Extremely-broad band metamaterial absorber for solar energy harvesting based on star shaped resonator

A new metamaterial absorber (MA) is investigated and shown numerically for solar energy harvesting for future solar cell applications. The structure consists of two metals and one dielectric layer having different thicknesses. Owing to this combination, the structure exhibits plasmonic resonance characteristics. In the entire spectrum of visible frequency region, the obtained results show that investigated structure has perfect absorptivity which is above 91.8%. Proposed structure also has 99.87% absorption at 613.94 THz and 99% absorption between 548 and 669 THz. The proposed structure also shows both polarization and angle independency for the entire visible region. The MA based solar cell proposes high absorption with an upper ratio of 90% in the widest range of visible spectrum comparing to the studies in literature. Hence, the proposed metamaterial absorber solar cells can be used for invisibility in entire spectrum of visible light. The absorption characteristics of the solar absorber are also investigated for infrared and ultraviolet region. The enhancement of absorption of the structure will provide new type of sensors in these frequency ranges.     

Efficient Integrated Graphene Photonics in the Visible and Near‐IR

Graphene photonics has emerged as a promising platform for providing desirable optical functionality. However, graphene's monolayer‐scale thickness fundamentally restricts the available light matter interaction, posing a critical design challenge for integrated devices, particularly in wavelength regimes where graphene plasmonics is untenable. While several plasmonic designs have been proposed to enhance graphene light interaction in these regimes, they suffer from substantial insertion loss due to metal absorption. Here we report a non‐resonant metamaterial‐based waveguide platform to overcome the design bottleneck associated with graphene device. Such metamaterial structure enables low insertion loss even though metal is being utilized. By examining waveguide dispersion characteristics via closed‐form analysis, it is demonstrated that the metamaterial approach can provide optimized optical field that overlaps with the graphene monolayer. This enables graphene‐based integrated components with superior optical performance. Specifically, the metamaterial‐assisted graphene modulator can provide 5‐fold improvement in extinction ratio compared to Si nanowire, while reducing insertion loss by one order magnitude compared to plasmonic structures. Such a waveguide configuration thus allows one to maximize the optical potential that graphene holds in the telecom and visible regimes.     

An ultra-broadband metamaterial absorber based on the hybrid materials in the visible region

In this paper, an ultra-broadband metamaterial absorber is successfully designed in the visible region. The structure of the absorber is just obtained by the two-dimensional plane structure which rotate 90° along x-axis. Furthermore, the formation of the structure for the hybrid materials is based on the four U-shaped structure of the metal titanium is embedded in the semiconductor (indium antimonide). The simulated results show that the proposed metamaterial absorber can achieve an ultra-broadband absorption with greater than 90% from 252.2 to 822.3 THz, and the relative absorption bandwidth gets to 106.1%. Finally, the simulated electric field, surface current and power loss density distributions further illustrate the absorption mechanism of the metamaterial absorber. And we believe the metamaterial absorber will have many potential applications in energy harvesting and stealth devices.     

Nearly perfect metamaterial plasmonic absorbers for solar energy applications

In this study, two different approaches for the design of broadband polarization-independent wide-angle metamaterial plasmonic absorbers (MPA) are presented. The proposed MPAs are made of periodic arrays of Nickel (Ni) or Wolfram (W) cubes. The top surfaces of the cubes are texturized using silicon dioxide (SiO₂). The proposed PMAs with two different optimized textures experience plasmonic resonance characteristics that enable near unity visible light absorption. The parametric studies carried on the proposed MPAs with the aid of 3D-FDTD method results in wide-angle near perfect absorption characteristic that is >?0.96 for all visible regimes. Additionally, the obtained results show almost perfect absorption of above 99% over the frequency ranges extending from?~?458 to?~?525 and?~?489 to?~?665 THz. Besides, numerical results demonstrate that the proposed PMAs also exhibit both polarization and angle independency for the whole visible regime. Further, the absorption characteristics of proposed MPAs near the infrared and ultraviolet regimes are investigated.     

