# Magnetic Levitation

views updated May 23 2018

# Magnetic Levitation

Principle of operation

MAGLEV vehicles

Superconducting magnets

Prospects for MAGLEV vehicles

Resources

Magnetic levitation, sometimes called magnetic suspension, is the phenomenon in which two magnetic objects are repelled from each other in a vertical direction. The phenomenon, also known as MAGLEV, has long been recognized as having some important commercial applications. The most significant of these is the construction of MAGLEV trains that are propelled a few inches above a track at very high rates of speed.

## Principle of operation

Imagine that two bar magnets are suspended one above the other with like poles (two north poles or two south poles) directly above and below each other. Any effort to bring these two magnets into contact with each other will have to overcome the force of repulsion that exists between two like magnetic poles. The strength of that force of repulsion depends, among other things, on the strength of the magnetic field between the two bar magnets. The stronger the magnet field, the stronger the force of repulsion.

If one were to repeat this experiment using a very small, very light bar magnet as the upper member of the pair, one could imagine that the force of repulsion would be sufficient to hold the smaller magnet suspendedlevitatedin air. This example illustrates the principle that the force of repulsion between the two magnets is able to keep the upper object suspended in air.

In fact, the force of repulsion between two bar magnets would be too small to produce the effect described here. In actual experiments with magnetic levitation, the phenomenon is produced by magnetic fields obtained from electromagnets. For example, imagine that a metal ring is fitted loosely around a cylindrical metal core attached to an external source of electrical current. When current flows through the core, it sets up a magnetic field within the core. That magnetic field, in turn, sets up a current in the metal ring that produces its own magnetic field. According to Lenzs law, the two magnetic fields thus produced one in the metal core and one in the metal ringhave opposing polarities. The effect one observes in such an experiment is that the metal ring rises upward along the metal core as the two parts of the system are repelled by each other. If the current is increased to a sufficient level, the ring can actually be caused to fly upward off the core. Alternatively, the current can be adjusted so that the ring can be held in suspension at any given height with relation to the core.

## MAGLEV vehicles

Credit for foreseeing the applications of magnetic levitation in the construction of vehicles is usually given to American scientist and rocket pioneer Robert Hutchings Goddard (18821945). In 1907, Goddard published a story in which he described a vehicle that traveled by means of the principle of magnetic levitation. French engineer Emile Bachelet constructed the first working model of such a vehicle in 1912. Bachelets vehicle was propelled by the repulsive forces set up between copper electromagnets suspended above an aluminum track. Bachelets model proved to be a dead end, however, because the amount of electrical energy needed to create suspension was much too great to produce economically.

In fact, that problem was the primary reason that MAGLEV vehicles remained a dream until very recently. In order to lift an object weighing many tons, a very strong force of repulsion between vehicle and track must be created. The force of repulsion, in turn, can be produced only by means of very powerful electromagnets. The weight of such magnets and the electrical energy needed to operate them placed the idea of MAGLEV vehicles out of the realm of real-life technology for many decades.

## Superconducting magnets

For many years, scientists have been aware of at least one obvious way of dealing with these practical problemssuperconducting 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 super-conducting 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 super-conducting 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 electrical current passing through the coils can control the speed of the train.

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.

Magnetic levitation as a means of transportation is not without its problems. For example, initial plans call for the construction of MAGLEV tracks in the United States adjacent to the nations interstate highway system. But passengers traveling in a 250-mile-per-hour MAGLEV train will feel much stronger gravitational forces in rounding an interstate curve than will passengers in a car moving at 65 mi (105 km) per hour. In addition, initial tests suggest that MAGLEV vehicles may produce a high level of noise when they operate at top speed. Tests have shown that sound levels of 100 decibels at a distance of 80 ft (24 m) from the guideway may be possible. Such levels of sound are, however, unacceptably high for any inhabited area.

