Magnetic Levitation

kitefleaUrban and Civil

Nov 15, 2013 (3 years and 9 months ago)

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Magnetic Levitation

Tori Johnson and Jenna Wilson

What is a magnet?


It is simply an object which produces a
magnetic field


North and South are the designations
made to describe the two opposite poles


North is attracted to South and repelled
by North


South is attracted to North and repelled
by South


There are three main types:



-

Permanent Magnets



-

Soft Magnets



-

Electromagnets

Permanent Magnets


Electrons fill atomic orbitals in pairs


If an orbital is full, then one electron
spins upward and the other spins
downward (Pauli Exclusion Principle),
so their magnetic fields cancel out


If an orbital is not full, then the
movement of the electron creates a
tiny magnetic field


Atoms with several unpaired orbitals
have an
orbital magnetic moment

Permanent Magnets


In metals, the orbital magnetic
moment causes nearby atoms
to align in the same direction,
creating a ferromagnetic
metal


The strength of the magnetic
field decreases inversely with
the cube of the distance from
the magnet’s center

Soft Magnets


These types of magnets do not have a
magnetic field of their own


However, when put in the presence of
another object’s magnetic field, they are
attracted (paramagnetic)


Once the external magnetic field is
removed, they return to their
nonmagnetic state

Electromagnets


The magnetic field is caused by the
flow of an electric current


The simplest example is a coiled
piece of wire


Using the right hand rule, it is
possible to determine the direction


An advantage over permanent
magnets is that the magnetic field
strength can be changed by
changing the current

Nine Ways to Magnetically
Levitate an Object


Mechanical constraint


Direct diamagnetic levitation


Superconductors


Diamagnetically
-
stabilized
levitation


Rotational stabilization


Servo stabilization


Rotating conductors beneath
magnets


High
-
frequency oscillating
electromagnetic fields


Translational Halbach arrays
and Inductrack

Direct Diamagnetic
Levitation


How it Works


Diamagnetic materials repel a
magnetic field


All materials have diamagnetic
properties, but the effect is very
weak, and usually overcome by the
object‘s paramagnetic or
ferromagnetic properties, which act in
the opposite manner


By surrounding a diamagnetic
material with a magnetic field, it can
be held in a stationary position (the
magnetic force is strong enough to
counteract gravity)

Direct Diamagnetic
Levitation


Applications


Water is primarily
diamagnetic, so water
droplets and objects that
contain large amounts
of water can be levitated


http://www.hfml.ru.nl/pic
s/Movies/frog.mpg

Superconductors


A superconductor is an element, inter
-
metallic alloy,
or a compound that will conduct electricity without
resistance below a certain temperature.


Resistance produces losses in energy flowing through
the material.


In a closed loop, an electrical current will flow
continuously in a superconducting material.


Superconductors are not in widespread use due to the
cold temperatures they must be kept at


Highest Tc found 150K

Applications


MagLev Trains
-

The magnetized coil
running along the track, repels the large
magnets on the train's undercarriage,
allowing the train to levitate


Biomagnetism
-

in MRI and SQUID
(measures slight magnetic fields)


Particle accelerators to accelerate sub
-
atomic particles to nearly the speed of light


Electric generators
-

made with
superconducting wire: They have a 99%
efficiency and have about half the size of
conventional generators.


Really fast computers
-

In "petaflop"
computers. A petaflop is a thousand
-
trillion
floating point operations per second.
Today's fastest computing operations have
only reached "teraflop" speeds.

Applications soon to
come…


Stabilizing momentum wheel (gyroscope) for earth
-
orbiting satellites
-

can reduce friction to near zero


Superconducting x
-
ray detectors and superconducting
light detectors
-

able to detect extremely weak amounts
of energy.


Superconducting digital router
-

for high
-
speed data
communications up to 160 Ghz


Power plants use to reduce greenhouse gas emissions

Advancements depend to a great degree on
advancements in the field of cryogenic cooling or
finding more high
-
temperature superconductors

Rotational magnetism


Also known as spin stabilized magnetic
levitation


Happens when the forces acting on the
levitating object
-

gravitational, magnetic,
and gyroscopic
-

are in equilibrium


Earnshaw’s theorem says it is impossible

Super Levitron


Two opposing neodymium
-
iron
-
boron permanent magnets.


original invention by Roy Harrigan and patented in 1983.


He didn’t known about Earnshaw’s theorem which many thought
said such an invention was impossible.


The rotation of a spinning object’s axis of spin creates a toriod of
genuine stability in a way that does not violate Earnshaw’s
theorem, but that went completely unpredicted by physicists for
more than a century.


The top remain levitating in a central point in space above the
base where the forces acting on the top
-

gravitational, magnetic,
and gyroscopic
-

are in equilibrium


Stops due to air resistance

http://www.levitron.com/images/levitron.mpg

http://www.levitron.com/images/levitron
-
drbob.mpg

Why it works


“The principle is that two similar poles
(e.g., two north's) repel, and two
different poles attract, with forces that
are stronger when the poles are
closer. There are four magnetic
forces on the top: on its north pole,
repulsion from the base's north and
attraction from the base's south, and
on its south pole, attraction from the
base's north and repulsion from the
base's south. Because of the way the
forces depend on distance, the north
-
north repulsion dominates, and the
top is magnetically repelled. It hangs
where this upward repulsion balances
the downward force of gravity, that is,
at the point of equilibrium where the
total force is zero.”

How to get it to Work


Correct magnetic strengths


Mass of the top must be
right within .5%


Magnets are temperature
dependent, weaker in
warmer temperatures


Correct spinning rate (not
too fast or slow)


Must be introduced onto a
small stabile region only
millimeters wide and high

References


http://www.physics.ucla.edu/marty/levitron/spinstab.pdf


http://www.superconductors.org/uses.htm


http://www.popsci.com/popsci/how20/be199aa138b84010vgnvcm
1000004eecbccdrcrd.html


http://www.chem.yale.edu/~chem125/levitron/levitron.html


http://science.howstuffworks.com/magnet3.htm


http://www.howstuffworks.com/electromagnet.htm


http://en.wikipedia.org/wiki/Magnet


http://en.wikipedia.org/wiki/Electromagnet


http://en.wikipedia.org/wiki/Magnetic_levitation


http://my.execpc.com/~rhoadley/maglev.htm


http://www.hfml.science.ru.nl/hfml/froglev.html