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:
“When science is learned in love, and its powers are wielded by love, they will appear the supplements and continuations of the material creation.”
—Ralph Waldo Emerson (1803–1882)
“The law before us, my lords, seems to be the effect of that practice of which it is intended likewise to be the cause, and to be dictated by the liquor of which it so effectually promotes the use; for surely it never before was conceived by any man entrusted with the administration of public affairs, to raise taxes by the destruction of the people.”
—Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)
“Surely the day will come when color means nothing more than skin tone, when religion is seen uniquely as a way to speak one’s soul; when birth places have the weight of a throw of the dice and all men are born free, when understanding breeds love and brotherhood.”
—Josephine Baker (1906–1975)
“Tears, idle tears, I know not what they mean,
Tears from the depth of some divine despair
Rise in the heart, and gather to the eyes,
In looking on the happy autumn-fields,
And thinking of the days that are no more.”
—Alfred Tennyson (1809–1892)