Wave propagation in negative-conductivity media

The problem of TEM wave propagation in a structure containing a medium exhibiting negative differential conductivity is solved. Some difficulties emerging from previous letters on the same argument are explained.     

Wave propagation in nonlinear electromagnetic media

This brief tutorial review first discusses the physical origin of nonlinear electric and magnetic susceptibilities of electro-magnetic media, from the audio through the microwave to the visible range of the electromagnetic spectrum. Wave propagation in non-linear media can be described by a combination of Maxwell's equations and the nonlinear constitutive equations. The Manley-Rowe relationships are verified for anisotropic lossless dielectrica. Microwave harmonic generation in ferrites and other materials, microwave modulation of light, light harmonic generation, light mixing and parametric conversion are all discussed from a general common viewpoint. The boundary conditions at the surface of a nonlinear medium lead to generalizations of the laws of reflection and refraction of light.     

Wave propagation and profile inversion in lossy inhomogeneous media

Using the Lagrangian approach, a time-domain analysis of wave propagation in an inhomogeneous lossy medium is described. We consider a half-space problem (x ≥ 0) in which the medium is plane stratified in the direction of propagation and can be modeled by a piecewise uniform lossy transmission line. A method of profile inversion which is based directly upon quantities measured in time at the sending end boundary is presented. The problem of uniqueness is discussed. For a given medium, computer simulation results obtained by using the known reflected waves at the boundary x = 0 are shown.     

Wave propagation and scattering in random media and rough surfaces

The author presents a comprehensive review highlighting historical as well as new developments in the area of random media. Both discrete and continuous media are considered as well as rough surfaces. The author discusses wave propagation in turbulence and in a random continuum where the refractive index is a random function of space and time. Examples are optical propagation in the atmosphere, microwaves in the troposphere, ionosphere, planetary atmosphere, and solar wind, and acoustic scattering in ocean turbulence. The author describes multiple scattering by random distributions of discrete scatterers. Examples are optical and microwave scattering by rain, fog, smog, snow, ice particles, and vegetation, optical and ultrasound scattering by tissues and blood, optical and acoustic scattering in the ocean, and scattering in composite materials. Scattering by rough surfaces and interfaces is discussed. Examples are acoustic scattering by ocean surfaces, microwave and optical scattering by vegetation, terrain, and snow cover, and ultrasound scattering by rough interfaces in biological media     

Wave propagation through random media: Contributions from ocean acoustics

Recent theoretical and experimental progress in understanding sound transmission through a random field of internal waves is reviewed. Some attempt is made to place this work in historical relation to similar efforts in radio-wave propagation through the ionosphere and light propagation through the atmosphere. It is emphasized that internal waves as a random medium possess several new features unfamiliar to those dealing with homogeneous isotropic turbulence. The effect of a background deterministic wave-speed variation (the ocean sound channel) is central to the theoretical treatment, which is based on a path-integral solution of the parabolic wave equation. A distinction is made between two sections of the saturated region and some emphasis is placed on the region of partial saturation. Comparison with experiment is discussed with examples from the two-point mutual coherence function of time, frequency, and vertical separation; the intensity correlation in time, frequency, and vertical separation; the spectra of phase and log intensity, pulse propagation, and the higher moments of intensity.     

Pulse propagation in random media

A new approach is developed to investigate pulse propagation in random media, taking into account the effects of multiple scattering. The technique is based on the idea of temporal moments of the signal. It is shown that these temporal moments are related to the coefficients of expansion for the two-frequency mutual coherence functionGammain terms of the frequency separation. These coefficients, and therefore the moments, can be solved analytically in sequence without making assumptions about the strength of the turbulence. Using these moments, a least square orthogonal polynomial expansion procedure is developed to obtain the average intensity of the pulse as it propagates through the turbulence. It is also shown that the technique can be used for propagation through random media with discrete scatterers. An example is given to demonstrate the procedure.     

Wave propagation in pyrolytic-graphite slow-wave circuits

The possibility of using an anisotropic resistive material to simulate sheath-type microwave slow-wave structures is investigated experimentally. The specific anisotropic material considered in the present study is pyrolytic graphite which has an anisotropic electrical conductivity. A sheath model of the Karp line is simulated by replacing wires and slots by a sheet of pyrolytic graphite. The mode of propagation in this waveguide structure is measured and compared with the theory. The Karp-line mode with a relatively high attenuation is found to be present in this structure.     

