From ChrisCoughlin: SkinDepth is a simple utility to calculate the depth of attenuation, or skin depth of an electromagnetic wave inside a conductive material. At the skin depth, a wave drops to around 37% its original amplitude, so by 4 times the skin depth the wave is almost completely attenuated. SkinDepth uses an approximation to the skin effect calculation - it's valid for metals up to at least the microwave (GHz) range for the most part, but for poor conductors (insulators) it may only be applicable to a few tens of KHZ. SkinDepth won't warn you if the frequencies you're using would make this approximation less than accurate so if you need the "real" results consult some of the above links for a more thorough background on the subject.
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