Radio Waves Paint Portraits of Obstacles express
When a radio wave encounters a building, it bends around it, leaving a radio shadow — a pattern of strong and weak signal zones. Scientists call this pattern a radio portrait. Like a painting, it encodes information about the object's shape, size, and distance.
Researchers have built a model that 'develops' this portrait, reading data with the precision available to ordinary Wi-Fi and cellular frequencies. The approach rests on the optical ideas of Huygens and Fraunhofer, unified for radio waves. A striking fact: the method is limited not by technology, but by a fundamental physical limit — the Cramér–Rao bound, which forbids extracting more information from the signal. In other words, radio portraits are as sharp as is physically possible in our world.
An ordinary Wi-Fi router, while transmitting data, simultaneously 'probes' the room with radio waves. Analyzing signal distortions reveals where a chair is and how big it is — without getting off the couch.
In 'The Dark Knight,' Batman turned phones into a sonar that could see through walls. This new technology comes close, but without any hacking — ordinary radio signals are enough.