基于几何遮蔽效应和法拉第旋光效应耦合的磁流体偏振光透过率

根据几何遮蔽效应和法拉第旋光效应耦合原理给出的解析表达式,通过数值模拟计算,研究了磁流体的纵场诱导偏振光透过率及磁流体的浓度、液态介电常量、磁性颗粒磁偶极矩热能比和单位磁性颗粒团聚体所含磁性颗粒数量四个参量的变化对其偏振光透过率的影响.结果表明,磁流体的浓度、液态介电常量和磁性颗粒磁偶极矩热能比对其偏振光透过率有显著影响,低浓度样品的偏振光透过率随着纵向磁场强度的增大而线性增加,而高浓度样品则随着纵向磁场强度的增大呈现振荡变化的特性.在一定范围内,磁流体偏振光透过率随其液态介电常量εliquid和磁性颗粒磁偶极矩热能比μd/(kT)的变大而增加.而单位磁性颗粒团聚体所含磁性颗粒数量对其偏振光透过率没有影响,磁流体参量依赖的偏振光透过率在低磁场区域和高磁场区域有明显区别.提出了磁流体纵场诱导偏振光透过率在几类光子器件中的可能应用.     

基于硅柱-磁性液体体系的光子晶体的可调谐负折射特性研究

本文研究了硅柱在MnFe₂O₄磁性液体背景中排列成六边形结构的二维光子晶体的可调谐负折射特性. 利用平面波展开法和时域有限差分法理论研究了硅柱-磁性液体体系二维光子晶体的带隙结构、等频曲线和负折射现象随外磁场强度的变化关系. 模拟结果表明, 硅柱-磁性液体体系二维光子晶体工作在TE模式时, 其负折射特性可由外磁场调节. 在固定背景溶液的磁性颗粒体积分数和入射光频率时, 所研究的折射光束的偏转角和光子晶体的负折射率绝对值随外磁场的增大而增大, 而在固定背景溶液的磁性颗粒体积分数和外磁场强度时, 负折射角和负折射率的绝对值随入射光归一化频率增大而减小. 固定外场强度和入射光频率时, 所研究结构的负折射特性随背景溶液的磁性颗粒体积分数增大而变弱.     

磁流体在非均匀磁场下的实验特性

由于磁流体中的磁性颗粒顺磁排布,在磁场作用下其表面自然形成山丘型结构.对小山丘结构的成因以及山丘属性进行理论分析,通过拍照技术与计算机PS技术相结合的方法,对山丘倾斜角度、高度、直径随磁感应强度、磁流体表面积、磁流体厚度、基液质量等参量的变化进行实验探究.结果表明:非匀强磁场中山丘倾斜角度的大小,取决于所在磁场磁感线的分布;山丘高度和直径与磁流体厚度、浓度、磁场强度密切相关.     

弱磁场中向列相液晶的磁光效应

当外磁场强度比较小时,液晶不会发生Freedericksz转变.利用介电张量分析了扭曲型向列液晶在弱磁场中的旋光效应.通过理论分析表明,线性偏振光经过磁场中的扭曲型向列液晶,会产生左右两束椭圆偏振光.这两束椭圆偏振光在该液晶中的传播速度不同,导致光经过液晶盒后光电场振动面发生偏转.进一步分析表明,对于同一种波长的光,磁场强度越大,其电场振动面旋转角度越大.在相同的磁场强度下,光波长越短,其电场振动面旋转角度越大.如果加上高的偏置电压,使向列型液晶分子长轴方向与外磁场方向平行,线性偏振光经过磁场中的该扭曲型向列液晶,其振动面会也发生偏转.     

磁流体粘度的实验研究

采用毛细法粘度计测量了水基Fe磁流体的粘度,分析了磁性粒子份额、表面活性剂含量以及外加磁场强度和方向对粘度的影响。实验结果表明,磁流体粘度随着磁性粒子和表面活性剂浓度的增加而增加;随着外加磁场强度的增大而增大,对于相同的磁流体,在外加磁场方向垂直于流动方向时的粘度大于外加磁场方向平行于流动方向时的粘度;表面活性剂含量的增大将减弱外加磁场对磁流体粘度的影响。     

一种用于60 GHz通信的S型结构左手材料的设计

基于对S型结构的理论分析,将中心频率设置为60 GHz,通过合理的改变单元结构中相应的尺寸以实现所需电谐振和磁谐振频率,并且经过优化以实现负介电常量和负磁导率的重合频段尽可能理想. 运用反演参量提取方法进行电磁参量提取,可以得到本设计在58.1~61.4 GHz频段内其ε和μ同时为负,即左手频段. 分析散射参量的仿真结果,在58~62 GHz频段内S₂₁大于-3 dB,在59.8~60.4 GHz频段内,S₁₁小于-20 dB,因此该设计结果可以运用于60 GHz通信滤波器和天线等器件的研究与设计.     

