High performance pressure sensor based on multi-material functional fiber

• Main Author: Yang, Boyu
• Other Authors: Wei Lei
• Format: Thesis-Master by Coursework
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering; Pressure sensor; Fiber
• Online Access: https://hdl.handle.net/10356/177277
• Institution: Nanyang Technological University

As an important part of flexible wearable electronic devices and smart textiles, flexible pressure sensors, especially flexible micro pressure sensors, finding extensive applications across a diverse range of fields, encompassing areas such as medical diagnostics, health surveillance, detection of human movement, and interactions between humans and computers, etc [1] [8] [9]. In this study, the new design, manufacturing process and comprehensive test results of a high-performance multi-material pressure sensor based on thermal drawing of polymer optical fiber are introduced. Thermal drawing technology can easily fabricate the fiber with complex internal structure and multiple materials. In the thermal drawing process, the macro preform with designed fiber structure is heated and then pulled the into long fibers, while accurately remaining the cross-sectional geometry at a reduced scale. The pressure sensor fiber is based on capacitive mechanism, in which the capacitance changes with the distance change between two separated electrodes. When the pressure is applied on the fiber, the electrode distance increases and results in an increase in the capacitance. Conductive polymer made of SEBS/carbon black composite can be used as composite electrode and ensure the flexibility of fiber; polymer made of PMMA can be used as sacrificial layer to construct cavity structure, and SEBS cladding can ensure the flexibility of fiber. The fabrication of multi-material fiber comprises the following steps: 1) preparing a conductive electrode composite material by magnetically stirring SEBS/ carbon black in toluene; 2) hot pressing SEBS and PMMA sheets; 3) accurately assembling these layers into a consolidated preform matching the designed cross section; 4) thermal drawing the preform into continuous fibers while maintaining the internal micro-structure; 5) using acetone to selectively dissolve the sacrificial PMMA layer to create an air gap. The comprehensive experimental characterization proves that the realized optical fiber successfully maintains the complex multi-material concentric cylindrical micro-structure of the preform design over the whole length. Upon evaluation as a pressure sensor, the fiber demonstrates high sensitivity and is capable of sensing minimal pressures down to 0.098N, has fast response time under cyclic loading/unloading within milliseconds, and has good stability over large number of cycles, with negligible drift. It is worth noting that this kind of optical fiber also shows good flexibility, which can be bent into a 720° tight ring and wound in a narrow radius without damage. Seamless integration of micro-structures of various materials, high-performance pressure sensing capability, simple and large-scale manufacturing by thermal drawing and good flexibility/consistency make this pressure sensor fiber have great prospects in flexible electronics products, wearable electronic products, electronic textiles, soft robots and human-computer interfaces. In the thermal drawing technology, the fiber featuring a complicated internal configuration can be easily achieved by creating the equivalent internal architecture within the macroscopic preform, thus, there is significant versatility in choosing the range, bandwidth, and sensitivity of the pressure response. Innovative design strategies and scalable manufacturing methods have opened up an exciting way to realize the next generation of multifunctional flexible devices.