An extremely small electric machine that generates electric power
from mechanical power.
One device to convert mechanical energy into electrical energy is
the electromagnetic generator. While there are several types of large electromagnetic generator,
the type whose rotor is a permanent magnet is suitable for miniaturization. Such generators are
roughly classified as axial gap types and radial gap types. The former have a relatively simple
structure, although, their efficiency is low. The latter promises high efficiency, sophisticated
technology is required for the production of cylindrical stators that have microscopic winding. A
microgenerator that generates electrical power by the movement of the human arm is already in use
for wristwatches that do not require button or solar batteries.