By: Pam Frost Gorder
Stealth radar system sees through trees, walls undetected
Ohio State engineers have invented a radar system that is virtually undetectable because its signal resembles random noise.
The radar could have applications in law enforcement, the military and disaster rescue.
Eric Walton, senior research scientist in Ohio State's
ElectroScience Laboratory, said that with further development the
technology could even be used for medical imaging.
He explained why using random noise makes the radar system invisible.
"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," Walton said. "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 TV 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.
Like traditional radar, the "noise" radar detects objects by
bouncing a radio signal off them and detecting the rebound. The
hardware isn't expensive, either; altogether, the components cost less
than $100.
The difference is that 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 couldn't detect the signal unless it knew exactly what random
pattern was being used.
The radar can be tuned to penetrate solid walls - just like the
waves that transmit radio and TV signals - 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 is inherently able to distinguish between many types
of targets because of its ultra-wide-band characteristics.
"Unfortunately, there are thousands of everyday objects that look like
humans on radar - even chairs and filing cabinets," he said. So the
shape of a radar image alone can't be used to identify a human. "What
tends to give a human away is that he moves. He breathes, his heart
beats, his body makes unintended motions."
These tiny motions could be used to locate disaster survivors
who were pinned under rubble. Other radar systems can't do that because
they are too far-sighted - they can't see people who are buried only a
few yards away. Walton said that the noise radar is inherently able to
see objects that are nearby.
"It can see things that are only a couple of inches away with as
much clarity as it can see things on the surface of Mars," he added.
That means that with further development, the radar might image
tumors, blood clots and foreign objects in the body. It could even
measure bone density. As with all forms of medical imaging, studies
would first have to determine the radar's effect on the body.
The university is expected to license the patented radar system.
