Sarang Joshi and Joey Wilson, University of Utah
Left, a person walks inside a square of 28 radio transceivers at the University of Utah. The person creates "shadows" in the radio waves, resulting in the image displayed at right.

Video may not have killed the radio star.

Two University of Utah researchers have found a viable use for radio wavelengths that can see through walls and be used in places video cameras cannot.

U. graduate student Joey Wilson and Neal Patwari, a professor in the department of electrical and computer engineering, have developed a technology that could help police nab intruders and help firefighters find victims in a burning home. It could even be used to help patrol the border.

"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," Wilson and Patwari wrote in one of two new studies on the method. Their method uses radio tomographic imaging, which can "see," locate and track moving people or objects in an area through inexpensive radio transceivers.

The small radio devices, which are typically placed at about waist height for an average person, can be put around an area that police or other emergency personnel want to monitor. The transceivers emit radio signals of differing strengths as they pass through various subjects, noting stronger signals as a person moves. The signal is then relayed as a bloblike image on a computer screen. Similar technology allows researchers to track that movement through walls.

The process is much less expensive than radar, which bounces signals off individual targets to provide the target's location and speed, and RTI has advantages other technology lacks, making it a possibly more efficient system for police and fire departments.

"(Radio frequency) signals can travel through obstructions such as walls, trees and smoke, while optical and infrared imaging systems cannot," the engineers wrote. "RF imaging will also work in the dark, where video cameras will fail." In many circumstances, video cameras violate privacy and prevent their use. "An RTI system provides current images of the location of people and their movements but cannot be used to identify a person."

The technique can't distinguish good guys from bad guys, but it can tell emergency personnel where people are located in a hostage situation or keep police from entering a building during a dangerous event.

Patwari said the method still needs some improvements and could be improved to detect people in a burning building. Wilson believes it could be used in a "smarter alarm system" for homes.

"Not only would your security system be triggered by an intrusion, but you could track the intruder online or over your phone," Wilson said. It could even be used to study where people spend time in stores, which displays are effective in marketing to consumers and more.

Radio image tracking could also help in caring for the elderly, who "want to stay in their homes but don't want a camera in their face all day," Wilson said. The images could track a person to see when they get up, where they go and if they've fallen down and can't get up.

Wilson demonstrated radio tomographic imaging during a mobile communication conference last year and won the MobiCom 2008 Student Research Demo Competition. The researchers now have a patent pending on the method.

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"I have aspirations to commercialize this," Wilson said of the method, which is currently in the testing stages. He has since founded a spin-off company named Xandem Technology LLC, in Salt Lake City, which will market the technology once it is made available.

The researchers are constantly refining the method and developing new potential uses for it, including automatic control of lighting, heating and air conditioning in buildings and perhaps directing sound to where people are located.

The authors' studies are expected to be published soon in IEEE Transactions on Mobile Computing, a journal of the Institute of Electrical and Electronics Engineers.

Video demonstration: