Transmission line array for explosive detection using nuclear quadrupole resonance

Abstract

A transmission line array is used for explosive/contraband detection using nuclear quadrupole resonance in which the array is driven in-phase with synchrony frequency-swept signals. Each of the balanced transmission lines is fed with a low power swept frequency source and stimulated emissions are picked out with a directional coupler. Location is provided using a cross grid array or a phase detector is used for each balanced line, with phase determining the distance to the sensed substance.

1 . In a system for detecting substances utilizing nuclear quadrupole resonance involving detecting of a substance between the elements of a balanced transmission line terminated with a resistive element in which the transmission line is driven through a circulator with a signal having a frequency equal to that of one of the spectral lines of the substance and in which the substance is detected by detection of the stimulated emissions from the substance as an output of the circulator, a method of detecting the substance over a wide area, comprising the steps of:
 providing an array of the balanced transmission lines, each terminated with a resistive element;   simultaneously driving each of the balanced transmission lines in the array with a signal having a frequency equal to that of one of the spectral lines of the substance; and,   detecting along which of the balanced transmission lines stimulated emissions exists.   
     
     
         2 . The system of  claim 1 , and further including the step of detecting the position along a balanced transmission line where the substance is located. 
     
     
         3 . The system of  claim 2 , wherein the step of detecting the position of the substance includes the step of measuring the phase between the input signal coupled to a transmission line and the signal from the transmission line, with the phase indicative of the distance from the feed point of the transmission line at which the substance exists. 
     
     
         4 . The system of  claim 1 , wherein the signals coupled to the balanced transmission lines arc CW signals and wherein the signals are in-phase. 
     
     
         5 . The system of  claim 1 , and further including the steps of sweeping the frequency of the signals coupled to the balanced transmission lines, and detecting in the frequency sweep a stimulated return that matches the return from the substance. 
     
     
         6 . The system of  claim 1 , and further including providing a number of additional terminated balanced transmission lines orthogonal to the first mentioned transmission lines to form a grid. 
     
     
         7 . The system of  claim 6 , and further including the step of determining at which of the crossed balanced transmission lines the substance is simultaneously detected, thus to provide the location of the detected substance. 
     
     
         8 . The system of  claim 1 , wherein the detecting step includes using a network analyzer to provide a complex ratio between a signal coupled to a balanced transmission line and the stimulated return therefrom. 
     
     
         9 . The system of  claim 1 , and further including the step of driving the array without the substance in between any of the balanced transmission lines, thus to provide a baseline measurement, and wherein the detecting step further includes comparing stimulated emission measurement, with the baseline measurement to determine the existence of the substance. 
     
     
         10 . The system of  claim 1 , wherein a substance lies between adjacent balanced transmission lines and wherein the detecting step includes determining the ratio of detected stimulated emission measurements from the adjacent transmission lines to detect the existence of the substance between the adjacent balanced transmission lines and the location thereof.