Tunable extinction and near-perfect absorption in graphene plasmonic terahertz metasurfaces

An extinction-centered framework is established for designing tunable graphene plasmonic metasurfaces in the terahertz (THz) regime. A deeply subwavelength, radially symmetric graphene resonator is analyzed using finite-difference time-domain and finite element method simulations, with explicit separation of absorption, scattering, and extinction cross sections. The structure supports localized plasmonic modes with normalized extinction that approaches or exceeds unity, demonstrating a strong resonant coupling between incident radiation and graphene plasmons over an effective electromagnetic area comparable to or larger than the physical footprint. The dominant resonance exhibits independent tunability via electrical gating, material loss, geometric scaling, and dielectric environment. Chemical potential controls resonance frequency, while carrier relaxation time primarily governs linewidth and peak extinction. Environmental permittivity and geometrical scaling enable predictable resonance positioning while preserving near-optimal efficiency. Using this extinction-driven design principle, we realize a graphene metamaterial absorber with electrostatically tunable near-unity THz absorption. The strong field confinement further yields high refractive index sensitivity and competitive sensing figure of merit values. These results establish extinction cross section as a unifying physical metric for tunable THz graphene metasurfaces, absorbers, and sensing platforms.