基于石墨烯-金属混合结构的可调超材料吸波体设计

利用石墨烯与金属相结合的方法提出了一种新型超材料吸波体结构,通过改变外加偏置电压来改变石墨烯的费米能级,在微波段分别实现了单频和宽频的振幅可调性,并阐述了其电磁吸波及振幅可调的机理。对单一频段下的超材料结构进行了模拟仿真,结果表明,当结构参数不变时,吸波体的吸收强度随石墨烯费米能级的增加而不断减小,最大调制深度达到了58.6%。当石墨烯费米能级为0eV时,吸波体的中心频率随结构参数的改变而改变。基于多吸收峰叠加扩展带宽的原理,利用不同尺寸单元的排列实现了宽频吸波的特性,并通过仿真模拟证明了该宽频吸波体具有振幅可调的性质。     

石墨烯和对称开口谐振环超材料中可调谐的双等离激元诱导透明现象（英文）

提出了由石墨烯和两对对称开口谐振环构成的等离激元诱导透明(PIT)超材料结构,该PIT超材料结构之间的耦合形式为暗-亮-暗模式.通过有限元方法模拟,观察到双PIT透明窗口,通过改变石墨烯的费米能级或者改变开口谐振环的几何参数来动态地调制PIT窗口.理论结果表明,当石墨烯与两对对称的开口谐振环之间的相互作用距离为0.5μm、石墨烯费米能级为1.5eV时,可得到最优的双透明窗口.双PIT效应在非线性器件、可调谐传感器、开关和慢光器件等方面有潜在的应用价值.     

基于液晶的广角太赫兹可调谐超表面吸波器

提出了一种结构简单的广角稳定太赫兹可调谐超表面吸波器,利用液晶材料电可调谐的性质,实现超表面吸波器吸收频率的调谐。利用液晶材料介电常数张量进行材料建模,模拟了液晶材料的各向异性特性。为了提高设计效率,得到良好的吸波性能和可调谐性能,利用粒子群算法对超表面吸波器单元结构进行了逆向设计;并对设计的超表面吸波器特性进行研究。结果表明,利用粒子群算法可以高效地逆向设计出性能良好超表面吸波器,当对吸波器施加的电压在0～10 V范围内连续调谐时,实现了TE模式吸波频率在404.4～444.4 GHz范围内连续可调谐,频率可调谐性为9%,吸收率大于99%;TM模式吸波频率在404.4～425.4 GHz范围内连续可调谐,频率可调谐性为4.64%,吸收率大于99%;当斜入射角度为60°时,吸收率仍大于94%,具有大角度入射稳定性和吸收频率稳定性。本文设计的太赫兹超表面吸波器具备高吸收率、大频率可调谐性、广角稳定性和低控制电压等优点,具有广泛的应用价值。     

光子晶体增强石墨烯THz吸收

研究了光子晶体表面石墨烯在应力赝磁场作用下的太赫兹(THz)吸收.由于应力赝磁场的存在使得石墨烯中电子出现朗道能级并对THz波呈现出一个较强的吸收.而光子晶体和石墨烯形成了表面微腔结构使得石墨烯对THz波的吸收比无光子晶体时增强了将近四倍.且可以通过改变应力赝磁场和间隔层厚度来调控石墨烯的THz吸收.     

基于石墨烯的太赫兹波散射可调谐超表面

设计了一个可调谐的太赫兹超表面,由在随机反射超表面基底中嵌入可偏置的双层石墨烯构成,可以实现对太赫兹波散射特性的动态调控.全波仿真试验结果证实了所预期的超表面散射可调性能.通过增大偏置电压提升石墨烯的费米能级,使得该超表面的太赫兹波散射样式从漫反射逐渐向镜面反射过渡,从而实现散射特性的连续调控,且该超表面具有对电磁波极化角度不敏感的特点.这些特性使得该超表面能很好地融合到变化的环境中,在太赫兹隐身方面具有潜在的应用价值.     

