Study On The Low Scattering Properties Of Metamaterials

Metamaterial has achieved more and more attention because of its singular response to the electromagnetic wave. Conventional materials derive their electromagnetic characteristics from the properties of their atoms and molecules, metamaterials enable us to design our own “atoms” and “molecules” and thus access new properties, such as near perfect absorption and imaging with unlimited resolution. The next stage of metamaterials will be the development of active, controllable, and nonlinear metamaterials.In this dissertation, we mainly focus on the the scattering modulating by the metamaterial. Our research consists of following three parts: by tuning the electromagnetic wave absorption of the metamaterial structure we can control the scattering of microwave; by controlling the propagation of microwave we can achieve the wave move around obejects, so as to get backward RCS reduction; the polarization control to get the wave we need, so to achieve perfect absorption. Further more, a RCS calculation of metal plane has been studied to choose the appropriate algorithm. The main works and conclutions are exhibited as following:1. By using the characteristics of capacitance value of varactor diodes changing with the bias voltage, we load varactor diodes in the absorbing structure, so as to change the inductance of absorbing structure, thereby achieving the tunability of the resonance frequency; Futhermore ultilizing the PIN diode resistor altered properties to change the impedance of the structure, so as to achieve the tunability of absortion amplitude; thus we have obtained a metamaterial structure with the ability that both resonant frequency and amplitude can be respectively tuned. Transmission line theory and the equivalent circuit theory are used to theoretically explain the tuning characteristics. Theoretical results, the simulation results and experimental results show that the designed structure has the feature of absorption tunability. Meanwhile, based on the idea of smart absorber proposed by other reseachers, we have improved the structure to achieve smart absorber. It canautomatically track and identify the information of incident wave, then through self-regulation to remain low reflection.2. We demonstrate the design of a low-scattering metamaterial shell with strong backward scattering reduction and a wide bandwidth at microwave frequencies. Low echo is achieved through cylindrical wave expanding theory. The EM parameters wr need is calculated by this theory. According to the effective media theory, proper structure is selected to realize the low EM parameters and low loss on the resonance brim region. The full-model simulations show good agreement with theoretical calculations, and illustrate that the backward RCS reduction is achieved with certain bandwidth.3. By using of the switch effect of PIN diodes we can change the equivalent impedance of metamaterial structure, thus to achieve the different phase separation of reflected waves. When the phase difference reaches a certain value, the polarization conversion of the reflected wave is obtained too. The simulation and experimental results have validated that the broadband circular polarition conversion has been realized by designed structure. On this basis, a two layer structure has been designed to achieve polarization switch, via the PIN diode on and off, arbitrary polarization conversion is achieved between the linear polarization, the left-hand circular polarization, right-hand circular polarization and cross-polarization.4. We use the GTD(Geometrical Diffraction Theory) and UTD(Uniform Geometrical Theory to theoretically calculate the RCS of a simple model-metal plane. The agreement between the theoretical calculations and experimental results show the effectiveness of the UTD in scattering calculations.