A Three-Axial Search Coil Magnetometer Optimized for Small Size, Low Power, and Low Frequencies

A compact and sensitive three-axial search coil magnetometer has been designed, built, and tested. The magnetometer sensitivity threshold equals 12 pT/Hz
^0.5
at 1 Hz, and the magnetometer dimensions are 72 mm × 69 mm × 69 mm. All the magnetometer coils, the electronics, and batteries are accommodated within a single electrostatic shield and a single housing. A close to 2 aspect ratio (30 mm diameter, 58 mm total length) of the search coils provides a very high (~70%) volume utilization factor. Such a small aspect ratio is obtained due to employing 30-mm diameter, 4-mm thick flux concentrators. The magnetometer is optimized for 20 mHz to 7 Hz frequencies and for ultra-low (252 μW) power consumption. The ultra-low-power consumption enables a seven-year continuous operation from the four 1/2AA lithium batteries. The effect of the integration of three orthogonal search coils on the magnetometer sensitivity and accuracy has been investigated.