FDTD Study on Back Scattering of Conducting Sphere Coated with Double-Negatibe Metamaterials

The shift operator method in finite-difference time-domain method for anisotropic double-negative (DNG) metamaterials is derived. The problem which incorporates both anisotropy and frequency dispersion at the same time is solved for the electromagnetic wave propagation in DNG media. By comparing with the mie series solution, the numerical verification of the method and program are confirmed by computing the back scattering of isotropic unmagnetized plasma sphere. The back scattering of conducting sphere coated with DNG media with different parameters is computed by using the shift operator method. One finds that the degree of DNG media’s match and isotropy plays important parts in the decrease of the back scattering of the conducting sphere.     

两媒质半空间复杂形体电磁散射

本文利用矢量波函数变换方法讨论了两媒质半空间的电磁散射问题，从Ｍａｘｗｅｌｌ方程出发，讨论了单矩法在三维复杂形体散射问题上的实施。并在数学球面上将内部区域的有限元解与外部区域矢量波函数变换的结果相匹配，从而得到复杂埋入体的电磁散射特性。作为检验和示例，本文计算了在平面波照射下自由空间导体球，埋入导体球，埋入介质覆盖钝锥等的散射场，其中一些结果与可供比较的经典解或其它算法的结果进行了比较，吻合较好。     

新型雷达波吸收材料导电聚合物的研究

介绍了新型雷达波吸收材料导电聚合物的研究现状及发展趋势，导电聚合物吸波剂在众多雷达波吸波剂分类中所属类型，导电聚合物的导电机理，提出了在进一步研究中，导电聚合物更好地应用于雷达吸波材料所要考虑的问题．     

导体球涂覆各向异性铁氧体介质电磁散射的解析解

该文用球矢量波函数对各向异性铁氧体介质涂覆导体球的电磁散射解析解开展研究。各向异性铁氧体介质中电磁场的球矢量波函数解可表示成第一、二、三、四类球矢量波函数之和。根据球Bessel函数的性质,可以得出导体球涂覆各向异性铁氧体介质的球矢量波函数解析解。应用铁氧体与自由空间分界面上电磁场切向连续和在导体球面上切向电场等于零的边界条件以及球矢量波函数切向正交性质,可分别得出铁氧体介质中电磁场和散射场的展开系数。给出了平面波入射情况下的数值计算结果。该文的结果可应用于有关微波器件、天线以及目标特征的分析和计算。     

Electromagnetic wave absorber with wide-band frequencycharacteristics using exponentially tapered ferrite

As a countermeasure of EMI or EMC, various types of electromagnetic wave absorbers are used. A wide-band design method of an electromagnetic wave absorber with using exponentially tapered ferrite, which has very wide-band frequency characteristics, is proposed and discussed. The wide-band electromagnetic wave absorber can be designed under some approximations by the theoretical model using the equivalent material constants (equivalent complex permittivity and permeability) method for the regions varying spatially in the shape of ferrite. Based on the model, wide-band electromagnetic wave absorbers with taper, which have not only excellent reflectivity frequency characteristics but also a bandwidth of 30 MHz to 2150 MHz or 2430 MHz under the tolerance limits of -20 dB reflectivity, were designed     

Radiation characteristics of wraparound microstrip antenna onspherical body

The radiation characteristics of a wraparound microstrip antenna on a conducting sphere are investigated for different radii, frequencies, permittivities, and thickness of dielectric substrate. The near fields are determined from the magnetic ring currents at the edges of the strip by the use of spherical wave functions. Radiation patterns are obtained from a near-field-to-far-field transformation by the method of spherical wave expansion     

