Date of Award
Doctor of Philosophy in Applied Physics - (Ph.D.)
Federated Physics Department
John Francis Federici
Robert Benedict Barat
N. M. Ravindra
Gordon A. Thomas
Hee Chuan Lim
The polarization imaging technique has been used to obtain high quality surface images of turbid media. This technique can be slightly modified and used for noninvasive sensing of strain and stress in soft stretchable materials, such as latex and human tissues. Previously this sensing method was developed with free space bulk optics. In this study, a fiber optic based system is developed to investigate the potential application of this technology on the strain/stress as well as surface roughness measurements of stretchable materials. In this system, polarizers are simply attached to the fiber ends to form a polarizing three-fiber probe. Furthermore, no collimating lens is employed thereby increasing the cost effectiveness and simplicity of the probe fabrication.
Two types of surface conditions are considered: 1) flat rough surface, 2) curved rough surface. The sinusoidal surface roughness model is employed for both kinds of surfaces for theoretical analysis and simulations. A theory is developed based on prior works to determine the behavior of the normalized reflectivity for different surface roughness parameters when the surface is under the applied strain. A variety of fiber probes with different configurations are fabricated and employed to measure the normalized reflectivity in the experiments. Polyvinyl samples with rough surfaces are continuously stretched to yield the necessary strains. The experimental results are discussed and compared with corresponding analytical predictions. Both experimental and simulation results suggest that for flat surface conditions, the fiber optic system can replace the bulk optic system and yet maintain good performance of the later. It is further shown that the performance of the fiber optic system on flat surface conditions is insensitive to the configuration of the fiber probe. However, for curved surface conditions, the performance of the fiber optic system shows a complicated dependence on the sensing circumstances, indicating that a collimating fiber lens in front of the incident fiber would be necessary to make the system to work properly under most surface conditions.
Zheng, Jianjun, "Design, fabrication and testing of a fiber optic stress/strain sensor for soft stretchable materials using polarization imaging technique" (2007). Dissertations. 838.