PARTICLE SEPARATION USING ACOUSTIC RADIATION FORCE AND ELECTROSTATIC FORCE

A method for separating particles in liquid by exploiting the competit ion between acoustic radiation force and electrostatic force is invest igated. The displacement of particles from the pressure node of an ult rasound standing wave varies according to the effective charges, radii , and stiffness of the particles, and the particles of different radii can thus be separated even when they consist of the same material. Wh en the particles are of different materials, they can also be separate d in relations to their effective electric charges or their stiffness. In this study, the efficacy of this method was theoretically estimate d and demonstrated by an experiment, with a mixture of polystyrene sph eres of different radii in water, using 500-kHz ultrasound and a 3.3-V /mm electric field. The measured ratio of the displacements of polysty rene spheres 10 and 20 mu m in diameter from the pressure node was 2:3 , which is consistent with the value predicted theoretically. Radiatio n forces on the polystyrene spheres were also measured by using this t echnique. (C) 1996 Acoustical Society of America.