Graphene-based metamaterial as a three-bit terahertz encoder: design, simulation, and equivalent circuit model

• Graphene-based metamaterial as a three-bit encoder composed of two ribbons and a circular resonator array enables eight distinct reflection states. • High performance with 99.98% modulation depth, 0.38 dB insertion loss, and 36.09 dB extinction ratio. • Transmission-line equivalent circuit modeling accurately predicts resonance behavior, validated by FEM simulations. • Compact design providing a conceptual platform for future THz signal encoding, routing, and digitally reconfigurable metamaterial applications. In this paper, a three-bit encoder based on a terahertz (THz) graphene metamaterial, composed of two ribbon resonators and a circular resonator array, is proposed and designed. The proposed design features a hybrid resonator configuration with independent Fermi-level tuning, enabling eight distinct encoding states. The normalized reflection spectrum of the encoder exhibits three distinct reflection dips, controlled by tuning the Fermi levels of the graphene resonators, enabling 3-bit encoding. The device operates within the 1–3.6 THz frequency range. The electric field and surface current distributions confirm that each resonance originates from a specific resonator and corresponds to an independently excited bright-mode resonance with magnetic characteristics arising from antiparallel currents between the graphene layer and the gold ground plane. The equivalent circuit modeling (ECM) approach is employed to validate the finite element method (FEM) simulation results. All results are obtained via full-wave CST simulations and validated using the ECM. The metamaterial provides three encoding frequencies at 1.49 THz, 2.02 THz, and 2.48 THz. Across its discrete THz encoding states, the metamaterial achieves a maximum modulation depth ( MD ) of 99.8%, a minimum insertion loss ( IL ) of 0.38 dB, and a maximum extinction ratio ( ER ) of 26.8 dB. Due to the independent bright-mode operation of each resonator, the proposed structure offers clear multi-frequency control and effective digital THz encoding performance. Beyond its role as a THz encoder, the proposed design may serve as a platform for terahertz signal control and reconfigurable photonic functionalities.