Current annealing of amorphous wire core for performance improvement of fundamental mode orthogonal fluxgate

Magnetic sensors adopting amorphous wires have advantages in high sensitivities and low noise characteristics, yet those performances would be irreproducible due to the inhomogeneity existing in amorphous wires. In this research, glass-coated Co-Fe-Si-B-Cr amorphous magnetic wire was adopted to a fundamental mode orthogonal fluxgate (FM-OFG) sensor to investigate its adaptability as a magnetic core. In as-cast wire form, non-repeatability and anomaly found in the magnetization process deteriorated the sensor noise performance. Current annealing was then performed to the wire core. It was confirmed that the current annealing greatly improved the repeatability in magnetization, reducing the sensor noise level to 30 % of the case obtained with the as-cast wire core. Further analyses on current annealing parameters implied that the internal stress relaxation of the wire was rapidly occurring at the beginning of the annealing, followed by the induction of circumferential anisotropy. The results revealed that those changes in magnetic property were repeatable and controllable, making the sensitivity and noise performance of the sensors highly reproducible. This feature will be a great advantage in further practical development of the sensors.