水蒸气对二氧化硅膜的影响：吸附性能与渗流效应

研究了在50和90 oC时水蒸气对孔径约为4 ?的二氧化硅膜的吸附性能和渗流效应影响,采用椭圆偏振光谱分析水蒸气的吸附性能,以及测定氦气-H₂O二元混合气体的透过性能. 研究表明水蒸气在二氧化硅膜上的吸附行为符合一阶Langmuir等温线,同时,在H₂O分子存在的条件下,氦气的透过率会急剧下降. 通常,在极小孔内气体分子的传输被认为是不连续的,而是在势能下从一个占有位置跳跃到另外一个空位上. 当在二氧化硅表面的H₂O分子覆盖率上升时,氦气的透过率急剧下降可能与渗流效应有关,其中吸附在二氧化硅表面的H₂O分子阻碍了氦气分子的跳跃.     

梯度磁场下磁流体三维结构的格子-Boltzmann方法模拟

考虑磁性颗粒受到的各种内力与外力包括重力、布朗力、van der、Waaks力、磁偶极-偶极作用力以及外磁场作用力,建立了描述磁流体结构的两相格子-Boltzmann三维模型,对外加梯度磁场条件下磁流体的介观结构进行了模拟.模拟结果表明:外加梯度磁场时磁流体粒子沿梯度方向聚集并出现分层现象,且随时间推移和外加磁场增大,分层现象越来越明显.     

偏振和衍射双重效应影响的Schmidt棱镜特性

一束偏振光经过Schmidt棱镜的两个不同路径,成为两个不同的偏振状态,使得出射光束的偏振态呈现非均匀分布.为了探索偏振态非均匀分布对Schmidt棱镜传光质量的影响机理,将两个路径对应的光波函数引入屋脊衍射积分方程,得到了偏振效应影响的屋脊衍射场强分布.场强分布的数字计算表明:在偏振效应和衍射效应的双重影响下,经Schmidt棱镜出射的光场分布出现了严重变形;对应同一入射线偏振光出现的P、S两分量位相差的差异,使得P、S分量的屋脊衍射光强分布I_P、I_S有很大差异,这种差异在入射线偏振光方位角为0°和90°时达到最大;而合光波的衍射光强I_P+I_S是分裂为有一定空间间距的多峰分布,但多峰分布随入射线偏振光方位角的变化比较小.实验拍摄了He-Ne激光经Schmidt棱镜衍射后出射光强分布图.实验结果和理论分析一致性表明:Schmidt棱镜中的偏振效应和屋脊衍射效应导致了一束入射线偏振光分裂为有一定空间间距的多峰光束,严重破坏了Schmidt棱镜的传光特性.     

利用轴向磁化的永磁环制造轴向梯度磁场

首先叙述了由单个轴向磁化环所产生的磁场,并就两个永磁环所产生的纵向磁场进行了分析.对于两个沿同一方向磁化的永磁体环,沿磁环中心线将会产生一个强度较为均匀的轴向磁场.如果两者的磁化方向相反,则在两磁铁间的区域将产生一个纵向的梯度磁场,其磁场强度介于-B₀到+B₀之间.设计制造了一个高梯度的轴向磁场,其磁场梯度为47.2Tm,测量结果与计算结果非常一致.文中还讨论了产生变梯度磁场的方法.由于永磁环所产生的磁场和螺线管的磁场较为相似,磁铁外部空间将有较大的漏场,最后还讨论了屏蔽漏场的问题.     

