一种基于旋转调谐的超材料

数值仿真研究了一种可调谐的双开口谐振环(DSRR)超材料.在平行入射的电磁波激励下,这种DSRR单元可以在不同的频段分别表现出磁谐振和电谐振.当外加电场E与DSRR的双开口平行时,DSRR受激励得到的磁谐振和电谐振强度最大.随着DSRR超材料沿外加磁场H方向顺时针旋转,其磁谐振和电谐振频率基本保持不变,但谐振强度均发生显著下降,同时对应透射相位的突变也逐渐降低.提出的超材料调谐方法只需要简单地旋转材料,而不需要改变原有超材料单元的结构或者增加额外的激励场,极大地简化了可调谐超材料的制备及应用,在电磁开关、相位调制等方面具有潜在的应用.同时,这种简单的方法有希望应用于更高频段的超材料调谐,可以有效地拓展太赫兹频段和光频段超材料的实际应用.     

对电磁波极化不敏感超材料吸波体的研究

设计了一个在微波频段对极化不敏感的超材料吸波体。该超材料微观单元由4个互相垂直的电谐振环和短导线构成,这种结构克服了Landy提出的结构对电磁波极化敏感的缺点,对垂直极化和水平极化电磁波都有很好的吸收效果。采用数值仿真方法,在12-180Hz波段提取了这种超材料的S参数,计算了其吸波率。单层超材料吸波体在14GHz处达到吸波峰,吸波率达57．4％;多层组合吸波体在150Hz处吸波率峰值达到87．6％。     

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.     

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.     

太赫兹波段电磁超材料吸波器折射率传感特性

太赫兹超材料吸波器作为一类重要的超材料功能器件,除了可以实现对入射太赫兹波的完美吸收外,还可以作为折射率传感器实现对周围环境信息变化的捕捉与监测.通常从优化表面金属谐振单元结构和改变介质层材料和形态两个方面出发,改善太赫兹超材料吸波器的传感特性.为深入研究中间介质层对太赫兹超材料吸波器传感特性的影响,本文基于金属开口谐振环阵列设计实现了具有连续介质层、非连续介质层和微腔结构的3款太赫兹超材料吸波器,并对其传感特性与传感机理进行了深入研究.结果表明,为了提高太赫兹超材料吸波器的折射率灵敏度、最大探测范围等传感特性,除了可以选用相对介电常数较小的材料作为中间介质层外,还可以改变中间介质层的形态,进而减小中间介质层对谐振场的束缚,增强谐振场与被测分析物之间的耦合.与传统的具有连续介质层的太赫兹超材料吸波器相比,具有非连续介质层和微腔结构的超材料吸波器具有更优越的传感特性,可应用于对待测分析物的高灵敏度、快速检测,在未来的传感领域具有更加广阔的应用前景.     

准全向平板超材料吸波体的设计

本文设计了一种具有准全向吸波特性的平板超材料吸波体,其准全向吸波特性是由超材料吸波单元的双面吸波、极化不敏感和宽入射角实现的.理论分析和仿真结果表明:该吸波体在6.18 GHz的确有一个双面吸波的吸收点,且吸收率对极化角和入射角均不敏感.提取的等效阻抗表明可以调节超材料的电磁响应使其在吸收频率处与自由空间阻抗匹配来抑制反射.仿真的能量损耗分布表明:该吸波体对电磁波的吸收主要源于基板的介质损耗;采用两种不同介质基板的设计可使前吸波体与后吸波体的耦合度明显降低、抑制耦合所导致的传输.该吸波体可能在许多领域具有 关键词： 准全向吸波 双面吸波 极化不敏感 宽入射角     

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     

双层螺旋环超表面复合吸波体等效电路模型及微波损耗机制

针对超材料吸波频带窄的问题,采用金属螺旋环超表面与碳纤维吸波材料相复合的方式,设计了宽频高性能复合吸波体.研究发现,在碳纤维吸波材料中引入双层螺旋环超表面能显著增强吸收峰值和吸波带宽,且适当增加螺旋环初始线长和吸收层厚度有利于提高复合吸波体的吸波性能, 9.2—18.0 GHz频段的反射损耗均优于–10 dB (带宽达8.8 GHz),吸收峰值达–14.4 dB.利用S参数计算得到螺旋环-碳纤维复合吸波体的等效电磁参数和特征阻抗呈现多频点谐振特性,通过构建双层螺旋环超表面等效电路模型,定量计算了复合吸波体的电磁谐振频点,发现由等效电路模型获得的谐振频点计算值与仿真值基本相符,说明该复合吸波体多频点电磁谐振是宽频电磁损耗的主要机制.     

