MIT Radar Sees Through Walls

From MITNewsOffice

Which kid hasn’t wished for X-Ray vision that could see through walls? Well, the big kids at MIT’s Lincoln Lab have done just that: developed new radar technology that provides real-time video of what’s going on behind eight-inch thick solid walls.

The concept behind this technology is similar to how our eyes see: just as visible light bounces off an object back onto our eyes, allowing us to see — similarly, radar sends radio waves to a target, bounce off it and return back to a receiver.

Radio waves can barely penetrate walls unless they are tuned to a certain frequency and even then only about 0.0025 percent make the travel back, which is then amplified. The challenge faced by the MIT researchers is how to build a real-time equipment that is fast enough, has the necessary resolution and range to be useful in urban combat situations. The Lincoln Lab team’s system may be used at a range of up to 60 feet away from the wall and it gives a real-time picture of movement behind the wall in the form of a video at the rate of 10.8 frames per second.

Interestingly, the researchers settled on using S-band waves, which have about the same wavelength as wireless Internet. How do they actually “see through the wall?” The solution is elegant: use an analog crystal filter which exploits frequency differences between the modulated waves bouncing off the wall and those coming from the target. The waves reflected back from the wall will have a different frequency that the waves reflected back from objects behind the wall. The filter is simply set to allow only waves in the range of the frequencies coming from behind the wall, effectively deleting the wall from the image.

There’s only one caveat with this system: it uses a subtraction method that compares each new picture to the last, and seeing what’s changed — in other words, the radar can only detect moving targets, not inanimate objects such as furniture. So, if you can stand very still, you may escape detection and soldiers deciding whether entering a building is safe or not may be deceived into believing it is empty. However, the system can detect very small movements and since even at rest, we move a little [think “camera shake”], that makes it very difficult for humans to escape detection.

Don’t get your hopes up yet that a consumer version will hit the stores soon. The system currently only sees “blobs” moving about the screen.

Also, I’m sure someone is even now building a counter-measure to prevent being scanned: say a special paint or other material with properties that absorb or detect radio waves…

via MITnews