Double-Sided Metamaterial for Sensitivity Enhancement in THz Impedance Spectroscopy

Multi-layer terahertz (THz) electric-LC (ELC) resonating metamaterials (MM) have demonstrated an increased sensitivity for detecting dielectric particles deposited in the active area of the MM's capacitive plates, manifesting a red-shift of the resonance frequency in THz spectroscopy. Various works on multi-layer metamaterials have suggested using complementary structures or unidentical structures for enhanced THz bandwidth. This work, aimed toward dielectric sensitivity enhancement, presents a double-sided MM architecture with perfectly aligned identical metasurfaces fabricated on both sides of a Si substrate showing enhanced metamaterial resonance strength. This leads to a greater resonance quality factor and increased plasmonic interaction between the incident THz radiation from the spectrometer and the metasurfaces. Due to identical and aligned resonating metasurfaces on both sides of substrate, a phenomenon of light-trapping is discovered inside the substrate acting as a cavity, which further contributes to the enhanced resonance strength. This strong plasmonic interaction directly correlates with increased dielectric spectroscopy sensitivity. By applying Fabry–Pérot oscillation – MM resonance decoupling methods to further increase the sensitivity of the double-sided MM sensor, the study achieves a 14-times enhancement in dielectric spectroscopy response compared to single surface MM, along with a high dielectric sensitivity of 1400 GHz/RIU and dielectric detection capability of up to 0.0212 µmol/L.