Characterization Studies Of The Electromagnetic Induction Response Of Compact Metallic Objects For Improved Unexploded Ordnance / Clutter Discrimination

A simple induced dipole model has been found to effectively fit a large collection of measured<br>data over many compact metallic objects using several different types of EM1 sensors. The<br>induced moment is determined by a set of response coefficients that depend on the object’s size,<br>shape, and material properties. To the extent that these response coefficients differ between<br>ordnance and clutter, discrimination using EMI sensors may be possible. Observed differences in<br>the relative strength of these coefficients between flat and long objects have already been applied<br>as a means of shape discrimination. Presently, these coefficients are determined by direct<br>measurement with a given EM1 sensor. In an effort to empirically understand how these<br>coefficients depend on the object, careful measurements have been made as a function of<br>frequency over simple shapes like spheres and cylinders. A baseline model has been found that<br>fits most of the data, even UXO and clutter. To first order, the model parameters can be related<br>to physical parameters. For ferrous cylinders, the frequency response curves can be scaled to<br>cylinder diameter and aspect ratio. From this baseline model, future measurements will try to<br>understand the effects of tapering the cylinders to UXO-like shapes and then the effects of<br>adding fins and driving bands.