FDTD Analysis of Electromagnetic Reflection by Conductive Plane Covered with Magnetized Inhomogeneous Plasmas

A novel finite-difference time-domain (FDTD) methodology which incorporates both anisotropy and frequency dispersion at the same time is developed for electromagnetic wave propagation in anisotropic magnetoactive plasmas in this paper. The numerical verification of the method are confirmed by computing the reflection and transmission of right-handed/left-handed circularly polarized (RCP/LCP) wave through a magnetized plasma layer, with the direction of propagation parallel to the direction of the biasing field. And, the right-handed / left-handed polarized wave reflection coefficients for electromagnetic signals normally incident upon a conductive plane covered with a layer of magnetized plasma are computed using the new FDTD method. The parabolic electron-number density profile varies only in the direction perpendicular to the plane. The function dependence of reflection coefficients on the number density, collision frequency and external magnetic field is studied.     

Investigation into absorption of the incident laser beam during Nd:YAG laser processing of metals

Laser materials processing is highly affected by the existence of surface plasma. The absorption of surface plasma during drilling alters the power intensity distribution of the incident laser beam across the irradiated spot. The present study is carried out to measure the electron number density and temperature using a Langmuir probe while a mathematical formulation is conducted for the absorption coefficients due to electron-ion, electron-neutral atom collisions, inverse Bremsstrahlung, and photoionization processes. Consequently, a computer program is developed to compute the relevant absorption coefficients as well as the overall absorption coefficient. The laser power intensity distribution before and after the plasma absorption is computed at a plane 2.6 mm above the workpiece surface. It is found that 13% of the reduction occurs in the incident laser output power intensity at this plane in the plasma.     

FDTD model of non-magnetized plasma coatings on metals based on collocated surface impedance boundary conditions

A finite-difference time-domain (FDTD) model is developed for non-magnetized plasma thin layers on metal surfaces illuminated by vertical polarization (TE) and parallel polarization (TM) plane waves at oblique incidence. The model is based on collocated first-order surface impedance boundary conditions (SIBCs), permitting one to remove the plasma coating and the substrate from the computational space. The reflection of TE and TM plane waves at varying oblique incident angles from the plasma coating surfaces is simulated. The results are numerically verified by the comparison with the exact results in the one-dimensional situation. Magnitude and phase error of the calculated reflection coefficients are studied to illustrate that the proposed model has greatly improved accuracy over the original SIBCs implementation. Finally, we calculate the radar cross-section (RCS) of a perfectly conducting cube covered with plasma coatings utilizing the proposed collocated SIBCs, which further demonstrates the practical application of the model.     

Kinetic theory of semibounded plasma with randomly scattering boundary

The electromagnetic fields created by an arbitraty distribution of sources in a semibounded plasma with random Scattering of charged particles by the boundary surface are calculated. A model boundary condition is employed that ensures simultaneously preservation of the number of particles and the absence of particle flow through the boundary. The electric-susceptibility tensors, surface impedances, and coefficients of reflection of plane electromagnetic waves from a plasma half-space are found. Invariance of the distributions of s-polarized electromagnetic waves with respect to the selected model of a randomly scattering boundary is established.     

电磁波在磁化等离子体中传播的时域有限差分模拟

基于Z变换形式的时域有限差分法计算公式,模拟了传播方向垂直于磁化磁场的电磁波在磁化等离子体层中的传播.通过离散傅立叶变换,给出了电磁波通过均匀和非均匀磁化等离子体后的反射系数和透射系数随频率的变化关系.还给出了电磁波经过均匀磁化等离子体层后的反射和透射系数和理论值的对比.     

L波段高功率波导缝隙阵设计与数值模拟

设计了一种基于宽边纵缝驻波阵的高功率射频微波辐射系统,系统由四路矩形波导以及聚四氟乙烯天线窗组成。天线内采用真空绝缘实现天线高功率容量,天线窗真空侧采用周期刻三角槽技术抑制高功率微波介质表面击穿。在波导缝隙阵与天线窗之间设计支撑板,除支撑天线窗外还可抑制表面波电流。采用HFSS数值模拟软件对辐射系统进行了优化设计。数值模拟结果表明,设计的辐射系统在频率为1.575 GHz时,增益为22.7 dBi,天线口径效率为98.3%,反射系数为-25 dB,带宽达到5%,带宽内天线增益波动小于等于0.4 dB、天线口径效率大于等于98%、主瓣指向偏差小于等于1.2。系统功率容量达到1.92 GW。     

Reflection and Transmission of Ion Acoustic Waves from a Plasma Discontinuity

We calculate transmission and reflection coefficients for an ion acoustic wave incident from the upstream direction upon a plasma discontinuity of width much less than the wavelength. In the limit of an infinitely strong discontinuity there is complete in phase reflection.     