Like with anything made by humans, mechanical problems and humans errors can occur with MAGLEV machinery. For instance, on August 11, 2006, the Shanghai commercial Transrapid had a fire onboard after leaving the station in Longyang. In addition, on September 22, 2006 a MAGLEV train crashed into maintenance wagon in northern Germany, injuring and killing dozens of people.

## Prospects for MAGLEV vehicles

The new age of MAGLEV technology can be traced to the early 1960s. During that period, many observers saw MAGLEV vehicles as a way of solving a number of problems confronting the United States and other developed nations. For example, they offered an apparently efficient way of moving large numbers of people quickly and efficiently through and around urban areas. They could be powered with almost any form of energy from which electricity could be made, not just with coal or petroleum. By 1970, then, a number of model MAGLEV vehicles had been constructed.

That research has been vigorously continued in a number of nations, including Japan, Great Britain, Germany, Korea, and France. All of these nations have developed a number of prototype vehicles that are moving into commercial operation. For example, Japanese engineers have designed a 27-mi (43.5 km) test line through the Yamanashi Prefecture that would carry up to 10,000 passengers per hour in 14-car trains traveling at 310 mi (499 km) per hour. Some German models have used a somewhat different form of magnetic levitation. The Germans Transrapid has nonsuperconducting magnets attached to the vehicle body and suspended beneath the guide rail. The magnets are attracted (rather than repelled) upward to the rail, lifting the train to within an inch of the guide rail. On December 31, 2002, the German Transrapid MAGLEV Train had its first commercially operated route in China from Shanghais Long Yang Road to the Pudong International Airport. It transports people 18.5 mi (30 km) in seven minutes, 20 seconds, at a top speed of 268 mph (431 km/h), with an average speed of 150 mph (250 km/h). The worlds first commercial automated MAGLEV system, called Linimo, began operations in March 2005 in Aichi, Japan.

In contrast to this kind of progress, however, the United States had by 1975 virtually abandoned research on magnetic levitation. That decision, made by the Office of Management and Budget, had been made on the belief that MAGLEV transportation would not be an economically feasible alternative in the US in the foreseeable future.

That attitude underwent a dramatic reversal in the early 1990s, largely as the result of the interest of one politician, Senator Daniel Patrick Moynihan (19272003) of New York. Moynihan had become convinced that MAGLEV vehicles were the means by which the nations interurban transportation problems could be solved. Furthermore, as the chairman of the Senate subcommittee responsible for the U.S. highway system,

### KEY TERMS

Electromagnetism The unified electrical and magnetic field of force generated by the passage of an electric current through matter.

Superconductivity The tendency of an electrical current to flow through a conductor with essentially no resistance.

Moynihan was in a position to put his beliefs into practice. In 1989, Moynihan inserted into the highway bill a special provision for the development of new MAGLEV technology, the Magnetic Levitation Prototype Development Program, with a budget of \$750 million. Given this seed money, many experts once again have high hopes for the eventual development of a commercial MAGLEV vehicles program in the United States. Studies are ongoing in 2006 for MAGLEV lines in southern California-Las Vegas (Nevada), Baltimore-Washington, DC, Honolulu (Hawaii), Daytona-St. Petersburg (Florida), San Diego (California), Pittsburgh (Pennsylvania), and Portland (Oregon)-Vancouver (British Columbia).

As MAGLEV systems are constructed more frequently in the world, the costs to develop and maintain them will decrease. For example, the Shanghai MAGLEV train cost 1.2 billion dollars to completely build, which is about six dollars per passenger. However, as of October 2006, the use of MAGLEV trains in the world are limited to only a few sites. Most MAGLEV trains are still in the experimental and developmental stages.

## Resources

### BOOKS

Dai, Huiguang. Dynamic Behavior of Maglev Vehicle/Guideway System with Control. Ann Arbor, MI: ProQuest/UMI, 2006.

