# Magnetic Levitation

## Superconducting Magnets

For many years, scientists have been aware of at least one obvious way of dealing with these practical problems—superconducting magnets. Superconductivity is the tendency of a conducting material (such as copper) to carry an electrical current with virtually no resistance. Although superconductivity had been discovered as early as 1911, its application to real-life inventions had always been limited by the fact that it was observable only at temperatures close to absolute zero. A MAGLEV vehicle that made use of superconducting magnets would, therefore, be much more efficient than one using traditional electromagnets. But the superconducting model would also have to be designed so as to operate at very low temperatures (close to -450°F [-268°C]).

Still, by the 1960s, researchers had begun to design and build prototype MAGLEV vehicles powered by superconducting electromagnets. Most such vehicles operated on a common principle. Superconducting coils are suspended beneath the body of the MAGLEV vehicle itself. As current begins to flow through these coils, a magnetic field is created. That magnetic field, as in the example noted earlier, sets up a magnetic field in the metal track beneath the vehicle. The force of repulsion between the two magnetic fields forces the train upward and keeps it suspended a few inches above the track. As the electrical current in the superconducting coils increases, so do the opposing magnetic fields and the force of repulsion between them.

Of course, the vehicle must not only be lifted above the track, but it must also be moved in a forward (or backward) direction. This propulsive force is provided by an electric current that flows through guideway coils in the track. As the current changes in the coils, so does the strength of the magnetic field. As a result, the MAGLEV vehicle is alternatively pushed and pulled by the changing magnetic field in the coils. The speed of the train can be controlled by the electrical current passing through the coils.

A MAGLEV train begins operation like any other railway train, with its wheels resting on the track. As electrical current begins to flow through its superconducting coils, the train is pushed forward on the track and then gradually lifted off it. At maximum speed, most trains are designed to travel a few inches above the track and at speeds of 250 mi (402 km) per hour or more.