By John McHale
STATE COLLEGE, Pa. - University and military scientists have wedded computer-based feedback control to a 50-year-old laboratory technology to develop a land-mine detector that identifies plastic-encased mines that are invisible to traditional metal detectors and ground-penetrating radar.
The detector, designed by engineers at Pennsylvania State University in State College, Pa., and the U.S. Army`s Construction Engineering Research Laboratory in Champaign, Ill., uses nuclear quadruple resonance (NQR) spectroscopy, an analytical tool developed in the late 1940s and early 1950s for crystal structure studies, combined with the feedback control algorithms.
The Chinese type 72 land mine, for example, is plastic and current devices cannot pick it up. It poses a serious problem that an NQR device can solve, says Jeffrey L. Schiano, Pennsylvania State assistant professor of electrical engineering and co-inventor of the detector with Mark D. Ginsberg, principal investigator at Construction Engineering Research Laboratory. The scientists dubbed the device fNQR with the f standing for feedback.
In the 1960s and 1970s, researchers in the U.S. and Russia independently developed experimental NQR-based detectors for use in mine fields, Schiano says. More recently, commercial NQR-based systems have been developed in the U.S. and in Britain for narcotics and explosive detection in airline baggage.
Hampering all of these instruments, however, is the small, short-duration NQR signal from explosives that background noise easily drowns out, he says.
The scientists have shown that they can overcome these problems by applying feedback control concepts to enhance the signal and separate it from background noise, Schiano says. For example, in operation, the fNQR, like the other NQR devices available, sends out a radio frequency pulse which can disturb the nuclear magnetization of nitrogen-based explosives, such as TNT, he explains. The disturbance in the nitrogen nuclei, in turn, produces a characteristic NQR signal, which is recorded on a graph, Schiano adds.
However, unlike the other available NQR-based detectors, the new detector is equipped with feedback control algorithms that automatically increase or decrease the repetition rate of the radio frequency pulse and quicken or slow the time that elapses between the creation and collapse of the disturbance in the nuclear magnetization, he continues. In this way, the Pennsylvania State detector can compensate for weak NQR signals or excessive background noise, Schiano says. In addition, the feedback algorithms enable the new detector to automatically calibrate itself, making it easy to operate even for unskilled personnel, he says.
Basically feedback technology enables precise fine-tuning of signals, resulting in a more accurate scan, Schiano says. The only drawback is feedback takes longer than other methods, he adds.
U.S. Navy researchers in San Diego developed an NQR device during the Vietnam war, but it did not use feedback technology, Schiano continues. "It is the further application of feedback concepts that will improve, if not enable, the use of NQR in land-mine detection," he says.
Scientists at Quantum Magnetics in San Diego are working on a hand-held device, with funding from The Defense Advanced Research Products Agency, better known as DARPA, Schiano says. While their device is smaller than the Penn State device, it uses fixed parameters instead of feedback algorithms, he explains.
The Pennsylvania State model is about 25 pounds and consists of a liquid crystal display attached to metal-detector like device with the electronics located in a satchel on the operator`s shoulder, Schiano says.
However, the device does not detect mines encased in metal, because metal blocks the radio frequency signal, Schiano adds. NQR will not replace current technology, but "I see it marrying with ground penetrating radar and other technologies" to create a more efficient mine-detection effort, he says.
Since the new device detects explosives based on their unique NQR response, there are fewer false alarms than with older devices, Schiano claims. The new NQR device reacts to the explosive not the metal case, shrapnel, or other clutter as metal detectors used for de-mining do, he says.
Normally when a detector is searching a bomb, a strong signal indicates without a doubt that a mine has been detected, Schiano says. With the fNQR, if a faint signal is detected and cannot initially be differentiated from background noise, the feedback algorithms are alerted and enhance the signal to verify if the target is a mine, thereby cutting down on false alarms, he explains.
Schiano was unable to provide data on the difference in false alarm rates because the data on the detectors has not been published, he says.
Ground-penetrating radar, another de-mining technique, does not perform well in dry soil and produces false positives from rocks and tree roots, the Penn State scientists say. Chemical sniffers, which can detect the presence of mines in a general area, cannot pinpoint their location as accurately as NQR can, the scientists claim.
U.S. mine specialists now poke a rod into the ground by hand to locate land mines, Schiano says. Feedback NQR promises to be safer and more accurate, he adds.
Currently, the device has been tested only with the nitrogen-bearing compound, sodium nitrite, rather than TNT or other explosives. fNQR can detect RDX and the combination of RDX and TNT, called Comp B; but not TNT, which is too unstable, Schiano says. Scientists have still not found the silver bullet for land-mine detection, he adds.
Pennsylvania State was specifically funded to demonstrate new techniques and technology in land mine detection, he says. Quantum received more funding for their hand-held device than we did, he says.
"Eventually if we receive the funding we should have a hand-held device within two years," he says. Currently the university scientists are working on methods to determine the burial depths of mines, Schiano adds.
For more information on fNQR contact Barbara Hale at Pennsylvania State University by phone at 814-865-9481, by email at [email protected] or on the World Wide Web at http//:www.psu.edu/ur/.