Superconducting Magnetic Gradiometers for Mobile Applications with an Emphasis on Ordnance Detection

Abstract

Passive magnetic sensors provide one means to conduct mobile area surveys and search operations, useful for a number of applications, including sea mine countermeasures and the detection of unexploded ordnance and packaged biological, chemical and radioactive waste for environmental cleanup. To date, the generally accepted method for such detection involves the generation of two-or three-dimensional magnetic anomaly field maps, using primarily total-field magnetometers. Sensor configurations measuring spatial gradients of magnetic field offer a new opportunity for better localization and classification. Sensors incorporating Superconducting Quantum Interference Devices (SQUIDS) provide the greatest sensitivity available with current technology for magnetic anomaly detection. During the late 1970’s and early 1980’s, the Naval Surface Warfare Center Coastal Systems Station (CSS) developed the Superconducting Gradiometer/Magnetometer Sensor (SGMS) specifically for mobile operations outside the laboratory environment. This sensor technology utilized niobium superconducting components cooled by liquid helium. The SGMS has demonstrated nagged, reliable performance even onboard airborne and undersea towed platforms. In this article, a general perspective for the use of passive magnetic sensors for mobile operations will be established. The SGMS design will be described in some detail. General design principles underlying its mobile application, fundamental sensor and environmental noise issues, and approaches to compensate for them, will be presented. The magnetic sensor detection and classification concept developed for sea mine countermeasures and results from that demonstration will be discussed. Recent developments and future opportunities, especially encompassing the use of high temperature (high-T_c) superconducting components cooled by liquid nitrogen, will be addressed.