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.     

Broad band metamaterial absorber based on wheel resonators with lumped elements for microwave energy harvesting

A new metamaterial absorber structure is designed and characterized both numerically and experimentally for microwave energy harvesting applications. The proposed structure includes four wheel resonators with different dimensions, from which the overall response of the structure can then be obtained by summing all the overlapping frequency responses corresponding to each dimension. The essential operation frequency range of the wheels is selected in such a way that the energy used in wireless communications and found within the environment that we live is absorbed. The dimensions are obtained using parametric study and genetic algorithm to realize wideband absorption response. When the simulation and measurement results are taken into account, it is observed that the metamaterial absorber based harvester has potential to absorb and convert microwave energy with an absorption ratio lying within the range of 80 and 99% for the frequency band of 3–5.9 and 7.3–8 GHz. The conversion efficiency of the structure as a harvester is found to be greater than 0.8 in the interval of 2–5 GHz. Furthermore, the incident angle and polarization dependence of the wheel resonator based metamaterial absorber and harvester is also investigated and it is observed that the structure has both polarization and incident angle independent frequency response with good absorption characteristics in the entire working frequency band. Hence, the suggested design having good absorption, polarization and angle independent characteristics with wide bandwidth is a potential candidate for future energy harvester using wireless communication frequency band.     

低雷达散射截面的超薄宽带完美吸波屏设计研究

提出了一种基于PMA单元结构的超薄宽带完美吸波屏设计方法. 该方法将多层拓展带宽的技术与单层多谐振方法有机结合, 实现带宽拓展的同时, 保持了完美吸波屏结构简单、无集总元件的特点, 易于实际加工和应用. 以双层三谐振超薄宽带完美吸波屏为例, 结合其等效电路, 理论上验证了所设计吸波屏的吸波机理, 同时验证了方法的有效性. 仿真分析该吸波屏具有低雷达散射截面、极化不敏感和宽入射角的特征. 仿真和实测结果表明: 该吸波屏在厚度为0.01 λ的条件下, 具有14.1%的半波功率带宽;-3 dBsm的雷达散射截面缩减带宽为18.9%, 在法线方向的最大缩减量为23 dBsm, 在法向±40°内具有较好的雷达散射截面减缩效果. 关键词： 完美吸波屏 宽带 雷达散射截面 等效电路     

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.     

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.     

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.     

Nearly Perfect Absorbers Operating Associated with Fano Resonance in the Infrared Range

We fabricate a three-layer metamaterial of metal patterns/dielectric/metal films.The optical properties associated with Fano resonance of the metamaterials are investigated experimentally and theoretically.The results indicate that the introduction of Fano resonance due to symmetry breaking leads to a much wider absorption range.Furthermore,the amplitude and phase of reflection can be modulated effectively by adjusting various free parameters using the proposed structure.     

Optical metamaterial absorber based on leaf-shaped cells

We present the model of an infrared metamaterial absorber composed of metallic leaf-shaped cells, dielectric substrate, and continuous metallic film. Numerical simulation confirms an absorptivity of 99.3% at the infrared frequency of 126.7 THz with this metamaterial model. The proposed metamaterial absorber could be fabricated with an electrochemical deposition technique. Our simulated results show the absorption feature of this metamaterial absorber could be well manipulated with different incident angles and radiation modes. The optical metamaterial absorber proposed in this paper has potential applications such as infrared imaging devices, thermal bolometers, wavelength-selective radiators, and optical bistable switches.     

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.     

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     

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     

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.     

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.     

Nanoparticle using parallel split rings and implementation of chain for creating Fano resonance with polarization independence for energy harvesting in mid-infrared

In optical devices, the polarization of the incident wave affects the Nano particle characteristics. Therefore, designing a polarization-independent device is significant in the process of designing optical structures. On the other hand, the concept of Fano resonance and dark mode has been utilized for achieving more energy enhancement. In this paper, we have developed a symmetrical Nano antenna by employing Fano resonance, which is independent of the incident wave polarization. The proposed Nano antenna is modified in mid infrared regime for biosensing and energy harvesting applications. The designed metamaterial antenna is made by Nano split ring resonators with etched capacitive gaps, which are utilized for concentrating energy. The introduced Nano antenna has a bright and dark mode with a weak enhancement of electric field. The effect of the incident wave polarization is investigated at wave incident angles between 0° and 45° to illustrate the independency of the polarization due to the symmetrical shape of the Nano antenna. In order to trigger the dark mode and enhance the electric field, a Nano chain is incorporated in the final structure. This arrangement has led to increasing of electric field drastically. Furthermore, the figure of merit has been calculated as an advantageous factor in sensing the surrounding materials with various refractive indices. Our findings illustrated that the chain arrangement has caused a peak in the linear form of the extinction cross section of the Nano antenna. This in turn has resulted in the appearance of Fano resonance with no impact on the resonance frequency that has been originally adjusted by capacitive gaps and inductive strips.     

