外电场与微波交互作用下BaTiO3电流变液的透射特征

分别考虑了微波传播方向与电流变液颗粒链相垂直和平行的情况,对BaTiO3电流变液微波透射行为进行了实验研究。发现BaTiO3电流变液微波透射率可由外电场调控。在垂直的情形,当流体浓度较低时,透射率随电场强度增加而减小,并且随浓度增加电场调节微波透射率的变化幅度增加。浓度超过一定值时,透射率随电场出现由减小向增加的改变,存在透射率的极小点。在平行的情形,发现透射率随电场强度增加而减小。另外透射率随电场强度变化具有延时性,对于给定浓度的情形,电场强度增加延时性明显减小。     

电流变液的微波透射调控行为

依据外电场作用下电流变液结构由各向同性转变为各向异性及介电性能改变的实验事实,建立了微波穿透电流变液样品的理论模型,导出了微波透射率的基本表达形式.理论模拟显示:当电流变液的介电常量小于所处环境的介电常量时,透射率随电场的增加而增加;反之则减小.实验研究表明:电流变液的微波衰减(透射率)的变化可以通过电场来调控.分析认为在外加电场作用下,电流变液结构转变和介电性能的变化是导致微波透射率可调控的主要原因.     

电流变液的微波透射调控行为

依据外电场作用下电流变液结构由各向同性转变为各向异性及介电性能改变的实验事实,建立了微波穿透电流变液样品的理论模型,导出了微波透射率的基本表达形式.理论模拟显示:当电流变液的介电常量小于所处环境的介电常量时,透射率随电场的增加而增加;反之则减小.实验研究表明:电流变液的微波衰减(透射率)的变化可以通过电场来调控.分析认为在外加电场作用下,电流变液结构转变和介电性能的变化是导致微波透射率可调控的主要原因.     

电流变液中的旋光现象

根据光波在介质中的传播理论，由麦克斯韦方程出发，对非均相结构电流变流导出在外电场与光场交互作用下旋光角ψ与入射线偏振光振动方向与外加电场方向间夹角θ及ζ（取决于电流变液材料本身及外加电场强度）的函数关系式。对不同浓度、不同场强下的SiO2电为液的旋光进行了测量，实验发现，同一场强作用下，旋光角ψ随浓度c的增大而增大；对于同一浓度，旋光角ψ随场强E增大而增大；在浓度c与场强E一定的情况下，旋光角ψ还随θ角而变化。实验结果与理论预测吻合较好。     

电流变液的旋光与椭偏光行为

本文研究了电流变液(ER流体)的旋光行为及椭偏光行为.激光束垂直于电场方向,利用HeNe激光器对SiO₂、Si₃N₄和硅油组成的ER流体进行测量.发现电流变液样品存在旋光现象,且对于同一种浓度的ER流体,随着电场强度的增大,旋光角度增大.在同一电场强度下,旋光角度随着浓度的增大而增大.当浓度大于某一值c₀时,旋光角度开始减小,在不同电场强度下,透过电流变液的椭圆偏振光性质不发生改变,且随着电场强度的增大,透射光强度随之增大.电流变液的旋光行为及椭偏光行为起因于在电场作用下ER流体由各向同性的液体转变为各向异性的液体.     

固液双相电流变系统流动过程的相转变特性

考虑电流变液多粒子近程相互作用，利用等效平板电导模型，研究了电流变液流动过程相转变点的特性，并设计实验观察了电流变液中的这种相转变现象.研究结果表明，电流变液在一定压力梯度作用下发生流动，此时为双相流；当外加电场达到某一值时，电流变液中颗粒不流动，由固液双相流转变为液体单相流动，发生场控相转变，理论模拟结果与实验观察结果基本相符.阈值电场随外加压力梯度的增加而加大，随颗粒浓度的增加而减小. 关键词： 电流变液 颗粒流 相转变     

