Eddy Currents and Skin Depth

Induced currents allow magnetic fields to penetrate conductors only to a certain depth, which is approximated by the formula

where:

• w is the angular frequency, which is equal to 2pf. (f is the frequency at which source currents and voltages oscillate during the solution.)
• s is the conductor’s conductivity, in siemens/meter.
• m_r is the conductor’s relative permeability, in amperes/meter.
• m₀ is the permeability of free space, which is equal to 4p x 10^-7 A/m.

Currents will be concentrated near the surface of the conductor, decaying rapidly past the skin depth. As the formula above indicates, the skin depth gets smaller as the frequency increases.