Continuous separation technique of suspended particles by utilizing acoustic radiation and electrostatic force

A particle separation technique in a sub-milli channel has been developed by utilizing acoustic radiation and electrostatic forces, which will be applicable to microfluidic devices. In the present study these forces act simultaneously on particles perpendicular to the flow direction. When the acoustic radiation force was applied by an ultrasound transducer, large and small particles in a buffer solution were trapped at nodal positions in the standing field, which was equal to half of the wavelength in the transverse direction. On simultaneous application of electric field to the channel, both forces acted on particles. Thus the magnitude of each force was estimated by using particle image and particle tracking velocimetry, by which the relationship between the acoustic radiation and electrostatic force acting on particles was investigated in order to separate particles in the flow field. Large particles were trapped at nodes by the acoustic radiation force without being affected by the electrostatic force, while small particles were moved toward anodes by the electrostatic force. This means that the particle separation based on diameter was accomplished by the present technique.