Broad-band polarization-independent metamaterial absorber for solar energy harvesting applications

A novel broad-band polarization-independent with wide-angle metamaterial absorber(MA) is investigated and demonstrated for solar energy harvesting applications. The proposed MA is composed of two metal layers which have different thickness and a dielectric layer which is sandwiched between these metal layers. By this combination, the proposed MA indicates plasmonic resonance characteristic. Numeric results show that proposed MA has perfect absorption characteristic which is above 88.28% with wide-angle for all visible region. It shows almost perfect absorption of 98.4% at the resonance frequency of 621.76 THz and has also 90% absorption between frequencies of 445 THz and 770 THz which is nearly all visible light region. Besides, numerical results validate that the proposed MA could achieve very high absorption at wide-angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves.. The proposed MA and its variations enable for solar cell applications due to have upper ratio of 90% in the widest range of visible spectrum comparing to the studies in literature. In order to show additional features of the proposed structure, parametric studies are realized and discussed. Furthermore, the absorption characteristic of proposed MA is investigated for infrared and ultraviolet region. The enhancement of absorption of the structure will provide new type of sensors in these frequency ranges.     

基于电阻型频率选择表面的低频宽带超材料吸波体的设计

基于电阻型频率选择表面(Resistance Frequency Selective Surface, RFSS) 设计了一种低频宽带、 极化不敏感和宽入射角特性的超材料吸波体. 该吸波体的基本单元由开槽十字型平面超材料(Cave Cross Planar Metamaterial, CCPM)、 RFSS、 电介质基板和金属背板组成. 采用FDTD方法数值模拟得到的结果表明: 相比于单纯的CCPM吸波体、 RFSS吸波体, CCPM和RFSS复合结构吸波体低频吸收特性得到极大改善, 在整个1-5 GHz频率范围内, 吸收率大于80%, 吸收峰值达到98%以上. 数值模拟得到的不同极化角和不同入射角下的吸收率表明: 该复合结构吸波体具有极化不敏感和宽角度吸收特性.     

基于电磁谐振的极化无关透射吸收超材料吸波体

仿真并实验验证了基于电磁谐振的极化无关透射吸收超材料吸波体, 该吸波体可以实现低频透射和高频吸收.实验测试结果表明, 该吸波体在6.77 GHz 吸收率峰值为83.6%, 半功率带宽为4.3%, 实现窄带强吸收.为进一步拓展该谐振型超材料吸波体的吸收带宽, 利用其低频透射特性, 将两个工作于不同频段的吸波体叠加在一起, 测试结果表明, 复合后超材料吸波体的半功率带宽可以增大到10.9%, 吸收率也略有增强. 该超材料吸波体设计简单, 具有较强的实用性和应用前景. 关键词： 极化无关 透射吸收 超材料吸波体     

An Infrared Metamaterial Broadband Absorber Based on a Simple Titanium Disk with High Absorption and a Tunable Spectral Absorption Band

A metamaterial absorber is proposed that functions in the medium- (3–5 µm) and long-wavelength (8–12 µm) infrared (medium-wavelength infrared, MWIR, and long-wavelength infrared, LWIR, respectively) regions. The proposed design, which consists of periodic cells, can be tuned to achieve single-band or dual-band light absorption by changing the periodicity of the structure. Each cell forming the metamaterial absorber consists of a bottom metal plate (Al), a top metal disk (Ti), and an intermediate dielectric medium (Si or ZnS) in which a metal disk (Ti) is embedded. For a period of 0.85 µm, the absorber achieves broadband absorption in the LWIR region, with an average absorption of 92.1%. Further, the absorber shows acceptable tolerance to irradiation at oblique incidence. For a period of 2 µm, a peak absorption of 99.05% is achieved in the MWIR region, thereby providing dual-band absorption. Tuning the periodicity of the structure enhances the localized surface plasmon resonance, with the absorption mechanism explained by establishing an equivalent parallel LC circuit. The absorption properties demonstrated by the proposed metamaterial absorber are promising for thermal imaging and infrared spectroscopy.     

