# MIT marshals Casimir force to combat MEMS friction

PORTLAND, Ore. — MIT researchers have demonstrated that minuscule Casimir forces caused by vacuum fluctuation—the quantum popping into existence of particles in otherwise empty space—can be harnessed to eliminate friction in microelectromechanical systems (MEMS).

The Casimir force has long been known to exist everywhere in free space, providing a source of immeasurable energy, albeit in tiny quantum amounts that would only match the requirements of commensurately tiny devices like MEMS. Until now, researchers have only been able to demonstrate the effect in extremely simple devices, but MIT has shown the effect can be modeled for arbitrary geometries.

Though negligible at larger scales, Casimir forces can cause the moving parts of micromachines, like the one shown here, to stick together. |

"In 2006, MIT professor Mehran Kardar demonstrated a way to calculate the effect for a plate and a cylinder," said MIT doctoral candidate Alejandro Rodriguez, who performed the work with fellow graduate student Alexander McCauley and professor Steven Johnson. "Now we have shown an easy way to calculate the Casimir effect for any shaped device, which should clear the way for MEMS architectures that use the Casimir effect to counter friction."

To demonstrate that their calculation technique works, the researchers effected a geometry originally conceived by physicist Michael Levin (now at Harvard University) consisting of a flat plate with a hole into which an ellipsoid is inserted. The resulting calculations show that if the plate and ellipsoid are cast at the nanometer scale, then the Casimir force causes repulsion between the parts, demonstrating the possibility of using the repulsion force to counter MEMS friction.

Dutch scientist Hendrick Casimir postulated the eponymous effect in 1948 when he proposed an experiment to demonstrate the quantum electrodynamics element of the quantum vacuum fluctuation theory proffered by Max Planck and Werner Heisenberg: the idea that space is not empty but is filled with spontaneously appearing and disappearing particles. Casimir reasoned that if the space between two very closely spaced parallel plates in a vacuum was made so small that it excluded the longer wavelengths of light, then particles would "pile up" outside the plates, exerting a force to drive the plates together.

Researchers subsequently demonstrated that the Casimir effect is real but were unable to find a general-purpose modeling technique that could easily predict the results of the effect for arbitrary geometries. Now the MIT researchers have shown that the well-known calculations predicting the strength of an electromagnetic field at various points between two objects are mathematically equivalent to direct calculations of the Casimir effect.

The Army Research Office, the MIT Ferry Fund and the Department of Energy funded MIT’s research.