A Study on Evanescent Wave Humidity Sensor Based on PEG-PMMA Microspheres With Enhanced Performance

In this study, we demonstrate fabrication of an evanescent wave fiber optic humidity sensor based on PEG-PMMA microsphere film as moisture-sensitive material. A three dimensional stacking structure of PEG-PMMA microspheres is formed by dip coating method on fiber core. A simultaneous fast response and recovery is optimized with equilibrium time of 13 s and 8 s between 30% RH and 80% RH, respectively. The sensor possessed a maximum sensitivity of 157.143 lux/% RH in the range of 70–80% RH and a good linear relationship between the logarithm of output optical intensity and relative humidity with a correlation coefficient of 0.998. Moreover, the sensor exhibits low hysteresis, excellent repeatability, short-term and long-term stability and electromagnetic immunity. Modulation of intensity is primarily attributed to scattering of evanescent wave on polymer microspheres in humidity sensing.