Low-Noise Fundamental-Mode Orthogonal Fluxgate Magnetometer Built With an Amorphous Ribbon Core

Fundamental-mode orthogonal fluxgate magnetometer is developed for the ribbon core sensor head. When the dc bias current is not large enough, the magnetometer is much noisier than that with a wire core sensor head. The source of the noise is attributed to many small jumps in the magnetization process of the ribbon core. The mechanism is explained with a simple model based on the Storner-Wohlfarth model. This noise can be reduced by increasing the dc bias current to 0.2 A or more for a 1 mm wide Metglas 2714A ribbon core. The noise becomes as small as that obtained with a wire core sensor head. An adaptor circuit is introduced to interface a ribbon core sensor head and driving circuit designed for a wire core sensor head.