The Atto-Tesla magnetometer

The MEA (magnetic expansion amplifier) magnetometer design achieves 25e-18 Tesla/√Hz sensitivity under favorable environmental conditions. The earth's magnetic field is 200 billion times larger. The MEA-based magnetometer operates at ocean temperatures, whereas the most sensitive predecessors require molten metal or cryogenics to get a fraction of the sensitivity. The passive, low-power MEA design detects a frogman pushing a few cubic meters of contraband through a harbor entrance. Small military submarines are detectable even if they use magnetic anomaly countermeasures. Underwater objects seldom match the diamagnetism of water exactly, causing them to bend the earth's magnetic field very slightly. Modeling the perturbation with a single magnetic moment (current loop) gives sufficient accuracy at distances far from the object. Other applications include mineral prospecting, locating buried or sunken objects, earthquake prediction, material studies, and passive detection of land mines.