Objective

Future advanced unexploded ordnance (UXO) detection and discrimination systems may require a combination of alternating current (AC) electromagnetic (EM) and direct current (DC) magnetic (Mag) measurements and 3-axis vector sensors to provide characterization of target shape and reduce the false alarm rate. The need for independent EM and Mag measurements increases system size, weight, and cost. Furthermore, a rigorously co-located measurement of the EM and Mag target response is difficult to achieve in practice. Present EM sensors used for UXO detection are predominantly air-core induction coils of order 0.5-m diameter (e.g., the EM61 coil has a size of 0.5 m x 1m, and the EM63 coil has a size of 1m x 1m), a fact that makes them bulky and difficult to integrate into a compact 3-axis configuration. To measure the DC field, a second sensor, usually an optically pumped magnetometer (OPM), is required. An OPM is a total field sensor that does not contain vector information. A fluxgate magnetometer has sufficient sensitivity for DC measurement of UXO. It is much cheaper than an OPM. However, using a separate induction sensor and fluxgate in close proximity is problematic because the signal detected will be dominated by the high permeability core and metal components of the other sensor, rather than by the target.

The objective of this project was to develop and demonstrate a single compact receiver that operates both as a fluxgate magnetometer to sense DC magnetic fields and as an electromagnetic induction sensor for AC magnetic fields, using the same high-permeability material for both sensors.