penetration depth

If an alternating current flows through an electrical conductor, the skin effect reduces the current density inside the conductor, while it is highest at the conductor surface.

The decrease in current density towards the interior of the conductor is determined by the penetration depth (small delta), skin depth or penetration depth. It is an exponential quantity determined from the current density at the conductor surface. Defined by 1/e, with "e" equal to 2.71, penetration depth is the 37% value of the current density at the conductor surface. Thefrequency (f) is inversely proportional to the calculation of the penetration depth, as are the conductivity and permeability of the conductor material.