Performance Evaluation of Fiber Optical Sensors for Health Monitoring of Civil Structures

Abstract

The presence of optical devices has made their deep place in our everyday life through various processes like sensing, communication, entertainment, fashion, security, medical diagnosis, industrial growth etc. In recent years, optical fiber has found major application in sensor technology due to inherent advantages such as immunity to electromagnetic interference, electrical isolation, chemical passivity, small size, low weight, long range operation, and ability to sense variety of measurands. Nowadays, optical sensors are commercially available to monitor the health of civil structures in real time scenario but still it is required to enhance the sensitivity. Multiparameter sensing using single sensor is an open area of research, so on existing optical sensors many things can be investigated to further enhance the performance of optical sensors. With same motivation, in this thesis, several optical sensors are proposed to sense the important parameters i.e. strain, vibration, temperature, refractive index, portlandite etc. for civil structures with high sensitivity and speed. To achieve the first objective, an optical refractive index (RI) fiber Bragg grating (FBG) sensor is proposed to monitor the chemical concentrations i.e. calcium hydroxide Ca(OH)2 and calcium analogue of brucite Mg(OH)2 which can introduce the corrosion and spalling in civil structures. The motivation to sense these parameters is that if the undesired level of these parameters can detect at early stage then structure against corrosion and spalling can be protected. At first stage, to sense Ca(OH)2 and Mg(OH)2, cladding etched sensor with uniform grating is used and it is observed that the sensitivity is required to enhance further.