Particle manipulation by ultrasonic progressive waves

This paper presents a numerical model to determine the trajectory of sphere particles when submitted to ultrasonic progressive waves. This model assumes that the following forces act on the particle: gravity, buoyancy, viscous forces and acoustic radiation force due to progressive wave. In order not to restrict the model to a small particle size range, the viscous forces that act on the sphere are modeled by an empirical relationship of drag coefficient that is valid for a wide range of Reynolds numbers. The numerical model requires the pressure field radiated by the ultrasonic transducer. The pressure field is obtained experimentally by using a calibrated needle hydrophone. The numerical model validation is done by dropping small glass spheres (on the order of 500 μm diameter) in front of a 1-MHz 30-mm diameter ultrasonic transducer. When the particles cross the transducer face, the radiation force produced by the transducer pushes the particles away. The glass particles trajectory is obtained by a CCD camera. The experimental trajectory shows good agreement with that predicted by the numerical model.