The active electromagnetic bearing is the principle which is actually used most often among the magnetic suspensions. The figure above explains the components and the function of a simple bearing. A sensor measures the displacement of the rotor from its reference position, a microprocessor as a controller derives a control signal from the measurement, a power amplifier transforms this control signal into a control current, and the control current generates the magnetic forces within the actuating magnet in such a way that the rotor remains in its hovering position. The control law is responsible for the stability of the hovering state as well as the stiffness and the damping of such a suspension.