Single-core fluxgate gradiometer with simultaneous gradient and homogeneous feedback operation

A novel configuration of a single-core gradiometer, utilizing both homogeneous and gradient feedback operation, is presented. The fluxgate gradiometer comprises of a standard pick-up/feedback coil and an additional gradient pickup/feedback coil with two separate electronic blocks. The 40-mm-long gradient coil is concentric and coaxial with the homogeneous pickup/feedback coil: the gradient coil assembly was slipped over an already existing race-track fluxgate sensor. The gradient coil works as a pick-up coil and it also generates the compensating field which well approximates a first-order gradient field with zero spatial-mean value. Together with the compensating field from the homogeneous feedback coil, it is thus always possible to measure in two independent feedback loops the homogeneous and gradient field components. The 1/f gradient noise is 4 nT/m/root Hz @ 1 Hz, and it can be further improved by separating the gradient feedback and compensating coil. (C) 2012 American Institute of Physics. [doi:10.1063/1.3676238]