一种基于超材料的宽带、反射型90°极化旋转体设计

根据各向异性媒质理论, 设计了一种宽带、反射型超材料极化旋转体, 能够将线极化波极化方向旋转90°, 极化转化率大于90%的工作带宽为5.5–14.5 GHz. 该极化旋转体由两层介质板、金属双开口谐振环和金属底板周期排列构成, 具有各向异性的特点, 单元两对角线方向的电场分量反射系数相同, 反射相位相差180°, 导致其极化旋转特性. 利用表面电流分布图, 分析不同极化波入射时该极化旋转体的谐振状态, 实验和仿真结果符合较好. 该极化旋转体在新型天线设计和隐身技术等方面具有广阔的应用前景.     

线电流与无限长磁介质圆柱系统的磁矢势的计算及讨论

用镜象电流法和分离变量法计算了线电流与无限长磁介质圆柱系统的磁矢势,指出线电流与无限大磁介质分界平面、线电流与超导体圆柱、均匀外磁场中有磁介质圆柱系统时的磁矢势都可以由线电流与磁介质圆柱系统的磁矢势的极限情形给出.     

分层球形导体中任意位置直流电流元产生电位的解析解

建立了任意层球形导体头模型.从泊松方程出发，利用电磁边界条件求解了分层球形导体中由任意位置直流电流元产生电位的一般解析解，并且给出了一种以矩阵形式表示的快速求解电位表达式中相关系数的方法.以表示头皮、颅骨、脑脊液和脑的四层球导体模型为例，对解析解进行了计算.结果表明，此解在除源点外的全域内收敛，且比仅用球谐函数展开形式的电位收敛快，计算量明显降低.给出了等位线图和流线图，表明低电导率对电位分布和电流流向的影响不可忽视.还给出了球表面电位分布特征，这有利于脑电逆问题的研究以及对脑电位测量结果的解释. 关键词： 电位 电流元 分层球形导体 脑电     

While rotating while cloaking

Invisible optical and thermal cloaking have been explored as the typical demonstrations of the transformation optics and thermotics theory. However, the existing cloaks are realized by only one-coordinate transformation, and the cloaking layout, i.e. the form of electromagnetic wave/heat passing around the invisible region, is single for a long time. Here, we propose a new rotated thermal cloak which can unify the conventional cloaking and rotating together, and realize the while-rotating–while-cloaking effect. The required anisotropic thermal conductivity tensor is deduced from the new geometric mapping. Though rotated, the heat flux can be tuned around the central invisible region perfectly by the proposed rotated thermal cloak. The underlying physics is explored by comprehensive analysis of the distribution of the thermal conductivity tensor, which is further compared with those of the conventional cloak and rotator. The experimental feasibility is also discussed by validating the practical while-rotating–while-cloaking effect through a proof-of-concept design. The proposed rotated thermal cloak is expected to extend the possibility of cloaking scheme, and open avenues for the multiple coordinate transformation in counterpart physical fields, like optics, electrics, acoustics, magnetics, mechanics, etc.     

Development of a numerical model for the electric current in burner-stabilised methane–air flames

This study presents a new model to simulate the electric behaviour of one-dimensional ionised flames and to predict the electric currents in these flames. The model utilises Poisson’s equation to compute the electric potential. A multi-component diffusion model, including the influence of an electric field, is used to model the diffusion of neutral and charged species. The model is incorporated into the existing CHEM1D flame simulation software. A comparison between the computed electric currents and experimental values from the literature shows good qualitative agreement for the voltage–current characteristic. Physical phenomena, such as saturation and the diodic effect, are captured by the model. The dependence of the saturation current on the equivalence ratio is also captured well for equivalence ratios between 0.6 and 1.2. Simulations show a clear relation between the saturation current and the total number of charged particles created. The model shows that the potential at which the electric field saturates is strongly dependent on the recombination rate and the diffusivity of the charged particles. The onset of saturation occurs because most created charged particles are withdrawn from the flame and because the electric field effects start dominating over mass based diffusion. It is shown that this knowledge can be used to optimise ionisation chemistry mechanisms. It is shown numerically that the so-called diodic effect is caused primarily by the distance the heavier cations have to travel to the cathode.     

Interband transitions in a narrow-band spherical InSb quantum layer in the presence of an electric field

The interband transitions in a narrow-band InSb quantum spherical layer are studied theoretically within the framework of the spherical rotator model. The electron and light-hole dispersions are described using the two-band Kane approximation, while for heavy holes the standard dispersion is considered. The absorption coefficients for transitions between conduction and lighthole, heavy-hole bands are calculated. The selection rules and threshold absorption frequencies are determined. It is shown that in the presence of a weak electric field the selection rules and threshold absorption frequencies for dipole transitions are modified.     

