General features of spatiotemporal instability induced by arbitrary high-order nonlinear dispersions in metamaterials

Spatiotemporal instability (STI) in metamaterials (MMs) with a Kerr-type nonlinear polarization is investigated. A general expression for instability gain, taking account of the effects of arbitrary high-order linear and nonlinear dispersions, is derived. Special attention is paid to the general features of instability induced by nonlinear dispersion effects originating from the combination of dispersive magnetic permeability and nonlinear polarization. It is shown that, just like their linear counterparts, all even-order nonlinear dispersions not only deform the original instability regions, but also may lead to the appearance of new instability regions. However, all odd-order nonlinear dispersions always suppress STI irrespective of their signs, quite different from their linear counterparts which exert no influence on instability. Moreover, we find that, unlike the linear dispersions, the nonlinear dispersions lead to the dependence of gain peak on the spatial modulation frequency. The role of the first-order nonlinear dispersion, namely self-steepening (SS), and second-order nonlinear dispersion (SND) in STI is particularly analyzed to illustratively demonstrate the general results.     

Tailoring photonic metamaterial resonances for thermal radiation

Selective solar absorbers generally have limited effectiveness in unconcentrated sunlight, because of reradiation losses over a broad range of wavelengths and angles. However, metamaterials offer the potential to limit radiation exchange to a proscribed range of angles and wavelengths, which has the potential to dramatically boost performance. After globally optimizing one particular class of such designs, we find thermal transfer efficiencies of 78% at temperatures over 1,000°C, with overall system energy conversion efficiencies of 37%, exceeding the Shockley-Quiesser efficiency limit of 31% for photovoltaic conversion under unconcentrated sunlight. This represents a 250% increase in efficiency and 94% decrease in selective emitter area compared to a standard, angular-insensitive selective absorber.PACS: 42.70.Qs; 81.05.Xj; 78.67.Pt; 42.79.Ek.     

三维超材料的非线性电、磁响应特性

理论研究了埋入在非线性介质中的由金属线和谐振环构成的具有三维周期性结构的超材料的有效电、磁响应,计算了该种超材料的有效磁导率和介电常数实部和虚部随外场的变化关系.结果表明,这种超材料有效磁导率和介电常数的实部对外磁场的响应具有回滞效应.在一定条件下,这种结构的属性可在右手材料、电单负材料与磁单负材料之间转换,且这种转换可适当选择在某些特定频率范围内的外磁场强度的方式控制.     

Design of Structural Left-handed Material based on Topology Optimization

An effective method to design structural Left-handed material(LHM) was proposed. A commercial finite element software HFSS and S-parameter retrieval method were used to determine the effective constitutive parameters of the metamaterials, and topology optimization technique was introduced to design the microstructure configurations of the materials with desired electromagnetic characteristics. The material considered was a periodic array of dielectric substrates attached with metal film pieces. By controlli...     

Active EIT-like Dependent on Polarization Angle with Graphene Metamaterial

Abstract

An active electromagnetically induced transparency (EIT) analog adopting graphene as microstructure of metamaterial is investigated. The analog consist interconnected graphene strip (GS) and graphene split ring resonator (GSRR), which can act as bright and dark elements alternately. The distinct EIT-like effect can be generated by bright-dark mode coupling in x and y polarization directions. Further investigations reveal that EIT peak can be actively controlled via Fermi level of graphene, and theoretical analysis based on two particles mode express the reason. Moreover, notable EIT-like effect can also be generated in a wide range of polarization angles, and impact of polarization angle on EIT peak is also discussed in detail. These characteristic paves the way for the applications of EIT-like in sensor device.     

What is negative refraction?

We review various published definitions associated with the phenomenon of negative phase velocity propagation of electromagnetic waves in meta-media, as observed through negative refraction. For the principal definition, based on the Poynting vector and the wave vector having negative scalar product, we summarise the various material constraints that have been derived. The distinction between criteria based on the Poynting vector and the group velocity are considered, both in respect of causality, and in the context of moving media. Instances where a fully covariant definition is necessary are also identified, and compared with other results from the extant literature. Satisfaction of the NPV propagation criterion is also considered for surface plasmons.     

三维螺旋超结构/介质的低频协同效应及其吸波蜂窝制备

目的 拓展蜂窝吸波材料的低频吸收性能，提出一种三维螺旋超结构复合吸波蜂窝的设计方法。方法 在吸波蜂窝中加载三维螺旋超结构，使用电磁场理论和等效电路理论定性分析螺旋超结构对复合蜂窝吸收性能的调控作用，以优化螺旋超结构的参数。结果 入射电磁波在螺旋超结构表面激发驻波电流，产生强烈的电共振和磁共振，与蜂窝损耗介质产生协同吸收效应，增强了吸波蜂窝的低频吸收性能。结论 仿真和实验结果表明，加载三维螺旋超结构使得吸波蜂窝的低频吸收性能显著增强，在1～6 GHz频段的平均反射损耗从-3 dB增强至-10 dB。