等效回路法在离子液体电极效应中的应用

利用等效电回路模型简化离子液体的电极系统,分析了电极效应中出现的3个特征频率和各自表征的物理意义.基于离子液体介电谱实验数据,获取了等效电回路的基本参数:本体电容、本体电阻和电双层电容,进而得到离子液体样品和电双层的基本介电参数,以及与离子迁移相关的物性参数如扩散系数、迁移率、离子液体中有效离子浓度,对深入理解离子液体导电和界面机制有重要的意义.     

双层介电薄膜结构双液体变焦透镜的研究

在双层介电薄膜结构双液体变焦透镜模型的基础上,分析了透镜焦距与外加电压、双层介电薄膜的介电常量、薄膜厚度等参量的关系.并以降低双液体变焦透镜驱动电压为目的,选择了相对介电常量较高的五氧化二钽薄膜作为内层介电层,相对介电常量较低的防水层为外层介电层,分析了双层介电薄膜的厚度以及厚度的匹配对双液体变焦透镜的变焦范围和驱动电压的影响,在保证一定的变焦范围并尽可能降低透镜驱动电压情况下获得最佳透镜工艺参量.模拟结果表明:疏水层薄膜厚度比高介电层薄膜厚度小很多时,双液体变焦透镜可实现低压驱动,且双液体变焦透镜在一定变焦范围内所需驱动电压可下降到10V以下,而疏水层薄膜厚度与高介电层薄膜厚度相当或高于高介电层薄膜厚度都不能有效利用高介电薄膜的高介电性能来降低双液体变焦透镜的驱动电压.     

电介质介电系数εr的测量

[引言] 电介质的介电系数ε_r是反映电介质性质的一个重要参数,它不仅是电磁学中一个极其重要的物理量,而且在工程技术中也常常被用来表明各种电介质的电性质。如何测定电介质的介电系数,应该成为电磁学实验的重要内容之一。本文介绍了电桥法和频率法测定液体和固体电介质介电系数的原理、实验方法与实验结果。通过这个实验,不仅可使学生掌握固体、液体电介质介电系数的测量原理和方法,而且可使学生学到万用电桥、频率计的使用技能。     

低压双液体变焦透镜的理论及工艺研究

通过对仅有单层介电薄膜双液体变焦透镜模型的相关理论分析,得出介电层薄膜的厚度及均匀性对双液体变焦透镜的性能影响很大,并绘制了双液体变焦透镜焦距与驱动电压、介电层厚度的关系曲线.在此基础上,以降低双液体变焦透镜的驱动电压为目的,对介电层的选择进行了分析,选择既可充当介电层又可充当疏水层的派瑞林材料作为双液体变焦透镜的介电层材料,通过真空蒸发镀膜工艺得到了合适厚度的介电层派瑞林薄膜,并对所镀薄膜表面形貌以及厚度进行了测试.选择氯化钾以及溴代十二烷作为导电液体和油性液体,利用离心方式除去液体中溶有的气体,进而制作完成双液体变焦透镜样品.电驱变焦实验得到低压双液体变焦透镜样品的变焦范围为±20mm,驱动电压约为30V,对于实验过程中出现的迟滞效应,通过对杨氏方程中引入摩擦力项,合理地解释了其原因.     

小尺度多孔介质燃烧室中火焰分布的电容层析成像测量

电容层析成像(ECT)是一项极具应用前景的过程成像测量技术,该技术具有非侵入、响应快、系统简单等诸多优点。本文成功地将ECT应用于小尺度多孔介质燃烧室中着火、熄火、不稳定燃烧等过程的参数分布检测,检测结果为微燃烧研究提供了重要的依据,同时验证了小尺度燃烧空间中填加多孔介质能显著提高燃烧效率及燃烧稳定性的特点。本文对火焰的介电特性进行了探讨,提出了火焰复等效介电系数模型,给出了火焰复等效介电系数与燃烧场宏观物理量之间定性关系,填补了ECT对火焰感应机理未知的空白。     

最大气泡压力法测液体表面张力系数的改进

对最大气泡压力法测定液体表面张力系数的实验原理、方法及仪器进行了研究,提出用螺旋活塞定量加压控制气泡的生成速度;用扩散硅气体压力传感器测量压强,测得值数字显示;用双毛细管制作实验探头,消除了毛细管插入液体一定深度产生的静压强及待测液体密度等对计算液体表面张力系数的影响,提高了液体表面张力系数的测量速度和精度.     

