Physics reminder: skin effect, proximity effect

Skin effect

The skin effect is the phenomena produced by flow of time varying currents through a conductor.

Experience and theory show that the current density is not uniformly distributed in the conductor cross-section. There is a concentration of current lines towards the outer surface of the conductor. This effect becomes more significant as the frequency of current variation increases.

The quantities associated with the electromagnetic field decrease by the z depth in the conductor, with an exponential law as shown below:

where:

• Us is the value at the conductor surface
• is the skin depth :

Proximity effect

The proximity effect is related to the phenomena that are produced when, in a system consisting of several current carrying conductors, the magnetic field generated by a conductor interferes with the current distribution in the other conductors.