Master thesis : Contribution au développement d'un capteur de polluants dans l'eau basé sur le principe d'onde évanescente dans une fibre optique

Abstract

The present thesis contributes to the development of a sensor for pollutants (BTEX) in water based on the evanescent wave principle in an optical fiber. This work is part of the MOUV project, MOUV which stands for "UV Sensor for continuous MOnitoring of organic pollutants in water". The work focuses mainly on the signal analysis and the determination of the detection threshold, as well as on the development of a self made detector. This prototype aims to demonstrate the feasibility of miniaturization of the sensor so that it does not have to rely on laboratory equipment on site. The first part of this work is a theoretical chapter presenting all the concepts associated with this project such as the optical fiber, the BTEX and the evanescent wave principle. The second part presents the different devices and objects used in this work. It presents the spectrophotometer which is used as a detector, and focuses on the development of the prototype and the selected electronic components of which it is composed. The third part gives the different steps about the sensor manufacture and the preparation of the pollutant solutions. The fourth part presents the results obtained with the laboratory devices and compares these results with those obtained with the prototype. The latter provided great outcomes in comparison to the laboratory equipment. However, some instabilities in the sensor itself prevented from obtaining better results. The next step will be to develop a complete electronic system with only the required features such as the signal analysis and the transmission of data. The method to power the system will have to be defined in order to develop the final prototype. A deeper study of the sensor will also be mandatory to understand the instabilities and being able to obtain repeatability between the tests.