non-destructive testing systems remain an unaddressed challenge due to the single-frequency operation of microwave sensors. This work introduces a multi-resonant microwave split ring resonator (SRR) sensor-based coating health monitoring system capable of providing spatial damage localization with environmental noise compensation. The system employs three SRRs, each operating at a distinct resonant frequency, along with a shielded reference SRR designed to mitigate the effects of environmental fluctuations. When coated with a 625 μm polyethylene layer, the SRRs operate at 1.992 GHz (SRR-1), 1.628 GHz (SRR-2), and 1.268 GHz (SRR-3), while the shielded reference SRR resonates at 2.428 GHz. Through controlled coating wear tests, the three SRRs demonstrate a total frequency shift of 230 MHz, 178 MHz, and 123 MHz for SRR-1, SRR-2, and SRR-3, respectively, yielding average sensitivities of ∼46, 35, and 25 MHz / 125 μm of coating wear, with an overall average of ∼35 MHz / 125 μm. These results highlight the system's capability to localize coating damage, providing a promising application in real-time monitoring of large-scale structures, including pipelines, and aerospace components.