Investigation On Electromagnetic Wave Absorbing Properties Of The Carbon Nanotubes

Particular attention was paid to promote the novel properties of stealthy materials, such as strong absorption, wide frequency band, light mass, thinness, multifunction, compatible absorption from infrared to microwave, and other predominant integrative properties. Carbon nanotubes can be used as stealthy material wildly because of its remarkable mechanic, electrical, magnetic, and electromagnetic wave-absorption properties.Based on the stealthy mechanism of wave-absorbed materials, the character of electromagnetic wave-absorption has been discussed in this paper at first. The valence-bond structure of carbon, the atomic structure, the properties of Brillouin zone of the tubes, its relations with the graphene and the conditions of forming the metal or the semiconductor style tubes were explored and described systematically. Furthermore, the analytic expression of the Ï€-eletronic energy dispersion (or state) relations for the perfect chiral SWNTs and TCNTs was derived based on tight-binding model. It was found that an external magnetic field might induce the change of the energy gaps resulting in the metal-semiconductor continuous transition with magneticflux Φ_i in the period Φ_i =Φ₀(h/e) for the perfect chiral SWNTs and type I andtype II TCNTs, this is obvious AB effect which influces the electromagnetic wave-absorption in evidence.The electromagnetic wave-absorption mechanism of carbon nanotubes is complicated. Carbon nanotubes have remarkable electromagnetic wave-absorption property at the frequency range from visible to infrared. The former corresponds to the transition between energy bands, and the latter to the excitation of the radial breathing mode. Starting from the direct interaction between vibration of crystal lattice and electromagnetic wave, we discussed the atom vibration mode and Raman scattering in SWNTs, we emphasing on study the infrared absorption mechanism of SWNTs, and built a theoretical model of radial breathing mode, then analysed and calculated the dependence of mode frequency on tube parameter. The microwave absorptionmechanism of carbon nanotubes and experimental results have been discussed in detail as well.Based on chirality electromagnetism theory, the models of intrinsic chirality and screw structure which making carbon nanotubes wave-absorption in millimeter to centimeter wave band has been presented. Chirality enhances the character of electromagnetic wave-absorption of carbon nanotubes distinctly. We have discussed the mechanism of wave-absorbed of chirality materials and the chiral carbon nanotubes, and how to realize wide frequency absorption by adjusting their chirality parameters.