| Large structures(ridges, tunnels, stadiums and high-rise buildings and other infrastructure)and healthy operatio n is directly related to people’s life and property safety. Through the various parts of the structure health monitoring system for real-time、automatic and continuous monitoring of the structural parameters and evaluation analysis of the service lifetime of the structure of data security, having a very important significance,and sensor is the core component of the health monitoring system. At present, there are few studies on the pressure resistance / piezoelectric composite sensor at home and abroad, which has not been systematically studied and applied in practice. In this paper, the development of carbon nanotubes(CNT) and Zinc O xide(ZnO) and the piezoelectric properties of the piezoelectric composite properties of research, proposed a structural monitoring system applied in the field of civil engineering. In this paper, the pressure resistance / piezoelectric composite thin film sensor is able to overcome the defects of flexible、poor toughness and small measuring range. Thin film made of CNT has excellent piezoresistive effect,and ZnO pressure piezoelectric ceramic has the adva ntages of no pollution、low cost、high sensitivity of the prepared CNT/ZnO sandwich type thin film sensor as a mounted sensor, has very important application value in practice. The main research contents and results were given as follows:(1)Using mixed acid to oxidation treatment of CNT, the oxidized CNT were investigated by scanning electron microscopy(SEM), infrared spectroscopy(FTIR), thermogravimetric analysis(TGA), the analysis showed:CNT carboxylated shortened the length,brought the CNT with carboxyl group(-COOH) and thinned the diameter.We got aminated CNT(CNT-NH2) by Al-N iC l-THF redction system.SEM、FTIR 、 TGA analysis showed :the diameter became small,the agglomeration improved,CNT was brought with amino(-NH2) functional group.(2)In order to prepare nano-Zinc O xide,we used Zn(NO3)2·6H2O and concentrated ammonia as raw materials with the high-speed shear emulsifying mixer. XRD, laser particle size analyzer, TGA and SEM were used to characterize and analyze the morphology and crystal structure of ZnO, and the piezoelectric properties were characterized by d33/d31 measuring instrument. The results showed : the diameter of prepared ZnO was about 700-800 nm, the crystal structure was hexagonal wurtzite structure and reaction time was 35 min, pH was 11, piezoelectric coefficient(d33) was the highest, the d33 was about 13.13pC/N, and piezoelectric performance was the best.(3)To adjust the voltage of DC power supply from 1V to 10 V, testing out the membrane voltage and current, and drawing voit-ampere characteristic curve.Through the voit-ampere characteristic curve,we found that resistance 3,6,9,12-layer film were 976.424kΩ,398.412kΩ, 96.25kΩ,14.072kΩ. The resistance of the thin film decreased with the increase of the number of layers. And the film resistance was small, indicating that the preparation of CNT films had good electrical conductivity. This was because that functionalized CNT dispersed well in water and organic solvents.we made compact and homogeneous film by the method of layer-by-layer. 3,6,9,12-layer film resistivity were 19.53 kΩ ? cm, 7.97 kΩ ? cm, 1.93 kΩ ? cm, 0.28 kΩ ? cm.(4)To test the performance of CNT/ZnO sandwich type thin film sensor and its piezoelectric properties. Through the experimental results,we could see that film sensor had excellent pressure resistance performance. The resistance change rate(?R/R) changes with linear strain. Dfferent layers of the thin film sensors and the strain showed a good linear relationship: the linear degree of the 6 layer of the film sensor was the largest, the linear degree of the 9 layer was greater than the 3 layer, the 12 layer was the littlest. Under cyclic loading, either tensile or compressive state, the sensor could keep a high sensitivity, which was stable.The degree of dispersion was small. The sensitivity coefficient of the 6 layer thin film sensor was about 1.3/mm, which owned the highest sensitivity. The 9 layer is about 1.1/mm, and the 3 layer is about 0.75/mm, and the 12 layer is about 0.55/mm. In addition, there is no relationship between the drag effect and the loading rate.(5) DASP vibration measurements showed:with the increasing of ZnO content,the vibration was getting faster and faster. The ZnO showed that it had better piezoelectric properties, and it could be sensitive to the changes in the electrical signal and acceleration. In addition, with the increasing of the stress, the output signal increased, which indicated that the sensor had good linearity, and the stress disappeared after unloading. |
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