Electromagnetic Induction Response Of Spherical Conductors Measured With The Gem-3 Sensor, And Compared To Analytic Models

Currently, most unexploded ordnance (UXO) remediation is carried out with magnetic and<br>electromagnetic induction (EMI) sensors. While highly effective in detecting metallic objects<br>such as UXO, present field techniques also result in many false targets from metallic scrap. To<br>reduce the cost of digging non-UXO, discrimination techniques are required. One approach to<br>UXO discrimination is to recognize features from broadband EM1 data that reflect the shape of<br>the target only, while filtering out other features which may relate to target depth, orientation,<br>sensor-dependent signals, or combinations of these factors. A thorough calibration of the sensor<br>against targets of known shape and material properties is required for proper interpretation of<br>field data. Toward this goal, controlled measurements were made using the GEM-3 (FDEM)<br>sensor on spherical conductors of various sizes at several distances. These data generally<br>compare very well against the analytic solution for a sphere in a spatially uniform, time varying<br>magnetic field, despite the fact that the GEM-3 sensor produces a primary field that is not<br>spatially uniform.