Wave reflection and transmission from a thin film with one-dimensional disorder

This paper deals with a TE plane wave reflection and transmission from a thin film with one-dimensional disorder by means of the stochastic functional approach. The relative permittivity of the thin film is written by a Gaussian random field in the horizontal direction with infinite extent, and is uniform in the vertical direction with finite thickness. Arandomwavefield is obtained in terms of a Wiener-Hermite expansion representation with approximate expansion coefficients (Wiener kernels) under a small fluctuation case. For a SiC thin film and a glass thin film having one-dimensional disorder with Gaussian correlation or an exponential correlation, numerical examples of the first-order incoherent scattering cross section and the optical theorem are illustrated in the figures. It is then found that ripples and four major peaks appear in angular distributions of the incoherent scattering. Such four peaks may occur in the directions of forward scattering, specular reflection, backscattering and in the symmetrical direction of forward scattering with respect to the normal to surface of the thin film. Physical processes that yield such ripples and peaks are discussed.     

Rocking Curves of X-Ray Asymmetric Bragg Diffraction with Two-Dimensional Curvature of Wave Front

The X-ray asymmetric Bragg diffraction in a perfect semi-infinite crystal with plane entrance surface is considered taking into account the two-dimensional curvature of the wave front of an incident wave. An expression for reflection coefficient using the Green function is obtained in the approximation of locally plane wave and the rocking curves are investigated as functions of angular departure from the selected exact Bragg direction in the diffraction plane and in the direction perpendicular to the diffraction plane. The shape, position and dimensions of total reflection region of rocking curves are studied depending on the degree of asymmetry of diffraction geometry. The requirements to the spatial and temporal coherence for obtaining the rocking curves are estimated.     

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：     

A generalization of image theory to predict the interaction of multipole fields with plane surfaces

A derivation and computational scheme, based on exact image theory, for the field produced by the interaction of an outgoing vector wave harmonic with an infinite-extent plane surface is presented. The method represents the angular-dependent Fresnel reflection coefficients of the surface as Laplace transforms of a spatially dependent function, which results in the reflected field appearing as a superposition of image sources located at complex points along the normal axis within the surface medium. Exact, analytical formulas are given for the transformed reflection coefficients for arbitrary surface refractive index, and an efficient computation scheme for evaluation of the scattered field coupling between a particle and the surface is presented.     

Ion focusing and blocking effects of surface scattering at a grazing angle

The effects of ion focusing and blocking on surface scattering at a grazing angle is investigated by computer simulation, where primary ions are bombarded along the semichannel direction. When varying the angle of incidence, the ion focusing effect is clearly observed in reflection coefficients at the specular reflection.     

Dispersion of surface plasmons in InSb-gratings

The reflection of a monochromatic plane electromagnetic wave by a grating consisting of grooves in the surface of a semiconductor plasma (InSb) is investigated theoretically, in particular in that region of frequencies where the complex permittivity of the semiconductor plasma has a negative real part. From the numerically obtained reflection factor pertaining to anH-polarized incident wave, the excitation and the dispersion of surface plasmons at the boundary of the medium is discussed. The grating problem is rigorously formulated as a boundary value problem employing a Green's function technique. Numerical results pertaining to the reflection factor are presented for different grating parameters.     

Bandgap characteristics of 2D plasma photonic crystal with oblique incidence:TM case

A novel periodic boundary condition (PBC), that is the constant transverse wavenumber (CTW) method, is introduced to solve the time delay in the transverse plane with oblique incidence. Based on the novel PBC, the FDTD/PBC algorithm is proposed to study periodic structure consisting of plasma and vacuum. Then the reflection coefficient for the plasma slab from the FDTD/PBC algorithm is compared with the analytic results to show the validity of our technique. Finally, the reflection coefficients for the plasma photonic crystals are calculated using the FDTD/PBC algorithm to study the variation of bandgap characteristics with the incident angle and the plasma parameters. Thus it has provided the guiding sense for the actual manufacturing plasma photonic crystal.     

