BAE Systems have developed a type of wallpaper designed to secure WiFi networks. The wallpaper uses a Frequency Selective Surface (FSS) to let only some radio frequencies through, whilst blocking others.
The upshot is that a site using the wallpaper can keep wireless LAN signals inside, but allow mobile phone and other EM signals through. This is much more convenient than turning an office building into a Faraday cage, as staff will still be able to use their mobile phones and emergency services signals will not be blocked.
The wallpaper can even be switched off in an emergency (if only it’d been around when Oscar Wilde needed it), to allow all signals through.
At UK£500 (€747) per square meter it’s a little pricey for home use but more practical for companies. Of course, wireless networks should be properly secured with user authentication and encryption before resorting to FSS techniques, but the product is a useful precaution against users setting up unauthorised unsecured wifi access points within organisations.
The wallpaper is composed of a top secret kapton and copper sandwich (kepton is that film that very thin circuit boards and connectors are made out of – prise the back of your iPod and you’ll see what I mean), and BAE are currently working on a thinner version for coating windows.