Magnetic Levitation

1. Magnetic Levitation Tori Johnson and Jenna Wilson

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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)

9. 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

10. 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

11. 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.

12. 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

13. 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

14. 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

15. 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.”

16. 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

17. References • http://www.physics.ucla.edu/marty/levitron/spinstab.pdf • http://www.superconductors.org/uses.htm • http://www.popsci.com/popsci/how20/be199aa138b84010vgnvcm1000004eecbccdrcrd.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