A miniature and ultralow power search coil optimized for a 20 mHz to 2 kHz frequency range

• Published in: Journal of applied physics Vol. 105; no. 7; pp. 07E708 - 07E708-3
• Main Authors: Paperno, Eugene, Grosz, Asaf
• Format: Journal Article
• Language: English
• Published: American Institute of Physics 01.04.2009
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.3072718

We describe the design of a miniature search-coil magnetometer that is optimized in terms of resolution and power consumption for frequencies down to 20 mHz. Our aim is to come close to the size and resolution of fluxgate magnetometers, while reducing the power consumption by at least an order of magnitude. To reach this goal, we attach flux concentrators in the shape of thin disks to a ferrite core, employ an ultralow power, zero 1 / f noise preamplifier, and finally optimize the diameters of the coil core and wire. The optimized search coil is of 54 mm length, 30 mm outer diameter, and includes 160000 turns of a 50   μ m copper wire. The coil resistance is 86   k Ω , the self-resonance frequency is 250 Hz, and the total weight is 210 g. Our experimental results are in close agreement with the theoretical calculations. For a power consumption of 5 mW, the coil resolution is 14   pT / √ Hz at 1 Hz and reaches 350   fT / √ Hz in the frequency range from 100 Hz to 2 kHz. For a power consumption of 0.17 mW, the coil resolution decreases only by 25%. As a result, the new search-coil magnetometer consumes power one to two orders of magnitude less than the commercial fluxgates having similar resolution and size.