Уақыт өзгеретін өрістерде магниттік левитация

Magnetic levitation by time varying fields
Electrodynamic suspension (EDS) is a form of magnetic levitation in which there are conductors which are exposed to time varying magnetic fields. This induces eddy currents in the conductors that creates a repulsive magnetic field which holds the two objects apart. These time varying magnetic fields can be caused by relative motion between two objects. In many cases, one magnetic field is a permanent field, such as a permanent magnet or a superconducting magnet, and the other magnetic field is induced from the changes of the field that occur as the magnet moves relative to a conductor in the other object. Electrodynamic suspension can also occur when an electromagnet driven by an AC electrical source produces the changing magnetic field, in some cases, a linear induction motor generates the field. EDS is used for maglev trains, such as the Japanese SCMaglev. It is also used for some classes of magnetically levitated bearings.

Many examples of this have been used over the years.

In this early configuration by Bedford, Peer, and Tonks from 1939, an aluminum plate is placed on two concentric cylindrical coils, and driven with an AC current. When the parameters are correct, the plate exhibits 6 axis stable levitation.

Unlike configurations of simple permanent magnets, electrodynamic levitation can be made stable. Electrodynamic levitation with metallic conductors exhibits a form of diamagnetism, and relative permeabilities of around 0.7 can be achieved (depending on the frequency and conductor configuration). Given the details of the applicable hysteresis loop, frequency dependent variability of behavior should be of minimal importance for those magnetic materials that are likely to be deployed.

This form of maglev can cause the levitated object to be subject to a drag induced oscillation, and this oscillation always occurs at a sufficiently high speed. These oscillations can be quite serious and can cause the suspension to fail. However, inherent system level damping can frequently avoid this from occurring, particularly on large scale systems. Alternatively, addition of lightweight tuned mass dampers can prevent oscillations from being problematic. Electronic stabilization can also be employed.