Research On Radiation And Scattering Of Carbon Nanotube At Terahertz Region

The hige-effecient, reliable, miniaturized terhaerta sources and detectors are the decisive factor in the practice applications of terhaetz radar and communication, terahertz dignosis and imaging, and terahertz time-domain spectroscopy. The lack of the high-power, low-cost, portable room-temperature terahertz sources and detectors is the most significant barriers of modern terahertz systems. Recently, the development of new materials has become an important way in the field of terhaertz wave radiation and detection, however, accompanying many of the fundamental theoretical problems to be solved. Given that the unique structure and excellent electrical properties of carbon nanotube as a new nano-material, the radiation and scattering properties of carbon nanotube antenna have been investigated at terahetz reigions. The results will provide theoretical guidance for the development of the new technoloogy of terahertz radiation and detection.Firstly, the electronic energy structrue of armchair and zigzag carbon nanoube are obtained by tight-binding approximation method. The conductive properties of two kinds of carbon nanotubes are confirmed using the disersion relation from the elelctronic energy structure. Then the feasibility of terahertz wave radiation from carbon nanotube is presented using the interaction of electrons and phonons in the low-dimensional systems combining with the selection rules of electons transition.Secondly, considering the fact that the carbon nanotube has four quantized condutive channels determinded by electron spin, the distributed parameters of carbon nanotube equivalent circuit are present based on the equivalent transmission line. In analysis of equivalent resistance, the infuence of the length scaling of carbon nanotube and the bias voltage of carbon nanotube on the resistance is considered, in addition to the quantum resistance. In analysis of distributed capacitance and inductance, the quantum capacitance and kenitic inductance determined by the quantum effect are established. The static and quantum capacitance are not ignored by calculated the both of zigzag carbon nanotube. However, the value of kinetic inductance is more three orders of magnitube than the value of magnetic inductance, which leads to the magnetic inductance ingnored in the equivalent inductance.Thirdly, based on the equivalent distributed parameter above, a carbon nanotube antenna model is proposed. The wave velocity of carbon nanotube antenna is slower than that of common metal antenna, and the wave velocity in the range of 0.004-0.02c. the carbon nanotube antenna shows the propertiy of plasma resoance. By moment method, the surface current distribution and radiation efficiency of carbon nanotube antenna have been studied. The surface current distribution form is agreeemt with that of normal dipole antenna, which is depended on the antenna structure. But, in the resonant frequency at teraherz range, the radiation efficiency of the order of 10-3 of carbon nantoube antenna is far below the efficiency of normal dipole antenna, which is due to carbon nanotube having too small radius.In view of singel walled carbon nanotube antenna with low-efficiency and high-return loss, the carbon nanotube bundle antenna is proposed. The propagation property, current distribution, and radiation properties have been studied by moment method. The results confirmed the retun loss of carbon nanotube bundle antenna is higher two orders of magnitue than the singel walled carbon nanotube antenn, and the radiation efficiency is improved significantly.Finally, the scattering model of carbon naotube is present using the equivalent boundary condition and the quantum conductance function. By modeling techniques with the Bessel and Hankel function, the scattering properties of electromagnetic wave incident on carbon nanotube are investigated at terahertz reigion, in addition to the scattering properies of carbon nanotube illuminated by line-electric source. The influence of frequencies, carbon naotube radius, and the electomagnetic polarization on the scattering properties is discussed. Theoretical results is agreement with experimental results reported in the literature, which demonstrates the theoretical model is correct and practical.The various theories of carbon nanotube antenna are developed in this dissertation work. These important researches not only broaden the appliaction field of carbon naotube but also profoundly demonstrat the unique electromagnetic properties of carbon nanotube. The results have important significance to the development of terahertz science and technology.