电磁编码超材料的理论与应用

本文系统地对编码超材料、数字超材料及现场可编程超材料的新进展进行了综述,讨论其对电磁波的实时调控和构造多功能器件的能力。首先,引入1-bit编码超材料,由"0"和"1"两种编码单元构成,分别对应于相位相反的电磁响应。通过控制不同的"0"和"1"编码序列,可以调控电磁波,并实现不同功能。这种1-bit编码超材料可以扩展到2-bit,甚至更高比特。其次,介绍了一种由开关二极管来控制的数字编码超材料,每个编码单元可通过二极管的开和关来获得不同的相位响应,进而获得不同的数字态。结合现场可编程门阵列(FPGA)控制系统,实现了对数字超材料的实时可编程设计,构造出现场可编程超材料。最后,研究了编码超材料对太赫兹波的调控,包括太赫兹波宽带漫散射及其对目标雷达散射截面(RCS)的缩减、各向异性编码超材料对太赫兹波的极化调控和波束调控等。数值仿真和实验测试结果吻合很好,验证了编码超材料的出色性能,展示了编码超材料调控电磁波的多功能性。编码超材料对微波及太赫兹波的实时控制可用于制作波束分离、波束偏折、极化转换等功能器件,也可在宽带范围内有效缩减目标RCS。

Theory and application of coding metamaterials

In this paper, we review the recent progress on coding metamaterial,digital metamaterial and programmable metamaterial, and discuss their capacities in manipulating the electromagnetic(EM) waves in real time and constructing the multi-functional devices. First, we present 1-bit coding metamaterials that are composed of only two types of unit cells with 0 and π phase responses, named as ‘0’ and ‘1’ elements, respectively. By encoding ‘0’ and ‘1’ elements with controlled sequences, we can manipulate EM waves and realize different functionalities. The concept of coding metamaterials can be extended from 1-bit coding to 2-bit coding or higher. Second, we introduce a unique metamaterial particle that has either 0' or 1' response electrically controlled by a biased diode. Based on this particle, we present digital metamaterials with unit cells that possess either 0' or 1' state. Using a field-programmable gate array(FPGA), we realize the digital controls over the coding metamaterial, thereby realizing a programmable metamaterial. Finally, we study the manipulations to terahertz waves using the coding metamaterial, such as to produce wideband diffusions of terahertz waves, achieving the efficient reductions of radar cross sections(RCSs), as well as to propose anisotropic coding metamaterials, realizing distinct coding behaviors for different polarizations. The measured results are in good agreements with the simulated results, demonstrating the powerful abilities of coding metamaterials to control EM waves. The property of coding metamaterials to manipulate EM waves can be used for designing beam splitter, realizing anomalous reflections and polarization conversions, and reducing RCSs of metallic objects in wide frequency bands.