Ultrasonic pumps are the pumps that use acoustic streaming effect to create fluid flow. The acoustic streaming effect arises from the interaction between the surface acoustic waves (SAW) traveling inside a piezoelectric substrate and the fluid. Attenuation of the SAW traveling inside the fluid (via reflection, diffraction, etc.) generates a body force within the fluid which is in the direction of wave propagation and converts acoustic energy into kinetic energy of the fluid . SAW devices can be used to transport droplets on a free surface between the input and output piezoelectric transducers (also known as interdigital transducer (IDT)). A schematic drawing of such a device is given in Fig. 1. Moreover, the same mechanism can be used to drive droplets as well as bulk fluid inside closed microchannels.