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Development of Fiber Bragg Grating Strain, Thermal, and Magnetic Sensors for Smart Structure Applications

  • Author(s): Emmons, Michael
  • Advisor(s): Carman, Gregory P
  • et al.
Abstract

Optical fiber Bragg gratings offer great potential for sensing pertinent phenomena in a wide range of applications. Such range is demonstrated in this dissertation with the utilization of fiber Bragg gratings (FBGs) in two different fields of research. Both of these fields are encompassed by an overarching goal of developing smart structures capable of providing necessary feedback to enhance performance and safety. FBGs are employed in the field of structural health monitoring by measuring strain and detecting damage when embedded within AS4/3501-6 quasi-isotropic composites. The grating sensors are also utilized in the field of ferroic materials to explore novel methods of coupling external phenomena to the optical fiber reflection signal. The desire to create smart structures is carried out by developing the Bragg grating measurements system created by NASA Dryden Flight Research Center. This development involves studying the validity of strain measurements provided by embedded Bragg gratings and expanding the capabilities of the measurement system by coupling the sensors to additional types of external phenomena such as magnetic fields.

Theoretical and experimental work is carried out for both phases of the dissertation. In the strain sensing phase, photoelasticity, electromagnetic wave propagation, and coupled mode theory are applied to understand the theoretical behavior of FBGs. Mechanical loads are applied to composite specimens with embedded FBGs to monitor the response of the reflection signal. Finite element analysis is then performed to further clarify how the load is transferred from the host composite to the embedded fiber. In the thermal and magnetic sensing phase, a description is given for the fabrication and experimental results of coating FBGs with thin film ferroic materials. Next, a more extensive electromagnetic wave propagation theory is described in the context of manipulating various fiber characteristics for magnetic field coupling. A FBG magnetometer is then fabricated and a magneto-optic coupling is demonstrated experimentally with an externally applied magnetic field.

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