基于等效介质原理的宽角超材料吸波体的理论分析

目前,很少有文章就如何实现宽角度吸波材料进行详细的理论分析和设计指导,设计宽角度吸波材料仍然是一件很困难的事情.本文基于等效介质理论对带有反射地板的单层介质超材料吸波体进行较为详细的理论分析.从基础电磁理论出发,推导TE波(横电波,电场方向与入射面垂直的平面电磁波)和TM波(横磁波,磁场方向与入射面垂直的平面电磁波)照射下吸波体的反射系数,分析实现宽角度吸波效果所需的等效电磁参数,为宽角度超材料吸波体的设计提供了理论基础.此外,论文还理论分析了实现宽带宽角吸波等效电磁参数所要满足的条件,并做了计算检验.结果表明,当介质等效电磁参数按照特殊曲线随频率发生变化时,理论上能实现宽带宽角的吸波效果.     

准全向平板超材料吸波体的设计

本文设计了一种具有准全向吸波特性的平板超材料吸波体,其准全向吸波特性是由超材料吸波单元的双面吸波、极化不敏感和宽入射角实现的.理论分析和仿真结果表明:该吸波体在6.18 GHz的确有一个双面吸波的吸收点,且吸收率对极化角和入射角均不敏感.提取的等效阻抗表明可以调节超材料的电磁响应使其在吸收频率处与自由空间阻抗匹配来抑制反射.仿真的能量损耗分布表明:该吸波体对电磁波的吸收主要源于基板的介质损耗;采用两种不同介质基板的设计可使前吸波体与后吸波体的耦合度明显降低、抑制耦合所导致的传输.该吸波体可能在许多领域具有 关键词： 准全向吸波 双面吸波 极化不敏感 宽入射角     

经典物理理论中电磁波的传播规律

为了处理波传播的相关问题,引用了麦克斯韦经典理论中波的传播规律.基于麦克斯韦方程组和伽利略变换,利用微分方程来计算不同参考系下同-电磁波的传播.由于介质的运动对波动有重要的影响,所以在多普勒效应中介质的运动也被考虑进来.同时,根据该经典物理理论中的波的传播规律从不同的角度来解释迈克尔逊-莫雷实验的结果.经典物理理论中电...     

考虑毛细滞后效应的未饱和含湿多孔介质传热和传质理论

毛细滞后是未饱和多孔介质中很重要的特性之一。在许多情况下，毛细滞后现象对介质中传热和传质过程有着显著的影响。本文引入最小梯度概念，用以描述多孔体中毛细水运动滞后的定量行为，进而建立了考虑毛细滞后效应的未饱和含温多孔介质传热和传质的系统理论，为进一步定量研究毛细滞后对传热传质的影响打下了理论基础。     

多尺度波致流非饱和孔隙介质波传播理论研究

弹性波在非饱和孔隙介质中传播时,孔隙流体会发生宏观Biot流、微观喷射流以及由于孔隙流体不同(气、液双相)导致的介(中)观流.将非饱和孔隙介质等效为含液相孔隙流体的背景介质中嵌入含气相孔隙流体的包裹体,在非饱和双重孔隙介质模型基础上,引入微观喷射流,建立了包含宏观、微观和介观三种尺度波至流的非饱和孔隙介质波传播方程.数值分析表明该模型可以更好地预测更宽频带内的波速频散和衰减.     

稳定激发介质中的不稳定螺旋波

采用Br模型研究了控制螺旋波破碎问题。考虑到螺旋波破碎是由于多普勒不稳定产生的,我们提出在均匀介质中引入不可激发介质缺陷和可变性介质缺陷,通过让螺旋波波头绕缺陷运动来稳定螺旋波。研究结果表明,不同的介质缺陷稳定螺旋波的能力有所不同,可变性介质缺陷防止螺旋波破碎的能力更强。这些研究结果能够为心脏学家防止心颤致死提供有用的信息。     

分布损耗加载回旋行波管多模稳态注波互作用理论与比较证实

基于目前国际上实验研究的均匀介质加载和周期介质加载结构,建立了一种分布式损耗加载回旋行波管(gyro-TWT)多模稳态注波互作用理论.利用这一理论,以TE01模式基波gyro-TWT注波互作用为例,将Ka和W波段的理论结果与实验和软件仿真进行比较,以证实理论的合理性.     

