From: Kim Helliwell (firstname.lastname@example.org)
Date: Tue Sep 19 2000 - 09:52:04 PDT
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.
prasanna kumar wrote:
> 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?
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-- Kim Helliwell Senior CAE Engineer Acuson Corporation Phone: 650 694 5030 FAX: 650 943 7260
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