Integral equation modeling of the scattering and absorption ofmultilayered doubly-periodic lossy structures

Previously, the scattering and absorption of a doubly-periodic array of pyramidal absorbers were analyzed using a surface integral equation (SIE) approach. This method is now extended to multilayered absorbers with arbitrarily shaped surfaces between the layers. The developed method is verified on planar stratified absorbers, on wedge absorbers, and rectangular absorbers showing the capability of the method to handle such structures as well. It is also shown that convergence depends critically on the discretization of the equivalent electric and magnetic current     

A doubly periodic moment method solution for the analysis anddesign of an absorber covered wall

A periodic moment-method solution for scattering from a doubly periodic array of lossy dielectric bodies is developed. The purpose is to design electromagnetic wedge and pyramidal absorbers for low reflectivity so that one can improve the performance of anechoic chamber measurements. The spectral-domain formulation and the moment-method volume polarization current approach are used to obtain the expressions for determining the scattering from a doubly periodic array of lossy dielectric bodies. Some wedge and pyramidal absorber configurations that have been designed, fabricated, and tested in the OSU/ESL compact range measurement facility are presented. By taking into account the complexity of real-world material structures, good agreement between calculations and measurements has been obtained     

Simple design of thin and wideband circuit analogue absorber

A new and simple design for thin and broadband circuit analogue absorbers is presented. The proposed absorber is composed of a two-dimensional periodic array of multiple patches printed on a conductor-backed substrate, which exhibits the property of multiple resonances and provides a wide absorbing bandwidth. Measured results show that this simple absorber has a bandwidth of 76% for 10 dB RCS reduction and its thickness is only one-eighth free-space wavelength at the centre frequency     

Efficient Terahertz Plasmonic Absorbers with V-Grooves Using Highly Doped Silicon Substrate and Simple Wet-Etching Techniques

We experimentally demonstrate that at terahertz frequencies perfect plasmonic absorbers made from a 3D V-groove array in a highly doped silicon wafer can be easily realized using simple wet-etching process. The surface plasmon modes can be excited by the V-groove array and get decayed when they propagate along the silicon surface and enter the grooves, inducing a broadband near-zero dip in the reflection spectra. The reflection spectrum of the fabricated absorber is characterized using a terahertz time-domain spectroscopy system, and the experimental results are in good agreement with numerical simulations. The high performance including high absorptivity and large bandwidth together with the easy fabrication processes presented in this paper make this plasmonic absorber promising for a wide range of practical applications in terahertz regime.     

一款具有双方环结构的有源电路模拟吸波材料

简单阐述电路模拟吸波材料的吸波原理,提出使用CST电磁仿真软件,通过电抗加载的方式对有源电路模拟吸波材料进行分析的方法。设计一款具有双方环结构的有源电路模拟吸波材料,并使用该方法对其进行分析。仿真结果表明这款吸波材料具有良好的双频吸波特性,通过改变两个方环的加载电阻(即改变PIN管的偏置电流),可改变吸波材料的吸波频率。     

PERIODIC DYADIC GREEN''S FUNCTION FOR FIELD ANALYSIS IN EMC CHAMBER

Herein a novel Dyadic Green's Function (DGF) is presented to calculate the field in ElectroMagnetic Compatibility (EMC) chamber. Due to the difficulty of simulating the whole chamber environment, the analysis combines the DGF formulation and the FEM method, with the latter deals with the reflection from absorbers. With DGF formulation for infinite periodic array structures, this paper investigates electromagnetic field in chamber with truncated arrays. The reflection from the absorber serves as the virtual source contributing to the total field. Hence the whole chamber field calculation can be separated from the work of absorber model set-up. Practically the field homogeneity test and Normal Site Attenuation (NSA) test are carried out to evaluate the chamber performance. Based on the method in this paper, the simulation results agree well with the test, and predict successfully the victim frequency points of the chamber.     

透明吸波体综述北大核心CSCD

吸波体是一种带有损耗特性的周期结构,能够吸收电磁波,将电磁能转化为热能,降低反射的电磁波能量。随着应用场景的特殊化,吸波体朝着特殊领域、特定功能、更具针对性的方向发展。由于各类含有光学窗口的应用环境对抗电磁干扰需求的不断提高,吸波体光学透明化成为研究的重点方向。为了对透明吸波体的发展状况有系统的认识,文章以制造材料为脉络梳理了近年来可见光透明吸波体的研究现状,包括氧化铟锡(ITO)、金属网栅、石墨烯等,综述了以它们为材料制备的透明吸波体优缺点以及发展趋势,最后对透明吸波体的未来发展进行了展望。     

