不均匀磁等离子体的隐身机理——圆极化电磁波的碰撞吸收

研究了圆极化电磁波在不均匀磁等离子体的传播和吸收。讨论了不均匀磁化等离子体片对平行于磁场方向传播的左、右旋圆极化电磁波的碰撞吸收，计算了不同条件下衰减率。计算表明，当电磁波的频率接近电子碰撞频率时，磁等离子体对电磁波的吸收达到最大值。当入射电磁波的频率很低时，不均匀磁化等离子体中磁撞对雷达波的吸收非常小。当入射电磁波频率较高时，等离子体的碰撞对入射电磁波的衰减很有效。     

不均匀非磁化等离子体覆盖三维目标的FDTD分析

针对典型的目标模型,采用RC-FDTD算法计算不均匀非磁化等离子体覆盖三维导体球的双站和单站雷达散射截面（RCS）。分析了等离子体电子密度分布和等离子体碰撞频率对目标RCS缩减的影响。数值结果表明,等离子体隐身技术显著;双站结果显示,不均匀非磁化等离子体能在较大双站角范围内减小目标的RCS;单站结果说明,等离子体包层能在较大的频率范围内对目标RCS的缩减起作用。选择合适的等离子体参数可以加强隐身效果。     

各向异性磁化等离子体的ZT-FDTD算法

把运用于处理各向同性媒质的基于z变换形式的时域有限差分(ZT-FDTD)方法进行拓展,用它处理了各向异性磁化等离子体的电磁问题,给出了该方法用于各向异性磁化等离子体的递推计算公式,计算了各向异性磁化等离子体层对电磁波的反射系数和透射系数,计算结果与解析解及分段线性递归卷积FDTD(PLRC-FDTD)方法结果比较,吻合很好,从而验证了该方法用于各向异性磁化等离子体的高效性和高精度.最后,用此方法计算了各向异性磁化等离子体圆柱的后向散射宽度.该文研究结果可应用于等离子体天线等领域.     

电磁波在均匀磁化等离子体中的衰减与反射

等离子体覆盖住金属导体,通过等离子体对入射电磁波的折射、吸收,使得入射波功率衰减,降低了反射功率,起到减小目标RCS的作用.对于均匀磁化等离子体,针对介电常数与等离子体粒子密度、外加磁场强度、电子碰撞频率以及入射波频率的关系,仿真计算了不同的等离子体粒子密度、外加磁场强度、电子碰撞频率以及不同等离子体厚度在毫米波波段对电磁波的衰减和反射特性的影响.     

基于等离子体反射特性的雷达诱饵技术研究

在研究等离子体与电磁波相互作用的基础上,得到了均匀非磁化等离子体对入射电磁波的反射系数,通过对反射特性的分析,讨论了等离子体用作雷达诱饵的有关问题．     

磁化等离子体涂覆目标散射特性的FDTD方法

基于分段线性递归卷积法(PLRC)把时域有限差分方法(FDTD)推广应用于三维各向异性磁化等离子体中,给出了三维计算公式,并且和电流密度卷积时域有限差分方法(JEC-FDTD)进行了对比,结果表明PLRC方法更精确.计算了磁化等离子体覆盖球锥体的双站雷达散射截面(RCS)与无涂敷以及涂敷非磁化等离子体球锥体的散射特性进行了对比,结果表明磁化等离子体有更加独特的特性.其隐身效果优于非磁化等离子体.     

电磁波在不均匀磁化等离子体中的吸收

本文讨论了不均匀磁化等离子体片对圆极化电磁波、异常模电磁波的吸收,计算了不同条件下衰减率.计算表明,当电磁波的频率接近电子碰撞频率时,磁等离子体对电磁波的吸收达到最大值.当入射电磁波的频率很低时,不均匀磁化等离子体中碰撞对雷达波的吸收非常小.当入射电磁波频率较高时,等离子体的碰撞对入射电磁波的衰减很有效.在磁场对电磁波衰减率的影响上,对右旋电磁波,磁场变大,衰减率曲线的峰值向较低的碰撞频率方向移动,且衰减率减小.而对左旋电磁波,磁场变大,衰减率曲线的峰值向高的碰撞频率方向移动,且衰减率也增大.同时,我们发现在一定条件下,磁场使电磁波的有效吸收带宽变宽.此时,等离子体对电磁波的吸收也最大.特别是当入射电磁波的频率较低时这一特性更显著.     