Perfect metamaterial absorber design for solar cell applications

A new perfect metamaterial absorber based on metal-dielectric layer combination is designed and investigated to be used in solar cell application. The designed structure is particularly presented in the range of solar spectrum in order to utilize the solar energy effectively. Parametric studies with respect to the dimensions of the structure are carried out to characterize the absorber. According to the results, it is found that the metamaterial absorber has 99.99% absorption at 403.5 THz. In addition, the fractional bandwidth (FBW) of the absorption region is calculated and 22.2% FBW is obtained. Moreover the simulation results showed that the proposed design is also polarization and incident angle insensitive. As a result, the proposed metamaterial absorber provides perfect absorption for visible and near infrared frequency ranges and can be used for the realization of more efficient new solar cells.     

基于石墨烯互补超表面的可调谐太赫兹吸波体

通过在石墨烯超表面设计周期性切条,实现了基于石墨烯互补超表面的可调谐太赫兹吸波体.通过改变外加电压来改变石墨烯的费米能级,吸波体实现频率可调谐特性.研究了石墨烯费米能级、结构尺寸对超材料吸波体吸收特性的影响,并利用多重反射理论研究了其物理机理并且证明了模拟方法的可行性.研究结果表明:当石墨烯费米能级取0.6 eV,基底厚度13μm,石墨烯上切条长宽分别为2.9μm,0.1μm时,吸波体在1.865 THz可以实现99.9%的完美吸收;石墨烯费米能级从0.4 eV增大到0.9 eV,吸波体共振频率从1.596 THz蓝移到2.168 THz,且伴随共振吸收率的改变,吸收率在0.6 eV时达到最大;通过改变费米能级实现的最大吸收率调制度达84.55%.     

基于二氧化钒宽、窄带可切换的双功能超材料吸收器研究

本文提出了一种宽、窄带可切换的双功能超材料吸收器.在超材料吸收器的结构中,引入了相变材料二氧化钒(VO2),仅利用单个可切换超表面就能实现不同的功能,其不同功能之间的相互转换通过VO2绝缘态和金属态之间的可逆相变特性实现.当VO2处于金属态时,设计的结构可以看作一个超材料宽带吸收器.仿真结果表明,在1.55THz至2....     

基于树枝结构单元的超材料宽带微波吸收器

本文设计并制作了一种基于树枝结构单元的超材料宽带微波吸收器.该超材料吸收器采用夹层结构,由按六边形密集排布的金属树枝阵列、双层介质基板和金属薄膜组成.通过调节树枝单元的几何参数和金属树枝阵列的排布方式,可以出现三个吸收峰,实现三频工作.通过调节三个吸收峰工作的频率形成宽频吸收,采用夹层结构提高吸收效率,从而对垂直入射到超材料表面的微波实现高吸收.实验表明吸收器的反射曲线从9.79 GHz到11.72 GHz出现了反射率小于10%的较宽吸收带,透射曲线恒等于0,吸收率大于90%的带宽为1.93 GHz.这种 关键词： 树枝状结构 夹层结构 吸收效率 吸收带宽     

基于超材料的偏振不敏感太赫兹宽带吸波体设计

本文设计了一种基于超材料的偏振不敏感太赫兹宽带吸波体.吸波体包含两层金属和一层中间介质,表面金属层每一个周期单元由五种尺寸接近的金属块按照相邻不同的规律排列成5×5的方形阵列.各种尺寸金属块分别产生单峰谐振吸收,五个谐振吸收峰相互靠近从而产生宽带吸收.通过研究吸波体表面电流和电场z分量分布情况可知,入射太赫兹能量的吸收主要是由y方向上电场引起的电偶极子振荡和z方向上磁场引起的磁极化产生,而且金属层的欧姆损耗起主要作用.仿真结果表明,吸波体吸收率在80%以上的带宽约为1.2 THz,最高吸收率可达98.7%,半峰全宽(FWHM)为1.6 THz,该宽带吸波体的厚度约为中心波长的二十分之一,对偏振方向不敏感,且能实现大角度吸收,在太赫兹频段的电磁隐身、测辐射热探测器以及宽带通信等领域有潜在的应用价值.     

