Tiny rotors spin into place

Researchers from Northwestern University, ProChimia Poland in Poland, and Harvard University have devised a way to automatically configure tiny, rotor-based machines.

The researchers made tiny rotors using photolithography, an etching process that involves light and chemicals, to construct rubber molds. The researchers filled the molds with a magnetically doped polymer, hardened the polymer using heat, then floated the pieces on a liquid.

Electromagnets beneath the surface of the liquid set the rotors spinning, causing currents that automatically arranged the rotors. By adjusting the electromagnetic field, the researchers were able to coax the rotors into different arrangements that carried out different jobs.

The researchers were able to form machines that performed simple operations like mixing, sorting particles floating on the surface of the liquid, and filling small containers with liquid.

The rotors can be switched in real-time, and are nearly free of friction, according to the researchers.

The researchers' prototype rotors were made up of magnetic cones three-quarters of millimeter in diameter and non-magnetic rings 3.6 millimeters across and two-tenths of millimeter thick. The method can be used with rotors as small as tens of microns across, according to the researchers. A micron is one thousandth of a millimeter.

The work appeared in the March 8, 2004 issue of Applied Physics Letters.