结构各向异性对传输平均自由程的影响研究

本文研究了由定向排布的椭球形粒子组成的无序介质中微纳结构的各向异性对辐射传输平均自由程的影响机理。采用离散偶极子算法(DDA)计算单个椭球形粒子的各向异性辐射特性,为了得到多重散射下的各向异性介质的辐射特性,采用随机行走方法研究了传输平均自由程随粒子浓度、长径比、分布角度的变化关系,并与各向同性理论的计算结果进行了对比,证明了现有理论的不足。最后,利用辐射传递方程的扩散理论得到了椭球形粒子各向异性介质的表面反射能量分布图。结果表明,微纳结构的各向异性对辐射传输平均自由程和表面辐射能量分布有较大影响,对于各向异性较强的介质,在理论计算中必须加以考虑。     

基于Berreman矩阵的双折射薄膜光谱响应特性计算

采用Berreman特征矩阵方法,通过数值计算研究了双折射薄膜的反射、透射等光谱响应特性。依据电磁场理论的电场分量、磁场分量的界面连续条件,推导了光波在各向异性双轴薄膜中的Berreman转移矩阵,用以分析含有各向异性介质层的复杂薄膜系统的光学性质。这些矩阵递推关系包含了界面处的多点反射,适用于一般的各向异性的多层膜系统,包括入射媒质或基底为各向异性的情况。在文中给出了各向同性入射媒质双轴各向异性膜层一各向同性基底薄膜系统的计算结果,验证了该计算方法的可行性,以此作为进一步研究各向异性薄膜和相关光学薄膜器件设计的理论基础。     

平板电容器介质中的矢量场

介绍了平板电容器真空及各向同性电介质中的电场，进一步计算了各向异性平板电容器电场中的电场强度、电位移矢量、电极化强度。根据计算的结果对平板电容器介质中的矢量场进行了力线描绘，说明了电介质矢量场的性质。并进一步比较了线性各向异性电介质与指数电介质对电场产生的影响。     

介质球的各向异性瑞利散射

基于电磁场的多尺度理论,研究了各向异性介质球内、外电场的规律,导出了各向异性目标散射场的表达式,得到了各向异性介质目标散射振幅、散射截面等的解析表达式,并对其正确性进行了检验.仿真结果表明:各向异性介质球的散射具有偶极辐射的特点,介电常量越大,产生的偶极矩也愈大,散射也越强.其结果可为各向异性目标监测、各向异性光散射研究等提供理论支持.     

平面电磁波在各向异性周期介质中的传输特性研究

将平面电磁波在一维介电各向同性周期介质中的传输矩阵问题扩展至一维介电各向异性周期介质,并得到了平面电磁波在此类介质中的传输矩阵.此矩阵的推导主要基于麦克斯韦方程组和电磁波在介质交界面的连续性条件,即电磁波在介质交界面的切向电场和磁场分量连续.通过此矩阵的推导可以加深学生对"电磁场与电磁波"这门课程的理解.此矩阵也是获得电磁波在一维介电各向异性周期介质中的场分布特性,色散关系和表面模式性质的基础.因此,此传输矩阵对科研和教学都有重要意义.     

双横向电光克尔效应

理论分析了克尔(Kerr)介质在两个横向电场作用下的电光调制特性.并由此确定了具有双横向电光克尔效应的光学材料种类.采用折射率椭球方法分析可知,各向同性克尔介质和一些晶体在横向外加电场作用下,其电光相位延迟与外加电场幅值的平方成正比,与电场方向无关;而其电光双折射主轴方位角与外加电场的方向角成正比,与电场幅值无关,称这种电光调制特性为双横向电光克尔效应.理论分析结果表明,排除兼有泡克耳斯(Pockels)效应和电致旋光效应的材料,立方晶系432,m3m点群和六角晶系6/mmm点群的晶体以及所有各向同性光学介质具有双横向电光克尔效应.目前已有克尔常数较大的陶瓷玻璃材料研制成功,将有力地促进双横向电光效应在光学各领域中的广泛应用.     

