THE FREQUENCY-DEPENDENCE AND NONLINEAR DIELECTRIC PROPERTY OF ER FLUID

The frequency dependence of the shear stress in ac field and the non-l inear dielectric property of ER fluid have been studied. We find that the shear stresses of some water-free ER fluids increase monotonously with the frequency and tend to reach saturated values at high frequenc y. The measurements on KNbO3/silicone ER fluid show that the shear str esses under 10(3) Hz frequency a.c. field are several times or even an order larger than that under d.c. field for the same field strength. The studies of non-linear dielectric proper?ies of ER fluids show that the permittivity of ER fluid increases linearly with increasing field strength when the electric field exceeds a threshold value E(1) and t ends to a saturated constant beyond a high field strength E(2). Corres pondingly the current density follows linear behavior no longer ill th e region between E(1) and E(2). A model based on the rearrangement of the particles under the electric field. which causes the variation of the dielectric property of the ER fluid, is proposed and the analysis is consistent with the measured results.