Optical fibre sensor for simultaneous temperature and relative humidity measurement: Towards absolute humidity evaluation

Abstract

Temperature and humidity are essential parameters in monitoring the health of patients in critical care. An optical fibre sensor has been developed for simultaneous measurement of relative humidity (RH) and temperature at a single optical fibre tip based on the reflected intensity. Combining these measurements enables absolute humidity values to be obtained. The fibre tip is first modified with a coating of poly(allylamine hydrochloride) (PAH) / silica nanoparticles (SiO2 NPs) for relative humidity (RH) measurement and then coated with thermochromic liquid crystal (TLC) for temperature measurement. Experimental results demonstrate that the RH and temperature sensitivity are respectively 0.43 %/RH% (intensity at a wavelength of 650 nm) from 55 to 90% RH (R2 = 0.973) and 3.97 nm/°C from 28 to 46 °C (R2>0.99). Moreover, the proposed sensor has low crosstalk between each of the sensing parameters, with a response time of 3.1 s temperature (30–38 °C) and 13.2 s for relative humidity (20–80 %). In comparison to grating based optical fibre sensors the proposed sensor is low-cost with a simple manufacturing process which has the potential to find widespread use in healthcare applications.