Radar Flashlight project promises COTS-based human vital signs sensor

ATLANTA-It is a moonless night. Outside a friendly defended perimeter, a soldier in a listening post hears leaves rustle 30 meters away. The wind? An animal? An enemy patrol? The soldier points a slim black tube the size of a long police flashlight toward the noise. Within seconds, the Radar Flashlight has distinguished definitively between harmless night noises and approaching foes.

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By Wilson Dizard III

ATLANTA-It is a moonless night. Outside a friendly defended perimeter, a soldier in a listening post hears leaves rustle 30 meters away. The wind? An animal? An enemy patrol? The soldier points a slim black tube the size of a long police flashlight toward the noise. Within seconds, the Radar Flashlight has distinguished definitively between harmless night noises and approaching foes.

It is the aftermath of a battle. In the rubble of a bombed-out town, a patrol searches buildings cautiously. Last-ditch defenders lurk in some crannies, while trapped civilians may survive under piles of rubble. Using the same Radar Flashlight technology now under development at Sensors and Electromagnetic Research Laboratory of the Georgia Institute of Technology in Atlanta, patrolling troops can sense the presence of the living through thick concrete walls or under collapsed wooden roofs.

Gene Greneker, senior research scientist with the Georgia Tech Research Institute, has developed laboratory versions of a product that holds promise as a dual-use technology for sensing the presence of humans behind concrete, wood, brick walls, and steel doors. The system, known now as the Radar Flashlight, uses commercial off-the-shelf (COTS) technology throughout.

"The Radar Flashlight system uses Doppler radar technology coupled with very fast signal processors," Greneker explains. Developments in commercially available signal processor (DSP) boards over the past decade are making fast Fourier transform calculations and very "sharp" filters necessary to distinguish human vital signs from clutter returns available at affordable prices, he says.

The system uses a commercially available antenna that serves as a microwave lens to focus the output beam into an arc of 15 to 20 degrees. Greneker declines to specify the exact components of the antenna and the signal processors that comprise the system, as it has commercial potential.

The Radar Flashlight is designed to sense the movement of the human thorax resulting from a heartbeat or breathing. The signal it receives is based on a homodyne microwave antenna. Greneker`s work began with 24.1 GHz microwaves. Now he is working with antennas that produce microwaves near 10.525 GHz because they penetrate walls more effectively than the higher-frequency microwaves.

The system`s signal processor essentially acts as a low-pass filter that ignores frequencies above the highest heart rate expected. The first filter rejects ambient clutter signals such as those from fluorescent lights. The analog time domain signal feeds into an analog to digital converter that converts the input to a 12-bit word, Greneker says. DSPs then discard clutter resulting from body motion and sensor motion.

"The signal from the Radar Flashlight will penetrate clothes and detect respiration through a heavy jacket," Greneker says. "In fact, the Radar Flashlight requires a body movement of only a few millimeters to detect human presence."

The amount of electromagnetic radiation exposure to a target individual from the system is very small, about 10 times less than the exposure leakage level allowed from microwave ovens in the U.S.

Research that evolved into the Radar Flashlight began in the mid-1980s, as a means of remotely checking the vital signs of battlefield wounded. The project went into abeyance until Greneker developed a system for the 1996 Olympic Games in Atlanta that could remotely sense and display how competition marksmen shoot only during their heart`s off-beats, to avoid the 5 milliradian motion a heartbeat imparts to a bow or rifle shooter`s arm.

Greneker wants to explore ways to further reduce clutter. "This is a challenge," he says. "The amount of signal returned from the chest area of a moving person due to body motion alone is approximately 1,000 to 10,000 times the heartbeat signature. We are working on a clutter-suppression algorithm to use in the Radar Flashlight`s signal processor circuit."

Greneker adds that because the system`s radar is sensitive enough to detect small motions of humans, it is also sensitive enough to detect its own motion. "When the platform [the Radar Flashlight itself] is moving, we have to be able to sense that and cancel that," he says.

One approach is to generate a signal 180 degrees out of phase with the motion of the platform to cancel out the undesirable signal. "We have asked the National Institute of Justice [an arm of the U.S. Justice Department] to fund research we believe is necessary to achieve platform stabilization," Greneker says. He declined to specify the amount of the grant request, but says it was less than $1 million and that Justice Department officials are due to decide on the application by the end of August.

"We have talked to the law enforcement community and they have shown interest in the technology," Greneker says. He notes that systems for sensing human presence would be of great value to police officers who must serve warrants to violent criminals, and sometimes arrest them in the process. Knowing whether a potentially armed suspect is hiding in a closet in a building where police are searching is one potential use.

Greneker says his goal is to produce a system that would cost about as much as a high-end police weapon - about $300 to $500 per unit. "Volume production could reduce that cost," he adds. "For example, the signal processor could be reduced to a chip set."

Because the Radar Flashlight is intended for marginally trained personnel, it may offer a simple indicator of the presence or absence of a human - perhaps even a red or green light indicator. "The goal is to have the signal processor do all the work," Greneker says, noting that his cost goal highly influenced the choice of COTS components. "Take the antenna for example. You can`t go out and design a custom component for a $500 target price."

Other potential civilian uses of the technology are for prison guards making bed checks, rescue workers searching for persons buried by collapsed buildings or landslides, and for police coping with hostage situations. The ability of the Radar Flashlight to distinguish human heart rate signals may permit its use as a biometric identification device as well.

In the medical field, technicians could use the technology developed in the Radar Flashlight project to gather and record vital signs of patients who are physically or mentally incapable of cooperating with normal heartbeat and respiration equipment. For example, it can sense vital signs of burn patients without touching their skin.

In military medicine, the system could monitor the vital signs of soldiers wearing chemical and biological warfare gear without removing their protective suits.

"We`d like to get the Pentagon involved," Greneker says. "Finding the right entry point has been a problem." For further information on the project, check the World Wide Web at http://www.gtri.gatech.edu/ res-news/FLASH_SP.html.

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Georgia Tech researchers hold the new Radar Flashlight, which detects human breathing and heartbeat. The device offers several military applications.

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