纤锌矿结构AlInN电子及光学性质的第一性原理研究

本文通过基于密度泛函理论的第一性原理,研究了纤锌矿结构Al1-xInxN在不同In浓度下的稳固结构,以及电子和光学性质的变化规律。研究表明,AlInN不同In浓度的晶格结构都很稳定,说明AlInN的兼容性很好。晶格常数随In浓度的增大不断增大,而混晶的带隙则不断减小。并且随In浓度的增大,混晶在紫外光区的吸收系数、反射系数及折射率增大,吸收边、吸收峰和反射峰蓝移,且这两个峰的峰值减小。AlInN的吸收、反射和折射率曲线在Eg处出现峰值行为,此Eg处的峰值大小随In浓度的增加而增大。当In浓度达到87.5%时,混晶AlInN在紫外光区的吸收、反射和折射能力均达到最强,表明此时的掺杂效果最好。     

纤锌矿结构AlInN电子及光学性质的第一性原理研究

本文通过基于密度泛函理论的第一性原理,研究了纤锌矿结构Al1-xInxN在不同In浓度下的稳固结构,以及电子和光学性质的变化规律。研究表明,AlInN不同In浓度的晶格结构都很稳定,说明AlInN的兼容性很好。晶格常数随In浓度的增大不断增大,而混晶的带隙则不断减小。并且随In浓度的增大,混晶在紫外光区的吸收系数、反射系数及折射率增大,吸收边、吸收峰和反射峰蓝移,且这两个峰的峰值减小。AlInN的吸收、反射和折射率曲线在Eg处出现峰值行为,此Eg处的峰值大小随In浓度的增加而增大。当In浓度达到87.5%时,混晶AlInN在紫外光区的吸收、反射和折射能力均达到最强,表明此时的掺杂效果最好。     

强电场作用下反铁电锆钛酸铅的介电行为研究

采用电滞回线方法和偏置直流电场中叠加小交变电场方法研究了锆钛酸铅反铁电陶瓷材料在强电场作用下的介电行为.测量结果显示，锆钛酸铅反铁电材料的介电常数随外加电场强度呈非线性变化，在反铁电 铁电转变的电场区间形成介电峰.表征极化强度随电场强度变化率的微分介电常数εd峰值出现在反铁电 铁电转换电场强度处，最高达到41000.随着偏置电场增加反铁电向铁电体转变过程中，小信号介电常数εc减小；在电场降低铁电回复成反铁电过程中，小信号介电常数εc增大，小信号介电常数εc峰先于微分介电常数εd峰出现.根据电场作用下反铁电 关键词： 锆钛酸铅反铁电陶瓷 介电行为 强电场条件     

电流变液电磁波散射理论研究

本文以近代电磁理论为基础，研究电流变液中电磁波散射性质。引入局域结构因子、盲点、正比点的概念，用局域结构因子描述电流变液微观粒子的分布。讨论了随外加电场增大时结构和介电常数对散射的影响。结果表明：在空间存在电磁波散射能量极小值，此类点存在的空间位置不定；随外加电场增加，盲点存在的几率变大而正比点存在的几率变小。     

Calculation of magnetic fluid parameters from the temperature dependence of the microwave reflection spectrum

We analyze the possibility of determining three parameters of a magnetic fluid (permittivity, volume fraction of the solid phase, and diameter of magnetic fluid particles) simultaneously from the temperature dependence of the reflection spectrum of microwave radiation. The reflected signal is detected using a microwave interferometer in a magnetic field, and the microwave interferometer is loaded with a layer of a magnetic fluid. Analysis of the spectral dependence of the reflection coefficient and its temperature dependence makes it possible to get information on the properties of the magnetic fluid under investigation, to refine the value of the permittivity of the magnetic fluid, and to obtain the effective permittivity of nanosize magnetic particles.     

