Fiber Bragg grating sensor for accurate and sensitive detection of carbon dioxide concentration

To accurately, sensitively, and rapidly detect carbon dioxide (CO 2 ) concentration, a novel fiber Bragg grating (FBG) CO 2 sensor was fabricated based on a polysulfone (PSF)/polyimide (PI) material, surfactant polyethylene glycol (PEG), and temperature-compensated FBG unit. The results indicate that the response sensitivity of the sensor is affected by the PI doping ratio, and the surfactant PEG can effectively shorten the response time of CO 2 sensing. The sensitivity and response time of the sensor are positively correlated with the thickness of the PSF/PI/PEG CO 2 -selective coating. The hydrophobic coating can prevent water molecules from moving into the CO 2 -sensitive film, and the FBG temperature-compensation unit can effectively eliminate the interference of temperature on CO 2 detection. When the PI doping ratio was 10 wt%, the surfactant doping ratio was 0.1 wt%, the thickness of the CO 2 -sensitive membrane was 49 µm, and the number of superhydrophobic membrane coatings was 15. In addition, the sensor could accurately measure the CO 2 concentration in the temperature range of 25–50 °C and relative humidity of 35–80%RH. The sensitivity of the proposed sensor was 3.39 pm/mM, response time was 310 s, limit of detection was 0.087 mM, maximum relative error was less than 7.28%, and the sensor exhibited high selectivity and long service life.