Fiber optic white light interferometric sensors for structural monitoring

Smart structure is constructed by associating the structure with a health monitoring system that can monitor the physical and mechanical properties of the structure such as temperature and strain, respectively, in real-time during the servicing period. Recent research interest is to use optical fiber sensors as embedded strain monitoring devices for examining the temperature variation and strain profile during manufacturing and loading processes for advanced composite and concrete materials. Fiber optic white light interferometric sensor is one of the most exciting technologies in the field of optical fiber sensors in recent years and appears to be ideally suited for structural health monitoring of composite materials and civil engineering applications. The aim of current study is to investigate and develop effective and practical fiber optic white light interferometric sensing techniques for strain and temperature measurement for smart structures.; In this thesis, an extensive review is given to describe the concept of smart structures and to discuss the present state of the art of the embedded fiber optic sensor techniques. The analytical models were developed to study the relationship between the embedded fiber optic sensor output and the engineering values of strain and temperature. Based on the white light interferometer principle, a fiber optic extensometer system was designed and constructed. The extensometer has been used for 1-dimensional and 2-dimensional strain measurements. A novel multiplexing technique based on a fiber optic ring resonator has been proposed and investigated. This technique has been applied to multiplex a serial and a parallel sensor array and MxN sensor matrix. In order to improve the reliability of the multiplexed fiber optic sensor array, a novel white light interferometric fiber optic sensor system consists of serial sensors connected in a loop topology has been proposed. The looped sensors network not only satisfies the redundancy requirement of a practical sensing system, but also provides a damage diagnosis methodology for large-scale smart structures. Finally, fiber optic ultrasonic sensors based on the Fizeau and Sagnac-like interferometers have been proposed and experimentally demonstrated. The ultrasonic sensor can be used for real-time instantaneous detection of cracks in structures. They should find applications in acoustic emission monitoring and non-destructive evaluation (NDE) of large structures.