液态电介质相对介电常数的测量

通过自制的专用电容器,采用电容测量仪测电容的方法,在物理实验中开设液体电介质的相对介电常数的测量实验。     

基于静电衰减规律的油品电导率测量

油品中的电荷遵循指数衰减规律,测出油品的相对电容率和时间常量,即可求出油品的电导率.通过电容比较测得油品的相对电容率,用放电过程电位的测量间接获得时间常量.采用静电自动测量系统采集数据,利用软件拟合出衰减曲线.该方法适用于电导率低于10-11S/m的油品测量.     

薄膜材料电容率的测量

利用阻抗分析仪测量了金属-介质薄膜-半导体结构的C-V特性曲线. 由积累区电容得到所制备HfO2薄膜的电容为1.24 nF,计算得其相对电容率为12.49.     

低温储罐电容液位计设计

低温液化气体的相对介电系数都很小 ,电容液位计传感器的电容变化量很小 ,传感器的灵敏度比较低 ,针对这一问题 ,对液位计设计进行分析 ,提出解决方案。低温液体的温度不是一直不变的 ,气体和液体的相对介电系数都将改变 ,需要进行修正。文中提出一种新的电容液位测量方法     

电容式液体浓度敏感元件实验研究

本文对引入典型传感实验作为大学物理实验教学内容的意义进行了探讨。通过测量特定电容器电容值的变化情况,对极性液体介质（如乙醇）和非极性液体介质（如汽油）混合时,电容值随液体浓度的变化关系进行了实验研究。     

FR4相对电容率测量实验设计

采用由微带线与射频信号源、频谱分析仪构成的简易实验装置,可准确测量出FR4介质板的相对电容率,降低了射频电路或微带天线设计实验的成本.     

测量电介质的电容率

简述了应用计算机技术改进测量电介质电容率的一种方法。     

LC串联电路测量液体电容率

基于LC串联电路存在"零电阻"状态的电路特性,利用标准电感线圈和自制液体电容器,设计了可以精确测量液体电容率的实验方法.利用该方法测量了蒸馏水以及不同体积分数乙醇溶液的电容率,测量结果与文献参考值的相对偏差在1%以内.     

测量空气的电容率

利用自制的可调间距的精密平行板电容器，配合交流电桥，通过一定的误差分析与数据处理，较为准确地测量了空气的电容率。     

一种局部相含率测量方法

在局部电导探针和单丝电容探针的基础上,提出一种新型局部电容探针,用于测量两相流的局部相含率。静态研究表明,局部电容探针能够测量空气水两相流的局部相含率,测量结果不受导电相电导率变化的影响。从工业蒸馏水变化到饱和食盐水(NaCl的质量分数0～5%),局部电容探针输出结果没有明显变化。电极距离在0～30 mm的范围内变化,测量结果变化小于1%。动态实验表明,局部电容探针测量的两相流的局部相含率,能够很好反映流动过程(以弹状流为例),和实验观察结果完全一致。只需要设置简单的阈值大小,就可以得到相含率的大小。     

Ein Verfahren zur Messung der komplexen Dielektrizitätszahl an kleinen Flüssigkeitsmengen im Frequenzbereich von 0,7–25 GHz mit Hohlraumresonatoren

A method is described for measuring the complex relative permittivity of liquids. Circular cylindrical TE₀₁₁-, TM₀₁₀- and coaxial-line-resonators are used. The liquid under test is contained in a narrow glass tube (volume<0.5 ml) which is placed concentrically along the axis of the cavity resonator. Besides the knowledge of the diameter of the glass tube and the dimensions of the resonator only frequency measurements are required. The accuracy of the method (error±5% of the absolute value for both, the real- and imaginary part of the permittivity) is comparable to other methods requiring a larger amount of liquid. Furthermore, permittivity variations can be measured very sensitively because these are indicated by shifts of the resonance frequency as well as changes of the quality constant, which can both be determined with an error smaller than 0.5%. Some experimental results for water and an aqueous phospholipid suspension are given to demonstrate the accuracy of the method.

     

The determination of the relative permittivity of periodic stratified media based on the iterative time-reversal method

In this paper, we present a new method to determine the relative permittivity of periodic stratified media using the iterative time-reversal method. Based on transmission line theory, the focal peak value of iterative time-reversal electro- magnetic waves, which contain information about the periodic stratified medium, is computed in pulse-echo mode. Using the relationship between the focal peak value and the relative permittivity of the periodic stratified medium, the relative permittivity can be obtained by measuring the focal peak value. Numerical simulations are conducted, and the results demonstrate the feasibility of the proposed approach to the measurement of the relative permittivity of a periodic stratified medium.     

Response properties at the dynamic water/dichloroethane liquid–liquid interface

ABSTRACT

We present a novel approach for calculating the static dielectric permittivity profile of a liquid–liquid interface (LLI) from molecular dynamics simulations. To obtain well-defined features, comparable to those observed at solid–liquid interfaces, we find it essential to reference to the instantaneous liquid–liquid interface rather than the more commonly used average Gibbs interface. We provide a coarse-grained approach for the practical definition of the instantaneous interface and present numerical results for the prototypical water/1,2-dichloroethane system. These results show that the parallel components of the dielectric permittivity tensor can be accurately extracted. In contrast, the perpendicular component does not converge to the correct bulk value at large distances from the LLI, highlighting a flaw in the regularly applied coarse-graining procedure.     

