Fiber optic magnetostrictive transducers for magnetic field sensing

Abstract

A number of fiber optic magnetostrictive transducers were fabricated using various metallic glass ribbons made of Co₇₀Fe₁₀B₂₀, Co₇₆Fe₄B₂₀, Co₈₀B₂₀, Ni, Fe₇₉B₁₆Si₅, and Fe₄₀Ni₃₈Mo₄B₁₈ and were characterized by a typical optical fiber Mach-Zehnder interferometer constructed by splicing the fiber transducers to the single-mode-fiber sensing arm. The ac magnetostrictive responses for the metallic glasses measured with the fiber optic sensing system show that the dc-bias field (<i>H_p</i>) for the maximum response with a Co₇₀Fe₁₀B₂₀ ribbon is ~ 0.97 Oe, that 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 magnetostrictive parameters and saturation magnetostrictions are 1.3 x 10^-7/Oe² to 7 x 10^-7/Oe² and -4.6 x 10^-6 to 5.7 x 10^-6, respectively. The optical fiber sensors exhibit minimum detectable fields <i>H</i>_min of the order of between 10^-5 Oe(rms)/√Hz and 10^-7 Oe(rms)/√Hz above 1 kHz at their respective dc-bias fields <i>H_p</i>. The <i>H</i>_min can be much further improved by reducing the level of noises that limit the phase resolution to ~ 10^-4 rad/√Hz in the interferometer.