Piezoelectric suppression for rapid detection of Methamphetamine Hydrochloride via N nuclear quadrupole resonance.

The ability to rapidly detect the presence of narcotic substances in baggage and on personnel is a prime requirement in airports, mail distribution centres and mass screening portals. Nuclear Quadrupole Resonance (NQR) is well-suited to detect selected narcotics as the resonances can be highly discriminating of a given substance due to the presence of narrow, non-overlapping spectral lines. Furthermore, the transparency of non-conductive materials to radio frequency (RF) magnetic fields allows for NQR to measure bulk volumes without any sample preparation. However, NQR as a spectroscopic technique is challenged by a relatively low signal-to-noise ratio (SNR) and the presence of interference sources like sample piezoelectric ringing. For NQR to be an effective tool for narcotics detection, these challenges must be overcome. Results of laboratory NQR measurements of the N ν transition in methamphetamine hydrochloride are presented, occurring at 1.217MHz at room temperature. A confident detection of 200g of pure methamphetamine hydrochloride in a 20L sample coil was achieved in less than one second. In addition, the presence of piezoelectric interference in some smaller samples was investigated and successfully suppressed using electrostatic shielding techniques. The efficacy of the electrostatic shielding design was proven experimentally and further supported through simulation of the electric and magnetic fields within the sample coil.