BOR-FDTD斜入射脉冲平面波一维时域算法

针对斜入射脉冲波不能直接引入BOR-FDTD计算的问题,根据柱坐标系统中入射波在对称轴方向只有时间延迟的特性,结合平面波的柱面波展开,提出了一种行之有效的计算BOR-FDTD中斜入射脉冲平面波的一维时域算法,从而避免了大量快速傅里叶变换运算,节省了计算时间.计算结果表明该算法运行速度比基于完全傅里叶变换的算法快50倍.就整个程序运行时间而言,一维时域算法可以节省约20%的计算时间.为了验证该算法的有效性,计算了高斯脉冲斜入射时有限长金属圆柱体的散射问题,提取出某一频率下圆柱体母线电流密度分布并与MoM计算结果比较,二者吻合较好.然后计算了金属球的单站RCS随频率的变化,所得结果与理论值一致性也很好.     

Polarization transformation of a wave field propagating in ananisotropic medium

The momentous experimental discovery of the Faraday (1846) effect is sketched from a historical perspective, through the eyes of several well-known scientists. This effect and its generalization can be explained theoretically by using the dispersion theory for waves propagating in an anisotropic medium. A wave of arbitrary initial polarization will have its wave polarization transformed continuously as it propagates. It is convenient to represent this continuous polarization transformation by a locus in the polarization-ratio plane. In a lossless medium, when both characteristic waves are propagating, this locus is a circle. Five cases in a magneto-ionic medium have been investigated for different propagation angles. The results are discussed and illustrated     

Calculation of the states of shallow donors in quantum wells in a magnetic field using plane wave expansion

A nonvariational method for calculating the states of shallow donors in quantum wells in a magnetic field is suggested. The method can be used in a wide range of magnetic fields, starting with zero. The method is based on the expansion of the electron-wave function in a basis of eigenfunctions of the Hamiltonian operator that describes a rectangular quantum well. The results obtained by this method are compared to the experimental data and to the results of calculations using different theoretical methods. The comparison shows that our method describes the observed spectrum of the shallow-donor states in quantum wells in a magnetic field with a higher accuracy than the methods used in the study by Chen et al.     

Polarization and angle-of-arrival fluctuations for a plane wave propagated through a turbulent medium

The correlation function of the fluctuations of the depolarized component of a plane wave as a function of the distance between two parallel line-of-sight paths is derived in terms of the index of refraction variations. A first-order solution to the wave equation is found using spectral analysis techniques. The mean square polarization fluctuation is predicted to have alambda^{2}dependence, in contrast to the work of another author which showed no wavelength dependence. Some numerical values are calculated and the restrictions on the solutions are discussed. At optical wavelengths the depolarized component is extremely small. From the point of view of minimizing the noise introduced by a turbulent atmosphere, polarization modulation seems attractive compared to amplitude or angle modulation. The problem of determining the angle-of-arrival fluctuations when using a wave optics formulation is discussed. If one accepts the statement that the angle-of-arrival is the normal to the wave front at any point, then the correlation function of the angle-of-arrival is simply related to the correlation function of the phase fluctuations and agrees with the ray optics results.     

A bidomain model for the extracellular potential and magnetic field of cardiac tissue

In this brief communication, a bidomain volume conductor model is developed to represent cardiac muscle strands, enabling the magnetic field and extracellular potential to be calculated from the cardiac transmembrane potential. The model accounts for all action currents, including the interstitial current between the cardiac cells, and thereby allows quantitative interpretation of magnetic measurements of cardiac muscle.     

Method for measuring the attenuation and phase constants of asurface wave propagating along an infinite plane

A method is presented for determining the attenuation and phase constants of a surface wave propagating along an infinite planar layer of metal-backed material. Two input impedance measurements of a rectangular waveguide partially filled with the test material are used to infer the propagation characteristics of the plane surface wave. Measurements are presented which validate the method     

Creeping wave diffraction by a junction with plane surface

The transformation of a creeping wave coming to the point of the junction of convex and plane parts of the surface is examined. The asymptotics in a vicinity of the junction is constructed in the leading approximation. The solution is given by the integral containing Airy function. The numerical results for that integral are presented. The results show the transition between a creeping wave like behaviour and a diverging wave behaviour.     

Beyond mean field and plane wave theories of bistable semiconductor lasers

The steady-state output of semiconductor lasers containing saturable absorbers is calculated using a model that includes transverse mode variation, high gain and absorption coefficient, and high mirror transmission. The results are compared to the predictions of the mean field theory, and they show that the mean field formulas underestimate the amount of hysteresis and overestimate the required amount of absorption compared to the high gain formulas.     