Wave propagation in a moving plasma

This letter comments on previous work by Scarf on wave propagation in a moving plasma and also adds new results.     

Laser irradiance propagation in turbulent media

The results obtained in recent years on laser irradiance propagation in random weakly inhomogeneous media with large scale index of refraction fluctuations are reviewed. Of particular concern are the problems of the cozrelation theory of fluctuations of irradiance propagating over large distances, where the effects of multiple scattering are greatly pronounced. Much attention is paid to the results on laser beams spread and phase fluctuations. Consideration is given to problem of the study of spatial spikes of irradiance that had passed through a turbulent media; which is comparatively new but important for practical applications. Systematic comparison of the theory with experiment is given where appropriate. The methods of analyses reviewed in this paper are applicable to a class of stochastic and dynamic partial differential equations and thus may be of interest in other areas of engineering reseach.     

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。     

Wave propagation on multifilar helices

The modes of the sheath helix are shown to be related closely to the space harmonics of real helices. Multiwire helices propagate many modes, the principal space-harmonic component of each approaching more closely the appropriate sheath helix mode as the number of wires is increased. Each mode can be excited by a certain phase sequence of exciting currents for the wires in one transverse plane. Experimental verification of the theory is reported using a bifilar helix tube. Phase velocities and impedances are measured, using Kompfner's null method and the start of backward-wave oscillations for the principal forward and backward components respectively.     

Wave propagation on helical antennas

The current distribution, the near field, and the far field of helical antennas are examined. It is found that the application of the helix as an endfire radiator is dependent on two higher Order modes of the helix wave functions. This differs from the application of the helix as a slow wave structure in a traveling wave tube where the lowest order mode of the helix wave functions is utilized.     

Electromagnetic beam propagation in turbulent media

The most recent developments on the propagation of optical beams in a turbulent medium, such as the clear atmosphere, are reviewed. Among the phenomena considered are beam spreading, beam wander, loss of coherence, scintillations, angle-of-arrival variations, and short-pulse effects.     

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.     

Wave propagation in transversely inhomogeneous dielectric waveguide

Guided mode propagation in inhomogeneous dielectric waveguides is calculated by a series expansion method which is particularly useful for analysing single-mode dielectric waveguides. As an example we estimate the error in the phase constant of waveguides whose dielectric constant profile is not necessarily near-parabolic.     

Wave propagation in relativistically moving warm magnetoplasma

The refractive index equation for electromagnetic waves propagating in a relativistically drifting warm magnetoplasma is derived by applying Lorentz and plasma parameters transformations to the refractive index equation in the rest system. Two cases are considered: 1) the nondrifting boundary and 2) the drifting boundary.     

Wave propagation in transversely inhomogeneous dielectric waveguide

The problem of guided mode propagation in inhomogeneous dielectric waveguides is solved by a Cheby?shev-like economised power-series approach. The formulation involved is shown to be quite simple. Numerical examples using a `P?schl-Teller? medium demonstrate the accuracy of this approach.     

色散媒质二阶时域参量的演绎

为了实现色散媒质二阶时域参量的变换, 提出将色散媒质二阶参量演绎为时域参量的方法.以德拜媒质水为对象, 依据其本构参量和平面波在空气-水分界面上频域反射和透射系数, 先建立其频域超越方程式; 再依据易于得到的本构时域参量和待求的时域参量建立起其相应的时域超越方程式, 对其用迭代方法可演绎出二阶时域参量.通过时-频变换技术已证明方法的有效性.给出演绎过程和技术要点, 并对所得结果进行了讨论, 展示了因果关系.本演绎技术具有拓展延伸的潜力.     

Wave packets in strongly dispersive media

An analytical study of the evolution of slowly varying wave pulses in strongly dispersive media which takes into account dispersive correction terms involving higher derivatives of the group velocity is given. A higher order differential equation for the envelope function is derived and solved recursively and by means of a procedure based on an analogy with the Schrödinger equation. The equation for the envelope function is used to obtain generalizations of the velocity of the pulse defined as the velocity of the center of inertia, and expressions are derived which determine the spreading of the pulse. Finally, we discuss how the presence of other wave modes affects the primary mode in the multimode case.