An Exotic Phase Change in Dynamic Electrorheological Fluids

It is well known that constant or time-varying electric fields can induce phase changes in electrorheological(ER) fluids, from a liquid to semi-solid state, provided the field strength is larger than some critical value. We describe here an experimental and theoretical study considering yet a different class of phase changes, specifically those for an ER fluid in the presence of both shear flow and a time-varying electric field. We note that as the frequency of the field is decreased, the ER fluid will go from a liquid to an intermediate transition state, and eventually to a shear banding state. Our theoretical analysis further indicates that this phase change originates from competing effects of viscous and electrical forces. Ultimately, we conclude that it is possible to achieve various states and corresponding(desired)macroscopic properties of dynamic colloidal suspensions by adjusting the frequency of the externally applied electric field.     

Basic considerations in flowing electrorheological fluids

The physical and chemical properties of electrorheological (ER) fluids are reviewed, and an outline theory of their mode of action is proposed. Rheologically, the Bingham plastic model gives an acceptable representation of ER fluids flowing in a field and it has recently been shown that the plastic viscosity may be field-dependent in some circumstances, as well as the yield stress. The variation of the former with field is strongly influenced by the specific chemical nature of the ER fluid, while the field dependence of the latter has a similar form in all the ER fluids investigated. However, interpretation of observations is complicated by concentration of solid in the working gap and interplay between local electrical conductivity and shear rate.     

Frequency dependence of the coefficient of microwave radiation reflection from magnetic fluid at liquid nitrogen temperatures

The coefficient of microwave radiation reflection from a plane layer of a magnetic fluid magnetized by a magnetic field of 11.5 kOe is measured in the temperature range 253–293 K. The concentration of the magnetic phase (magnetite) is 15 vol %. In this temperature range, the dynamic susceptibility of nanoparticles exhibits strong dispersion (ferromagnetic resonance). Experimental data are treated by invoking the theory of high-frequency magnetization of an ensemble of interacting isotropic superparamagnetic particles. It is shown that, when the temperature drops below the room value, the trends observed at elevated temperatures (a decrease in the fraction of the power reflected from the magnetic fluid and an increase in the frequency of a minimum in the frequency dependence of the power) are retained.     

Determination of the magnetic fluid parameters from the microwave radiation reflection coefficients

The interaction of microwave radiation with a magnetic fluid that completely fills a waveguide and is bounded by a dielectric insertion is studied at frequencies between 20 and 40 GHz. The frequency dependence of the alternating interference maxima and minima that are associated with the reflection from the front and back walls of the dielectric insertion is found. The reason for such a dependence is the variation of the complex magnetic susceptibility of the magnetic fluid. The inverse problem, i.e., the determination of the ferromagnetic particle diameter and the volume content of the solid phase in the magnetic fluid, is solved based on the frequency dependence of the reflection coefficient.     

分散相颗粒几何因素对电流变液体反应时间的影响

瞬变的反应时间是电流变液体的一个重要参数．本文通过实验和理论分析，建立了考虑分散相颗粒几何因素的电流变反应时间模型根据此模型，长椭球状颗粒的电流变液体反应时间比等效球状颗粒的短，扁椭球状和片状颗粒的电流变液体反应时间比等效球状颗粒的长，而棒状颗粒的电流变液体反应时间则视ε_p/ε_f比值大小或快于或慢于等效球状颗粒的反应时间．且反应时间与分散相尺寸的关系是（１）随体积增大，各种形状颗粒的电流变液体反应时间均变短；（２）同体积下，随长径比增大，长椭球状颗粒的电流变液体反应时间变短，而扁椭球状颗粒和片状颗粒的电流变液体反应时间变长，棒状颗粒的电流变液体反应时间则视。ε_p/ε_f比值大小或增快或减慢．因此，要获得反应快的电流变液体，颗粒形状除选择球状外，还可在使雷诺数较小范围内，选择一定尺寸的长椭球状或棒状颗粒。 关键词：