Frequency selective detection of NQR signals in the presence of multiple polymorphic forms

Nuclear quadrupole resonance (NQR) is a radio frequency (RF) technique that detects compounds in the solid state and is able to distinguish between different polymorphic forms of certain compounds. For example, a typical sample of trinitrotoluene (TNT) will contain at least two polymorphic forms with rather different NQR properties. In this paper, we propose a frequency selective hybrid detector that exploits the presence of such polymorphic forms. The presented detector offers both improved probability of detection, as compared to recently proposed detectors, and allows for an estimation of the relative proportions of the multiple polymorphic forms.