Control of particles in a standing wave field using ultrasonic vibration

Abstract

In order to control the motion of micromachines by acoustic power, the behavior of particles falling in several liquids with a standing wave field was studied experimentally. A PZT transducer with a frequency of 28 kHz was fixed to the bottom of a cylinder. Several small tubes were inserted in this cylinder, and glass particles with a diameter of about 1.5–3.5 mm were dropped in these tubes, respectively. Since cavitation bubbles are observed by applying ultrasonic vibration to a liquid, cavitation intensity as estimated from the erosion loss of an aluminum sheet was measured to investigate the effect of cavitation generation on the radiation pressure. Cavitation intensity in degassed water was weaker than that in ion-exchanged water; however, the decrease in velocity of the glass particles by applying ultrasonic vibration exhibited the greatest deceleration in the degassed water. Ultrasonic power effectively acts on a particle as a radiation force when cavitation does not occur and there is almost no damping of the ultrasonic wave. When varying the tube diameter, as the ratio of the diameter of tube to the particle diameter increased, so did the deceleration. All particles were levitated by the ultrasonic radiation force in a ratio of more than 0.6.