Researchers at MIT have developed radar that allows them to see people and moving objects behind a concrete wall in real time. As the radar passes through a wall, it loses about 99 percent of its strength. The same is true on the way back. By the time their computers are analyzing the signal, it's at about 0.0025 percent of its original strength. Stationary objects do not appear. The scientists say that their technology will help the military in urban combat.
They explain how their radar works in the above video.