均匀各向异性介质球散射的解析研究

将均匀各向异性介质重构为电学上的无耗各向同性介质,得到了重构目标的散射截面;进而得到了主坐标系中无耗各向异性介质球的散射截面,将介质退化到各向同性介质时,各向异性介质球的散射截面与Mie理论完全一致,验证了所得结果的正确性;仿真结果表明:散射截面正比于目标介电常数张量的元素且随入射方向的变化而变化;所得结果为复杂形体各向异性介质目标的散射评判提供了理论基础。     

基于各向异性介质的偏振分束器

利用各向异性介质与各向同性介质构造了一维光子晶体,利用传输矩阵方法分析了它的能带结构,指出利用各向异性介质可以构造高消光比,全角度的偏振分束器件,并分析了它的理论基础.对影响偏振分束带宽的因素进行了分析.为进一步改进设计提出了方向.     

均匀磁化介质椭球的退磁因子及退磁场

在椭球坐标系中求解了均匀椭球磁介质在匀强磁场中的磁化问题,得到了空间磁标势、磁场、介质中退磁场和退磁因子的表达式,研究了椭球形状与退磁因子的关系,分析了介质磁化率对退磁场方向的影响.结论为:椭球磁介质内的退磁场是匀强磁场;退磁因子的大小与椭球形状有关,与椭球大小无关,沿椭球长轴方向的退磁因子较小;一般而言退磁场方向与外磁场方向既不相同也不相反.铁磁质椭球内的退磁场几乎与外磁场反向.     

光子晶体介质性质及手性特征的一种判别方法

通过研究各向同性以及各向异性介质中电磁场的波矢量与波印廷矢量之间的角度关系,给出了利用电磁场的单位波矢量与单位群速度的点积值来判断光子晶体介质性质及其手性特征的一种方法.并指出,可以利用光子晶体手性特征临界点的特性来解决多光束的合束问题.最后,利用解析计算讨论了上述结论.上述研究结果为进一步丰富“电动力学”等相关课程的教学内容打下了基础.     

Electric fields inside and outside an anisotropic dielectric sphere

Analytical expressions of electric fields inside and outside an anisotropic dielectric sphere are presented by transforming an anisotropic medium into an isotropic one based on the multi-scale transformation of electromagnetic theory. The theoretical expressions are consistent with those in the literature. The inside electric field, the outside electric field and the angle between their directions are derived in detail. Numerical simulations show that the direction of the outside field influences the magnitude of the inside field, while the dielectric constant tensor greatly affects its direction.     

Investigation of electric fields inside and outside a magnetised cold plasma sphere

Based on the scales transformation of electromagnetic theory,the analytical expressions of electric fields inside and outside a magnetised cold plasma sphere are presented by reforming the spherical electromagnetic parameter.The obtained results are in good agreement with that in the literature.The angle between the direction of inside field and that of outside field is derived.In S wave band,calculations for the effects induced by parameters of the inner field are established.Simulations show that the angle between incident field and the outside magnetic field influences the inner field remarkably.The inner field will increase as the electron density increases.The inner field varies with frequency nonlinearly.There is an angle between the inner field and the incident field,it changes nonlinearly with the frequency.     

磁化冷等离子体球的太赫兹散射特性

基于位函数的引入与介质参量无关,将各向异性目标内外的电场展为级数形式,得到了任意各向异性目标n阶散射场、目标内场的递推表达式,给出了介电常量张量的变换关系,在平面波任意入射的条件下,并给出了传播单位矢量与极化单位矢量的一般关系.以磁化冷等离子体为例,给出了一阶散射场的具体表达式,并对二阶散射场引起的误差进行了评估.在THz波段和光波段,对所得结果进行了部分仿真.结果表明:微分散射对电波频率和极化状态等因素的影响较为敏感,介电常量张量的非对角元素对散射的影响不大,当波长与目标尺寸一定时,仿真结果不仅适用于THz波段,对其它波段也成立.     

双向隐形传态方案及安全性分析

基于位函数的引入与介质参量无关,将各向异性目标内外的电场展为级数形式,得到了任意各向异性目标n阶散射场、目标内场的递推表达式,给出了介电常量张量的变换关系,在平面波任意入射的条件下,并给出了传播单位矢量与极化单位矢量的一般关系.以磁化冷等离子体为例,给出了一阶散射场的具体表达式,并对二阶散射场引起的误差进行了评估.在THz波段和光波段,对所得结果进行了部分仿真.结果表明:微分散射对电波频率和极化状态等因素的影响较为敏感,介电常量张量的非对角元素对散射的影响不大,当波长与目标尺寸一定时,仿真结果不仅适用于THz波段,对其它波段也成立.     

