进气道内衬筒形等离子体隐身性能三维模拟

针对飞机进气道等离子体隐身问题,建立了三维筒形进气道模型,采用有限元求解波动方程,计算了腔体内壁覆盖均匀等离子体时的雷达散射截面。研究表明:腔体内覆盖等离子体时可以有效吸收入射电磁波能量;吸收随电磁波频率增加而减弱,但由于腔体结构作用,会存在几个吸收峰;吸收随电子数密度增加而增强,但电子数密度过高时,吸收效果会变差;最佳碰撞频率虽然与电磁波频率和电子数密度有关,但其值可约为9GHz;吸收随等离子体厚度增加而变大,但在较大电子数密度时,由于电磁波在等离子体与空气交界面处反射导致厚度增加,从而使得吸收变小;选取合适的入射角度和等离子体数密度可以在1~3GHz频段实现明显的隐身效果。     

非对称耦合量子阱的吸收非线性增强

基于V 形三能级模型运用密度矩阵方程推导了非对称耦合量子阱三阶光学非线性极化率. 具体分析了三阶吸收非线性效率（三阶光学非线性极化率与线性吸收系数之比）随阱间电子相干振荡频率的变化规律. 理论结果表明：三阶吸收非线性效率对阱间电子相干振荡频率相当敏感，当阱间电子相干振荡频率增大时三阶吸收非线性效率显著增强，而当阱间电子相干振荡频率为零时，这种非线性效率类似于单量子阱情况. 与单量子阱相比，对于已设计好的非对称耦合量子阱结构其突出特征表现在，其非线性吸收与色散特性可经由沿材料生长方向偏压进行控制. 据此，我们预期利用这种非对称耦合量子阱结构能设计成光通信中的光限幅器和可控克尔光开关.     

Ce∶KNSBN晶体光扇效应的入射光强度阈值特性研究

采用非同时读出条件下的两波耦合实验装置,以单束光入射Ce∶KNSBN光折变晶体,系统研究了Ce∶KNSBN晶体中光扇效应随入射光偏振态、入射光强度、光入射角的变化情况。结果表明异常偏振光入射晶体时光扇效应明显,且存在明显的入射光强度阈值特性,入射光强度阈值为38.2mW/cm2;相同光入射角下,稳态光扇强度随入射光强度的增强而明显变大;对应相同的入射光强度,稳态光扇强度随光入射角θ的增大而增大,当θ为15°时到达峰值,而后随θ的增大而逐渐减小。同时对光扇效应的入射光强度阈值特性以及稳态光扇强度随入射光偏振态、入射光强度、光入射角的变化作出了相应的物理解释。     

Ce:KNSBN晶体光扇效应的入射光强度阈值特性研究

采用非同时读出条件下的两波耦合实验装置,以单束光入射Ce:KNSBN光折变晶体,系统研究了Ce:KNSBN晶体中光扇效应随入射光偏振态、入射光强度、光入射角的变化情况.结果表明异常偏振光入射晶体时光扇效应明显,且存在明显的入射光强度阈值特性,入射光强度阈值为38.2 mW/cm2;相同光入射角下,稳态光扇强度随入射光强度的增强而明显变大;对应相同的入射光强度,稳态光扇强度随光入射角θ的增大而增大,当θ为15°时到达峰值,而后随θ的增大而逐渐减小.同时对光扇效应的入射光强度阈值特性以及稳态光扇强度随入射光偏振态、入射光强度、光入射角的变化作出了相应的物理解释.     

磁化碰撞等离子体对雷达波的共振吸收

使用平板几何对雷达工作频段的电磁波在磁化碰撞等离子体中的传播作了数值计算,计算结果表明,在均匀等离子体中,当等离子体碰撞频率f∞=0.1,0.5,1GHz及电磁波频率接近高混杂频率时,电磁波衰减和被吸收功率出现最大峰值,即出现共振吸收;当fen=1,10GHz时,电磁波衰减、被吸收功率和透射功率曲线变得很平坦;衰减和吸收功率随等离子体密度的增大而增大,在n=10^11cm^-3时,衰减可达100dB,吸收比可达80％。在非均匀等离子体中,电磁波的反射功率峰值比在均匀等离子体中大。因此,磁化均匀等郭了体更有利于等离子体隐身。     

