Polymer-coated fiber Bragg grating for relative humidity sensing

Abstract

A fiber-optic-based humidity sensor has been fabricated using a fiber Bragg grating (FBG) coated with a moisturesensitive polymer. The sensing concept exploits the inherent characteristics of the FBG and is based on the strain effect induced in the Bragg grating through the swelling of the polymer coating. A direct indication of the humidity level is given by the shift of the Bragg wavelength caused by the expansion of the sensing material. The FBG sensor used in this work has an approximate coating thickness of 33 m and was exposed to different humidity levels at room temperature. The sensitivity of the sensor was estimated to be about 4.5 pm/%RH at a wavelength of 1535 nm, this being obtained through a process of linear regression. The resulting uncertainty in the measurement is 4%RH and the response time of the sensor and the moisture expansion coefficient of polyimide were obtained from a series of experimental investigations and cross compared with the results of previous work.

Development of optical fibre humidity sensors for assessing the quality of housing insulation materials

“…Sensing elements were annealed at 180℃ for at least 4 hours after writing for stability. Subsequently, FBG2 underwent the coating process, using a multi-layer 'dip coating' method, after first being treated with 3-Aminopropyltriethoxysilane solution (0.1% 3-APTS) to enhance bonding [8]. A tailor-made package using a perforated stainless steel tube of 20cm length, outer diameter of 1mm and thickness of 0.2mm was developed, following which it was wrapped in Teflon to prevent the ingress of solid impurities.…”

Polyimide-coated fiber Bragg grating for relative humidity sensing

“…5. An operable method to investigate the hysteresis has been proposed by Yeo et al [11]. In the experiment, sensors were fixed in the stable humidity environment created by the saturated salt solution at the temperature of 25 ℃.…”

“…Some experiments have verified the excellent linear relationship between the relative humidity and Bragg wavelength shift of the FBG coated with the moisture sensitive material, e.g., PI [10]. The temperature and humidity responses of polyimide-coated FBG humidity sensors have been studied by Yeo and other researchers [10][11][12][13].…”

Phase-shifted fiber-Bragg-grating-based humidity sensor

“…Fiber Bragg Gratings (FBGs) have received more attention in the past decades due to their numerous strain [2][3], temperature [2], humidity [4][5] and acoustic [6][7] properties. Compared to other types of sensors, FBG sensors have demonstrated three major advantages.…”