Re: [SI-LIST] : Re: Skin effect (Was: Nil)

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From: Vinu Arumugham (vinu@cisco.com)
Date: Tue Sep 19 2000 - 11:12:27 PDT


Another way of looking at it:

When an alternating current flows through a conductor, a magnetic field is
created around it. If the conductor has finite dimensions, some of the
magnetic field is contained within the conductor. Such a changing magnetic
field inside a conductor, creates eddy currents that tend to oppose the
main current at the center of the conductor and strengthen the current at
the surface of the conductor, resulting in the skin effect.

Vinu

Kim Helliwell wrote:

> I don't know how in-depth (pun not intended!) an answer you're seeking.
> The name of this effect is the skin effect. It comes
> directly out of Maxwell's equations when considering
> electric fields in conductors. What happens is that
> an electromagnetic wave gets damped out inside the
> conductor, and the penetration distance, or skin depth,
> is inversely proportional to the square root (to a first
> approximation) of the frequency of the wave. Since charges
> in a conductor are propelled by electric fields, current
> can only flow where the electric fields have not been damped
> to (essentially) zero. Which is near the surface.
>
> Nearly any good graduate level E&M text will discuss this
> effect with all the mathematical machinery. My reference is
> _Classical_Electrodynamics_, by J.D. Jackson.
>
> Jackson says that the skin depth for copper at 60 Hertz is
> 8.5 mm, and for 100 MHz, it's about 7 microns.
>
> Kim Helliwell
>
> prasanna kumar wrote:
> >
> > Hi,
> > i have a small doubt.
> > in high frequencies why does the signal is confined
> > only to the surface of the conductor?
> > ie,(if i am putting it right)why does the current
> > flows only at the surface of the conductor?
> > thanks.
> > Prasanna.
> >
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> --
> Kim Helliwell
> Senior CAE Engineer
> Acuson Corporation
> Phone: 650 694 5030 FAX: 650 943 7260
>
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