**9. Future development**

During this last decade, the research has been focused mainly on issues regarding orthogonal fluxgates, like noise reduction, increment of sensitivity, and simplification of the sensors' configuration and development of wires with new structures.

Orthogonal Fluxgates 41

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Atalay, S.; Ripka, P. & Bayri, N. (2010). Coil-less fluxgate effect in (Co0.94Fe0.06)72.5Si12.5B15

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Butta, M. & Ripka, P. (2008b). Two-domain model for orthogonal fluxgate. *IEEE Transactions on Magnetics*. Vol. 44, Iss. 11, pp. 3992-3995, ISSN: 0018-9464 (November, 2008) Butta, M.; Ripka, P.; Infante, G.; Badini Confalonieri, G.A. & Vázquez, M. (2009a). Bi-metallic

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magnetic wire with insulating layer as core for orthogonal fluxgate. *IEEE* 

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orthogonal fluxgate by optimization of excitation current. Accepted in *IEEE* 

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752-757, ISSN 0022-3727

e974-e978, ISSN: 0304-8853

ISSN: 0018-9464

ISSN: 0018-9464

0018-9464

*Transactions on Magnetics* 

2238-2243, ISSN: 0304-8853 (August 2010)

**Patents** 

**Papers in journals** 

These efforts strongly improved the performances of orthogonal fluxgates, making this sensor competitive in the field of magnetic measurement at room temperature.

However, even if sensors like orthogonal fluxgates in a fundamental mode already achieved noise levels similar to cheap parallel fluxgates, other issues have to be faced.

Currently, we still do not have extensive information about the long-term offset stability of orthogonal fluxgates as well as the temperature dependence of both offset and sensitivity, which are critical points for many magnetometers.

Another important field, which has to be investigated, is the dependence of the orthogonal fluxgate's performance on the geometrical dimensions of the core. So far, different structures have been proposed, but a comprehensive study that explains the effect of different core sizes on sensitivity and noise has yet to be reported. In particular, the effects of the demagnetization factor have not been properly investigated, mainly due to the fact that the excitation field is applied to a circumferential direction facing a toroidal shape, which is not affected by the demagnetizing effect. Nevertheless, a measured field is applied in the axial direction over a finite length specimen so that the internal field distribution will be affected by the demagnetizing effect. This applies especially to multi-core orthogonal fluxgates. Indeed, when operated out of resonance, the output sensitivity will strongly depend on the distance between the wires, because it affects the demagnetization factor. A detailed study on the core's size dependence of orthogonal fluxgates' parameters will be also useful to optimize the geometry of micro-fluxgates, where the small dimension strongly affects the achieved sensitivity and noise.

Finally, further steps should be made towards developing manufacturing techniques for the production of magnetic wires to be used as the core of orthogonal fluxgates, as a means of assuring mass production of cores with very similar parameters. Such efforts are an important requirement for the industrialization of this type of sensor.
