Maglev: the history
on the magnetic field lines.10 A type-II superconductor is used because it can preserve its superconducting properties in the presence of intense magnetic fields in the system. 11
2. EMS
A typical train that uses the EMS system is designed slightly differently from a conventional train, having C-shaped arms below its body instead of wheels. Inside its arms, the upper and sideways sections are connected to the track, while the bottom edge, containing the magnets, is attracted to the steel rail. A constant gap (approx. 15mm) is controlled by a complicated feedback system (servomechanism). Eric Laithwaite was initially worried that the dynamic stability demands could lead to delicate track tolerances as unreasonably large magnets would need to be used to meet these tolerances. 12 An improved feedback system alongside ‘ Hybrid Electromagnetic Suspension ’ was used to address the problem where electropermanent magnets are in control. Electropermanent magnets have two sections: the permanent magnet section provides lift while the electromagnets maintain the air gap. 13
Figure 6: Floating globe, a simple example of magnetic levitation with a feedback loop
3.
EDS
In an EDS system, it has been explained previously that the train is levitated by both the repulsive and attractive forces between the two magnetic fields from the train and track, with the second one caused by the induced current that is carried by the initial moving magnetic field. A major advantage here that the EMS system doesn’t have is that the attractive and repulsive forces achieve dynamic stability, eliminating the need for a complex feedback system. However, unlike the EMS system, at low speeds, the train would not be able to levitate due to the current and magnetic flux not being high enough. For this reason, the train would need sufficient landing gear, such as wheels.
Figure 7: The C-shaped arms on a Transrapid train connecting to the track
Figure 8: An example of an EDS system from Japan's SCMaglev. Magnetic fields are induced on both sides of the train
11 https://home.cern/science/engineering/superconductivity; consulted: 29/7/2023. 12 ‘Maglev: How They’re Getting Trains Off the Ground’, Popular Science (D ec 1973), p. 134; available at https://books.google.co.uk/books?id=pdvMRoDOTbMC&redir_esc=y; consulted: 29/7/2023. 13 https://en.wikipedia.org/wiki/Maglev#Electromagnetic_suspension_(EMS); consulted: 29/7/2023.
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