Under funding from the Air Force Research Laboratory at Hanscom Air Force Base, Quantum Magnetics has been developing a room temperature, multi-axis magnetic gradiometer for the detection and characterization of underground structures. The gradiometer uses small, inexpensive, but highly sensitive magnetoresistive (MR) sensors operating with a flat frequency response from DC to several MHz and employs an innovative sensor configuration; called the three-sensor gradiometer (TSG) invented at IBM. The TSG affords unprecedented dynamic range that enables detection of signals near the sensor noise floor even when the system is in motion in the earth's field. The wideband response and high sensitivity of these sensors make them ideal for both passive and active detection techniques. A single sensor can detect perturbations in the earth's magnetic field from ferrous materials used in the construction of the structure, emissions at power and mechanical frequencies from equipment within the structure, and eddy currents in metallic materials within the structure induced by externally applied probe signals. These complimentary data sets can be combined in a sensor fusion scheme to minimize sensor clutter and discriminate against false targets. The sensing technology under development supports deployment by way of unattended ground sensors as well low-flying unmanned aerial vehicles.
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