雷达目标瑞利区划分和散射特性研究

为了解决简单目标瑞利区划分不明确,复杂目标瑞利区划分缺乏依据的问题,在研究简单目标和复杂目标雷达散射截面的基础上,详细分析了其雷达散射截面变化的特性,提出了适合简单目标和复杂目标的瑞利区划分新方法,给出了在瑞利区雷达截面的估算方法.     

Rayleigh hypothesis in scattering problems

It is shown that the validity of the Rayleigh hypothesis is dependent on the distribution of singularities in the analytic continuation of the exterior scattered field; the hypothesis is fulfilled if, and only if, these are concentrated in a sufficiently small domain. Conclusions reached by Burrows in a recent letter are criticised.     

Rayleigh scattering and power conservation

In the usual formulation of Rayleigh scattering in terms of the quasi-static dipole moments of the scatterer, the scattered field is evaluated exactly to the lowest order(k_{0}a)^{3}whereais a characteristic dimension of the scatterer. Although the scattered power may be found correctly to order(k_{0}a)^{6}in terms of the scattered field, power conservation does not hold. To achieve power conservation the scattered field must be determined exactly to order(k_{0}a)^{6}. It is shown that the term of order(k_{0}a)^{6}may be found by including radiation reaction as part of the polarizing field. The scattered power can then be found by using the forward scatter theorem (optical extinction theorem) and leads to power conservation correct to lowest order.     

Rayleigh and Mie scattering in polymer optical fibers

In this article, the influence of Rayleigh and Mie scattering, which are the main causes of mode mixing in polymer optical fibers (POFs), is investigated. Measurement results obtained from a variety of different POF types ranging from standard POF, high-temperature POF, up to custom-made POF are presented. These measurements are compared to theoretical results obtained from a simplified scattering model. By comparing both results, the contribution of the different scattering sources and mechanisms is characterized independently.     

Rayleigh scattering in ZrF4-based glasses

Light scattering in a 51.53 ZrF4 - 20.47 BaF2 - 5.27 LaF3 - 3.24 AlF3 - 19.49 LiF glass was investigated for the first time both as a function of wavelength and of angular distribution. The measured total scatter loss exhibits a characteristic Ray-leigh ?-4 dependence. The total scattering attenuation coefficient has been reduced to that of the best synthetic silica, and nearly reaches the theoretically predicted minimum.     

消除WDM-PON中瑞利散射的研究(本期优秀论文)

在无色化波分复用无源光网络(WDM-PONs)中,基于反射半导体光放大器(RSOA)的单光纤WDM-PON倍受青睐,但沿光纤传输时由于瑞利散射的影响,性能有较大下降,因此主要讨论和研究在WDM-PON中如何消除瑞利散射的影响.首先介绍了无色化的WDM-PON,描述了瑞利散射的产生机理,然后总结当前国内外研究者消除瑞利散射的方法,并具体阐述其中的3个方案.最后用optisystem对新型WDM-PON结构中瑞利散射的消除方案进行仿真.     

Double Rayleigh scattering noise in lumped and distributed Raman amplifiers

An improved analytical expression of the multiple path interference (MPI) induced by double Rayleigh scattered signal in fiber Raman amplifiers (FRAs), valid both for lumped and distributed FRAs, is derived with a small signal model. The expression is validated both by comparison with an exact solution and by MPI measurements on four different lumped and distributed Raman amplifiers.     

Eddy currents: theory and applications

The theory and applications of eddy currents induced in conducting materials by time-varying magnetic fields are reviewed. The mathematical methods employed in solving the relevant problems are presented. Both analytical and numerical methods are described. Applications based on effects arising from eddy currents are discussed in detail. These applications are to magnetic levitation, electromagnetic launching, hyperthermia treatment of cancer, and nondestructive testing     

Equivalence of the Rayleigh solution and the extended-boundary-condition solution for scattering problems

Methods based on the Rayleigh hypothesis (e.g. the point-matching method) for numerically solving wave-diffraction problems are shown to be equivalent to the exact extended-boundary-condition method. It is concluded that the Rayleigh hypothesis is exact, although, in general, it is necessary to interpret it in the generalised function sense.     

