Development of carbon dioxide sensor using fiber optic-based refractometer

In this work, a fiber optic-based refractometer has continuously been developed for measuring carbon dioxide (CO2) using the evanescent wave method. Consequently, this technique is utilized to determine the light absorption values. Further, the chemical compound is also used to coat onto the modified sensing probe. However, this probe is, generally, made from multi-mode fiber (MMF). Moreover, the principle of altering the refractive index (RI) value is applied by removing the cladding of the sensing probe using hydrofluoric acid (HF). In addition, the zinc oxide (ZnO) mixed with the sodium silicate (Na2SiO3), known for its CO2 absorption capabilities, is used as a compound to coat the modified cladding. Besides, the sensing probe has been developed in three selected lengths (L) which are 10, 20, and 25 mm, and then tested from 0 to 40 % of CO2 concentration. Moreover, a biogas analyzer has been operated as a standard reference instrument. Afterward, an engineering application software is also developed for data processing to analyze the data in the relationship between the differential voltage, percentage of attenuation, and percentage of concentration versus time domain, respectively. The experimental results reported that the developed sensing can detect CO2 in any sensing length from 8.11 to 38.25 % with a sensitivity of 0.0102 mV/%concentration. In addition, a percentage attenuation of 2.11 %, 14.52 %, and 29.29 % is achieved in whole sensing lengths. However, this analyzes that at 10 mm the probe is more suitable due to its high responsibility to detect the CO2. Furthermore, the experimental results showed that the selected compound can recover with a recovery time of approximately 6 min.