A world of ubiquitous wireless networking poses numerous opportunities for theft. Hence the fancy new trend of RFID wallets to secure credit cards. Of course, new credit cards aren’t the only thing people want to protect. Whether you’re incredibly concerned about someone hacking into your home wireless network or maybe you own a Panera and wish everyone at the neighboring burger bar would quit stealing your free Wi-Fi (I might have done this when working out of town one summer…), the stumbling block to applying this to your home was our society’s inability to make wallets that can hold people. Or maybe you didn’t feel like making your home follow neo-survivalist decor by covering your walls in chicken wire and/or aluminum foil (I’m scared to link to sites on that one, so just Google that on your own).
So leave it to the French to create a fashionable Faraday cage. Researchers at the Grenoble Institute of Technology have made a wallpaper containing electrically conductive ink. The ink, which contains silver particles, forms a snowflake pattern on the wallpaper. This pattern is similar to something like chicken wire and so it forms a selective Faraday cage that prevents the electromagnetic waves of a Wi-Fi signal from transmitting through the paper. It doesn’t affect the network in the room (or perhaps your house if you only paper exterior walls). Even better, the team expects this to be no more expensive than original wallpaper. And if metal snowflakes aren’t your thing, you can cover this with an additional layer of wallpaper without ruining the Faraday effect.
The researchers also make another claim about cell phone signals. The original article is in French, which I don’t understand, but looking at it through Google Translate says they claim it doesn’t interfere with “emergency service” calls, but does block three kinds of signals. Another English article I found says the wallpaper shouldn’t interfere with cell phone signals at all. The claim about emergency services strikes me as weird because a call to 911 isn’t physically different from a call to your friend. But I also don’t buy that it shouldn’t affect any cell phone signals. If the photo is a somewhat accurate representation of the wallpaper, the pattern looks like there’s only about an inch of space between lines. Since the “cage” isn’t solid, it does allow electromagnetic waves smaller than this space to pass through. Wi-Fi uses radio frequencies in the 2400-2485 MHz range and cells phones work somewhere between 1700 and 2155 MHz (the exact range depending on your carrier). Dividing the speed of light (300,000,000 meters a second) by the frequency, we see that the wavelength of Wi-Fi signals is about 12.5 cm while your phone’s signal has something between a 17.6 and 14 cm wavelength. So based on my quick and dirty math, it doesn’t seem like either signal should get through ever.
P.S. The French researchers do also point out the survivalist/paranoid applications of this, saying you could also wallpaper your house in this to prevent some electromagnetic radiation from getting in.