单层和多层有缝金属板电磁波透射的FDTD分析

采用在入射波一侧的总场边界处同时引进入射波和反射波作为激励源的FDTD方法来分析斜入射时单层和多层有缝金属板电磁波透射问题.通过计算金属板缝隙附近的散射场,提取缝隙口径面上的等效面磁流,进而得到透射截面.计算机仿真结果证实了算法的有效性.数值计算结果表明,两金属板上所开缝隙的相对偏移以及两板间插入介质板将会改变屏蔽效应.该方法可以有效分析平面波斜入射时多层金属板上任意形状缝隙的散射和透射,包括缝隙内或金属板之间填充有介质情形.     

Equivalent Series Inductivity of a Narrow Transverse Slit in Microstrip

The series inductivity introduced by a narrow transverse slit in a microstrip transmission line has been evaluated theoretically, and a simple formula for this inductivity is presented. Experimental results for slits of different depth obtained with the resonant ring method compare well with theory. Applications of such a slit include the fine tuning of the electrical length of stubs and the compensation of excess capacitances at discontinuities.     

Analysis of a narrow slit in a parallel-plate transmission line: E-polarisation case

The integro-differential equation is formulated for the equivalent magnetic current in the narrow slit in a parallel-plate transmission line when excited by an E-polarised, dominant (TE) mode wave. A solution (magnetic current) is presented to the approximated integro-differential equation for the narrow slit case. From knowledge of the magnetic current, the normalised resistance and reactance of the slit are computed.     

The Electromagnetic Problems of a Cylinder or Elliptic Cylinder with Infinite Axial Slits and Others

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Diffraction characteristics of a slit in a thick conducting screen

The diffraction of a plane electromagnetic wave by a slit in a conducting screen of finite thickness is investigated using the Wiener-Hopf and generalized matrix techniques. For purposes of the analysis, the diffraction by two identical semi-infinite parallel-plate waveguides forming a tandem slit configuration is treated first in order to determine the interaction between the open ends of the waveguides. This interaction term is then utilized in solving for the thick slit geometry which is obtained by filling the parallel-plate regions with a dielectric whose relative permittivity is allowed to approach infinity. Although the integral equations occurring in the tandem slit configuration are similar to those given by Jones for the parallel-strip case, they are solved here by a somewhat different method. In contrast to the limitation on the strip-strip separation imposed by Jones, our solution is not restricted to the special case of large separation between the two slits. For anE-polarized incident plane wave, the far field diffracted by each edge of the thick slit is viewed in ray-optical terms as that due to a thin edge centered at the middle of the thick edge modified by a multiplication factor. The thick edge-edge interaction term, on the other hand, is also modified such that each thick edge is viewed by the other as a combination of a line source as well as a line dipole which vanishes when the thickness approaches zero. It is shown that for ratios of screen thickness to slit width belowapprox0.5, the beamwidth is larger than that of the thin slit, while for larger ratios the beamwidth is smaller. Typical diffraction patterns, which are in good agreement with experiment, are presented to illustrate this phenomenon.     

Natural-mode representation of transient scattered fields

Electromagnetic scattering from a perfectly conducting body of finite extent is considered from an integral equation point of view. It is shown that the operator inverse to the integral operator of the magnetic field formulation is an analytic operator-valued function in the complex frequency plane except at certain points (the natural frequencies) where it has poles. Furthermore, a representation of the inverse operator in terms of the natural frequencies and the nontrivial solutions of the homogeneous integral equation is given. Explicit expressions for the scattered field in terms of exponentially damped sinusoidal oscillations are given for the special case where the incident wave is a delta-function plane wave and the inverse operator has only simple poles.     

Diffraction From A Material Loaded Tandem Slit

In this paper, we consider plane wave diffraction by a tandem slit loaded with a homogenous material. The boundary value problem is formulated into a pair of simultaneous Wiener-Hopf equations via Fourier transformation. After decoupling these equations by elementary transformation, each modified Wiener-Hopf equation is reduced to a Fredholm integral equation of the second kind. The integral equations are then solved approximately to yield the Fourier transform of the diffracted fields. The inverse transform is evaluated asymptotically to obtain the far field expressions. Measurements and numerical simulations are also performed for several different geometry and material configurations. The analytic solutions compare well with measured and simulated results. The possibility of reducing beamwidth and increasing power coupled through the loaded tandem slit is explored.      

