ABSTRACT KAPOOR, ASHISH. Fiber-based Sensors for Electronic Textiles. (Under the direction of Dr. Tushar K. Ghosh). Electronic textiles are textiles integrated with electrical functionalities like sensing, actuation and energy harvesting. Wearable e-textiles with sensing functionality have recently attracted a lot of scientific and commercial interest because of their uses in healthcare, security systems and other areas. Electronic sensing capabilities can be integrated into textiles at fiber, yarn, or fabric level but unobtrusive integration of sensing capabilities while preserving all desirable textile qualities like comfort and flexibility requires introduction of desired electrical characteristics at the fiber level. In this research, I have demonstrated a transformative sensing technology through the design of a multimodal and multifunctional woven sensor array by employing dumbbell shaped bicomponent fibers consisting of insulating and electrically conducting segments. Each cross‐over point in the woven fabric structure acts as a sensing pixel. These fibers have been fabricated using sequential extrusion printing method and coextrusion method. The insulating segments are made using an ultraviolet (UV) curable poly(dimethyl siloxane) (PDMS) while the conducting segments are made from a conducting polymer composite (CPC) containing PDMS and carbon black (CB). The multimodal characteristic of the sensors is demonstrated through the measurement of capacitive and resistive response while multifunctional capabilities were explored by measuring tactile (normal force), tensile, and shear deformations, as well as wetness and biopotential (heart rate). As a potential biomedical application, these fiber based sensing arrays were integrated into prosthesis socket to monitor pressure within inner socket environment of lower limb amputees. Also, a large channel sensor array was fabricated and its potential for contactless sensing of gestures was demonstrated as a potential textile-based human-machine interface. Although this dimensionally scaled-up elastomeric fiber poses challenges for textile fabrication using conventional fabric formation techniques, this fiber based sensing approach can be used for scalable manufacturability of advanced e‐textile products. © Copyright 2020 by Ashish Kapoor All Rights Reserved Fiber-based Sensors for Electronic Textiles by Ashish Kapoor A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Fiber and Polymer Science Raleigh, North Carolina 2020 APPROVED BY: _______________________________ _______________________________ Dr. Tushar K. Ghosh Dr. Alper Bozkurt Committee Chair _______________________________ _______________________________ Dr. Ericka Ford Dr. Xiangwu Zhang DEDICATION To my parents Mr. Narinder Kapoor and Mrs. Urvashi and my brother Aayush Kapoor along with my teachers. ii BIOGRAPHY Ashish Kapoor received his Bachelor’s degree in Textile Engineering in 2013 from Jawaharlal Nehru Government Engineering College, India followed by Master’s degree in Textile Engineering from Indian Institute of Technology Delhi, India in 2015. He joined the Fiber and Polymer Science Ph.D. program at Wilson College of Textiles, North Carolina State University in August 2015 and started working under the direction of Dr. Tushar K. Ghosh in the field of electronic textiles. He worked towards the development of fiber based multimodal and multifunctional active sensory textiles. He received the NC State University’s Provost Doctoral Recruitment Fellowship for 2015-16, DAAD (German Academic Exchange Service) RISE Professional Scholarship in 2018 and NC State University’s Graduate School Summer Fellowship in 2019. Upon completion of PhD, he will be joining Intel in Hillsboro, Oregon as TD Etch Module Engineer. iii ACKNOWLEDGMENTS I would like to thank my advisor Dr. Tushar Ghosh for giving me the opportunity to work in the growing field of electronic textiles and inspiring me do quality research work so that I can make valuable contribution to the overall body of knowledge in this field. I would like to thank Dr. Alper Bozkurt for serving as a Graduate School Representative on my committee and for his insights on electrical characterization of sensors and support at every step in the degree program. I also extend my thanks to Dr. Helen Huang for providing useful suggestions in navigating the experiments with prosthetics and supporting my efforts in this regard. I would also like to thank Dr. Ericka Ford and Dr. Xiangwu Zhang for serving on my committee and for their suggestions on improving my work. I would like to thank my Textile research teammates, Kony and Jordan. Kony helped in assembling the extrusion printing setup and created the extrusion die design which were significant tasks for the progress of my research work. I would like to thank Jordan for helping with the initial coextrusion experiments. I would like to thank the ECE teammates, Michael and Talha without whom this research would not have been possible. Michael helped in developing methods for testing sensing response of fibers and Talha fabricated the printed circuit boards and algorithms for data collection for various experiments. I would also like to thank Hannah for helping with experiments with extrusion printed fibers and Brendan for his help in data collection and plotting of prosthetic experiments. I would like to thank Aaron for setting up the artificial limb test bench and his support in executing prosthetic experiments. I would also like to thank Dr. Ming Liu for his support in prosthetic experiments. I thank Judy Elson for helping with the optical microscopy of fibers and Dr. Philip Bradford for allowing to use the laser cutting machine. I am thankful to iv Dr. Shannon Madden for her support in revisions and overall support during the writing process and Parth Chansoria for helping with creating designs on SolidWorks. I would like to thank my past and current lab-mates; Xiaomeng, Kony, Shuzhen, Jordan and Aaloka for their support at every step. I am also grateful to the funders who supported my PhD work namely the Provost Fellowship, NSF and Graduate School Summer Fellowship. I would also like to thank Dr. John Rust, Dr. Andre West and Dr. Kavita Mathur for supporting me in my final years of PhD as without their support this journey would not have been possible. Lastly, I express sincere thanks to my wonderful parents and lovely brother who always encouraged, inspired and supported me throughout this process. v TABLE OF CONTENTS LIST OF TABLES ...................................................................................................................... viii LIST OF FIGURES ...................................................................................................................... ix Chapter 1: Introduction .............................................................................................................. 1 Chapter 2: Textile-based Sensors: A Critical Review .............................................................. 5 2.1 Introduction ................................................................................................................ 5 2.2 Sensing Mechanisms and Performance Characteristics ............................................. 8 2.3 Materials ................................................................................................................... 24 2.4 Applications of E-textile Sensors ............................................................................. 29 2.5 Summary and outlook .............................................................................................. 47 Chapter 3: Extrusion printed multimodal and multifunctional sensors .............................. 64 3.1 Abstract .................................................................................................................... 64 3.2 Introduction .............................................................................................................. 64 3.3 Materials and Methods ............................................................................................. 73 3.4 Results and Discussion ............................................................................................. 76 3.4.1 Electromechanical characterization ................................................................. 76 3.4.2 Sensory response ............................................................................................. 77 3.5 Conclusion ................................................................................................................ 85 Chapter 4: Fabrication of Multimodal Fiber-based Sensors via Coextrusion: A Microfluidics-Inspired Approach ............................................................................................. 91 4.1 Introduction .............................................................................................................. 91 4.2 Materials and Methods ............................................................................................. 92 4.3 Results and Discussion ........................................................................................... 100 4.4 Conclusion .............................................................................................................. 110 Chapter 5: Prosthetic Environment Monitoring using Fiber Sensor arrays ..................... 116 5.1 Introduction ...........................................................................................................