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#1
June 17th 04, 06:01 AM
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#2
June 17th 04, 08:44 PM
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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/ |
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