Linear electric motor is a device that generates motion along a straight path. In a rotary motor, the more common type of electric motor, an outer, stationary part called a stator and an inner, moving part called a rotor each produce a magnetic field. Depending on the motor’s design, the poles of one of the two fields are reversed at regular intervals, causing the rotor to turn. A linear motor can be thought of as a rotary motor whose stator and rotor have been cut and straightened out. The magnetic fields produced by a linear motor move objects along a straight path. The stator of a linear motor is often called the primary, and the rotor is often called the secondary. In some designs, the stator is the moving part and the rotor is the stationary one.
A well-known use of linear motors is in maglev (magnetic levitation) trains. A maglev train is suspended by magnetic forces above a track. The two types of linear motors used for maglev trains are (1) linear induction motors and (2) linear synchronous motors. Both types rely on a basic property of magnets—unlike magnetic poles attract each other but like poles repel each other.
A linear induction motor usually has a rotor made of strips or coils of a nonferrous conductor—that is, material that contains no iron and carries electric current. The stator consists of rows of electromagnets, which are coils of wire that become magnets when current flows through them. When current flows in the stator, the magnetic field produced around the stator creates a current in the rotor through a process called induction. The current in the rotor produces a magnetic field around the rotor that interacts with the stator’s magnetic field. Switching the stator’s electromagnets on and off in sequence results in linear motion.
A stator of a linear synchronous motor also consists of rows of electromagnets. It operates in the same way as the stator of a linear induction motor. The rotor typically consists of multiple electromagnets powered by a constant current, which creates, in effect, a permanent magnetic field. The stator’s electromagnets are switched in a sequenced order to create a magnetic field that moves in the direction of travel. The fields of the stator and rotor interact, resulting in linear motion.
