Skin Effect

Skin EffectThe essence of the skin-effect is that as the frequency increases the current is forced out of the depth of the conductor to its surface. That is where the "skin" part of the name comes from: in technical context the English word "skin" means the outer layer, the shell. The simplest parameter describing the skin effect is the ratio of AC and DC cable resistances per unit of length (Rac/Rdc). The depth at which the current density is in 1/e times less than at the surface is called skin depth. Here "e" is the base of natural logarithm and equals approximately 2.72. At low frequencies the skin depth is much bigger than the radius, which means of the current is equal over the entire cross section of the conductor. The skin effect may become noticeable when the ratio is much higher than a unity. We say "may" because it happens only when the sound changes obviously and thus shows the increased resistance. For frequencies above 15 kHz the Rac/Rdc ratio is equal to 1.1 when using a solid wire gauge 15. In case of a stranded wire we can't really speak about the specific value of the skin depth. Multiple interweavings and contacts between individual wires, which form the electroconductive strand, make it impossible to calculate and estimate the value accurately. To a lesser extent the skin-effect influences stranded wires, in which each strand is covered with an insulating varnish, i.e. it has lesser influence on litzendraht wire. This wire is used to make high Q inductance coils. In case of such wires, it is theoretically possible to calculate the exact surface area, which will be greater in comparison with a solid conductor with the same cross-sectional area. By the way, such wires in inductance coils of radio receivers (i.e., at high frequencies) are widely used mostly because of that small skin effect.

Category:

Science & Technology

Tags:

• conductivity
• effect
• electricity
• frequency
• physics