Dual-core fluxgate gradiometer with gradient feedback

A fluxgate magnetic gradiometer with two fluxgate sensors and gradient feedback loop is presented. The two feedback coils, gradient and homogeneous, are common to both fluxgate sensors. The signal from the two sensors acts as regulating input in the two feedback loops, improving stability of the gradiometer. The presented gradiometer overcomes the problems of state-of-the art gradiometers which do not allow to decrease the sensor spacing. Because the information about homogeneous field is also available at the gradiometer output, it is possible to astatize the gradiometer. The presented gradiometer has a gradient base of 20-mm with overall sensor head size of 10-cm only and its noise is less than 1.1 nT/√Hz @ 1 Hz.