Material Effect On Skin Depth
In a good conductor, skin depth varies as the inverse square root of the conductivity. This means that better conductors have a reduced skin depth. The overall resistance of the better conductor remains lower even with the reduced skin depth. However the better conductor will show a higher ratio between its AC and DC resistance, when compared with a conductor of higher resistivity. For example, at 60 Hz, a 2000 MCM (1000 square millimetre) copper conductor has 23% more resistance than it does at DC. The same size conductor in aluminum has only 10% more resistance with 60 Hz AC than it does with DC.
Skin depth also varies as the inverse square root of the permeability of the conductor. In the case of iron, its conductivity is about 1/7 that of copper. However being ferromagnetic its permeability is about 10,000 times greater. This reduces the skin depth for iron to about 1/38 that of copper, about 220 micrometres at 60 Hz. Iron wire is thus useless for A.C. power lines. The skin effect also reduces the effective thickness of laminations in power transformers, increasing their losses.
Iron rods work well for direct-current (DC) welding but it is impossible to use them at frequencies much higher than 60 Hz. At a few kilohertz, the welding rod will glow red hot as current flows through the greatly increased A.C. resistance resulting from the skin effect, with relatively little power remaining for the arc itself. Only non-magnetic rods can be used for high-frequency welding.
Read more about this topic: Skin Effect
Famous quotes containing the words material, effect, skin and/or depth:
“Our life on earth is, and ought to be, material and carnal. But we have not yet learned to manage our materialism and carnality properly; they are still entangled with the desire for ownership.”
—E.M. (Edward Morgan)
“The reason why women effect so little and are so shallow is because their aims are low, marriage is the prize for which they strive; if foiled in that they rarely rise above disappointment ... [ellipsis in source]”
—Sarah M. Grimke (1792–1873)
“Smooth white skin invites something that will leave a trace, a kiss or a slap.”
—Mason Cooley (b. 1927)
“It is thus that the few rare lucid well-disposed people who have had to struggle on the earth find themselves at certain hours of the day or night in the depth of certain authentic and waking nightmare states, surrounded by the formidable suction, the formidable tentacular oppression of a kind of civic magic which will soon be seen appearing openly in social behavior.”
—Antonin Artaud (1896–1948)