Studies on particle separation by acoustic radiation force and electrostatic force

A method for separating particles in liquid by exploiting the competition between acoustic radiation force and electrostatic force has been investigated. To elucidate the size and charge dependence of the shift of the particles away from the sound pressure node, the effective charges of polystyrene spheres and alumina particles, which have opposite signs of electric charge on the surface, were measured for particles of various diameters. The shift of the particles from the pressure node due to the electrostatic force was also measured. Polystyrene spheres smaller than 10 mu m in diameter showed same mobility in a 1 Hz, 13.4V(pp)/mm alternating electric field, which indicates that the effective charge of the particle is directly proportional to the radius of the particle. Using 500 kHz ultrasound and a 0.5 V/mm electric field, 7 mu m polystyrene spheres and 10 mu m alumina particles were shifted in opposite directions, according to the sign of the effective charge on the particles.