Triaxial fluxgate gradiometer of high stability and linearity

A novel highly stable magnetic fluxgate vector gradiometer is presented in this paper. It is based on two triaxial fluxgate sensors with the Compact Spherical Coil (CSC) feedback to demonstrate the feasibility of such instrument (the full gradient instrument will consist of at least four triaxial sensors for measuring all the components of the gradient tensor). The sensors have been designed and constructed for the geopotential German satellite CHAMP, and are based on the instrument flying on the Danish satellite Ørsted dedicated to measure the Earth's magnetic field with very high precision. The transducers are of the ringcore type with very low noise and high thermal stability. They use amorphous metal magnetic core (Vitrovac 6025). The cores have been annealed in two different processes with different temperatures and stress. With this instrument, three components of the gradient tensor can be measured with a precision better than 100 pTrms/m. The noise of the gradiometer is 93 pTrms/m in the band 0.01-10 Hz (30.1 pTrms/(Hz1/2 m) at 1 Hz).