A Multimode Eight-Band Tunable Terahertz Absorber Based on Electric-Dipole-Dominated Resonances for Multi-Channel Sensing

This paper proposes a tunable narrowband perfect absorber with eight distinct absorption peaks in the terahertz band. The structure employs a typical three-layer stack: a gold reflector, a SiO ₂ dielectric spacer, and a top-patterned graphene layer. The graphene pattern integrates disks with cross-shaped slits and central petal-like units, exciting multiple resonance modes. Within 1-10 THz, the design achieves eight narrowband peaks, seven of which exceed 90% absorption, exhibiting excellent multi-frequency selectivity. Physical mechanisms are clarified through impedance matching theory, multiple interference reflection theory, and multipole decomposition. Absorption originates mainly from dipole-dominated plasmonic resonances in graphene-localized edge resonances at lower frequencies evolve into global in-plane resonances across disks and slits at higher frequencies, with additional magnetic dipole contributions at the highest band. Absorption frequency and intensity can be dynamically tuned by adjusting graphene’s Fermi level and relaxation time. The symmetric design ensures polarization insensitivity and maintains stable performance up to 50° incident angle. The absorber shows high environmental refractive-index sensitivity, up to 3000 GHz/RIU, alongside a high quality factor and figure of merit, highlighting its potential for multi-channel sensing. Compared to existing designs, this work offers more narrowband peaks, a simpler structure, and enhanced tunability, providing a promising platform for THz sensing, spectral filtering, and communication switching devices.