The linear motor had its first major development in the early 1960s. This type of motor is essentially a cylindrical induction motor that has been cut along its length and unrolled, as shown in Figure 1. The field moves down the windings of what used to be the stator at a velocity V given by v = 2pf, where p is the distance between the pole pieces and f is the frequency of the field. In the example shown a field is induced in the 'rotor' and this is then propelled along between the fixed field windings.
A very wide range
of speed may be obtained with these motors and they have been used to propel shuttles on
textile looms, drive trains, as launchers for aircraft, to move conveyor belts and at low speed
even to open curtains!
A linear induction motor is used to power the Maglev train running between Shanghai airport and the centre of the city.