左手介质中电磁波的传播速度

在同向介质中,电磁波的群速度一般是能量传播的方向,并且电磁波的相速度和群速度在大部分情况下都满足瑞利关系.为了研究左手介质的电磁特性,本文从理论上导出了左手介质中电磁波的相速度、群速度及其关系,得出左手介质中电磁波的群速度为负,并介绍了左手介质的一些应用前景.     

On the orthogonality of the phase velocity and its feasibility for plane waves

Phase and group velocities of plane waves may have different directions in a linear and homogeneous medium. This difference may lead to interesting situations such as the phase reversal propagation and the orthogonal phase velocity. Although the former has been analyzed in depth and it has found many applications, the latter has been left as a hypothesis. Actually, due to our best knowledge there is no evidence of such media where the phase velocity is orthogonal to the group velocity. In this paper we discuss this situation thoroughly. We show that a plane wave with orthogonal phase velocity cannot possess linear momentum. Moreover, we show that a plane wave without the linear momentum cannot propagate at all, so the orthogonality of the phase velocity does not take place in reality for electromagnetic plane waves.     

Electromagnetic Waves in a Medium with Screw Dislocations

It is shown that in a medium with screw dislocations oriented predominantly along one axis the rotational velocity of the plane of polarization of an electromagnetic wave is much greater when it propagates in the direction perpendicular to this axis than in the parallel direction. For a given dislocation density tensor, the conditions under which the rotational velocity of the plane of polarization of the electromagnetic wave reaches its maximum are found.     

Relationship between the velocity of hypersonic vehicles and the transmission efficiency of radio waves

Analyzing the flow field distributions around a near-space blunt-cone vehicle at different flight speeds, we observe that, when the flight speed exceeds a certain threshold, the relationship between the flow field density and the vehicle speed presents a characteristic opposite to that at the flight condition of the speed lower than the threshold. On this basis, the Runge–Kutta method is applied to solve the ray equations in non-uniform plasma, in which the electron density at any computing point is obtained by the Lagrange interpolation based on the discrete data of the flow field. Then the EM wave attenuation in the sheath is determined by the subsection integral method combining with the electromagnetic theory. The numerical results also show that when the flight velocity is lower than the threshold, the energy transfer efficiency of the EM waves decreases with the increase of the vehicle velocity. However, when the flight speed is greater than the threshold, the energy transfer efficiency increases as the vehicle speed increases. This conclusion will be helpful to further understand the EM wave propagation characteristics for hypersonic vehicles, and to provide a reference for the channel selection of antennas.     

Causality and the velocity of acoustic signals in bubbly liquids

Several versions of the dispersion formula governing the acoustic propagation in bubbly liquids are shown to exhibit acausal behavior. The cause of this behavior is due to the inappropriate application of a low frequency approximation in the determination of the extinction of the signal from radiative scattering. Using a corrected causal formula, several principles of wave propagation in bubbly media consistent with the general theory of wave propagation in dispersive media are demonstrated: There exist two precursors to any finite signal. Both propagate without regard to the source characteristics at velocities, frequencies, and amplitudes dependent wholly upon the characteristics of the medium supporting the wave motion. The first travels at the infinite frequency phase velocity that is coincident with the infinite frequency limit of the group velocity. That part of a propagating wave oscillating at the source frequency arrives at a time determined by the signal velocity. Analogous to the well known signal velocity of electromagnetic wave propagation in conducting media, the value of the signal velocity depends on the detailed structure of the dispersion formula in the complex frequency plane.     

Small amplitude approximation and stabilities for dislocation motion in a superlattice

Starting from the traveling wave solution, in small amplitude approximation, the Sine-Gordon equation can be re- duced to a generalized Duffing equation to describe the dislocation motion in a superlattice, and the phase plane properties of the system phase plane are described in the absence of an applied field. The stabilities are also discussed in the presence of an applied field. It is pointed out that the separatrix orbit describing the dislocation motion as the kink wave may transfer the energy along the dislocation line, keep its form unchanged, and reveal the soliton wave properties of the dislocation motion. It is stressed that the dislocation motion process is the energy transfer and release process, and the system is stable when its energy is minimum.     

General relativistic shock waves in fluids for which pressure equals energy density

A shock wave in a self-gravitating fluid obeying the equation of state: pressure equal to energy density is shown to travel with the velocity of light in a space-time determined by the Einstein field equations. The jump conditions that must be satisfied by the hydrodynamic variables are derived and discussed as are those that must be satisfied by the metric tensor and its derivatives. The latter conditions are obtained by using a variational principle.     

