Multifunctional THz Absorber Using a Hybrid VO₂-Graphene Metasurface: Modeling and Performance Analysis

We present a tunable terahertz metamaterial absorber featuring a fabrication-convenient structure that combines a vanadium dioxide (VO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>) square patch and a graphene loop for multifunctional operation. This paper demonstrates an absorber that can selectively operate in narrow-band, dual-band, or broad-band modes. Combining graphene’s electrical tunability with VO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>’s thermally induced phase transitions, this absorber realizes dynamically switchable and tunable absorption properties. When VO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is in its metallic state with chemical potential of graphene, E<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>f</i></sub> = 0 eV, and relaxation time, τ = 0.1 ps, the structure achieves a broad-band absorption bandwidth of 6.31 THz (>90% absorptance from 5.04 THz to 11.35 THz), with an average absorption of 97.24% and a relative absorption bandwidth of 77.12%. By adjusting graphene’s E<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>f</i></sub> to 1 eV and τ to 0.7 ps, the absorber transitions to a dual-band response, exhibiting peak absorptions of 91.13% at 2.62 THz and 95.48% at 10.81 THz. Conversely, when VO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> remains in insulating state and graphene’s E<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>f</i></sub> is tuned to 0.6 eV and τ to 0.2 ps, a narrow-band absorption peak of 98.18% emerges. Furthermore, we demonstrate the narrow-band configuration as an ultra-sensitive biosensor, where the resonance peak undergoes a significant redshift while maintaining high absorption efficiency with minimal changes in the surrounding medium’s refractive index. The design exhibits polarization insensitivity and wide-angle stability, validated through electric field analysis, impedance matching theory, and equivalent circuit modeling. To the best of our knowledge, this is the first reported structure to integrate such a wide absorption bandwidth of 6.31 THz with ultra-high biosensing sensitivity of 1929 GHz/RIU in a single fabrication-friendly configuration. These capabilities make the absorber highly promising for applications in energy harvesting, stealth technology, and biochemical sensing.