One of the tiny windmills.
(Credit: University of Texas, Arlington)

A microscopic windmill could one day provide a portable method of charging devices: at just 1.8 millimetres at its widest point and able to fit 10 on a single grain of rice, the tiny machines can harvest energy from the movement of air.

They are the work of research associate Smitha Rao and electrical engineering professor J.-C. Chiao, who envision smartphone cases embedded with hundreds of windmills, which could charge the phone therein just by waving it through the air, or holding it by an open window on a windy day.

The windmills were crafted using origami techniques that allow two-dimensional shapes to be electroplated on a flat plane, then self-assembled into 3D moving mechanical structures. They're made of a durable, flexible nickel alloy that can stand up to strong winds without fracturing, helped by a minimal, aerodynamic design.

Rao and Chiao created the windmill for a Taiwanese superconductor company called WinMEMS, which developed the fabrication technique and was interested in Rao based on her work in micro-robotics.

"It's very gratifying to first be noticed by an international company and second to work on something like this where you can see immediately how it might be used," said Rao. "However, I think we've only scratched the surface on how these micro-windmills might be used."

Chiao added that perhaps the windmills could be crafted into panels of thousands, which could then be attached to the sides of buildings to harvest wind energy for lighting, security or wireless communication.