There are two primary types of maglev technology:
1. Electromagnetic suspension ( EMS ) which use the attractive magnetic force of a magnet beneath a rail to lift up the train up. In current EMS systems, the train levitates above a steel rail while electromagnets, attached to the train, are oriented toward the rail from below. The electromagnets use feedback control to maintain a train at a constant distance from the track, at approximately 15 mm ( 0.6 in ).
2. Electrodynamic suspension ( EDS ) which use a repulsive force between two magnetic fields to push the train away from the rail. In EDS, both the rail and the train exert a magnetic field, and the train is levitated by the repulsive force between these magnetic fields. The magnetic field in the train is produced by either electromagnets or by an array of permanent magnets. the repulsive force in the track is created by an induced magnetic field in wires or other conducting strips in the track. At slow speeds, the current induced in these coils and the resultant magnetic flux is not large enough to support the weight of the train. For this reason, the train must have wheels or some other fome of landing gear to support the train until it reaches a speed that can sustain levitation. Propulsion coils on the guideway are used to exert a force on the magnets in the train and make the train move forward. The propulsion coils that exert a force are effectively a linear motor. The frequency of the alternating current is syncronized to match the speed of the train. The offset between the field exerted by magnets on the train and the applied field create a force moving the train forward.