Maglev: the history
Linear induction motor
The linear induction motor, unlike a traditional motor, produces a linear force along its path instead of rotational force (torque). Its first working model was developed and demonstrated in the late 1940s by British electrical engineer Eric Laithwaite, who will later be known as the ‘ Father of maglev ’ for his work in the field. 3 It is important to note first that the model developed is of a low-acceleration linear motor instead of its high-acceleration counterpart, which is used for railguns and coilguns. In this design, a linearly moving magnetic field is used, which will naturally lead to an induced current in all the conductors within the field. According to Lenz’s law, which states that ‘ the magnetic field created by the induced current opposes the changes in the initial magnetic field that caused the induced current ’ , the two opposing magnetic fields will create a repulsion force that moves the conductor away from the stator (component providing the magnetic field) along the direction of the initial magnetic field. 4 This forms the essence of his next improvements to the design, which he called ‘ magnetic river ’ . Figure 2: A transverse flux linear induction motor with two sets of opposite poles side by side.
The improved magnetic river is an example of one of the two main types of technology used in a maglev system, electrodynamic suspension (EDS), which will be explained in a later section. The principle it uses is called transverse flux, and it was found in 1969 that by turning the rotor (the component that rotates in a motor) 90 degrees to align it perpendicularly rather than parallel to the track with the opposite poles positioned side by side (see figure 2), the magnetic flux would move through the entirety of the stator plate. The conductors were bent around the plate, forming a long U-
Figure 3: The original Air-Rail Link shuttle that ran from 1984-1995
shape. This caused repulsive forces over the loop and attractive forces between them. This meant that if the motor strayed from the plate, it would naturally feel a force pulling it back to the centre while using long coils to stabilize the levitation by restraining its movements laterally with a repulsive and attractive force. By adding another LIM (linear induction motor) between the coils, it was able to lift and propel an object forward. 5 However, it was later found that it was more beneficial to use a series of U- shaped cores, each with its own loop. By further connecting this to a 3-phase power supply, a travelling magnetic field was obtained, eliminating the need for the LIM. 6 This final system allowed for high speed and efficiency as long poles could be used while also providing stability along the track, like the flow of water in a river; hence, it was given its name. This formed the essence of the technology behind the
3 https://www.theguardian.com/uk/1999/oct/11/timradford; consulted: 26/7/2023. 4 https://en.wikipedia.org/wiki/Linear_induction_motor; consulted: 27/7/2023. 5 https://en.wikipedia.org/wiki/Magnetic_river; consulted: 27/7/2023. 6 Curtis, A. (1973) ‘Magnetic river mixes lift and thrust’ , New Scientist : 805; available at https://books.google.co.uk/books?id=S0nn3r855xsC&pg=PA805&redir_esc=y#v=onepage&q&f=false
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