Gieras, Jacek F. Linear Synchronous Motors: Transportation and Automation Systems. Boca Raton, FL: CRC Press, 2000.

Moon, Francis C. Linear Superconducting Levitation: Applications to Bearings and Magnetic Transportation. New York, Wiley, 1994.

### OTHER

ACF Newsource. New high-speed trains without rails or wheels go 300 mph. <http://www.acfnewsource.org/science/mag_lev.htm> (accessed October 15, 2006).

HowStuffWorks Inc. How Maglev Trains Work. <http://www.howstuffworks.com/maglev-train.htm> (accessed October 15, 2006).

Muller, Christopher, Railserve.com. Magnetic Levitation for Transportation. <http://www.railserve.com/maglev.htm> (accessed October 15, 2006).

David E. Newton

# Magnetic Levitation

views updated May 18 2018

# Magnetic levitation

Magnetic levitation is the phenomenon in which two magnetic objects are repelled from each other in a vertical direction. The phenomenon, also known as MAGLEV, has long been recognized as having some important commercial applications. The most significant of these is the construction of MAGLEV trains which are propelled a few inches above a track at very high rates of speed.

## Principle of operation

Imagine that two bar magnets are suspended one above the other with like poles (two north poles or two south poles) directly above and below each other. Any effort to bring these two magnets into contact with each other will have to overcome the force of repulsion that exists between two like magnetic poles. The strength of that force of repulsion depends, among other things, on the strength of the magnetic field between the two bar magnets. The stronger the magnet field, the stronger the force of repulsion.

If one were to repeat this experiment using a very small, very light bar magnet as the upper member of the pair, one could imagine that the force of repulsion would be sufficient to hold the smaller magnet suspended—levitated—in air. This example illustrates the principle that the force of repulsion between the two magnets is able to keep the upper object suspended in air.

In fact, the force of repulsion between two bar magnets would be too small to produce the effect described here. In actual experiments with magnetic levitation, the phenomenon is produced by magnetic fields obtained from electromagnets. For example, imagine that a metal ring is fitted loosely around a cylindrical metal core attached to an external source of electrical current. When current flows through the core, it sets up a magnetic field within the core. That magnetic field, in turn, sets up a current in the metal ring which produces its own magnetic field. According to Lenz's law, the two magnetic fields thus produced—one in the metal core and one in the metal ring—have opposing polarities. The effect one observes in such an experiment is that the metal ring rises upward along the metal core as the two parts of the system are repelled by each other. If the current is increased to a sufficient level, the ring can actually be caused to fly upward off the core. Alternatively, the current can be adjusted so that the ring can be held in suspension at any given height with relation to the core.

## MAGLEV vehicles

Credit for foreseeing the applications of magnetic levitation in the construction of vehicles is usually given to rocket pioneer Robert Goddard. In 1907, Goddard published a story in which he described a vehicle that traveled by means of the principle of magnetic levitation. The first working model of such a vehicle was constructed in 1912 by the French engineer Emile Bachelet. Bachelet's vehicle was propelled by the repulsive forces set up between copper electromagnets suspended above an aluminum track. Bachelet's model proved to be a dead end, however, because the amount of electrical energy needed to create suspension was much too great to produce economically.

In fact, that problem was the primary reason that MAGLEV vehicles remained a dream until very recently. In order to lift an object weighing many tons, a very strong force of repulsion between vehicle and track must be created. The force of repulsion, in turn, can be produced only by means of very powerful electromagnets. The weight of such magnets and the electrical energy needed to operate them placed the idea of MAGLEV vehicles out of the realm of real-life technology for many decades.

## 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.

Magnetic levitation as a means of transportation is not without its problems. For example, initial plans call for the construction of MAGLEV tracks in the United States adjacent to the nation's interstate highway system. But passengers traveling in a 250-mile-per-hour MAGLEV train will feel much stronger gravitational forces in rounding an interstate curve than will passengers in a car moving at 65 mi (105 km) per hour. Also, initial tests suggest that MAGLEV vehicles may produce a high level of noise when they operate at top speed. Tests have shown that sound levels of 100 decibels at a distance of 80 ft (24 m) from the guideway may be possible. Such levels of sound are, however, unacceptably high for any inhabited area.

