Metamaterial absorber and extending absorbance bandwidth based on multi-cross resonators

In this paper, we report the design, simulation, and measurements of a broadband metamaterial absorber (MA) based on a periodic array of multi-layer cross-structure resonators. A perfect narrowband MA consists of cross-structure resonator, dielectric substrate, and continuous metal films, and the absorption frequency can be tunable by changing the geometrical parameters based on L-C resonance circuit theory. Furthermore, the absorption band of our design is effectively extended by simply stacking several such structural layers with different geometrical dimensions. Finally, the 4-layer cross-structure MA is only 2 mm, which can achieve a full width at half maximum (FWHM) bandwidth of 2 GHz by numerical simulations, and 90 % bandwidth of 1.9 GHz by experiments.     

吸收波长和吸收效率可控的超材料吸收器

为了使超材料完美吸收器(metamaterial perfect absorber,MPA)能够同时实现吸收效率和吸收波长的控制,本文提出利用二氧化钒(VO2)和石墨烯作为MPA的材料,通过对MPA的结构设计,在红外波段实现了高吸收,吸收效率最高可达99％.研究发现通过改变VO2的温度和石墨烯的化学势,可同时实现MPA...     

An intrinsic fiber ring laser based sensor with saturable absorber

A novel configuration of fiber ring laser acoustic sensor, which adopts single-mode fiber as sensing element, is proposed and demonstrated. Linewidth less than 1 kHz is achieved by introducing a segment of erbium-doped fiber in the reflecting arm as saturable absorber. A polarization independent unbalanced Michelson interrogation interferometer and phase generated carrier demodulation technique are adopted to recover signal. Experiments demonstrate that the phase sensitivity is 0.018 rad/nm in good linearity and equivalent minimum detect able length change reaches 19.1 pm.     

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     

一种基于金属开口谐振环和杆阵列的左手材料宽带吸收器

用数值仿真在微波X波段研究了金属开口谐振环和杆阵列这一最基本的谐振结构.通过合理的参数调节,这种结构在10.91GHz附近可以表现出高达98%的吸收率,并且半高峰宽达到3.5GHz.用散射参量提取法计算其有效电磁参数,发现在谐振频率附近其介电常数、磁导率和折射率的实部均为负值.相比于传统的左手材料,这种结构的电磁参数在谐振区域均具有较大的虚部,是形成高吸收率的根本原因.本文的左手材料吸收器在电磁加热、电磁隐身等领域具有许多潜在的应用.     

Broadband visible metamaterial absorber based on a three-dimensional structure

In this paper, a broadband metamaterial absorber is successfully designed by a three-dimensional structure. And the three-dimensional absorber is just obtained by a two-dimensional structure which rotates 90°along x-axis. The simulated results show that the absorption of the three-dimensional metamaterial absorber is much better than the two-dimensional absorber. Moreover, the absorber is polarization-sensitive for the incident electromagnetic waves due to the asymmetry of the structure. Compared with the Y-polarization wave, the proposed absorber can realize broadband absorption with greater than 90% from 355.6 to 737.7 THz for X-polarized wave. Finally, based on the analysis of the electric field and surface current distributions, it can demonstrate that the localized surface plasmons and dipoles resonances will play an important role in the broadband absorption. And we believe that the metamaterial absorber will have many potential applications in emitter and energy harvesting.     

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.     

Metamaterial beam scanning leaky-wave antenna based on quarter mode substrate integrated waveguide structure

In this paper, we first propose a metamaterial structure by etching the same two interdigital fingers on the upper ground of quarter mode substrate integrated waveguide(QMSIW). The simulated results show that the proposed QMSIWbased metamaterial has a continuous phase constant changing from negative to positive values within its passband. A periodic leaky-wave antenna(LWA), which consists of 11 QMSIW-based metamaterial unit cells, is designed, fabricated,and measured. The measured results show that the fabricated antenna achieves a continuous beam scanning property from backward-43° to forward +32° over an operating frequencyrange of 8.9 GHz–11.8 GHz with return loss better than 10 d B.The measured antenna gain keeps consistent with the variation of less than 2 d B over the operating frequency range with a maximum gain of 12 d B. Besides, the measured and simulated results are in good agreement with each other, indicating the significance and effectiveness of this method.     

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.     

Asymmetric chiral metamaterial circular polarizer based on four U-shaped split ring resonators

An asymmetric chiral metamaterial structure is constructed by using four double-layered U-shaped split ring resonators, which are each rotated by 90° with respect to their neighbors. The peculiarity of the suggested design is that the sizes of the electrically and magnetically excited rings are different, which allows for equalizing the orthogonal components of the electric field at the output interface with a 90° phase difference when the periodic structure is illuminated by an x-polarized wave. As a result, left-hand circular polarization and right-hand circular polarization are obtained in transmission at 5.1 GHz and 6.4 GHz, respectively. The experiment results are in good agreement with the numerical results.     

A dual-band polarization insensitive metamaterial absorber with split ring resonator

A dual-band polarization insensitive absorber has been proposed . Unlike the previous dual band absorber composed of composite structures, only one square metal ring with a slit at the middle of each side can be used to achieve the dual-band absorption. The calculated results show two distinct absorption peaks of 0.96 at 10 GHz and 0.99 at 20 GHz. In addition, the positions of the two peaks are strongly influenced by the width of the slit (g). More importantly, the absorptions of the two peaks keep higher than 0.9 while g changing. The dual-band absorber may have many potential applications in scientific and technological areas because of its excellent absorption characteristics and concise structure.     

