Re: Faraday Cages....

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

Original poster: "Metlicka Marc by way of Terry Fritz <twftesla-at-uswest-dot-net>" <mystuffs-at-orwell-dot-net>


jim, all


Tesla list wrote:
> 
> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<jimlux-at-earthlink-dot-net>
> 
>
> 
> Perimeter is the key.. If you have a narrow slot, but the perimeter is on
> the order of 1/2 wavelength (i.e. the slot is 1/4 wavelength long and very
> narrow), you'll get significant leakage.  The slot can be any shape, round,
> linear, etc. because the EM wave will propagate along the conductive
> surface.
> 
> If you really are hard core, you make the surfaces not a perfect conductor,
> but lossy. The amount of loss is best determined empirically.  (It's akin to
> reducing radar cross section for stealth... little details make a big
> difference..)

this is the thinking i have about using sprayed on graphite, this could
be built to, say, 1/16" thickness and doubled around any conduit coming
into the room. the graphite has a high resistance but it was actually
your mention of this resistance being cut back at higher frequencies
that got me to thinking. it would present an almost seamless conductor
of no openings other then the door frame. the graphite we used on
mandrels had a very high adhesion so it wouldn't come loose. would be a
good experiment.

>
> 
> I think that radiated fields (which is what screen rooms are for) are the
> least of your problems.  Worry about magnetic fields, and transients (also
> magnetic fields).  I once spent several months struggling with isolating
> 60Hz (and harmonics) interference from EEG recordings with all manner of
> shielding, iso transformers, all sorts of grounding. What finally worked the
> best was NO shielding, and careful attention to wiring layout (lots of
> twisted pairs and NO ground loops).  You want to minimize the area of any
> "victim" loops.

this is something that has baffled me, i have been in mcr's that the
magnetic fields were almost palatable when 8 or 10 1200 hp motors were
under full load, but yet i could plug my laptop into a drive and check
faults or make timing changes? i never understood why these fields
didn't act on the pc or even the floppy's that were stored in them? is
the magnetic in a strong pulse more damaging then a steady, but
fluctuating field?


> 
> EMP and lightning protection are the areas to research... After all, what
> you are doing is basically making lightning.....not building radio
> transmitters.