Polarization-insensitive multi-bit encoding tunable graphene-based terahertz identification tag

Abstract This paper introduces a 1-bit terahertz identification (THID) tag with a three-layer composite structure, comprising a hexagonal graphene loop, a Topas dielectric substrate, and a gold ground plane, designed for THz frequency applications. The graphene loop enables binary encoding logic (1) or (0) by modulating its chemical potential (0.8 or 0.0 eV) via DC bias. A distinct absorption peak occurs at 3.75 THz with near-100% absorption for logic (1) and 5% for logic (0). Simulations reveal a sharp reflection coefficient dip (0.1 for logic (1) against 0.99 for logic (0)) and a 225° phase difference, ensuring robust distinguishability. The tag’s polarization-insensitive response, validated for TE and TM waves, maintaining absorption stability under varying incidence angles (70% at θ inc = 70°). Parametric studies show that varying the graphene loop’s side length and width shifts resonance frequencies (2.36–5.1 THz) and optimizes absorption (82–100%). Multi-bit encoding (2-bit and 3-bit) is achieved by cascading tags with independent control of resonance frequencies via chemical potential adjustments. Multi-bit encoding is achieved by integrating multiple graphene loops on the same cell, each independently controlling distinct resonance frequencies (e.g., 2.33 THz and 5.1 THz for 2-bit; 1.9 THz, 3.1 THz, and 5.3 THz for 3-bit), enabling up to eight unique encoding states. Equivalent circuit models, optimized via particle swarm optimization, accurately replicate absorption responses with minimal error (0.18% for 1-bit, 0.6% for 2-bit, and 0.5% for 3-bit). The proposed THID tags demonstrate high absorption, tunable resonance, and scalability for advanced identification systems, offering significant potential for high-capacity, polarization-insensitive tagging applications in sensing and communication systems.