Active underwater detection with an array of atomic magnetometers

We report on a 2 × 2 array of radio-frequency atomic magnetometers in a magnetic induction tomography configuration. Active detection, localization, and real-time tracking of conductive, nonmagnetic targets are demonstrated in air and saline water. Penetration in different media and detection are achieved thanks to the sensitivity and tunability of the sensors, and to the active nature of magnetic induction probing. We obtained a 100% success rate for automatic detection and a 93% success rate for automatic localization in air and water, up to 190 mm away from the sensor plane (100 mm underwater). We anticipate magnetic induction tomography with arrays of atomic magnetometers finding applications in civil engineering and maintenance, the oil and gas industry, geological surveys, marine science, archeology, search and rescue, and security and surveillance.