Time-domain electromagnetic plane waves in static and dynamicconducting media. I

Solutions are derived for the time-domain Maxwell equations for static (J=σE) and dynamic (τ∂/∂t+J= σ₀ E) conducting media where the field is assumed to vary with respect to only one spatial direction, i.e., plane-wave propagation. The plane wave is introduced into the media via the imposition of an electric field boundary condition at the plane boundary of a half-space and it is assumed that the fields inside the half-space are initially zero. Solutions are derived directly from the first-order system of partial differential equations and it is shown that once the electric field at the plane boundary is imposed, the magnetic field is automatically determined for causal solutions. It is shown that the form of the Maxwell equations, without a magnetic conductivity term added, is sufficient to allow well and uniquely defined solutions of this problem     

Time-domain simulation of spherical electromagnetic waves

Spherical electromagnetic waves excited by external surface electric currents in a homogeneous isotropic space are considered. It is shown that, in contrast to the harmonic excitation, in the case when the electromagnetic field is excited by external-current pulses, there is always an isolated convergent spherical wave in a bounded space-time region. The possibility of the existence of an isolated convergent spherical wave in a bounded spatial region at all instants is investigated for the cases of harmonic and pulse electromagnetic field excitations. It is proved that such a wave can exist when the divergent spherical wave arriving from the origin is compensated with the use of additional external currents. The excitation of isolated convergent spherical waves is illustrated by examples.     

Riemann-Green function solution of transient electromagnetic plane waves in lossy media

B. Riemann's (1953) solution of the Cauchy problem for the linear wave equation is used to find a closed-form solution for the problem of transient nonsinusoidal waves is lossy media. A method for finding the required Riemann-Green function is discussed. The evolution of a wavefront propagating in a semi-infinite lossy medium is studied, and a series solution for the corresponding electric field is obtained.<>     

Transmission of electromagnetic waves into time-varying media

Expressions are obtained for the electromagnetic fields transmitted into the time-varying medium when a plane wave is incident upon either a dielectric or dispersive half-space. Solutions are obtained for the case when the medium is changed in a stepwise fashion, and also for the case when the medium varies slowly and continuously.     

Reflection and transmission of plane electromagnetic waves in uniaxial bianisotropic materials

Electromagnetic waves in the most general linear reciprocal uniaxial media are considered. The theory is appropriate for novel reciprocal microwave materials which have properties of chiral composites and omega structures (or both) and can be modeled by uniaxial bianisotropic constitutive relations. Field coupling terms in the media equations are assumed to be the most general uniaxial dyadics with symmetric and antisymmetric components. Plane eigenwaves in unbounded media are studied and the theory of reflection and transmission in plane layers is constructed.     

Scattering of electromagnetic plane waves by a circular cylinder

Numerical investigation of scattering electromagnetic plane waves by a circular conducting cylinder is considered. The results presented are 1) validity of asymptotic far-field expressions when it is applied to calculate near-field around the cylinder and 2) equicontours of amplitude and phase of total field around the cylinder.     

Lateral electromagnetic waves along plane boundaries: A summarizing approach

Lateral electromagnetic waves along a plane boundary between homogeneous half-spaces are reviewed. The electromagnetic fields generated by vertical and horizontal electric dipoles near the boundary between air and the earth (salt or fresh water, soil, ice, etc.) are summarized in terms of a new unified theory of lateral-wave propagation. Complete theoretically determined fields are displayed and compared with measured fields at f = 601 MHz relative to the boundary between air and salt water (σ = 3.5 S/m, εr= 80). Near, intermediate, and asymptotic fields are related graphically to the new general theory and to the approximate and restricted formulas of Norton and Baños as well as to the Zenneck wave. Application is made to the specific problem of communication with submerged submarines by means of transmitters consisting of electrically short monopoles in air and horizontal traveling-wave antennas and directional arrays in sea water. The properties of the antennas are evaluated in the frequency range 10 ≤ f ≤ 30 kHz which is optimum for receiver depths near 10 m, and at f = 1 kHz which is optimum for depths up to 50 m. The effects of reflections from the ionosphere and of the earth's curvature are not included.     

