Patent ID: 6204667
Filing Date: 2001-03-20
Classification: G01V

Abstract:
An electromagnetic field gradiometer, comprising:a) a transmitter for generating a time varying primary electromagnetic field and inducing a secondary electromagnetic field about a hidden object;b) a primary detector having a first sense and disposed at a first location for measuring the strength of the combined primary and secondary electromagnetic fields at said first location and for generating a first output based on said strength;c) a plurality of secondary detectors having a sense and disposed at a plurality of secondary locations for measuring the strength of the combined primary and secondary electromagnetic fields at said secondary locations simultaneously with the measurement of said combined primary and secondary electromagnetic field at said first location by said primary detector; wherein said sense of said secondary detectors is opposite said first sense; each of said secondary detectors generating a secondary output indicative of said strength of the combined primary and secondary electromagnetic fields at the respective secondary location;d) a logic circuit for selectively combining said first output with said secondary outputs; ande) wherein said electromagnetic gradiometer determines a plurality of gradients of said secondary electromagnetic field based on said combined first output and said selected secondary outputs and the distance between said first location and the respective secondary locations.