Pretty much everywhere we go, from walking down the street to sitting in front of the television at home, we are bombarded with Wi-Fi signals. And they may be revealing more than we thought. Researchers from the Technical University of Munich have managed to demonstrate how stray Wi-Fi radio waves can be used to produce a 3D hologram of objects in a room, reports Science Magazine.
Under normal circumstances, lasers are used to produce a hologram; a light beam is split so that half of the laser is reflected off the object onto the photographic plate, and the other half shone directly onto the plate as a reference. The difference between the two halves of the beam is then used to create the hologram when a second laser beam is shone directly on the photographic plate.
But instead of creating a hologram using lasers, the team of scientists, whose work is to be published in Physical Review Letters, found a way to do something similar with Wi-Fi signals. They placed an aluminum cross in front of a Wi-Fi router, coupled with a reference router to one side, and then record the differences in signals as they hit a receiver at the other end of the room. Decoding the received signals on a computer, the team were able to create an image of the cross as a hologram.
There are limitations, however. They suspect that the receiver would struggle if the room was cluttered, for example, and it does still need to be inside the room for it to work. But it does raise the interesting possibility that stray Wi-Fi signals, so ubiquitous to modern life, can be used in ways as yet unconsidered.
The authors suspect that the receivers could be adapted so that they could be placed outside of the room, which would mean that, in theory at least, the contents of a room could be imaged from the other side of a wall. But this would bring up a whole host of technical issues, reports Science, namely if there are other objects within the wall space that could reflect the Wi-Fi signals, such as metal struts, they may distort the picture that would then be constructed.
This is an interesting development, but it is not the first time researchers have co-opted Wi-Fi signals to peer through solid walls. A few years ago, it was shown how the signals can be used to identify people in other rooms, and was subtle enough to distinguish the outline of bodies. Through this they could identify, with 90 percent accuracy, up to 15 different individuals, as well as track people as they moved around using their heat beats.
