  A steady fluid flow, called microstreaming, can be generated in the vicinity
of a micro-bubble excited by ultrasound. In this article, we use this
phenomenon to assemble and power a microfabricated rotor at rotation speeds as
high as 625 rpm. The extractible power is estimated to be on the order of a few
femtowatts. A first series of experiments with uncontrolled rotor shapes is
presented, demonstrating the possibility of this novel actuation scheme. A
second series of experiments with 65 micron rotors micromanufactured in SU-8
resin are presented. Variables controlling the rotation speed and rotor
stability are investigated, such as the bubble diameter, the acoustic
excitation frequency and amplitude, and the rotor geometry. Finally, an outlook
is provided on developing this micro-rotor into a MEMS-based motor capable of
delivering tunable, infinitesimal rotary power at the microscale.
