Dipole moment detector and localizer

A method of detecting and localizing a magnetic dipole using an array of spatially distributed magnetic sensors, said method comprising the steps of:

• a) collecting a set of actual magnetic field measurements of a magnetic dipole using a plurality of magnetic sensors;
• b) filtering the actual magnetic field measurements using a predetermined filter;
• c) storing position matrices corresponding to hypothesized locations of the magnetic dipole relative to the array of sensors;
• d) estimating the orientation and magnitude of the dipole from the magnetic field measurements using an electromagnetic moment equation that generates a minimum least-squares estimate that minimizes the sum of squared errors between the actual magnetic field measurements and magnetic field measurements that would be generated by a dipole having an optimal orientation and magnitude;
• e) computing expected magnetic field measurements that would be generated at the sensors by the dipole having the optimal orientation and magnitude;
• f) filtering the expected magnetic field measurements using the predetermined filter;
• g) comparing the actual magnetic field measurements with the expected magnetic field measurements;
• and
• h) repeating steps c) through g) for all hypothesized locations within the detection range of the array of magnetic sensors to detect and localize the magnetic dipole.

Apparatus for detecting and localizing a magnetic dipole comprising:

• an array of magnetic sensors;
• processing means coupled to the array of magnetic sensors, for storing position matrices corresponding to hypothesized locations of the magnetic dipole relative to the array of sensors, for estimating magnetic field values comprising the orientation and magnitude of the dipole at said plurality of hypothesized locations from magnetic field measurements using an electromagnetic moment equation that generates a minimum least-squares estimate that minimizes the sum of squared errors between the actual magnetic field measurements and magnetic field measurements that would be generated by a dipole having an optimal orientation and magnitude, for collecting magnetic field signals indicative of the magnetic field measured at each of the sensors in the presence of the magnetic dipole that is to be detected to provide measured magnetic field values, for removing spatial and temporal variations in the magnetic field measured at each of the sensors by temporally and spatially filtering the measured magnetic field signals, for correlating the measured magnetic field values with each of the estimated magnetic field values by multiplying the estimated magnetic field values with the measured magnetic field values and summing the results over the array of sensors, for identifying the location of the dipole if one of the correlations has a significantly larger value than the others and if it is greater than a predetermined threshold, and if the trajectory location of the dipole corresponds to the location represented by the measured magnetic field signals that produced in the significantly larger value;
• and
• display means for displaying the location of the identified dipole.