▎ 摘　　要

In this paper, for the first time, a new generation of multi-bit graphene-based bias-encoded metasurfaces (MGBMs) is proposed for real-time reflected wavefront manipulation at terahertz (THz) frequencies. The architecture of the designed MGBM is composed of several meta-atoms whose operational status can be independently switched between eight digital states of "000" - "111" in a real-time manner. By mere changing the distribution of chemical potentials through an external electronic source, the occupying meta-atoms can be dynamically combined in different gradient, spiral-like, and spiral-parabola-like coding sequences. Different from earlier works, the proposed MGBM can be re-programmed for accomplishing multiple outlandish missions from generation of vortex wavefronts carrying a controllable amount of orbital angular momentum (OAM) toward emitting multiple arbitrarily-oriented pencil beams at the same time. By exploiting the addition theorem and convolutional principle, multi-type functionalities, such as multiple pencil beams, multiple vortex beams with different topological charges, and multiple pencil-vortex beams are simultaneously realized. The full control of reflected wavefronts is corroborated with numerical simulations and theoretical predictions. By offering new attractive degrees of freedom to EM waves, various future directions are expected for the proposed versatile MGBM such as controllable displays, modern information systems, moving target detection, etc. (C) 2019 Elsevier Ltd. All rights reserved.