Re: Faraday Cage

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

The Chomerics web site has a good tutorial on shielding, etc.  Other sources
of information are web sites specializing in EMI/EMC testing and those
selling screen rooms.

There's no real frequency where RF (or any electromagnetic radiation, for
that matter, including light) becomes particularly directional.  However,
when objects, holes, etc, are a significant fraction of a wavelength,
thinking in terms of optics becomes easier than in terms of induced currents
and fields. For microwaves, where wavelengths are a few centimeters, there
are lots of things that are bigger than a wavelength. For HeNe lasers, which
have a wavelength of 628 nm (some 470 THz), optics is really the way to
conceptually approach things. For tesla coils, at 100 kHz and 3000 meter
wavelengths, or even 1MHz and 300 meters, there aren't a whole lot of things
that are many wavelengths in size, so fields are an easier way to deal with
it.  At intermediate frequencies/wavelengths, you can do either.

There's also the thing about near field vs far field for things that radiate
fields. Basically, the near field is where energy flows back and forth
between the field and the radiator. The far field is all radiating away.
Again, there are both physical size and wavelength effects here. The other
thing to think about, as some have recently pointed out, is that the
magnetic fields might actually be a bigger concern (and MUCH harder to
shield) than the E field. Faraday cages don't stop magnetic fields (in fact,
sensitive magnetic sensors are put inside a Faraday shield to reduce
electrostatic pickup).


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, December 17, 2002 3:17 PM
Subject: Re: Faraday Cage


 > Original poster: "G by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<bog-at-cinci.rr-dot-com>
 >
 > Hello All,
 >
 > Regarding all of this cage design, about what frequency does RF become
 > highly directional (like microwaves)? Would coving the floor be relevant?
 > Will the RF simply radiate toward the floor and the earth underneath,
 > without curving upwards into the house (or horizontally and out into the
 > neighborhood)?
 >
 > Thanks,
 > Gregory
 >
 > >I did not originaly think of the floor, due to the effects of a spark
cage I
 > >built to protect myself when I first started coiling.  The cage fit over
the
 > >top half of the coil. Flourescent and neon lamps would only come to light
at
 > >a 45 degree outward angle from the bottom of the cage.  At 2 1/2" to the
 > >mesh and 6" to the water table, I didn't think it would be a problem for
 > >this cage.  Tying it into the water table is the main reason for the
ground
 > >rod.
 >
 > --
 > "Without ZIM, I am lost."
 > GeekID#-1229
 > http://thegeekgroup-dot-org
 >
 >
 >
 >