Researchers at MIT have created a radar array that can detect people through eight-inch concrete walls from up to 60 feet away. The system emits wavelengths in the range of wireless networks, or about 10cm. Larger wavelengths are better at penetrating walls, but they also require a larger radar array — at 8.5 feet this one is small enough to be mounted on the side of a truck for urban warfare applications.
Only 0.6 percent of the signal passes through the wall, and a fraction of that energy reflects off people and back through the wall again, reaching the detector at 0.0025 percent of its original strength. The System filters out the frequencies reflected from the wall itself, amplifies the rest, and creates a real-time bird's eye view of the scene behind the wall at 10.8 frames per second. The display currently shows red blobs, but the team is working on a detection algorithm that will display distinct squares to make the technology more user-friendly.