The most common type of resolver is the brushless transmitter resolver. In most of these types of resolver there is a reference coil and two signal coils. The reference coil is supplied with a sinusoidal signal from the controller. This signal is electrically coupled to the two sine and cosine signal coils.
As the resolver rotates the coupled signal varies in amplitude in proportion to the rotor position. This is interpreted by the controller to give an absolute position within one mechanical revolution.
Resolvers are extremely robust and are often found in applications where there is extreme heat, radiation, vibration and dirty environment.