圆环结构人工电磁吸波材料的仿真与实验研究

提出了两种圆环型微波电谐振结构,这两种谐振结构分别与金属线进行适当的组合形成电磁耦合单元,对正入射的电磁波产生谐振响应并具有强烈的吸收作用.通过对两种耦合单元的电磁仿真和优化计算使其各自获得最佳的吸波性能.在微波段8—12 GHz利用自由空间法对这两种耦合结构的电磁特性(即反射系数S₁₁和透射系数S₂₁)进行实验测量,在10.7 GHz和10.07 GHz吸收率分别达到95%和98%以上. 关键词： 耦合单元 吸收率 阻抗匹配     

基于电磁谐振分离的宽带低雷达截面超材料吸波体

基于超材料的电磁谐振特性, 设计、制作了一种极化无关的宽带低雷达散射截面 (radar cross section, RCS)超材料吸波体. 通过场分布和反演法分析了其吸波机理, 利用波导法和空间波法测试了其吸波率和RCS特性. 理论分析表明: 在平面波的作用下, 该吸波体对某一吸波频率在不同的位置分别提供电谐振和磁谐振, 对不同的吸波频率, 利用不同的介质层提供主要的能量损耗, 从而有效减弱了电磁耦合, 保证了宽频带的强吸收特性. 实验结果表明: 设计的三层结构吸波体吸波率达90%以上的带宽是单层结构的4.25倍, RCS减缩10 dB以上的带宽为5.1%, 其单元尺寸为0.17λ, 厚度仅为0.015λ. 该吸波体的低RCS特性还具有极化无关、宽入射角的特点, 且通过改变吸波体的夹层结构可以实现工作带宽的灵活调节. 关键词： 超材料吸波体 雷达散射截面 宽带 电磁谐振     

Metamaterial absorbers realized in an X-band rectangular waveguide

In this paper,we demonstrate six types of metamaterial absorbers(MMAs) by measuring their absorptivities in an X-band(8-12 GHz) rectangular waveguide.Some of the MMAs have been demonstrated previously by using the free space measurement method,and the others are proposed firstly in this paper.The measured results show that all of the six MMAs exhibit high absorptivities above 98%,which have similar absorbing characteristics to those measured in the free space.The numerically obtained surface current densities for each MMA show that the absorbing mechanism is the same as that under the free space conditions.Such a demonstration method is superior to the conventional free space measurement method due to the small-scale test samples required,the simple measure device,and its low cost.Most importantly,the proposed method opens a way to enable MMAs to be used in microwave applications such as matched terminations.     

A simple design of ultra-broadband and polarization insensitive terahertz metamaterial absorber

Ultra-broadband metamaterial absorbers have attracted considerable attention due to their great prospect for practical applications. These absorbers are usually stacked by many (no. <20) different shaped or sized subunits in a unit cell, making it quite troublesome to be fabricated. Simple design for ultra-broadband absorber is urgently necessary. Herein, we propose a simple design of ultra-broadband and polarization insensitive terahertz metamaterial absorber based on a double-layered composite structure on a metallic board, and each layer consists of two sets of different sized square metallic plates. Greater than 90 % absorption is obtained across a frequency range of 0.85 THz with the central frequency around 1.60 THz. The relative absorption bandwidth of the device is greatly improved to 53.3 %, which is much larger than previous results. The mechanism of the ultra-broadband absorber is attributed to the overlapping of four closely resonance frequencies. The proposed metamaterial absorber has potential applications in detection, imaging and stealth technology.     