各向异性圆锥体的平面光波散射特性

基于通用的矢量电位和标量电位与介电常数张量无关的原理,由激发的电偶极子与位函数的关系得到了任意各向异性目标散射场的表达式。得到了通用的介电常数张量的变换关系,具体地给出了介电常数张量在球坐标系中的表达式,将目标的内外电场展为级数,得到了各向异性晶体圆锥体一级散射场的解析表达式。理论结果与文献一致,验证了算法的正确性。在光波波长与粒子尺寸相近的情况下,对所得结果进行了仿真,表明各向异性圆锥体的散射具有偶极辐射的特点。所得结果简单、通用,为研究形状更为复杂的各向异性目标、纳米粒子等的光散射研究提供了理论基础。     

Estimation of biophysical properties of cell exposed to electric field

Excitable media,such as cells,can be polarized and magnetized in the presence of an external electromagnetic field.In fact,distinct geometric deformation can be induced by the external electromagnetic field,and also the capacitance of the membrane of cell can be changed to pump the field energy.Furthermore,the distribution of ion concentration inside and outside the cell can also be greatly adjusted.Based on the theory of bio-electromagnetism,the distribution of field energy and intracellular and extracellular ion concentrations in a single shell cell can be estimated in the case with or without external electric field.Also,the dependence of shape of cell on the applied electronic field is calculated.From the viewpoint of physics,the involvement of external electric field will change the gradient distribution of field energy blocked by the membrane.And the intracellular and extracellular ion concentration show a certain difference in generating timevarying membrane potential in the presence of electric field.When a constant electric field is applied to the cell,distinct geometric deformation is induced,and the cell triggers a transition from prolate to spherical and then to oblate ellipsoid shape.It is found that the critical frequency in the applied electric field for triggering the distinct transition from prolate to oblate ellipsoid shape obtains smaller value when larger dielectric constant of the cell membrane and intracellular medium,and smaller conductivity for the intracellular medium are used.Furthermore,the effect of cell deformation is estimated by analyzing the capacitance per unit area,the density of field energy,and the change of ion concentration on one side of cell membrane.The intensity of external applied electric field is further increased to detect the change of ion concentration.And the biophysical effect in the cell is discussed.So the deformation effect of cells in electric field should be considered when regulating and preventing harm to normal neural activities occurs in a nervous system.     

Electric double layer of anisotropic dielectric colloids under electric fields

Anisotropic colloidal particles constitute an important class of building blocks for self-assembly directed by electrical fields. The aggregation of these building blocks is driven by induced dipole moments, which arise from an interplay between dielectric effects and the electric double layer. For particles that are anisotropic in shape, charge distribution, and dielectric properties, calculation of the electric double layer requires coupling of the ionic dynamics to a Poisson solver. We apply recently proposed methods to solve this problem for experimentally employed colloids in static and time-dependent electric fields. This allows us to predict the effects of field strength and frequency on the colloidal properties.     

Dynamics of a dielectric droplet suspended in a magnetic fluid in electric and magnetic fields

The behavior of a microdrop of dielectric liquid suspended in a magnetic fluid and exposed to the action of electric and magnetic fields is studied experimentally. With increasing electric field, the deformation of droplets into oblate ellipsoid, toroid and curved toroid was observed. At the further increase in the electric field, the bursting of droplets was also revealed. The electrorotation of deformed droplets was observed and investigated. The influence of an additional magnetic field on the droplet dynamics was studied. The main features of the droplet dynamics were interpreted and theoretically examined.     

电场调控双层石墨烯纳米带的电子结构和光学性质

利用基于密度泛函理论的第一性原理方法,研究了外加电场作用下双层AA堆垛的Armchair边缘石墨烯纳米带(BAGNRs)的电子结构和光学性质. BAGNRs具有半导体特性,其带隙随带宽(宽度为4～12个碳原子)的增加而振荡性减小.当施加电场后,BAGNRs的带隙随着电场强度的增加而逐渐减小,带隙越大对电场值的变化越敏感.当电场值为0.5 V/?时,所有BAGNRs的带隙都为零. BAGNRs具有各向异性的光学性质,其介电函数在垂直极化方向为半导体特性,而在平行极化方向为金属特性.在外加电场的作用下,BAGNRs的介电函数、吸收系数、折射系数、反射系数、电子能量损失系数和光电导率,其峰值向低能量区域移动,即产生红移现象.电场增强了能带间的跃迁几率.纳米带宽度对这些光学性质参数具有不同程度的影响.研究结果解释了电场调控BAGNRs光学性质的规律和微观机理.