The diffraction of an inhomogeneous plane wave by an impedancewedge in a lossy medium

The diffraction of an inhomogeneous plane wave by an impedance wedge embedded in a lossy medium is analyzed. The rigorous integral representation for the field is asymptotically evaluated in the context of the uniform geometrical theory of diffraction (UTD) so that the asymptotic expressions obtained can be employed in a ray analysis of the scattering from more complex edge geometries located in a dissipative medium. Surface wave excitations at the edge and their propagation along the wedge faces are discussed with particular emphasis on the effects of losses     

UTD solution for plane wave diffraction at an edge in an artificially hard surface: Oblique incidence case

The three-dimensional plane wave scattering from an anisotropic wedge is described. The particular kind of anisotropic surface impedance considered for the wedge faces is suitable for modelling the artificially hard boundary condition     

Radiation from an aperture in an infinite conducting wedge

In this paper the problem of the far field radiation of an infinite aperture occupying one side of an infinite conducting wedge is solved. For uniform illuminations as well as for illuminations tapered to zero at the edges, it is shown that the radiated field can be effectively represented by line sources situated along the edge of the wedge. Also, for the special case of illuminations which taper to zero at the edges within a few wavelengths, it is shown that the shadow region radiation is proportional to the rate of taper.     

Diffraction by an arbitrary-angled dielectric wedge. I. Physicaloptics approximation

A complete form is presented of the physical optics solution to diffraction by an arbitrary dielectric wedge angle with any relative dielectric constant in cases of both E- and H-polarized plane waves incident on one side of two dielectric interfaces. The solution, which is obtained by performing the physical optics (PO) approximation to the dual integral equation formulated in the spatial frequency domain, is constructed by the geometrical optics terms, including multiple reflection inside the wedge and the edge diffracted field. The diffraction coefficients of the edge diffracted field are represented in a simple form as two finite series of cotangent functions weighted by the Fresnel reflection coefficients. Far-field patterns of the PO solutions for a wedge angle of 45°, relative dielectric constants 2, 10, and 100, and an E-polarized incident angle of 150° are plotted in figures, revealing abrupt discontinuities at dielectric interfaces     

Diffraction by an arbitrary-angled dielectric wedge. II. Correctionto physical optics solution

For pt.I see ibid., vol.39, no.9, p.1272-81 (1991). The error of the physical optics solution for the E-polarized plane wave incidence in connection with diffraction by an arbitrary-angled dielectric wedge is corrected by calculating the nonuniform current distributed along the dielectric interfaces. Two kinds of series expansions to the nonuniform current are employed. One is an asymptotic expansion as the multipole line source located at the edge of the dielectric wedge, since the correction field seems to be a cylindrical wave emanating from the edge in the far-field region. The other is arbitrary electric and magnetic surface currents expanded by infinite series of the Bessel functions, i.e. the Neumann expansion, of which fractional order is chosen to satisfy the edge condition near the edge of the dielectric wedge in the static limit. Both of the two different expansion coefficients for a wedge angle of 45°, relative dielectric constants 2, 10, and 100, and the E-polarized incident angle of 150° are evaluated by solving the dual series equation numerically after finite truncation     

采用光折变全息干涉计量术对光楔特性的测量

光折变晶体是一种新型的记录材料,应用光折变效应,不需显影、定影等处理,就可实现实时观测。文章探讨了光折变实时全息干涉法在光学检测中的应用,提出同时确定光楔楔角和折射率的新方法,从而改变了只有光楔的折射率和楔角中一个已知时才可测量另一个未知量的传统测量方法。介绍了实验过程,分析得出了最后实验结果。     

Uniform diffraction coefficients for an impedance wedge

Uniform diffraction coefficients for an astigmatic electromagnetic wave normally incident on a wedge having curved faces with given surface impedances are derived from the earlier work of Maliuzhinets. These coefficients are to be used with standard formulas in the geometrical theory of diffraction to predict diffraction effects from structures having impedance surfaces terminating in an edge.     

Scattering by an imperfect right-angled wedge

A solution is obtained for the problem of a plane electromagnetic wave at skew (oblique) incidence on a right-angled wedge one of whose faces is imperfectly conducting. An exact integral expression for the total field is derived, and the geometrical optics and edge diffracted fields are obtained. These are used to produce a uniform solution in the uniform asymptotic theory (UAT) format. Plots of the edge diffracted and total fields are presented to show the effect of the impedance of the wedge face.     

Diffraction by a rounded wedge with an hybrid method MM/PO

The paper deals with an hybrid method, combining a method of moments and physical optics, to compute the diffraction by wedges with arbitrary rounded edges. The vicinity of the rounded part of the wedge is meshed and the current is computed by using the mom. Far from the rounded part, the current is assumed to be equal to the physical optics current. The results of the hybrid method are compared to the results available in the literature for the special case of a wedge with a circular edge.     

