Skin effect
Skin effect is the tendency of an alternating electric current to flow towards the perimeter of a conductor and leave the center part of the conductor without (or barely) any electricity flow. This effect increases as frequency increases.
Skin Effect Media
Induction cookers use stranded coils (Litz wire) to reduce heating of the coil itself due to skin effect. The AC frequencies used in induction cookers are much higher than standard mains frequency ‒ typically around 25–50 kHz.
Cause of skin effect. A current I flowing through a conductor induces a magnetic field H. If the current increases, as in this figure, the resulting increase in H induces circulating eddy currents IW which partially cancel the current flow in the center and reinforce it near the skin.
The internal component of a round wire's inductance vs. the ratio of skin depth to radius. That component of the self inductance is reduced below μ/8π as skin depth becomes small (as frequency increases).
The ratio AC resistance to DC resistance of a round wire versus the ratio of the wire's radius to the skin depth. As skin depth becomes small relative to the radius, the ratio of AC to DC resistance approaches one half of the ratio of the radius to the skin depth.
Skin depth vs. frequency for some materials at room temperature, red vertical line denotes 50 Hz frequency:Template:Ubl*
