July 7, 1998 University Park, Pa -- By adding state-of-the-art computer-based feedback control concepts to a decades-old analytical laboratory technology, a Penn State-led team has developed a prototype land mine detector that promises to be safer, more accurate and easier to operate than existing models.
Dr. Jeffrey L. Schiano, Penn State assistant professor of electrical engineering, and Dr. Mark D. Ginsberg, principal investigator, at the U.S. Army's Construction Engineering Research Laboratory, developed the detector which is the first to apply feedback technology along with nuclear quadrupole resonance (NQR) spectroscopy, an analytical tool developed in the late 1940s and early 1950s for crystal structure studies. They recently filed a patent disclosure for their concept and have also presented their findings at scientific meetings, most recently at the 39th Experimental Nuclear Magnetic Resonance Conference in California.
Schiano says that in the 1960s and 1970s, researchers in the U.S. and Russia each independently developed experimental NQR-based detectors for use in mine fields. More recently, commercial NQR-based systems have been developed in the U.S. and in Britain for narcotics and explosive detection in airline baggage. However, all of these instruments are hampered by the fact that the NQR signal generated by explosives is small, easily drowned out by background noise and has a short duration.
Schiano and Ginsberg have shown that they can overcome these problems by applying feedback control concepts to enhance the signal and separate it from background noise. For example, in operation, their detector, like the other NQR devices available, sends out a radio frequency (RF) pulse which can disturb the nuclear magnetization of nitrogen-based explosives, such as TNT. The disturbance in the nitrogen nuclei, in turn, produces a characteristic NQR signal, which is recorded on a graph.
However, unlike the other available NQR-based detectors, Schiano and Ginsberg's new device is equipped with feedback control algorithms that automatically increase or decrease the repetition rate of the RF pulse and quicken or slow the time that elapses between the creation and collapse of the disturbance in the nuclear magnetization. In this way, their detector can compensate for weak NQR signals or excessive background noise. In addition, the feedback algorithms enable the new detector to automatically calibrate itself, making it easy to operate even for unskilled personnel.
Since the new device detects explosives based on their unique NQR response, there are fewer false alarms than with older devices. The new NQR device reacts to the explosive not the metal case, shrapnel or other clutter as metal detectors used for de-mining do.
Ground penetrating radar, another de-mining technique, does not perform well in dry soil and produces false positives from rocks and tree roots. Chemical sniffers, which can detect the presence of mines in a general area, can't pinpoint their location as NQR can.
Prodding or poking a rod into the ground by hand is currently the technique that is most often employed to locate land mines. Feedback NQR promises to be safer and more accurate.
Currently, the device has been tested only with the nitrogen- bearing compound, sodium nitrite, rather than TNT or other explosives. However the results have been so positive that Schiano says, "It is the further application of feedback concepts that will improve, if not enable, the use of NQR in land mine detection."
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