Reflection and transmission of electromagnetic plane waves from an uniaxial chiro-omega slab

Chiro-omega medium is a combination of the reciprocal chiral and omega media, and can be obtained by mixing helical and Ω — shaped wire elements in the host medium. In this article the most general uniaxial chiro-omega medium is studied. The solutions for the dispersion equations and corresponding eigenwaves are derived. Transmission and reflection properties of a chiro-omega slab at a normal incidence are studied, and the polarization, direction of the polarization ellipse, and relative powers of transmitted and reflected waves are given. The results are applied to find suitable parameters for designing a polarization transformer. These results are compared with those obtained in earlier studies on wave propagation in a free uniaxial chiral space, where the effect of the boundaries of a proposed polarization transforming device have been neglected.     

Spectral and transient response of a circular disk to plane electromagnetic waves

Extensive theoretical far-field amplitude and phase data are presented for the monostatic scattering of an electromagnetic plane wave normally incident upon a thin circular metallic disk. These data are used to synthesize the impulse response of the disk. Comparisons are made with various approximate techniques in both the frequency and time domains.     

Recursive asymptotic impedance matrix method for electromagnetic waves in bianisotropic media

A recursive asymptotic impedance matrix method is presented for simple and stable analysis of electromagnetic waves in bianisotropic media. The method overcomes the numerical instability problem associated with the transition matrix method. It requires only elementary matrix operations along with thin-layer asymptotic approximation and bypasses the intricacies of the eigenvalue-eigenvector approach. Exploitation of its self-recursion algorithm with geometric subdivision of a layer leads to high computation efficiency. The method also facilitates the trade-off between accuracy and speed for various applications.     

在时域内计算色散媒质中光脉冲的传输

得到了时域内色散媒质中光脉冲传输的计算公式，并提出了时域内色散媒质中显式的光束传播法。计算了短脉冲在具有二阶色散效应的定向耦合器内的传输、计算结果同参考文献中的一致，但本文的计算方法简单、方便、实用。     

Some new results on propagation of electromagnetic waves in strongly turbulent media

New results for the covariance of the intensity fluctuations of a plane wave propagating in a strongly turbulent medium are presented, and the consequences of these new results on aperture averaging, angle of arrival fluctuations, and the temporal frequency spectrum of the intensity scintillations are evaluated. The differences between the strong turbulence and weak turbulence cases are generally quite significant.     

An anisotropic lens for transitioning plane waves between media ofdifferent permittivities

A particularly simple geometry is considered in which an inhomogeneous and anisotropic lens is specified for the transitioning of plane waves between media of different permittivities. The permittivities of the regions outside of the lens can be constant, but the permittivity of the lens region depends on position. Results are presented for a plane wave in the second medium propagating normally to the assumed plane boundary of that medium. The results for the case of normal incidence are then generalized to the case of nonnormal incidence. The conditions of transit time conservation and impedance matching are related to the Brewster angle     

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.     

A new approach to diffraction analysis of conductor grids. II.Perpendicular-polarized incident plane waves

For pt.I see ibid., vol.37, no.1, p.84-88 (1988). Diffraction analysis is given for infinite planar conducting-strip grids illuminated by normally incident (perpendicular-polarized) plane waves, the electric fields of which are perpendicular to the strip axes. Iris-surface electric field integral equations are used which are based on the equivalent waveguide theory, and then the electric field is solved for using the moment method. This is a universal approach applicable to infinite planar grids made of conducting strips of rectangular cross section, uniform or periodic, dense or sparse, single layer or multilayer     

Time-domain measurements of the electromagnetic backscatter ofpyramidal absorbers and metallic plates

A wideband time-domain measurement system has been developed for the evaluation of the backscatter performance of dissipative macrostructures. Backscatter measurements have been performed in an ordinary room environment on metal plates as well as samples of pyramidal absorbing material. The backscattering performance of pyramidal absorbers is evaluated in the 50- to 1000-MHz frequency range with a varying incident field angle of incidence. In the case of rectangular metal plates, numerically generated results are compared with measured data in order to gauge the accuracy of the system     

Surface electromagnetic waves in a metal

Microwave surface electromagnetic waves are observed on a plane metal/dielectric interface in a frequency range of 0.5–20 GHz. The problem of separation of surface and spatial waves simultaneously excited by a source located on the medium interface is solved.     

Dynamic and static communication in electronic media

Some years before electronic mail and Web-based hypertext became important features of professional communication, Robert Pirsig observed that information has always had higher value if it was organized in small chunks that could be accessed and sequenced at random. The paper discusses dynamic and static communication in electronic media