Comb drive
From Wikipedia, the free encyclopedia
Comb-drives are linear motors that utilise electrostatic forces that act between two metal combs. While comb drives built at normal human scales (size) are extremely inefficient there is the potential to minimize them to microscopic or nanoscale devices where more common designs will not function. Almost all comb-drives are built on the micro or nano scale and are typically manufactured using silicon.
The electrostatic forces are created when a voltage is applied between the combs causing them to attract. The force developed by the motor is the force between the two combs (which increases with voltage difference, the number of comb teeth, and the length of the teeth, and decrease as the combs are further apart). The combs are arranged so that they never touch (because then there would be no voltage difference). Typically the teeth are arranged so that they can slide past one another until each tooth occupies the slot in the opposite comb.
Restoring springs, levers, and crankshafts can be added if the motor's linear operation is to be converted to rotation or other motions.
V = applied electric potential, 
= relative permitivity of dielectric, 
= permitivity of free space (8.85 pF/m),
n = number of pairs of electrodes, t = thickness of electrodes, g = gap between electrodes
