Abstract |
Vapor sensors are devices that can detect the presence and concentration of
specific substances. Several types of vapor sensors are available and their
characteristics depend on the requirements of each application. The purpose of
this study is the development and study of two optical fiber sensors for the
detection of vapors of volatile organic compounds and aqueous ammonia,
respectively. Optical fiber sensors offer specific advantages compared to
electronic sensors such as high sensitivity, resistance to adverse conditions,
immunity to electromagnetic interference, small size and weight and remote
operation.
Ammonia in gas (NH3) or aqueous (Ammonium hydroxide-NH4OH) phase is
used in various applications including fertilizers, pharmaceutical products,
cleaning fluids, plastics, and other industrial products. Despite its widespread
use, ammonia is a toxic substance harmful to humans. The ammonia sensor
developed in the frame of this work is based on a tilted fiber Bragg grating
(TFBG) with a fluorinated graphene overlayer. When exposed to Ammonia
vapors the properties of Graphene are modified alerting the guiding properties
of the TFBG and thus allowing its detection.
Volatile Organic Compounds, (VOCs), are organic chemicals with a high vapor
pressure at room temperature. As a result, they readily evaporate into the
atmosphere, creating potentially harmful conditions for humans and the
environment. VOCs are emitted by a wide array of products such as dyes,
pesticides, and fuels. The sensor for volatile organic compounds, specifically
alcohols, that was developed, consists of a cavity of photopolymerizable resin at
the end of a single-mode fiber, thus creating a Fabry-Pérot interferometer. The
presence of alcohol vapors (Methanol, Ethanol and Isopropanol) induce changes
in the refractive index and length of the cavity thus altering the spectral
characteristics of the reflected light.
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