**6. Fundamental mode**

Orthogonal fluxgates have been ignored in the past because they have higher noise than parallel fluxgates. This, in fact, moved the mainstream of research to focus on parallel fluxgates, since noise is one of the most important parameters for high precision magnetometers (other parameters such as linearity or sensitivity can be compensated to a large extent by proper design of electronics or sensors). Despite the fact that orthogonal fluxgates have recently gained new popularity due to their high spatial resolution and simple structure, their noise is still an issue for these kinds of sensors. Micro fluxgates are reported to have noise around units of nT/√Hz at 1 Hz, while wire core orthogonal fluxgates typically have 100÷400 pT/√Hz noise at 1 Hz. Without substantial reduction of noise, orthogonal fluxgates cannot be considered competitive to parallel fluxgates.

An important step forward in the field of noise reduction in orthogonal fluxgates was made by Sasada, who proposed to operate the sensor in fundamental mode rather than in second harmonic mode (Sasada, 2002a).
