极化控制的双波段宽带红外吸收器研究

红外吸收器在红外隐身、辐射制冷、红外探测、传感器等方面有重要的应用前景.一维光栅型吸收器由于其结构简单、易于加工的优势备受关注,然而其不足之处是频带很窄,且只对一种极化有效.本文提出了一种基于简单一维周期结构的双波段宽带吸收器,对横磁波和横电波都有效,且吸波频段随入射波的极化方式而改变.该结构的基本单元由八个梯度排列的子单元构成,每个子单元由两层金属-介质双层膜垂直层叠组成.全波仿真结果表明,在1.68—2μm波段,该结构对横磁波吸收超过90%,而对横电波吸收很小(小于6%);在3.8-3.9μm波段,该结构对横电波吸收超过90%,而对横磁波吸收很小(小于5%).另外,该结构具有宽角度吸收特性,当入射角增大到60°时仍然能够保持较高的吸收率和较宽的吸收频带.     

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.     

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...     

Ultra-thin broadband metamaterial absorber

The design, fabrication, and measurements of a broadband metamaterial absorber are reported. The proposed metamaterial absorber consists of circular metallic patches and a metallic ground plane separated by a dielectric layer. Increasing the number of metallic patches can broaden the frequency range when their resonances are closely packed together, thereby resulting in a broadband resonance. Experimental results show that the proposed absorber has high absorptivity, with a full width at half maximum absorption bandwidth of 2.8 GHz and the relative FWHM absorption bandwidth of 25.3?%. In addition, the absorber can operate at a wide range of incident angles under both transverse electric and transverse magnetic polarizations.     

Broadband,polarization-insensitive,and wide-angle microwave absorber based on resistive film

A simple design of broadband metamaterial absorber(MA) based on resistive film is numerically presented in this paper.The unit cell of this absorber is composed of crossed rectangular rings-shaped resistive film,dielectric substrate,and continuous metal film.The simulated results indicate that the absorber obtains a 12.82-GHz-wide absorption from about 4.75 GHz to 17.57 GHz with absorptivity over 90% at normal incidence.Distribution of surface power loss density is illustrated to understand the intrinsic absorption mechanism of the structure.The proposed structure can work at wide polarization angles and wide angles of incidence for both transverse electric(TE) and transverse magnetic(TM) waves.Finally,the multi-reflection interference theory is involved to analyze and explain the broadband absorption mechanism at both normal and oblique incidence.Moreover,the polarization-insensitive feature is also investigated by using the interference model.It is seen that the simulated and calculated absorption rates agree fairly well with each other for the absorber.     

Perfect metamaterial absorber based on a split-ring-cross resonator

In this paper, we present a polarization-insensitive metamaterial (MM) absorber which is composed of the dielectric substrate sandwiched with split-ring-cross resonator (SRCR) and continuous metal film. The MM absorber is not limited by the quarter-wavelength thickness and can achieve near-unity absorbance by properly assembling the sandwiched structure. Microwave experiments demonstrate the maximum absorptivity to be about 99% around 10.91 GHz for incident wave with different polarizations. The surface currents distributions of the resonance structure are discussed to look into the resonance mechanism. Importantly, our absorber is only 0.4 mm thick, and numerical simulations confirm that the MM absorber could achieve very high absorptivity at wide angles of incidence for both transverse electric (TE) wave and transverse magnetic (TM) wave. The sandwiched structure is also suitable for designing of a THz and even higher frequency MM absorber, and simulations demonstrate the absorption of 99% at 1.105 THz.     

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.     

Numerical study of metamaterial absorber and extending absorbance bandwidth based on multi-square patches

A simple design of metamaterial absorber (MA) was proposed based on a periodic array of metal patch at microwave frequencies. Our design could exhibit absorption of 99.9% confirmed by numerical simulation. Such high narrowband absorption which mainly based on strong electric and magnetic resonances overlapping in a certain frequency range and perfect impedance-matched (z = 1) to the free space. Numerical simulations demonstrate that the MA could achieve very high absorptivity at wide angles of incidence for both transverse electric (TE) wave and transverse magnetic (TM) wave. The absorption band of our device is effectively extended by patterning multi-square patches of different dimension elements with appropriate geometrical parameters in a co-planar. Finally, the composite MA is only 0.4 mm thick, with a maximum absorption of 99.8% at 15.8 GHz, and a full width at half maximum (FWHM) bandwidth of 2 GHz by numerical simulation, which may have potential applications in the detection of explosives and stealth.     

