Electromagnetic diffraction of an obliquely incident plane wavefield by a wedge with impedance faces

A uniform asymptotic solution is presented for the electromagnetic diffraction by a wedge with impedance faces and with included angles equal to 0 (half-plane), π/2 (right-angled wedge), π (two-part plane) and 3π/2 (right-angled wedge). The incident field is a plane wave of arbitrary polarization, obliquely incident to the axis of the wedge. The formal solution, which is expressed in terms of an integral, was obtained by the generalized reflection method. A careful study of the singularities of the integrand is made before the asymptotic evaluation of the integral is carried out. The asymptotic evaluation of the integral is performed taking into account the presence of the surface wave poles in addition to the geometrical optics poles near the saddle points. This results in a uniform solution which is continuous acros the shadow boundaries of the geometrical optics fields as well as the surface wave fields     

High-frequency surface currents induced on a perfectly conducting cylindrical sheet by an obliquely incident plane wave

Explicit expressions for the surface currents of different kinds induced on a perfectly conducting cylindrical sheet by an obliquely incident high-frequency plane wave are derived. The results are in such forms that they can both be used directly in numerical applications and permit us to understand the structure of the induced surface current. It is shown that the components due to the surface and edge diffractions propagate along certain geodesic lines on which the transfer coefficients as well as the attenuation constants are dependent only on the curvature radius.     

On the diffraction of an electromagnetic skew incident wave by a non perfectly conducting wedge

We study the diffraction by a wedge of an electromagnetic plane wave with skew incidence on the edge, when boundary conditions give us two equations by face with combined electric and magnetic fields. The problem is reduced principally to a non linear scalar functional equation with one unknown. As an example of application, the solution for a wedge with arbitrary angle and relative impedance unity (the most usual model for absorbing material) is given.     

Diffraction of a normally incident plane wave at a wedge withidentical tensor impedance faces

Diffraction of a normally incident plane wave by a wedge with identical tensor impedance faces is studied and an exact solution is obtained by reducing the original problem to two decoupled and already solved ones. A uniform asymptotic solution then follows from the exact one and agrees excellently with numerical results due to the method of parabolic equation     

Diffraction of a plane skew electromagnetic wave by a wedge with general anisotropic impedance boundary conditions

The three dimensional problem of diffraction of a skew incident plane wave by a wedge with anisotropic impedance boundary conditions is explicitly solved by the probabilistic random walk method. The problem is formulated in terms of two certain components of the electric and magnetic fields which satisfy independent Helmholtz equations but are coupled through the first-order boundary conditions. The solution is represented as a superposition of the geometric waves that are completely determined by elementary methods and of the waves diffracted by the apex of the wedge. The diffracted field is explicitly represented as the mathematical expectation computed over the trajectories of a two-state random motion which runs in a complex space and switches states under the control of stochastic equations determined by the problem's geometry and by the boundary conditions.     

On the scattering of an obliquely incident plane wave by a biisotropic cylinder

Scattering of an obliquely incident electromagnetic plane wave by an infinitely long, homogeneous, biisotropic cylinder is addressed. The ambient host medium considered is isotropic, homogeneous and dielectric-magnetic. It is observed that the constitutive coupling of the electric and the magnetic fields in the biisotropic material causes the cross-polarization component of the scattered field not to vanish even for the normal incidence case.     

Beam scattering by a right-angled impedance wedge

Following earlier developments, a uniform asymptotic solution for two-dimensional high frequency scattering by a right-angled impedance wedge is presented. The wedge supports surface waves on both faces and numerical examples show the relative significance of these surface waves for different surface parameters, source directivities and positions of source and receiver. Surface parameters extracted from experimental data for buildings are used to show that for near grazing incidence surface waves can have a very significant effect along the direction of specular reflection even in the far field. These results should be important in urban propagation modeling.     

