Measurement of the velocities of dielectric particles in ER fluids with laser speckle

摘要

Usually, it is regarded that the movement of dielectric particles in ER fluids is related to the generation of electrorheological effect In this paper, the principle of measuring infinitesimal displacement by laser speckle is proposed to measure the velocities of particles in ER fluids. It is verified that speckles can be formed by illuminating laser beam on the starch ER fluids. The speckle patterns was recorded with high speed CCD camera, and the speckle patterns sequences with short time intervals was obtained by intercepting laser speckle video. Displacements parallel to electric field and perpendicular to electric field were obtained by processing the two consecutive speckle patterns. The experimental results showed the velocities of particles exhibit the trend towards an oscillatory decreased with time, and a critical electric field and a critical sample concentration exist, when lower than this critical electric field (concentration), the mean particle velocity tends to increase; when high than that, decrease instead. Moreover, the horizontal velocity of particle is almost zero, there is only small oscillatory movement of particles in the vertical direction of electric field when the particle chain of ER fluid forms a relatively stable structure.