A Faraday cage is an enclosure formed by conducting material, or, usually, by a mesh of such material. Such an enclosure nullifies external electrical fields. They are named after a physicist, Michael Faraday, who first describe them.
When an external electrical impulse impacts the Faraday cage, the charges within the cage material redistribute and cancel out the effects of the field inside. They also shield the interior of from electromagnetic radiation -- if the holes are small enough.
Faraday cages are used in the laboratory to shield equipment from stray electrical impulses. This is especially important in doing electrophysiological experiments (a technique in neuroscience), where the voltages and currents measured are very small, and the electromagnetic field from even computers contributes significant electrical noise.
More common examples are places like elevators and stairwells, where cellular phones tend to lose signal, because of the phone being surrounded by a metal cage, formed by either the elevator itself or the metal beams in the walls. Another commonly used Faraday cage is a microwave oven -- the shielding of the oven prevents the microwaves from escaping into the surrounding area.
So, that's a Faraday cage, and the science word for today. You can learn more and see some nice examples at Wikipedia and Davidson College, and read a practical application at the Mad Sci Network.
TTFN,
Doc
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