A Low-Noise Fundamental-Mode Orthogonal Fluxgate Magnetometer

We introduce a low-noise fundamental-mode orthogonal fluxgate magnetometer for use in magnetotelluric surveys. The fluxgate makes use of rapidly quenched amorphous wire having vanishing value of saturation magnetostriction constant (λ ≈ 10^-7) and displaying ultrasoft magnetic behavior. The design of the fluxgate consists of multiple U-shaped sensor heads where pairs of wire pieces are inserted as core material. The novelty of this system resides in the use of a quadruple sensor head. Digital signal processing with effective electronic noise suppression allows this magnetometer to achieve a noise floor of 0.8 pT/Hz^1/2 for frequencies above 10 Hz. The possibilities of in situ application are discussed and guidelines on noise suppression strategies are given.