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     

宽带超薄完美吸波体设计及在圆极化倾斜波束天线雷达散射截面缩减中的应用研究

为了缩减天线带内雷达散射截面(radar cross section, RCS), 在双频带完美吸波材料的基础上, 通过缩小两吸波率峰值之间的距离, 设计出了一种频带较宽的超薄完美吸波体.该吸波体由两层金属及其中间的有耗介质组成, 底面金属不刻蚀, 顶面由方形贴片和绕其四周的开口方环组成, 该结构具有低频点LC谐振和高频点偶极子谐振的特征.仿真和实验结果表明: 该吸波体具有极化不敏感和宽入射角的特征, 其在厚度小于0.01λ的条件下, 具有8.2%的半波功率相对带宽, 最大吸波率的峰值为91.6%和96.5%. 将吸波体用于圆极化的倾斜波束 (tilted beam, TB)天线, 仿真和测试结果表明: 该天线在保持增益不变的条件下, 不仅轴比得到改善, 有效带宽得到拓展, 且在5.5–6.5 GHz范围内TB天线的RCS缩减至少在3 dBsm以上, 在谐振频点处最大缩减幅度分别为11 dBsm和8 dBsm; 在两谐振点处鼻锥方向-36°–+36°范围内, TB天线的RCS缩减均有明显效果. 关键词： 超薄完美吸波体 TB天线 雷达散射截面 圆极化     

Wideband optical absorber based on plasmonic metamaterial cross structure

The optical absorber with Fano response is valuable for various applications such as solar cells or optical sensors. In this paper, we have modeled an optical plasmonic metamaterial absorber which contains a broken cross as an elementary cell along with four rectangular loads to improve the absorbance and achieve a Fano response within a wide bandwidth at 190–245 THz (25%). The bandwidth of the proposed structure is more than conventional metamaterial absorbers. The prototype absorber has a remarkable enhancement in the electric field in comparison with the simple cross model and the reflection value has reduced to ??47 dB. The parametric studies show how the gap capacitance controls the bandwidth, resonance frequency and the reflection value of the absorber, therefore we can consider this technique as a way to enhance the metamaterial absorber’s bandwidth. The proposed structure can be used as an optical refractive index sensor while the Fano line-shape provides a higher figure of merit (FOM) compared with many others. For this structure, the FOM has obtained as 10,660. The Finite Integration Technique with Perfect Boundary Approximation used for the simulation.     

Equivalent electromagnetic parameters for microwave metamaterial absorber using a new symmetry model

Transmission line theory uses the complex nature of permeability and permittivity of a conventional magnetic absorber to evaluate its absorption properties and mechanism. However, because there is no method to obtain the electromagnetic parameters of a metamaterial-absorber integrated layer(composed of a medium layer and a periodic metal array), this theory is seldom used to study the absorption properties of the metamaterial absorber. We propose a symmetry model to achieve an equivalent complex permittivity and permeability model for the integrated layer, which can be combined with the transmission line theory to calculate metamaterial absorption properties. The calculation results derived from both the transmission line theory and the high-frequency structure simulator are in good agreement. This method will be beneficial in practical investigations of the absorption mechanism of a metamaterial absorber.     

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...     

极化无关双向吸收超材料吸波体的仿真与实验验证

设计并制作出极化无关双向吸收超材料吸波体.仿真结果表明,该吸波体对斜入射横电极化和横磁极化电磁波具有较好的吸收效果,其强损耗主要来自介质基板的介电损耗.实验测试结果表明,该吸波体在11.1 GHz对垂直入射电磁波实现双向强吸收,吸收率分别为95.9％和90.8％.该吸波体厚度较薄,工作波长约为1/34.该超材料吸波体具有吸收率高、厚度薄、设计简单、易于加工等优点.