Noisy radar sees through walls

Ohio State University engineers have invented a radar system capable of penetrating walls that is virtually undetectable, because its signal resembles random noise.

The radar could have applications in law enforcement, the military, disaster rescue and medical imaging.

Eric K. Walton, senior research scientist in Ohio State's ElectroScience Laboratory, said, "Almost all radio receivers in the world are designed to eliminate random noise, so that they can clearly receive the signal they're looking for. Radio receivers could search for this radar signal and they wouldn't find it. It also won't interfere with TV, radio, or other communication signals."

The radar scatters a very low-intensity signal across a wide range of frequencies, so a television or radio tuned to any one frequency would interpret the radar signal as a very weak form of static.

"It doesn't interfere because it has a bandwidth that is thousands of times broader than the signals it might otherwise interfere with," Walton said.

The noise radar generates a signal that resembles random noise, and a computer calculates very small differences in the return signal. The calculations happen billions of times every second, and the pattern of the signal changes constantly. A receiver could not detect the signal unless it knew exactly what random pattern to look for.

The radar can be tuned to penetrate solid walls so the military could spot enemy soldiers inside a building without the radar signal being detected, Walton said. Traffic police could measure vehicle speed without setting off drivers' radar detectors. Autonomous vehicles could tell whether a bush conceals a more dangerous obstacle, like a tree stump or a gulley.

The radar can detect tiny motions that could be used to locate disaster survivors trapped under rubble. Other radar systems cannot do that, because they unable to detect close-up targets. Walton said that the noise radar is inherently able to see objects that are nearby.

That means that with further development and testing, the radar might image tumours, blood clots, and foreign objects in the body. It could even measure bone density.