Compositional influence of CuAlMn SMA coated optical fiber towards sensing low temperature

Abstract

Low temperature sensing with currently available sensors is a challenging task due to the several limitations in usage under harsh environmental conditions. Hence, optical fiber-based sensors could be a better alternative for sensing and monitoring applications due to their immunity at extreme temperatures (both Cryogenic and high temperature), pressure, electromagnetic interference, and power fluctuations. Moreover, the sensing properties are further improved by applying metal coating on optical fiber. In this respect, Shape Memory Alloy (SMA) coating on optical fiber shows enhanced sensitivity due to its unique property of shape memory effect. Particularly, copper-based SMAs are investigated in this regard because of their solid-state actuation characteristics at extreme temperature conditions. Hence, we have coated the optical fiber with CuAlMn SMA by thermal evaporation technique. We have varied the composition of SMA to control the transformation temperature (TT) at low-temperature regions. In the CuAlMn system, TTs are highly dependent on the concentrations of Al and Mn content. We have varied the weight percentages of Al and Mn present in CuAlMn SMA, to achieve the actuation at sub-zero temperature. We have used 2 different wire compositions (Cu-9Al-12.6Mn, and Cu-8.8Al-12.2Mn) for the preparation of the CuAlMn SMA thin films. The film obtained using the Cu-9Al-12.6Mn wires, has shown the lowest transformation temperature and maximum actuation/ displacement (∼10 mm) at low temperature (liquid N2) region. Such actuation of SMA-coated fiber results in significant optical signal attenuation (∼ 8 V peak-to-peak voltage difference under liquid N2 exposure) at the detector end. Thus, we can claim that the CuAlMn-coated optical fiber can be used as a cryogenic sensor due to its significant optical signal attenuation.