Wave penetration through slits on stacked thick plates

Wave penetration through slits on single and stacked metal plates of finite thickness is studied by using the Galerkin method. The limiting case of slits on infinitesimally thin plates are also formulated to compare the shielding effectiveness of metal plates with slits against incident plane waves. It is observed that the wave penetrating through slits on stacked plates with a proper separation is much less than that through a single slit on a plate with twice the thickness     

A General Multisegment Artificial Neural Network Architecture for the Efficient Evaluation of Electromagnetic Plane-Wave Wedge Diffraction

A multisegment artificial neural network (ANN) is proposed as an interpolation technique for the evaluation of the electromagnetic field diffracted at the edge of anisotropic impedance wedges under plane wave illumination at oblique incidence. Multisegmentation is needed as the high-frequency wedge diffracted field is characterized by a number of discontinuities at the shadow boundaries of the geometrical optics and surface wave fields. The proposed approach is applied, as a test case, to the problem of an anisotropic impedance right-angled wedge illuminated by a skewly incident plane wave. Some exact analytical solutions valid for specific surface impedance tensors are used to obtain numerical data for the ANN training phase as well as to show the interpolation capabilities of the implemented ANN. Nevertheless, the proposed ANN structure is general and can be trained with data obtained from other available solutions (analytical, perturbative, numerical) valid for more general wedge configurations, eventually leading to a single software tool encompassing all of them and providing accurate approximations of the wedge diffracted field in a relatively short time, comparable to that of a closed form analytical solution.     

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     

有限厚导电平板上任意缝隙的耦合特性分析

利用边界积分方程法结合广义网络原理和连接算法分析了有限厚导电平板上任意二维缝隙的散射及传输特性,并以ＴＥ波为例给出了具体的分析方法和结果。该方法不仅可用于任意形状和复杂介质填充缝隙的分析,还可考虑缝所在导体板的厚度。边界积分方程和连接算法的采用,使得分析该问题所需的计算机容量大大降低,计算效率大大提高。     

彩虹全息术综合狭缝的理论分析

本文从像面光场移动的观点对一步无狭缝彩虹全息术中平移物体和透镜形成的综合狭缝进行了理论分析，并提出了一种新的综合狭缝二步彩虹全息方法．     

FDTD simulation of TE and TM plane waves at nonzero incidence in arbitrary Layered media

Plane wave scattering is an important class of electromagnetic problems that is surprisingly difficult to model with the two-dimensional finite-difference time-domain (FDTD) method if the direction of propagation is not parallel to one of the grid axes. In particular, infinite plane wave interaction with dispersive half-spaces or layers must include careful modeling of the incident field. By using the plane wave solutions of Maxwell's equations to eliminate the transverse field dependence, a modified set of curl equations is derived which can model a "slice" of an oblique plane wave along grid axes. The resulting equations may be used as edge conditions on an FDTD grid. These edge conditions represent the only known way to accurately propagate plane wave pulses into a frequency dependent medium. An examination of grid dispersion between the plane wave and the modeled slice reveals good agreement. Application to arbitrary dispersive media is straightforward for the transverse magnetic (TM) case, but requires the use of an auxiliary equation for the transverse electric case, which increases complexity. In the latter case, a simplified approach, based on formulating the dual of the TM equations, is shown to be quite effective. The strength of the developed approach is illustrated with a comparison with the conventional simulation based on an analytic incident wave specification with half-space, single frequency reflection and transmission for the edges. Finally, an example of a possible biomedical application is given and the implementation of the method in the perfectly matched layer region is discussed.     