A pure dielectric metamaterial absorber with broadband and thin thickness based on a cross-hole array structure

A pure dielectric metamaterial absorber with broadband and thin thickness is proposed, whose structure is designed as a periodic cross-hole array. The pure dielectric metamaterial absorber with high permittivity is prepared by ceramic reinforced polymer composites. Compared with those with low permittivity, the absorber with high permittivity is more sensitive to structural parameters, which means that it is easier to optimize the equivalent electromagnetic parameters and achieve wide impedance matching by altering the size or shape of the unit cell. The optimized metamaterial absorber exhibits reflection loss below -10 dB in 7.93 GHz-35.76 GHz with a thickness of 3.5 mm, which shows favorable absorption properties under the oblique incidence of TE polarization (±45°). Whether it is a measured or simulated value, the strongest absorbing peak reaches below -45 dB, which exceeds that of most metamaterial absorbers. The distributions of power loss density and electric and magnetic fields are investigated to study the origin of their strong absorbing properties. Multiple resonance mechanisms are proposed to explain the phenomenon, including polarization relaxation of the dielectric and edge effects of the cross-hole array. This work overcomes the shortcomings of the narrow absorbing bandwidth of dielectrics. It demonstrates that the pure dielectric metamaterial absorber with high permittivity has great potential in the field of microwave absorption.     

Broadband and ultra-low reflection metamaterial absorber embedded with magnetic materials

In this study, we design, prepare and characterize a broadband, ultra-low reflectivity and incidence angle-insensitive metamaterial absorber. The design of this absorber not only provides a novel idea for the design of broadband absorbers, but also enhances the application prospects of metamaterial absorbers. By introducing FeSiAlp/epoxy magnetic composite and optimizing the structural parameters, the absorption performance of the metamaterial absorber has been significantly improved. The effective absorption bandwidth (bandwidth with reflectivity less than −10dB) is increased by 3.4 times from 2.19 GHz to 7.49 GHz, and the RL_min (minimum reflection loss) value reaches −38.31 dB at 17.83 GHz, that is the absorption rate reaches 99.99%. Meanwhile, the experimental results also verify the simulation design results. Therefore, the absorber not only plays the characteristics of strong absorption of metamaterial, but also absorbs the advantages of broadband of magnetic material.     

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.     

SU-8 based planar metamaterials with fourfold symmetry as selective terahertz absorbers

We report on the absorption properties of polarization-insensitive transmissive and reflective metamaterial absorbers based on two planar aluminium periodic structures and SU-8 epoxy resist. These absorbers were investigated using numerical simulation and experimental methods in the terahertz range (below 2 THz). SU-8 is a very promising organic material for dielectric layers in planar metamaterials, because its application simplifies the process of fabricating these structures and significantly reduces the fabrication time. The experimental absorption of the metamaterial absorbers has narrowband characteristics that were consistent with the numerical simulations. Power flow analysis in the transmissive metamaterial unit cell shows that the absorption in the terahertz range occurs primarily in the SU-8 layer of the absorber.     

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.     

对称折叠通道结构的低频通风吸声体*

为了消除或减少低频噪声,该文 提出了一种低频通风超材料吸声体,该吸声体由对称的折叠通道结构组成,具有深度亚波长、高通风空间占比和低频高效吸声的特性.通过传递矩阵方法、有限元模拟和四麦克风实验法,揭示了对称折叠通道结构通风吸声的物理机制.首先在理论上分析单个吸声体的通风吸声性能并进行了仿真模拟,在共振频率423 Hz附近,吸声系数大于0.9,通风空间占比高达40%.吸声单体的共振频率可通过改变折叠通道的长度来灵活调控,组合多个不同共振频率的吸声单体可以拓宽吸声体的有效吸声带宽.由四个吸声单体组合的通风吸声体可实现314－366 Hz频率范围内的高效声吸收(吸声系数大于0.8),且通风空间占比达到35%,而结构厚度仅为314 Hz时波长的1/10.该低频通风吸声体具有结构简单、结构强度高和容易制造等特点,在低频通风降噪领域有着潜在的应用前景．     

基于多阶等离激元谐振的超薄多频带超材料吸波体

本文设计了一种超薄螺旋结构超材料吸波体,其厚度(1.034 mm)约为其工作波长(4.81 GHz,6.59 GHz,9.16 GHz,12.69 GHz和13.71 GHz)的(1/60,1/44,1/32,1/23,1/21).仿真和实验结果表明,该吸波体在4.81 GHz,6.59 GHz,9.16 GHz,12.69 GHz和13.71 GHz处吸收率分别达到94.55%、99.89%、99.73%、99.26%和99.41%,实现了多频带强吸收.从表面电流和功率损耗密度两个方面分析了产生强吸收的原因,理论分析表明,多频带强吸收能在五个相邻频率处产生多阶局域表面等离激元谐振,螺旋结构之间强烈的电谐振使超材料结构单元产生强烈的吸收.该超材料吸波体设计简单、易于制作和应用,在电磁波吸收中具有应用价值.