基于一维随机硅光栅的石墨烯表面等离子体安德森局域

提出了一种中红外波段下探究表面等离子体在石墨烯与硅光栅混合结构中传输安德森局域的方法.在石墨烯片下设计一维随机硅光栅结构来实现石墨烯表面等离子体随机硅光栅.通过调节石墨烯的费米能级来改变由硅光栅的无序引起的石墨烯表面等离子体安德森局域的共振波长.当费米能级是0.6eV时,局域石墨烯表面等离子体在随机硅光栅结构中的场强强度比在周期性硅光栅结构中大70倍.该结构有望应用于可调集成滤波器,宽带调制器以及等离子体传感器等.     

石墨烯和对称开口谐振环超材料中可调谐的双等离激元诱导透明现象

提出了由石墨烯和两对对称开口谐振环构成的等离激元诱导透明(PIT)超材料结构,该PIT超材料结构之间的耦合形式为暗-亮-暗模式.通过有限元方法模拟,观察到双PIT透明窗口,通过改变石墨烯的费米能级或者改变开口谐振环的几何参数来动态地调制PIT窗口.理论结果表明,当石墨烯与两对对称的开口谐振环之间的相互作用距离为0.5 μm、石墨烯费米能级为1.5 eV时,可得到最优的双透明窗口.双PIT效应在非线性器件、可调谐传感器、开关和慢光器件等方面有潜在的应用价值.     

一种宽频带超材料吸波体的设计及其特性

为了获得吸收率高、吸波带宽宽的超材料,设计了一种谐振超材料吸波体.该吸波体由多个开口圆环组成,采用商业软件CST Studio Suite 2009频域求解器计算了其在25～35 GHz波段内的S参量,并计算了其吸波率A(ω),在28.4 GHz处吸收率达到86％,带宽达到3.5 GHz.利用不同吸波频段的叠加效应,设计了一种谐振超材料吸波组合体,计算了在25～35 GHz波段的S参量,在29.7 GHz处吸波率达99.9％,吸波带宽达到3.1 GHz,吸收率明显增加.将GHz波段的结构缩小1 000倍,在THz波段同样可以达到高吸收,说明超材料吸波体可以通过对结构尺寸调节改变吸收波段.同时,对其阵列进行仿真计算,发现不同的排列方式仿真结果不同.由于各个谐振环之间的相互作用对吸收效果影响较大,吸收率减小.该吸波材料由金属组成,能灵活地对介电常量和磁导率进行调节,从而实现高吸收.     

基于石墨烯振幅可调的宽带类电磁诱导透明超材料设计

基于石墨烯的电控特性提出了一种由金属线谐振器和"H"型谐振器组成的宽带可调的类电磁诱导透明(类EIT)超材料结构.首先,利用CST Microwave Studio软件对该超材料结构的透射特性进行了仿真.该结构在1.05—1.46 THz内的透射窗由金属线谐振器的等离子谐振和"H"型谐振器的电感-电容谐振干涉相消引起,且暗模式谐振器的数量增多导致了透射窗带宽的增加.其次,仿真模拟了该结构在不同石墨烯费米能级下的透射特性.当石墨烯费米能级由0 eV逐渐增加到1.5 eV时,该结构透射窗在1.05—1.46 THz内的平均透射振幅由87%逐渐减少到25%,实现了宽带可调.同时,通过仿真模拟该结构在1.26 THz下的电场分布对其透射机理进行了分析,并实验制备了类EIT超材料结构样品,且利用太赫兹时域光谱对样品进行了透射性能测试,测试结果与仿真分析的趋势基本一致.     

