Re: Stealth Buildings Was Re: "X-Ray Gun" for imperceptible searches
At 8:58 PM 8/16/96, Alan Horowitz wrote:
TIm, a layer of tin foil is not the same as a professionally installed and maintained Faraday cage.
I can envision circulating currents on the tinfoil. Ie, ground loop type of situation.
All imaging is depenmdant upon the target having some radiating characteristic. If the gun shields a gun-shaped peice of the body from radiating in millimeter waves, you can build a gun detector.
There's no other way to say this: you simply don't know what you're talking about. Your protestations to the contrary, reconstruction of an image from point sources of leakage is essentially impossible ("the phase problem"). Analyze the solutions for sources behind screens. (A simple model is to analyze the radiation patterns one one side of conducting plate, with various sources on the other side.) For an intuitively visualizable model, consider a pattern of some sort (like a gun) behind a screen, with light leaking around the edges. (The less light leaks, the more the example is similar to the case of deliberate shielding of RF sources, but even the simple example here makes the point.) This is what crystallographers and DNA analysts call "the phase problem." Spatial frequency (pattern) information is indeterminate. If you still believe what you say, that a gun can be imaged even when behind a conducting screen, based solely on leakage around the edges (or similar small leaks), I challenge you to produce a paper which demonstrates this, or, even better, an actual demonstration. --Tim May Boycott "Big Brother Inside" software! We got computers, we're tapping phone lines, we know that that ain't allowed. ---------:---------:---------:---------:---------:---------:---------:---- Timothy C. May | Crypto Anarchy: encryption, digital money, tcmay@got.net 408-728-0152 | anonymous networks, digital pseudonyms, zero W.A.S.T.E.: Corralitos, CA | knowledge, reputations, information markets, Licensed Ontologist | black markets, collapse of governments. "National borders aren't even speed bumps on the information superhighway."
YOu are correct that a gun cannot be imaged behind an actual screen. I am correct that a peice of tinfoil doesn't comprise an actual screen. Go price a shield room, and see how much is for materials, and how much is for labor. Go talk to the crew that's putting it in; you'll see that they travel all the hell over the world putting these things in, because the vendor can't just hire some pick-up electricians and dry-wall types. If the source radiates its EM waves, which reach and intercept the tinfoil, unless the tinfoil is correctly bonded, shielded, grounded, etc, the tinfile will re-radiate. That can be imaged. I do this class of imaging, from signals that are weaker than these, for a living. In fact, we sometimes have to apply attenuation at the front end to stop overload of the amplifiers and signal processors. No, I'm not going to talk about it. Not because I'm a hot-shit keeper of classified information, rather because I'm lazy, or maybe because I'm accustomed to getting paid for teaching? Most of the concepts are discussed in IEEE journals and other sources. You could hand all the open sources, and a few billion dollars, to the Botswanians tomorrow; it would still take them a dozen years to get it working reliably. It's as much art as science. I guess the fancy word is "engineering". You don't know how to do it; so what. I know how to troublehoot and repair it.
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