System and method for contraband detection using nuclear quadrupole resonance

A system for detecting a target substance within a class of explosives and narcotics containing quadrupolar nuclei in a specimen employing the phenomenon of nuclear quadrupole resonance (NQR), said system comprising:

• a sequence controller configured to provide timing and programming pulses to said system;
• a radio frequency (RF) subsystem comprising a variable frequency RF source to provide pulsed RF excitation at a frequency generally corresponding to predetermined characteristic nuclear quadrupolar resonant frequency of the specimen, wherein nuclear quadrupolar resonant frequency is the frequency of nuclear precession due to quadrupolar interaction with molecular electric field gradients;
• a detection subsystem comprising:
• a distributed RF coil sheet shaped and configured to define a cavity of predetermined volume therein and to receive the specimen within the cavity defined by said RF coil, said cavity having a first end and a second end, the RF signal from said RF source being transmitted within said cavity and being applied to the specimen within said RF coil cavity, said RF coil also functioning as the pickup coil for the NQR signals from the specimen and providing an NQR output signal;
• apparatus for adaptively tuning said RF coil to about the desired characteristic nuclear quadrupolar resonant frequency for the specimen under test;
• and
• an electrically conductive RF shield surrounding and spaced from said RF coil, said RF shield being shaped and configured to provide electromagnetic interference and radio frequency interference (EMI/RFI) shielding from external noise and to prevent RF and magnetic flux from escaping from said RF coil cavity and RF shield combination, said RF shield being an electrically integral part of said RF coil and being shaped and configured to improve the Q and the efficiency of said RF coil and contributing to the effectiveness of the flux field applied to the specimen within said RF coil, said RF coil and RF shield together forming a scanner;
• a signal capture and data processing subsystem comprising:
• a receiver for the NQR output signal from said RF coil;
• a memory which stores characteristics of NQR signals from at least one target substance in the class of explosives and narcotic compounds;
• a processor for the NQR output signal from said RF coil;
• and
• a comparator for comparing characteristics of the processed NQR output signal
• with the characteristics in memory and emitting a final output signal;
• and
• an indicating device receiving the final output signal from said signal capture and data processing subsystem and, in response thereto, said display device indicating the presence of the target substance.