电场对单层有机电致发光二极管复合发光的影响

以电流连续性方程为基础，用易测量的注入电流密度来确定载流子浓度的边界值，得出载流子浓度和电流密度的解析表达式。计算并讨论了电子密度和电子电流密度在器件中的分布，电场对它们的影响以及电场与势垒对复合效率的影响。该模型较好地解释了有关实验现象。     

不同电场下碳纳米管场致发射电流密度研究

本文运用密度泛函理论和金属电子论, 深入研究了碳纳米管场致发射电流的变化规律. 结果显示其发射电流密度取决于体系的态密度、赝能隙、管长和局域电场, 在不同范围电场下的变化规律不同. 在较低电场下, 发射电流密度随电场增强而近似线性增大(对应的宏观电场须小于18 V· μm^-1); 但在较高电场下, 发射电流密度随外电场增加呈现非周期性振荡增长趋势, 碳纳米管表现为电离发射. 本文进一步研究了金属性碳纳米管电导率在不同电场下的变化规律.     

光纤布拉格光栅电流传感的理论和实验研究

对皮磁致伸缩棒调谐光纤布拉格光栅为基础的新型电流传感器进行了理论和实验研究。将一个光纤布拉格光栅牢固地粘贴在一置于多层螺线管中心部分的磁致伸缩棒上，构成传感头。当通过螺线管的电流改变时，磁致伸缩材料在均匀磁场的作用下产生沿纵向的应变并传递到光纤光栅上，从而导致光纤光栅的布拉格波长移动。外加电流和波长移动之间的关系是线性的，线性调谐的波长范围为0.9nm，电流强度范围为900mA，灵敏度约为1000mA/nm，电流强度可精确到10mA。理论和实验符合得很好。     

微纳尺度多铁异质结中电驱动磁反转

近年来,多铁异质结中电控磁性研究引起了广泛关注,已成为多铁领域的热点.现代自旋电子学器件(如磁内存)通常利用电流产生的磁场或自旋转移扭矩效应驱动磁反转来实现数据擦写,但这带来高额能耗和热量,成为亟待解决的关键难题.而利用多铁异质结实施电场驱动磁反转则有望大幅降低能耗,从而实现高速、低能耗、高稳定性新型高密度磁存储、逻辑及其他自旋电子学器件.在当前器件发展的微型化趋势下,探索可集成化的微纳尺度电场驱动磁反转方案显得越发重要.本文针对发展新型磁电器件所面临的微型化关键问题,回顾了微纳尺度电场驱动磁反转研究的新进展,主要关注小尺度多铁异质结中电控磁的新特点、新方法及相关物理机理的实验和理论成果,讨论了进入纳米尺度将面临的挑战,并对未来研究工作提出一些展望.     

均匀外电场中无限长介质圆柱壳的场分布的计算和讨论

用圆柱坐标系中的分离变量法计算了位于均匀外电场中的无限长介质圆柱壳各区域的电势和电场,由计算结果分析了无限长介质圆柱壳对外电场的屏蔽效果,并指出均匀外电场中的无限长导体圆柱壳、无限长介质圆柱体、无限长导体圆柱及无限大均匀电介质中开有一无限长的圆柱形空腔的电势和电场都可以由均匀电场中的无限长介质圆柱壳电势及电场给出.     

Forward and inverse problem for cardiac magnetic field and electric potential using two boundary element methods

This paper discusses the forward and inverse problem for cardiac magnetic fields and electric potentials.A torso-heart model established by boundary element method(BEM) is used for studying the distributions of cardiac magnetic fields and electric potentials.Because node-to-node and triangle-to-triangle BEM can lead to discrepant field distributions,their properties and influences are compared.Then based on constructed torso-heart model and supposed current source functional model-current dipole array,the magnetic and electric imaging by optimal constrained linear inverse method are applied at the same time.Through figure and reconstructing parameter comparison,though the magnetic current dipole array imaging possesses better reconstructing effect,however node-to-node BEM and triangleto-triangle BEM make little difference to magnetic and electric imaging.     

夫兰克-赫兹实验栅极电流的研究

测量了夫兰克赫兹实验中氩气管的经典线性伏安特性曲线,分别从栅极电流和板极电流的实验数据中反应出的氩原子第一激发能级量子化吸收的特性,并对量子吸收理论在实验中的体现加以探讨。     

高压电场浓缩液体物料技术的研究及进展

高压电场干燥技术是一种全新的干燥技术 .文章对高压电场浓缩液体的机理进行了探讨 ,认为是内部离子注入、非均匀电场和外部离子风吹动三合一的结果 .通过以自来水、葡萄糖酸钠溶液等液体物料为样品 ,首次在高压电场下进行浓缩实验 ,表明高压电场能够加速水分子的脱出 .文章对当前的研究状况进行了介绍     

Investigation of transport properties of perovskite single crystals by pulsed and DC bias transient current technique