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     

A note on a circular panel sound absorber with an elastic boundary condition

Panel sound absorbers are typically used to absorb low-frequency noise in concert halls, auditoriums, recording studios, and other architectural applications. These systems are composed of flexible panels mounted over an air space that can be either partly or completely filled with a porous material. In this paper, a theoretical model is derived for predicting the sound-absorption coefficient of a cylindrical low-frequency absorber made of a circular plate. The theory takes into account the mass, bending stiffness, damping loss and the elastic boundary condition of the circular plate. The effects of the stiffness of an air-back cavity and of partially adding a porous material into the cavity are also considered. It is observed that the low-frequency resonances of such a system are dependent upon the clamping condition, the width of the air-back cavity, and mechanical properties of the plate. There is good agreement between theoretical and experimental results.     

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     

Optical bistability in gaussian inhomogeneously broadened ring lasers with saturable absorber

The optical bistability (OB) in Gaussian inhomogeneously broadened ring lasers with saturable absorber (LSA) in both resonance and out-of-resonance is theoretically analyzed in the rate-equation approximation based on the dual two-level model. The OB effect may appear for appropriate sets of LSA control parameter values which can be displayed in phase diagrams. The characteristics of the OB curves as well as their stability behavior are analytically and numerically studied in detail. The influence of the control parameters, including detuning, are investigated and displayed in the figures. A brief comparison with the Lorentzian case is given as well. Paper submitted by authors in English April 20, 1999.     

一种基于十字镂空结构的低频超材料吸波体的设计与制备

设计了一种十字镂空的超材料结构,与传统的铁磁吸波材料相结合,实现了低频吸收频带的扩宽.仿真结果显示,吸波体在2-4 GHz范围可以实现-10 dB以下的吸收,相比于没有加载超材料的情况,吸收带宽扩展了0.5 GHz.实验结果在2.5-5.1 GHz范围内也显示了相似的吸收曲线,低于-9 dB的吸收频带有0.48 GHz的扩宽,扩展了23%.不同结构的能量损耗密度分布表明,相比于无镂空的十字结构,镂空十字结构可以增加磁场能量损耗,加强单元结构之间的耦合,降低超材料对传统吸波材料性能的破坏.探索了传统铁磁吸波材料厚度的变化对吸波体吸收性能的影响,发现由超材料引入的附加峰位置不随着吸波材料厚度的改变而明显地移动.根据这个结果,进一步设计了由两种超材料叠加组合而成的吸波体,仿真结果和实验结果均显示,在降低了1.1 mm铁磁吸波材料层厚度的情况下,使低频吸收带宽又扩展了0.9 GHz.     

Cavity soliton laser based on VCSEL with saturable absorber

We study theoretically a broad-area vertical cavity surface emitting laser (VCSEL) with a saturable absorber. We show numerically the presence of cavity solitons in the system: they exist as solitary structures formed through a modulationally unstable homogeneous lasing state that coexists with a background with zero intensity. Such a peculiar scenario endows the solitons with unique properties compared to cavity solitons in most previously studied optical systems. In particular, these solitons do not as such rely on a proper phase of the addressing pulses to be either created or deleted. We show that exciting and deleting the solitons depend crucially on whether a threshold in the soliton peak has been reached.     

Tuned mass absorber on a flexible structure

The classic design of a tuned mass absorber is based on a simple two-mass analogy in which the tuned mass is connected to the structural mass with a spring and a viscous damper. In a flexible multi-degree-of-freedom structure the tuned mass absorber is typically introduced to provide damping of a specific mode. The motion of the point of attachment of the tuned mass absorber to the structure has not only a contribution from the targeted mode, but also a background contribution from other non-resonant modes. Similarly, the force provided by the tuned mass absorber is distributed between the targeted mode and the background modes. It is demonstrated how this effect can be included via a non-dimensional dynamic background flexibility coefficient, extracted from a classic modal analysis for the particular frequency of the selected mode. An explicit calibration procedure is developed starting with the desired maximum amplification, from which the device damper, mass and stiffness are determined, accounting for the background flexibility. Examples demonstrate the influence of the flexibility effect and the efficiency of the proposed procedure.     

Flow structure of the entrance of a T-junction duct without/with a circular cylinder

The flow characteristics of the trailing edge of vertical vanes installed at the intersection of a T-junction duct were experimentally investigated using particle image velocimetry. The measured velocity field in the branch duct with/without single circular cylinder was studied under different cross velocities and velocity ratios. Additionally, the effect of the locations of cylinder on the flow field was discussed. The positive velocity region, the unsteady flow region and the trailing edge flow region of the vane, have been observed. The positive velocity region existed in almost one half of the measured area. As for the unsteady flow region, the unstable double-vortex structure transformed into a single-vortex structure as the velocity ratio increased. As for the trailing edge flow region of the vanes, the vortex streets could be visualised. Furthermore, the location of cylinder has revealed significant influence on the flow distributions in the trailing edge flow regions of the vanes. The flow structure without cylinder in the measured area is dependent on combinations of the cross velocity and velocity ratio, whereas that with cylinder is dependent on the velocity ratio. The vorticity fields were analysed in each region, and the velocity components revealed the cause of airflow trajectory.