Washington, October 12 : University of Utah engineers have developed a wireless network of radio transmitters that can track people moving behind solid walls.

The system could help police, firefighters and others nab intruders, and rescue hostages, fire victims and elderly people who fall in their homes. It also might help retail marketing and border control.

"By showing the locations of people within a building during hostage situations, fires or other emergencies, radio tomography can help law enforcement and emergency responders to know where they should focus their attention," according to Joey Wilson and Neal Patwari from the University of Utah.

Their method uses radio tomographic imaging (RTI), which can "see," locate and track moving people or objects in an area surrounded by inexpensive radio transceivers that send and receive signals.

The study involved placing a wireless network of 28 inexpensive radio transceivers - called nodes - around a square-shaped portion of the atrium and a similar part of the lawn.

In the atrium, each side of the square was almost 14 feet long and had eight nodes spaced 2 feet apart. On the lawn, the square was about 21 feet on each side and nodes were 3 feet apart.

The transceivers were placed on 4-foot-tall stands made of plastic pipe so they would make measurements at human torso level.

Radio signal strengths between all nodes were measured as a person walked in each area.

Processed radio signal strength data were displayed on a computer screen, producing a bird's-eye-view, blob-like image of the person.

A second study detailed a test of an improved method that allows "tracking through walls."

The study details how variations in radio signal strength within a wireless network of 34 nodes allowed tracking of moving people behind a brick wall.

The method was tested around an addition to Patwari's Salt Lake City home. Variations in radio waves were measured as Wilson walked around inside.

The system successfully tracked Wilson's location to within 3 feet.

The wireless system used in the experiments was not a Wi-Fi network like those that link home computers, printers and other devices.

According to Patwari, the system is known as a Zigbee network - the kind of network often used by wireless home thermostats and other home or factory automation.

The researchers now have a patent pending on the method. "I have aspirations to commercialize this," said Wilson. (ANI)