Bulk Magnetization Effects in EMI-Based Classification and Discrimination
MR-1711
Objective
One of the goals of current research and development activity in SERDP's Munitions Management focus area is developing effective technologies for classifying buried objects as munitions or clutter. That research has shown that electromagnetic induction (EMI) sensors offer the greatest potential for effective classification. There are two basic components in the EMI response to munitions and clutter items: magnetization of the object by the primary field transmitted by the sensor and the evolution of eddy currents set up in the object by changes in the primary field. Most research activity has focused on the latter, leading to the development of sophisticated time domain EMI sensor systems which accurately measure the eddy current response following a transmitted primary field pulse. Although these sensors have proven to be quite effective in classifying buried objects, they do not exploit all of the information that is available in the EMI response. This project will determine the extent to which classification performance can be improved with sensors that exploit the information available in both the bulk magnetization and the eddy current components of the EMI response.
The objectives of this research are to determine the extent to which classification performance can be improved with sensors that exploit the information available in both the bulk magnetization and the eddy current components of the EMI response, and to develop the sensor and processing technology necessary to exploit all of the information available in the EMI response that is useful for classifying buried objects as UXO or clutter.
Technical Approach
The bulk magnetization response produces a demagnetizing field in the object that is related to the applied magnetic field by a demagnetizing factor í. Most munitions items are basically steel cylinders with ~ 4:1 length to diameter aspect ratio. They have demagnetizing factors n ~ 0.1 for an axially applied field, and ~ 0.4 for a transverse field. Demagnetizing factors for clutter items can be anywhere in the range 0 < n < 1. The demagnetizing factor can be extracted from the EM response during times when the primary field is turned on (i.e., the on-time response) by fitting a simple parametric model to the measured response.
Benefits
The characterization and remediation activities conducted at Department of Defense sites contaminated with unexploded ordnance (UXO) using currently available technology often yield unsatisfactory results and are too expensive. In part, this is due to the inability of current technology to distinguish between UXO and non-hazardous items. Indeed, most of the remediation costs at a typical cleanup site are spent on excavating targets that pose no threat. Successful completion of the research proposed here will result in a better understanding of the basic elements of UXO/clutter discrimination and will lead to improved UXO/clutter discrimination performance.
Project Documents
Points of Contact
Principal Investigator
Dr. Thomas Bell
SAIC
Phone: 703-312-6288
Fax: 703-414-3904
Project Documents
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