极薄宽角度平面超材料吸波体仿真与实验验证

仿真和实验验证了厚度极薄的平面结构超材料吸波体, 该吸波体采用加载交指电容的耶路撒冷十字结构, 通过增加单元间的耦合电容显著降低了其工作频率. 测试结果表明, 该超材料吸波体在1.58 GHz, 吸收率峰值为88.48%, 其厚度为2 mm, 约为1/95工作波长, 吸波体的单元尺寸为11 mm, 约为1/17工作波长. 此外, 通过金属通孔将耶路撒冷十字结构与金属底板相连接, 使其对斜入射横电和横磁极化电磁波具有宽角度吸收特性, 在60°时依然具有较高的吸收率, 且吸收峰频率几乎不发生偏移, 从而使其更具实用价值. 关键词： 极薄 宽角度 超材料吸波体     

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.     

Ultra-broadband absorber based on cascaded nanodisk arrays

An ultra-broadband perfect absorber consisting of cascaded nanodisk arrays is demonstrated by placing insulator-metal-insulator-metal nanodisks on insulator-metal film stacks. The absorber shows over 90% absorption in a wavelength range between 600 nm and 4000 nm under transverse magnetic (TM) polarization, with an average absorptivity of 91.5% and a relative absorption bandwidth of 147.8%. The analysis of the electric field and magnetic field show that the synergy of localized surface plasmons, propagating surface plasmons, and plasmonic resonant cavity modes leads to the ultra-broadband perfect absorption, which accords well with the results of impedance-matched analysis. The influences of structural parameters and different metal materials on absorption performance are discussed. Furthermore, the absorber is polarization-independent, and the absorption remains more than 90% at a wide incident angle up to 40° under TE polarization and TM polarization. The designed ultra-broadband absorber has promising prospects in photoelectric detection and imaging.     

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     

Analytical study of an active piezoelectric absorber on vibration attenuation of a plate

The attenuation of the transverse vibration of a plate, subjected to a harmonic force, is studied. This goal can be achieved by using an active dynamic absorber. The active absorber is made of a pair of piezoelectric sheets, attached to both sides of the plate, and closed electric circuits. One piece of the piezoelectric material provides a sensor for detecting the motion of the plate. Another piece serves as an active dynamic absorber. The equations of motion of the composite plate, including the plate and the piezoelectric material, and the circuit equations of the sensor and the absorber are derived. The displacements of the plate and the currents in the circuits are calculated. The active absorber can successfully attenuate the vibration. The numerical results show that the proposed active absorber can offer more reduction than that using a passive absorber while the absorber is designed to suppress the resonance of a particular vibration mode. Moreover, the active absorber can also reduce the displacements corresponding to other uncontrolled modes. The effects of altering various parameters of the active absorber are studied and discussed.     

基于宽边耦合螺旋结构的低频小型化极化不敏感超材料吸波体

设计、仿真并实验验证了基于宽边耦合螺旋结构的低频小型化超材料吸波体. 实验测试结果表明, 该超材料吸波体在1.39 GHz吸收率达到最大为98%, 其单元尺寸和总厚度均为6.8 mm, 约为1/32工作波长, 实现小型化窄带吸波. 由于吸波体中螺旋结构是旋转对称排列的, 因而其对垂直入射电磁波的极化方向是不敏感的. 此外, 该超材料吸波体对斜入射横电和横磁极化电磁波在60°时, 仍具有强吸收. 关键词： 超材料 吸波体 小型化     

缺陷组合嵌入VO2薄膜结构的可调太赫兹吸收器

提出一种多缺陷组合嵌入VO2薄膜结构的可调太赫兹吸收器,它由上表面金属图案层、基体和底层金属板三层结构组成,在上表面和基体之间嵌入二氧化钒介质.计算结果表明在f=4.08 THz和f=4.33 THz两频点吸收率分别为99.8%和99.9%.通过改变外界环境温度可控制二氧化钒相变,从而使两个频点吸收率从99.8%变化到1.0%.改变入射角和偏振态,计算结果表明在入射角0°-40°,吸收器在TE和TM两种极化波下吸收率都能在98%以上.该太赫兹波吸收器具有高吸收、动态调谐、极化不敏感等特性,本文所设计的可调太赫兹吸收器在太赫兹波相关领域,例如探测器、开关、动态调制器、隐身技术等方面具有很好的应用前景.     

