Patent ID: 6924644

Claim:
A magnetic field gradiometer detector for detecting a material of interest positioned in a detecting region outside the detector, comprising: a transmitter for generating an output signal at a selected frequency; a receiver for detecting the signal; a probe; a switch coupling said receiver and said transmitter with said probe for alternately connecting and disconnecting said receiver and said transmitter to said probe, thereby switching said detector between a transmitting mode and a receiving mode; and wherein said probe comprises a gradiometer coil array including a first surface coil and a second surface coil wound in an opposite sense, said probe has a first side and an opposite second side, and wherein said first and second surface coils are configured asymmetrically such that the probe projects a magnetic field in the outside detecting region adjacent to said first side and is self-shielded on said second side of the probe to thereby detect the material of interest while shielding the detector from outside RF sources.