Development of Advanced Fiber Bragg Grating Based Sensors

The discovery of fiber optics opened the door to a vast new world of possibilities in sensing technology. One important class of fiber optic sensor is the fiber Bragg grating (FBG) structure. The compactness and low loss properties of the FBG make it a highly versatile sensor, and has allowed efficient deployment of FBGs in many different technological fields. This dissertation describes five innovative designs and applications of FBG-based sensors. An FBG sensor was used as a contact level sensor allowing surgeons to gauge their level of contact with the heart wall in order to avoid perforation during cardiac ablation procedures. The sensor was able to determine the onset of contact and was also able to observe a potential warning sign of impending perforation. The second FBG-based sensor was developed for detecting harmful water ingress in civil structures. Through the use of super absorbent polymers (SAPs) and an innovative sensor design, the sensor was able to undergo multiple loading cycles (up to 1 mL was tested) as well as survive flooding conditions. The third FBG-based sensor comprised of two wavelength matched FBG for the measurement of high frequency vibrations. Measurement of acoustic vibrations generated by a piezoelectric wafer up to 100 KHz was demonstrated. A basic identification of a model wind turbine blade was performed using this set up. An FBG sensor network consisting of multiplexed strain, temperature, and water sensors (23 sensors total) was deployed for the monitoring of a grout cube that models the wall of a nuclear containment facility. Cracking, thermal fluctuations and water ingress were detected by the FBG sensor network over a period of about two months. Finally, FBG strain sensors were used to develop a method for the local measurement of bond slip in reinforcing tendons of a prestressed concrete bridge girder. The method allowed the tracking of the entire bond slip process from a local perspective, which was, up to now, not yet accomplished using conventional sensors.