Method and apparatus for operating an arrangement of gradiometers

Abstract

A magnetic screening system uses directional gradiometers with high resolution and accuracy to measure magnetic field signatures of target objects (e.g., gun, knife, cell phone, keys) in a volume of interest. The measured signatures can be compared to signatures of known objects stored in a local database. Various mathematical processes may be used to identify or classify target object signatures. In a network of magnetic screening systems, the magnetic screening systems can transmit signatures to a central signature database, and a management computer can share the central signature database with all of the magnetic screening systems on the network. The magnetic screening system can operate in multiple modes, such as a tracking mode, measurement mode, and self-test mode. Through use of unique processes and designs, the magnetic screening system can achieve a high rate of processing persons for target objects.

1 . A magnetic field sensing device, comprising:
 an arrangement of gradiometers, each including at least three magnetometers; and   a processor in communication with the magnetometers that scales the outputs from the magnetometers with unequal weights and combines the scaled outputs to orient a direction of sensitivity of the respective gradiometer toward a volume of interest.   
     
     
         2 . The device according to  claim 1  wherein the processor scales the outputs with non-integer weights. 
     
     
         3 . The device according to  claim 2  wherein the processor uses output weights calculated using a deterministic mathematical technique. 
     
     
         4 . The device according to  claim 1  wherein the processor adjusts the output weights digitally. 
     
     
         5 . The device according to  claim 1  wherein the processor adjusts the output weights in real-time. 
     
     
         6 . The device according to  claim 1  wherein spacing of the magnetometers is determined before the output weights are determined. 
     
     
         7 . The device according to  claim 1  wherein the outer two magnetometers are arbitrarily positioned, and the magnetometers are positioned relative to the outer magnetometers to orient the direction of sensitivity toward the volume of interest. 
     
     
         8 . The device according to  claim 1  wherein the number of magnetometers and associated weights are selectable to develop arbitrary response patterns. 
     
     
         9 . The device according to  claim 1  wherein the gradiometers are uniaxial. 
     
     
         10 . The device according to  claim 1  wherein the gradiometers are electromagnetically passive. 
     
     
         11 . The device according to  claim 1  wherein the arrangement of gradiometers define at least one boundary of the volume of interest. 
     
     
         12 . The device according to  claim 1  wherein the arrangement of gradiometers define a portal. 
     
     
         13 . The device according to  claim 1  wherein an arrangement of gradiometers on a first boundary sense disturbance external from the volume of interest on an opposite side of a second boundary, but gradiometers on the second boundary closer to the disturbance do not sense the disturbance. 
     
     
         14 . The device according to  claim 1  wherein the processor causes the arrangement of gradiometers to operate in a tracking mode in which a plurality of the gradiometers generate real-time tracks of target objects in three dimensions. 
     
     
         15 . A method of sensing a magnetic field, comprising:
 applying unequal weights to outputs of at least three magnetometers in a gradiometer in an arrangement of gradiometers; and   combining the unequally weighted outputs to orient a direction of sensitivity toward a volume of interest.   
     
     
         16 . The method according to  claim 15  wherein scaling the outputs includes scaling the outputs with non-integer weights. 
     
     
         17 . The method according to  claim 15  further including calculating the weights using a deterministic mathematical technique. 
     
     
         18 . The method according to  claim 15  further including adjusting the weights digitally. 
     
     
         19 . The method according to  claim 15  further including adjusting the weights in real-time. 
     
     
         20 . The method according to  claim 15  further including determining spacing of the magnetometers before determining the weights. 
     
     
         21 . The method according to  claim 15  further including arbitrarily positioning the outer two magnetometers and positioning other magnetometers in the gradiometer relative to the outer magnetometers to orient the direction of sensitivity toward the volume of interest. 
     
     
         22 . The method according to  claim 15  further including selecting a number of magnetometers and associated weights to develop arbitrary and associated weights to develop arbitrary response patterns. 
     
     
         23 . The method according to  claim 15  further including operating the magnetometers with processing assuming uniaxial alignment in the gradiometer. 
     
     
         24 . The method according to  claim 15  wherein the gradiometers are electromagnetically passive. 
     
     
         25 . The method according to  claim 15  further including taking measurements and with the arrangement of gradiometers defining at least one boundary of the volume of interest. 
     
     
         26 . The method according to  claim 15  further including taking measurements with the arrangement of gradiometers defining a portal. 
     
     
         27 . The method according to  claim 15  further including taking measurements and sensing a disturbance external from the volume of interest on a side opposite a first boundary defined by the arrangement, but not sensing the disturbance by the gradiometers defining a second boundary on a side closer to the disturbance. 
     
     
         28 . The method according to  claim 15  further including operating the arrangement of gradiometers in tracking mode by configuring a plurality of the gradiometers to generate real-time tracks of target objects in three dimensions. 
     
     
         29 . A magnetic field sensing device, comprising:
 an arrangement of gradiometers, each gradiometer including at least three magnetometers;   means for scaling outputs from the magnetometers with unequal weights; and   means for combining the unequally weighted outputs to orient a direction of sensitivity toward a volume of interest.