Research Of Carbon-based Composite Materials Based On FDTD Method

Carbon nanotubes(CNTs)and polymer have complementary advantages.The polymer is generally used for the preparation of composite materials with CNTs because of its light weight and easy processing.CNTs composites with both advantages have wide range of applications,and have far-reaching impact on the imaging technology,spectroscopy technology and safety testing.Different kinds of polymer make the CNTs composites have different physical and chemical properties.Carbon composite also can be applied in high conductivity materials and microwaving absorption.And the carbon nanotube is a kind of excellent composite filler.So far most of researches are analyzed by experimental data.But there are still few researches on it with specific dispersion model.In this thesis,the electromagnetic propagation characteristics of CNTs and CNTs composites under normally incident is investigated and the improvement of carbon nanotubes in composites are introduced in detail.The second part displays several commonly used dispersion models and boundary absorbing condition.The permittivity,dielectric loss tangent and real conductivity of CNTs composite varies with frequency are given.The third part briefly introduces the finite-difference time-domain method.The field and current equations that describe waves in CNTs composites with Cole-Cole dispersive model are derived and discretized based on the fractional derivate method.The field equations of the Debye,Lorentz and Drude dispersion models are given based on the fractional derivate method.The shielding effects of multi-walled carbon nanotubes/high density polyethylene(MWNTs/HDPE)with different thicknesses are compared.Numerical result demonstrates that the shielding effect increases with the increase of the thickness.Besides,the silica substrate is considered in calculation.The different thicknesses of MWNTs/HDPE attach to SiO2 are compared to analyze the transmission coefficients.Then,the chirality parameter of CNTs in composites is considered to analyze the electromagnetic properties,especially the microwave absorption of MWNTs/HDPE.Numerical results indicate that chirality parameter has an influence on the polarization of the electromagnetic wave to a certain extent.The chirality parameter of CNTs derived from its special helical structure which also brings particularly properties of microwave propagation.Analyzing the electromagnetic characteristics and electric field in space,the optical rotation and circular dichroism of chiral carbon nanotubes are clearly observed.