Energy flow model considering near field energy for predictions of acoustic energy in low damping medium

The Acoustic Energy Flow Boundary Element Method (AEFBEM) is developed to predict the acoustic energy density and intensity of an engineering system. Up to now, the acoustic energy flow model has been used only for analysis of high frequencies or radiation noise because of plane wave and far-field assumptions. In this research, a new energy flow governing equation that can consider the near field acoustic energy term and spherical wave characteristics is derived successfully to predict the acoustic energy density and intensity of a system in the medium-to-high frequency range. A near field term of acoustic energy in spherical coordinate is added to the relationship between energy density and energy flow. But with the far-field assumption, this term vanishes, so the relationship between energy density and energy flow becomes the same as that of the plane wave. By considering the near field energy term without far-field assumption, the energy density at medium frequencies can be estimated. However, the governing equation has to be numerically manipulated for use in the analysis of complex structures; therefore, the Boundary Element Method (BEM) is implemented. AEFBEM is a numerical analysis method formulated by applying the boundary element method to an acoustic energy flow governing equation. It is very powerful in predicting the acoustic energy density and intensity of complex structures in medium-to-high frequency ranges, and can analyze interior noise and radiating sound. To verify its validity, several numerical results are provided. BEM and AEFBEM were compared with respect to energy density, and the results from both methods were similar.     

Accuracy of the conservation of the adiabatic invariant of a charged particle in plane waves

The conservation of the adiabatic invariant of a charged particle, entrapped by a transverse plane electromagnetic wave, is studied using a well-known method, both for the case when the phase velocity of the wave does not exceed the velocity of light, and for the opposite case. An expression is obtained for the variation of the adiabatic invariant, from which it is seen that the latter is conserved with exponential accuracy in the region of its existence.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 61–66, April, 1979.     

Diffuse wavefields in cylindrical coordinates

A diffuse wavefield is normally defined in terms of plane waves--to quote one textbook definition "plane waves are incident from all directions with equal probability and random phase." In some vibro-acoustic problems the response of a two-dimensional component such as a plate is more conveniently expressed in terms of cylindrical waves, and it is not immediately obvious what properties should be assigned to the cylindrical waves to constitute a diffuse field. It is shown here that a diffuse wavefield can be modeled as a summation of statistically independent cylindrical waves, apart from the fact that each outgoing wave of a particular order is fully correlated to an incoming wave of the same order. A simple relationship is derived between the energy flow P in each wave component and the energy density e of the wavefield: P = ec(g)/k, where c(g) is the group velocity and k is the wavenumber. This result is shown to hold true for both bending waves and in-plane waves (longitudinal and shear) in a plate. The work has application to the calculation of coupling loss factors in statistical energy analysis.     

Zero energy of plane-waves for ELKOs

We consider the ELKO field in interaction through contorsion with its own spin density, and we investigate the form of the consequent autointeractions; to do so we take into account the high-density limit and find plane wave solutions: such plane waves give rise to contorsional autointeractions for which the Ricci metric curvature vanishes and therefore the energy density is equal to zero identically. Consequences are discussed.     

Linear gravitational waves and electrodynamic formalism in cosmology

The propagation of linear gravitational waves is studied in open and multiply connected Robertson-Walker cosmologies. In order for the group velocity of the gravitational wave packets to coincide with the speed of light, the linear wave equation must be conformally coupled. This opens the possibility of using the electromagnetic formalism. The gravitational analogue to the electromagnetic field tensor is introduced, and a tensorial counterpart to Maxwell's equations on the spacelike 3-slices is derived. The energy-momentum tensor for linear gravitational waves is constructed without averaging procedures, a strictly positive energy density is obtained, and it is shown that the overall energy of a gravitational pulse scales with the inverse of the expansion factor.     

光子晶体理论研究的新方法——混合变分法

利用混合变分法研究了二维光子晶体的能带结构,得到了通带、禁带和群速度,并详细分析光子晶体中的电磁场分布和能流密度分布.该方法方便实用,理论上能够应用于任意维度任意周期结构的光子晶体的计算.     