基于石墨烯超材料的宽频带太赫兹吸收器

为了拓展太赫兹吸收器的相对吸收带宽,设计了一种基于石墨烯超材料的超薄、宽频带、可调谐的太赫兹吸收器,其由图案化石墨烯层、电介质层和金属反射底板层叠构成。仿真结果表明：该吸收器在4.48 THz频率处的吸收率为99.98%,通过调节石墨烯的化学势可使该频点处的吸收率变化至25.08%;同时,该吸收器表现出对入射波极化不敏感的吸收特性,且在太赫兹波倾斜入射的情况下仍能保持一定的宽频带吸收特性。在此基础上设计了基于三层图案化石墨烯的太赫兹吸收器,其可进一步拓展吸收频带宽度,仿真结果表明该吸收器在1.90～5.49 THz频率之间的吸收率高于90%,相对吸收带宽为97%。     

基于石墨烯和二氧化钒的太赫兹宽带可调谐超材料吸收器

太赫兹超材料吸收器作为一种重要的太赫兹功能器件,被广泛应用于生物医学传感、电磁隐身、军用雷达等多个领域.但这种传统的超材料吸收器结构具有可调谐性差、功能单一、性能指标不足等缺点,已经无法满足复杂多变的电磁环境的要求,因此可调谐超材料吸收器逐渐成为了太赫兹功能器件领域的研究热点.为实现超材料吸收器吸收特性的调谐,通常从调...     

Polarization insensitive, broadband terahertz metamaterial absorber

We present the simulation, implementation, and measurement of a polarization insensitive broadband resonant terahertz metamaterial absorber. By stacking metal-insulator layers with differing structural dimensions, three closely positioned resonant peaks are merged into one broadband absorption spectrum. Greater than 60% absorption is obtained across a frequency range of 1.86?THz where the central resonance frequency is 5?THz. The FWHM of the device is 48%, which is two and half times greater than the FWHM of a single layer structure. Such metamaterials are promising candidates as absorbing elements for bolometric terahertz imaging.     

一种宽频带超材料吸波体的设计及其特性

为了获得吸收率高、吸波带宽宽的超材料,设计了一种谐振超材料吸波体.该吸波体由多个开口圆环组成,采用商业软件CST Studio Suite 2009频域求解器计算了其在25~35 GHz波段内的S参量,并计算了其吸波率A(ω),在28.4 GHz处吸收率达到86%,带宽达到3.5 GHz.利用不同吸波频段的叠加效应,设计了一种谐振超材料吸波组合体,计算了在25~35 GHz波段的S参量,在29.7 GHz处吸波率达99.9%,吸波带宽达到3.1 GHz,吸收率明显增加.将GHz波段的结构缩小1 000倍,在THz波段同样可以达到高吸收,说明超材料吸波体可以通过对结构尺寸调节改变吸收波段.同时,对其阵列进行仿真计算,发现不同的排列方式仿真结果不同.由于各个谐振环之间的相互作用对吸收效果影响较大,吸收率减小.该吸波材料由金属组成,能灵活地对介电常量和磁导率进行调节,从而实现高吸收.     

Actively tunable dual-broadband graphene-based terahertz metamaterial absorber

A tunable metamaterial absorber (MA) with dual-broadband and high absorption properties at terahertz (THz) frequencies is designed in this work. The MA consists of a periodic array of flower-like monolayer graphene patterns at top, a SiO₂ dielectric spacer in middle, and a gold ground plane at the bottom. The simulation results demonstrate that the designed MA has two wide absorption bands with an absorption of over 90% in frequency ranges of 0.68 THz-1.63 THz and 3.34 THz-4.08 THz, and the corresponding relative bandwidths reach 82.3% and 20%, respectively. The peak absorptivity of the absorber can be dynamically controlled from less than 10% to nearly 100% by adjusting the graphene chemical potential from 0 eV to 0.9 eV. Furthermore, the designed absorber is polarization-insensitive and has good robustness to incident angles. Such a high-performance MA has broad application prospects in THz imaging, modulating, filtering, etc.     

Polarization insensitive terahertz metamaterial absorber

We present the simulation, implementation, and measurement of a polarization insensitive resonant metamaterial absorber in the terahertz region. The device consists of a metal/dielectric-spacer/metal structure allowing us to maximize absorption by varying the dielectric material and thickness and, hence, the effective electrical permittivity and magnetic permeability. Experimental absorption of 77% and 65% at 2.12 THz (in the operating frequency range of terahertz quantum cascade lasers) is observed for a spacer of polyimide or silicon dioxide respectively. These metamaterials are promising candidates as absorbing elements for thermally based terahertz imaging.     