Longitudinal field-induced polarized light transmittance of magnetic fluids

The complete optical transmittance for a polarized light passing through the magnetic fluids is investigated theoretically and experimentally, when the externally magnetic field is applied along the propagation direction of the incident light. Hybrid effects due to the geometric shadowing and Faraday rotation are considered simultaneously. The Langevin-like functions are employed to describe the magnetic-field-dependent volume concentration of the particle-aggregation (φ′) and the approximate number of magnetic nanoparticles in the particle-aggregation (βN₀). Based on the experiments on the geometric shadowing effect of our magnetic fluid sample, the analytical expression for the total transmitted power with externally magnetic field after an analyzer is derived. Theoretical simulations disclose the influence of certain critical parameters of the magnetic fluids on the field-dependent optical transmittance. For the entire polarized light transmittance, qualitative agreement between the calculations and the experiments is achieved. Applications of magnetic fluids to several polarized devices operating in longitudinal field arrangement are proposed and discussed. The results presented in this work may be useful for designing the corresponding magnetic-fluid-based optical devices.     

Resonant Lattice Kerker Effect in Metasurfaces With Electric and Magnetic Optical Responses

To achieve efficient light control at subwavelength dimensions, plasmonic and all‐dielectric nanoparticles have been utilized both as a single element as well as in the arrays. Here we study 2D periodic nanoparticle arrays (metasurfaces) that support lattice resonances near the Rayleigh anomaly due to the electric dipole (ED) and magnetic dipole (MD) resonant coupling between the nanoparticles. Silicon and core‐shell particles are considered. Our investigations are carried out using two independent numerical techniques, namely, the finite‐element method and the method of coupled‐dipole equations based on the Green function approach. We numerically demonstrate that choosing of lattice periods independently in each mutual‐perpendicular direction, it is possible to achieve a full overlap between the ED‐lattice resonance and MD resonances of nanoparticles in certain spectral range and to realize the resonant lattice Kerker effect (resonant suppression of the backward scattering or reflection). At the effect conditions, the strong suppression of light reflectance in the structure is appeared due to destructive interference between electromagnetic waves scattered by ED and MD moments of every nanoparticle in the backward direction with respect to the incident light wave. Influence of the array size on the revealed reflectance and transmittance behavior is discussed. The resonant lattice Kerker effect based on the overlap of both ED and MD lattice resonances is also demonstrated.     

Extinction of polarized light in ferrofluids with different magnetic particle concentrations

The magnetic field intensity and nanoparticle concentration dependence of the polarized light extinction in a ferrofluid made of magnetite particles stabilized with technical grade oleic acid dispersed in transformer oil was experimentally investigated. The magnetically induced optical anisotropy, i.e. the dichroism divided by concentration, was found to decrease with increasing sample concentration from 2% to 8%. The magnetically induced change in the optical extinction of light polarized at 54.74° with respect to the magnetic field direction was found to be positive for the less concentrated sample (2%) and negative for the samples with 4% and 8% magnetic nanoparticle concentrations, the more negative the higher the concentration and field intensity. Based on the theoretically proven fact [11] that the particle orientation mechanism has no effect on the extinction of light polarized at 54.74° with respect to the field direction, we analyzed the experimental findings in the frames of the agglomeration and long-range pair correlations theories for the magnetically induced optical anisotropy in ferrofluids. We developed a theoretical model in the approximation of single scattering for the optical extinction coefficient of a ferrofluid with magnetically induced particle agglomeration. The model predicts the existence of a polarization independent component of the optical extinction coefficient that is experimentally measurable at 54.74° polarization angle. The change in the optical extinction of light polarized at 54.74° is positive if only the formation of straight n-particle chains is considered and may become negative in the hypothesis that the longer chains degenerate to more isotropic structures (polymer-like coils, globules or bundles of chains). The model for the influence on the light absorption of the long-range pair correlations, published elsewhere, predicts that the change in the optical extinction of light polarized at 54.74° is always negative, the more negative the higher the magnetic field intensity and particle concentration.     

