Seeing Through Walls Using… WIFI

Wi-Vi demo (Credit: MIT)
It might not be Superman’s X-ray vision, but researchers from MIT are working on a technology which could track humans moving behind walls using inexpensive WIFI technology.
Several companies have been working on developing technologies that can see through walls. Israeli start-up Camero has been working for the past several years to develop radar system for military and law enforcement forces which can penetrate walls and allow users to track individuals inside the room. However, radar technology is typically expensive and bulky and uses a part of the electromagnetic spectrum only available to the military.
The new system known as Wi-Vi was developed by professor Dina Katabi, from MIT’s Department of Electrical Engineering and Computer Science, and her graduate student Fadel Adib. According to Katabi: “The Wi-Vi could give all of us the ability to spot people in different rooms 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”.
The Wi-Vi uses low-power Wi-Fi signals in order to “see behind walls” by measuring electromagnetic reflections and can even track movement in real time inside a room. According to Katabi, her team had to develop a way to “cancel out all other reflections [from the room and different objects], and keep only those from the moving human body”. In order to achieve this goal, Katabi’s team used two transmit antennas and a single WIFI receiver. The 2 antennas transmit very similar signals, however the signal from the second antenna is the inverse of the one put out by the first one. As a result, the two signals interfere with each other and cancel each other out. Because any static objects that the signals hit also create identical reflections, they too are cancelled out. However signals coming from moving objects don’t cancel out and arrive back at the receiver.
Previous attempts to track moving subjects behind walls typically required an array of spaced antennas – however this method is too expensive and bulky for use in a handheld portable device. Wi-Vi uses a different – simpler – method to track individuals moving behind a wall. By carefully measuring the time it takes for the reflected signal to make its way back from the moving person inside the room to the receiver they can pinpoint the movement of that person with real-time accuracy.

Wi-Vi has many potential applications. besides the expected military and law-enforcement uses it could also be adapted for search and rescue operations (searching for movement under a ruined building), the system can theoretically be used for controlling devices for gaming or smart home in cases where the user does not stand directly in front of the system camera (and may even be on a different room entirely and would like to turn off the light or music in the other room for example).

More information on the Wi-Vi can be found on MIT’s website.

A quick video demostration of Wi-Vi

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