一种基于等离子体超材料的吸波器设计

为了在TE波下获得可调谐的吸收频谱,设计了一款基于等离子体超材料的吸波器。采用全波仿真方法对该吸波器的吸收率和表面电流图进行了计算,并探讨了结构参量c,v和入射角度θ对吸收率的影响。结果表明,通过激励不同的等离子体谐振区域不但可以改善其吸收特性,而且还能获得可调谐的吸收频谱;改变结构参量c和v可以在实现拓展吸收带宽的同时,使得吸收频域也发生移动;改变入射角度θ的大小对吸收率的影响不大。该吸波器具有很好的角度稳定性。     

Transient scattering by conducting surfaces of arbitrary shape

The time-domain electric field integral equation (EFIE) is used along with the method of moments to develop a simple and efficient numerical procedure for treating problems of transient scattering by arbitrary shaped conducting objects. The conducting surface is modeled by planar triangular patches for numerical purposes. Because the EFIE is used in the solution procedure, the method is applicable to both open and closed bodies. the EFIE approach is applied to the scattering problems of Gaussian plane wave illumination of a flat square plate and sphere. Comparisons of surface current densities and far-scattered fields are made with previous computations and good agreement is obtained in each case     

电磁超材料吸收器的研究进展

基于电磁超材料的电磁谐振吸收器通过合理设计器件的物理尺寸及材料参数可对入射到吸收器的特定频率的电磁波实现100％的完美吸收,因而受到国内外学术界的高度关注.综述了当前国内外基于电磁超材料的电磁波完美吸收器在微波和太赫兹波段的研究进展,分类介绍了吸收器的结构及性能特点,最后对电磁超材料吸收器的发展趋势和待解决的问题作了探...     

基于熔融沉积成型的多层石墨烯吸波体的快速制备及其性能

在制备石墨烯/聚乳酸(PLA)复合材料的基础上,利用熔融沉积成型技术快速制备了单层均质样件,研究了石墨烯含量对其电磁参数的影响规律,并基于传输线理论计算分析了其吸波效果;选择石墨烯含量较低的复合材料作为透波层的打印材料,石墨烯含量较高的复合线材作为吸收层和再次吸收层的打印材料,并基于四分之一波长匹配理论确定了吸收层、再次吸收层的匹配厚度范围。设计制造了由不同石墨烯/PLA复合材料组合而成的三层吸波体,测试结果表明:三层吸波体的吸波效果远优于单层均质吸波体,且当选取石墨烯质量分数分别为5%、7%、8%的复合材料作为透波层、吸收层和再次吸收层打印材料时,可以获得最佳的吸收效果,此吸波体在13.3~18GHz频段内的反射率均小于-10dB,在17GHz时有-30dB的最大吸收峰值。     

Dielectric absorber design for wide band–wide oblique incidence angle using genetic algorithm

With an aim to design a V-shape absorber using a global optimization algorithm, the reflectivity value of the absorber is calculated as a cost function by using an equivalent multilayered absorber model, and is minimized by the optimization algorithm. Both normal and oblique incidences of plane wave are analyzed. The optimization parameters are the relative permittivity and the length of the multilayered absorber over a wide frequency band and wide oblique incidence angle of a plane wave. The optimized results for different frequency bands and incidence angles show that the minimized reflection coefficients and corresponding relative permittivity are within an acceptable range for each application considered in this work.     

一种基于二氧化钒材料的可调谐吸波器设计

为了在THz波段获得TE波下的可调谐吸收频谱, 采用全波仿真的方法, 设计了一款基于二氧化钒材料的可调谐THz吸波器, 对该吸波器的吸收频谱、电场图、表面电流图以及能量损耗图进行分析, 并讨论了结构参量h₄, k以及入射角度θ对吸收频域和吸收带宽的影响。结果表明, 通过外部温控的方式改变二氧化钒谐振单元的物理特性可以获得可调谐的吸收频谱并改善吸波器的吸收性能, 该吸波器在温度T≥68℃时, 可以实现在2.70THz~3.36THz频段的宽带吸收(吸收率在90%以上), 相对带宽达到21.8%;在T＜68℃时, 可以实现多个单频点的吸收; 改变结构参量h₄, k可以改变吸收频点的位置以及吸收带宽, 改变入射角度θ可以影响吸波器的吸收效果。该研究对可调谐太赫兹器件的进一步探究是有帮助的。     