Diffraction of electromagnetic plane wave by an infinite slit in a screen with surface impedance

Diffraction of an electromagnetic plane wave by an infinite slit in a screen with surface impedance is solved analytically as a boundary value problem under the assumption that the plane of incidence is normal to the slit in a screen of zero thickness surrounded by a homogeneous medium. The field expressions and the transmission coefficient are derived asymptotically, and their numerical solutions are presented for a special case of perfect conducting screen.     

Analysis of transient electromagnetic scattering from closedsurfaces using a combined field integral equation

In the past, both the time-domain electric and magnetic field integral equations have been applied to the analysis of transient scattering from closed structures. Unfortunately, the solutions to both these equations are often corrupted by the presence of spurious interior cavity modes. In this article, a time-domain combined field integral equation is derived and shown to offer solutions devoid of any resonant components. It is anticipated that stable marching-on-in-time schemes for solving this combined field integral equation supplemented by fast transient evaluation schemes such as the plane wave time-domain algorithm will enable the analysis of scattering from electrically large closed bodies capable of supporting resonant modes     

Solution of the vector wave equation for general dielectricwaveguides by the Galerkin method

Numerical guided mode solutions for vector waves of general dielectric waveguides are obtained by expanding the unknown field vectors in a double series consisting only of sine functions. The authors formulate solutions by series expansion for the electric and magnetic vector wave equations that yield different matrix equations but identical eigenvalues. The general results are applied to a simple step-index fiber with a large core-cladding index difference and to a fiber core in proximity to a semiinfinite dielectric half space     

应用改进的试探函数法求非线性数学物理方程精确解

应用改进的试探函数法求得Jimbo-Miwa方程和非线性传输线电位方程的精确解,这些解包括双曲函数解、三角函数解。当对双曲函数解中的参数取特殊值时,可以得到了孤立波解。当对三角函数解中的参数取特殊值时,可以得到对应的周期波函数解。实践证明,试探函数法对于研究非线性数学物理方程具有非常广泛的应用意义。     

EM pickup and scattering by a wire

This article treats pickup and scattering by a single wire in free space or over a ground plane. The wire may be uniform or nonuniform and infinite or finite. We only treat the case where wire radius is so small compared to a wavelength and the other problem dimensions that scattering by the wire is independent of azimuth. Solutions based directly on Maxwell's equations are compared with solutions based on the telegrapher's equations; for 1 mm radius Cu wire at 1 GHz, equilibrium CW currents as computed from the two models, for a uniform, infinite wire, differ by 6 dB. In general, the wire-current solutions are separated into a homogeneous part and a particular or driven part. The driven part couples and scatters fields, while,at least on an infinite wire in the far field, the homogeneous part does not     

Electromagnetic Transmission through a Filled Slit in a Conducting Plane of Finite Thickness, TE Case

A solution is developed for computing the transmission characteristics of a slit in a conducting screen of finite thickness placed between two different media. The slit may be filled with Iossy material while the two regions on either side of the screen are assumed Iossless. A magnetic line source excitation is used (TE case) which is parallel to the axis of the slit. The equivalence principle is invoked to replace the two slit faces by equivalent magnetic current sheets on perfect electric conductors. Two coupled integral equations containing the magnetic currents as unknowns are then obtained and solved for by the method of moments. Pulses are used for the expansion and testing functions. Quantities computed are equivalent magnetic currents, the transmission coefficient, the gain pattern, and the normalized far field pattern.     

Inverse electromagnetic scattering by cylindrical bodies buried in a slab or a half-space

An exact theory of the inverse scattering problems related to cylindrical bodies buried in a slab is established in two-dimensional scalar case. The theory dwells on two functional equations interrelating the outgoing wave solutions of the wave equation, which can be observed physically, with incoming wave solutions that are physically meaningless and irrealizable. One of these functional equations involves the measured radiation pattern in its kernel (material relation) while the other is independent of the measured data (universal relation). To establish the material relation one has to make far-field measurements with various incidence angles at various observation points and frequencies. The universal relation which guarantees some analytical properties of the field function results in a Stieltjes type integral equation. By solving these equations one gets the location, shape and permittivity of the inaccessible body. When the material of the half-space below the slab is made identical to that of the slab, then the results are reduced to that of the bodies buried in a half-space.