Ultra-Wideband Electromagnetic Induction for UXO Discrimination

Book excerpt: - 18 - The material in this section consists of extracts from, summaries of, and comments on results that appear in more detail in the following chapters of the report. For the most part, literature references are not provided in this section, when they are present adequately in the more detailed report sections. At the inception of the project, reliable, accurate means were needed to analyze EMI UWB target responses, both to identify phenomena in the new frequency frontiers and to integrate them into patterns continuing through the more familiar parts of the EMI band. Much was lacking in this regard in terms of both analytical and numerical models. To address this, formulations were developed to provide analytical solutions, for the first time, for basic non-spherical shapes (elongated and flattened spheroids). A parallel development was also undertaken in the numerical realm, designed to treat arbitrary shapes and material composition, in 3-D, from the low frequency limit to the high frequency limit. Work was successful in - 19 - both realms. All models were based on first-principles physics, in particular Maxwell's fundamental equations of electromagnetics. These are typically simplified somewhat in induction problems, as phenomena are justifiably treated as quasi-magnetostatic (MQS). In mathematical practice, this means that a term is eliminated that contains the time derivative of the electric field. At higher, e.g. radar frequencies, this term cannot be eliminated.