Wood‐Derived Nanocellulose‐Biocarbon Fresnel‐Zone Plate Lenses for Sub‐THz Frequency Applications

ABSTRACT The realization of future holographic technologies, including extended reality, the Internet of Things, and autonomous transportation, enabled by next‐generation telecommunications, demands sustainable, advanced components capable of operating at sub‐terahertz (sub‐THz) frequencies. Herein, fully bio‐based Fresnel zone plate (FZP) lenses are fabricated as high‐performance focusing elements for the sub‐THz range using wood‐derived cellulose nanofibers (CNFs) and biocarbon (BC) microparticles. The integration of mechanically robust, low dielectric loss CNF network with BC (0–50 wt.%) yields CNF–BC composite films exhibiting tunable thickness, electrical conductivity, and dielectric response, as well as stable structural integrity across a wide range of humidity and temperature conditions. At moderate BC loadings (5–10 wt.%), high tensile strength (>70 MPa) and enhanced ductility (>9%) are preserved, while controlled increases in permittivity and conductivity are achieved without compromising the low dielectric loss required for efficient sub‐THz operation. Nested nine‐ring FZP lenses constructed from laser‐patterned CNF–BC integrated with ultralight CNF aerogel substrates deliver excellent focusing performance. Simulated and experimental results demonstrate high directivities exceeding 30 dBi at 0.3 THz, with gains comparable to or surpassing those of geometrically identical metallic lenses under low‐gain waveguide excitation. The CNF–BC composites provide a scalable and sustainable platform for high‐performance sub‐THz electromagnetic applications.