Magnetic levitation train, also called maglev train, is a vehicle that uses magnetic forces to float above a fixed track, called aguideway, without touching it. The train's speed is not limited by the friction or vibration that contact with a track would cause.
Maglev trains have several advantages over conventional wheeled trains. For example, they can reach higher speeds and operate more quietly. Their guideways, which are usually elevated, require little maintenance. They use electric current for power and therefore produce little pollution themselves. Researchers are developing maglev trains for urban and high-speed intercity travel in Germany, Japan, the United States, and other countries.
Types of maglev technology
There are two important types of maglev technology: electrodynamic and electromagnetic. Electrodynamic maglev uses magnetic repulsion (pushing away) to make the train float. Electromagnetic maglev uses magnetic attraction.
Electrodynamic maglev
Japanese researchers have developed electrodynamic maglev test vehicles that have reached speeds of 340 miles (550 kilometers) per hour. Their design is based on work done in the 1960's by nuclear engineer James R. Powell and physicist Gordon T. Danby of the United States. The Japanese maglev trains use superconducting magnets—that is, electromagnets that are cooled to extremely low temperatures, and which then conduct electric current without resistance. These electromagnets are cooled using liquid helium. They are placed low on the sides of the train. As the train moves, the magnetsinduce (create) currents in wire coils set in the sides of the guide way, which is U-shaped. The magnetic force between the electromagnets and the induced currents lifts the vehicle. The train runs on wheels until it gains enough speed to lift off the guideway. It then travels with a clearance of about 4 inches (10 centimeters).
Electromagnetic maglev
A group of German companies began developing a series of electromagnetic maglev test vehicles in the early 1970's. They have tested full-sized trains that run as fast as 310 miles (500 kilometers) per hour. The undersides of these trains carry conventional electromagnets that ride beneath a T-shaped guideway. When current flows through the electromagnets, they are attracted upward to steel rails on the guideway. The cars travel with a clearance of only about 3/8 inch (1 centimeter). To prevent the magnets from hitting the guideway, the lifting currents must continually be adjusted by a fast-acting control system. A German-designed system operates in China, between Shanghai's Pudong International Airport and downtown Shanghai. Commercial service began in 2004, with trains reaching speeds of up to 270 miles (430 kilometers) per hour. A low-speed electromagnetic maglev operated as an airport shuttle in Birmingham, England, from 1984 to 1995.
Maglev propulsion
A maglev train may be propelled by either a linear synchronous motor or a linear induction motor. A linear synchronous motor works with coils in the guideway that carry electric currents. The currents produce a magnetic field that travels along the guideway and pushes the train forward, much as an ocean wave pushes a surfer. The speed of the train remains constant, even during travel uphill or downhill. A linear induction motor operates similarly, but the coils that carry the current are mounted on the train, and they induce currents in either coils or conducting plates mounted on the guideway.
