Principle analysis for the micromanipulation probe-type ultrasonic nanomotor

Abstract

The micromanipulation probe-type (MMP-type) ultrasonic nanomotor (UNM) has proven to be a type of robust and versatile tool for controllable rotary driving, dynamic trapping and high-precision orientation of a single one-dimensional (1D) nano object. The manipulation functions of the MMP-type UNM are implemented in the probe-liquid-substrate (PLS) system, in which a MMP is inserted into a liquid film of nano suspension on a stationary substrate. When the MMP elliptically vibrates parallel to the substrate surface, the acoustic streaming can be engendered to rotate a single silver nanowire (AgNW) at the liquid-substrate interface. Although the experimental results have demonstrated the effectiveness and high performance of the developed UNM, there have been no simulation results and quantitative analysis method to show the details of acoustic streaming field and to perform principle analysis for the MMP-type UNM, which has hindered a deeper understanding of the underlying physical mechanisms as well as optimization for the MMP-type UNM. In this work, to deeply analyze the principle for our developed UNM, we carry out numerical investigations on the thermo-viscous acoustic field and acoustic streaming field in the PLS system of the MMP-type UNM based on the finite element method (FEM). The simulation result shows that the elliptical vibration of the MMP parallel to the substrate surface can induce the reversed acoustic streaming vortex (compared to the MMP’s vibration trajectory direction) at the liquid-substrate interface, which enables controllable rotary driving of a single AgNW. With the simulation results of acoustic streaming fields, we theoretically predict the driving angular velocities of the AgNW at the liquid-substrate interface, and verify that the quantitative simulation results agree well with the reported experimental results. Moreover, the effects of device’s parameters and working conditions such as the distance between the MMP’s tip and substrate surface, the MMP’s length and radius and the liquid film’s thickness on the acoustic streaming field and the angular velocity of the AgNW are analyzed and clarified through both simulation results and experimental verifications, and the effect of the MMP’s material is also predicted via simulations.