A Low-Cost Relative Humidity Sensor Using Polymer Optical Fiber Based on Intensity Variation
Abdul Ghaffar, Sadam Hussain, Abbas Musavi, Mujahid Mehdi, N.U.H.H. Zalkepali, Jie Lin, Jianping Yu, Muhammad Chhattal, Kun Lan, Lei Cao
Abstract
In sensor systems, most sensors are single-point detection, and it is challenging to develop a multipoint sensor where multiple points can be sensed. This work reports a low-cost relative humidity (RH) sensor relying on intensity variation based on the side coupling technique using polymer optical fiber (POF), where three sensors are integrated into a single illuminating fiber. The sensor structure contains the twisting of two fibers three times and is coated with agarose gel, while a rise in humidity causes a change in refractive index (RI) between two twisted fibers. The experimental results reveal that the sensors provide a linear relationship between 20% and 80% RH with a sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.4636 \mu {W}$ </tex-math></inline-formula> /%, 0.4402 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu {W}$ </tex-math></inline-formula> /%, and 0.4153 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu {W}$ </tex-math></inline-formula> /%. Detection limits are 1.57%, 1.79%, and 2.02%, for sensor-1, sensor-2, and sensor-3, respectively, while the bend radius of the sensor probe is 10 mm. When RH is increased from 80%, it results in more sensitivity, and the sensor’s sensitivity also rises when the bend radius reduces. A lower detection limit and increased sensitivity are obtained with a coating of agarose gel. In addition, the novel RH sensor is a cost-effective solution that offers the benefits of decent reversibility, rapid reaction time (about 1 s), and temperature dependency.