Resonance absorption at scattering by a metamaterial cylinder

The problem of scattering of the field induced by a filament of magnetic current by a metamaterial cylinder is solved using the method of continued boundary conditions. The effect of the frequency dispersion of permittivity and permeability of the cylinder material on the phenomenon of resonance absorption is investigated.     

Wave scattering by a prism made of a lossy metamaterial

The results of rigorous calculation of the scattering pattern of a Gaussian beam incident onto a finite prism made of a metamaterial are presented for different values of the refractive index n _r < 0 and loss factor ν of the medium. It is shown that geometric optics can correctly predict the tilt of the scattering-pattern maximum, while consideration for the medium’s loss factor 0.001 ≤ |ν| ≤ 0.1 affects the amplitudes of the transmitted and reflected fields.     

Small-angle scattering by a finite cone

High-frequency scattering by a finite perfectly conducting right-circular cone is analyzed by modifying geometrical diffraction theory for application at and near nose-on aspects. Formulas appropriate for predicting principal-polarization radar cross sections as functions of frequency and aspect angle are presented. Calculations on a cone are in very good agreement with monostatic measurement data in the limited aspect interval0 leq phi leq gamma, wheregamma, is the half-angle of the cone.     

关于双频光栅对物体实时测量的研究

为了既可以高精度测量有突变的物体又能达到实时的目的,采用软件VC++生成双频光栅的方法,用LCD投影机直接投射到物体表面,只需采集一幅图像经过傅里叶变换便可得到相位差,还原出物体形貌。实验结果表明,该方法简单方便、精度高,可以达到实时的要求,对基于双频光栅的傅里叶变换轮廓术的发展有很大的推动作用。     

Circumferential distribution of scattering current and small hole coupling for thin finite cylinders

The scattering current induced on a thin finite conducting cylinder immersed in a"theta"-polarizedE-field is studied. Particular attention is paid to the circumferentially nonuniform mode as theE-field angle of incidence varies. This nonuniformity is shown significant (peak-to-average ratio of 3 dB at cylinder midlength) at certain incidence angles for wavelength long cylinders with diameters as small as0.067lambda. Also investigated is the relationship between scattering current and cavity response patterns for narrow thin-walled cylindrical cavities with small holes through which energy is coupled. It is demonstrated theoretically, with experimental verification, that the circumferential variation of scattering current strongly affects the fields within thin cylindrical cavities having apertures with small circumferential extents. It is noted, however, that for most thin-body radiation and scattering problems (in contrast with aperature coupling) only the uniform current mode is significant.     

Electromagnetic scattering by a straight thin wire

The traveling-wave energy, which multiply diffracts on a straight thin wire, is represented as a sum of terms, each with a distinct physical meaning, that can be individually examined in the time domain. Expressions for each scattering mechanism on a straight thin wire are cast in the form of four basic electromagnetic wave concepts: diffraction, attachment, launch, and reflection. Using the basic mechanisms from P.Ya. Ufimtsev (1962), each of the scattering mechanisms is included into the total scattered field for the straight thin wire. Scattering as a function of angle and frequency is then compared to the moment-method solution. These analytic expressions are then extended to a lossy wire with a simple approximate modification using the propagation velocity on the wire as derived from the Sommerfeld wave on a straight lossy wire. Both the perfectly conducting and lossy wire solutions are compared to moment-method results, and excellent agreement is found. As is common with asymptotic solutions, when the electrical length of wire is smaller than 0.2 λ the results lose accuracy. The expressions modified to approximate the scattering for the lossy thin wire yield excellent agreement even for lossy wires where the wire radius is on the order of skin depth     

Electromagnetic scattering by a thin resistive wire

A theoretical investigation concerning scattering of a plane electromagnetic wave by a straight resistive wire of finite length in an isotropic homogeneous medium is reported. The work is based on the travelling-wave solution obtained by repeated use of the Wiener-Hopf method. Some numerical data for backscattering cross-section at broadside incidence are given.     

Surface waves guided by a plate made from a bianisotropic resonance metamaterial

The dispersion characteristics, the distribution of energy fluxes, and the polarization of the magnetic field of surface waves formed in free space by a bianisotropic-material layer with resonance and anisotropic chirality, permittivity, and permeability are studied theoretically. The transmission and reflection spectra for lattices of resonance planar elements exhibiting magnetoelectric interaction are investigated experimentally. The nonreciprocity of microwave transmission in structures consisting of a lattice and a transversely magnetized ferrite plate is also investigated experimentally. The qualitative agreement of experimental results and theoretical predictions is established.     

