We have designed a fluxgate magnetometer which utilizes the detection of ultra-low DC fields down to (even less) 3 nT. In addition to high sensitivity, it also has quite a large dynamical measurement range. The second harmonic voltage used as the sensor signal shows linear dependence on the applied field up to 1 Oe. We report some critical factors affecting the noise level and sensitivity of magnetometer. The core diameter and magnetic properties are some of them. We will report optimal core dimensions resulting in minimal electrical noise. During experiments, we have recognized that ring-shaped six-layered ribbon core must be well attached to the template, since otherwise, it may vibrate on its original position as a function of the excitation frequency. Thus, additional electrical noises become unavoidable.

This paper presents the optimal conditions for the design of a single-rod fluxgate magnetometer using Co-based amorphous magnetic wires with reduced geometrical dimensions of 100 μm in diameter. In order to enhance the performance of the current sensor (i.e. the noise level, the sensitivity, the dynamical range, the scaling factor, etc), the core materials were subjected to annealing at different annealing temperatures in a longitudinal magnetic field ranging from 0 to 0.5 T. The B–H measurements have shown that the heat treatments significantly change the magnetic parameters of the cores (the saturation field, the initial and apparent permeabilities). For instance, the initial permeability μi attains values of between 3500 and 4700 depending on the treatment conditions. These magnetic parameters were subsequently correlated with the sensor performance by using the principles of the fluxgate physics. Consequently, the enhanced fluxgate effect with improved sensing characteristics has been obtained by annealing the wire core at 250 °C (B  =  0 T). It is shown that this magnetic wire with a sensing area of 0.00785 mm2 is suitable as a sensor core for the nondestructive testing of metallic objects and the surfaces of magnetic cards. The sensor signal shows perfect linear dependence to dc or low frequency fields up to ~1 Oe. The fitting parameters R2 of 0.9998 could be achieved in a dc field interval of  −1.0 Oe and 1.0 Oe (when R2  =1.0, all points lie exactly on the curve with no scatter). Such linearity has not been seen in such a large dynamical range until now in the rod-type single-core fluxgates. It is also shown that there is no hysteresis on the V2f–Hdc graphs (the V2f is the sensor signal) even after applying fields as high as 100 Oe. Besides, the cross-field effect is almost zero due to the geometry of the long-thin wire.

In this study, we have shown that fluxgate sensors can be used for different application areas. Alternative sensor configurations have been developed for three different application areas. These are mainly rod-and ring-type fluxgate sensors. In the first study, a measurement system with the rod-type fluxgate sensor has been developed in order to monitor the local magnetic field distributions on a magnetic tape (e.g., credit card). With this system, the magnetic recording data on the credit card were measured and imaged successfully. The second and the third application areas, which are monitoring the influence of solar storms on the earth field and heartbeat analysis of mankind, were carried out by using a ring-core fluxgate sensor geometry.

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