At DC, current density is distributed throughout a conductive material.  As frequency increases, the depth of current density decreases.  The current density depth is called “Skin Depth”.

Skin Depth

Skin depth is the depth, from the surface, where the current density is equal to 1/e of the surface value. 

e = Euler’s Number ≈ 2.718


The Math to calculate the skin depth



 = Material Resistivity (Ω/m)

π = 3.14…

  = Frequency (Hz)

 = Permeability (H/m)

H = Henries (Ω·s)