Optimizing the sensing performance of a single-rod fluxgate magnetometer using thin magnetic wires

Abstract

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.

Modelling and Measurement of Magnetically Soft Nanowire Arrays for Sensor Applications

“…For the FEM simulations of large wire arrays, we proposed a simplified 2D equivalent model based on hollow cylinders. We also verified this model on small wire arrays of up to 90 wires [37] by comparison with 3D simulation and by measurement.…”

“…The mentioned properties make microwires ideal for microfluxgate sensors [34,35] which have applications in mobile devices, motion tracking, medical devices, non-destructive testing and in the mining industry [36]. A 20 mm long fluxgate sensor based on a single amorphous microwire achieved a noise of 1.4 nT/ √ Hz at 1 Hz [37] In 2009, we studied transverse fluxgates with cores made of several microwires. We found that the performance is strongly affected by the magnetostatic coupling between the wires, which depends on their distance [38].…”

Design of Fluxgate Sensors for Different Applications from Geology to Medicine

“…For this reason, the use of fluxgate sensors in different application areas is increasing day by day [12][13][14][15][16][17]. Finding an optimal design of fluxgate sensor suitable for nondestructive testing (NDT) and other small area applications requiring local field information were extensively investigated in our previous work [18]. With this study, i.e., minimizing the detectable sizes of flaws, cracks, and other small area field sources, a rod-type fluxgate sensor with a sensing area of 0.00785 mm 2 has been fabricated.…”

“…For this reason, it is needed to use different methods and magnetometers to measure weak magnetic fields which could replace SQUID magnetometer. Recently developed fluxgate magnetometers which have very sensitive measurement capability, low cost, and easy to manufacture can be an alternative to SQUID magnetometers [18,19].…”

Effect of Field Annealing Induced Magnetic Anisotropy on the Performance of Meander‐Core Orthogonal Fluxgate Sensor

“…In this regard, the effect of different annealing treatments (including field annealing) on sensor performance have been widely investigated for joule heating, current annealing, stress or field annealing . Although there have been many studies of orthogonal fluxgate behavior in annealed amorphous wires, in general, the accuracy of the measurements of orthogonal fluxgate has been significantly improved in recent years . However, investigators have not paid much attention to the effect of field annealing‐induced anisotropy on the orthogonal fluxgate characteristics with amorphous ribbon cores.…”