Theoretical and Experimental Investigation of Temperature-Compensated off-diagonal GMI Magnetometer and its long-term Stability

The off-diagonal Giant magneto-impedance magnetometer (GMI) offset drift was investigated regarding its temperature dependence and long-term stability. First of all, the theoretical GMI effect model was upgraded as to include temperature dependency which was presumed to influence the magnetic permeability and the electrical resistivity of the GMI sensing element. This model allows to estimate the GMI magnetic field sensitivity as well as its temperature sensitivity. We then defined the ratio of these two quantities as a criterion of merit representing the sensor thermal dependence and expressed as an equivalent magnetic drift in nT/K. Besides this modeling, a compensation method able to reject temperature dependency is proposed. It is based on a periodical inversion of the dc bias current which is superimposed on the usual high frequency excitation current. This method is supported by analytical equations obtained from physical modeling of the GMI effect and electronic model of the conditioning circuitry. Finally, several experimental measurements were performed to characterize long-term stability and thermal drift. Obtained results clearly demonstrate the effectiveness of the rejection method, which exhibits better stability compared to the classical conditioning circuitry. Equivalent magnetic thermal drift as low as −1.8 nT/K and long-term stability of 130 pT/h for 12 hours acquisition were obtained when using the rejection method.