一种新的用于低温强磁场下测温的电容元件

本文报道了微型陶瓷电容系列CT41的低温介电特性并给出了元件的电容-温度曲线C(T)、损耗-温度曲线tgδ(T)、及液氦温度下的电容-磁场行为等的初步测量结果。     

介电层粗糙对电容式RF MEMS开关down态电容退化的影响

电容式RF MEMS开关在控制高功率射频信号时会发生自锁失效,由于开关桥膜与介电层之间的粗糙接触,开关的down态电容会发生退化,因此很难建立开关自锁失效阈值功率的高保真预测模型。提出了3D电磁-等效电路仿真对比建模的方法。建立开关的3D电磁仿真模型,仿真得到具有任一表面粗糙度水平的介电层粗糙开关的隔离度(S21)曲线;再建立同一开关的等效电路模型,通过调谐其down态电容值,使得仿真得到的S21曲线与3D电磁模型仿真结果尽可能吻合;此时,可以确定一组根据开关3D电磁仿真模型设定的表面粗糙度水平与等效电路模型调谐好的down态电容值的关系;改变开关介电层的表面粗糙度水平,并重复上述步骤,确定了任一开关的介电层表面粗糙度与开关down态电容退化的关系。采用文献的down态电容实测数据,初步验证了该方法的可行性和合理性。并利用所得的开关down态电容随介电层表面粗糙度退化的特性,对简化的(介电层光滑)开关自锁失效阈值功率解析计算式进行了修订,可扩展用于预测介电层粗糙开关的功率容量。     

用天平测定电介质的相对介电常量

利用分析天平，测出了带电平行板电容器两金属板间的相互吸引力F，根据F与两极板间电压U的函数关系，对测量数据进行回归计算，得出平行板电容中电介隔片的相对介电常量。     

介电弹性体驱动液体透镜的设计与分析

介电弹性体具有结构紧凑、形变量大、响应速度快及易集成等特点,为了降低驱动电压,将介电弹性体应用于液体透镜中,采用介电弹性体和透镜薄膜分离结构,建立了介电弹性体主动薄膜变形、透镜薄膜变形以及液体透镜焦距的数学模型。仿真结果表明,当初始液体压力为500 Pa、驱动电压为1000 V时,液体透镜的变焦范围为15.13～22.80 mm,焦距增加了为51%。分析了介电弹性体的杨氏模量、残余应力、初始厚度及半径对液体透镜焦距的影响,结果表明,同等增加倍率下,介电弹性体的初始厚度对液体透镜焦距的影响最大,其次为残余应力,该研究结果可为优化设计介电弹性体驱动的液体透镜提供参考。     

Influence of dielectric materials on uniformity of large-area capacitively coupled plasmas for N_2/Ar discharges

The effect of the dielectric ring on the plasma radial uniformity is numerically investigated in the practical 450-mm capacitively coupled plasma reactor by a two-dimensional self-consistent fluid model. The simulations were performed for N2/Ar discharges at the pressure of 300 Pa, and the frequency of 13.56 MHz. In the practical plasma treatment process,the wafer is always surrounded by a dielectric ring, which is less studied. In this paper, the plasma characteristics are systematically investigated by changing the properties of the dielectric ring, i.e., the relative permittivity, the thickness and the length. The results indicate that the plasma parameters strongly depend on the properties of the dielectric ring. As the ratio of the thickness to the relative permittivity of the dielectric ring increases, the electric field at the wafer edge becomes weaker due to the stronger surface charging effect. This gives rise to the lower N_2~+ ion density, flux and N atom density at the wafer edge. Thus the homogeneous plasma density is obtained by selecting optimal dielectric ring relative permittivity and thickness. In addition, we also find that the length of the dielectric ring should be as short as possible to avoid the discontinuity of the dielectric materials, and thus obtain the large area uniform plasma.     