基于集总电阻加载吸波器的紧耦合超宽带天线

基于集总型电阻频率选择表面吸波器,设计一款超宽带紧耦合天线阵列。在天线阵列与地板之间加入两层结构集总型电阻频率选择表面吸波器,改变天线与地板之间的传输特性,有效抑制天线短路零点出现,扩展天线带宽;同时利用天线间强耦合效应,减小天线单元结构尺寸。使用集总电阻和金属环构成的吸波器代替常规阻抗型频率选择表面结构,降低天线阵列设计与加工难度,同时可有效改善天线阻抗匹配。仿真实验表明,通过调节集总频率选择表面吸波器物理结构、加载电阻阻值和天线间耦合电容值等参数,当天线单元驻波比小于3 时,可实现带宽范围达12.6:1 (1.5～19 GHz)的超宽带性能;并在2.2～18.3 GHz 范围内具有驻波比小于2 的良好匹配性能。     

Periodic Dyadic Green’s Function for Field Analysis in EMC Chamber

Herein a novel Dyadic Green＇s Function （DGF） is presented to calculate the field in ElectroMagnetic Compatibility （EMC） chamber. Due to the difficulty of simulating the whole chamber environment, the analysis combines the DGF formulation and the FEM method, with the latter deals with the reflection from absorbers. With DGF formulation for infinite periodic array structures, this paper investigates electromagnetic field in chamber with truncated arrays. The reflection from the absorber serves as the virtual source contributing to the total field. Hence the whole chamber field calculation can be separated from the work of absorber model set-up. Practically the field homogeneity test and Normal Site Attenuation （NSA） test are carried out to evaluate the chamber performance. Based on the method in this paper, the simulation results agree well with the test, and predict successfully the victim frequency points of the chamber.     

超薄型电磁带隙吸波结构的最优化设计

Salisbury 屏是一种基本的吸波结构,在谐振频率点具有良好的吸波性能,但是它的厚度必须为四分之一倍的波长,这不利于工程的应用。本文在Salisbury 屏的阻抗层设计中引入了有耗的频率选择表面贴片,有效减小了Salisbury屏的厚度,形成一个电磁带隙吸波结构。应用微遗传算法对频率选择表面贴片的几何图形及表面阻抗、结构的周期大小、介质的厚度等参数进行最优化处理。设计得到的两个在谐振频率点处具有良好吸波性能的超薄电磁带隙吸波结构验证了本文方法的正确性与可靠性。     

Electromagnetic scattering by pyramidal and wedge absorber

Electromagnetic scattering from pyramidal and wedge absorbers used to line the walls of modern anechoic chambers is measured and compared with theoretically predicted values. The theoretical performance for various angles of incidence is studied. It is shown that a pyramidal absorber scatters electromagnetic energy more as a random rough surface does. The apparent reflection coefficient from an absorber wall illuminated by a plane wave can be much less than the normal absorber specifications quoted by the manufacturer. For angles near grazing incidence, pyramidal absorbers give a large backscattered field from the pyramid side-faces or edges. The wedge absorber was found to give small backscattered fields for nuclear-grazing incidence. Based on this study, some new guidelines for the design of anechoic chambers are advocated because the specular scattering models used at present do not appear valid for pyramids that are large compared to the wavelength     

外壳为聚苯乙烯硬泡沫的角锥吸波材料

随着使用频率的降低,微波暗室角锥吸收体的高度也相应增加。传统的聚氨脂泡沫角锥吸收体由于在浸渍和烘干方面存在困难,因而不易制作。为避免聚氨脂泡沫角锥吸收体在大尺寸时浸渍和烘干的困难,以聚苯乙烯硬泡沫板为外壳,以聚苯乙烯泡沫小球和吸波材料混合体为充填物的新型角锥吸波材料已开发成功。聚苯乙烯泡沫具有低密度,高阻燃和低介电常数的特点,因而保证了吸收体的重量轻,阻燃好,吸收性能高的要求。而且吸收体表面平整,洁白,采光好。试验结构表明,500mm高度的吸收体,在2.6-18GHz频率范围内,反射率基本上都优于-50dB。     

Application of a parallel particle swarm optimization scheme to the design of electromagnetic absorbers

The application of parallel (synchronous) particle swarm optimization (PSO) to electromagnetic absorber design is described. Synchronous PSO is a version of PSO that allows for parallelization and hence faster optimization. The velocity updating rule is empirically determined, and a simple approach is presented to improve its robustness. Absorbers designed with the PSO approach are compared with absorbers designed by genetic algorithms (GAs). Numerical results demonstrate that the PSO is able to deliver absorbers with comparable performance to GA-designed absorbers, with much less computational cost.     

