November 7, 2006

Prof Sees Magnetic Future

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Levitation popularized by David Blaine is an impressive trick but it isn’t just for magicians, Prof. Greg Boebinger, Florida State University, can also perform levitation and he’s even willing to tell you how he did it.

Boebinger used magnets to levitate along a track, much like the levitating trains in Germany or Japan. His magnets though could also be trained to “lock-in” a particular magnetic field. This property requires a very specific magnet but allows the magnet to ride on the track upside down, literally suspended in the air with no physical attachment to anything. Beat that David Blaine.

Boebinger, who spoke at yesterday’s physics colloquium, is the director of the National High Magnetic Field Laboratory and as such plays with the biggest magnets around. The strongest magnets he uses are called pulse magnets and they use a lot of power, approximately 1.4 gigawatts. That’s more than the 1.21 gigawatts needed to power the flux capacitor in “The Back to the Future” series and approximately two-thirds of the power produced by the Hoover Dam. When turning on the magnet, the scientists have to evacuate the building and when they re-enter they find the magnet in pieces. One of the largest constraints to high strength magnet building is finding materials that won’t collapse under the stress. These one-use magnets provide up to 70 Tesla of magnetic strength.

For contrast, the average kitchen magnet is about one thousandth of a Tesla. These permanent magnets are historically what most people think of as magnets. In fact, recordings date human discovery of magnets to 600 B.C. with the discovery of magnetite. It is rare because it only becomes magnetized in nature when lightning strikes it. Only four elements out of over a hundred known can hold permanent magnetizations at room temperature (Iron, Nickel, Cobalt and Gadolinium). The Earth’s magnetic field, which pulls compasses towards the North has a strength of about 0.5 Tesla, a field much stronger and much larger than any reasonable permanent magnet could produce.

So how is the Earth’s magnetic field produced? The Earth’s outer core is thought to be liquid Iron and electric current flowing through creates the magnetic field. Moving charge is responsible for magnetic fields and while a current is not obvious in permanent magnets, it is responsible for those too. Since the fields of permanent magnets aren’t that strong and some of the necessary elements are rare, most modern technology that relies on magnets use electromagnets. These like the Earth’s core rely on currents of electricity. The most popular of these is the solenoid, which is many coils of wire wrapped around a cylinder. When electricity is pumped through the wires an electromagnet can produce the same magnetic properties as the permanent magnets but at much higher strengths.

This technology plays an extremely important role in our daily lives from power windows to headphones. New developments in magnets will allow better Magnetic Resonance Images (MRIs) and maybe someday you’ll be riding to work suspended from nothing but magnetisms firm grip.