Simultaneous humidity and temperature measurement sensor based on coated multiplexed fibre bragg gratings

Fibre Bragg Grating (FBG) sensors are preferred over traditional electrical sensors due to their high sensitivity, electromagnetic immunity, and multiplexing capability. However, the simultaneous measurement of humidity and temperature remains challenging due to cross-sensitivity issues. This study presents the development of a simple and efficient coated multiplexed FBG sensor to address this challenge. The sensor was fabricated using two separate single-mode fibre FBGs, each coated with polydimethylsiloxane (PDMS) and polyvinyl alcohol (PVA), respectively. Experimental results demonstrated that PDMS exhibited excellent temperature sensitivity, while PVA showed high moisture sensitivity. The measured sensitivities were 0.0989 pm/% RH (equivalent to 9.89 pm.φ-1) and 28.775 pm/°C (equivalent to 28.775 pm/°K) for PDMS-coated FBG, and 12.593 pm/% RH and 14.515 pm/°C for PVA-coated FBG, indicating that PDMS had minimal response to humidity, whereas PVA exhibited a degree of temperature sensitivity. To mitigate cross-sensitivity, a sensitivity matrix was employed, enabling accurate simultaneous measurement of humidity and temperature. The experimental validation confirmed that the sensor achieved a percentage error below 10%, demonstrating high accuracy and reliability. Given the simplicity of fabrication and calibration, the proposed coated multiplexed sensor exhibits strong potential for practical applications in environmental monitoring and industrial sensing.