Improvement of the Rayleigh approximation for scattering from asmall scatterer

An improvement of the Rayleigh approximation for electromagnetic scattering from an arbitrary small scatterer is developed through solving the conventional integro-differential equation governing the electric field inside the scatterer. The improvement is represented by an equivalent polarizability tensor differing from that used in the Rayleigh approximation in two aspects: (i) it is frequency dependent, and (ii) it gives a scattering amplitude tensor satisfying energy conservation. The energy conservation is investigated through formulating the extinction, scattering, and absorption losses according to the equivalent polarizability tensor. Numerical calculations on spheres and spheroids indicate that the present extinction loss formulation has a wider validity range than the extinction loss formulation according to the Rayleigh approximation     

南极中山站瑞利散射激光雷达的初步探测结果

一套瑞利散射激光雷达已部署在南极中山站（69.4° S, 76.4° E）用于探测大气密度和温度。该激光雷达的光源为二倍频Nd:YAG脉冲激光器,重复频率30 Hz,单脉冲能量约400 mJ,同时使用一台0.8 m口径的垂直指向望远镜作为接收望远镜,可以探测平流层上层及中间层下层（USLM）区域的大气密度及温度廓线。在垂直分辨率为300 m,时间分辨率为30 min的情况下,由光子噪声引起的大气密度和温度测量不确定性分别小于1.5%和1 K。该激光雷达自2020年3月开始在中山站开展常规观测,有助于研究极区USLM区域的大气密度、温度的变化特征以及大气波动的传播特性。     

Singularity expansion representations of fields and currents in transient scattering

A unified treatment of the natural mode representations for induced currents and scattered fields is obtained by use of fundamental concepts regarding causality and superposition. The transient scattered field response is shown to have the form of a constant coefficient complex exponential sum only in the "late-time," after the last driven reponse is received from the object. Prior to this, the "early.time" response is found to be due to direct physical optics fields as well as a sum of temporally modulated natural modes produced by the progressive illumination of the incident wavefront. Alternate representations ands-plane behaviors are considered. The implications of these results on natural resonance target identification schemes are discussed.     

Rayleigh scattering by a bianisotropic ellipsoid in a biisotropic medium

The Rayleigh scattering response of an electrically small bianisotropic ellipsoid immersed in an ambient biisotropic medium has been obtained using coupled volume integral equations. This work will be of interest for studying the electromagnetic properties of particulate matter.     

Rayleigh scattering effect on the gain efficiency and noise oferbium-doped fiber amplifiers

The effect of the internal Rayleigh scattering on the gain efficiency and noise of the erbium-doped fiber amplifier has been considered in detail. It is shown that excess background loss due to Rayleigh scattering at the signal and pump wavelengths dramatically reduces the optimum gain efficiency of either high NA, low-concentration or confined-dopant erbium-doped fibers. Distributed feedback due to Rayleigh backscattering, on the other hand, degrades the noise performance of high gain amplifiers considerably. In applications where high gain and low noise figure are required, increasing the fiber NA and dopant confinement above an optimum value are shown to increase the required pump power dramatically due to the deleterious effects of Rayleigh backscattering     

Strain sensing based on coherent Rayleigh scattering in an opticalfibre

A fibre optic strain sensor based on Rayleigh backscatter using a time division multiplexing scheme with an optical pulse is presented. The sensor has a gauge length of <0.5 m and a strain sensitivity of <1 nϵ/√Hz at 2 kHz     

基于瑞利散射和布里渊散射的自调Q双包层掺镱光纤激光器研究

结合光纤干涉环原理和受激布里渊散射效应数值求解描述双包层掺镱光纤激光器的速率方程,得到构建光纤干涉环的耦合器耦合率及泵浦功率与输出脉冲重频的关系;进一步采用掺镱双包层光纤激光器中光子数守恒的半数值模型得到耦合器耦合率、泵浦功率与输出平均功率、脉冲能量的关系。实验测试了不同泵浦功率对输出平均功率和脉冲能量的影响,实验结果与仿真结果吻合。研究表明:提高泵浦功率只能提高脉冲重复频率和平均功率,并不能提高脉冲能量;选择合适耦合率的耦合器构建光纤干涉环才能获得较高脉冲能量;泵浦功率较高时会激发二阶斯托克斯光脉冲。     

GENERALIZED SCATTERING PARAMETERS AND THEIR APPLICATIONS

The physical concepts of power waves,exchangeable power,power wave reflection coefficientsand generalized scattering parameters are interpreted in this paper.Extensions are made.Several examples forapplication are cited.It is proved that these tools are very useful when dealing with microwave active circuits,especially those including negative resistances.