tromagnetic suspension while the latter is referred to as electrodynamic sus- pension. In an attractive system, the moving compo- nent, or carrier, is suspend-.
OVERCOMING THE GRIP of the Earth’s gravity has been a major challenge for years. However, the work of scientists and engineers who have found many ways to levitate a variety of objects is being applied in the field of transportation in several countries. A helicopter, for example, may be regarded as a levitation device that uses a stream of air to keep floating. Magnetic levitation (maglev) is a way of using electromagnetic fields to levitate objects without any noise or the need for petrol or air. It has been proved that it is not possible to achieve static levitation using any combination of fixed magnets and electric charges. Static levitation means stable suspension of an object against gravity. Magnetic levitation employs diamagnetism, which is an intrinsic property of many materials referring to their ability to temporarily expel a portion of an external magnetic field. As a result, diamagnetic materials repel and are repelled by strong magnetic fields.
Materials Materials in a magnetic field will become magnetized. Most materials such as water, wood, and plastic are diamagnetic, which means that they are repelled by magnetic fields. This repulsive force, however, is very weak compared with the attractive force a ferromagnetic material such as iron will experience due to a magnetic field. As shown in Fig. 1, if the repulsive force due to a magnetic field on a diamagnetic object is exactly equal to the weight of the object, then the object may be levitated in air. The magnetic fields required for this type of levitation are very large, typically 17 T. Producing such large fields requires using superconductive magnets. Thus, maglev relies on superconductors in practical applications. Superconductors are ideal diamagnetics and completely expel magnetic fields at low temperatures. It is possible to levitate superconductors and other diamagnetic materials. It has become
MARCH/APRIL 2006
Magnetic levitation
There are two types of maglev. Electromagnetic levitation (EML) uses the attractive force between electromagnets on the levitated object and the circuit on the ground. Electrodynamic leviMATTHEW N.O. SADIKU tation makes use of the repulsive force AND CAJETAN M. KUJUOBI between magnets (superconductive magnets) on the levitated object and induced current in the secondary circuit on the ground. Thus, we may classify magnetic levitation systems into two groups: attractive systems and repulsive systems. The former is referred to as electromagnetic suspension while the latter is referred to as electrodynamic suspension. In an attractive system, the moving component, or carrier, is suspended under the fixed component, or guide track. The attractive system uses feedback control, is complicated, and requires power to levitate a carrier. The repulsive system utilizes permanent magnets and air-core electromagnet coils running constant current to provide repulsive force. It has a simple configuration and does not require power to levitate a carrier. Any maglev system consists of the following three subsystems: a magnetic suspension, a propulsion motor, and a power system. The magnetic suspension is © PHOTO F/X2 & MASTERSERIES supposed to ensure a stable suspension of a vehicle in its own magcommon place to see the new high netic field. The propulsion motor temperature superconducting materials should produce a propulsion force suflevitated in this way. A superconductor ficient for a continuous flight of the is perfectly diamagnetic, which means it vehicle along an assigned track with a expels a magnetic field. Other diamaggiven speed. The power system pronetic materials are common place and vides uninterrupted power supply. A can also be levitated in a magnetic field source of energy (an engine or a batif it is strong enough. tery, at least) is always required to keep an object afloat. Maglev Maglev is the means of floating one magnet over another. According Applications to a theorem attributed to Earnshaw, Maglev has been successfully impleit is impossible to achieve static levitamented for many applications in tion using any combination of fixed research and industry. Levitating trains magnets and electric charges. There and levitating displays are but two are, however, ways to levitate by getexamples of electromagnetic levitation. ting round the assumptions of the theThe need for fast and reliable transorem. Magnetic levitation employs portation is increasing throughout the diamagnetism. world, particularly in developing
0278-6648/06/$20.00 © 2006 IEEE
41
Levitation Force
Magnetic Field (B)
California are considering building maglev systems. However, the full potential of application has not yet been realized, and the introduction of maglev systems has been slow to occur. Cost and complexity may be among the reasons.
