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.
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Timothy C. May              | Crypto Anarchy: encryption, digital money,
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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.