Microelectromechanical devices were supposed to change the world, so where are they?
A few designs have leaked out, such as the accelerometers in air bags. But most have remained stubbornly, and literally, stuck in the lab.
One of the troubling secrets about MEMs is that many designs simply don’t work because their moving parts become stuck fast and refuse to budge.
Engineers call this “stiction”: a vaguely defined force that affects small parts but not large ones (where inertia plays a greater role in overcoming these forces). Stiction is thought to be caused variously by Van der Waals forces, electrostatic forces, hydrogen bondng and even the Casimir force, perhaps in combination. That’s why it’s so hard to avoid.
Now Raul Esquivel-Sirvent and a buddy at the Universidad Nacional Autonoma de Mexico in Mexico City, have a potential solution based on the acoustic Casimir force, an acoustic analogue of the more famous quantum Casimir force which was discovered 10 years ago by Andres Larraza, then at the Naval Postrgraduate School in Monterey.
Here’s the idea: place a couple of parallel plates close together and blast them with sound waves of a specific frequency range. If the waves are larger than the gap between the plates, they will tend to push them together but if they are smaller, they will squeeze into the gap and tend to push them apart. So changing the wavelength or the distance between the plates switches the direction of the force.
That could be useful for microswitches in MEMs devices, says Esquivel-Sirvent. But more interestingly, it could also be used to separate microcomponents that have become stuck together. Perhaps the promise of MEMs will be realised at last.
Ref: arxiv.org/abs/0812.2213: Pull-in Control in Microswitches Using Acoustic Casimir Forces