Quote:
Originally Posted by Lui
To be effective, a Faraday cage must be made of very good conducting metal. Typically copper or brass is used. Also the way it is built is critical. The ones I have worked in (radio technician) were made of brass screening material. Looked very much like a window bug screen. There were 2 layers of it and the 2x4 structure was covered in solid brass sheets. The sliding door also had the brass screening, double layers, and both the top and bottom of the door was recessed about 4 inches into the structure, again to avoid any direct path for RF energy to enter/leave. By their nature, Faraday cages prevent energy from entering or leaving, and the physical design ensures they protect over a very wide spectrum of frequencies and can handle high power as well. If using a solid sheet of steel/iron/sheet metal, it lacks the conductivity of the better material and thus its resistance to both high power and broad frequencies is seriously compromised. Using a microwave oven as a Faraday cage is also most likely not to be an effective option. Microwave ovens are designed to reduce (significantly) a very narrow range of frequencies, namely in the low microwave region of the spectrum (1 to perhaps 5 Giga Hertz). So its spectrum coverage is too narrow to effectively block an nuclear bomb induced EMP. That kind of EMP is very wide spectrum in nature and massively powerful. All this depends on the yield of the nuclear bomb of course, and how far one is from the detonation point. Perhaps, for those on the very fringe of an EMP coverage could get away with the design show above, but I personally would not bother with it, and go with aluminum screening to emulate the Faraday cages I have worked in. Hope this provides some insight into EMP protection. Take care and keep experimenting. Lui
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there is no such thing as a faraday cage (microwave oven cavity) designed to protect from a narrow spectrum os RF frequencies, unless there are filters in the cavity wal specifically designed to allow lower frequencies in.
any faraday cage will essentially work from it's top cut off frequency (determined by the largest diameter hole, and the depth of said hole, in the wall of the cavity - al lthe way down to DC. now this cavity may have different attenuation at different frequencies, but it will work across that entire spectrum.
people who put a call into a microwave or other faraday cage a s a test are using an unreasonably high standard. a cell phone in the us runs at at least 900 mhz, if not 2 gig plus. with an emp MOST of the power is at 30 mhz and lower. furthermore cell phones are INCREDIBLY sensitive receivers. they can pick up -100 dbm signals. to put that into perspective, the light of a bright star falling on one square meter of the earths surface is about -60 dbm - thats a factor of 1000 times more signal than a cell phone can find!
05-23-2012, 08:32 PM
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