Solar broadband metamaterial perfect absorber based on dielectric resonant structure of Ge cone array and InAs film

The broadband metamaterial perfect absorber has been extensively studied due to its excellent characteristics and promising application prospect. In this work a solar broadband metamaterial perfect absorber is proposed based on the structure of the germanium (Ge) cone array and the indium arsenide (InAs) dielectric film on the gold (Au) substrate. The results show that the absorption covers the whole ultraviolet-visible and near-infrared range. For the case of A > 99%, the absorption bandwidth reaches up to 1230 nm with a wavelength range varied from 200 nm to 1430 nm. The proposed absorber is able to absorb more than 98.7% of the solar energy in a solar spectrum from 200 nm to 3000 nm. The electromagnetic dipole resonance and the high-order modes of the Ge cone couple strongly to the incident optical field, which introduces a strong coupling with the solar radiation and produces an ultra-broadband absorption. The absorption spectrum can be feasibly manipulated via tuning the structural parameters, and the polarization insensitivity performance is particularly excellent. The proposed absorber can possess wide applications in active photoelectric effects, thermion modulators, and photoelectric detectors.     

Magnetic medium broadband metamaterial absorber based on the coupling resonance mechanism

In this paper, we present a design, simulation and experimental measurement of a metamaterial absorber (MMA) in the microwave regime. The proposed MMA structure consists of periodic cross electric resonators separated from the ground metal plane using a magnetic composite layer. The broadband absorption can be ascribed to the periodic cross electric resonators. The anti-parallel currents are observed at the peak frequency on the surface of the MMA and the ground metal plane, respectively, and thus the coupled resonance magnetic field occurs in the magnetic medium resulting in the magnetic loss. The new absorption peak located at 2.8 GHz broadens the whole absorption spectrum. The frequency of this peck is lower than that of the cross resonator of 3.7 GHz, suggesting the distinguish resonance mechanism: the absorbing properties are ascribed to the phase cancellation, Ohmic loss, dielectric loss at the end of the cross pattern, and the magnetic loss caused by the above mentioned coupled magnetic field. The obvious absorption peak at 2.8 GHz is also observed experimentally verifying the simulation result. All these results indicate the proposed MMA structure is promising for microwave absorbing application.     

Low-frequency and broadband metamaterial absorber based on lumped elements: design,characterization and experiment

In this paper, we propose and experimentally validate a low-frequency metamaterial absorber (MMA) based on lumped elements with broadband stronger absorptivity in the microwave regime. Compared with the electric resonator structure MMA, the composite MMA (CMMA) loaded with lumped elements has stronger absorptivity and nearly impedance-matched to the free space in a broadband frequency range. The simulated voltage in lumped elements and the absorbance under different substrate loss conditions indicate that incident electromagnetic wave energy is mainly transformed to electric energy in the absorption band with high efficiency and subsequently consumed by lumped resistors. Simulated surface current and power loss density distributions further clarify the mechanism underlying observed absorption. The CMMA also shows a polarization-insensitive and wide-angle strong absorption. Finally, we fabricate and measure the MMA and CMMA samples. The CMMA yields below ?10 dB reflectance from 2.85 to 5.31 GHz in the experiment, and the relative bandwidth is about 60.3 %. This low-frequency microwave absorber has potential applications in many martial fields.     

Simulation-based analysis of performance parameters of microstrip antennas with criss-cross metamaterial-based artificial substrate

In this paper, we present the design of a metamaterial-based microstrip patch antenna, optimized for bandwidth and multiple frequency operations. A criss-cross structure has been proposed, this shape has been inspired from the famous Jerusalem cross. The theory and design formulas to calculate various parameters of the proposed antenna have been presented. Design starts with the analysis of the proposed unit cell structure, and validating the response using software– HFSS Version 13, to obtain negative response of ε and μ– metamaterial. Following this, a metamaterial-based-microstrip-patch-antenna is designed. A detailed comparative study is conducted exploring the response of the designed patch made of metamaterial and that of the conventional patch. Finally, antenna parameters such as gain, bandwidth, radiation pattern, and multiple frequency responses are investigated and optimised for the same and present in table and response graphs. It is also observed that the physical dimension of the metamaterial-based patch antenna is smaller compared to its conventional counterpart operating at the same fundamental frequency. The challenging part was to develop metamaterial based on some signature structures and techniques that would offer advantage in terms of BW and multiple frequency operation, which is demonstrated in this paper. The unique shape proposed in this paper gives improvement in bandwidth without reducing the gain of the antenna.     

Fano resonance sensing based on coupled sub-wavelength dielectric grating and periodic photonic crystal

Based on the diffraction effect of sub-wavelength dielectric grating and the optical property of periodic photonic crystal, a hybrid structure of sub-wavelength grating all-dielectric multilayer thin film containing periodic photonic crystal is proposed. The transmission property of the structure is simulated by finite element method (FEM). The result shows that the discrete state generated by the sub-wavelength waveguide grating will be coupled with the continuous state generated by the photonic crystal cavity and the Fano resonance can be formed. The Fano resonance sensing model based on structural parameters and resonance wavelength are established, the influence of structural parameters on the Fano resonance spectral curve is quantitatively analyzed by numerical simulations, and the dynamic detection of the refractive index of samples is realized. The above structure can realize the optical refractive index sensing with high figure of merit (FOM) value and provide an effective theoretical reference for the formation of Fano resonance in the all-dielectric hybrid structure.     

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.