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.     

基于集总元件的低频宽带超材料吸波体设计与实验研究

提出一种基于集总元件的超材料吸波体结构设计, 并进行了理论分析和实验验证. 仿真结果表明, 该吸波体在2.5 GHz到4.46 GHz的低频带内具有吸收率超过95%、半高宽达到70.4%的良好吸收特性. 反演计算得到的等效输入阻抗表明集总元件的加入可以使该结构在较宽的频率范围内有较好的阻抗匹配特性, 介质表面能量损耗分布的模拟计算结果说明能量主要损耗在了集总电阻中, 从而实现低频宽带的吸收特性. 制备了实验样品并用自由空间法进行测试, 测试结果与模拟结果符合得较好. 进一步的实验测试结果表明FR4基板的厚度对该吸波体的吸收特性有明显的调控作用, 且对于固定参数的结构存在最佳匹配厚度. 关键词： 集总元件 超材料吸波体 低频 宽带     

Broadband microwave absorption properties of polyurethane foam absorber optimized by sandwiched cross-shaped metamaterial

The effect of a sandwiched cross-shaped metamaterial absorber(CMMA) on microwave absorption properties of the double-layered polyurethane foam absorber(PUFA) is investigated. Combining with the sandwiched CMMA, the bandwidth of -10-dB reflection loss for PUFA is broadened from 7.4 GHz to 9.1 GHz, which is attributed to the overlap of two absorption peaks originating from CMMA and PUFA, respectively. The values of the two absorption peaks located at 10.15 GHz and 14.7 GHz are -38.44 dB and -40.91 dB, respectively. Additionally, distribution of surface current,electromagnetic field and power loss density are introduced to investigate the absorption mechanism of the CMMA. The electromagnetic field distribution of the double-layered PUFA and the three-layered hybrid absorber are comparatively analyzed to ascertain the influence of CMMA. The results show that the proposed hybrid absorber can be applied to the anti-electromagnetic interference and stealth technology.     

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.     

Broadband metamaterial absorber on a single-layer ultrathin substrate

In this article, a broadband metamaterial microwave absorber on a low-cost FR-4 Epoxy substrate is proposed. The unit cell of the absorber consists of a staircase shape metallic patch placed on the top of the metal-backed ultrathin dielectric substrate having a thickness of 1.9 mm (0.07 λ₀). The absorption of more than 90% is achieved with this proposed low profile single-layer microwave absorber throughout the operation band from 8.86 to 15.5 GHz. The performance is analyzed for different values of incident angle, polarization angle, substrate height, and dielectric constant. The surface current and the power loss density at the top and bottom planes at the two absorption peaks of 9.46 and 13.90 GHz are also analyzed to elaborate the absorption mechanism of the structure. Experimental result closely follows the simulated one. The broadband characteristics of the design with relative absorption bandwidth (RAB) of 54.51% at both TE and TM polarizations of incident wave for a wide incident angles makes it versatile for applications in the X and Ku bands of microwave frequencies. The proposed work is very compact (unit cell size: 0.22 λ₀) with ultrathin substrate height (0.07 λ₀) and giving RAB performance of 54.51% comparable with that of others. Thus with this single-layer low-cost substrate material a broadband absorber is achieved.     

宽带透射吸收极化无关超材料吸波体

提出了一种新的基于磁性吸波体材料的具有低频透射和高频宽带吸收特性的超材料吸波体.该超材料吸波体在1 GHz的透射系数为-0.5 dB,具有较好的低频透射特性,可以实现对低频信号的相互通信;在频率大于8.4 GHz的频段,吸收率均大于80%,基本覆盖整个X波段和Ku波段,实现高频宽带吸收.此外,由于该超材料吸波体的单元金属周期结构具有较好的四重旋转对称性,因而是极化无关的.该透射吸收超材料吸波体设计简单,实用性强,具有较强的潜在应用价值.     

基于超材料的微波双波段吸收器

基于闭合双环单元结构, 设计、仿真、测试了对偏振无依赖性的双波段超材料吸收器. 实验结果表明, 该设计在频率4.06 GHz和6.66 GHz存在两个显著吸收峰, 吸收率分别为99.60%和95.83%, 并且在入射角达到50°时, 吸收率仍然保持在83%以上. 由于单元结构具有旋转对称性, 使得该吸收器对偏振不敏感, 能同时实现横电波和横磁波的双波段吸收. 吸收频率决定于闭合环大小, 调节闭合环尺寸能够灵活实现特定频率的吸收. 这些优点使我们的设计在多频谱成像、热辐射探测等应用中表现出较大的潜力.     

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.     