动态质量密度和声学超常介质

复合介质的质量密度通常认为是组成它的各种成分的质量密度的体平均值.体平均质量密度常常被用于计算在长波长极限下的声波速度,在此极限下波长比复合介质中的特征尺度要大得多.作者通过严格的数学推导证明,计算(长波长极限下的)波速时所用到的动态质量密度与静态的体平均质量密度有显著的不同.这一发现与最近的实验结果符合得非常好,并且使得声学超常介质的实现成为可能.这两种质量密度之所以不同的物理根源就在于,在波场中复合介质中的各个成分之间有相对的运动.也就是说,隐含的假定——在长波长极限下复合介质中的各个成分必定会全体同相地运动——将不再正确,尤其是当各个成分的声学阻抗之间有较大的差异时.实验和理论显示,对于局域共振声学材料而言,动态质量密度甚至还会变成是负的.文章探讨了这一发现的物理意义,以及它在声学超常介质领域的应用.     

平面电磁波在任意方向运动的介质-介质界面上的反射和透射

研究平面电磁波从一种介质入射到另一种以任意方向运动的介质时,在介质界面上发生的反射和透射现象,从Maxwell方程组、运动界面的边值关系和运动介质的本构关系出发,得到了反射波和透射波电磁场矢量与入射波电磁场矢量的关系的表达式、反射和透射系数,讨论了反射波、透射波与入射波之间的能量关系,电磁波对运动介质作用力的性质,并得出一些新的结论． 关键词：     

一种极化不敏感和双面吸波的手性超材料吸波体

基于手性结构设计了一种极化不敏感和双面吸波的超材料吸波体.该吸波体的结构单元由手性结构和介质基板组成.仿真的电磁波正、反向入射时超材料吸波体的吸收率表明:该吸波结构的正、反面是互易的,具有双面吸波特性.仿真的不同极化角下超材料吸波体的吸收率表明:该超材料吸波体具有极化不敏感特性.仿真的不同入射角下超材料吸波体的吸收率表明:该超材料吸波体的入射角较窄.仿真的吸波体单元的表面电流和磁能密度分布表明:电、磁场之间存在交叉耦合,吸波与手性有关.仿真的不同损耗情况下超材料吸波体的吸收率表明:基板的介质损耗在吸波过程中起主导作用,金属的电阻热可以忽略不计.该超材料吸波体可能在要求双面吸波的领域中具有潜在的应用. 关键词： 极化不敏感 双面吸波 手性结构 超材料吸波体     

Mass change of dielectric media induced by propagation of electromagnetic waves

It has been experimentally confirmed that an electromagnetic wave carries momentum and thus exerts forces on dielectrics. Combining wave-particle duality with the theory of relativity, it was shown in the present work that the electromagnetic wave also increases the mass of the dielectric medium through which the incident wave propagates. The change in the mass density of the medium, or the mass density of the electromagnetic wave in the medium, was found to be proportional to the energy density of the incident wave. At an absolute temperature T, the mass density of the black body radiation was shown to be proportional to T⁴. “Weighing” the light wave in a glass fiber provides a novel technique to study the particle nature of electromagnetic waves in dielectric media.     

A local-ether model of propagation of electromagnetic wave

It is pointed out that the classical propagation model can be in accord with the Sagnac effect due to earth's rotational and orbital motions in the high-precision GPS (global positioning system) and interplanetary radar, if the reference frame of the classical propagation medium is endowed with a switchability according to the location of the wave. Accordingly, it is postulated that, as in the obsolete theory, electromagnetic waves propagate via a medium like the ether. However, the ether is not universal. It is proposed that in the region under sufficient influence of the gravity due to the earth, the sun, or another celestial body, there forms a local ether, which in turn is stationary with respect to the gravitational potential of the respective body. For earthbound and interplanetary propagation, the medium is stationary in a geocentric and a heliocentric inertial frame, respectively. An electromagnetic wave propagates at a constant speed with respect to the associated local ether, independent of the motions of source and receiver. Based on this local-ether model of wave propagation, a wide variety of earthbound, interplanetary, and interstellar propagation phenomena are accounted for. Strong evidence of this new classical model is its consistent account of the Sagnac effect due to earth's motions among GPS, the intercontinental microwave link, and the interplanetary radar. Moreover, as examined within the present precision, this model is still in accord with the Michelson–Morley experiment. To test the local-ether propagation model, a one-way-link rotor experiment is proposed. Received: 11 January 2001 / Revised version: 10 May 2001 / Published online: 19 September 2001     

Bremmer级数之推广

本文叙述了在普遍的介质与入射波情况下Bremmer理论之推广,并给予简要证明。对下列三种具体情况导出了Bremmer级数之表达式:1.平面分层介质,平面波斜入射;2.柱状分层介质,直线波源与柱轴重合;3.球状分层介质,点光源位于球心。最后,对于波动过程可以用射线严格描写的条件之数学形式作了探讨,并指出Bellman和Kalaba的一篇文章中的不严格处。     

时间的客观性、钟的同步与相对论的错误

定义时间和钟的同步。设计钟的同步的实现方法。指出相对论有关时间问题的错误。     

Longitudinal waves in carbon nanotubes in the presence of transverse magnetic field and elastic medium

