False positive detections account for a great part of the expense associated with unexploded ordnance (UXO) remediation. Presently fielded systems like pulsed electromagnetic induction systems and cesium-vapor magnetometers are able to distinguish between UXO and other metallic ground clutter only with difficulty. The discovery of giant magnetoresistance (GMR) has led to the development of a new generation of integrated-circuit magnetic sensors that are far more sensitive than previously available room-temperature-operation electronic devices. The small size of GMR sensors makes possible the construction of array detectors that can be used to image the flux emanating from a ferrous object or from a non-ferrous object with eddy currents imposed by an external coil. The purpose of a GMR-based imaging detector would be to allow the operator to easily distinguish between UXO and benign objects (like shrapnel or spent bullets) that litter formerly used defense sites (FUDS). In order to demonstrate the potential of a GMR-based imaging technology, a crude magnetic imaging system has been constructed using commercially available sensors. The ability to roughly determine the outline and disposition of magnetic objects has been demonstrated. Improvements to the system which are necessary to make it into a high-performance UXO detector are outlined.

The goal of the project was to demonstrate the feasibility of the detection of buried unexploded ordnance (UXO) using giant magnetoresistive (GMR) sensor arrays. 3x3 and 5x5 arrays of off-the-shelf GMR sensors were purchased from Nonvolatile Electronics (NVE) and were interfaced with a data acquisition card and a personal computer. Magnetic images were obtained from a number of ferrous objects, such as threadstock, bolts, and rebar. These images can be interpreted in terms of the remanent magnetic state of the objects. The ability of the GMR sensor approach to discriminate among magnetic objects is assessed and the design of a more realistic UXO detection system is discussed.