Landmine detection using feedback NQR

Nuclear quadrupole resonance (NQR) is well suited for detecting land mines with non-metallic cases. It provides both spatial localization and chemical identification of explosives. A search coil produces a train of radio frequency (RF) magnetic pulses that perturb the orientation of nitrogen nuclei contained within the explosive material. Following each RF pulse, the nuclei rotate back to orientations of lower energy. As the nitrogen nuclei possess a magnetic moment, their motion following an RF pulse induces a detectable voltage in the search coil. The NQR signal strength depends on the amplitude, frequency, duration and repetition rate of the applied RF pulses. The optimal selection of RF parameters requires knowledge that is not available in practice, such as the location of the explosive with respect to the search coil. Existing NQR detection systems sacrifice signal intensity by using fixed pulse parameters. We demonstrate that feedback control provides a means for automatically adjusting multiple pulse parameters so that the maximum NQR signal strength is obtained. The advantages afforded to landmine detection using feedback NQR are summarized.