In the present paper, the coupling effect of transverse magnetic field and elastic medium on the longitudinal wave propagation along a carbon nanotube (CNT) is studied. Based on the nonlocal elasticity theory and Hamilton's principle, a unified nonlocal rod theory which takes into account the effects of small size scale, lateral inertia and radial deformation is proposed. The existing rod theories including the classic rod theory, the Rayleigh-Love theory and Rayleigh-Bishop theory for macro solids can be treated as the special cases of the present model. A two-parameter foundation model (Pasternak-type model) is used to represent the elastic medium. The influence of transverse magnetic field, Pasternak-type elastic medium and small size scale on the longitudinal wave propagation behavior of the CNT is investigated in detail. It is shown that the influences of lateral inertia and radial deformation cannot be neglected in analyzing the longitudinal wave propagation characteristics of the CNT. The results also show that the elastic medium and the transverse magnetic field will also affect the longitudinal wave dispersion behavior of the CNT significantly. The results obtained in this paper are helpful for understanding the mechanical behaviors of nanostructures embedded in an elastic medium.     

Anomalous waveforms observed in laboratory-formed gas hydrate-bearing and ice-bearing sediments

Acoustic transmission measurements of compressional, P, and shear, S, wave velocities rely on correctly identifying the P- and S-body wave arrivals in the measured waveform. In cylindrical samples for which the sample is much longer than the acoustic wavelength, these body waves can be obscured by high-amplitude waveform features arriving just after the relatively small-amplitude P-body wave. In this study, a normal mode approach is used to analyze this type of waveform, observed in sediment containing gas hydrate or ice. This analysis extends an existing normal-mode waveform propagation theory by including the effects of the confining medium surrounding the sample, and provides guidelines for estimating S-wave velocities from waveforms containing multiple large-amplitude arrivals.     

Compressional and shear wave properties of marine sediments: comparisons between theory and data

According to a recently developed theory of wave propagation in marine sediments, the dispersion relationships for the phase speed and attenuation of the compressional and the shear wave depend on only three macroscopic physical variables: porosity, grain size, and depth in the sediment. The dispersion relations also involve three (real) parameters, assigned fixed values, representing microscopic processes occurring at grain contacts. The dispersion relationships are compared with extensive data sets, taken from the literature, covering the four wave properties as functions of all three physical variables. With no adjustable parameters available, the theory matches accurately the trends of all the data sets. This agreement extends to the compressional and shear attenuations, in that the theory accurately traces out the lower bound to the widely distributed measured attenuations: the theory predicts the intrinsic attenuation, arising from the irreversible conversion of wave energy into heat, whereas the measurements return the effective attenuation, which includes the intrinsic attenuation plus additional sources of loss such as scattering from shell fragments and other inhomogeneities in the medium. Provided one wave or physical property is known, say the compressional speed or the porosity, all the remaining sediment properties may be reliably estimated from the theory.     

Scattering of electromagnetic wave from perfect electromagnetic conductor cylinders placed in un-magnetized isotropic plasma medium

The two dimensional analytical formulation of scattering of electromagnetic wave from a perfect electromagnetic conductor (PEMC) cylinder placed in un-magnetized isotropic plasma medium is presented. The extended classical scattering theory is used. The incident wave is taken as linearly polarized wave. The analytical theory is formulated for parallel polarization (TM) and also for perpendicular polarization (TE). The numerical computation results show that backscattering and forward scattering are sensitive to electron density and effective collision frequency of plasma medium. We placed different types of cylinders (PEC, PMC and PEMC) in un-magnetized plasma medium and concluded that stealth capability of plasma increases with the placement of PEMC cylinder in plasma medium.     

A comparison of the results of a numerical simulation and an approximate calculation of the statistical characteristics of radio waves in a layer with random inhomogeneities of dielectric permittivity

We consider the formation algorithm for a random inhomogeneity field of dielectric permittivity of a medium that is used in simulations of the statistical characteristics of a wave that has propagated through a randomly inhomogeneous layer. We carry out a comparison of the statistical characteristics of a geometrical-optics wave, obtained via a numerical simulation, with the results of calculations of these characteristics by approximate formulae obtained using perturbation theory. It is pointed out that the applicability limits of the perturbation method, when solving geometrical-optics equations in a randomly inhomogeneous medium, depend on the formulation (one- or two-point) of the trajectory problem. It is shown that a calculation of the spatial correlation function of the field can be carried out using the perturbation method, even in the case of relatively strong fluctuations of dielectric permittivity. This is due to the fact that, in the region where this function differs markedly from zero, the correlation function of the eikonal obtained by the perturbation method is sufficiently accurate, and amplitude fluctuations are small.