High-sensitivity fiber optic sensor for carbon dioxide monitoring in IoT-Enabled biogas systems

Abstract This research presents a high-sensitivity fiber optic refractometric sensor integrated with Internet of Things technology for real-time monitoring of carbon dioxide in biogas applications, addressing critical industrial requirements for continuous gas composition analysis while providing remote accessibility and electromagnetic immunity. The sensing mechanism employs polyhexamethylene biguanide (PHMB) functionalized coating applied to de-cladded fiber regions, enhancing selectivity toward carbon dioxide detection through evanescent wave interactions at the core-cladding interface, where carbon dioxide-induced refractive index variations produce measurable optical intensity changes in single-mode fiber architecture. Experimental validation demonstrates robust performance across carbon dioxide concentrations ranging from 34.7% to 93.3%, achieving a high sensitivity of 0.196%/s with response and recovery times of approximately 120 seconds and 180 seconds, respectively, while multiple measurement cycles confirm excellent repeatability and stability without baseline drift or signal degradation. The integrated Internet of Things platform enables seamless data acquisition and web-based visualization through secure interfaces, facilitating real-time monitoring with three-second update intervals and maintaining an average latency of 70 milliseconds for immediate response capabilities. Microstructural analysis confirms chemical stability and adhesion integrity of the PHMB coating following extended carbon dioxide exposure, ensuring long-term operational reliability for continuous monitoring applications. This fiber optic-Internet of Things integration demonstrates significant advantages for industrial gas sensing applications, including compact design, remote monitoring capabilities, and enhanced safety protocols that support process optimization in biogas production facilities while addressing electromagnetic interference concerns common in industrial environments, indicating strong feasibility for commercial deployment in high-sensitivity real-time monitoring systems. Highlights • A fiber-optic refractometric sensor (FOR) incorporating Internet of Things technology for instantaneous carbon dioxide monitoring in biogas is formulated. • The sensor utilizes a polyhexamethylene biguanide (PHMB) coating on the de-cladded fiber zones to achieve selective carbon dioxide detection via evanescent-wave interactions at the core-cladding boundary. • Experimental validation demonstrates high sensitivity of 0.196% per second across carbon dioxide concentrations ranging from 34.7% to 93.3%, with response and recovery times of approximately 120 seconds and 180 seconds, respectively. • The integrated Internet of Things platform enables seamless data acquisition and web-based visualization through secure interfaces, maintaining three-second update intervals and an average latency of 70 milliseconds for immediate monitoring capabilities. • Microstructural analysis confirms the chemical stability and adhesion integrity of the coating following extended carbon dioxide exposure, ensuring long-term operational reliability for continuous industrial monitoring applications without baseline drift or signal degradation.