Radiator-excited cavity for nqr detection

Abstract

Nuclear quadrupole resonance measurement using two or more wire loop(s) within a space to define a portal, and driving the wire loop(s) with a baseband digital transmitter generating a chirped or stepped signal, to create a corresponding varying electromagnetic field within the portal. Coherent emissions reflected thereby are detected through a directional coupler feeding the transceiver. The detected coherent emissions are processed with a matched filter to determine presence of a target object within the portal.

What is claimed is: 
     
         1 . A method for detecting a substance comprising:
 disposing a first and second planar conductive surface in parallel with one another and spaced apart from one another to define a space between them;   disposing a first wire conductor within the space, the first wire conductor having a first end and a second end, the second end electrically terminated through a resistance to the first conductive surface;   disposing a second wire conductor within the space, the second wire conductor having a first end and a second end, the second end electrically terminated through a resistance to the second conductive surface;   driving the first and second wire conductors with a baseband chirped radio frequency transmitter through a directional coupler to create a time varying electromagnetic field within the space;   receiving resulting coherent radio frequency emissions through the same directional coupler through which the transmitter is coupled; and   is processing the coherent radio frequency emissions with a radio frequency filtering step to determine characteristics of a substance in the space.   
     
     
         2 . The method of  claim 1  additionally comprising:
 disposing a third and fourth conductive surface adjacent the first and second conductive surface to define the space as a generally rectangular portal. 
 
     
     
         3 . The method of  claim 1  wherein the first wire conductor is disposed within the space adjacent the first conductive surface, and the second wire conductor is disposed within the space adjacent the second conductive surface. 
     
     
         4 . The method of  claim 1  additionally comprising:
 disposing multiple wire conductors adjacent one another and adjacent a selected conductive surface. 
 
     
     
         5 . The method of  claim 4  with adjacent wire conductors driven with radio frequency signals of alternating polarities. 
     
     
         6 . The method of  claim 1  additionally comprising:
 detecting a portion of transmitter power with a directional coupler, to provide a reference signal, and where the step of processing the coherent emissions further uses the reference signal to determine characteristics of the substance. 
 
     
     
         7 . The method of  claim 1  wherein the stimulated emissions are limited to between about 10 −8  and 10 −13  of the transmitted energy incident on the space. 
     
     
         8 . The method of  claim 6  wherein the directional coupler has a linear response. 
     
     
         9 . The method of  claim 6  wherein the directional coupler is free of ferrite material that would otherwise introduce non-linearities. 
     
     
         10 . An apparatus for detecting a substance comprising:
 a first planar conductive surface;   a second planar conductive surface;   the first and second planar conductive surfaces spaced apart from each other and disposed in parallel with each other to define a space between the first and second planar conductive surfaces;   a first wire conductor disposed adjacent the first planar conductive surface and disposed within the space, the first wire conductor having a first end and a second end, the second end electrically terminated through a resistance to the first conductive surface;   a second wire conductor disposed adjacent the second planar conductive surface and disposed within the space, the second wire conductor having a first end and a second end, the second end electrically terminated through a resistance to the second conductive surface;   a chirped radio frequency transmitter coupled to the second end of the first wire conductor and to the second end of the second wire conductor, to create a time varying electromagnetic field within the cavity, the time varying electromagnetic field stimulating continuous transitions between two energy states in the nucleus of a substance disposed within the space; and   a radio frequency receiver for receiving resulting coherent radio frequency emissions from the substance.   
     
     
         11 . The apparatus of  claim 10  additionally comprising:
 a third conductive surface extending between the first and second conductive surfaces; 
 a fourth conductive surface extending between the first and second conductive surfaces at a location opposite the third conductive surface; 
 wherein 
 the first end of the first conductor is located adjacent the third conductive surface; 
 the second end of the first conductor is located adjacent the fourth conductive surface; 
 the first end of the second conductor is located adjacent the third conductive surface; and 
 the second end of the first conductor is located adjacent the fourth conductive surface. 
 
     
     
         12 . The apparatus of  claim 11  wherein multiple wire conductors are disposed adjacent one another and adjacent a same selected one of the conductive surfaces. 
     
     
         13 . The apparatus of  claim 12  wherein the multiple wire conductors are disposed with adjacent ones of the wire conductors driven with radio frequency signals of alternating polarities. 
     
     
         14 . The apparatus of  claim 10  additionally comprising:
 a first directional coupler, connected between the transmitter and the first and second wire conductors. 
 
     
     
         15 . The apparatus of  claim 14  additionally comprising:
 a second directional coupler, connected to detect a portion of transmitter power as a reference signal. 
 
     
     
         16 . The apparatus of  claim 10  wherein multiple wire conductors are disposed adjacent one another and adjacent a same selected one of the conductive surfaces.