Study Of Dielectric Properties And Electromagnetic Shielding Effectiveness Of Carbon Nanotubes And Their Composite Materials Based On Artificial Intelligence

Carbon nanotubes(CNTs), Which can be thought of as graphitic sheets with a hexagonal lattice that have been wrapped up into a seamless cylinder, have attracted scientific interest due to their unique and outstanding properties, such as excellent elongation, elastic modulus, resistance to strong acids and alkaline, and thermal conductivity.With the rapid development of computer science and technology, computers play a more and more important role in today’s modern world. In this thesis, the artificial neural network expert system of carbon nanotube composite materials have been established, which includes the following aspects. Firstly, the expert system has possessed of its database management, its neural network training function and its neural network prediction. While, its database management of CNTs composite was established by using SQL Server 2005. And the improvement of the BP neural network was finished by training its neural network structure according to the relationships among the properties and the technology factors of CNTs composite. Accordingly, the prediction of CNTs composite can be successfully operated. For example, at 8.5~12GHz, the electromagnetic shielding effectiveness of single-walled carbon nanotube/polyurethane composites with 20% CNTs content is about 15.27~15.81 d B, while the changes of its dielectric constant are relatively stable. Besides, at 100~1000MHz, the electromagnetic shielding effectiveness of multi-walled carbon nanotube/silicone rubber composites with 8% CNTs content is about 24.79~26.71 d B. Moreover, at 8.5~12GHz, the electromagnetic shielding effectiveness of single-walled carbon nanotubes/epoxy resin composite with 15% CNTs content is about 22.8~23.56 d B, while the changes of its dielectric constant are relatively stable.Moreover, in this thesis, the dielectric properties, optical properties and electromagnetic shielding effectiveness of carbon nanotubes are also researched, and the band structure and the density of states of single-walled carbon nanotubes are analyzed. According to the calculation results of the first principles, the results are as follows.(1) The Energy gap of zigzag tubes shows oscillation with the increase of the diameter, the energy gap of the armchair tubes first increases then decreases with the change of diameter, andthese calculated results according to the first principle method are different from those of the tight-binding method.(2) The different structures of the SWCNTs has different optical properties. The corresponding frequency range of the extinction coefficient characteristic peak is decreasing; The strongest absorption peak tends to weaken, and the corresponding frequency of the strongest peak tends to decrease; the corresponding frequency range of(n,0) type reflection peaks is decreasing, and the strongest reflection peak frequency with the corresponding reflection coefficient is oscillating; the frequency range of(n,n) type reflection peaks is also decreasing, and the frequency of the strongest peaks is about 5.38~6.20 e V.(3) The dielectric constant 2e of single-walled carbon nanotubes is in infrared area, which is about 0~1.5e V, the peak slowly changes with the increase of carbon nanotube diameter, and the corresponding frequency change is oscillating.(4) The electromagnetic shielding effectiveness of single-walled carbon nanotubes in high frequency is higher than that in low frequency, and at 0~400THz, electromagnetic shielding effectiveness gradually increases with the increase of frequency. For zigzag tube, at 0~450THz, the larger the diameter is, the smaller the absorption loss is; at 650~810THz, the larger the diameter is, the bigger the absorption loss is. For armchair tube, at 0~420THz, the larger the diameter is, the bigger the absorption loss is.Various properties of materials can be comprehensively improved by putting the excellent physical properties of carbon nanotubes into composite materials. According to the calculation results of the first principles, the properties of materials can be optimized by adding single-walled carbon nanotube with proper type. All of these will provide the important reference for the using of single-walled carbon nanotubes and the related CNTs composites in optoelectronic devices and electromagnetic shielding applications.