Read more about it
Gravity Fig. 1 A levitated object
nations. High-speed rail has been the solution for many countries. Trains are fast, comfortable, and energy efficient. Conventional railroads, however, operate at speeds below 300 km while maglev vehicles are designed for operating speeds of up to 500 km. A maglev train is a train-like vehicle that is suspended in the air above the track and propelled forward using the repulsive and attractive forces of magnetism, as shown in Fig. 2. A major advantage of maglev systems is their ability to operate in almost all weather conditions; they are prepared for icy conditions because they do not require overhead power lines that are subject to freezing on conventional railroads. The epoch-making technology would change the train control system from conventional manual control to ground-based control. The United States is lagging behind European countries in high-speed rail research and development. In 1986, the U.S. government stopped all funding toward maglev technology. Meanwhile, in Germany and Japan, magnetic levitation is being implemented to solve public transportation problems. Germany is the furthest into their development efforts and the closest to beginning construction of a commercial maglev route. In 1991, the German government approved a maglev route for public transportation that will run from Hamburg to Berlin.
Conclusions While America appears to be many years from the first maglev demonstration, this practical form of high-speed transportation will soon be a reality in Germany and Japan. Japan and Germany have invested billions of dollars into the research and development of their maglev systems. In the United States, communities from Florida to
42
• M.T. Thompson, “Eddy current magnetic levitation,” IEEE Potentials, vol. 19, pp. 40–44, Feb./Mar. 2000. • D. Vischer and H. Bleuler, “Selfsensing active magnetic levitation,” IEEE Trans. Magn., vol. 20, no. 2, pp. 1276–1281, Mar. 1993. • E. Riches, “Will Maglev lift off?,” IEE Review, vol. 34, no. 11, pp. 427–430, Dec. 1988. • F.C. Moon, Superconducting Levitation: Applications to Bearings and Magnetic Transportation. New York: Wiley, 1994.
er communications networks. He is a Senior Member of the IEEE. Cajetan M. Akujuobi is a professor of electrical engineering at Prairie View A&M University and the founding director of the Center of Excellence for Communication Systems Technology Research (CECSTR). He is also one of the researchers with the NASA Center for Applied Radiation Research (CARR). He belongs to many professional organizations. He is a Senior Member of the IEEE and ISA. He is also a member of ASEE, SPIE, and Sigma XI, the Scientific Research Society. He has over 20 years experience in engineering education, research, and development. His current research interests include mixed signal systems, high speed (broadband) network access technologies, and all areas of signal and image processing and communication systems using such tools as wavelet and fractal transforms.
Call for papers
Fig. 2 Maglev train
About the authors Matthew N. O. Sadiku is a professor at Prairie View A&M University. He is a former professor of Temple University, Philadelphia and Florida Atlantic University, Boca Raton. He is the author of many technical papers and books including Elements of Electromagnetics (Oxford, 3rd ed., 2000), Numerical Techniques in Electromagnetics (CRC, 2nd ed., 2001), Metropolitan Area Networks (CRC Press, 1995) and Fundamentals of Electric Circuits (McGraw-Hill, 3rd ed., 2007, with Charles Alexander). His current research interests are in numerical techniques in electromagnetics and comput-
Manuscripts can deal with theory, practical applications or new research. They can be tutorial in nature. 1) Please keep equations to a minimum; however, an article without equations is preferred. 2) Please list only the important references at the end of your manuscript. There should not be any embedded reference numbers. If you need to cite authors for key points or quotes, state their names in the text and give the full reference at the end. 3) Please include four to six lines about yourself. 4) Graphs and diagrams must reproduce well at published size. This means a minimum of 300 dpi for jpeg-, tiff- or eps-formatted figures at published size. 5) Articles should be 2,000– 4,000 words in length.
Please submit your articles at
IEEE POTENTIALS
