VO₂-Integrated metasurface for thermally tunable broadband terahertz absorption

Vanadium dioxide (VO₂), owing to its reversible insulator-metal phase transition, has emerged as a promising functional material for actively tunable terahertz (THz) devices. In this work, a VO₂-integrated metasurface absorber is numerically investigated to achieve thermally tunable broadband THz absorption. The proposed structure consists of concentric VO₂ ring resonators coupled with a dielectric spacer and a metallic ground plane, forming a multiresonant cavity that enhances electromagnetic energy dissipation. Under transverse electric (TE) polarized excitation, the proposed structure exhibits three near-perfect absorption resonances with peak absorptance values of 95.24% at 3.67 THz, 98.65% at 6.19 THz, and 99.99% at 9.18 THz. Simulation results further show that, at a VO₂ conductivity of 2.0 × 10⁵ S m^-1, the absorber achieves an ultra-broad absorption bandwidth of 6.67 THz, extending from 2.92 THz to 9.59 THz, corresponding to a relative bandwidth of 106.6%. The absorption mechanism is elucidated through electric- and magnetic-field distributions, which reveal strong field confinement and resonant current loops that enable effective impedance matching. By exploiting the reversible insulator-to-metal phase transition of VO₂, with conductivity tunable from 2 × 10² S m^-1 to 2 × 10⁵ S m^-1, continuous and dynamic absorption control is achieved. Furthermore, polarization- and angle-dependent analyses confirm polarization insensitivity and wide-angle stability, demonstrating that the proposed absorber provides a compact, high-performance, and tunable platform for terahertz detection, biosensing, and adaptive stealth applications.