On the Condition for Transformation of a Fast Surface Wave into a Slow Surface Wave

Surface plasmons (polaritons) along the boundary between vacuum and a dissipative half-space with given complex permittivity, including the case of placing an electrically thin dielectric layer (system of layers) on the boundary, are considered. Conditions for transformation of a fast gliding Zenneck surface wave (polariton) into a slow wave (slow surface plasmon) are considered. The behavior of the group velocity and the energy velocity of motion (transfer) in such structures are analyzed. The reflection coefficient of the Zenneck wave along the sea for the ice pack of a given thickness is determined. It has been shown that rigorous solution of the Sommerfeld problem by means of numerical calculation of integrals in the near zone allows obtaining the solution of the inverse problem of the structure of the surface region on the basis of redundant experimental data on components of the electromagnetic field on the surface at different ranges from the antenna.     

TM waves in nonlinear saturable thin films: a multilayered approach

The dispersion of guided TM (transverse magnetic)-polarized waves in a thin nonlinear saturable film bounded by linear media is investigated. The film is assumed to be isotropic with both of the electric field components contributing to its dielectric function. The variation of the wave effective index with the guided power and also with the surface magnetic field intensity is obtained. Different mechanisms giving rise to the nonlinearity of the film are shown to result only in small quantitative differences in the dispersion behavior. A recursive scheme for solving the nonlinear wave equation within the film is fully described. The scheme relates to the saturable dielectric function used and its based on the stratification of the film region into a large number of linear sublayers     

Nonuniform Layer Model of a Millimeter-Wave Phase Shifter

The electromagnetic wave propagation of millimeter waves in dielectric waveguides with thin surface plasma layers is characterized. The phase and attenuation of a 94-GHz wave are computed for various surface plasma layer thicknesses as a function of earner density levels. The electron/hole pairs generated in the vicinity of the dielectric waveguide surface by photo excitation are assumed to have an exponential profile due to either carrier diffusion or the exponential absorption of the optical field. Field computations made for a uniform plasma layer are compared with those of the nonuniform plasma to illustrate the effects of the exponential tails of the carrier profiles on both the phase and attenuation of the millimeter wave. The thin plasma layers slightly affect the field profile of the transverse electric modes (fields polarized parallel to the plasma layer). The transverse magnetic fields are highly distorted at plasma densities greater than 10/sup 16/ cm/sup -3/.     

Theoretical and experimental characterization of theEMP-interaction with composite-metallic enclosures

A numerical procedure is developed for the prediction of the electric and magnetic field distribution inside an enclosure having aluminum and carbon-fiber reinforced composite (CFRC) walls, illuminated by a transient electromagnetic plane wave. The composite panel is simulated by an effective layer model; time-domain surface impedance boundary conditions are enforced on the external faces of the composite slab, to express the relations among the tangential electric and magnetic field components. A coupling model for the calculation of the current induced along thin wires inside the enclosure is presented. The proposed models are implemented in a three-dimensional (3-D) finite-difference time-domain (FDTD) procedure, which is applied to the analysis of the shielding performances of an aluminum box with one CFRC face, illuminated by a transient electromagnetic wave. The computed results are compared with measured data obtained by using a full scale EMP generator     

The launching of surface waves on an axial-cylindrical reactive surface

The excitation of the dominant TM surface wave on an axial-cylindrical reactive surface is discussed. The surface wave launcher consists of a perfectly conducting, infinitely thin cylindrical surface of radiusbcoxial with a cylindrical reactive surface of a radiusawhereb > a. The reactive surface extends from-infty , and the perfectly conducting surface extends from-infty. The incident field is the dominant TM mode in the coaxial portion of the structure propagating in the positivez-direction. Numerical results are obtained for the reflected field, the surface wave field, and the radiation field. These results are then compared with the results that use two approximate aperture distributions. This method of excitation was very efficient over a large range of frequencies and over wide variations in the surface reactance.     

