【作者】 王志峰；

【导师】 叶雄英；

【作者基本信息】 清华大学 ， 仪器科学与技术， 2013， 博士

【摘要】 柔性力敏传感器是一种用于感知表面作用力分布的柔性电子器件，能贴附于各种不规则表面，在机器人、生物力学、医学测量等领域有着广泛的应用前景，逐渐受到人们的重视。碳纳米管（CNT）具有良好的导电性和超高的长径比，与聚合物复合有望得到灵敏度更高、柔性更好的力敏材料，为柔性力敏传感器性能的提高提供了一条新的途径。本论文以优化碳纳米管/聚合物复合材料的力敏特性为目标，开展了碳纳米管网络导电特性和力敏效应微观机理研究，提出了优化力敏特性的方法，并通过实验进行了验证，设计制作了一种基于该复合材料的柔性力敏阵列传感器及其信号读出系统。论文首先分析了CNT导电网络的特征，建立基于隧道效应的CNT网络仿真计算模型，得出CNT之间的隧道效应结电阻是决定网络导电性的主导因素，CNT网络可以简化成由隧道结电阻组成的导电渗流系统。建立了网络导电性微观机理模型，指出决定复合材料导电性的微观因素包括：参与导电的CNT段浓度和等效隧道结电阻系数。仿真计算结果表明力敏效应来源于材料变形引起的CNT段浓度和等效隧道结电阻系数的改变，两者均可以用平均隧道结间隙变化（AJGV）来量化。基于AJGV建立了复合材料电阻应变灵敏系数的微观量化描述，指出提升灵敏系数的基本原则是增大单位应变引起的AJGV和降低CNT段浓度，并给出具体优化方法，提出通过使CNT取向和调节聚合物交联度来提升复合材料灵敏系数的方法。研究了CNT在聚苯乙烯和聚二甲基硅氧烷中的分散方法及其复合材料制备工艺，测试了复合材料在正负小变形下的力敏特性，验证了泊松比对力敏特性的影响。实验结果显示材料灵敏系数随CNT浓度的减小、旋涂取向转速的增大、交联度的减小而增大，与理论仿真结果吻合。实验中达到的最大电阻应变灵敏系数为44，约为单晶硅最大值的1/2；旋涂取向使灵敏系数提高了1倍，降低交联度提高了2倍。选择CNT/聚二甲基硅氧烷作为柔性传感器的敏感材料，研究了其与金属电极的接触电阻和压阻粘弹性现象，设计制作了16×16单元的柔性力敏阵列传感器，以及带有串扰隔离功能的扫描读出电路和LabVIEW数据处理软件，对传感器的基本性能参数进行了初步测试，实现了压力分布的实时测量。更多还原

【Abstract】 Flexible electronic devices have received growing attentions because theirexcellent flexibility allows them working with irregular or deformable objects. Flexibleforce sensors can be used for measuring of surface force distribution on a curvedstructure, which are indispensable in many fields, such as robotics, biomechanics andmedical measurements. Carbon nanotube (CNT) filled polymer composites are one kindof hopeful piezoresistive material as they combined excellent conductivity andsuper-aspect ratio of CNTs and good flexibility of polymers, which provide a new wayto improve the performance of flexible force sensors. In this dissertation, in order toenhance the piezoresistivity of CNT/polymer composites, the microscopic mechanismof the conductivity and piezoresistivity of CNT networks embedded in polymer matrixwas investigated, and an optimizing method was proposed and verified by experiments.A flexible thin-film pressure sensor array based on a CNT/polymer composite and itsscanning readout system are also fabricated and tested.A simulation model that takes account of the tunneling conduction between CNTswas established for the mechanism investigation of the CNT network. Tunnelingjunction resistances between CNTs were found as the dominant factor of the networkresistivity and the complicated CNT conducive network was hence simplified into apercolation system which is composed of junction resistors. A mechanism model of thenetwork resistivity in the microscopic aspects was introduced for the followingpiezoresistivity analyses and the key factors that dominate the network resistivity werefound as the conductivity CNT segments density and the effective tunneling junctionresistance.Simulation results showed that the piezoresistivity of a CNT network is originatedfrom the strain induced variations of the conducting CNT segment density and theequivalent tunneling junction resistance, which both can be quantitated by averagejunction gap variation (AJGV). The network piezoresistivity model was then developedbased on AJGV and a optimizing principle that includes maximizing the strain inducedAJGV and minimizing the conducting CNT segment density was proposed. Theorientation of CNTs to the normal plane of strain and a lower cross-linking density weresuggested to enhance the piezoresistivity of CNT/polymer composites. The dispersion process of CNTs in polystyrene and polydimethylsiloxane wascarried out and the composites were prepared for the piezoresistivity optimizing methodverification. The resistance variations with small tensile and compressive strains of thecomposites were measured and the influence of Poisson’s ratio on the piezoresistivitywas validated. The results showed that composites with lower CNT concentration,higher orientation degree, and lower cross-linking density have a higher piezoresistivity,and coincide well with the simulation predictions. The largest gauge factor obtained inour experiments is44, which is about one half of the largest value of silicon. Besides,the piezoresistivity was doubled by orientation of CNTs and was increased2times bydecreasing the cross-linking density.The CNT/polydimethylsiloxane composite was chosen as the sensitive material for itsexcellent flexibility, and then the electrical contact property with electrodes and thehysteresis of the piezoresistivity was measured. A flexible thin-film force sensor arraywith16×16elements was designed and fabricated. To measure the force distribution, ascanning readout circuit with crosstalk isolation and a LabVIEW program for dataprocessing were developed. Finally, the fundamental performance parameters of thesensor array are measured preliminarily and the sensor system can measure surfaceforce distribution in real-time.更多还原