基于石墨烯的太赫兹漫反射表面快速设计方法

漫反射电磁表面能够提高目标被探测的难度,实现电磁消隐的功能.太赫兹漫反射电磁表面有望在下一代雷达与通信场景中作为一种智能隐身蒙皮使用,具有广阔的应用前景.本文利用石墨烯在太赫兹频段优异的电磁可调特性,并基于谐振模式的开关机理设计了一种反射场具有反相位的石墨烯/金属协同单元结构.且相位的切换由偏置电压动态控制.另一方面,不同于金属材料,石墨烯具有不可忽略的损耗特性,导致了所设计的结构在谐振/非谐振两种反相位状态对应的反射幅度不一致,根据场的干涉与叠加原理,其不利于远场相干相消,难以获得理想的漫反射效果.本文提出了一种将反相位单元结构进行二次组合形成"分子"结构的方法,并将其作为反射表面的基本元素,进而运用粒子群算法,优化"分子"结构的排布方式.计算结果表明,使用这种方法设计的动态漫反射表面,具有收敛速度快、远场峰值小的优势.

A method of rapidly designing graphene-based terahertz diffusion surface

Electromagnetic diffusion surface can reduce the radar cross section,thus profiting stealth of targets.Terahertz diffusion surface has a wide prospect in the field of next-generation radar and communication,promising to act as a kind of intelligent smart skin.In this paper,utilizing the excellent tunable properties of graphene in the terahertz band,a hybrid structure of graphene and metal which has inverse phase response of reflecting waves is proposed.The reflection phase switches in the mechanism of resonant modes and can be controlled efficiently by the bias voltage.Meanwhile,unlike metal materials,graphene has a non-negligible loss characteristic,which leads the response amplitudes corresponding to the two different switching states to be inconsistent with each other.According to the interference and superposition principle of electromagnetic field,it is not conducive to eliminating the coherent far-field,leading to an unsatisfactory diffusion result.In this paper,we present a"molecular"structure by secondary combination of the above-mentioned reverse phase element states,and take it as the basic element of the diffusion surface.Finally,we use particle swarm optimization to optimize the arrangement of"molecular",structures.The final diffusion surface consists of a combinatorial design of"molecules"rather than randomly distributed reflection units.In addition,molecules designed artificially have similar amplitude responses but different phase responses,which improves the convergence speed and reduces the computation quantity during algorithm evolution.The method of designing molecular structure,described in this paper,is simple,rapid and widely applicable,which effectively improves the amplitude-to-phase modulation ability of graphene metasurface against electromagnetic waves.When diffuse reflection optimization is applied to most of graphene metasurfaces,the method described in this paper can achieve the results that are the same as or even better than the results after a large number of iterations of traditional particle swarm optimization in the most computation-efficient manner.The results show that the dynamic diffusion surface designed by this method has the advantages of fast convergence speed and small farfield peak.