Low-noise flux-gate magnetic-field sensors using ring- and rod-core geometries

We have fabricated ring-core and single-domain rod-core flux-gate magnetic field sensors with l/f noise levels at 1 Hz of 1.4pT/√Hz and 3.5pT/√Hz, respectively. These noise sensitivities were achieved by applying an electrical current through the core of the flux gate to magnetically bias the magnetic rotation of the core perpendicular to the easy-axis direction. We also found that in the rod-core sensor, the spatial correlation lengths of the magnetic fluctuations were 25 and 40 mm with and without the biasing current. The cross-power spectrum magnitude at 1 Hz was less than 200 fT/√Hz. © 2007 American Institute of Physics.