Dynamic multifunctional control of terahertz beam based on graphene coding metamaterial

Abstract

Terahertz (THz) waves have aroused tremendous research interest due to its some unique features and widespread applications in broadband communication, military radar, non-destructive detection, biomedical, security check, etc. With the development of THz applications, dynamic control beam of THz wave with wide bandwidth and multifunction has become a key issue in the field THz technology. The metamaterial with a kind of artificial material provides an approach to controlling the terahertz beam. However, the characteristics of metamaterials based on the equivalent medium parameters are limited by the structural configuration, which usually causes disadvantageous problems including the real-time dynamic control, narrow bandwidth, modulating efficiency, complicated design, etc. The coding metamaterial based digital elements provide an approach to wideband and flexible control terahertz wave by different sequences. However, the THz waves are still hard to tune in dynamic ways due to the limitation of material properties and processing capability. Graphene with a new two-dimensional material has excellent photoelectric properties such as tunable band gap, flexibly dynamic performance, and low material loss. Therefore, the graphene with coding metamaterial can offer a new way of dynamically controlling beam. In this paper, we design a 1 bit coding metamaterial based on graphene ribbon, which can be expected to realize multi-modulation to the number of beams, frequency and amplitude of THz wavers. The mechanism of controlling electromagnetic wave by coding metamaterial can be explained by the reflective array antenna. And the characteristics of the proposed metamaterial based on the graphene ribbon and the far-field scattering of coding metamaterial are simulated using the CST Microwave Studio. A composite structure which consists of gold metal, polyimide, silicon, silicon dioxide, graphene ribbon is designed and characterized in the THz range. The simulation results show that by gating different graphene ribbons, the coding state (digital element) on each column can be independently controlled as well, thus the ‘0’ and ‘1’ digital elements with a phase difference of 180° in a certain frequency range can be realized, and then the coding sequence on metamaterials is dynamically modulated. Full-wave simulation results also show that different-sequence coding metamaterials can achieve the control of the number of scattering THz beams, from one, double, multi scattering in a wide frequency range (from 1.7 to 2.2 THz). For coding sequence ‘010101...’ realized by gating different voltages on coding elements ‘0’ and ‘1’, the frequency at which double scattering beams are produced, presents shift. For the coding metamaterial of periodic sequence of 000000 or 111111 with different voltage for different graphene ribbon, which can be expected to realize amplitude modulation from -12 dB to -23 dB of THz beam steering at f1=1 THz. Therefore, this graphene coding metamaterial can control the THz beam flexibly and may offer widespread applications in stealth, imaging, and broadband communication of THz frequencies.