Electromechanical Properties Of Intrinsically Conductive Fiber Assembles, Its Textile Structure And Applications As Strain And Pressure Sensors

With the development of science and technology, traditional textile products exhibit more functional, intelligent properties due to the cooperating with high technologies. Smart textile is such a novel fields that provide more fantasy to our daily life.To be used as textile sensor is a kind of smart textile and it has advantages such as flexible, wearable, breathable, thin and cheap, etc. Many research groups have been focusing on the applications of textile sensor based on the textile structure and material properties, because wearability is the trend of the next generation electronics.Most of the textile structural sensor is based on the conductive polymers which have the advantages of high sensitivity, ease polymerization, etc. However the disadvantages are also existed in the practical application such as poor environmental stability, low usage temperature, toxicity. etc. Therefore, intrinsically conductive materials such as carbon, metal, silicon, etc are the best candidates to overcome the disadvantages of conductive polymer in the fabrication of fabric sensor.Although many successful intrinsically conductive fabric mechanical sensors have been used in the practical application, however, very few systematic works has been done in the sensing mechanism, sensor structure designing, etc. In order to fabricate high quality fabric sensor, some works were done in our research to find out the key factors which governor the sensing mechanism of the fabric sensor and put forward some useful guidelines to help design this sensors. The conducting and sensing mechanisms of single fiber, fiber assembly and fabric structure were analyzed theoretically by the circuit model and verified experimentally. From the analysis, the best structures of yarn and fabric are abstained when design the fabric sensors. It is found out from the research that the contact resistance between two contacting fibers in the yarn is the key factor governing the sensing mechanism. How to design a suitable yarn and fabric structures that distribute the fiber contacts is the most important factor when design a high quality fabric strain/pressure sensor. Meanwhile, the intrinsic properties of fiber such as mechanical properties, surface morphology are also important factors effecting the properties of fabric sensor.It can be concluded from the experimental results that, for strain sensor, stable yarn which can provide more fiber-fiber contacts has high sensitivity and repeatability than continuous filament yarn. High bend modulus and smooth surface yarn has higher repeatability and lower hysterisis. Compared to woven fabric, knitted fabric can be used as large strain sensor due to its easy deformation under stress and have larger sensitivity for its loop structure that can provide more contact resistance of yarns. For single warp structure, fabric density is the key factor effecting the fabric sensor characteristics. As to pressure sensing fabric, woven is the best structure because it can provide regular distributed contact resistance grids and it is sensitive to lateral pressure. For the fabrication of strain sensor, knitting machine can be used and for pressure mapping sensor, embroidery machine is the best tool for its accurate distribute the sensing grid on the surface of the fabric. It is found that coating of the grids can improve the sensitivity, repeatability and enlarge the sensing region. As to wiring, separate and "common ground" method can decrease the "crosstalk" effect of current than full scanning methods. Some application prototypes were also introduced at the end of the thesis.