Radio Waves Peer Into Luggage to Find Contraband

Explosives or narcotics concealed in luggage, mailboxes or on a person can't hide from low frequency radio wave pulses which swiftly and safely detect the presence of the offending substance.

Based on technology developed by researchers at the Naval Research Laboratory (NRL) in Washington, D.C.,with support from the Federal Aviation Administration, the Technical Support Working Group of the Department of Defense, and Office of Naval Research, luggage detection equipment is being tested in airports in the U.S. under an NRL license to Quantum Magnetics, Inc., of San Diego, CA.

The technique used to zero in on explosives and narcotics is a process called nuclear quadrupole resonance (NQR). To find the target materials, low frequency radio wave pulses are emitted which momentarily disturbs the alignment of certain nuclei within the material. The pulsing causes the nuclei to realign and send out a unique weak radio signal. A sensor coil, patented by NRL, then hears this signal, which a computer analyzes to determine the presence and type of material found.

NQR is especially effective for land mine detection because today's plastic-encased land mines have tiny metal firing mechanisms that require extremely sensitive metal detectors that also hone in on shell casings, nails and wire - leading to more false alarms than actual mines. With NQR, the explosives, the very essence of the mine, are being detected.

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