64 Ë 3 Magnetic levitation
by about a factor of 10 than that of automobiles and airplanes. If all automobile,
air, and rail passenger traffic in the USA States was accomplished using Maglev
at an average speed of 322 km/h, the total electrical energy usage would be only
about 3% of all current traffic electric energy usage. In 1998, the USA announced the
Transportation Equity Act TEA-21 for the 21st century to provide the legal form for the
development of Maglev transportation technology in the USA, and a Maglev line of
969 km was planned and reviewed.
China, Japan, Germany, USA, and other countries have begun to put Maglev trains
into commercial operation, commissioning and project construction. We believe that
in the near future, Maglev train will bring a new era of traffic.
3.4 Levitation phenomenon
Levitation phenomenon not only attracted wide attention of the public, but also
attracted the interest of scientists and engineers. In fact, levitation and suspension
can be achieved by some physical methods.
Maglev technologies have a series of advantages (see Tab. 3.2). Maglev is
currently attracting worldwide interest for both high-speed intercity vehicles and
low-speed urban transit vehicles, especially high- or ultra-high-speed intercity
traffic.
In 1842, Earnshaw [15] theoretically studied the classical inverse-square law
forces for gravity, electrostatics, and magnetism field and proved mathematically
that stable levitation is impossible for an object placed in a repulsive or attractive
static force field. Earnshaw wrote it before Maxwell’s work and the discovery of the
electron. According to Earnshaw’s theorem, magnetic levitation in many common
situations is not possible. However, this is not generally true. The theorem applies
only to individual particles. Braunbeck [16] went further to show that the instabi-
lity is due to the relative permeability of the materials involved being greater than
unity.
In the 19th century, buoyancy was considered and studied to support objects
without contact to the ground. Scientists have proposed several suspension princip-
les, for example, levitation using water pressure, levitation based on the aircushion
principle, levitation and propulsion with a blower, etc. A model train levitated by
water pressure based on an idea of Girard was demonstrated at the Paris Exposition
of 1889 [17].
On March 19, 1912, Bachelet [18] was awarded a patent for an electromagnetic
suspension (EMS) system, the “levitating transmitting apparatus”. His invention
was first intended to be applied to smaller mail-carrying systems, but its potential
application to larger train-like vehicles is certainly clear. Bachelet’s invention opened
the door to human Maglev application.