Scattering by a rotating conducting sphere

The scattering of a plane wave by a rotating sphere with finite conductivity is investigated. The problem is solved by means of the "instantaneous rest-frame" hypothesis. It is shown that a surface current must be taken into account to calculate the jump in the tangential magnetic field at the surface of the sphere, even in the case of finite conductivity. The analytical solution shows that the influence of the rotation becomes negligible in the limit of a perfectly conducting sphere.     

Surface currents on impedance bodies of revolution

The surface currents induced by a plane wave axially incident on a rotationally symmetric body are determined by solving numerically extended form of Maue's integral equation. The relative surface impedance is independent of the azimuthal angle but may vary along the profile of the scatterer in any plane containing the axis of symmetry. Numerical results are shown for a sphere and a cone-sphere that are either perfectly conducting or perfectly absorbing. Apart from internal resonances, the computer code is found to provide accurate results well into the high-frequency region. A simple line-integral representation of the far field is given, and internal resonances are discussed for the backscattering radar cross section of a perfectly conducting and a perfectly absorbing sphere     

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.     

Poincaré sphere representation of partially polarized fields

The use of points on the surface of the poincaré sphere to represent the polarization state of fully polarized electromagnetic fields is extended to partially polarized fields by representing their polarization by points inside the sphere. The coordinates of a pointbar{W}representing the polarization state are shown to be simply related to the Stokes parameters. The center of the sphere represents a completely unpolarized wave, and the degree of polarization is given by the distance of the pointbar{W}from the center of the sphere. A simple formula is derived for calculating the power received by an antenna illuminated by a partially polarized wave. A method is described for measuring the polarization state by a number of intensity measurements.     

用瞬态电磁场测量目标的冲激响应和宽带雷达截面

突破传统的时域散射区域技术的限制，采用基于瞬态电磁测试系统的实验性冲激雷达，在实际空间对导体球和导体长椭球进行了瞬态磁脉冲响应测量。用修正最速下降法由实测瞬态电磁脉冲响应较发地反演了导体球和导体长椭球的冲激响应。提出了时域测量目标宽带雷达截面的瞬态响应法，并用此法测得了导体球、导体长椭球的雷达截面和谐振频率。     

Frequency series expansion of an explicit solution for a dipoleinside a conducting sphere at low frequency

The electromagnetic field generated by a current dipole situated at an arbitrary position inside a conducting sphere is derived using the expansions of the spherical vector wave functions. The first few terms in a series expansion of this field with respect to the frequency are given for the normal magnetic field (used in magnetoencephalogram) and the tangential electric field (used in electroencephalogram) outside the conducting sphere at low frequency. It is shown that the first correction term to the static solution is linear in the frequency ω (the second correction term is proportional to ω^3/2 ) and, thus, the static solution can be used as a good approximation for the solution at a very low frequency     

Scattering of a beam wave by a spherical object

The theoretical analysis of the scattering of a beam wave by a small spherical object, which exists at the neighborhood of the beam waist on the propagation axis, is treated. In this analysis, the property of a spherical object is generalized so as to have anr-dependent dielectric constant. Through numerical calculations for the case of the conducting sphere, the difference between the scattering of a beam wave and that of a plane wave are discussed.     

Spherical wave sources in FDTD

A method is described which simulates the propagation of electromagnetic waves as spherical wave modes, approximated by an FDTD method. Modal equations in radius and time are discretized for explicit time-stepping. Angular functions are implemented analytically as required. Computed results for two examples are compared with analytic solutions - a resonator and a dipole near a conducting sphere - to demonstrate the validity of the method with very good agreement. This method is intended as a source condition in total/scattered FDTD methods, to allow for modeling of near-field object interactions without explicitly modeling the source