Fracture Induced CNT-paper Composites for Wearable Sensors

Abstract

Wearable sensors have been widely applied in the fields of human-machine interface, medical care, and disease diagnosis. Various types of wearable sensors with different materials and fabrication methods have been developed. However, high fabrication cost, low sensitivity and large form factors have hampered their popularity of wearable applications. Paper-based sensors have shown merits of simple fabrication, high sensitivity and light weight. Biomedical, chemical, and physical wearable sensors have been developed by using paper substrate. In this dissertation, a novel manufacturing method of carbon nanotube (CNT)-paper composite is studied with characterization of mechanical and electrical properties. A fracture-induced fabrication method of a CNT-paper composite (CPC) is studied in terms of reorganization of a CNT-cellulose fiber matrix. By precise control of the applied strain, resistive and capacitive sensors are produced to enable the measurement of heart beats, grabbing force, finger motion, and eye movement. Using a CPC, a humidity sensor is developed for wearable applications. The enhancement of sensor response due to swelling of CPC coated with polyacrylic acid (PAA) is studied for detection of water vapors in air. The humidity sensor is applied for measurement of surface moisture. The CPC sensor provides a low-cost, highly sensitive, light-weight flexible platform potentially beneficial for sweat monitoring. An unobtrusive light-weight, low-cost eye tracking sensor is developed by using a capacitive sensor made of a fractured CPC. The eye movement is measured by the capacitance changes induced by the distance and permittivity change between eye ball, muscles and CPC sensors. The fabrication procedures and sensor design are optimized for best sensing performance. Finite element analysis is applied to understand the capacitive sensor made of the fracture induced nanoscale electrodes. The sensitivity and resolutions are characterized in terms of the capacitive geometry. In summary, the dissertation presents the characteristics of fractured CPC and the applications to multiple wearable sensors. A CPC coated with PAA is investigated for detection of relative humidity and moisture. The low cost, high sensitivity, light weight and easy fabrication will offer a stepping stone to advance current wearable sensing platforms.