The Adjustable Character Of Microwave Transmission Through ER Fluids

Theoretically microwave transmission in electrorheological fluids was studied. According to the experimental facts that the structure transformation of ER fluids from isotropy to anisotropy, and the dielectric properties of ER fluids change with the external electric field, the model of microwave propagation through ER fluids has been established. The theoretical simulation shows that the microwave transmittance increases with the dielectric constant of ER fluids if the dielectric constant of the ER fluids is larger than that of the container. Otherwise it decreases with the dielectric constant.Since the direction of the particle chains is different from that of microwave transmission, which was considered to have different effect on microwave attenuation. Two different ERF containers for measuring the microwave transmittance were made.In this article, the experimental results revealed that the microwave transmittance in starch and starch/nickel ER fluids could be adjusted by changing DC field strength. The microwave transmittance increases with field strength when the concentration of the fluid is low; otherwise it decreases, which is in qualitative agreement with the theoretical model.As barium titanium is a typical ferroelectrics medium, in which the variation of the polarization intensity with the field strength is nonlinear under the external electric field. The behavior of microwave propagation in BaTiO3 ER fluids was also studied when considering the microwave propagation in a direction perpendicular and parallel to the particle chains, respectively. The microwave transmittance in the fluids could be adjusted by the electric field. In the former case, the transmittance decreases with field strength when the concentration of the fluid is low. When the concentration exceeds a critical value, the transmittance decreases first, then increases with field strength, and there is a minimum value of the transmittance. The transmittance can increase with the concentration of the fluid. There is a saturation electric field strength. If the field strength is lower than the saturation one, themicrowave transmittance changess with field strength rapidly. Otherwise, it is not obvious. On the other hand, in the case of microwave propagation parallel to the particle chains the microwave transmittance decreases with the field strength monotonously. With certain field strength, an increase in the space length of electrodes can increase the microwave attenuation. However, the increase of space length of electrodes can increase the microwave attenuation that is adjusted by unit space length of electrodes in a nonlinear way.Moreover, the behavior of microwave transmission displays the relaxation effect, which is related to the field strength and the concentration of the fluid.The phenomenon that the microwave transmission could be adjusted in ER fluids can be attributed to the changes of the structure and the dielectric properties of ER fluids under the electric field. Especially, the structure change of BaTiO3 ER fluids in coordination with the polarization of BaTiO3 can be responsible for the adjustable character of microwave attenuation in BaTiO3 ER fluids.