Green's function for arbitrarily shaped dielectric bodies of revolution

In this paper, a solution is developed to calculate the electric field at one point in space due to an electric dipole exciting an arbitrarily shaped dielectric body of revolution (BOR). Specifically, the electric field is determined from the solution of coupled surface integral equations (SIE) for the induced surface electric and magnetic currents on the dielectric body excited by an elementary electric current dipole source. Both the interior and exterior fields to the dielectric BOR may be accurately evaluated via this approach. For a highly lossy dielectric body, the numerical Green's function is also obtainable from an approximate integral equation (AIE) based on a surface boundary condition. If this equation is solved by the method of moments, significant numerical efficiency over SIE is realized. Numerical results obtained by both SIE and AIE approaches agree with the exact solution for the special case of a dielectric sphere. With this numerical Green's function, the complicated radiation and scattering problems in the presence of an arbitrarily shaped dielectric BOR are readily solvable by the method of moments.     

Low-frequency reflectivity approximation for two- andthree-dimensional EM absorbers

Large-size electromagnetic absorbers are mainly used in anechoic and semi-anechoic chambers for electromagnetic compatibility testing. Therefore, the determination of the reflectivities in the low-frequency range (30-300 MHz) are of paramount importance in the performance evaluation of the absorber and, finally, in a “dark room” design. We here present a low-frequency approximation of the reflectivity based on a boundary and surface integral equation technique. This approach makes it possible to compare the approximation to the rigorous integral equation approach and to other approximations in the literature. The validity of the new low-frequency approximation is discussed based on reflectivity calculations of representative two- (2-D) and three-dimensional (3-D) absorber structures     

超宽带宽角极化不敏感的电路模拟吸波材料设计

传统的电路模拟吸波材料设计只考虑正入射时的吸波性能,当入射角较大,尤其是大于30°时,雷达吸波器的吸波效果明显恶化。随着现代双站雷达探测技术的发展,雷达探测电磁波可能来自不同的空间方向,这就要求雷达吸波材料不仅在电磁波正入射时具有较高的吸波性能,在斜入射时同样实现良好的隐身特性。为此,该文提出了一种新型的宽带吸波材料。...     

A single-layer tuneable microwave absorber using an active FSS

An experimental single-layer active microwave absorber in described. The absorber is a planar structure based upon the topology of a Salisbury screen, but in which the conventional resistive layer is replaced by an active frequency selective surface (FSS) controlled by pin diodes. The resulting structure has superior reflectivity-bandwidth characteristics compared to conventional passive absorbers of corresponding thickness. Measured data are presented and show that the reflectivity response of the absorber can be controlled over the frequency band from 9 to 13 GHz.     

Photogeneration and carrier recombination in graded gap Cu(In, Ga)Se/sub 2/ solar cells

We investigate photogeneration and carrier recombination in Cu(In, Ga)Se/sub 2/ based thin-film solar cells with graded gap absorbers. The graded gap in the absorbers is obtained by variation of the Ga/In ratio during the coevaporation process from elemental sources. The devices exhibit conversion efficiencies up to /spl eta/=16.7%. In these graded gap devices, the open circuit voltage depends on that bandgap which corresponds to the Ga content close to the absorber surface (i.e., the bandgap in the space charge region). In contrast, the short circuit current density relates to the overall minimum of the bandgap in the graded gap structure. We show that in our graded gap devices, two different bandgaps, one for recombination and one for photogeneration, are experimentally realized.     

Novel planar electromagnetic absorber designs using genetic algorithms

A new type of absorber is proposed created by drilling holes in a single layer of lossy material. The new absorber is designed using genetic algorithms to achieve low reflectance over a wide frequency band. Results based on genetic algorithms demonstrate that the new absorber outperforms multilayer absorbers and absorbers embedding frequency selective surfaces between lossy materials. Numerical results are presented for different bandwidths, wave incidence angles, and polarizations.     

Scattering of E-polarized waves from conducting strips inthe presence of a magnetically uniaxial half-space-a singular integralequation approach

A method based on the theory of singular integral equations (SIE) is presented for treating analytically scattering by perfectly conducting infinitely long strips in the presence of a magnetically uniaxial half-space. A uniform plane wave, polarized parallel to the strip axis, is incident from the isotropic region. As a prerequisite to this approach, the E-mode scalar Green's function of the structure is developed. Use of the reciprocity theorem then leads to a SIE for the current density induced on the scatterer's surface. The solution of the SIE is carried out in the case of a strip parallel or perpendicular to the interface, either located above or embedded in the anisotropic space. Numerical results for the induced current density and for the scattered far field in a variety of cases are presented in graphical form