电子-声子相互作用对正切平方量子阱中光吸收系数的影响

从理论上研究了电子-声子相互作用对正切平方量子阱中光吸收系数的影响,首先利用微扰论方法求出考虑极化子效应时正切平方量子阱的波函数和能级,然后利用密度矩阵算符理论和迭代法得到光吸收系数的解析表达式,最后以典型的GaAs/AlGaAs正切平方量子阱为例进行数值计算。结果表明,极化子效应对线性吸收系数、三阶非线性吸收系数和总吸收系数都有显著的影响,在相同光强的情况下极化子效应使光饱和吸收现象更加明显;考虑电声相互作用后,总吸收系数的改变量随着势阱宽度b的减小和势阱深度V0的增加而增大。     

碳纳米管吸收电磁波特性

本文研究碳纳米管阵列的介电谱函数与吸收电磁波的特性。应用等离激元和无规相近似方法给出碳纳米管的介电谱函数,进而求出吸收系数和反射功率比。介电函数随电磁波的频率变化,在光子能量与系统电子的能谱差相匹配时产生共振吸收,吸收系数出现多个大的吸收峰。反射功率比随薄层厚度的增加而指数衰减,其衰减速率和饱和值与电磁场的频率和碳纳米管的结构有密切的联系。     

用恒定光电导分析非晶硅薄膜的次带吸收

表1列出测量薄膜样品吸收系数的几种方法.对于1μm左右的非晶硅,当吸收系数 a<10-2cm-1时,透射法因受到测量精度的限制不再适用.由于非晶硅是良好的光电导体,用光电导分析法延长其低吸收区.是一种简便方法. 一、用恒定光电导法测低 吸收区吸收系数的原理 当光电导体吸收了一定能量的光子后,产生非平衡的电子-空穴对,这种光生载流子提供给回路的电流就是光电流.所以,当吸收的光子数与光电流成正比时,就可以通过光电导测量得到材料的吸收系数.具有欧姆接触的光电导率可写为其中分别为光生电子,空穴浓度,μn和μp分别为电子和空穴的扩展态迁移…     

量子环中极化子的温度效应

采用求解能量本征方程和LLP幺正变换方法,研究了量子环中极化子的温度效应.数值计算表明:当温度较低时,温度对极化子的基态能量无影响,当温度较高时,极化子的基态能量随温度的升高而增大;还表明极化子的基态能量随电子-声子耦合强度的增大而减小,随电子受限程度的增强(即量子环内径增大或外径减小)而增大,说明其量子尺寸效应非常显著.     

量子环中极化子的温度效应

采用求解能量本征方程和LLP幺正变换方法,研究了量子环中极化子的温度效应.数值计算表明：当温度较低时,温度对极化子的基态能量无影响,当温度较高时,极化子的基态能量随温度的升高而增大;还表明极化子的基态能量随电子—声子耦合强度的增大而减小,随电子受限程度的增强（即量子环内径增大或外径减小）而增大,说明其量子尺寸效应非常显著.     

A Thin Self-Feeding Janus Metasurface for Manipulating Incident Waves and Emitting Radiation Waves Simultaneously

A thin metasurface has shown powerful capabilities in controlling either incident electromagnetic (EM) waves or radiation waves, but is difficult for both. Here, a self-feeding Janus metasurface (SFJ-MS) is proposed to manipulate the incident EM waves and emit the radiated waves simultaneously, which can realize the polarization conversion of incident waves, scattering control, EM wave radiation, and radiation-beam steering. On the upper of SFJ-MS, a diagonal-split square ring and a rectangular patch with rotation for radiation are designed to introduce anisotropy in the meta-atom for converting the polarization of incident EM waves. On the bottom of SFJ-MS, a self-feeding microstructure converts the alternating current into the excitation of SFJ-MS to emit the EM waves to free space. The multiple functions of SFJ-MS are comprehensively substantiated by measured results, which are in agreements with the stringent simulations. This SFJ-MS, with lightweight, compact, low profile, and power-efficient features, can find potential applications in phased array radar systems, wireless communication systems, polarimetric radar imaging systems, and target detection systems.     

