Magnetic Levitation, or Maglev, is an advanced  transportation technology that employs magnetic forces to suspend the transporting vehicle in air so it can travel effortlessly over its guideway.  The levitated vehicle is often propelled by a linear induction motor, although a propeller or jet engine can also be used.

A Maglev transport system has the following advantages over conventional ones: 1) minimal resistance to motion which allows the use of higher gradients and sharper curves; 2) no contact vibration which results in less noise and minimum maintenance requirements; 3) high degree of reliability and safety even at relatively high speeds (up to 500 kph only, since aerodynamic issues emerge beyond this limit); and 4) no need for a catenary since power is supplied directly to the guideway.

Maglev technology currently has three primary ways of suspending a vehicle in air: 1) electromagnetic suspension (EMS); 2) electrodynamic suspension (EDS); and 3) stabilized permananet magnet suspension (SPM).

Figure 1.   Photos of Maglev Trains

In an EMS system, the levitation is achieved using electromagnets that are attached to the train itself but positioned under the steel rail by structures that extend down below the rail and then curve up again towards the rail. Once activated, the electromagnets are attracted to the rail and rise, levitating the train above the tracks. The amount of magnetic attraction must be just enough to levitate the train while maintaining a gap between the train and the rail.  This gap is maintained using an electronic monitoring system.

In an EDS system, repulsive forces are at work, i.e., both the train and the rail exert magnetic fields that repel each other. These repulsive forces cause the train to 'float away' from the rail. The train's magnetic field is produced either by electromagnets or a set of permanent magnets, while the magnetic field of the rail is usually induced from current-carrying coils.

In an SPM system, opposite arrays of strong permanent magnets are placed under the train and over the tracks, producing repulsive magnetic forces that also keep the train suspended over the rail. Thus, like the EDS, SPM also employs repulsive forces to achieve levitation. However, unlike EDS, SPM needs no external power to achieve the levitation since the permanent magnets provide the magnetic fields continuously and passively.

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