Dual-Frequency Self-Referenced Terahertz Metamaterial Sensor for Monitoring Electric Vehicle Battery Films

Terahertz metamaterial sensors offer potential for non-contact monitoring of electric vehicle battery-related films. This study proposes a dual-frequency self-referenced terahertz metamaterial sensor based on a metal–dielectric–metal structure comprising a split-ring resonator, an I-shaped resonator, a TOPAS dielectric layer, and a continuous metal reflector. Without a loaded film, the sensor exhibits near-perfect absorption peaks at 0.8354 and 1.3250 THz, with absorptivities of 99.95% and 99.99%, respectively. Field and current analyses identify the low-frequency I-shaped-resonator mode as the reference channel and the high-frequency split-ring-resonator mode as the sensing channel. A film thickness of 4 μm was selected from the thickness-response analysis for refractive-index sensing. For equivalent refractive indices of 1.30–1.60, the low- and high-frequency peak sensitivities are 96.43 and 272.57 GHz/RIU, respectively. The dual-peak frequency interval results in a fitted sensitivity of 176.14 GHz/RIU and provides enhanced stability against common-mode perturbations rather than higher raw refractive-index sensitivity. Under ±3% and ±5% TOPAS-permittivity perturbations, the interval drift (1.8–25.2 GHz) is lower than the high-frequency peak drift (12.6–39.6 GHz), producing suppression ratios of 36.36–85.71%. The proposed numerical design provides a potential self-referenced sensing approach for equivalent dielectric perturbations in electric vehicle battery-related films.