Plane wave diffraction by a thin dielectric half-plane

Expressions that apply for all observation points are derived for the field produced by a plane wave incident on a thin dielectric half-plane when the electric vector of the incident wave is parallel to the edge. Away from shadow boundaries the total field comprises an edge wave and a surface wave in addition to the transmitted and reflected waves of geometrical optics. The nature of the edge wave differs from that of a perfectly conducting half-plane in that both the amplitude and phase vary with the observation angle, for a given angle of incidence.     

Electromagnetic pulse (EMP) penetration through circular apertures in the frequency domain

Equations and curves are given for estimating field coupling from a normally electromagnetic pulse (EMP) incident plane wave through a circular aperture within a thin planar surface.     

On computation of electromagnetic fields on planar surfaces from fields specified on nearby surfaces

A technique is presented for solution of the inverse problem of calculating the electric field on a planar surface from the electric field specified on a nearby surface. An integral equation is derived that relates two orthogonal components of the electric field on the nearby surface to the respective components of the plane wave spectrum of the planar electric field. The integral equation is solved by an iterative technique, and the planar near field is calculated by an inverse Fourier transform of the plane wave spectrum.     

Currents induced in a wire cross by a plane wave incident at an angle

The currents induced in a thin-wire cross with equal mutually perpendicular arms by an incident plane electromagnetic wave are determined when the normal to the wave front is perpendicular to the horizontal wire and is at an anglethetawith respect to the vertical wire; the direction of the electric vector in the wave front is arbitrary. The analysis is formulated in general terms but explicit formulas are obtained only for the zero-order currents which are generally adequate to determine the scattered field of very thin wires. The relatively simple formulas consist of even and odd parts for both the vertical and horizontal wires; they include components due to mutual coupling as well as those excited directly by the incident field.     

Scattering by circular metallic disks

The eigenfunction solution for the far-field scattering by a thin, circular metallic disk is summarized. This solution yields both components of the scattered electric field for an incident plane wave of arbitrary polarization and arbitrary incidence directions. Sample amplitude, phase, and cross section results are presented.     

Experimental study of the field structure of the surface electromagnetic wave in an anisotropically conducting tape

It is shown that, in the frequency band 3–5.2 GHz, a tape of metal conductors supports slow waves. The field structure of the surface wave in an anisotropically conducting tape is studied experimentally. It is found that the electromagnetic field of the tape has three electric and two magnetic components. Intensity distributions of all field components, the slowing factor of the surface wave, and the loss per unit length are measured.     

Analysis of a dielectrically loaded traveling wave tube

A circular waveguide periodically loaded with dielectric disks forms a slow wave structure which can be used in a traveling wave tube. For solid disks, the field pattern in the guide can be determined exactly and the characteristics of the structure, when used as a traveling wave tube, can be predicted using Pierce's small signal theory. The gain, bandwidth, operating frequency, and required beam voltage have been calculated for a wide range of structure dimensions. The power capability of the disk-loaded guide is also discussed.     

The Radiation Properties of a Parallel-Plane Waveguide in a Transversely Magnetized, Homogeneous Plasma

The Wiener-Hopf technique is used to study the radiation from a parallel-plane waveguide embedded in a homogeneous anisotropic plasma in which the external magnetic field is perpendicular to the direction of propagation and parallel to the perfectly conducting planes of the guide. The incident field in the guide is a TEM wave, which propagates in the positive z direction. The parallel-plane guide terminates at z = 0, causing a reflected field in the waveguide, a radiation field, and a surface wave that is guided along the outer surface of one of the perfect conductors. Expressions are found for these field components, and the results are discussed for the different frequency ranges.     

Radiation characteristics of a dielectric disk-loaded circularcylindrical waveguide

The radiation pattern of a circular cylindrical waveguide that is loaded inside with periodically spaced dielectric disks is derived by considering the region between two disks as a medium with anisotropic permittivity and using Schelkunoff's equivalence principle. The far-field electric field components and their relationship to cross-polarization ratio are determined. The variation of the latter quantity with the size, spacing, and dielectric constant of the dielectric disks is studied     

