Four-channel multistate spectral coding in a VO2-Integrated terahertz metasurface absorber with a hollow rectangular resonator

A four-channel reconfigurable terahertz metasurface absorber is numerically investigated using a hollow rectangular resonator integrated with vanadium dioxide (VO 2 ). The resonator geometry supports four spectrally separated resonances with distinct spatial field distributions and different sensitivities to the incident polarization. Under the low-conductivity condition of VO 2 ( σ = 2 × 10 2 S/m), absorption resonances appear at 0.545, 1.768, 2.867, and 3.157 THz, with peak absorptivities of 93.4%, 86.6%, 99.8%, and 93.6%, respectively. As the conductivity of VO 2 is increased, these resonant features are gradually weakened, and a strongly suppressed absorption regime is reached at σ = 2 × 10 5 S/m. Rotation of the incident polarization further produces channel-dependent changes in the spectral response. The four resonance frequencies identified under the reference condition are used as fixed sampling channels, and the corresponding absorptivities are converted into binary values using a predefined threshold. Seven distinct four-bit codes—1111, 0111, 0110, 0011, 0100, 0001, and 0000—are obtained. The Q-factors of the four channels are 7.11, 20.89, 31.05, and 43.66, respectively, supporting spectral discrimination among the four readout channels. Electric-field, magnetic-field, and surface-current distributions further reveal different localization and current-flow characteristics for the four resonances, supporting their assignment to distinct electromagnetic responses of the hollow rectangular resonator. The proposed approach provides a geometry-assisted route for converting tunable THz absorption spectra into discrete digital codes, with potential applications in spectral labeling, information encoding, and reconfigurable THz photonic systems.