Plastic optical fiber coated with zinc oxide for relative humidity sensing application / Zuraidah Harith

Zuraidah , Harith (2019) Plastic optical fiber coated with zinc oxide for relative humidity sensing application / Zuraidah Harith. PhD thesis, Universiti Malaya.

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Abstract

In recent years, plastic optical fiber (POF) has been studied and developed in various applications including sensors as POF-based sensors do not require rare materials to develop and they can be employed at room temperature. In this thesis, relative humidity sensor, employing tapered polymethyl methacrylate (PMMA) fiber and microfiber are proposed and demonstrated. The tapered PMMA fibers are fabricated based on chemical etching method while PMMA microfibers are fabricated using a direct drawing technique. For relative humidity measurement, changes in the behavior of the evanescence field passing through the media, whose refractive indices are influenced by the water molecules absorbed or desorbed. To increase the sensitivity of sensor, the probes are coated with Zinc Oxide (ZnO) nanostructures. ZnO nanostructure materials able to provide a suitable platform for developing relative humidity sensor due to its unique properties such as high catalytic efficiency and strong adsorption ability. Subsequently, ZnO is doped with other group III metal, which is Aluminium (Al) as Al doping is more highly conductive due to its close covalent bond length of Al–O to that of Zn–O. ZnO and Al-doped ZnO are grown using both seeded and non-seeded techniques and they are synthesized using the sol–gel and hydrothermal methods. The measurement is based on intensity modulation technique to detect the changes in relative humidity. These nanostructures on the tapered fiber induce changes of the optical properties in response to an external stimulus. Results show that tapered POF with ZnO and Al-doped ZnO nanostructures enables the increase in sensitivity of fiber for detection of changes in relative humidity. The proposed sensor provides numerous advantages, such as simplicity of design, low cost of production, higher mechanical strength, and is easier to handle compared with silica fiber-optic.

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