BOR-FDTD斜入射脉冲平面波一维时域算法

针对斜入射脉冲波不能直接引入BOR-FDTD计算的问题,根据柱坐标系统中入射波在对称轴方向只有时间延迟的特性,结合平面波的柱面波展开,提出了一种行之有效的计算BOR-FDTD中斜入射脉冲平面波的一维时域算法,从而避免了大量快速傅里叶变换运算,节省了计算时间.计算结果表明该算法运行速度比基于完全傅里叶变换的算法快50倍.就整个程序运行时间而言,一维时域算法可以节省约20%的计算时间.为了验证该算法的有效性,计算了高斯脉冲斜入射时有限长金属圆柱体的散射问题,提取出某一频率下圆柱体母线电流密度分布并与MoM计算结果比较,二者吻合较好.然后计算了金属球的单站RCS随频率的变化,所得结果与理论值一致性也很好.     

Reflection of a transient plane wave obliquely incident on compressible plasma half-space

The expression for the reflected transient pulses from the sharp surface of a compressible plasma half-space are obtained in a series form with the first perturbation order explicitely evaluated and valid for small to moderate compressibility (α = u/C0≤ 0.3, u is the electron acoustic velocity and C0is the velocity of light in free space). The reflected waveform are close to the waveform of cold plasma (α = 0) with noticeable change of amplitude and time delay of the first maxima.     

Ie transmission properties of stratified chiroferrite media with obliquely incident plane wave

A parameter study of electromagnetic wave propagating through the air-chiro ferrite inter face and through a chiro ferrite slab is presented, and such bianisotropic medium can be made from chiral and gyrotropic ferrite materials artifically. The partial differential equations of the fourth order defining the field components E_y and H_y in chiroferrite are derived. The influence of different constitutive parameters on the transmission coefficients and refraction angles of transmitted fields are demonstrated. The results show that chirality causes strong effect of energy conversion between mode 1 and 2.     

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．     

Electromagnetic scattering by a wedge with anisotropic impedancefaces

Electromagnetic scattering from the edge of an anisotropic impedance wedge, illuminated at oblique incidence, is addressed. In particular, the paper provides a review of existing solutions for this important topic in diffraction theory. Both numerical and analytical techniques, suitable to properly account for the scattering properties of the wedge's anisotropic impedance faces, are considered     

Exact solution to diffraction problem by wedges with a class of anisotropic impedance faces: oblique incidence of a plane electromagnetic wave

This paper studies diffraction of an obliquely incident, arbitrarily polarized plane electromagnetic wave by an anisotropic impedance wedge with an opening angle 2/spl Phi/ between 0 and 2/spl pi/, and presents a closed-form exact solution to a class of impedance wedge faces and the related uniform asymptotic solution (UAS). On use of a unitary similarity transform, the boundary conditions on the wedge faces is brought into a form, which makes the exactly soluble class of impedance faces evident. The exact solution is found with help of the Sommerfeld-Malyuzhinets (1896, 1958) technique, a generalized Malyuzhinets function /spl chi//sub /spl Phi// and the so-called S-integrals. A standard procedure yields therefrom the UAS. The exact solution agrees with known analytical results in special cases, and the numerical results of UAS are confirmed by that of parabolic equation method (PEM).     

Incremental length diffraction coefficients for an impedance wedge

An incremental length diffraction coefficient (ILDC) formulation is presented for the canonical problem of a locally tangent wedge with surface impedance boundary conditions on its faces. The resulting expressions are deduced in a rigorous fashion from a Sommerfeld spectral integral representation of the exact solution for the canonical wedge problem. The ILDC solution is cast into a convenient matrix form which is very simply related to the familiar geometrical theory of diffraction (GTD) expressions for the field on the Keller cone. The scattered field is decomposed into physical optics, surface wave, and fringe contributions. Most of the analysis is concerned with the fringe components; however, the particular features of the various contributions are discussed in detail     

Skew incidence diffraction by an anisotropic impedance half plane with a PEC face and arbitrarily oriented anisotropy axes

