Abstract
Pollution in cities induces harmful effects on human health, which continuously increases the global demand of gas sensors for air quality control and monitoring. In the same manner, the industrial sector requests new gas sensors for their productive processes. Moreover, the association between exhaled gases and a wide range of diseases or health conditions opens the door for new diagnostic applications. The large number of applications for gas sensors has permitted the development of multiple sensing technologies. Among them, optical fiber gas sensors enable their utilization in remote locations, confined spaces or hostile environments as well as corrosive or explosive atmospheres. Particularly, Lossy Mode Resonance (LMR)-based optical fiber sensors employ the traditional metal oxides used for gas sensing purposes for the generation of the resonances. Some research has been conducted on the development of LMR-based optical fiber gas sensors; however, they have not been fully exploited yet and offer optimal possibilities for improvement. This review gives the reader a complete overview of the works focused on the utilization of LMR-based optical fiber sensors for gas sensing applications, summarizing the materials used for the development of these sensors as well as the fabrication procedures and the performance of these devices.
Highlights
During the past few decades, a lot of effort has been dedicated to detecting the concentration of gases due to the wide and relevant applications where this action is needed [1]
This review gathers valuable information about optical fiber gas sensors based on the Lossy Mode Resonance (LMR) phenomenon or with high potential to be used for this purpose
The latter are mainly associated with materials that have been studied separately for LMR generation but not for gas sensing purposes, or are prone to be used for the generation of LMR because the dielectric properties of the material comply with the LMR condition
Summary
During the past few decades, a lot of effort has been dedicated to detecting the concentration of gases due to the wide and relevant applications where this action is needed [1]. The subsequent sections describe the utilization of LMR-based optical fiber gas sensors for the detection of particular gaseous species, starting with ammonia, followed by water vapor (better known as humidity sensors), a compilation of volatile compounds (VCs), such as ethanol, methanol and acetone, and finishing with an examination of other gases, including hydrogen sulfide, hydrogen and nitrogen oxides. Physical changes in the sensor can induce resonance wavelength shifts in the spectrum Due to this condition, the LMR phenomenon is suitable to be used for sensing applications measuring different parameters depending on the characteristics of the structure. Regarding the utilization of LMR-based optical fiber sensors for gas sensing applications, they can take advantage of the use of optical fiber as an optimal structure that allows the measuring of gases in remote places and harsh environments. The sensors described in this work are classified in different sections depending on the gas target for a better understanding and comparison of the devices, covering ammonia (NH3), water vapor (relative humidity) H2O, volatile compounds (VCs) and other gaseous species such as hydrogen sulfide H2S, hydrogen H2 and nitrogen oxides NOx
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