复合鱼鳞型超构材料中光控Fano谐振的设计

为解决传统超构材料存在的结构一旦形成,其谐振特性便无法进行动态可调的问题,本文将鱼鳞型超构材料与光电导材料硅相结合,实现了太赫兹波段Fano电磁响应的动态调控。该复合超构材料由鱼鳞型金属线、硅层以及聚酰亚胺组成。在鱼鳞型结构的金属弧线无、有缝隙两种情况下,研究了电磁波的入射角度和硅的电导率对Fano谐振的影响。当硅的电导率达到1×103S/m时,多频点电磁响应的调制深度都接近1。结果表明,调节缝隙宽度可以成为Fano谐振工作频率调控的有效方式。本文为实现超构材料中Fano谐振的可调谐特性提供了一种可行途径,对实际应用中太赫兹波的主动调控、传感等方面具有重要意义。     

Investigation of wide-angle thin metamaterial absorber at infrared region

In the practical application, a wide-angle absorption with simple structure is still crucial property of metamaterial absorbers (MAs). A single-band infrared MA is introduced to analyze the angle insensitive mechanism. Numerical simulation reveals that a perfect absorption peak with 99.9% (7.55 μm) is achieved at normal incidence, as well as the absorptivity is respectively 69.7% (7.46 μm) and 93.5% (7.46 μm) for transverse electric (TE) and transverse magnetic (TM) modes at 70° incidence. By changing substrate thickness, the absorption ratio at 70° is increased to 91% (7.46 μm) for TE mode. Our design can also keep the good absorption stability for the geometric parameters. The Ez-field distributions for different incident angles are given to investigate the physical mechanism. The designed MA can realize good wide-angle tolerance. This MA owns great applications, including infrared spectroscopy, solar harvester and plasmonic sensors.     

High-Q resonanaces of surface waves in thin metamaterial cylinders

The 2D problem of excitation of a circular metamaterial cylinder by a filament source is numerically investigated. It is found that, when the relative permittivity and permeability are close to minus unity, high-Q resonances occur in cylinders of an electrically small diameter. Near- and far-field patterns are calculated. It is discovered that, under resonance conditions, a multilobe scattering pattern typical of superdirective antennas is formed. The influence of loss on the resonance characteristics is investigated.     

基于电偶极共振的极化独立宽带吸收超材料

基于电偶极共振设计了一种工作在W波段、对极化不敏感的宽带吸收超材料。宽带吸波超材料基于不同尺寸铜箔排列构成的周期阵列,在结构上高度对称。通过时域有限差分算法,对超材料在W波段的吸收性能进行仿真,通过电场和电荷分布探讨了导致共振吸收的物理机制。最后,利用印制电路板工艺加工实现了设计的超材料结构,并给出关于吸收性能的仿真与实验结果的对比。实验结果表明,超材料在W波段平均吸收率达到84.7%,与仿真结果接近。     

The resonance properties of the near field in finite thin Veselago and Pendry lenses

The problem of excitation of a finite thin plate made from a metamaterial with the electrodynamic parameters ? _r ?? ?1, ?? _r ?? ?1 and ? _r ?? ?1, ?? _r = 1 by a point source is considered. Resonance phenomena in the near field of plates are found that are caused by the interaction of the formed surface waves. It is shown that the near field of the plate has the form of standing surface waves localized near wide faces of the plate, and the high Q factor of the observed resonances leads to the extremely strong dependence of the excited near-field amplitude on the electric and geometric parameters of the plates.     

An open surface integral formulation for electromagnetic scattering by material plates

Using the surface equivalence theorem, four coupled integral equations are developed for electromagnetic scattering by a thin material plate. Using symmetry properties, it is shown that these equations can be written as open surface integral equations. Surface impedance relationships are obtained and used to eliminate two of the four integral equations. The remaining two equations are solved using the method of moments (MM). Numerical results for penetrable and impenetrable material plates are in reasonable agreement with measurements.     

Excitation of an electrically thick metamaterial waveguide of a finite length

The problem of diffraction of a cylindrical wave by a plate whose medium has a negative refractive index (a metamaterial) is numerically solved. The near and far fields are investigated for the case when a cylindrical wave source is located near the narrow butt-end of a long plate and when the metamaterial of the plate has various values of the permittivity and permeability. The results obtained are interpreted in terms of the geometric optics. It is shown that a plate made from such a metamaterial can be applied for fabricating antennas with multi- and single-lobe patterns.     

多导线散射中的广义谐振分析

利用矩量法分析了多导线散射中存在的广义谐振问题,并利用开路传输线腔理论很好地解释了这类散射结构的谐振特性。     

Multimode network representations for the scattering by an array ofthick parallel plates

In this paper, we describe two multimode network representations for the analysis of radiating array of thick parallel plates. Due to periodicity and infinite extent, only one period of the structure needs to be studied. The key step is then the derivation of the equivalent network representation for the transition from a free-space region limited by phase-shift walls to a parallel plate waveguide. Two solutions to the problem are discussed. In the first solution, the relevant boundary value problem is cast into a network form that leads to an integral equation. The equation is then solved with the method of moments (MoMs). In the second solution, the elements of the multimode coupling matrix representing the grating are evaluated directly in terms of their network definition. The two solutions are then compared and the relative merits are discussed. The main feature of the approach presented in this paper, is that once the network representation of the key transition is obtained, it allows for the study of a wide class of scattering problems involving, for instance, corrugated surfaces and single or cascaded thick gratings. Comparison with published data are also presented, indicating that the two network representations developed are indeed very accurate     

The resonance properties of multiturn wire helices filled with a metamaterial

The 2D problem of the excitation of a multiturn cylindrical wire helix filled with a metamaterial by electric- and magnetic-current filaments is considered. High-Q resonances in the low-frequency region are found and investigated. It is shown that, depending on the values of the constitutive and geometric parameters of the anisotropically conducting cylinder, the resonance fields can have both linear and circular polarizations. On the basis of a rigorous calculation, the amplitude-frequency characteristic of this structure and near- and far-field patterns are considered. Approximate analytic expressions are obtained for the resonance frequencies.