Very low frequency noise reduction in orthogonal fluxgate

In this paper we present a simple, cheap and effective method to obtain reduction of very low frequency noise in an orthogonal fluxgate in fundamental mode. This method consists in the application of a layer of silicone over the magnetic core of the sensor filling the whole space inside the pick-up coil. In this way we avoid fast variations of temperature to affect the offset of the sensor (which is very sensitive to temperature changes). Eventually the offset will still drift to the same value, but it will do it slower, thus reducing the component of the noise in the sub-Hz region. Using this method we could simply reduce the noise at 100 mHz from 23 to 8 pT/√Hz, with no additional hardware on the excitation or signal conditioning circuits.