微波脉冲与带介质孔缝矩形腔体耦合的数值模拟研究

利用时域有限差分(FDTD)方法对微波脉冲与带介质孔缝矩形腔体的耦合过程进行了数值模拟研究. 如果孔缝填有介质, 则预期对微波耦合进入腔体的物理过程有重要影响, 研究了微波与带介质孔缝矩形腔体耦合的过程中影响介质孔缝耦合共振峰和共振频率点的因素, 包括孔缝长度、宽度和介质相对介电常数等物理量的影响. 通过大量不同孔缝尺寸的模拟研究, 发现孔缝的介质对孔缝耦合共振频率有明显影响, 我们对微波与带介质孔缝耦合发生共振的公式进行了拟合, 最后得出了微波脉冲与带介质孔缝矩形腔体耦合的共振条件.     

A hybrid long-range surface plasmon waveguide comprising a narrow metal stripe surrounded by the low-index dielectric regions

A novel hybrid long-range surface plasmon waveguide structure comprising a narrow metal stripe, two relative low-index dielectric regions and dielectric ridges is proposed and analyzed. With the dielectric ridges and the two relative low-index dielectric regions symmetrically distributed on both sides of the narrow metal stripe, a symmetric hybrid long range mode with low electromagnetic transmission loss and subwavelength scale confinement is achieved. By optimizing the parameters, the propagation length of the proposed waveguide is increased to over two times to that of the conventional symmetric dielectric loaded surface plasmon waveguide, but the mode size only increases about 20%. For this benefit, the hybrid long-range surface plasmons waveguide is a good candidate for realizing high density photonic integration circuits.     

Effects of the dielectric discontinuity on the photodetachment of H− ion

Using the closed orbit theory, we studied the effects of dielectric discontinuity on the photodetachment of H^? ions. The photodetachment cross-section of H^? in a medium with dielectric discontinuity was derived and calculated. The results have shown that the relative dielectric constants of the medium have a significant influence on the photodetachment of H^?. If H^? is kept in a medium with a relative small dielectric constant, the photodetachment cross-section of H^? becomes oscillating only in a small region above the ionization threshold. However, if H^? is kept in a medium with a relative large dielectric constant, the oscillation in the photodetachment cross-section becomes much stronger. Besides, the distance between H^? and the dielectric dividing interface also influences the photodetachment of H^?. For a given dielectric medium, the oscillation in the cross-section decreased with increasing distance between H^? and the dielectric dividing interface. Therefore, we can control the photodetachment of a negative ion by changing the dielectric constant and the ion–interface distance. This study provides a new understanding of the photodetachment process of negative ions in the presence of a dielectric medium.     

Effect of variation of dielectric constant on the magnetic field modulation of exciplex luminescence

The effect of variation of dielectric constant on the relative magnetic field effect in singlet luminescence has been studied using a typical exciplex system at a saturating field. The study indicates strong specificity in the perturbation of the magnetic field effect by alcoholic solvents. In contrast to alcohols where relative singlet magnetic field effect is of the order of 2% only, the magnetic field effect in non-alcoholic medium reaches as high as 9%. Moreover, dielectric constant variation in alcohols yields curves which are distinctly different from those in non-alcoholic media. It turns out that this dependence of magnetic field effect on dielectric constant is similar in all non-alcoholic solvent mixtures. An analytical study based on Hong and Noolandi’s solution of Smoluchowski equation has been made. Derived expressions can interpret experimental curves reasonably well.     