Time-of-flight (ToF) transient current method is an important technique to study the transport characteristics of semiconductors. Here, both the direct current (DC) and pulsed bias ToF transient current method are employed to investigate the transport properties and electric field distribution inside the MAPbI$_{3}$ single crystal detector. Owing to the almost homogeneous electric field built inside the detector during pulsed bias ToF measurement, the free hole mobility can be directly calculated to be about 22 cm$^{2}\cdot$V$^{-1}\cdot$s$^{-1}$, and the hole lifetime is around 6.5 μs-17.5 μs. Hence, the mobility-lifetime product can be derived to be $1.4\times 10^{-4}$ cm$^{2}\cdot$V$^{-1}$-$3.9\times 10^{-4}$ cm$^{2}\cdot$V$^{-1}$. The transit time measured under the DC bias deviates with increasing voltage compared with that under the pulsed bias, which arises mainly from the inhomogeneous electric field distribution inside the perovskite. The positive space charge density can then be deduced to increase from 3.1$\times10^{10}$ cm$^{-3}$ to 6.89$\times 10^{10}$ cm$^{-3}$ in a bias range of 50 V-150 V. The ToF measurement can provide us with a facile way to accurately measure the transport properties of the perovskite single crystals, and is also helpful in obtaining a rough picture of the internal electric field distribution.     

Electrohydrodynamic behaviors of droplet under a uniform direct current electric field

The electrohydrodynamic behaviors and evolution processes of silicone oil droplet in castor oil under uniform direct current(DC)electric field are visually observed based on a high-speed microscopic platform.Subsequently,the effects of different working conditions,such as electric field strength,droplet size,etc.,on droplet behaviors are roundly discussed.It can be found that there are four droplet behavior modes,including Taylor deformation,typical oblique rotation,periodic oscillation,and fracture,which change with the increase of electric field strength.It is also demonstrated that the degree of flat ellipse deformation gets larger under a stronger electric field.Moreover,both of the stronger electric field and smaller droplet size lead to an increase in the rotation angle of the droplet.     

电场辅助溶解法实现玻璃表面金纳米粒子的形貌控制

贵金属纳米粒子由于其非常独特的光学特性和表面活性, 在光子学、 催化和生物标识等方面都有非常重要的应用. 采用离子溅射和后续热处理相结合的方法在玻璃表面形成了尺寸大约为60-80 nm的单分散的球形金纳米粒子. 在适当的温度条件下, 采用步进式增加的强直流电场, 实现了金纳米粒子的电场辅助溶解过程. 在玻璃表面的不同颜色区域, 初始球形的金纳米粒子溶解成月蚀状形貌. 结合不同颜色区域内金纳米粒子的表面等离子体共振吸收性质和扫描电镜照片, 研究了实验条件对金纳米粒子性质的影响. 结合电场辅助溶解实验过程中的电流-电压特性, 分析了金纳米粒子在强直流电场辅助下溶解的物理过程: 金粒子中动出的电子向阳极的隧穿过程作为开始, 随后是金阳离子向玻璃基体中的传输过程和阴极提供的电子与带有正电荷的金粒子相结合的过程. 详细讨论了电场辅助溶解法实现金纳米粒子形貌控制的物理机制.     

电磁学教学中值得关注的几个问题

讨论了电磁学教学中的3个基本问题即非静电力与非静电场、电流的定义与分类以及有电介质时静电场场强的计算.作者在文中阐述了自己的观点,希望引起重视和讨论.     

电弧增材成形中熔积层表面形貌对电弧形态影响的仿真

电弧增材成形常采用单道多层或多道搭接的熔积方式,不同的熔积方式下对应的熔积层表面形貌不同,从而影响电弧的形态及其传热传质过程.本文建立了纯氩保护电弧增材成形的电弧磁流体动力学三维数值模型,以及不同表面形貌的熔积层模型,并在保持阳极与阴极之间距离和熔积电流不变的条件下,通过模拟计算获得增材成形特有的单道和多道搭接熔积条件下的不同表面形貌对应的电弧形态以及相应的温度场、流场、电流密度、电磁力、电弧压力分布.数值模拟结果表明:平面基板上起弧情况下电弧中心具有较高的温度、速度、电流密度以及压强;单道多层熔积情况下熔积层数对电弧的各个参量影响较小;多道搭接熔积情况下电弧呈非对称分布,电弧中心温度较前两者低,电流密度、电磁力和电弧压强的分布偏向熔积层一侧.     

QUANTUM FLUCTUATIONS IN MESOSCOPIC RESISTANCE-INDUCTANCE-CAPACITANCE ELECTRIC CIRCUITS AT FINITE TEMPERATURE

By using the charge and current in a quantization resistance-inductance-capacitance (RLC) electric circuit, we construct a pair of canonical variables. Using this pair of variables and the thermal field dynamics, we obtain the fluctuations of charge and current in the RLC electric circuit at finite temperatures. It is shown that the fluctuations increase with increasing temperature and decrease with prolonging of time.