FEM analyses of acoustic streaming in a water droplet at the center of an ultrasonic stage

In this work, a droplet-ultrasonic stage system, in which a micro droplet located at the center of the ultrasonic stage is used to concentrate nanoscale material in the droplet, is modeled and analyzed by the finite element method. The computation method is verified by experimental results, and the acoustic streaming pattern inside the droplet is revealed. The result can well explain the operating principle. Moreover, the effects of the vibration velocity and droplet size on the acoustic streaming field are also investigated and clarified. The results show that the concentrating capability can be maximized without sacrificing the concentrating stability by properly increasing the droplet volume.