Linear Electric Motor

Linear electric motor is a device that generates motion along a straight path. Linear motors operate such devices as moving sidewalks and sliding gates. A linear motor can operate these devices more efficiently than can a motor that generates rotary motion. A rotary motor is less efficient because it requires gears or other devices to convert its rotary motion to linear motion. Another use of linear electric motors is in maglev (magnetically levitated) vehicles. A maglev vehicle floats above a track, suspended in midair by magnetic force. In some maglev vehicles, magnets that generate this force are part of the motor.

There are two types of linear electric motors: (1) induction and (2) synchronous. Both types rely on a basic property of magnets--unlike magnet poles attract each other but like poles repel each other. Both kinds consist of a stator (a stationary part such as a track) and a rotor (a moving part).

Linear induction motors have a stator made of a strip of a conductor (a substance through which electric current flows easily). The rotor contains a row of electromagnets (devices that become magnets when current flows through them). When the electromagnets are switched on, current flows in the rotor, establishing a magnetic field in and around the rotor. This field, in turn, generates current in the stator. The stator current then creates a wave of magnetic force in and around the stator. The wave interacts with the rotor field, pulling the vehicle forward.

Linear synchronous motors have a stator made up of overlapping electromagnets. The rotor consists of a row of permanent magnets or electromagnets. When the stator is switched on, current in the wires sets up a wave of magnetic force in and around the stator. The wave interacts with the rotor's magnetic fields, moving the rotor along the stator.

Contributor: Richard J. Gran, Ph.D., Director, Advanced Concepts, Grumman Corporation.

Linear Electric Motor

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