二维光子晶体禁带特性研究

采用平面波展开法对二维光子晶体分别在E和H极化下的带隙进行了计算. 考虑了填充比、晶格结构、介电常数对最大绝对帯隙的影响. 结果表明,不论是正方晶格还是三角晶格,TM模在介质柱型光子晶体中更容易形成带隙;TE模在空气孔型光子晶体中更容易形成带隙. 填充比一定,最大绝对帯隙宽度并非随着介电常数增大总是增大,而是存在一个峰值. 相对介电常数一定,最大绝对帯隙宽度随填充比的变化也存在一个峰值. 不论空气孔型还是介质柱型结构,三角晶格比正方晶格更容易形成帯隙. 关键词： 平面波展开法 TE模 TM模 最大绝对帯隙     

Investigation of the properties of extraordinary mode in three-dimensional magnetized plasma photonic crystals with diamond lattices as Voigt effects are considered

In this paper, the properties of extraordinary mode for two types of three-dimensional magnetized plasma photonic crystals (3D MPPCs) composed of homogeneous dielectric and magnetized plasma with diamond lattices are theoretically investigated for electromagnetic (EM) wave based on a modified plane wave expansion (PWE) method, as Voigt effects are considered. As EM wave propagates in such 3D MPPCs, the EM wave can be divided in two modes due to the influence of Lorentz force. One is named extraordinary mode and another is ordinary mode. The equations for calculating the dispersive relationships for extraordinary mode as propagating through two types of structures (dielectric spheres immersed in magnetized plasma background or vice versa), are theoretically deduced. The influences of dielectric constant of dielectric, plasma collision frequency, filling factor, the external magnetic field and plasma frequency on the properties of extraordinary mode for both types of MPPCs are investigated in detail, respectively, and some corresponding physical explanations are also given. From the numerical results, it has been shown that not only the locations but also bandwidths and relative bandwidths of the photonic band gaps obtained by extraordinary mode for both types of 3D MPPCs can be manipulated by plasma frequency, filling factor, the external magnetic field and the relative dielectric constant of dielectric, respectively. However, the plasma collision frequency has no effect on the frequency ranges and relative bandwidths of PBGs for two types of 3D MPPCs. The locations of flatbands regions cannot be tuned by any parameters except for plasma frequency and the external magnetic field.     

2π工作模式下可调谐同轴辐射相对论磁控管的模拟研究

采用三维粒子模拟,开展了2π工作模式下同轴辐射相对论磁控管的频率调谐研究.利用在互作用区的谐振腔中填充固体电介质来实现器件的频率调谐.通过改变电介质的相对介电常数以及内半径考察了所研究的同轴辐射相对论磁控管的工作频率、平均输出功率以及效率的变化情况,并对电介质的频率调谐作用进行了简单的理论分析.模拟结果表明:在不改变基本结构参数以及工作点的情况下,仅调整固体电介质的相对介电常数或内半径实现了所研究的同轴辐射相对论磁控管S波段到L波段的跨频段调谐;电介质的插入同时也改善了输出性能,当相对介电常数在6–15且内半径在4.18–4.40 cm之间时,功率效率得到提升,提升幅度可达80%,单边调谐宽度小于55%. 关键词： 频率调谐 同轴辐射磁控管 粒子模拟 高功率微波     

The error of brightness temperature of sea water caused by the error of dielectric constant

Comparing three formulas of calculating complex dielectric constant of saline solutions shows that two of them will yield errors of no more than 5% at frequency 34.88GHz except at temperature 0°C. An expression of the relative error of brightness temperature has been developed, which claims that the relative error of brightness temperature is at least less than half of the relative error of complex dielectric constant.     

电场作用下的气泡受力分析

本文在蠕动流近似的基础上分析计算了具有不同介电常数工质的气泡在外电场力作用下的受力状况。计算结果表明电场力的水平分力使气泡沿场强方向伸长,并且液体和气体相对介电常数之比越大的工质所受的电场力越大。从而,沸腾换热过程中外加电场对液体和气体相对介电常数比值较大的工质能够产生更大的影响。