Effect of Amorphous Wire Core Diameter on the Noise of an Orthogonal Fluxgate

Cobalt-rich amorphous wires have been extensively used as a core of many types of magnetic field sensors, notably of a fundamental model orthogonal fluxgates, because they allow us to manufacture sensors with very low noise. However, commercial wires are available only in one diameter, namely, 125 μm; therefore, most of the literature is always referred to this diameter. In this paper, we investigated the effects of different diameters versus the noise of the sensor. Our purpose is to understand that if there is a room for improvement of noise by producing amorphous wires with different diameters. We casted wires with (Co0.94Fe0.06)72.5Si12.5B15 composition and a diameter spanning from 80 to 220 μm, and we discovered that the wires show crystalline structure starting from 200 μm. This means we can increase the diameter to values higher than 125 μm and still achieve an amorphous structure, considering the upper limit of 200 μm. Then, we studied the noise of the sensors based on wires with three different diameters, namely, 80, 120, and 175 μm. Because the diameter affects the demagnetizing factor, we also changed the length of the wire in the range from 40 to 120 mm. We discovered that increasing the diameter of the wire always decreases the noise, regardless of the demagnetizing effect, which indicates larger cross section of the wire is a predominant factor.