Effects at high frequencies

A direct current flows constantly and uniformly throughoutENI-21

 the cross-section of a uniform wire. An alternating current of any frequency is forced away from the wire's center, toward its outer surface. This is because6502B

 the acceleration of an electric charge in an alternating current produces waves of electromagnetic radiation that cancel the propagation of electricity toward the center of materialsIR2136

 with high conductivity. This phenomenon is called skin effect.At very high frequencies the current no longer flows in the wire, but effectively flows on the surface of the wire, within a thickness of a few skinDIG-12-08-010

 depths. The skin depth is the thickness at which the current density is reduced by 63%. Even at relatively low frequencies used for high power transmission (50?¡ìC60 Hz), non-uniform distribution of current2SJ19

 still occurs in sufficiently thick conductors. For example, the skin depth of a copper conductor is approximately 8.57 mm at 60 Hz, so high current conductors are usually hollow to reduce their mass and cost.