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Re: ISEF display
>
> I thought of that also, it could add a level too the experiment, you
could
> show the uses and properties of faraday shielding, by using a portable
> radio inside the cage, and outside the cage, when the coil is run. But
> won't a ungrounded or poorly grounded Faraday cage act more as a antenna
> and radiate some of the RF?
Shielding RF is sort of a black art, but, as a rule of thumb, if the holes
in the shield are less than 1/10 wavelength in circumference (shape doesn't
really matter), then RF won't go through. If any conductor passes through
the hole, all bets are off, because now you've got a transmission line.
Woven wire mesh is not a good shielding material because it is woven (all
those wires go from one side to the other), unless all the joints are
welded or soldered. The sort of hardware cloth where the wires are laid in
a criss-cross and just spot welded works much better, because all the
horizontal wires stay on one side and the verticals on the other. The ideal
is perforated metal sheet. A significant area of concern for shielding
would also be magnetic fields, particularly if the shield is close to the
the radiating wire (close in wavelength terms, at 100 kHz, wavelength is 3
km, so it is safe to say you are in the near field with a TC). For magnetic
shielding, you want a lossy soft magnetic material. Fortunately, magnetic
fields drop off really rapidly with distance.
I suggest you check out the catalogs from companies like Chomerics for more
info on shielding in general.
The power lines will probably be your most likely leakage path. The usual
run of the mill RFI filter may or may not have very good attenuation at 100
kHz to 1 MHz (your frequencies of interest). Mount the filter in the wall
of the box, and bond really well from the box all around the case of the
filter.
By the way, it doesn't matter if the box is grounded or not (except for
safety). If the source is entirely enclosed in a conductive shell, no
energy gets out.
Another interesting shielding material, which may be a bit tricky for home
application, but you might have a source for it, is a thin indium oxide
film. Transparent and a good conductor. It's what they use on LCD displays
for the front electrode (which you have to be able to see through).
Practically speaking, you have to know someone with a vacuum deposition
apparatus to put it on, but, you never know...