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Simultaneous Measurement of Temperature and Relative Humidity with Polymer Optical Fiber Sensors Based on Induced Stress-Optic Effect

LEAL-JUNIOR, A. ; Frizera-Neto, A. Frizera-Neto ; Marques, C. ; Pontes, M. J.

Sensors Vol. 18, Nº 3, pp. 916 - , April, 2018.

ISSN (print): 1424-3210
ISSN (online): 1424-8220

Journal Impact Factor: 2,033 (in 2015)

Digital Object Identifier: 10.3390/s18030916

This paper presents a system capable of simultaneously measure temperature and relative humidity with polymer optical fiber (POF) sensors. The sensors are based on the variation of the Young and shear moduli of the POF with the variation of temperature and relative humidity. The system comprises of two POFs, each one with a predefined torsion stress, which leads to a variation of the fiber refractive index due to the stress-optic effect. Since the stress is related to the material properties, the variation of temperature and humidity cause a variation of the fiber stress, which leads to deviation in the fiber refractive index. The interrogation is made with only two photodiodes, resulting in a simple and low-cost system capable of measuring humidity on the range of 5% to 97% and temperature on the range of 21°C to 46°C. The results of the tests for simultaneous measurement of temperature and relative humidity show a root mean squared error (RMSE) between the proposed sensors and the reference of 1.12°C and 1.36% for temperature and relative humidity, respectively. In addition, an etching is made on the fiber, which resulted in a sensor with response time of 1.3 seconds, which is one of the lowest for intrinsic POF humidity sensors.