Patent ID: 8710837

Claim:
A method for detecting substances including contraband and explosives housed in a metal container, comprising: irradiating the container with electromagnetic energy below 4 MHz utilizing a terminated balanced transmission line outside the container; and, measuring the stimulated emissions from the substance that is the result of nuclear quadrupole resonance utilizing the terminated balanced transmission line, the step of measuring nuclear quadrupole resonance from stimulated emissions including measuring irradiation below 4 MHz, wherein measuring the stimulated emissions includes measuring the stimulated emission spectra of the stimulated emissions, the measuring step including providing a network analyzer having a S21 ratio output and having the capability of generating a signal below 4 MHz coupled to an antenna and having a directional coupler for separating the transmitted signal from the stimulated response signal, the directional coupler being coupled to the network analyzer such that stimulated emission response is measured by the S21 ratio.