Development of the hydrogen gas sensor for the nondestructive test evaluation (NDE) application

In this paper, a sensor material with Fe/Zr multilayer thin film, in which the change in the magnetization and strain with hydrogenation is maximized, was developed. Compositionally modulated Fe/Zr multilayers with a Fe₈₀Zr₂₀ composition and modulation wavelengths 3-50 angstroms were deposited by sequentially sputtering (RF diode) elemental Fe and Zr targets. The films were electrolytically hydrogenated to select the optimum Fe/Zr multilayers that show the maximum increases in the magnetization and strain with hydrogenation. The changes in the magnetic properties of the thin films after hydrogenation were measured using a hysteresis graph and the strains induced in the films by hydrogenation were measured using a laser heterodyne interferometer. The optimum sensor material selected was incorporated in a fiber-optic hydrogen sensor by depositing it directly on the sensing arm of a fiber-optic Michelson interferometer. The developed sensor is expected to be useful for detecting easily and accurately the subsurface corrosion in structural systems