Abstract-Tailoring polarization and magnetization of absorbing terahertz metamaterials using a cut-wire sandwich structure

Hadi Teguh Yudistira, Shuo Liu,  Tie Jun Cui,  Han Zhang

a) Illustration of cut-wire sandwich structure. W, L, g, Zd and Zg are width of cut wire (20 µm), length of cut wire (100 µm), the gap size of cut wire with its neighbor (5 µm), polyimide substrate thickness (5 µm), and tge cut-wire structure thickness (100 nm), respectively. D is the lattice constant (D = L + g). b) Sample 1: cut-wire sandwich structure, c) Sample 2: cross-shaped sandwich structure, d) Sample 3: star-shaped sandwich structure.

https://www.beilstein-journals.org/bjnano/articles/9/136

The permittivity and permeability of a cut-wire sandwich structure can be controlled by laterally shifting the upper and lower layers. The use of this process for designing specific application-oriented devices may lack clear-cut guidelines because the lateral misalignment will significantly change the permittivity and permeability simultaneously. Therefore, in this work, we designed, fabricated and characterized a cut-wire sandwich device capable of tailoring the polarization and magnetization separately, thereby providing a promising recipe for achieving specific application objectives, such as a high-performance absorber. Accumulated charges effectively provided the polarization at the edge of cut-wires, and the surface current density on the cut-wires at top and bottom layers effectively generated the magnetization. By controlling and optimizing the geometrical configurations of the entire sandwich device (without lateral misalignment), the impedance could be matched to that of free space while generating a large imaginary part in the refractive index. This work characterizes the absorption performance of such sandwich structures in the terahertz regime. This mechanism could be further extended to other metamaterial devices in the terahertz and other frequency ranges because polarization and magnetization can now be selectively controlled in a straightforward manner.

Abstract-Concepts, Working Principles, and Applications of Coding and Programmable Metamaterials

Shuo Liu,Tie Jun Cui,

http://onlinelibrary.wiley.com/doi/10.1002/adom.201700624/abstract

As a digital version of metamaterials, coding and programmable metamaterials have experienced rapid development since they were initially proposed in 2014. Unlike conventional metamaterials that are characterized by the sophisticated effective medium theory, coding metamaterials are described in a much simpler manner with binary codes, which builds up a bridge between the physical world and the digital world. In this article, the development of coding and programmable metamaterials in the past three years is reviewed, focusing primarily on the basic concept, working principle, design method, fabrication, and experimental validation. First, reflection-type and refraction-type coding metamaterials, along with two bifunctional coding metamaterials, are presented in the microwave, terahertz, and acoustic regimes. Second, the digital convolution theorem and information entropy of coding metamaterials are introduced to demonstrate the strong connection between metamaterials and information science. Then, recent progresses on engineering realization of field-programmable metamaterials are demonstrated, including the compensation technique of plane waves under point source illumination, and applications in single-sensor single-frequency imaging systems. Finally, future directions and potential applications are summarized, followed by discussions on major challenges encountered in the design and fabrication of programmable metamaterials at higher frequencies.

Abstract-Full-State Controls of Terahertz Waves Using Tensor Coding Metasurfaces

Shuo Liu, Hao Chi Zhang, Lei Zhang, Quan Long Yang, Quan Xu, Jian Qiang Gu, Yan Yang, XiaoYang Zhou, Jiaguang Han, Qiang Cheng, Weili Zhang, and Tie Jun Cui

ACS Appl. Mater. Interfaces, Just Accepted Manuscript

DOI: 10.1021/acsami.7b02789

Publication Date (Web): June 5, 2017

Copyright © 2017 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acsami.7b02789?journalCode=aamick

Coding metasurfaces allow us to study metamaterials from a fully-digital perspective, enabling many exotic functionalities such as anomalous reflections, broadband diffusions, and polarization conversion. Here, we propose a tensor coding metasurface at terahertz frequency that could take full-state controls of electromagnetic wave in terms of its polarization state, phase and amplitude distributions, and wave-vector mode. Due to the off-diagonal elements that dominant in the reflection matrix, each coding particle could reflects the normally incident wave to its cross polarization with controllable phases, resulting in different coding digits. A 3-bit tensor coding metasurface with three coding sequences is taken as example to show its full-state controls in reflecting normally incident terahertz beam to anomalous directions with cross polarizations, and making a spatially propagating wave (PW) to surface wave (SW) conversion at the terahertz frequency. We show that the proposed PW-SW convertor based on tensor coding metasurface supports both x and y-polarized normal incidences, producing cross-polarized transverse- magnetic (TM) and transverse-electric (TE) modes of terahertz SWs, respectively.