Reflection of Electromagnetic Waves by a Nonuniform Plasma Layer Covering a Metal Surface

Reflection coefficients of electromagnetic waves in a nonuniform plasma layer with electrons, positive ions and negative ions, covering a metal surface are investigated by using the finite-difference-time-domMn method. It is shown that the reflection coemcients are influenced greatly by the density gradient on the layer edge, layer thickness and electron proportion, i.e., the effect of the negative ions. It is also found that low reflection or high attenuation can be reached by properly choosing high electron proportion, thick plasma layer, and smooth density gradient in the low frequency regime, but sharp density gradient in the high frequency regime.     

Study on the polarization properties of electromagnetic waves with arbitrary magnetic declination in magnetized plasma

The polarization characteristics of oblique incidence electromagnetic waves in magnetized cold plasma layer are studied using the finite-difference time-domain (FDTD) method based on the trapezoidal recursive convolution (TRC) technology. The TRC-FDTD formulations are derived in detail and are confirmed by computing the reflection and transmission coefficients for the elliptically polarized wave through a magnetized cold plasma slab with arbitrary magnetic direction. Particularly, when the propagation direction of the EM wave is parallel to the magnetic direction, the right-circular-polarized and left-circular-polarized wave should be considered. When the propagation direction of the EM wave is perpendicular to the magnetic direction, the ordinary polarized wave and extraordinary polarized wave should be considered.     

新型低混杂波发射天线设计研究

描述了一种新型低混杂波天线／有源／无源波导间隔排列的阵列天线，给出了其物理模型和计算方法，对其发射波谱和反射特性进行了研究。计算了这种波导阵列中的有源波导的平均反射系数和发射波谱的方向性系数随等离子体参数和天线参数的变化关系，以及不同参数下的发射波谱，并对ＨＬ－１Ｍ装置上现有低混杂波天线特性做了更进一步的分析计算。     

Enhanced sound transmission from water to air at low frequencies

Excitation of acoustic radiation into the air from a low-frequency point source under water is investigated using plane wave expansion of the source spectrum and Rayleigh reflection/transmission coefficients. Expressions are derived for the acoustic power radiated into air and water as a function of source depth and given to lowest order in the air/water density ratio. Near zero source depth, the radiation into the water is quenched by the source's acoustic image, while the power radiated into air reaches about 1% of the power that would be radiated into unbounded water.     

一种高效计算各向异性磁化等离子体的时域有限差分算法

利用电流密度和电场强度的卷积关系,引入电流密度和电场强度分段线性近似,导出一种适合各向异性磁化等离子体介质的FDTD算法的计算公式.计算各向异性碰撞磁化等离子体平板对平行于磁场传播的电磁波的反射和透射系数,与解析结果比较,验证该算法的高效性和高精度,与电流密度卷积(JEC)算法和分段线性电流密度卷积(PLCDRC)算法相比,计算精度及计算效率显著提高.此外,用该算法验证了法拉第旋转效应.     

A theory of rheed

Elastic Reflection High Energy Electron Diffraction (RHEED) by solid surfaces is studied theoretically. First, the problem of finding the electron reflection and transmission coefficients of a crystal slab is formally solved. Following this, it is shown how the formal solution may be used in a practical computation of the diffracted beam intensities. These two results are applied to a study of high energy (20 keV) electron diffraction by the Ag(001) surface. Rocking curves are computed to illustrate the dependence of the reflection coefficients on the glancing angle of the incident beam, the incident beam azimuth being in the [110] direction. The curves are shown to have several features in common with a typical set of LEED I-V plots: primary Bragg peaks, secondary Bragg peaks and resonance peaks are all present. The dependence of the reflection coefficients on the deviation of the incident beam azimuth from the [110] direction is also described. Additional computations are made to illustrate the sensitivity of the RHEED pattern to the details of the surface structure: the relative heights of the peaks in the rocking curves are shown to be quite sensitive to the spacing of the topmost atomic layers.