Conductivity in electrorheology

Analytical models for the quasi-static ER behavior of suspensions have been developed which take into consideration both the conductivity and dielectric mismatches between the components and the supra-ohmic behavior of the host liquid. Included are models for: (a) slightly conducting particles, (b) insulating particles with a conducting film and (c) highly conducting particles with an insulating film. Both de and ac fields are treated. Good agreement between predicted and experimental results occur. The models indicate that promising ER suspensions for use over a wide frequency range are those which contain highly conducting particles coated with an "insulating" film which has a high dielectric constant and a high electrical breakdown strength. It is conceivable that with proper design a yield strength of 20-100 kPa may be obtained with an acceptable current density.