Abstract
Inspired by the information theory, a new concept of re-programmable encrypted graphene-based coding metasurfaces was investigated at terahertz frequencies. A channel-coding function was proposed to convolutionally record an arbitrary information message onto unrecognizable but recoverable parity beams generated by a phase-encrypted coding metasurface. A single graphene-based reflective cell with dual-mode biasing voltages was designed to act as “0” and “1” meta-atoms, providing broadband opposite reflection phases. By exploiting graphene tunability, the proposed scheme enabled an unprecedented degree of freedom in the real-time mapping of information messages onto multiple parity beams which could not be damaged, altered, and reverse-engineered. Various encryption types such as mirroring, anomalous reflection, multi-beam generation, and scattering diffusion can be dynamically attained via our multifunctional metasurface. Besides, contrary to conventional time-consuming and optimization-based methods, this paper convincingly offers a fast, straightforward, and efficient design of diffusion metasurfaces of arbitrarily large size. Rigorous full-wave simulations corroborated the results where the phase-encrypted metasurfaces exhibited a polarization-insensitive reflectivity less than −10 dB over a broadband frequency range from 1 THz to 1.7 THz. This work reveals new opportunities for the extension of re-programmable THz-coding metasurfaces and may be of interest for reflection-type security systems, computational imaging, and camouflage technology.
Highlights
Inspired by the information theory, a new concept of re-programmable encrypted graphene-based coding metasurfaces was investigated at terahertz frequencies
Regarding the Fourier relation between the coding layout and its radiated beams, diverse theorems and analytical tools in digital communication and information theory can serve for the design of coding metasurfaces, leading to various interesting functionalities
This paper firstly proposes a new concept in which the THz coding metasurface can contribute to data transmission/reception regardless of the conventional digital communication with time-modulated signals
Summary
Inspired by the information theory, a new concept of re-programmable encrypted graphene-based coding metasurfaces was investigated at terahertz frequencies. This issue can significantly enhance the capability of communication through creating parallel channels in addition to the traditional ones (i.e. one channel occupied with time-modulated signals carrying the information of the encoded message sequences and at the same time, another channel occupied with multiple parity beams carrying the information of the encoded message sequences) To implement such a platform, a single graphene-based reflective cell fed by dual-mode biasing voltages is designed whose operational status can be dynamically switched between the two states of “0” and “1”. Armed with such a re-programmable device, the real-time mapping of information messages onto various protected far-field patterns generated by convolutionally encrypted metasurfaces is available. By targeting the maximum Renyi entropy of the generated parity beams, the optimal diffusion layout is extracted using a Binary Bat optimization algorithm to prove that the proposed convolutional encryption scheme convincingly offers a straightforward, reliable, and fast alternative design manner of diffusion coding metasurfaces of arbitrarily large size
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