Research On Time Dependence Of Resistance For Multiple Outputs Viscoelastic Pressure-Sensitive Component Under Constant Pressure

Carbon nanotubes have excellent conductivity and great length to diameter ratio. For the reason that silicon rubber filled with a handful of carbon nanotubes can form a conductive network, while ensure the flexibility and piezoresistance sensitivity of composites, it can be used as flexible pressure sensor. Because of influence of substrate material composites is viscoelastic and great time dependent, all of which influence sensor precision seriously. Domestic and foreign researchers have been committed to weaken its time dependence, for instance, increasing the content of conductive filler or adding other solid particles, but these methods can not work significantly, furthermore, lower the flexibility of the composite. This thesis presents a new type of structure, which makes the pressure-sensitive work in incomplete pressure areas and extracts signal from different positions. This thesis is committed to weaken the time dependence of resistance with studying piezoresistive characteristics of composites.The main research contents of this thesis include the following items:(1) Flexible pressure-sensitive component was made with multi-walled carbon nanotubes for conducting filler, silicone rubber for matrix materials, by using co-solution method, assisting with ultrasonic wave and stirring dispersion treatment. Mulitple electrodes circuit boards were used as the above and underside boards of pressure-sensitive component.(2) A real-time automatic resistance collection system was desgined. MSP430F149was used as the control circuit chip. CD74HC4051was used as multi-channel analog switch. Resistance could be inputed through the multi-channel analog switch by acquiring voltage signal in turn. Then data were sent to PC through a serial port for saving and analysis after analog-to-digital conversion.(3) Experimental data analysis, the resistance-pressure-time characteristics were analysed quantitatively. Fitting formula of composites resistance creep was derived, and piezoresistive model was established preliminarily to explain the piezoresistive characteristics of composites. Impact of electrodes positions on piezoresistive characteristics and resistance creep was summarized. Resistance creep is suppressed effectively with changing positions of electrodes. The minimum of resistance creep is less than2%. Piezoresistive characteristics are directly related to distance of electrodes and relative position between electrode and the area under pressure. Resistance increases and resistance creep is suppressed at larger mass ratio. Because of stress degradation; resistance of composites decline gradually in the process of repeated loading.