## Prospects for MAGLEV vehicles

The new age of MAGLEV technology can be traced to the early 1960s. During that period, many observers saw MAGLEV vehicles as a way of solving a number of problems confronting the United States and other developed nations. For example, they offered an apparently efficient way of moving large numbers of people quickly and efficiently through and around urban areas. They could be powered with almost any form of energy from which electricity could be made, not just with coal or petroleum . By 1970, then, a number of model MAGLEV vehicles had been constructed.

That research has been vigorously continued in a number of nations, including Japan, Great Britain, Germany, and France. All of these nations have developed a number of prototype vehicles that may soon move into commercial operation. For example, Japanese engineers have designed a 27-mi (43.5 km) test line through the Yamanashi Prefecture that would carry up to 10,000 passengers per hour in 14-car trains traveling at 310 mi (499 km) per hour. Some German models have used a somewhat different form of magnetic levitation. The German's Transrapid 07 has nonsuperconducting magnets attached to the vehicle body and suspended beneath the guide rail. The magnets are attracted (rather than repelled) upward to the rail, lifting the train to within an inch of the guide rail.

In contrast to this kind of progress, however, the United States had by 1975 virtually abandoned research on magnetic levitation. That decision, made by the Office of Management and Budget, had been made on the belief that MAGLEV transportation would not be an economically feasible alternative in this country in the foreseeable future.

That attitude underwent a dramatic reversal in the early 1990s, largely as the result of the interest of one politician, Senator Daniel Patrick Moynihan (1927-2003) of New York. Moynihan had become convinced that MAGLEV vehicles were the means by which the nation's interurban transportation problems could be solved. And, as chairman of the Senate subcommittee responsible for the U.S. highway system, Moynihan was in a position to put his beliefs into practice. In 1989, Moynihan inserted into the highway bill a special provision for the development of new MAGLEV technology, the Magnetic Levitation Prototype Development Program, with a budget of \$750 million. Given this seed money, many experts once more have high hopes for the eventual development of a commercial MAGLEV vehicles program in the United States.

## Resources

### books

Rhodes, R.G., and B.E. Mulhall. Magnetic Levitation for Rail Transport. Oxford: Clarendon Press, 1981.

### periodicals

Rossing, Thomas D., and John R. Hull. "Magnetic Levitation." The Physics Teacher (December 1991): 552-562.

Singer, Sanford S. "Advanced Transportation Systems." Magill's Survey of Science: Applied Science Series Vol. 6. Pasadena, CA: Salem Press, 1993. pp. 2724-2730.

Stix, Gary. "Air Trains." Scientific American (August 1992): 102-113.

### other

"High-Speed Ground Transportation Oversight." Hearing before the Subcommittee on Surface Transportation of the Committee on Commerce, Science, and Transportation, United States Senate, One Hundred Second Congress, Second Session, August 6, 1992.

"High-Speed Rail Transportation." Hearing before the Subcommittee on Transportation and Hazardous Materials of the Committee on Energy and Commerce, House of Representatives, One Hundred Third Congress, First Session, April 29, 1993.

David E. Newton

## KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Electromagnetism

—The unified electrical and magnetic field of force generated by the passage of an electric current through matter.

Superconductivity

—The tendency of an electrical current to flow through a conductor with essentially no resistance.

# maglev

views updated May 29 2018

mag·lev / ˈmagˌlev/ • n. [usu. as adj.] a transportation system in which trains glide above a track, supported by magnetic repulsion and propelled by a linear motor: maglev trains.

# maglev

views updated May 17 2018

maglev (ˈmæg, lɛv) magnetic levitation