On Thu, 17 Jun 2004 00:01:38 -0500, matt weber wrote
(in article ):

On 16 Jun 2004 12:50:47 -0700, (AC/DC) wrote:

I am assuming that a microwave oven is a Faraday cage. Since it keeps
the radiation trapped, bouncing around inside to heat up the food
instead of you. I am betting you would loose signal on a cell phone
completley if it were placed inside of a microwave with the door
closed. This should work even with the oven unplugged from the wall
outlet, which then would be ungrounded.

The electric field inside a Faraday cage is zero, regardless of what
the outside is doing or is connected to. But the reverse is also true.
The charges that are built up from components inside of the Faraday
cage are trapped to bounce around like the radiation inside of a
microwave. So that makes me think it needs to be grounded. On the
other hand, if the shell of a microwave is grounded. Then what keeps
the radiation inside from going to ground instead of bouncing around
and cooking your food?
It is better if the cage is grounded, but it doesn't have to be.

Yeah, it pretty much does - results inside the cage could be
questionable if it is not grounded, at least in the kc/mc freqs.
However, realize that my example of the first stage in a receiver
and a 2,000 watt jammer being worked on at the same time in the
same room was /not/ a hypothetical but something I've had to deal
with in both the U.S. and in Korea.

The
cage does have to be several skin thickness thick to be effective

Additionally, it can have holes all over it (I know 25-40%). I've
never used "solid" copper.


however, Fortunate at Microwave oven frequencies, the skin depth is
sub micron. without grounding the cage, it is possible for the cage to
re-radiate some of the energy, but for the most part, the changing
field are either reflected back into the chamber, or induce currents
in the cage, which become I^r losses in the conductor the cage is
made of. How much goes which way is a function of how good the
conductor is, how thick it is, and the frequency of the field, the
skin depth is zero, and field are 100% reflected.

Okay. /gray/