Dissolved oxygen monitoring using coating-free, surface-activated, intensity-modulated coreless termination fibre sensors and transducers

Abstract

The study on the structural change of the coreless termination fibre (CTF) sensing region as a result of surface modification through wet cleaning under three conditions (organic, alkaline, and acidic solutions) resulted in excellent DO sensing and monitoring performance at zero salinity and ambient pressure and temperature. The modulation of light and detection of DO by absorbance-evanescent field sensing mechanism is also disclosed. Coating-free with improved surface-activated, intensity-modulated evanescent field sensor and transducer for DO sensing and monitoring is presented. The experiment showed that the optimised sample, CTF treated with 1 M of sulphuric acid, H2SO4 had produced a good sensitivity of 1.93 × 10−3 a.u./% (with an R-squared value of 0.99 and achieved more than 120% sensitivity improvement as compared to the untreated sensing region of the CTF), stability with variance and standard deviation values of 2.92 × 10−5 and 5.41 × 10−3 respectively and a detection limit of 8.40 %, equivalent to 0.69 mg/L, The optimised sample provided a good selectivity in DO sensing and monitoring in comparison with common colourless and odourless soluble gasses in deionised water, in this study. The sensor also offered a good relative response time compared to a commercial galvanic-based DO transducer used as a reference with the value of 2 µs. Owing to the advantages of structural change of the CTF sensing region with improved optical responses, surface activation, wettability, surface morphology, and surface roughness, the proposed design of the sensor and transducer provides a powerful choice for DO sensing and monitoring.