Distributed sensing has been an attractive alternative to the traditional single-point sensing technology when measurement at multiple locations is required. Traditional distributed sensing methods based on silica optical fiber and electric coaxial cables have some limitations for specific applications, such as in smart textiles and wearable sensors. By adopting the fiber thermal drawing technique, we have designed and fabricated multi-material electrode-embedded polymer fibers with distributed sensing capabilities. Polymers sensitive to temperature and pressure have been incorporated into the fiber structure, and thin metal electrodes placed inside fiber by convergence drawing have enabled detection of local impedance change with electrical reflectometry. We have demonstrated that these fibers can detect temperature and pressure change with high spatial resolution. We have also explored the possibility of using polymer optical fiber in a Raman scattering based distributed temperature sensing system. Stokes and Anti-Stokes signals of a PMMA fiber illuminated by a 532 nm pulsed laser was recorded, and the ratio was used to indicate local temperature change. We have also developed a unique way to fabricate porous polymer by thermal drawing polymer materials with controlled water content in the polymer. The porous fibers were loaded with a fluorescent dye, and its release in tissue phantoms and murine tumors was observed. The work has broadened the scope of multi-material, multi-functional fiber and may shed light on the development of novel smart textile devices. / PHD / In recent years smart textiles and wearable gadgets have already changed the way we live. There has been increasing industrial interest to develop novel flexible, stretchable devices that can interact with human and the environment. Thermal drawing technique originally invented for manufacturing telecommunication optical fiber has been used by researchers to fabricate fibers with more functionality. In this work, we report the progress made on the fabrication of multi-material fiber. Soft polymer fibers capable of measuring temperature and pressure were designed and made by the thermal drawing technique. Submillimeter fibers with thin copper electrodes have shown potential to be readily embedded in a smart fabric to provide 1D information in one direction or woven into a 2D pattern for area monitoring. We have also explored another temperature measurement scheme using polymer optical fibers with a pulsed laser. Compared with the electronic fibers, it is less susceptible to electrical noise and more robust. Lastly, we have shown a unique way to generate porosity in thermally drawn polymer fibers. The elongated pores in the fibers come from water escaping the fiber during the fabrication process. The three aspects of the project expand the scope of multi-material, multi-functional fiber and can shed light on the future development of electronic textile devices.

Polymer fiber sensors have been extensively explored over the past few decades for biomedical, structural health monitoring, and environmental monitoring applications. Their low melting point and well-established processing methods make them easily integrable with other materials, such as metals, semiconductor devices, and composites, to create multimaterial sensors with versatile sensing capabilities. However, the high viscoelasticity of polymer materials and the limitations of existing sensing mechanisms constrain the precision and stability of these sensors. This research focuses on enhancing the sensitivity of multimaterial polymer sensors by improving both the sensing mechanisms (chapter 2 and 3) and sensor structures (chapter 4 and 5). Chapters 2 and 3 discuss the integration of silica optical fiber sensors into magnetostrictive composite materials for distributed magnetic field sensing. A series of Fiber Bragg Gratings (FBGs) were inscribed in the core of a silica fiber, which was then thermally embedded at the center of a magnetostrictive composite made of Terfenol-D and thermoplastic elastomers. The magnetostrictive properties of the composite, using various polymer matrices, were thoroughly investigated. A detailed study of the sensor's response under different boundary conditions and applied tensions demonstrated its tunable frequency response and bandwidth capabilities. Furthermore, the sensor's magnetic field sensing performance was characterized under applied AC magnetic fields, showing a responsivity of up to 4.5 ppm/mT and a resolution of 0.1 mT. Theoretical modeling of the magnetostrictive fiber's behavior was also conducted, with the strain transfer coefficient being calculated and compared to the bulk material's response. This thermally drawn magnetostrictive fiber exhibits significant potential for fully distributed sensing applications. In Chapters 4 and 5, the development of a stretchable fiber strain sensor is presented, with improvements in sensitivity achieved through structural optimizations. Polymer fibers, known for their high stretchability, flexibility, and softness, are promising candidates for sensing applications. However, their high viscoelasticity often leads to significant hysteresis. To address this, a double-coil strain sensor was introduced in this research. A theoretical model of the double-coil capacitance was developed to inform future sensor designs. Based on this model, a stretchable miniature fiber sensor was constructed, featuring a stretchable core tightly coiled with parallel conductive wires. This sensor demonstrated low hysteresis, a theoretical resolution of 0.015%, a response time of less than 30 milliseconds, and outstanding stability after more than 16,000 cycles of testing. Its potential as a wearable device was showcased by embedding it into belts, gloves, and knee protectors, with applications ranging from bladder monitoring to life safety rope systems. The dissertation concludes with a discussion of the research findings and suggestions for future directions in the development of multimaterial fiber sensors. / Doctor of Philosophy / This research focuses on enhancing the sensitivity of polymer fiber sensors, which are widely used in healthcare monitoring, infrastructure safety, and environmental observation. These sensors offer the advantage of integrating with other materials to create versatile, multi-functional devices. However, their soft nature and limited sensing mechanisms pose challenges to measurement accuracy and stability. This dissertation proposes improvements in the sensitivity of multimaterial polymer fiber sensors by enhancing both their sensing mechanisms and structural designs. In the first part, new techniques were developed to improve magnetic field sensing by embedding optical fibers into magnetically responsive materials. A scalable method called thermal drawing was used to fabricate magnetostrictive fibers, enabling the sensors to measure magnetic fields at various locations with a minimum detectable change of 0.1 mT. This approach enhances the accuracy of magnetic field detection, which is valuable for monitoring magnetic field distributions in industrial applications. The second part introduces a stretchable sensor designed for strain detection in wearable, biomedical, and structural health monitoring applications. Featuring a double-coil design, this sensor demonstrated stability, durability, and accuracy in real-time monitoring by detecting changes in relative capacitance. Overall, this research offers significant insights into improving the reliability and effectiveness of polymer fiber sensors, paving the way for future innovations in smart sensing technologies. The dissertation concludes with a discussion of potential improvements and future research directions.