磁化等离子体覆盖导体散射问题的FE/BI方法分析

基于矢量有限元方法和边界积分方程,推导了分析三维导体表面覆盖各向异性磁化等离子体电磁散射问题的矢量有限元/边界积分(FE/BI)方法公式,并将该方法推广到外磁场沿任意方向时磁化等离子体的情形。应用该方法计算了磁化等离子覆盖导体目标的双站雷达散射截面(RCS),分析了等离子体厚度、密度、碰撞频率和外磁场方向对雷达散射截面的影响。数值计算结果表明:在导体表面覆盖各向异性磁化等离子体并且选取合适的参数,能够有效地减少雷达散射截面。     

1维3元非磁化等离子体光子晶体禁带特性研究

为了研究1维3元非磁化等离子体光子晶体的禁带特性,采用传输矩阵法仿真计算了电磁波在1维3元非磁化等离子体光子晶体的传播规律,用计算得到的电磁波透射系数讨论了周期常数、介电常数、介质层厚度和等离子体参量对其禁带特性的影响。结果表明,改变介电常数、介质层厚度和等离子体频率可以实现对带隙的调制,增加周期数和等离子体频率不能实现对禁带的拓展。这一结果为设计1维3元非磁化等离子体光子晶体器件提供了理论参考。     

垂直入射空变等离子体光子晶体带隙特性研究

采用改进的磁化等离子体电磁散射的时域有限差分(FDTD)算法,分别研究了一维空变磁化和非磁化等离子体光子晶体(PPC)的禁带特性.以微分高斯脉冲为激励源,计算了等离子体光子晶体的反射系数和透射系数.讨论了在垂直入射情况下等离子体频率随空间呈脉冲形式变化的周期函数对禁带的影响.结果表明:通过改变等离子体频率在空间的不同变化可以实现对禁带的控制.     

斜入射到非均匀等离子体上的电磁波反射系数计算

等离子体雷达隐身理论和技术的日益成熟引起了国内外的广泛关注和高度重视。本文给出了平面电磁波斜入射到一维非均匀等离子体上时其反射系数的数值计算方法,并定量分析了金属平板表面电子密度呈抛物线分布的一维非均匀等离子体的雷达隐身效果。     

Electromagnetic Reflection from Conductive Plate Coated with Nonuniform Plasma

Based on the theories of electromagnetic (EM) field and generalized reflection coefficient, a simple method is put forward to deal with the EM reflection coefficient of conductive plate coated with nonuniform plasma. The plasma slab is modeled by a series of subslabs, in which the electron-number density is assumed to be constant. The overall number density profile across the whole slab follows any practical distribution function. The reflection coefficient is then deduced and its functional dependence on the number density, incident wave frequency, collision frequency, and background magnetic field is discussed.     

电磁波在不均匀尘埃等离子体中的衰减特性

基于WKB近似方法, 研究了高频电磁波入射不均匀尘埃等离子体中的衰减特性.对弱电离尘埃等离子体复相对介电常数的分布特征进行了分析, 讨论了电子数密度、尘埃颗粒数密度对复相对介电常数虚部的影响.利用电子密度分布的抛物模型, 数值计算了电磁波以不同角度入射不均匀尘埃等离子体的衰减特性, 对入射角、电子数密度、尘埃颗粒半径和尘埃颗粒数密度对衰减系数的影响进行了分析.结果表明:随着电子数密度、尘埃颗粒数密度和半径增大, 衰减系数也会变大.     

感应耦合等离子体刻蚀机二维放电模拟

为研究感应耦合等离子体(ICP)刻蚀机腔室与线圈结构以及工艺参数对等离子体分布均匀性的影响,基于商业软件CFD-ACE 中等离子体与电磁场等模块建立了ICP刻蚀机二维放电模型.仿真研究了典型工艺条件(1.33Pa,200W,200sccm)下氩等离子体电子温度与电子数密度的空间分布,对比了不同气压与功率条件下等离子体参数在硅片表面的一维分布.结果表明,电子数密度随气压与功率的增加而升高;电子温度随气压的增加而降低,随功率增加在较小范围内先降低再升高.通过分析屏蔽板对等离子体参数的影响,发现其有助于提高等离子体密度.进而发现屏蔽板的孔隙率越大,电子温度越高,电子数密度则越低.     