Tunable broadband metamaterial absorber consisting of ferrite slabs and a copper wire

A tunable broadband metamaterial absorber is demonstrated at microwave frequencies in this paper.The metamaterial absorber is composed of ferrite slabs with large resonance beamwidths and a copper wire.The theoretical analysis for the effective media parameters is presented to show the mechanism for achieving the perfect absorptivity characteristic.The numerical results of transmission,reflectance,and absorptivity indicate that the metamaterial absorber exhibits a near perfect impedance-match to free space and a high absorptivity of 98.2% for one layer and 99.97% for two layers at 9.9 GHz.The bandwidth with the absorptivity above 90% is about 2.3 GHz.Moreover,the absorption band can be shifted linearly in a wide frequency range by adjusting the magnetic bias.This metamaterial absorber opens a way to prepare perfectly matched layers for engineering applications.     

基于超材料吸波体的低雷达散射截面波导缝隙阵列天线

提出利用超材料吸波体减缩波导缝隙阵列天线带内雷达散射截面的设计方法. 设计具有超薄(厚度仅为0.01λ, λ为吸波体中心频率对应波长)、无表面损耗层和高吸波率的超材料吸波体, 将其加载到波导缝隙天线E面方向辐射缝隙间的金属表面上, 并与辐射缝隙保持一定的间距. 该加载方式没有破坏天线的口径馈电振幅分布, 并利用超材料吸波体对电磁波的强吸收特性降低了天线阵的结构模式项散射. 仿真和实验结果表明, 加载超材料吸波体后天线阵的反射系数、增益、波瓣宽度保持不变, 在x极化和y极化条件下, 波导缝隙阵列天线的带内雷达散射截面减缩量均在6 dB 以上, 且在-25°-+25°范围内天线雷达散射截面均有明显的减缩, 鼻锥方向减缩超过10 dB. 该研究成果对阵列天线雷达散射截面减缩具有重要的借鉴意义和工程应用价值.     

Ultra-broadband metamaterial absorber for infrared transparency window of the atmosphere

The broadband absorber at the wavelength range from 8 to 13 μm has attracted much attention because this range is exactly the infrared transparency window of the atmosphere. In this Letter, we propose a new structure of ultra-broadband absorber, which is composed of a periodic array of single-sized titanium (Ti) patches and a sandwich (Ti/SiO₂/Ti) plane. In the infrared transparency window of the atmosphere, the structure proposed can achieve nearly perfect absorption with the maximal absorptivity up to 99% for the wavelength range from 9.77 to 10.69 μm, and a high average absorptivity of 96.7% from 8 to 13 μm. The strongly localized electric field, at the interface of the top thin Ti film and the dielectric spacer of sandwich plane, leads to the ultra-broadband high absorption. In addition, this structure demonstrates the insensitivity of polarization and oblique angle. This metamaterial absorber with high performances in both bandwidth and absorptivity shows a promising prospect in applications such as thermal emitters, thermal coolers, and infrared sensors.     

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.     

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.     

Broadband LWIR and MWIR absorber by trapezoid multilayered grating and SiO<Subscript>2</Subscript> hybrid structures

A broadband metamaterial absorber with high absorption simultaneously in mid-wave infrared (MWIR) and long-wave infrared (LWIR) was proposed. In the MWIR, the absorption higher than 0.8 is from 4 to 6.3 µm, while the absorption in the LWIR is from 8.7 and 9.6 µm. The absorber is insensitive to the incident angle. The broadband absorption in the MWIR is due to the slow-light effect of the trapezoid multilayered grating structure. And the broadband absorption in the LWIR is due to the phonon polariton resonant of trapezoid SiO₂ layer. In the broadband high absorption region, the atmosphere is transparent, which may greatly promote the practical application of the absorber in double-color IR imaging, detecting, infrared stealth and thermal emitting.     

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.     

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.     

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.     

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.     

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     

Broadband low-frequency acoustic absorber based on metaporous composite

Broadband absorption of low-frequency sound waves via a deep subwavelength structure is of great and ongoing interest in research and engineering. Here, we numerically and experimentally present a design of a broadband low-frequency absorber based on an acoustic metaporous composite (AMC). The AMC absorber is constructed by embedding a single metamaterial resonator into a porous layer. The finite element simulations show that a high absorption (absorptance A>0.8) can be achieved within a broad frequency range (from 290 Hz to 1074 Hz), while the thickness of AMC is 1/13 of the corresponding wavelength at 290 Hz. The broadband and high-efficiency performances of the absorber are attributed to the coupling between the two resonant absorptions and the trapped mode. The numerical simulations and experimental results are obtained to be in good agreement with each other. Moreover, the high broadband absorption can be maintained under random incident acoustic waves. The proposed absorber provides potential applications in low-frequency noise reduction especially when limited space is demanded.