Build your own Faraday Cage

Post #10,083 by marlowe 9/21/01 11:20:40 AM Reply	Build your own Faraday Cage [link\|http://www.boatsafe.com/nauticalknowhow/lightning.htm\|For hobbyists and survivalists alike]. [link\|http://www.angelfire.com/ca3/marlowe/index.html\|http://www.angelfir...e/index.html]
Post #10,088 by inthane-chan 9/21/01 11:47:12 AM Reply	Anybody know a way to detect an EMP? When my wife and I buy a house, I'm thinking about turning it into a faraday cage, or at least one room of it. What I would like to add is some way of detecting the initial surge and then using that to physically sever the connection to the local power grid. I don't want this triggering on just a regular power outage, so it's got to be something good... "He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche
Post #10,143 by kmself 9/21/01 5:11:50 PM Reply	Surge protector Googling [link\|http://www.google.com/search?q=surge+protector+emp\|surge protector emp] should be useful. Note that the surge is proportional to the length of the dipole (antenna). Your cage will protect you and your equipment. The next issue is keeping external surges outside the cage. `-- Karsten M. Self [link\|mailto:kmself@ix.netcom.com\|kmself@ix.netcom.com] What part of "gestalt" don't you understand?`
Post #10,089 by inthane-chan 9/21/01 11:47:20 AM Reply	Anybody know a way to detect an EMP? When my wife and I buy a house, I'm thinking about turning it into a faraday cage, or at least one room of it. What I would like to add is some way of detecting the initial surge and then using that to physically sever the connection to the local power grid. I don't want this triggering on just a regular power outage, so it's got to be something good... "He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche
Post #10,134 by jb4 9/21/01 4:10:46 PM Reply	Not likely... Early detection is not likely. The definition of an Electro-Magnetic Pulse (EMP) is a surge of electromagnetic energy with a very rapid (nanosecond) rise time. This very short rise time results in many harmonics of high intensity. These harmonics can induce currents on antennae (such as tracings on PCBs) that happen to be of the correct length to receive the harmonic. These induced currents anr generally of several orders of magnitude higher than ciucuitry attached to these antennae (tracings) are expecting to see, and the components burn out (sometimes spectacularly). Given the short(!) risetime of the pulse, and the fact that it is electromagnetic (which means no "bow-wave" effect), early warning is nigh-on impossible. Your best bet is a high-frequency filter that disconnects you from the grid on detection of a large spike of energy above a certain frequency (say 50Khz). Behind that, another, bigger, lower frequency filter that has an fc of about 1Khz. This would absorb the energy that would come down the line until the higher frequency filter isolates the grid. Not exactly early warning, but better than nothing. jb4 (Resistance is not futile...)
Post #10,163 by Ashton 9/21/01 7:35:11 PM Reply	That strategy might work for secondary effects, quite delayed, but as you observe - nothing is fast enough to "disconnect" nSec (even pSec) magnetic phenomena. As to the article and practicability of the nice drawings - dunno about 50 MAmps, VS the # of joules storable in today's practical-sized even exotic caps. A watt is a joule/sec. Q=CV re the cap bank's max energy storage. 50 MA --> ~ 10x Avogadro's number of electrons flowing, but at what potential ??? Unless the voltage is humongous at source - megavolt/meter has been a ballpark re military EMP via nuclear source - and given inverse-cube attenuation.. I don't see this dream becoming a nightmare. But the principle is right - we've made selves so techno-dependent (down to the steam iron) that the loss of a quadrillion xsistor junctions would turn us all OFF - including the xsistor fabs themselves. Not a new idea amongst physics folk - for >40 years. A.

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