Maglev Trains And The Technology Behind Them
Magnetism is a phenomenon that occurs when a moving charge exerts a
force on other moving charges. The magnetic force caused by these
moving charges sets up a field which in turn exerts a force on other
moving charges. This magnetic field is found to be perpendicular to
the velocity of the current. The force of the field decays with
distance from the charge. Most magnets we come across are weak
permanent magnets, such as fridge magnets and door catches. A
permanent magnet is a material that is naturally magnetic, they set up
magnetic fields by electrons circling an atom setting up magnetic
fields. They are based on oxides of barium and iron. They have low
field strength and would not be strong enough for use in Maglev
trains. Lately, developments in magnet research have found rare
earth-permanent magnets that have a much stronger magnetic field.
These new magnets have become an important part of our everyday life
being used in many everyday applications such as computers, CD players
and mobile phones. It is these high performance magnets that are used
in Maglev trains. The rare earth elements are scandium 21, yttrium 39
and lanthanide's 57-71.
The principle of a Maglev (Magnetic Levitation) train is that it
floats on a magnetic field and is propelled by a linear induction
motor. They follow guidance tracks with magnets and have been seen to
have great potential in the transport world.
[IMAGE]An example of a maglev train from http://www.newscientist.com
A maglev train will float about 10mm above the guideway on a magnetic
field. It is propelled not by an onboard engine, but by the guideway
itself by changing the magnetic field of the electromagnets along the
length of the guideway. Once the train is pulled into the next section
the magnetism switches so that the train is pulled on again.
The repulsive force between magnets with like poles facing explains
how permanent magnets can be used to provide a levitating and thrust
force to the train.
We know that magnets have a north and south pole and if we bring them
together they will repel each other. We can see this effect in the
picture below with the area between the two magnets having the iron
filings being repelled away from the area in between the two magnets.
We can use this theory to determine the strength of repulsion. We use
the following formulas.
The magnetic flux density is another word for the strength of the
magnetic field. Lines of magnetic force of flux are used to describe