Skin effect
From ScienceZero
The skin effect is the tendency of an alternating electric current to distribute itself within a conductor so that the current density near the surface of the conductor is greater than that at its core. That is, the electric current tends to flow at the "skin" of the conductor.
The skin depth (d) is the depth where the current is 1/e (about 0.37) times the current at the surface:
- <math>d=\sqrt{{2\rho}\over{2\pi f \mu}}</math>
where
- ρ = resistivity of conductor
- f = frequency of current
- μ = absolute magnetic permeability of conductor
For a round wire, the AC resistance is approximately:
- <math>R={{\rho \over d}\left({L\over{\pi (D-d)}}\right)}</math>
where
- L = length of conductor
- D = diameter of conductor
Example - for copper
| frequency | depth |
|---|---|
| 60 Hz | 8.57 mm |
| 10 kHz | 0.66 mm |
| 100 kHz | 0.21 mm |
| 1 MHz | 66 µm |
| 10 MHz | 21 µm |
