Microwave Permittivity Sensor Using 1D Photonic Crystal Resonator

This paper presents a 3D-printed, all-dielectric, one-dimensional photonic crystal (1D PhC) resonator for wireless dielectric permittivity sensing. The structure consists of alternating high- and low-permittivity layers forming Bragg reflector pairs around a central defect layer. The 80 mm × 80 mm resonator is excited in free space, showing a backscattering notch near 14 GHz for a 5.5 mm-thick defect. Full-wave EM simulations are performed by placing thin dielectric layers (ϵ_r=1.0-12.0) on the defect side, producing measurable resonance shifts that depend on both permittivity and thickness. Average sensitivities of 460 MHz/RIU and 718 MHz/RIU are obtained for 0.3 mm and 0.5 mm layers. The sensor is 3D-printed from low-loss cyclic olefin copolymer (COC) and experimentally validated using thin plastic layers. Clear resonance redshifts up to 495 MHz are observed for three stacked 0.5 mm layers.