Bulk Magnetization Effects in EMI-Based Classification and Discrimination
Abstract
The goal of this research project is to develop improved capabilities for classifying buried objects as unexploded ordnance (UXO) or clutter that exploit all of the information available in the electromagnetic induction (EMI) response of the object. There are two basic components in the EMI response: magnetization of the object by the primary field and the evolution of eddy currents set up in the object by changes in the primary field. The first is accessible only with sensors which measure the secondary (induced) response while the primary field is present (on-time response). Such sensors must null out the direct effect of the primary field on the receiver in order to see the much weaker secondary field. Current sensor systems used for classification are transient or time domain EMI (TEM) systems which measure the response after the primary field is shut off. They only measure the eddy current response. The technical objectives for the initial phase of this project are to (1) establish, through analysis and supporting measurements, what the bulk magnetization response adds to classification performance and (2) develop a comprehensive understanding of the engineering challenges of primary field cancellation that can support a rational evaluation of whether or not it is possible to build an instrument that can reliably access both the bulk magnetization response and the eddy current response. This report documents our findings relative to the first of the technical objectives. We used a lab bench setup to measure the on-time response of clutter items that were misclassified as munitions in recent ESTCP classification demonstrations. We find that the demagnetizing factors which characterize the bulk magnetization response do indeed convey information that is useful for distinguishing between smaller munitions items (20 mm, 37 mm etc.) and fragments of exploded larger caliber munitions whose TEM signatures are similar.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 2012
- Accession Number
- ADA578931
Entities
People
- Thomas Bell
Organizations
- Leidos