Editing Linear induction motor (section)

==History==
The history of linear electric motors can be traced back at least as far as the 1840s to the work of [[Charles Wheatstone]] at [[King's College London|King's College]] in London,<ref>{{cite web|url=http://www.kcl.ac.uk/college/history/people/wheatstone.html |title=Charles Wheatstone - College History - King's College London |publisher=Kcl.ac.uk |access-date=2010-03-01 |url-status=dead |archive-url=https://web.archive.org/web/20091021162729/http://www.kcl.ac.uk/college/history/people/wheatstone.html |archive-date=October 21, 2009 }}</ref> but Wheatstone's model was too inefficient to be practical. A feasible linear induction motor is described in US patent 782312 (1905; inventor Alfred Zehden of Frankfurt-am-Main), and is for driving trains or lifts. German engineer [[Hermann Kemper]] built a working model in 1935.<ref>{{cite web|url=http://cem.colorado.edu/archives/fl1997/thor.html |title=CEM - Fall/Winter 1997 Issue - Germany's Transrapid |access-date=2011-08-24 |url-status=dead |archive-url=https://web.archive.org/web/20110928000224/http://cem.colorado.edu/archives/fl1997/thor.html |archive-date=2011-09-28 }}</ref> In the late 1940s, professor [[Eric Laithwaite]] of [[Imperial College]] in [[London]] developed the first full-size working model.

[[File:Magnetic river 3.png|thumb|upright=1.2|FEMM simulation of a Cross-section of Magnetic River, coloured by electric current density]]
In a single-sided version, the magnetic field can create repulsion forces that push the conductor away from the stator, levitating it and carrying it along the direction of the moving magnetic field. Laithwaite called the later versions a [[magnetic river]]. These versions of the linear induction motor use a principle called ''transverse flux'' where two opposite poles are placed side by side. This permits very long poles to be used, and thus permits high speed and efficiency.<ref>Patent number 3585423, 1971 Laithwaite et al</ref>