FIBER OPTIC MAGNETOSTRICTIVE TRANSDUCERS FOR MAGNETIC-FIELD SENSING

A number of fiber optic magnetostrictive transducers were fabricated u sing various metallic glass ribbons made of Co70Fe10B20, Co76Fe4B20, C o80B20, Ni, Fe79B16Si5, and Fe40Ni38Mo4B18 and were characterized by a typical optical fiber Mach-Zehnder interferometer constructed by spli cing the fiber transducers to the single-mode-fiber sensing arm. The a c magnetostrictive responses for the metallic glasses measured with th e fiber optic sensing system show that the de-bias field (H-p) for the maximum response with a Co70Fe10B20 ribbon is similar to 0.97 Oe, tha t with a Ni ribbon is 23 Oe, and with a Fe79B16Si5 ribbon is 5.7 Oe. A magnetostriction function describing the magnetostrictive response of the transducer was also empirically found. The measured effective mag netostrictive parameters and saturation magnetostrictions are 1.3 x 10 (-7)/Oe(2) to 7 x 10(-7)/Oe(2) and -4.6 x 10(-6) to 5.7 x 10(-6), resp ectively. The optical fiber sensors exhibit minimum detectable fields H-min of the order of between 10(-5) Oe(rms)/root Hz and 10(-7) Oe(rms )/root Hz above 1 kHz at their respective de-bias fields H-p. The H-mi n can be much further improved by reducing the level of noises that li mit the phase resolution to similar to 10(-4) rad/root Hz in the inter ferometer.