电流变液微波反射及频率选择特征

【作者】 黄敏；

【导师】 赵晓鹏；

【作者基本信息】 西北工业大学 ， 光学工程， 2004， 硕士

【摘要】 电流变液是一种典型的软物质，通常是由高介电常数的微小颗粒分散在低介电常数的绝缘液体中形成的悬浮体系。当对它施加电场时，其粘度和剪切强度瞬间变化几个数量级，表现出固体的性质，具有快速可逆的特点。电流变液的微波响应行为较少见报道。作为一种典型的软物质，电流变液在外加电场作用下结构将发生变化，在特定的条件下将形成特殊的结构。由于外加电场作用下电流变液分散相颗粒之间的偶极相互作用导致了内部结构变化，这使得体系的等效介电常数大小以及分布发生变化。本文以钛酸钡、掺杂钛酸钡、掺杂二氧化钛、二氧化钛包覆高岭土复合颗粒以及复相微胶囊为分散相颗粒，研究了电流变液在外加电场作用下的微波反射以及频率选择性特征，取得如下研究成果： 1．在微波频率为9G时，研究了纳米二氧化钛包覆高岭土、钛酸钡以及钇掺杂钛酸钡三种电流变液的微波反射可调控特征。实验发现，在垂直电场作用下，二氧化钛包覆高岭土、钇掺杂钛酸钡两种电流变液微波反射系数均随电场强度的增大而增大；钇掺杂钛酸钡电流变液微波反射系数变化幅度比二氧化钛包高岭土电流变液宽；对钛酸钡电流变液存在一个临界浓度，高于这个浓度，电场的调控能力随电场强度的增加单调减小，低于这个浓度，电场的调控能力随电场的增加先减小后增大。 2．二氧化钛包覆高岭土电流变液反射回波相位随电场强度的增大出现最大值后逐渐减小趋于平稳；钇掺杂钛酸钡和钛酸钡电流变液反射系数相位随电场强度增大而增大。 3．当微波频率位于8G～12G之间时，研究了钛酸钡、铈掺杂二氧化钛以及复相胶囊电流变液在8～12G频段范围内的微波透射频率选择性特征。实验发现，加电场时，在8～12G范围内电流变液的微波响应发生明显变化，在某些波段微波透过率随电场减小，而在某些波段随电场增大，且随电场强度的变化， 西北工业大学硕士论文 透过强度可以调控。4.对于钦酸钡电流变液，在8一gG频段范围内，微波透过率存在最小值，而且 随电场强度增加透过率最小值点向低频方向移动。b1j掺杂二氧化钦电流变 液，在SG附近微波透过率存在最小值。对由复相胶囊组成的电流变液，在 8一9.5G之间微波透过率随电场强度减小;在10.3一10.6G之间随电场强度增 大，在10.7一n.3G之间则又减小。初步认为频率选择性及透过强度可调控 性与电流变液和微波之间的相互作用导致的极化激元之间的祸合有关。更多还原

【Abstract】 Liquids are divided into single and complex fluids according to theirs structure. Complex fluids are called soft materials too. Electrorhological fluids compose of high dielectric constant particles and lower dielectric constant carrier fluids. A reversible changes happens when exposed to an external electric field. Apparent suspension viscosities and shear stress can increase several orders of magnitude.A few researches about the interaction between microwave and soft materials were reported. As a classical soft material, the structures of ER fluids change under the external field. So the value and distribution of the dielectric constant in ERF change. In this paper the coupling between the microwave and ERF was investigated. The experimental results are given as the following:(1) The amplitude of microwave and phase of reflected microwave can be modulated by external field in electrorheological fluids. There is a turning particle concentration for BaTiO3 ERF under which the reflection coefficient decreases linearly and above which it originally decreases to a minimum value then increases to a constant value with the external filed. The reflection coefficient of kaolinite coated TiO2 ERF and Y doped BaTiO3 ERF increases with the external field. As to kaolinite coated T1O2 ERF the reflection coefficient range of sample 1 is from 0.47 to 0.55, sample 2 from 0.39 to 0.46, sample 3 from 0.25 to 0.33. As to Y doped BaTiO3 ERF the modulating ability is larger with a range of 0.17 ~ 0.657 which is between that of silica oil and empty container.(2) As to kaolinite coated TiO2 ERF the reflection microwave phase angle increases to a maximum value then decreases to a constant value. By comparison it increases with the electric field as to Y doped BaTiO3 andBaTiO3 ERF, the phase angle modulating range is larger than that of kaolinite coated TiO2 ERF.The modulation ability of ERF is related to the structure shift and dielectric properties of the disperse phase. Dielectric property changing of disperse phase under external field is the reason that the modulating ability is strengthened.(3) Microwave transmitting characters of ERF with particles of BaTiO3,TiO2 doped Ce and colloid were investigated. We found that microwave transmission changed greatly with the external field. Microwave transmissivity became large at some frequency however it decreased as to other frequency. At the range from 8 to 12GHz, microwave transmissivity of ERF is the function of the frequency under the external field. Also the external field can modulate wave-transmitting strength. At the range from 8 to 9 GHz, the minimum transmissivity value existed as to BaTiO3 ERF; The frequency where the minimum value existed was tend to the lower frequency under the external field. The minimum transmissivity of ERF with TiO2 Doped Ce existed near the frequency of 8GHz. The value of the minimum transmissivity was tend to smaller when the amount of Ce increasing. When the frequency was among the range from 8 to 9.5 GHz, microwave transmissivity decreased with the external field as to colloid ERF. However it increased with the external field from 10.3 to 11.3 GHz; From 10.7 to 11.3 GHz it decreased with the external field too. We considered the frequency chosen character of ERF and its modulatory ability may be owe to the coupling of microwave and the polaritons. At the same time there may be other coupling effect and excitation too.更多还原