Reflections, diffractions, and surface waves for an interiorimpedance wedge of arbitrary angle

The asymptotic-impedance wedge solution for plane-wave illumination at normal incidence is examined for interior wedge diffraction. An efficient method for calculating the diffraction coefficient for arbitrary wedge angle is presented, as previous calculations were very difficult except for three specific wedge angles for the uniform geometrical theory of diffraction (UTD) expansion. The asymptotic solution isolates the incident, singly reflected, multiply reflected, diffracted, surface wave, and associated surface wave transition fields. Multiply reflected fields of any order are considered. The multiply reflected fields from the exact solution arise as ratios of auxiliary Maliuzhinets functions; however, by using properties of the Maliuzhinets functions, this representation can be reduced to products of reflection coefficients which are much more efficient for calculation. A surface-wave transition field is added to the surface wave boundaries. Computations are presented for interior wedge diffractions although the formulation is equally valid for both exterior and interior wedges with uniform but different impedances on each face for both soft and hard polarizations. In addition, the accuracy of the high-frequency asymptotic expansion is examined for small diffraction distances by direct comparison of the exact and asymptotic solutions     

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     

A uniform geometrical theory of diffraction for an edge in a perfectly conducting surface

A compact dyadic diffraction coefficient for electromagnetic waves obliquely incident on a curved edse formed by perfectly conducting curved ot plane surfaces is obtained. This diffraction coefficient remains valid in the transition regions adjacent to shadow and reflection boundaries, where the diffraction coefficients of Keller's original theory fail. Our method is based on Keller's method of the canonical problem, which in this case is the perfectly conducting wedge illuminated by plane, cylindrical, conical, and spherical waves. When the proper ray-fixed coordinate system is introduced, the dyadic diffraction coefficient for the wedge is found to be the sum of only two dyads, and it is shown that this is also true for the dyadic diffraction coefficients of higher order edges. One dyad contains the acoustic soft diffraction coefficient; the other dyad contains the acoustic hard diffraction coefficient. The expressions for the acoustic wedge diffraction coefficients contain Fresenel integrals, which ensure that the total field is continuous at shadow and reflection boundaries. The diffraction coefficients have the same form for the different types of edge illumination; only the arguments of the Fresnel integrals are different. Since diffraction is a local phenomenon, and locally the curved edge structure is wedge shaped, this result is readily extended to the curved wedge. It is interesting that even though the polarizations and the wavefront curvatures of the incident, reflected, and diffracted waves are markedly different, the total field calculated from this high-frequency solution for the curved wedge is continuous at shadow and reflection boundaries.     

High-frequency approximations for electromagnetic field near a face of an impedance wedge

We employ the exact solution given by G.D. Maliuzhinets (see Sov. Phys. Doklady, vol.3, p.752-5, 1958) for the canonical problem of diffraction of a plane wave by an arbitrarily angled impedance wedge to derive asymptotic approximations to the field components in a region contiguous to a face of the wedge. The asymptotic solution accounts for terms of order (k/spl rho/)/sup -3/2/ (k is the wave number and /spl rho/ is the distance from the edge), is uniform with respect to observation and illumination aspects and includes the case of grazing illumination of a wedge face, which is known to be particularly difficult for high-frequency analysis (Uflmtsev's singularity).     

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.     

The diaphanous wedge

Complete solutions for the scattering by a diaphanous wedge, meaning a wedge with identical wavenumbers inside and outside the wedge, are presented. The results are obtained from an integral equation for the fields on the wedge, which is solved by the Mellin and Kantorovich-Lebedev transforms in the static and dynamic cases, respectively. Pertinent formulations of Gegenbauer's addition theorems play an important part in the derivation of the results, which are presented in closed form     

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     

电小尺寸凹槽的远区数值绕射系数

应用时域有限差分（FDTD）方法和时域加窗技术从物体的时域散射场中分离出劈和凹槽一类散射中心的贡献,计算其远区数值绕射系数。对于电小尺寸凹槽的远区数值绕射系数,结合微扰法给出了其计算结果。     

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     

阻抗劈一致性绕射系数的一种简洁表达式

本文给出了阻抗劈一致性绕射系数的一种简洁易算的表达式，避免了原绕射系数表达式的复杂性和不易实现计算机     

Computed fields near the edge of a dielectric wedge

The behavior of the electromagnetic field near the edge of an infinite sharp dielectric wedge has not been unequivocally established in the theory. A numerical experiment is performed to learn more about this behaviour. The fields scattered by a finite wedge are determined by solving an integral equation for a function defined on the boundary. The fields near the edge of the wedge are computed from this function by integration. The accepted theory of the fields near the edge of the dielectric wedge is based on a power series expansion that does not exist. The conclusion from this numerical experiment is that only the radial fields along the bisector of the wedge in the transverse magnetic mode follow the expected power law. The corresponding problem for the perfectly conducting wedge is well understood and is used to verify the numerical methods