Wi-Fi hitchhikers, take note: British defense contractor BAE Systems had some material lying around, used for stealth bombers/to cloak the location of radar used in military operations, and discovered – hey, this stuff works as a security block for Wi-Fi, too...
The FSS (Frequency Selective Surface) panels are manufactured in the same way as printed circuit boards, with layers of copper on Kapton polymer. The panels are 50 to 100 microns thick; they can be applied to most surfaces, including glass. Which is half-useful; get ready to dig deep, to cough up for the additional artificial lighting expense.
The panels prevent third parties from snagging a free Wi-Fi ride into company data traffic, while allowing other traffic through, including cell phone signals.
'Course, if you're really determined, and use a bit of ingenuity (and a blowtorch)...
Find more sci/tech news in the August 2004 issue of "Arte Six".