X-Ray Vision Almost Here, Researchers Report

X-ray vision could become a reality thanks to researchers at Massachusetts Institute of Technology currently developing a new system that can detect humans through walls using low-cost Wi-Fi technology.

"We wanted to create a device that is low-power, portable and simple enough for anyone to use, to give people the ability to see through walls and closed doors," Dina Katabi, a professor in MIT's department of electrical engineering and computer science and lead author, said in a press release.

While the method doesn't represent the first attempt at a device capable of seeing people through walls, previous efforts have involved the use of expensive and bulky radar technology using a part of the electromagnetic spectrum only available to the military.

The system under development is called "Wi-Vi" and is based on a concept similar to radar and sonar imaging.

In contrast to radar and sonar, however, it transmits a low-power Wi-Fi signal, a portion of which penetrates the wall and reflects off of moving humans.

Only a tiny fraction of the signal makes it through to the other room, with the rest being reflected by the wall or by other objects. For this reason, the scientists had to develop a technology to cancel out all other reflections and only keep those from a moving body.

To do this, the system uses two antennas that transmit almost identical signals, only the signal from the second antenna is the inverse of the first, resulting in a cancelling out of both when they encounter static objects, which produce identical reflections.

As a result, only those reflections that change between the two signals, such as those from a moving object, arrive back at the receiver.

"So, if the person moves behind the wall, all reflections from static objects are cancelled out, and the only thing registered by the device is the moving human," explained graduate student Fadel Adib.

With all reflections of static objects erased, the device can then focus its attention on tracking the person as he or she moves around the room.

Unlike previous attempts that have required an array of antennas to capture the signal reflected off a person moving through an environment, the newer method is conducive to smaller, even handheld devices as it uses just one receiver that tracks the difference in time it takes for the reflected signal to make its way back.

Wi-Vi's makers believe the system could be helpful and even life-saving in a number of scenarios, such as aiding search-and-rescue teams find survivors trapped in rubble after an earthquake, or allow police officers to identify the number and movement of criminals within a building to avoid walking into an ambush.

It could also be used as a personal safety device, Katabi explains.

"If you are walking at night and you have the feeling that someone is following you, then you could use it to check if there is someone behind the fence or behind a corner."

The device could further prove useful in more everyday scenarios, such as turning off the lights with the wave of an arm or, because Wi-Vi does not require a line of sight between the user and the device itself, Venkat Padmanabhan of Microsoft Research says he sees a possible use in the entertainment industry.

"Such an interface could alter the face of gaming," he said.