求解埋入体电磁散射问题的矢量波函数展开法

本文利用矢量波函数展开法求解了任意激励原埋入体的电磁散射问题。通过导出圆柱和圆球矢量波函数的转换关系,使场量满足分界平面和数学球面边界条件,从而方便地利用矢量波函数展开求解了这一复杂边值问题。作为示例,本文计算了在平面波和偶极子激励下,埋入导体球和介质球的散射场。     

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。     

第一类球波函数的柱波函数展开

本文首先给出了第一类标量球波函数的标量柱波函数展开式,然后根据矢量波函数的定义给出了第一类矢量球波函数的矢量柱波函数展开式。这些展开式在求解具有复杂边界的电磁辐射和散射问题时是十分有用的     

两层旋电磁介质球电磁散射的球矢量波函数解

在均匀旋电磁介质球矢量波函数的基础上,利用球Bessel函数的特性,给出了两层旋电磁介质球内的电磁场用波函数表示的表达式.在平面波入射情况下,应用电磁场在球边界上切向电场和磁场连续与远区辐射条件,导出了两层各向异性旋电磁介质中电磁场用矢量波函数表示的展开函数所满足的方程组,求出了两层旋电磁介质球的散射场用均匀各向同性波函数展开的展开系数,进而得出了两层旋电磁介质球对平面波的电磁散射特性.理论分析和数值计算的结果表明:当两层旋电磁介质球的媒质参数相同时,本文所得的结果可退化为单层各向异性旋电磁体解析解.     

阻抗球涂覆均匀等离子体电磁散射的解析解

均匀无源各向异性等离子体介质中的电磁场是第一、第二类各向异性等离子体球矢量波函数的线性叠加,在阻抗球表面满足阻抗边界条件、等离子体与自由空间表面满足电磁场切向连续的边界条件,可得出各向异性等离子体涂覆阻抗球在平面波入射情况下,均匀等离子体介质中电磁场用各向异性等离子体球矢量波函数表示的系数满足的矩阵方程,进而得出散射场由球矢量波函数展开的展开系数和雷达散射截面.数值计算的结果表明:当阻抗球的半径趋于0时,其结果和均匀各向异性等离子体球对平面波的电磁散射结果相同.最后还给出了一些数值计算的结果.     

各向异性材料部分涂覆导体的散射特性研究

利用物理光学法(PO)与有限元法(FEM)混合方法,研究了有各向异性媒质局部涂覆的电大导体目标的电磁散射问题.在有复杂媒质涂覆的电小结构区域采用有限元法,在未涂覆媒质的电大导体区域采用物理光学法结合等效电磁流法.将两部分区域的边界进行消隐处理,考虑耦合效应,并利用共同的等相位面,将不同区域产生的散射场矢量叠加得到总散射场.文中的实例结果与传统的FEM很好的一致,说明了该方法的有效性和精确性.     

在轴零阶贝塞尔波束对手征介质球的散射特性分析

贝塞尔波束自产生以来,凭借其无衍射、自修复特性已经获得了越来越多学者的关注。基于广义洛伦兹米理论, 将在轴贝塞尔波束与手征介质球相互作用的入射场及散射场展开为球矢量波函数的表达式。结合球矢量波函数的正交完备性及电磁场的连续性边界条件,推导出了在轴零阶贝塞尔波束对手征介质球电磁散射的解析解。数值模拟了散射强度随散射角的分布,将在轴贝塞尔波束退化为平面波照射手征介质球的散射结果与文献比较,吻合得较好。分析了波束及介质球参数、介质球偏离波束中心位置对散射强度的影响。该理论为手征材料和手征涂覆目标在微波工程及目标隐身中的应用提供了很好的理论应用价值。     

涂覆长旋转椭球散射场的解析解及其远场双站散射截面计算

利用长旋转椭球矢量波函数和涂覆椭球表面的阻抗边界条件，给出了平面电磁波沿主轴方向入射时涂时涂覆长旋转椭球散射场的解析表达式及其远场双站散截面的计算公式和计算结果。本文的主要结论：不仅几种典型形状理想导体目标对平面电磁的散射场可用解析公式表示，这些形状的涂覆目标的散射场也可用解析公式表示。     

随机球粒媒质的弹性多散射

从多散射场的基本积分方程出发,利用场的矢量球波函数展开及矢量球波函数的坐标变换迭加公式,导出了求解随机球粒媒质的弹性多散射场矢量球波函数展开系数的一组耦合线性方程,从而建立起一种新的分析随机球粒媒质的弹性多散射理论。不同于现有方法,本文方法得到了整个空间的多散射场。     

单轴各向异性球对任意方向入射平面波的散射

基于球矢量波函数的正交完备性,给出了具有任意传播方向两种极化模式的平面波用球矢量波函数展开的形式,导出了其展开系数的具体表达式.研究了单轴各向异性介质球对任意方向入射平面波的散射,利用球矢量波函数及傅里叶变换方法得到了各向异性介质球的内场展开式,结合切向连续边界条件给出了散射系数.数值分析了介电常数张量元、有耗、无耗、尺寸参数、入射角和方位角等对单轴各向异性介质球的雷达散射截面的影响.     

Design of wave absorber for small conducting sphere

An electromagnetic wave absorber for a small sized conducting sphere is designed by applying the Newton-Raphson method to the eigenfunction series solution for a coated conducting sphere. The parameters for the perfect absorbing condition are the constitutive parameters and the thickness of coating for a given radius of conducting sphere. The wave absorber designed by this method exhibits a superior absorption performance to that designed using flat plate absorber theory     

VECTOR WAVE FUNCTION EXPANSION FOR SOLVING ELECTROMAGNETIC SCATTERING BY BURIED OBJECTS

An analysis of solving the electromagnetic scattering by buried objects using vectorwave function expansion is presented.For expanding the boundary conditions both on the planarair-earth interface and on the spherical surface,the conversion relations between the cylindricaland spherical vector wave functions are derived.Hence the vector wave function expansion isconveniently applied to solve this complex boundary-value problem.For the excitation of the in-cident plane wave and the dipole above the earth,the scatterlng patterns of the buried conductingand dielectric spheres are presented and discussed.     

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.     

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     

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     

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.     

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.     

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