High-frequency expressions for the field scattered by a half-plane with a perfectly conducting and an anisotropic impedance face are provided in the format of the uniform geometrical theory of diffraction (UTD), when the half-plane is illuminated by an arbitrarily polarized plane wave obliquely incident on its edge. The loaded face is characterized by a tensor surface impedance with principal anisotropy axes arbitrarily oriented with respect to the edge; a vanishing surface impedance is exhibited in one of the principal directions. This kind of tensor surface impedance can be suitably applied for analyzing the effects on the scattered field of corrugated surfaces or grounded dielectric slabs periodically loaded by metallic strips. This solution extends previous high-frequency formulations valid in those cases in which the direction of corrugations or strips is either parallel or perpendicular to the edge. The analysis is performed by resorting to the Sommerfeld-Maliuzhinets method. To determine the spectral solution, a special function is needed that differs from the standard Maliuzhinets one and was originally introduced to study the electromagnetic scattering by a wedge embedded in a gyroelectric medium.     

Diffraction of an obliquely incident high-frequency wave by a cylindrically curved sheet

In the application of the geometrical theory of diffraction (GTD) to practical problems, a main role is played by the diffraction coefficients of different kinds. Nevertheless the explicit expressions of the diffraction coefficients associated with edges on certain curved sheets are known only in the case of normal incidence. The canonical problems from which these coefficients are derived can always be reduced to scalar diffraction problems involving two space variables, in which either the electric or the magnetic field is parallel to the edge. Nevertheless, when the incident ray is not normal to the edge at the diffraction point, the related canonical problems inevitably involve three space coordinates and at least two dependent functions. The complexity inherent in such problems caused a lack of knowledge about the diffraction coefficients connected with the edges on curved sheets in the case of oblique incidence. The case of oblique incidence on a perfectly conducting cylindrical sheet is considered and some explicit expressions for the matrix diffraction coefficients are derived. These matrices connect the diffracted far fields of different kinds to the incident electric and magnetic field components parallel to the edge at the diffraction point. The expressions are rather simple and involve the coefficients related to the case of normal incidence in whichkis replaced byk sin theta_{0}(kandtheta_{0}are the wavenumber and the incidence angle, respectively). The effect of the incidence angle in the attenuation constants associated with the creeping waves are dependent upontheta_{0}only via the curvature radius of the geodesic lines.     

Two-dimensional diffraction by a wedge with impedance boundary conditions

The two dimensional problem of diffraction by a wedge with impedance boundary conditions on its faces is explicitly solved in a form that admits effective numerical simulation by simple perfectly scalable algorithms with unlimited capability for parallel processing. The solution is represented as a superposition of the geometric field that is completely determined by elementary ray analysis and of the waves diffracted by the tip of the wedge. The diffracted field is explicitly represented as a mathematical expectation of a specified functional on trajectories of a random motion determined by the configurations of the problem and by the boundary conditions. The numerical results confirm the efficiency of this approach.     

VIRTUAL-RAY METHOD AND ITS APPLICATION IN THE PLANE WAVE SCATTERING BY AN IMPEDANCE WEDGE

The virtual-ray method for treating HF electromagnetic scattering problems is derived from the plane wave of free space, and using this the plane wave scattering by an impedance wedge is studied. In the solution process a novel concept of generalized circle is introduced so that the complete amplitude function is obtained. And a reasonable physical interpretation for the term W2, which was neglected previously, is given. The calculated results agree well with those of the analytical solution obtained by G.D. Maliuzhinets(1958).     

Scattering of obliquely incident waves by an impedance cylinderwith inhomogeneous bianisotropic coating

A propagator matrix approach for cylindrical structures is applied to solve scattering problems featuring inhomogeneous bianisotropic media. The involved propagator matrix, which describes the relation between the transverse fields at the two boundaries of an inhomogeneous cylindrical layer, is obtained by utilizing Fourier series expansions for the fields as well as material parameter functions. The presented formalism is capable of analyzing the scattering of plane waves which are obliquely incident on an impedance cylinder that is covered with an inhomogeneous bianisotropic layer. We provide typical examples showing the applicability of the method