ONR Fact Sheet: Multi-Mode Magnetic Detection System (3MDS)

The concept of using magnetic sensors on aircraft to detect submerged submarines has been around for approximately 60 years. Previous generations of Magnetic Anomaly Detection (MAD) sensors were limited in their detection range. Beginning in the late 1990s, investments from the Office of Naval Research (ONR) and other agencies, along with system manufacturer Polatomic, Inc., moved the technology towards laser cell pumping and away from inefficient high-intensity optical lamps. This new method for optical pumping, coupled with improvements in GPS and in processing capability, has enabled this major step in non-acoustic detection of submarine threats.

The Multi-Mode Magnetic Detection System (3MDS) consists of two glass cells filled with He4 molecules that are stimulated by laser light. The precession of the pumped molecules is sensed by fixed coils around cells consisting of several thousand turns of fine wire. Very small changes in the ambient magnetic field cause changes in the precession characteristics and these are sensed by the pickup coils. The pickup cell signals are digitized in the sensor unit. Control of the laser source as well as most other aspects of system operation is also contained in the sensor unit (including GPS, accelerometers, vector magnetometer, etc.). A computer/power unit internal to the aircraft provides serial communications and DC power to the sensor unit, and either a laptop or a small military display provides the operator interface. 3MDS will work in a single aircraft scenario, but two systems flying at the same time give optimum performance.