多层金属纳米点阵的制备及其光学性质的研究

采用纳米球刻蚀法结合热蒸发技术制备了银和氧化硅交替层叠的纳米颗粒阵列. 扫描隧道显微镜测量结果表明, 该纳米阵列呈锥形多层结构. 分光光度计测量样品表明, 该纳米阵列在近红外波段存在明显的透射谷, 该透射谷来源于金属纳米颗粒局域等离激元的激发, 随着金属/介质层数的增多, 透射谷的位置向短波方向移动. 利用HFSS软件对该纳米阵列进行了仿真, 并分析了透射谷蓝移的原因. 关键词： 纳米球刻蚀技术 金属/介质纳米颗粒 表面等离子激元     

Tailoring magnetic and electric resonances with dielectric nanocubes for broadband and high-efficiency unidirectional scattering

The interference of optically induced electric and magnetic resonances in high-refractive-index dielectric nanoparticles provides a new approach to control and shape the scattering patterns of light in the field of nanophotonics. In this Letter, we spectrally tune the electric and magnetic resonances by varying the geometry of a single isolated lead telluride(Pb Te) dielectric nanocube. Then, we overlap the electric dipole resonance and magnetic dipole resonance to suppress backward scattering and enhance forward scattering in the resonance region.Furthermore, a broadband unidirectional scattering is achieved by structuring the dielectric nanocuboids as a trimer antenna.     

Colossal magnetoresistance in manganites and related prototype devices＊

We review colossal magnetoresistance in single phase manganites, as related to the field sensitive spin-charge interactions and phase separation; the rectifying property and negative/positive magnetoresistance in manganite/Nb：SrTio3 p-n junctions in relation to the special interface electronic structure; magnetoelectric coupling in manganite/ferroelectric structures that takes advantage of strain, carrier density, and magnetic field sensitivity; tunneling magnetoresistance in tunnel junctions with dielectric, ferroelectric, and organic semiconductor spacers using the fully spin polarized nature of manganites; and the effect of particle size on magnetic properties in manganite nanoparticles.     

Particle agglomeration and properties of nanofluids

The present study demonstrates the importance of actual agglomerated particle size in the nanofluid and its effect on the fluid properties. The current work deals with 5 to 100 nm nanoparticles dispersed in fluids that resulted in 200 to 800 nm agglomerates. Particle size distributions for a range of nanofluids are measured by dynamic light scattering (DLS). Wet scanning electron microscopy method is used to visualize agglomerated particles in the dispersed state and to confirm particle size measurements by DLS. Our results show that a combination of base fluid chemistry and nanoparticle type is very important to create stable nanofluids. Several nanofluids resulted in stable state without any stabilizers, but in the long term had agglomerations of 250 % over a 2 month period. The effects of agglomeration on the thermal and rheological properties are presented for several types of nanoparticle and base fluid chemistries. Despite using nanodiamond particles with high thermal conductivity and a very sensitive laser flash thermal conductivity measurement technique, no anomalous increases of thermal conductivity was measured. The thermal conductivity increases of nanofluid with the particle concentration are as those predicted by Maxwell and Bruggeman models. The level of agglomeration of nanoparticles hardly influenced the thermal conductivity of the nanofluid. The viscosity of nanofluids increased strongly as the concentration of particle is increased; it displays shear thinning and is a strong function of the level of agglomeration. The viscosity increase is significantly above of that predicted by the Einstein model even for very small concentration of nanoparticles.     

Nondipole optical scattering from liquids and nanoparticles

Nondipolar contribution to optical scattering in liquids and nanoparticle suspensions has been discerned for the first time from the dominant electric dipole scattering by assigning the observed polarization and azimuthal angular distribution of scattered polarized light to pure magnetic dipole and/or electric quadrupole radiation and ruling out other (the impurity of laser polarization, multiple scattering, optical activity, and optical anisotropy) explanations. The observed scattering has potential use in the optical study of nanoparticles.     

In situ imaging of field-induced hexagonal columns in magnetite ferrofluids

Field-induced structures in a ferrofluid with well-defined magnetite nanoparticles with a permanent magnetic dipole moment are analyzed on a single-particle level by in situ cryogenic transmission electron microscopy (2D). The field-induced columnar phase locally exhibits hexagonal symmetry and confirms the structures observed in simulations for ferromagnetic dipolar fluids in 2D. The columns are distorted by lens-shaped voids, due to the weak interchain attraction relative to field-directed dipole-dipole attraction. Both dipolar coupling and the dipole concentration determine the dimensions and the spatial arrangement of the columns. Their regular spacing manifests long-range end-pole repulsions that eventually dominate the fluctuation-induced attractions between dipole chains that initiate the columnar transition.