RE: [SI-LIST] : Question on propogation of high freq. signal in conductors

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From: prasanna kumar (prasan8181@yahoo.com)
Date: Thu Sep 21 2000 - 05:58:31 PDT


Hi all,
Thanks for the answers.But i still dont have my doubts
cleared.
I have learnt about skin effect but had the idea that
it is only concerned with EM waves travelling from one
medium(say air) to another(a conductor).I am unable to
digest the concept of using skin effect here.Please
clarify.
And why is it that more flux is linked with inner part
of a conductor so that by Lenz's law the opposing
force for current is high and hence no current flows
in the inner parts of the conductor?
As quoted by Mr.Clewell,
   "'First slice a wire lengthwise to make concentric
tubes, like growth rings on a tree trunk. Now if you
consider the inductance of each ring separately
the inner rings would be long and skinny and have more
inductance than the outer rings which are fatter.'
and what here is meant by sayin that the inner rings
are long and skinny?Why should the inductance be more
for such rings?"
Thanks,
Prasanna.

--- "Jian X. Zheng" <jian@zeland.com> wrote:
> Hi,Prasanna:
>
> In short, the skin effect causes the current to be
> flowing on the surface of
> a conductor. In fact, you can demonstrate such a
> phenomenon on a plane wave
> incident onto a big sheet of metal:
>
> \
> \ plane wave
> \
> ---------------------------------------- top surface
> of the metal sheet
> |
> | plane wave in the metal
> |
> ---------------------------------------- bottom
> surface of the metal sheet
> \
> \ transmitted plane wave
> \
>
> When a plane wave is incident onto the surface, you
> will see the electric
> field is exponentially decaying in the -z direction.
> J = Sigma * E, where E
> is the electric field, J is the current and Sigma is
> the conductivity. In
> the other word, the J is exponentially decaying and
> the decaying factor is
> very big. It is just like the current only exists on
> the surface of the
> metal sheet. Thanks!
>
> Best regards,
>
>
-----------------------------------------------------------------------
> Jian-X. Zheng, Ph.D
> Zeland Software, Inc., 48890 Milmont Drive, 105D,
> Fremont, CA 94538, U.S.A.
> Tel: 510-623-7162, Fax: 510-623-7135, Web:
> http://www.zeland.com
>
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> --
>
> > -----Original Message-----
> > From: owner-si-list@silab.eng.sun.com
> > [mailto:owner-si-list@silab.eng.sun.com]On Behalf
> Of prasanna kumar
> > Sent: Tuesday, September 19, 2000 6:26 AM
> > To: si-list@silab.eng.sun.com
> > Subject: [SI-LIST] : Question on propogation of
> high freq. signal in
> > conductors
> >
> >
> > 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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