磁场对螺旋波等离子体波和能量吸收影响的数值研究

本文考察在径向电子数密度呈抛物形分布的情况下,外加稳恒磁场,射频通过螺旋波天线在等离子体中激发电磁波的传播性质.采用线性扰动波假设,数值求解Maxwell方程组,得到80—800 G(1 G=10-4T)磁场条件下等离子体中径向电、磁场强度及能量沉积密度的分布情形.计算结果表明,磁场增大(80→800G)时,螺旋波受到的阻尼较小,可深入等离子体传播;Trivelpiece-Gould(TG)波受到的阻尼增大,在等离子体-真空边界处衰减增强;整体的能量吸收向边界集中.磁感应强度小于100 G时,TG波可深入主等离子体区传播,等离子体径向能量吸收相对均匀.     

介质分界面上电磁波传播特性的一个理论问题研究

本文对平面电磁波在不同介质分界面传播时其能流关系出现形式上的不平衡现象作了介绍。指出，采用平面电磁波来研究其在界面上的传播特性时必然会引起一种虚波流。对引起此波的原因及其对能流分配不平衡现象的影响作了讨论，并与入射电磁波口径为有限宽度波束的情况作了比较。     

Exact equations for radiative transfer of energy and momentum in free electromagnetic fields

In a recent paper a new theory of radiative energy transfer in free electromagnetic fields was formulated. The basic quantities in this theory are the so-called angular components of the average electromagnetic energy density and of the average Poynting vector. In the present paper it is shown that these angular components obey differential equations that may be considered to be rigorous equations for the radiative transfer of energy and of momentum in free electromagnetic fields.     

Nuclear magnetic resonance measurements and the energy band structure of PtSn

Nuclear magnetic resonance measurements of the Knight shift and spin-lattice relaxation time for ¹⁹⁵Pt and ¹¹⁹Sn in PtSn are reported. The energy band structure as determined by the relativistic orthogonalized plane wave method is also presented. The band model developed has holes in the Pt d-band but does not have a large density of states associated therewith.     

Electromagnetic scattering from a two dimensional perfect electromagnetic conductor (PEMC) strip and PEMC strip grating simulated by circular cylinders

Electromagnetic scattering of an incident plane wave from a rectangular strip and strip grating, are presented semi-analytically. The strip and strip grating are simulated by joining parallel perfect electromagnetic conductor (PEMC) circular cylinders and are illuminated by a TM_z incident plane wave. The PEMC medium does not allow electromagnetic energy to enter. An interface of this medium serves as an ideal boundary to the electromagnetic field. The solution is based on the application of the boundary conditions on the surface of each cylinder in terms of its local coordinate system. The technique is used to predict the scattered field pattern of PEMC strip and PEMC strip grating.     

Nonlinear Theory of the Instability of a Modulated Electron Beam of Low Density in a Plasma. I. Conservation Laws of Energy and Momentum for Electromagnetic Waves in a Nonequilibrium Dispersive and Dissipative Medium in the Case of a Slow Change of Amplitude and Phase of the Wave

A formula is given for the energy and momentum conservation laws for a narrow spectrum of electromagnetic waves in an unstable dispersive and dissipative medium by any level of dissipation and on condition that the amplitude and phase change slowly in the time and space period of oscillations. It is shown that the density of energy and momentum of the motion of resonant particles, connected with the propagation of the electromagnetic wave, generally cannot be expressed by the dielectric function of the unstable system. For example it is demonstrated that the well known Landau formula for determining the density of the wave energy in a unstable monoenergetic beam-plasma system in general is not applicable as it is often done in literature.     

Ultrasonic transcutaneous energy transfer using a continuous wave 650 kHz Gaussian shaded transmitter

This paper proposes ultrasonic transcutaneous energy transfer (UTET) based on a kerfless transmitter with Gaussian radial distribution of its radiating surface velocity. UTET presents an attractive alternative to electromagnetic TET, where a low power transfer density of less than 94 mW/cm² is sufficient. The UTET is operated with a continuous wave at 650 kHz and is intended to power devices implanted up to 50 mm deep. The transmitter was fabricated using a 15 mm diameter disc shape PZT (Lead Zirconate Titanate) element (C-2 grade, Fujiceramics Corporation Tokyo Japan), in which one surface electrode was partitioned into six equal area electrodes (∼23 mm² each) in the shape of six concentric elements. The UTET was experimented using pig muscle tissue, and showed a peak power transfer efficiency of 39.1% at a power level of 100 mW. An efficient (91.8%) power driver for the excitation of the transmitter array, and an efficient rectifier (89%) for the implanted transducer are suggested.To obtain the pressure field shape, the Rayleigh integral has been solved numerically and the results were compared to finite element simulation results. Pressure and power transfer measurements within a test tank further confirm the effectiveness of the proposed UTET.