Effect of geometric design on the motion of microrobots due to acoustic streaming flows

Recent work has shown that the geometric design of microrobots powered by acoustic streaming has a significant impact on their motion. To date, most studies focus on a single acoustically responsive structure, either a bubble or thin structure, to power microrobot locomotion. By actuating such microrobots containing multiple acoustically responsive structures with discrete, single frequency acoustic fields, multiple patterns of streaming flows can be generated, leading to frequency-dependent motion with distinct trajectories.

We have experimentally and computationally studied a bubbled-based microrobot with a thin fin protruding from its body. We used eigenfrequency analyses and a perturbation theory fluid mechanical model to predict i) the resonance frequencies of the bubble and fin and ii) the streaming flows generated by their oscillations. We confirmed our computational predictions by fabricating the microrobot with two-photon lithography, actuating the microrobot with surface acoustic waves, and visualizing the fluid flow with microparticle image velocimetry. The computed streaming flows may be used to predict how the trajectory of the microrobot changes when actuated at different frequencies. Findings from this work provide a means to rationally design new types of acoustic microrobots, using an integrated computational and experimental framework, with tunable, frequency-dependent motions.