skin_depth

Stan Zurek, Skin depth, Encyclopedia Magnetica, E-Magnetica.pl |

**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.

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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), *μ _{r}* - relative permeability of the conductor,

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

- light grey (
**Al**) - metallic aluminium - orange (
**Cu**) - metallic copper - green (
**steel 410**) - magnetic stainless steel, grade 410 - blue (
**Fe-Si**) - grain-oriented electrical steel - dark grey (
**Fe-Ni**) - permalloy (80%Ni-20%Fe)

^{S. Zurek, E-Magnetica.pl, CC-BY-4.0}

skin_depth.txt · Last modified: 2021/04/17 14:49 by stan_zurek

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