Fabrication of Fluxgate Sensor Heads by Milling with a Circuit Board Plotter and Influence of Core Annealing Conditions on Sensor Performance

This paper presents an alternative way of the fabrication of the ring-shaped fluxgate cores using a classical circuit board milling machine. The rings with an outer diameter of 16 mm and an inner diameter of 10 mm were constructed by milling out the thin sheets with a thickness of 25 mu m. Such a fabrication procedure is certainly more economical and easier than the mostly used chemical etching, and so, this may facilitate the mass production of these sensor heads. In order to eliminate the structural defects, which may occur during the fabrications of the sheets and after milling process, the cores were heat treated at different conditions. Three different routes were followed. The first core was used without any treatment process. The second core was annealed at 230 C-ay for 1 h in an argon atmosphere with an applied longitudinal magnetic field of 0.5 T to the sensing direction of the sensor. The third core was annealed at 320 C-ay for 1 h in an argon atmosphere without a magnetic field. These temperatures were chosen considering the Curie temperatures of materials, which is around 225 C-ay. For the characterization of the cores, the M-H, sensitivity, and noise measurements were carried out. The sensitivities of the developed sensors were found to be 147.3, 241.3, and 481.9 kV/T for the as-cast cores heat treated at 230 C-ay for 1 h in B= 0.5 T and at 320 C-ay for 1 h in B= 0 T, respectively. The noise power densities were determined to be 63.0, 5.0, and 18.0 pT/ aeHz at 1 Hz, respectively.