Plural Frequency method and system for identifying metal objects in a background environment
United States Patent 5654638
Abstract:
A system for detecting metal targets located in a background environment such as the ground evaluates metal targets by processing components of signals at two or more different frequencies. A component of the received signal induced by the ground can be eliminated by subtracting signal components measured at two different frequencies. The received signal can be processed to account for changes in the background response with frequency. The type of an unknown target can be identified by processing background excluded components to produce data characterizing the target type.
http://www.freepatentsonline.com/pdfb/documents/uspt/patent_pdf/5654/US5654638/pdf/US5654638.pdf
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