Subject:  Re Faraday's cage
Date:     Tue, 15 Jul 1997 102559 -0500 (CDT)
From:     "John Salmen" <terrain@seaside.net>
To:       Multiple recipients of list <emf-l@mail.llion.org>
--------------------------------------------------

Peter,
I tried to find some references on the effects of concrete walls and
failed. I know two months have not passed but in two months I might
somehow be incapacitated and not be able to bug you for the information.
Does the reference speak of the effects of steel grids of reinforcement
normally placed in walls or does it concern the concrete mass or similar
areas of masonry mass? Please
thanks
John Salmen
TERRAIN E.D.S.

Peter Heindl wrote:
>
> Hello there,
>
> Haldun is right, a Faraday cage does not have to be earthed, a car
> standing
> on rubber tyres, in dry weather or in rain, is a perfect Faraday cage!
> Let
> lightning strike! - Your antenna and car radio, might however not be
> so
> lucky.
>
> BTW, did you know that for IONS contrete walls also work similar to a
> FARADAY
> CAGE? This could be harmful to your health, too. It causes the so
> called
> CONCRETE SYNDROME, as described in a German book I have!
> - Sorry no time for translation right now! - Remind me at a later
> stage in
> about 2 months or so, when my urgent work should be finished.
>
> Best regards.
>    Peter
>
> ----------
> > From: Haldun Ozaktas 
> > To: Multiple recipients of list 
> > Subject: Re: Faraday's cage
> > Date: 09 July 1997 15:43
> >
> >
> > > For the Faradys cage to work properly is does NOT, repeat not,
> need to
> be
> > > "grounded". Ground, earth or soil has nothing to do with Faradys
> cage.
> > > What the cage does is to equalize the potential differences at all
> points at
> > > the surface (boundary) of a contained space. Inside that space
> there is
> no
> > > potential differences and thus no electric field.
> > >
> > > Clas Tegenfeldt       ,,,
> >
> >
> > Another way of putting it is as follows:
> >
> > 1) The E-field inside a conductive enclosure will always be zero,
> > even if not grounded. ("Proof"= step1: The E-field inside the metal
> must
> > be zero since if not, charge movement will continue until it is
> > and the potential everywhere on the conductor is the same. step2: If
> > one has a closed regions whose boundary is at uniform identical
> > potential, then the inside is also at the uniform potential by the
> > uniqueness theorem, and there is no field inside.
> >
> > 2) However, to shield yourself from a source by using a conducting
> > finite barrier, that barrier must be grounded to be able to attract
> > from earth the charges to terminate the E-field lines.
> > (Example: grounded conducting monitor shields)
> >
> > Haldun
> >
> >
> ________________________________________________________________________
> > Haldun M. Ozaktas
> > Bilkent University                      (90) (312) 266 40 00 / 1619
> > Department of Electrical Engineering    (90) (312) 266 43 07
> (secretary)
> > TR-06533 Bilkent, Ankara, Turkey        (90) (312) 266 41 26 (fax)
> > www.ee.bilkent.edu.tr/~haldun           haldun@ee.bilkent.edu.tr


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