Alternating dc bias enables eliminating offset in orthogonal fluxgates operated in fundamental mode. However, the alternating dc bias reversals increase the fluxgate magnetic noise. It is shown in this work that the excess magnetic noise is related to the dynamics of the magnetic domains in the fluxgate core. The alternating dc bias reverses the fluxgate core magnetization causing nucleating domains and generating an intensive magnetic noise. To suppress the excess noise, two methods are suggested. The first method is based on eliminating the adequate parts of the fluxgate output appearing right after each dc bias reversal. The second method is based on introducing idle intervals between the dc bias reversals and subsequently eliminating the corresponding idle samples in the fluxgate output. Both methods suppress one and the same noise attributed to the domains relaxation dynamics and, hence, lead to similar results. In both cases, the fluxgate noise has been reduced down to its value in the excitation mode, where the dc bias is constant, and there are no reversals in the fluxgate core magnetization. The second method, however, has an advantage of lower power consumption due to the absence of both the ac and dc excitations during the idle intervals. Reducing the excess noise in the alternating dc bias mode, paves the way for developing a low-noise orthogonal fluxgates with practically no offset.
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