Triaxial Fluxgate Sensor Excitation and Core Shape Study

Triaxial fluxgate sensors working in parallel mode with electroplated Permalloy $({\rm Ni}_{80}{\rm Fe}_{20})$ cores were manufactured utilizing a low-cost printed circuit board technology and subsequently characterized. Sensor versions with various core shapes are compared and they are all shown to be capable of measuring low intensity magnetic field in three axes. It was found that the sensor sensitivity in the $xy$ plane is influenced by the core material anisotropy (133 and 151 V/T in $x$ and $y$ axes respectively for T-shaped core sample). Despite much higher demagnetization ratio the sensitivity in $z$ axis is higher (310 V/T for T-shaped core sample) as a result of higher core cross-section and pickup coil construction. The effects of two excitation modes – serial and separated – are investigated. It is shown, that serial excitation mode results in sensor axes tilt within $xy$ plane, the actual tilt value being dependent on the core shape (14$^{\circ}$ /6$^{\circ}$ /6$^{\circ}$ with Cross-/T-/X-shaped core sensor, respectively). The results suggest that the narrower the core, the lower axes tilt results. The alternative separated excitation mode substantially reduced the axes tilt below 2$^{\circ}$ but increased the sensor output hysteresis in $z$ axis reading (from less than 0.3% to 1.5% in $\pm 50\ \mu{\rm T}$ sweep).