An ultra-thin dual-band wide-angle polarization-insensitive metamaterial absorber with near-unity absorbance

In this paper, a dual-band metamaterial absorber (MMA) with wide-angle and polarization-insensitivity is proposed. The MMA consists of two copper layers with a layer of FR-4 between them. And its top layer consists of a cross-shaped resonator and a square ring resonator. The calculation result demonstrates that there are two distinct absorption peaks, whose absorptivity are 99.933% at 3.8441 GHz and 99.99% at 9.1094 GHz. And its thickness is only 1.34% of the wavelength of the lowest absorption frequency. The dual-band MMA shows polarization-insensitivity for normal incident wave and shows high absorptivity in a wide incident angle for both TE and TM polarization wave. In addition, we discuss the working mechanism. The influences of main parameters on the dual-band MMA's absorption are also analyzed. The proposed ultra-thin MMA has simple structure and high absorptivity, which has many potential applications, such as thermal radiometer, detection sensor, stealth technology.     

Design of Broadband Metamaterial Absorbers for Permittivity Sensitivity and Solar Cell Application

A broadband and ultra-thin absorber for solar cell application is designed. The absorber consists of three layers,and the difference is that the four split ring resonators made of metal gold are encrusted in the gallium arsenide(GaAs) plane in the top layer. The simulated results show that a perfect absorption in the region from 481.2 to 684.0 THz can be obtained for either transverse electric or magnetic polarization wave due to the coupling effect between the material of GaAs and gold. The metamaterial is ultra-thin, having the total thickness of56 nm, which is less than one-tenth resonance wavelength, and the absorption coefflcients at the three resonance wavelengths are above 90%. Moreover, the effective medium theory, electric field and surface current distributions are adopted to explain the physical mechanism of the absorption, and the permittivity sensing applications are also discussed. As a result, the proposed structure can be used in many areas, such as solar cell, sensors, and integrated photodetectors.     

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.     

Microwave metamaterial absorber for sensing applications

A metamaterial absorber (MA) based sensor is designed and analysed for various important applications including pressure, temperature, density, and humidity sensing. Material parameters, as well as equivalent circuit model have been extracted and explained. After obtaining a perfect absorption (PA) at around 6.46 GHz and 7.68 GHz, surface current distributions at resonance points have been explained. Since bandwidth and applicability to different sensor applications are important for metamaterial sensor applications, we have realized distinctive sensor demonstrations for pressure, temperature, moisture content and density and the obtained results have been compared with the current literature. The proposed structure uses the changes on the overall system resonance frequency which is caused by the sensor layer’s dielectric constant that varies depending on the electromagnetic behaviour of the sample placed in. This model can be adapted to be used in sensor applications including industrial, medical and agricultural products.     

On the acoustic properties of parallel arrangement of multiple micro-perforated panel absorbers with different cavity depths

The acoustic properties of a compound micro-perforated panel (MPP) absorber array are investigated. The absorber array consists of three parallel-arranged MPP absorbers with different cavity depths. A finite element procedure is used to simulate its acoustic behaviors under normal incidence. Experimental studies are carried out to verify the numerical simulations. Due to different reactance matching conditions in the absorber array, strong local resonance occurs and the corresponding local resonance absorption dominates. Compared with single MPP absorber, the absorber array requires lower acoustic resistance for good absorption performance, and the resonance frequencies shift due to inter-resonator interactions. The different acoustic resistance requirement is explained by considering the reduced effective perforation rate of the MPP in the absorber array. The performance of the absorber array varies with the sizes and spatial arrangement of the component absorbers. When the distance between component absorbers is larger than a quarter-wavelength, the above-mentioned parallel absorption mechanism diminishes. In the experimental study, the normal incidence absorption coefficients of a prototype MPP absorber array are tested. The measured results compare well with the numerical predictions. The experimental study also shows that although other absorption mechanisms may exist, dissipation by the MPP is dominant in the MPP absorber array.