基于FEM/BEM方法的表面声场体波模式数值研究

采用有限元/边界元法(FEM/BEM),分析了有限长叉指换能器在半无限大压电晶体128°YX-LiNbO3中激发的表面波和体波在晶体表面上的分布情况。通过对频域内表面声场的分析,得到了表面上三个位移场分量含有的声波模式,对相应时域内各场分量的体波脉冲振幅进行处理,详细分析了各个模式的体波脉冲振幅随时间的分布关系。结果表明,除Rayleigh型表面波外,各场分量中还包含不同成分和比例的体波模式;在场分量1和场分量3中占主要成分的准纵波,以及在场分量2中占主要成分的准慢切变波,在表面上其传播损耗以指数衰减。     

Electrolytic Tank Solution of Electric Field Associated with Two Circular Disks on the Surface of an Isotropic Homogeneous Medium

The electric field associated with two disks on the surface of a semi-infinite isotropic homogeneous medium is found on a plane perpendicular to the disks and passing through their centers. To an accuracy which is primarily determined by the finite dimensions of the electrolytic tank, the solution is presented as families of curves. In this presentation, the magnitude of the electric field (normalized in terms of the distance of the field point from the surface, conductivity of the medium, and applied power) and the angular orientation of the field vector are plotted as functions of the ratios of the linear dimensions which characterize the geometry of the system to the distance of the field point from the surface.     

Polarimetric channel characterization of foliage for performanceassessment of GPS receivers under tree canopies

The attenuation, depolarization, and fluctuation of a microwave signal going through a tree canopy are investigated by developing a Monte Carlo based coherent scattering model. In particular, the model is used to analyze the performance of Global Positioning System (GPS) receivers under tree canopies. Also the frequency and time-domain channel characteristics of a forest are investigated when a transmitter is outside and a receiver is inside a forest. A fractal algorithm (Lindenmayer system) is used to generate the structure of coniferous or deciduous trees whose basic building blocks are arbitrarily oriented finite cylinders, thin dielectric needles, and thin dielectric disks. Attenuation and phase change of the mean field through foliage is accounted for using Foldy's approximation. Scattering of the mean field from individual tree components and their images in the underlying ground plane are computed analytically and added coherently. Since tree trunks and some branches are large compared to the wavelength and may be in the close proximity of the receiver, a closed-form and uniform expression for the scattered near-field from dielectric cylinders is also developed. Monte Carlo simulation of field calculation is applied to a cluster of trees in order to estimate the statistics of the channel parameters, such as the probability density function (pdf) of the polarization state of the transmitted field, path loss, and the incoherent scattered power (the second moment of the scattered field), as a function of the observation point above the ground     

Magnetically tuned surface-acoustic-wave phase shifter

A novel technique for achieving variable phase shift in surface-acoustic-wave devices is demonstrated. By depositing a thin film of magnetostrictive material onto the surface of a conventional surface-acoustic-wave delay line, the wave velocity can be varied by adjusting an externally applied magnetic field. Experimental results are presented for a nickel film on a lithium-niobate substrate, and several possible applications are mentioned.     

Scattering by thin dielectric strips

A plane wave incident on a thin dielectric strip with infinite length is considered, letting the incident electric field vector be parallel with the edges of the strip. The field is expanded in the dielectric region as the sum of three plane waves (the forced wave and two surface waves). Thex-axis andy-axis propagation constants are known for each wave, and Galerkin's method is employed to determine the amplitudes of these waves. Finally, the far-zone scattered field is determined by considering the polarization currents radiating in free space. Numerical data are presented to illustrate the scattering properties of lossless and lossy dielectric strips as a function of the angle of incidence and the width of the strip. The calculations show excellent agreement with an earlier moment method using pulse bases and point matching.     

Electromagnetic Diffraction by a Planar Array of Circular Disks

The diffraction of a plane electromagnetic wave by a planar rectangular array of perfectly conducting circular disks is considered. The diffracted field is calculated from the induced electric and magnetic dipole moments and higher-order multipole moments. Static and dynamic interactions between the induced dipole moments are being considered, first by using a plane-wave approximation for the dipole fields (for cases where the separation of the disks is large compared with the wavelength) and then by calculating the actual fields at each disk. The formulas are applied to calculate the input susceptance of a disk-loaded rectangular waveguide. Satisfactory agreement with experimental results is obtained.