Excitation of surface waves during diffraction by a circular impedance cylinder

Under certain conditions, surface waves are excited during diffraction by a body with an impedance surface. In the problem on the incidence of a plane wave on a circular cylinder, the total field is decomposed in the fields of such surface waves, and this decomposition is a Watson series constructed similarly to the corresponding series for a metal sphere. The amplitudes of the excited waves and the field structure of these waves are found.     

Scattering by a multilayer chiral cylinder

An efficient recursive eigenfunction solution for the problem of scattering by a multilayer chiral circular cylinder, with or without a surface impedance center cylinder, is presented. For an M layer cylinder, the solution requires the multiplication of M4×4 matrices, versus the solution of a 4M×4M matrix equation in a standard approach. The problem of a transverse electric (TE) incident plane wave differs from that of a transverse magnetic (TM) wave only by a plus/minus sign at one step in the solution. The addition of the surface impedance center cylinder requires only one additional matrix multiplication. Numerical results, including echo width and internal fields, are presented for several sample cylinders     

复射线展开法分析圆柱面对平面波散射的精度问题

讨论了用复射线展开法计算圆柱面对入射平面波散射时的计算误差特性,提出了控制其计算精度的复射线展开参数选择方法,证实了通过恰当选择展开参数可以有效地提升计算精度、实现误差控制。     

Computation of near-field aperture diffraction by a cylinder

A method of computing the effect of a cylindrical obstacle in the near field of an aperture antenna is described. The measured and calculated results for a typical case are then presented and other results discussed.     

High-frequency diffraction of a line-source field by a half-plane: Solutions by ray techniques

The diffraction of an arbitrary cylindrical wave due to a line source and incident on a half-plane is treated by the uniform asymptotic theory of edge diffraction. For large wavenumberk, an asymptotic solution for the total field up to and including terms of orderk^{-3/2}relative to the incident field is derived. This solution is uniformly valid for all observation points, including points near the edge and the shadow boundaries. In particualr, two special cases are considered: A) the line source is located on the half-plane, and radiates anE-polarized wave and B) the line source is located in the aperture complementary to the half-plane and radiates anH-polarized wave. A companion paper will show that our asymptotic solution for Case A) is in complete agreement with the asymptotic expansion of the exact solution. For the same diffraction problem, asymptotic solutions obtained by the method of slope diffraction coefficients and the method of equivalent currents are also discussed. It is found that the latter solutions agree with the exact one only when i) the observation point is away from the edge and the shadow boundaries, and/or ii) the terms of orderk^{-3/2}in the field solution are ignored.     

On diffraction by a rippled convex surface

A perturbation analysis is employed to obtain a modal equation for diffraction by a perfectly conducting cylindrical surface with a sinusoidal perturbation of the height profile. It is found that the surface impedance concept has a measure of validity in describing the fields averaged over one period of the surface.     

Creeping wave diffraction by a junction with plane surface

The transformation of a creeping wave coming to the point of the junction of convex and plane parts of the surface is examined. The asymptotics in a vicinity of the junction is constructed in the leading approximation. The solution is given by the integral containing Airy function. The numerical results for that integral are presented. The results show the transition between a creeping wave like behaviour and a diverging wave behaviour.     

A diffraction coefficient for a cylindrically truncated planar surface

A numerically derived solution of the diffraction coefficient for a source mounted on a perfectly conducting planar surface which is smoothly terminated by a circular cylinder is obtained using the hybrid approach which combines the moment method (MM) with the geometrical theory of diffraction (GTD). This solution is valid not only in the region away from, but also in the region near, the shadow boundary. The accuracy and usefulness of this solution is demonstrated as various structures are treated using it.     

Electromagnetic scattering by a multilayer elliptic cylinder undertransverse-magnetic illumination: series solution in terms of Mathieufunctions

An exact solution to the electromagnetic scattering by a dielectric multilayer infinite cylinder of elliptic cross section is proposed. The interfaces between different media, which are assumed to be lossless and nonmagnetic, are confocal elliptic cylinders. Starting from the series expansions in terms of Mathieu functions, an efficient recursive procedure for the computation of fields and radar cross sections per unit length under a transverse-magnetic illumination is developed. The mathematical formulation is detailed and some numerical results are provided     

A uniform GTD treatment of surface diffraction by impedance andcoated cylinders

In the context of the uniform geometrical theory of diffraction (UTD), computation of the scattered fields near the shadow boundary of a smooth convex surface requires values for the Pekeris-integral function p*(ξ,q). While in a small number of cases such as the case of perfect conductivity (q=0 and q→∞), tabulated values of the function are available; in the general case, these values must be obtained by some numerical method. A procedure for approximating p*(ξ,q) by residue-series means is introduced. In contrast with traditional residue-series representations, the new procedure requires only a limited knowledge of pole locations even in the shadow boundary transition region and thereby extends the regime of practical applicability of residue-series methods beyond the deep shadow. It is demonstrated that the new procedure can be combined with an earlier residue-series representation derived by Hussar and Albus (1991), and with geometrical optics, to provide a computationally efficient procedure for computing fields scattered by an impedance or coated cylinder     

A uniform GTD analysis of the diffraction of electromagnetic waves by a smooth convex surface

The problem of the diffraction of an arbitrary ray optical electromagnetic field by a smooth perfectly conducting convex surface is investigated. A pure ray optical solution to this problem has been developed by Keller within the framework of his geometrical theory of diffraction (GTD). However, the original GTD solution fails in the transition region adjacent to the shadow boundary where the diffracted field plays a significant role. A uniform GTD solution is developed which remains valid within the shadow boundary transition region, and which reduces to the GTD solution outside this transition region where the latter solution is valid. The construction of this uniform solution is based on an asymptotic solution obtained previously for a simpler canonical problem. The present uniform GTD solution can be conveniently and efficiently applied to many practical problems. Numerical results based on this uniform GTD solution are shown to agree very well with experiments.     

