magnetic levitation, maglev or magnetic suspension is a method by which an object is suspended with no support other than magnetic field. Magnetic pressure is used to counteract the effects of the gravitationa and any other accelerations. Earnshaw’s theorem proves that using only ferromagnetic or paramagnetic materials it is impossible to stably levitate against gravity, however, servomechanisms, the use of di magnetic materials, superconduction, or systems involving eddy currents allow to achieve that. lift
Magnetic materials are able to attract or press each other apart or together with a force dependent on the magnetic fieldand the area of the magnets, and a magnetic pressure can then be defined. The magnetic pressure of a magnetic field on a superconductor can be calculated by:-
Static stability means that any small displacement away from a stable equilibrium causes a net force to push it back to the equilibrium point Earnshaw’s theorem proved conclusively that it is not possible to levitate stably using only static, macroscopic, paramagnetic field. The forces acting on any paramagnetic object in any combination of gravitational, electrostatic, and magnetostatic fields will make the object’s position, at best, along at least one axis, and it can be unstable equilibrium along all axis. . However, several possibilities exist to make levitation viable, for example, the use of electronic stabilization or diamagnetic materials (since relative magnetic permeability is less than one); it can be shown that diamagnetic materials are stable along at least one axis, and can be stable along all axes. Conductors can have a relative permeability to alternating magnetic fields of below one, so some configurations using simple AC driven electromagnets are self stable. Dynamic stability[edit source | editbeta]
Dynamic stability occurs when the levitation system is able to damp out any vibration-like motion that may occur. Magnetic fields are conservative forces and therefore in principle have no built-in damping, and in practice many of the levitation schemes are under-damped and in some cases negatively damped. This can permit vibration modes to exist that can cause the item to leave the stable region. Damping of motion is done in a number of ways:
external mechanical damping (in the support), such as dashpots, air drag etc. eddy current damping (conductive metal influenced by field)
tuned mass dampers in the levitated object
electromagnets controlled by electronics
Maglev, or magnetic levitation, is a system of transportation that suspends, guides and propels vehicles, predominantly trains, using magnetic levitation from a very large number of magnets for lift and propulsion. This method has the potential to be faster, quieter and smoother than wheeled mass transit systems. The technology has the potential to exceed 6,400 km/h (4,000 mi/h) if deployed in an evacuated tunnel. If not deployed in an evacuated tube the power needed for levitation is usually not a particularly large percentage and most of the power needed is used to overcome air drag, as with any other high speed train. The highest recorded speed of a maglev train is 581 kilometers per hour (361 mph), achieved in Japan in 2003, 6 km/h faster than the conventional TGV speed record.