Abstract
In this paper, the design and simulation of a new optical fiber-based relative humidity (RH) sensor formed by spherical hydrogel droplets over the no-core fiber is stablished. The introduced sensor is capable of detecting humidity changes based on Evanescent waves and splice losses. Refractive index of PEGDMA hydrogel sphere changes with variation of humidity which can cause intensity changes in fiber. The sensor structure includes a no-core fiber in the length of 4 mm connected to two multimode fibers which performs sensing by three hydrogel spheres with diameter of 1 mm. The sensor operation wavelength is adjusted at 631nm. The results show that the designed structure has linear response for humidity in the range of 20 to 95%RH. In the meantime, the obtained sensitivity is about 0.13643 mW /% RH. The simulated sensor has some useful advantages in addition to having some associated with the two primary sensors including the simplicity of the structure and the sensor's function which can be explained by reduction of the length of sensing portion and increase in the sensitivity and range of humidity detection.
Highlights
Today, in the industrial world, humidity is an effective parameter in protecting the environment, meteorology, warehousing, industry, agricultural and medical products, so, it is a very important physical quantity
Humidity is a term used to describe the amount of water vapor found in a gas mixture, and relative humidity (RH) can be defined as the ratio of the actual water vapor partial pressure in the air mixture to the saturated water vapor pressure at the given temperature [1]
The intensity-based optical fiber sensors offer a powerful combination of simplicity and low cost compared to examples of optical fibers based on fiber Bragg gratings [10], long period gratings [11], photonic crystal fiber interferometers [12,13] and so on
Summary
In the industrial world, humidity is an effective parameter in protecting the environment, meteorology, warehousing, industry, agricultural and medical products, so, it is a very important physical quantity. The optical fiber-based humidity sensors are secondary devices against electronic and mechanical counterparts, but show applicable features such as remote or multi-sensing capability [3,4]. Hydrogels have a wider dynamic range for humidity sensing in a shorter response time due to their bigger irregular pores which can be controlled for reducing the cross-sensitivity They contain a high light transparency and mechanical strength [14]. The transmission ratio of the fiber is reduced at once by increasing the refractive index in a certain range of humidity and the sensing operation begins (in a refractive index greater than 1.43) The reduction of this power transmission is influenced by the changes in the number, size, and distance between the spheres.
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