Er Fluid Microwave Reflection And Frequency Selection Characteristics

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.