# Encyclopedia Magnetica

Encyclopedia of magnetics and electromagnetics.

skin_depth

# Skin depth

 Stan Zurek, Skin depth, Encyclopedia-Magnetica.com, {accessed 2019-12-08} This page contains mostly images (see: Review process). (list)

Skin depth (often denoted by lower-case Greek letter delta δ) - such a depth of penetration of alternating current or electromagnetic field, at which the amplitude is reduced to a value of 1/e (around 37%), as compared to the amplitude at the surface of the conductor.

Skin depth is a function of frequency of current, as well as magnetic permeability and electric resistivity (or conductivity) of the conductor in question.

For good conductors (like most metals) the function can be defined as:1)

 $\delta = \sqrt{\frac{2 · \rho }{\omega · \mu_r · \mu_0}} = \frac{1}{\sqrt{\pi · f · \mu_r · \mu_0 · \sigma}}$ (m)

where: π - mathematical constant, f - frequency (Hz), μr - relative permeability of the conductor, μ0 - magnetic permeability of free space (H/m), σ - electric conductivity (S/m), ρ = 1 - electric resistivity (Ω·m), ω = 2·π·f - pulsation frequency (rad/s).

Skin depth vs. frequency for some materials (red line denotes 50 Hz):

by S. Zurek, E. Magnetica, CC-BY-3.0 