3.4 Levitation phenomenon Ë 65In 1934, Kemper [19] was awarded a patent for a “monorail vehicle with no
wheels attached”. These inventions eventually led to the development of the Trans-
rapid Maglev train program begun in 1969 in Germany. This magnetic levitation was
called the electromagnetic suspension (EMS). EMS was achieved by the attraction
forces between an electromagnet and the iron rail. Stable levitation was produced by
electromagnets using an active feedback loop.
Powell and Danby [20, 21] are the inventors of the superconducting Maglev trans-
portation systems. They filed a patent application (No. 684775) for an electromagnetic
inductive suspension and stabilization system for a ground vehicle on November 21,
1967, and the patent was granted (No. 3470828) on October 7, 1969. This magnetic
levitation is called the electrodynamic suspension (EDS). The time-varying magnetic
fields induce eddy currents in the conductors which create a mutually repulsive
magnetic field. The time-varying magnetic fields can be produced by motion of a
magnet. Their inventions included inductive levitation and stable guidance, null flux
geometry, and the linear synchronous motor for vehicle propulsion. This invention of
the EDS using LTS magnets is the basis for the 500-km/h LTS Maglev train route from
Tokyo to Osaka now under construction.
In 1933, Meissner and Ochsenfeld [22] found that when a sphere is cooled below
its transition temperature in a magnetic field, it expels the magnetic flux. In 1945, the
stable levitation of a permanent magnet over a superconductor was first discovered
for a magnet above a concave lead (lowTcsuperconductor) disk by Arkadiev [23, 24],
at Moscow State University, USSR.
For both diamagnetic materials [16, 25] and high-Tcsuperconductors [26, 27],
stable levitation is possible in static magnetic fields. The levitation of high-Tcsuper-
conductors is a most conspicuous phenomenon. It is really static (requires no energy
input), quiet, and exceedingly stable. It is called the unique self-stable levitation. A
high-Tcsuperconductor can be levitated above or below a PM.
HTS bulk could realize very stable levitation without any active control. The phy-
sical characteristics of self-stabilizing of a HTS bulk Maglev is a unique phenomenon
in nature. A lot of progresses have been made in the theory and application of HTS
Maglev, especially in the fields of energy storage and transportation. In 2001, Jia-Su
Wang and Su-Yu Wang were awarded a patent for “a superconducting Maglev system”
[28], for a manned HTS Maglev vehicle.
Other types of stable levitation such as aerodynamic, acoustic, optical, electric,
and radio-frequency (RF) levitation, etc., can be found elsewhere [29].
The invitation keynote speeches from Japanese, Chinese, German, American, and
Korean experts at the 2011 Conference (21st International Conference on Magnetically
Levitated Systems and Linear Drives, October 10–13, 2011, Daejeon, Korea) reported
several main Maglev systems using EMS, EDS, HTS, etc.
In order to compare and understand the unique advantage of HTS Maglev,
traditional magnetic levitation will be reviewed first.