Robust Multi-Sensor Detection of Polymorphic NQR Signals

Nuclear quadrupole resonance (NQR) is a radio frequency (RF) technique, able to distinguish between polymorphic forms of compounds containing quadrupolar nuclei, a requirement fulfilled by many high explosives and narcotics. To alleviate the problems of low signal to noise ratio and strong RF interference in NQR detection, various multi-sensor NQR signal detection algorithms have recently been proposed. These algorithms, however, assume the presence of a single polymorph with its associated amplitudes known to within a scaling, and any error in this a priori information will lead to performance degradation. In this paper, we develop a robust multi-sensor hybrid algorithm able to process NQR signals from multiple polymorphs while allowing the associated amplitudes to vary within an uncertainty hyper-sphere. Numerical investigations indicate that the proposed algorithm provides significant performance gains as compared to existing algorithms when there are multiple polymorphs present and/or when uncertainties in the amplitudes exist.