Magnetic Levitation

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Magnetic Levitation

• Tori Johnson and Jenna Wilson

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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

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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

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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
  magnets center

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Soft Magnets

• These types of magnets do not have a magnetic
  field of their own
• However, when put in the presence of another
  objects magnetic field, they are attracted
  (paramagnetic)
• Once the external magnetic field is removed, they
  return to their nonmagnetic state

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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

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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

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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 objects 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)

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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/pics/Movies/frog.mpg

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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

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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.

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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

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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
• Earnshaws theorem says it is impossible

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Super Levitron

• Two opposing neodymium-iron-boron permanent
  magnets.
• original invention by Roy Harrigan and patented
  in 1983.
• He didnt known about Earnshaws theorem which
  many thought said such an invention was
  impossible.
• The rotation of a spinning objects axis of spin
  creates a toriod of genuine stability in a way
  that does not violate Earnshaws 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
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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.

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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

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References

• http//www.physics.ucla.edu/marty/levitron/spinsta
  b.pdf
• http//www.superconductors.org/uses.htm
• http//www.popsci.com/popsci/how20/be199aa138b8401
  0vgnvcm1000004eecbccdrcrd.html
• http//www.chem.yale.edu/chem125/levitron/levitro
  n.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