A dual-tunable terahertz absorber using graphene-ZnO-VO2 hybrid structure for quad-band absorption, broadband-narrowband switching, and refractive-index sensing
Abstract
An optimized dual-tunable terahertz (THz) absorber based on a graphene-ZnO-VO 2 hybrid architecture is proposed for tunable absorption, switching, and refractive-index sensing applications. The absorber consists of a connected four-cut graphene resonator integrated with a ZnO dielectric spacer and a VO 2 ground layer, enabling the dynamic control of the absorption response through both graphene chemical-potential modulation and VO 2 conductivity variation. The resonator geometry, dielectric thickness, and graphene relaxation time were systematically optimized to maximize the absorption efficiency and electromagnetic confinement. The optimized absorber exhibited four near-unity absorption resonances at 0.34, 5.14, 10.11, and 15.27 THz. Under metallic-state VO 2 conditions, strong localized electric-field, magnetic-field, and power-loss distributions confirm efficient electromagnetic energy trapping and resonance formation. By varying the VO 2 conductivity from 10 to 1 × 10 5 S/m, reversible broadband-narrowband switching behavior was achieved, while graphene chemical-potential tuning from 0.1 to 1.0 eV provided active spectral reconfigurability with a maximum tunability factor of 152.2% and modulation depth of 74.26%. The absorber also demonstrated polarization-insensitive performance and stable absorption characteristics up to an incidence angle of approximately 80°. Refractive-index sensing analysis over the range n = 1.0–2.0 reveals systematic resonance-frequency red shifts with a maximum sensitivity of 1.03 THz/RIU, a figure of merit of 0.26 RIU −1 , and a Q-factor of 3.83 at the 15.27 THz resonance. The combination of quad-band absorption, dual tunability, broadband-narrowband switching, angular stability, and refractive-index sensing establishes the proposed graphene-ZnO-VO 2 absorber as a promising platform for terahertz sensing, biochemical detection, optical filtering, modulation, imaging, and reconfigurable-photonic applications. The present study is based entirely on full-wave numerical simulation; experimental fabrication and characterization are proposed as future work to validate these predicted results.