畸形波电磁散射特性分析及其特征识别标识的研究

针对弱非线性的Longuet-Higgins模型在模拟强非线性畸形波海面时所存在的问题,采用修正的相位调制法模拟一维畸形波时间、空间波面,该方法能够实现畸形波的定时定点生成,并且其波形既能保持目标谱的频谱结构,又能较大程度地满足波浪序列的统计特性.同时,基于改进的双尺度(TSM)法及时域有限差分法建立畸形波的电磁散射模型,经过相对平均偏差和均方根偏差误差分析后,基于TSM法研究分析了畸形波及其背景海面波的归一化雷达散射截面(NRCS)的计算结果.实验表明,合成孔径雷达成像中畸形波的NRCS比背景波要小,即畸形波的合成孔径雷达图像成像比背景波要灰暗,因此可以将NRCS作为畸形波的特征识别标识.通过分析研究不同极化方式、入射角、入射频率条件下畸形波与背景波面的电磁散射特性实验数据得出:当二者的NRCS差值大于-11.8 dB及以上时,即认为产生畸形波,这为实际的工程应用提供了参照标准.     

Attenuation characteristics of obliquely incident electromagnetic wave in weakly ionized dusty plasma based on modified Bhatnagar–Gross–Krook collision model

The attenuation characteristics of obliquely incident electromagnetic(EM) wave in L-Ka frequency band in weakly ionized dusty plasma are analyzed based on the modified Bhatnagar-Gross-Krook(BGK) collision model.According to the kinetic equation and the charging theory,the total complex dielectric constant of the weakly ionized dusty plasma is derived by considering that the minimum velocity of the electron accessible to the dust particle surface is non-zero and the second potential part of the collision cross-section contributes to the charging.The attenuation characteristics within the modified model are compared with those within the traditional model.The influence of the dusty plasma parameters and the incident angle of EM waves on the attenuation in weakly ionized dusty plasma is further analyzed.Finally,the influence of different reentry heights on the attenuation characteristics of the obliquely incident EM wave is discussed.The results show that the effect of the minimum electron velocity and the second term of the collision cross-section on the attenuation characteristics of EM waves cannot be ignored.When the dust density and dust radius are changed,the trends of the attenuation of obliquely incident EM waves are consistent,but the influence of dust density is weaker than that of dust radius due to the constraint of orbit-limited motion(OLM) theory.The plasma thickness,electron density,and incident angle are proportional to the attenuation amplitude of EM waves.The effect of different reentry heights on the attenuation obliquely incident EM waves is related to the electron density and plasma thickness.     

Electromagnetic modelling of 3D periodic structure containing magnetized or polarized ellipsoids

Coupling matrix and coupling coefficient concepts are applied to the interaction of an incident plane wave with a regular array of small magnetized or polarized ellipsoids, placed in a homogeneous surrounding medium. In general case, the angle of incidence and polarization of the plane wave upon an array of ellipsoids can be arbitrary. In this model, it is assumed that all the ellipsoids are the same, and the direction of their magnetization is also the same. The direction of magnetization is arbitrary with respect to the direction of the propagation of the incident wave and to the boundary plane between the first medium, where the incident wave comes from, and the array material under study. Any magnetized or polarized ellipsoid is represented as a system of three orthogonal elementary magnetic radiators (EMR) and/or three orthogonal elementary electric radiators (EER). Mutual interactions of individual radiators in the array through the incident plane wave and corresponding scattered electromagnetic fields are taken into account. The electrodynamic characteristics — reflection from the surface of the semi-infinite array (in particular, containing uniaxial hexagonal ferrite resonators), transmission through the array, and absorption are analyzed.     

磁化分层等离子体中电磁波传播特性研究

采用混合矩阵法,分析了磁化分层等离子鞘套对斜入射电磁波传播特性的影响,分别计算了不同入射角以及外加磁场下电磁波透射系数和极化特性的变化。以GPS导航信号右旋圆极化波(RCP)为例,研究了磁场、电子密度对电磁波右旋圆极化特性的影响。结果表明,外加磁场能够使右旋圆极化波在等离子体中的阻带向高频方向移动,此外,外加磁场能在一定程度上改善斜入射是圆极化波的极化特性,有利于GPS信号接收。     

电磁波辐照下量子线的电子自旋极化输运性质

理论上研究Rashba自旋-轨道相互作(SOI)量子线在外电磁波辐照下的电子自旋极化输运性质.在自由电子模型下利用散射矩阵方法,发现当Rashba SOI较弱时,自旋极化率与外电磁场频率和电子入射能量无关,而当Rashba SOI较强时,自旋极化率则强烈依赖于外场频率和电子入射能量,其物理根源是Rashba SOI使子带混合引起的.此外,当电子的入射能量增加到打开另一通道阈值时,电子的透射率出现一个反常的台阶结构,这来源于电子与光子的非弹性散射而使电子在子带间的跃迁. 关键词： 量子线 电磁波 自旋极化输运 散射矩阵     