Radiation from a line source in a ground plane covered by a warm plasma slab

The problem of a magnetic line source in a ground plane coated with a warm plasma slab is investigated. Consideration is given to electromagnetic and plasma waves in the slab and to the coupling at the boundaries between these waves and the free-space fields. An integral expression for the radiation field is obtained and is evaluated by the method of steepest descent. The resulting radiation patterns display interesting effects due to electron pressure near the electron plasma frequency, and these are discussed with the help of the transmission line analog to the problem. The surface-wave poles are located and discussed using this same analog.     

Propagation of Waves through Magnetoplasrna Slab Within a Parallel-Plate Guide

By applying the variational equation is established for handling wave reaction theory, a variational propagation in a parallel-plate guide within which a magnetized inhomogeneous lossy plasma slab is inserted. The equation is then solved by the finite-element method along with the frontal solution algorithm. With such an approach, the reflection coefficient and the field distribution in the slab are obtained. In this study, the factors which may influence the propagation characteristics of the guide are studied. These factors include the plasma electron density, the strength and the direction of the static magnetic field, the width and the thickness of the slab, and the electron collision Iosses. A special modal expansion solution is also incorporated to investigate an anomalous numerical instability associated with the present numerical algorithm.     

A 26- to 40-GHz fast-acting plasma waveguide switch

A fast-acting broad-band plasma waveguide switch has been developed which provides greater than 60-dB isolation and less than 0.25-dB cold loss over the 26-to 40-GHz frequency range. Switching times are under 200 ns, and the actuating trigger signal is a 150-volt 0.5-µs pulse from a high-impedance source. Geometrical enhancement of plasma density by employing metallic convergence cones is used. This technique provides a moderately ionized plasma from a beam whose strength would normally provide only a weakly ionized plasma in the absence of the convergence cone. A computer program of the transmission equation using a plasma slab model yielded the average plasma density and slab thickness in the waveguide; electric probes were used to detect electron temperatures along the cone axis.     

Modeling of oxide breakdown from gate charging during resist ashing

Plasma damage was observed after exposing an antenna capacitor structure to an O₂ plasma in a single wafer resist asher. The observed early breakdown is well modeled by surface charging caused by plasma nonuniformity. Here, the plasma nonuniformity was induced by gas flow and electrode configuration. The present results agree well with our previous results where magnetic field leads to a nonuniform plasma. In this model, nonuniformity leads to a local imbalance of ion and electron currents which charge up the gate surface and degrade the gate oxide. Using SPICE, a circuit model for the test structure and plasma measurements, the Fowler-Nordheim current through the thin oxide regions at different points on the wafer was calculated and found to agree well with the observed damage. The important implication of this work on oxide reliability is that the modeling gives a clear picture to this breakdown mechanism. The charging model can also be applied to any ashing process in any nonuniform plasma. Moreover, this model provides a physical basis for design rules of device structures for the fabrication of reliable gate oxides in submicron MOS technology     

FDTD Simulation of Electromagnetic Pulse Interaction with a Switched Plasma Slab

This paper deals with the Finite Difference Time Domain (FDTD) simulation of interaction of an electromagnetic wave with a switched plasma slab. In formulating the simulation the well-known concepts of (a) total-field/scattered-field formulation (b) and PML lattice truncation are adapted to suit the simulation under consideration. FDTD is particularly well suited to handle the switched (time-varying) medium (including sudden switching) since the time varying parameters of the medium can be easily interpreted in the algorithm. The technique is applied to the difficult problem of interaction of an electromagnetic pulse source wave of frequency ω₀ and a gaussian envelope with a newly created plasma slab of time-varying and space varying electron density profile. The creation of a pulse of Wiggler magnetic field in the slab is illustrated.     

A Helicon Plasma Source

The parameters of a helicon plasma source was studied for an rf power to 500 W and a magnetic field ranging from 0 to 200 G under an argon pressure of 3 mtorr. The electron density in the plasma was found to reach 10¹² cm^–3. Axial and radial electron distributions were studied. Helicon waves were excited by antennas of three types, a loop antenna being the most efficient. It is shown that the electron density in the plasma can significantly be increased if the system is under a nonuniform magnetic field such that its lower-value (relative to the rest of the system) part is applied to the antenna.