Modeling And Simulation Of Carbon Nanotube Bundle Antennas

Since the discovery of carbon nanotubes (CNTs), a huge amount of research interest has been aroused due to their unique electrical, thermal and mechanical properties, with many potential applications demonstrated. Among these applications, one should mention that the possibility of using CNTs to build some antennas. In the traditional antenna design, it is difficult to achieve miniaturization and high-gain simultaneously, but the novel CNT antennas may potentially sort out the above difficulties. The previous studies, however, have shown that the radiation efficiency of a single-walled CNT antenna is very low, which is mainly attributed to the strong retarded surface wave and the problem of impedance mismatch. In response, CNT bundle antennas are proposed and their characteristics are studied comprehensively by modeling and simulation in this thesis.We first briefly introduce the structure, properties, fabrication of CNTs, and the current research status of CNT antennas at home and abroad. Then based on fundamental physical theory, the equivalent circuit models and their electrical parameters of a single CNT and CNT bundle are proposed and discussed, respectively. Since the skin effect in CNT bundle is significantly reduced in high frequency, and each CNT has radiation effects, the CNT bundle, used to fabricate antenna, can be equivalent to a multiconductor transmission line (MTL) system.Considering that directly solving the MTL equations will be very time-consuming when the number of CNTs in the bundle is tremendous, two other methods is put forward to analyze CNT bundle antenna: 1) First, the MTL model of the CNT bundle is equivalent to an equivalent single conductor (ESC) model, and then a circuit model for two parallel SWCNT bundles with differential mode excitation is developed to study the antenna performance by flaring the two CNT bundles transmission line. In order to make the obtained current distribution more accurate, the propagation constant is modified based on the transmission line theory; 2) Due to the current technology and practical application of CNT antennas, the performance of CNT bundle monopole antenna is predicted using the classical Hallen's integral equation in wire antenna theory. And the characteristics of CNT bundle, including its quantum mechanical conductivity and wave number of the surface wave, are taking into account in the process of establishing the integral equation. Then the current distribution on the monopole antenna is obtained through solving the Hallen's integral equation by method of moment (MOM) to study the antenna performance. Furthermore, the effects of tube diameter, bundle cross-sectional structure, antenna length, and operating frequency are investigated.The aforementioned two methods have advantages and disadvantages, the former is simple and fast, and the latter is more accurate. Simulation results demonstrate that compared with the single CNT antenna, the efficiency of CNT bundle antenna has been greatly improved. The research results of this study have important implications for future analysis and design of CNT antenna.