Flexible Terahertz Encryption Platform Integrating Metallic Composite and Metasurface Pattern for Physically Concealed Authentication

ABSTRACT

Conventional anti‐counterfeiting technologies that utilize optical devices often rely on visible or near‐infrared features; however, directly exposed optical signatures can be vulnerable to duplication or environmental degradation in simple tag‐based systems. In this study, we demonstrate a flexible terahertz (THz) encryption platform based on visibly concealed metasurface patterns, called the THz‐encoded metasurface pattern (TEMP), enabling robust physical anti‐counterfeiting authentication. The TEMP is fabricated by integrating a flexible double‐split ring resonator metasurface with a metallic composite layer that is opaque in the visible region but transparent and tunable in the THz region. The metasurface exhibits polarization‐dependent LC resonances, providing polarization‐selective spectral responses. Meanwhile, the refractive index of the composite layer is tailored by adjusting the composition of the conductive fillers; when the layer is integrated with the metasurface, an intrinsic physical key is generated for authentication. The resulting THz transmittance spectra are further encrypted through affine transformation and stored in quick response (QR) codes, achieving stable and reversible spectral reconstruction with even after 1000 bending cycles. By combining optical concealment, spectral uniqueness, and mechanical robustness, the flexible TEMP platform offers a practical THz‐based pathway for nondestructive and physically encrypted authentication.