Modeling and analysis of the droplet-ultrasonic stage system for nano concentration

In this work, a droplet-ultrasonic stage, in which a micro droplet located at the center of the ultrasonic stage is used to concentrate nanoscale material, 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, which can well explain the operating principle. Moreover, the effects of the vibration velocity, droplet size, ultrasonic stage topology and size, and droplet's sound attenuation coefficient 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, and disposing a cylindrical groove in the center of the ultrasonic stage's substrate. Also, it is found that a thin substrate and thick piezoelectric ring are helpful to enhancing the concentrating capability without sacrificing the concentrating stability.