Microelectromechanical systems bimaterial terahertz sensor with integrated metamaterial absorber

This Letter describes the fabrication of a microelectromechanical systems (MEMS) bimaterial terahertz (THz) sensor operating at 3.8 THz. The incident THz radiation is absorbed by a metamaterial structure integrated with the bimaterial. The absorber was designed with a resonant frequency matching the quantum cascade laser illumination source while simultaneously providing structural support, desired thermomechanical properties and optical readout access. Measurement showed that the fabricated absorber has nearly 90% absorption at 3.8 THz. A responsivity of 0.1°/μW and a time constant of 14 ms were observed. The use of metamaterial absorbers allows for tuning the sensor response to the desired frequency to achieve high sensitivity for potential THz imaging applications.     

基于圆台结构的超宽带极化不敏感太赫兹吸收器

本文提出一种基于圆台形吸收单元的超宽带、极化不敏感的超材料太赫兹吸收器. 该超材料吸收器采用金属薄膜金和介质层二氧化硅交替叠加的多层结构. 采用商业软件CST Studio Suite 2009时域求解器计算了其在0–10 THz波段内的吸收率A（ω）,在2–10 THz之间实现了对入射太赫兹波的超宽频带强吸收. 仿真结果表明,由于其圆台形单元结构,在器件垂直方向上形成一系列不同尺寸的微型吸收器,产生了吸收频点相连的多频吸收峰. 利用不同吸收峰的耦合叠加效应,获得超过8 THz的超宽带太赫兹波吸收,吸收强度达到92.3%以上. 这一结构具有超宽带强吸收,360°极化不敏感以及易于加工等优越特性,因而在太赫兹波探测器、光谱成像以及隐身技术方面具有潜在的应用. 关键词： 太赫兹波 超材料吸收器 圆台结构 超宽带     

Planar terahertz metamaterial with three-resonant frequencies

In this paper, we study a three-resonant metamaterial with the combination of dual-resonant and single-resonant metamaterials. We present a new method to design multi-resonant metamaterial, which has a smaller dimension than general symmetric and asymmetric multi-resonant metamaterials. Theoretical and experimental results show that the structure has three distinct absorption frequencies centering around 0.29 THz, 0.46 THz, and 0.92 THz, and that each of them corresponds to a different resonant mode. Due to the good separation of the different resonances, this design provides a unique and effective method to construct multiband terahertz devices.     

Polarization-Independent Broadband Optical Regime Metamaterial Absorber for Solar Harvesting: A Numerical Approach

In this article, a broadband metamaterial (MTM) absorber is proposed that exhibits near-unity absorption in the terahertz regime. The proposed metamaterial absorber was initiated on a quartz (fused) substrate, whereas the resonator and backplane are constructed with tungsten. The resonator is designed with a square ring loaded with a face-to-face E structure at the center. It also consists of diagonally extended arrow-like shapes loaded from the corners and a concave-shaped structure extended from the middle of the square ring. Near-perfect absorption is observed at the frequencies of 465.2 THz, 585.2 THz, 648.8 THz, and 762.8 THz with absorption peaks of 99.8%, 99.9%, 99.92%, and 99.92%, respectively. Moreover, it exhibits broadband absorption properties above 90% absorption with bandwidths 20.4 THz, 80.8 THz, 41.6 THz, and 90 THz, respectively, at these resonance frequencies. Due to its symmetrical structure, it shows polarization-insensitivity behavior up to 90° with maximum absorption greater than 90% both in transverse (TE) and transverse magnetic (TM) modes. It also exhibits insensitivity to changes of incident angle from 0°–45°. Metamaterial properties of the proposed absorber are also analyzed, showing single negative behavior. Absorber property has been examined through surface current and equivalent circuit electric and magnetic field analysis. The effect of the cross-polarization is negligible and is verified through simulation. Due to its large bandwidth, polarization-insensitive behavior, and low PCR, the proposed MTM absorber can be incorporated into photovoltaic devices as a solar-energy harvester.