Measurement of complex permittivity and permeability of materials by quasi-optical method

A quasi-optical method for measuring the complex permittivity and permeability of materials at millimeter and submillimeter wavelengths is proposed. In principle, this method is applicable not only to solid samples but also to liquid and composite samples. The theory and experiment are described in this paper.     

Polarizability of nonpolar atoms and molecules in a medium

We obtain relations between the dielectric permittivity and the density of monatomic and polyatomic nonpolar dielectrics in the gas and liquid states. The relations lead to a constant value of the polarizability of atoms and molecules over a wide range of the state parameters.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 63–67, April, 1988.     

Determination of the relative permittivity of the AlGaN barrier layer in strained AlGaN/GaN heterostructures

Using the measured capacitance--voltage curves and the photocurrent spectrum obtained from the Ni Schottky contact on a strained Al_0.3Ga_0.7N/GaN heterostructure, the value of the relative permittivity of the AlGaN barrier layer was analysed and calculated by self-consistently solving Schr?dinger's and Poisson's equations. It is shown that the calculated values of the relative permittivity are different from those formerly reported, and reverse biasing the Ni Schottky contact has an influence on the value of the relative permittivity. As the reverse bias increases from 0 V to --3~V, the value of the relative permittivity decreases from 7.184 to 7.093.     

Lattice Boltzmann equation method in electrohydrodynamic problems

A consistent lattice Boltzmann equation (LBE) model for simulating different electrohydrodynamic (EHD) phenomena is developed. The model includes fluid dynamics, electric charge transport via advection and conduction currents, and action of electric forces upon space charges in liquid. Problems with different thermodynamic phases (liquid and gaseous) and phase transitions, and with inhomogeneous and density-dependent electric permittivity and conductivity can also be simulated, as well as charge injection and recombination. Deformations and breakup of conductive vapor bubbles, bubble deformation due to electrostriction, dynamics of drops with different electric permittivity were simulated. Simulations show the great potential of the method especially for problems with free boundaries (systems with vapor bubbles and multiple components with different electric properties).     

On the instability of conical protrusions of liquid surface in electric field

Electric field is analyzed at the tip of the conical protrusion of a conductive liquid surface that forms as the field strength approaches certain threshold values. When the field exceeds the threshold, the cone tip generally becomes unstable and emits a slender jet. The field strength at the sharp tip of a conducting liquid cone tends to infinity. Even though the field has a singularity, the cone tip becomes unstable only if the semi-cone angle decreases below the Taylor angle, which is the same for all conducting liquids. It is shown that similar conical protrusions can form if the liquid is a dielectric and its permittivity is sufficiently high. In this case, the equilibrium cone angle depends on the permittivity. When the permittivity is lower than approximately 17.60, cones cannot form, and the ensuing phenomena do not occur.     

On the stability of capillary waves on the surface of a space-charged dielectric liquid jet moving in a material medium

We have derived and analyzed the dispersion equation for capillary waves with an arbitrary symmetry (with arbitrary azimuthal numbers) on the surface of a space-charged cylindrical jet of an ideal incompressible dielectric liquid moving relative to an ideal incompressible dielectric medium. It has been proved that the existence of a tangential jump of the velocity field on the jet surface leads to a periodic Kelvin–Helmholtz- type instability at the interface between the media and plays a destabilizing role. The wavenumber ranges of unstable waves and the instability increments depend on the squared velocity of the relative motion and increase with the velocity. With increasing volume charge density, the critical value of the velocity for the emergence of instability decreases. The reduction of the permittivity of the liquid in the jet or an increase in the permittivity of the medium narrows the regions of instability and leads to an increase in the increments. The wavenumber of the most unstable wave increases in accordance with a power law upon an increase in the volume charge density and velocity of the jet. The variations in the permittivities of the jet and the medium produce opposite effects on the wavenumber of the most unstable wave.     

SiO2 nanoparticles doped nematic liquid crystal system: An experimental investigation on optical and dielectric properties

The aim of this work is to investigate the effect of silica (SiO₂) nanoparticles (NPs) on optical and dielectric properties of BBEA nematic liquid crystal (NLC). For optical analysis the photoluminescence (PL) and UV-absorbance experiments have been performed. The doped system is showing enhancement in the intensity of photoluminescence with varying concentration of nanoparticles. A red shift is observed in the emission spectra of NLC doped with silica nanoparticles. The PL emission peak of NLC is observed at 377.3 nm which is shifted to 379.7 nm in the presence of silica nanoparticles. We have also observed the enhancement in the value of UV absorption for silica doped systems in comparison to the pure system. Energy band gap of pure and doped systems has been calculated and it is found that the energy band gap is decreasing with concentration which is a promising result of this study. The dielectric parameters of the pure and doped NLC systems were carried out as a function of frequency and temperature. Different dielectric parameters such as relative permittivity, loss factor and dielectric conductivity have been measured. The pure and silica nanoparticles doped systems has shown decreased value of dielectric permittivity and loss factor at lower frequency region and at higher frequency regions these values became constant. The value of relative permittivity also decreases with concentration. The increased value of a.c. conductivity for doped systems can be utilized in device designing. Moreover, the temperature dependence of the birefringence (Δn) was determined from the transmitted intensity of light for pure and doped systems and the improvement in its value for both composites has been observed. Improved value of birefringence has pronounced applications in optical devices.