Electro-magneto-rheological effects in parallel-field and crossed-field systems

Rheological measurements of electro-magneto-rheological (EMR) fluids were carried out by use of modified parallel-plate rheometers equipped with electrodes and magnetic coils. The electric field and magnetic field either parallel or perpendicular to each other were applied to a suspension of spherical iron particles under a constant shear flow. The EMR effects, evaluated as the stress increase induced by these fields, were compared. It was found that the parallel field gives a marked EMR effect in the spherical iron suspension and that the crossed field also results in an EMR effect though the increase of stress value under the crossed field is not so large. The difference in these EMR effects has been interpreted in terms of the different orientations of the dispersed particles toward the field directions. Similar experiments using a suspension of needle-like iron particles have also indicated that particle orientation plays a major role in the EMR effects.