Optical fibre magnetic field sensors using ceramic magnetostrictive jackets

Optical fibres coated by magnetostrictive ceramic films were tested using a Mach-Zehnder interferometer in open-loop mode. The sensors exhibited excel lent linearity and good sensitivity. The response of ceramic-jacketed fibre s was not affected by small DC fluctuations due to the linear behaviour of tested ceramic coatings in low magnetic fields. Tested ceramic materials in cluded magnetite, gamma-Fe2O3, nickel ferrite and cobalt doped nickel ferri te Ni0.97Co0.03Fe2O3 jackets. The latter one showed the best performance. A minimum detectable field of 3.2 x 10(-3) A/m for optical fibre jacketed wi th 2-mu m-thick and 1-m-long Ni0.97Co0.03Fe2O3 material has been achieved. A capability of detecting magnetic fields as low as 2.6 x 10(-7) A/m using a 10-mu m-thick and 1-m-long Ni0.97Co0.03Fe2O3 fibre jacket is proposed. (C ) 2000 Elsevier Science S.A. All rights reserved.