Generating a plane wave with a linear array of line sources

Creating a plane wave across an antenna under test is important for accurate antenna measurements. This paper optimizes the location and weightings of an array of line sources in order to approximate a plane wave at a given location in space. The amplitude and phase ripples across a desired test aperture are optimized to be much less than that of a uniform array with the same number of elements. Results are presented for a nine-element array with optimized amplitude and phase weights, with optimized weights and spacing in the x-direction, and with optimized weights and spacing in the x and z directions. The optimized approximate plane wave is a significant improvement over a uniform array or a single line source.     

The currents on a cylinder illuminated by a generalobliquely-incident plane wave

A relation is presented that determines the total current induced by a general plane wave obliquely incident or a perfectly electrically conducting cylinder of arbitrary cross section from the total current induced by a normally incident plane wave. Remarkably, this same relation ran also be used to determine the physical optics (PO) and nonuniform (NU) currents for oblique incidence directly from the PO and NU currents, respectively, for normal incidence     

斜程大气传输光束孔径平滑到达角与像点起伏

像面到达角起伏、波面抖动和像点抖动通常是研究大气干扰情况下高分辨成像系统波前特性的重要方法之一。采用Rytov近似、包含湍流内外尺度影响的修正von Karmam近似谱和接收光学系统孔径滤波函数和传输权重函数中的Airy函数的高斯函数近似,研究了斜程湍流大气中传输束状波的波面抖动、像面到达角起伏和像点抖动规律,导出了圆孔接收系统测量到的包含湍流内外尺度影响的束状波孔径平滑波面抖动、像点抖动和像面到达角方差理论模型。     

About the localization of a converging spherical wave going through the plane boundary of a medium

The focusing properties of a converging spherical wave that passed the plane boundary of a medium are investigated in the ray approximation. Models of the medium of the two types are considered—ignoring and taking into account the wave energy loss in the medium. The dimensions of the localized volume spot of the field formed instead of the focusing point are estimated.     

Filter functions for computing multipole moments from the magnetic field normal to a plane

A technique for calculating the magnetostatic multipole moments (and therefore complete biomagnetic information) from measurements of the normal component of the magnetic field on a plane is described. The technique involves multiplying the measured values by a set of unique filtering functions and integrating. A new formulation and method for calculating the filtering functions is introduced. The method uses expansions in basis sets and matrix inversion. Proofs are given of the nonsingularity of the matrices. Computer simulations of the application of the technique to a circular current loop and a current dipole in a spherical conductor are described.     

Propagation of microwaves through InSb in a transverse dc magnetic field

Experiments on the propagation of microwave power through InSb in a transverse dc magnetic field demonstrate the feasibility of low-loss propagation. The results correlate well with theoretical predictions.     

Scattering of a plane wave by a circular cylinder with uniformlyincreasing radius

The interest in the problems of diffraction by moving objects has become obvious due to the applications of nonstationary models for the simulation of different processes. Among them are radar control for the industry ejections or military explosions in the atmosphere and scattering by moving fronts of ionization, or by mobile artificial space objects. The detailed analysis of such processes implies the choice of an adequate model that on the one hand can be effectively investigated but on the other hand ensures a reliable approximation for the complex nonstationary processes. From this point of view, the set of canonical problems that can be solved accurately has great practical significance. We study the diffraction of an electromagnetic plane wave by a circular cylinder with a uniformly increasing radius. The formulation and analysis include propagating singularities as well as the continuous component of the solution. An accurate result is developed by means of separation of variables. Some numerical examples are discussed     

The wave theory of a plane lens made from a negative material

A plane lens made from a negative material (metamaterial) is considered. The wave theory that was developed earlier is generalized to the case when the wave-energy loss in the lens and in the ambient medium is taken into account. The dimensions of the spot that is formed in the field-focusing region in the presence of loss, instead of the focal point existing in the absence of loss, are analytically estimated. It is shown that the dimensions of the spot are related to the loss parameters in the media and to the lens’ thickness. The dependence of the dimensions of the spot on the field frequency (and wavelength) is due only to the frequency dispersion of the loss parameters. The dimensions of the spot formed owing to the finite dimensions of the lens are estimated.     

Analysis of diffraction of a plane wave and of the field of a point source by a multirow grating

A multirow grating of impedance or dielectric elements is considered. The 2D problem of scattering by such a grating is solved with the help of the modified null field method and the pattern equation method. A system of integral equations is derived and the reflection and transmission coefficients are determined as functions of various parameters of the problem. The excitation of the grating by a current filament is investigated. An asymptotic solution is obtained for the case when the periods of the grating rows and interrow distances are rather large. In the low-frequency approximation, a solution to the problem for a grating of circular cylinders is presented.