Transverse or off-axis localization of electromagnetic waves in random one- and two-dimensional dielectric systems which are periodic on average

We study the transverse or off-axis localization of electromagnetic waves for several different random dielectric systems which are periodic on average. Unlike previous scalar wave treatments of transverse localization, in the present work we present results based on a full vector treatment of the electromagnetic fields based on Maxwell's equations. In a first system, we consider a random semi-infinite array of slabs with plane waves or finite beams of electromagnetic waves obliquely incident on the slab surfaces. The localization of the fields in a region near the surface of illumination is studied as a function of the oblique angle of incidence. In a second system, an array of semi-infinite slabs with random thickness is considered with an incident finite beam of electromagnetic waves initially directed parallel to the slab surfaces. The spreading of the beam width is computed as it propagates through the array of semi-infinite slabs. In a final system, we consider a semi-infinite array of random dielectric rods (2D system) with obliquely incident plane waves. The localization length of the plane-wave fields is computed as a function of the oblique angle of incidence and as a function of the strength of the disorder of the dielectric medium. All the random media we consider, when averaged over their randomness, are periodic on average. The above systems are studied for both p- and s-polarizations of incident electromagnetic waves, and the difference in the transverse localization of the electromagnetic field for these two polarizations is determined.     

电磁波在大面积等离子体片中传播特性的分析

脉冲磁约束线形空心阴极放电形成的大面积等离子体片可应用于等离子体天线、隐身及模拟超音速飞行器表面的等离子体鞘套. 本文首次利用实测等离子体片电子密度时空分布和横向场传播矩阵法, 研究了电磁波在等离子体片中反射率、透射率、吸收率随频率及脉冲放电时间的变化特征. 结果表明: 极化方向平行磁场的电磁波, 在小于截止频率的低频带内具有较高的反射率和吸收率, 增大电流, 反射率增加, 吸收率下降, 在大于截止频率的高频带内反射率和吸收率较低, 增大电流, 透射率下降, 吸收率升高; 极化方向垂直磁场的电磁波在高混杂谐振频率附近存在吸收率明显增强的吸收带, 谐振吸收峰值与放电电流无关; 脉冲放电期间, 电磁波的反射率、透射率与吸收率由不稳定过渡到稳定的时间约为100 μs, 过渡时间随着放电电流的增加而增大, 极化方向垂直磁场、小于截止频率的电磁波在稳定放电阶段谐振吸收较强. 本文的研究成果对利用等离子体片实现对电磁波的稳定高反射作用具有重要意义.     

线偏光闪耀反射光栅衍射特性研究

通过数值方法对线偏光在Littrow装置中的理想导体闪耀光栅的偏振特性进行研究.用时域有限差分程序计算出任意偏振方向线偏光经过闪耀光栅衍射后的电磁场分布,提取衍射波的S偏振和P偏振分量,讨论了与光栅闪耀角和入射光波偏振角的关系.分析了在1530～1570nm光谱范围内,入射光波为线偏振波和园偏振波时,衍射光波的偏振色散特性与光栅闪耀角的关系,并给出了存在偏振色散的光栅闪耀角范围.这些分析和结果对工程设计具有一定的指导意义.     

Three-dimensional surface current loops in broadband responsive negative refractive metamaterial with isotropy

We propose a bulk negative refractive index (NRI) metamaterial composed of periodic array of tightly coupled metallic cross-pairs printed on the six sides of a cube for applications of superlenses. The structural characteristics of the three-dimensional (3D) metamaterial consist in the high symmetry and the superposition of metallic cross-pairs, which can increase the magnetic inductive coupling between adjacent cross-pairs and realize a broadband and isotropic NRI. The proposed 3D structure is simulated using the CST Microwave Studio 2006 to verify the design validity. The simulation results show that the proposed structure can not only realize simultaneously an electric and magnetic response to an incident electromagnetic (EM) wave, but also exhibit a broadband NRI whose relative bandwidth can reach up to 56.7%. In addition, the NRI band is insensitive to the polarization and the incident angle of the incident EM wave. Therefore, the proposed metamaterial is a good candidate material as three-dimensional broadband isotropic NRI metamaterial.