Re: Faraday cage

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jimlux-at-earthlink-dot-net>
> 
> The general guideline is that the perimeter of the holes should be less than
> the wavelength of the energy you are trying to shield (give or take a factor
> of 2 or 3)...
> 
> Any conductor penetrating the holes makes it useless for shielding (woven
> screen isn't all that wonderful, for this reason... use welded mesh)
> 
> Magnetic shielding is a true and royal pain in the .....
> 
> ----- Original Message -----
> From: "Tesla list" <tesla-at-pupman-dot-com>
> To: <tesla-at-pupman-dot-com>
> Sent: Friday, May 10, 2002 7:09 AM
> Subject: Re: Faraday cage
> 
> > Original poster: "Paul Benham by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <paulb-at-woodanddouglas.co.uk>
> >
> > Hi Terry,
> >
> > If you construct it properly so all the seams are soldered and the door
> has
> > berilyum copper fingering all the way around, ie no slots, and the
> material
> > is conductuve enough, then it will attenuate the magnetic fields as well
> as
> > the electric fields, and work as a true faraday cage.  If you are only
> > interested in attenuating the electric fields then you do not need to be
> > that fussy regarding continuous conductivity all the way around with no
> > slots or holes.  I think that getting chicken wire or screen mesh and only
> > soldering the sides at the corners is not a good idea.  The size of the
> mesh
> > will determine the highest frequencies that it will attenuate.
> >
> > Cheers,
> >
> > Paul.

	A better size is 1/10 wavelength.  But, for a frequency of 1 MHz the
wavelength is 983.5 feet!  So, 100 foot diameter holes should be fine. 
Obviously the rules break down here.  Galvanized "chicken wire" is
lightweight, cheap, and easy to solder so would make an excellent
material for a screened room intended to keep TC radiation inside.  Not
much good for high frequency work if you're trying to keep stuff out,
but that's a different matter.  Some of the screened rooms I've worked
in had double walls of fine mesh bronze screening, plus doors with
elaborate blade seals.  That's to give perhaps 120 dB to signals up
through microwaves.

Ed