An asymptotic solution for the diffraction by a discontinuity in curvature coupled with surface diffraction

An extension is developed for the asymptotic theory of electromagnetic diffraction by a discontinuity in curvature on a smooth convex perfectly-conducting surface. It covers the case where the rays incident on and diffracted from the discontinuity are nearly tangent to the surface or are creeping rays, so that surface diffraction is involved. This extension is restricted to those diffracted rays lying on the same side of the discontinuity as the incident ray; this includes backscatter but excludes forward scattering.     

Equivalent-circuit representation and characteristics of a radiating cylinder driven through a circumferential slot

The problem of an infinitely long coaxial cylinder with a single circumferential slot in the sheath is investigated analytically. When the slot width is small compared with the radius of the outer cylinder, an exact integral equation for the aperture field is formulated and subsequently solved by a quasi-static technique. Equivalent circuit representation of the coupling between the outside antenna and the inside coaxial line is obtained in closed form. Due to the highly localized nature of the coupling, the result thus obtained is applicable to finite cylindrical antenna with multiple feed slots.     

Incremental length diffraction coefficients for the shadow boundaryof a convex cylinder

Incremental length diffraction coefficients (ILDCs) are obtained for the shadow boundaries of perfectly electrically conducting (PEC) convex cylinders of general cross section. A two-step procedure is used. First, the nonuniform (NU) current in the vicinity of the shadow boundary is approximated using Fock (1965) functions. The product of the approximated current and the free-space Green's function is then integrated on a differential strip of the cylinder surface transverse to the shadow boundary to obtain the ILDCs. This integration is performed in closed form by employing quadratic polynomial approximations for the amplitude and unwrapped phase of the integrand. Examples are given of both the current approximations and the integration procedure. Finally, as an example, the scattered far field of a PEC sphere is obtained by adding the integral of the NU ILDCs of a circular cylinder along the shadow boundary of the sphere to the physical optics (PO) far field of the sphere. This correction to the PO field is shown to significantly improve upon the accuracy of the PO far-field approximation to the total scattered field of the sphere     

Excitation of surface modes along a semi-infinite dielectric cylinder

Expressions for the amplitude and power of surface-waveguide modes excited by a plane wave along a semi-infinite dielectric cylinder are presented. Approximations for small dielectric differences are given, which result in a simple expression for the power of the modes. Application of these results to light propagating along the human retinal receptors is discussed.     

Monolithic integration of multilayer filter on vertical surface ofsemiconductor substrate by a bias-sputtering technique

The selective formation of dielectric film on a vertical surface of a substrate by a bias-sputtering technique is discussed. Using this technique it has been possible to achieve the monolithic integration of a multilayer wavelength filter and waveguide photodetector on a vertical surface of a semiconductor substrate. The wavelength filter can be applied to an integrated demultiplexer and photodetector by fabricating an optical waveguide directly on the substrate     

A global scattering center representation of complex targets usingthe shooting and bouncing ray technique

We present a methodology to extract a global scattering center model a complex target. Using the shooting and bouncing ray technique, we first extract the three-dimensional (3-D) scattering center representations of the target at various aspect angles. Next the correspondence between scattering centers across angles are established by utilizing 3-D location information. The data are grouped based on 3-D scattering center locations and are organized in the form of angular visibility maps. Such data organization gives good insights into target physics and feature stability. Furthermore, we define a stability measure to quantitatively rank order the scattering centers based on their angular stability. Finally, we demonstrate the usefulness of such stable features by carrying out a five-target template-based matching experiment to estimate the angular pose of an unknown target     

激光衍射法测量液体的表面波速度和表面张力

实验上实现了低频液体表面波的激光衍射,提出了激光衍射法测量几百赫兹液体表面波的相速度、群速度和液体的表面张力.当激光斜入射到几百赫兹的液体表面波上,反射的激光产生稳定、清晰的衍射光斑,理论上导出了衍射光斑的角宽度与液体表面波速度的解析关系,实验上测得几百赫兹液体表面波的相速度和群速度,并测量了液体的表面张力.根据其机理,建立起一种实时、非接触的测量液体表面波的相速度、群速度和表面张力的实用方法.     

High-frequency surface field excited by a magnetic line source on an impedance cylinder

The evaluation of the transverse electric (TE) surface field on an impedance boundary circular cylinder, excited by a magnetic current on the same surface is discussed. The source is of infinite axial extent. The integral which describes the field due to a single surface ray is evaluated numerically and asymptotically. The results compare well with each other as well as with the eigenfunction solution. The surface ray field has a uniform representation in the sense that it remains valid in the immediate vicinity of the infinitesimal source as well as in the deep shadow region. A comparison is made with a flat impedance plane to indicate the influence of curvature on the surface field.     

Electromagnetic diffraction from a dielectric-filled slit-cylinderenclosing a cylinder of arbitrary cross section: TM case

A simple moment solution to the problem of the diffraction of a TM plane wave from an infinite, perfectly conducting slotted cylinder of an arbitrary cross section is summarized. The slit cylinder encloses a smaller perfectly conducting cylinder of an arbitrary cross section, and the space between the cylinders is filled with a dielectric material. The equivalence principle is used to obtain a set of coupled integral equations for the induced/equivalent surface currents on the cylinders, and the method of moments is used to solve numerically the integral equations. The electric field integral equation formulation is used. The advantages and the limitations of the method are discussed. Sample results for the induced current, aperture field, internal field, and scattering cross sections are given. These are in good agreement with some of the available published data