Abstract-Frequency-Dependent Dual-Functional Coding Metasurfaces at Terahertz Frequencies

http://onlinelibrary.wiley.com/doi/10.1002/adom.201600471/full

A frequency-dependent dual-functional coding metasurface is proposed at terahertz frequencies using two layers of metamaterial structures, each of which is responsible for the independent control of reflection phases at two distinct frequencies. The zero interference between the functionalities at the lower and higher frequencies are promising for possible applications in multicolor holography for color displays or a frequency beam splitter.

Abstract-Controlling the Bandwidth of Terahertz Low-Scattering Metasurfaces

1. Jie Zhao^1,2, 
2. Qiang Cheng^1,3,*, 
3. Xin Ke Wang⁴, 
4. Min Jie Yuan⁴, 
5. Xiao Zhou^1,2, 
6. Xiao Jian Fu^1,2, 
7. Mei Qing Qi^1,2, 
8. Shuo Liu^1,2,
9. Hai Bin Chen^1,2, 
10. Yan Zhang^3,4 and
11. Tie Jun Cui^1,3,*

Version of Record online: 11 JUL 2016

DOI: 10.1002/adom.201600202

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

http://onlinelibrary.wiley.com/doi/10.1002/adom.201600202/abstract

Low-scattering metasurfaces in the terahertz region can benefit a number of applications such as imaging, radar, and novel light sources. Such metasurfaces can efficiently suppress specular reflection and diffuse the energy that comes back without preferred direction. However, the accurate bandwidth control of low-scattering metasurfaces is still a main issue to be investigated. To solve the problem, here a new strategy to realize the low-scattering metasurfaces with desired bandwidths is proposed. Different from the earlier work, the current design is carried out within a broad spectrum instead of at a single frequency, giving rise to the arbitrarily desired bandwidth. Three basic elements are proposed to construct the new metasurface, and the diffuse reflection feature can be attributed to their destructive interferences with the change of operating frequency. The intrinsic loss of the meta-atoms is also taken into account to make the theoretical model more accurate in the practical design. Excellent scattering-suppression features are observed in the predefined frequency bands in both simulated and experimental results, which have very good agreements with the theoretical predictions.

Abstract-Anisotropic coding metamaterials and their powerful manipulation of differently polarized terahertz waves

Shuo Liu^1,2,*, Tie Jun Cui^1,3,*, Quan Xu⁴, Di Bao^1,2, Liangliang Du⁴, Xiang Wan^1,2, Wen Xuan Tang^1,2, Chunmei Ouyang⁴, Xiao Yang Zhou^1,2,5, Hao Yuan⁵, Hui Feng Ma^1,2, Wei Xiang Jiang^1,2, Jiaguang Han⁴, Weili Zhang^3,4 and Qiang Cheng^1,3

1. ¹State Key Laboratory of Millimeter Waves, Southeast University, Nanjing 210096, China
2. ²Synergetic Innovation Center of Wireless Communication Technology, Southeast University, Nanjing 210096, China
3. ³Cooperative Innovation Centre of Terahertz Science, Chengdu 610054, China
4. ⁴Center for Terahertz Waves and College of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin 300072, China
5. ⁵Jiangsu Xuantu Technology Co., Ltd., Nanjing 211111, China

Correspondence: TJ Cui, Email: tjcui@seu.edu.cn

^*These authors contributed equally to this work.

Received 29 September 2015; Revised 19 January 2016; Accepted 20 January 2016
Accepted article preview online 26 January 2016

http://www.nature.com/lsa/journal/v5/n5/full/lsa201676a.html

Metamaterials based on effective media can be used to produce a number of unusual physical properties (for example, negative refraction and invisibility cloaking) because they can be tailored with effective medium parameters that do not occur in nature. Recently, the use of coding metamaterials has been suggested for the control of electromagnetic waves through the design of coding sequences using digital elements ‘0’ and ‘1,' which possess opposite phase responses. Here we propose the concept of an anisotropic coding metamaterial in which the coding behaviors in different directions are dependent on the polarization status of the electromagnetic waves. We experimentally demonstrate an ultrathin and flexible polarization-controlled anisotropic coding metasurface that functions in the terahertz regime using specially designed coding elements. By encoding the elements with elaborately designed coding sequences (both 1-bit and 2-bit sequences), the x- and y-polarized waves can be anomalously reflected or independently diffused in three dimensions. The simulated far-field scattering patterns and near-field distributions are presented to illustrate the dual-functional performance of the encoded metasurface, and the results are consistent with the measured results. We further demonstrate the ability of the anisotropic coding metasurfaces to generate a beam splitter and realize simultaneous anomalous reflections and polarization conversions, thus providing powerful control of differently polarized electromagnetic waves. The proposed method enables versatile beam behaviors under orthogonal polarizations using a single metasurface and has the potential for use in the development of interesting terahertz devices.