Experimental considerations of droplet manipulation mechanism using surface acoustic wave devices

Abstract

Droplet manipulation is one of the important applications of the SAW device. When a droplet is placed on a SAW device, the longitudinal wave radiates into the droplet. Nonlinear acoustic phenomena are caused by the radiated longitudinal wave from the SAW. Droplet manipulation is one of those phenomena. It is important to investigate the minimum radiation force to manipulate the droplet by the SAW. In this paper, the radiation force in a droplet is experimentally measured. The radiation force was measured by varying an applied electrical power, water volume, and concentration of glycerol-water mixture. The minimum radiation force for manipulating 10 micro little was 0.168 mN. Also, the water droplet manipulated was observed by a high speed camera. When the longitudinal wave radiates into the droplet and the radiation force is larger than the surface tension of the water, the tip of the droplet is extended in the SAW propagation direction. In other words, the radiation force is acting only tip of the droplet. The extended length depends on the applied power and the duty factor. Other parts of the droplet act as binding force. The force only acts the tip of the droplet and the end part is dragged.