skin effect

The phenomenon by which electrical signals tend to distribute themselves within a conductor so that the current density is greater near the surface, or skin, of the conductor than at the core. The higher the frequency, the more pronounced the phenomenon. For example, through a 24-gauge conductor with a diameter of 0.0201 inches, a signal at 20 kHz travels at a skin depth of 0.0181 inches, approximately the diameter of the wire. At 20 kHz, therefore, the skin effect is negligible. A signal at 25 MHz travels at a depth of only 0.00052 inches. In fact, much of the signal at this frequency is in the form of an electromagnetic field surrounding the conductor and traveling through the dielectric insulation.