Research On The Application Of Electromagnetic Metamaterials In Microwave Absorber And Antenna

Metamaterials are artificial media structured on a scale smaller than the wavelength of external stimuli. The electromagnetic properties they possessing are not found in nature. Conventional materials derive their electromagnetic characteristics from the properties of atoms and molecules, whereas metamaterials enable us to design our own "atoms". A famous example is the well-known microwave "invisibility cloak", gaining exotic electromagnetic properties from their structure as opposed to their intrinsic material composition. Metamaterials have attracted tremendous attention in academia because of their potential applications,for example, in the field of antenna, microwave circuit, microwave absorber and so on. Researches on the application of electromagnetic metamaterials in microwave absorber and antenna have been done in this dissertation. The main contents of this dissertation can be summarized as follows:1. Two types of metamaterial structures are designed and researched. The first type of metamaterials is the monolayer windmill structure. This kind of single type metamaterials has the advantages of simple manufacture and convenient being added lumped active elements on such structures to control their left-handed properties. Fristly, the equivalent permittivity, permeability and refractive index were extracted from the numerical simulations. Then two frequencies were taken from the left and right bands to do prism simulation in order to intuitively display negative refraction and positive refraction. We also studied the relationship between the structure parameters, electrical resonance and magnetic resonance frequency. Finally, this metamaterial was analyzed by the equivalent circuit model and then the analytic formula of equivalent permeability was obtained. Using the analytic formula, the relationship between the structure parameters and magnetic resonance frequency is explained in detail. The left-handed bandwidth of this single windmill shaped metamaterial is very small, only 500 MHz. In order to expand the left-handed bandwidth, we designed a double-sided metamaterial. It is found that the left bandwidth is greatly improved through numerical simulations and experiments.2. A dual-band polarization-/angle-insensitive metamaterial absorber is designed and researched. Firstly, the sensitivity of this absorber to incident angle is researched for TE and TM wave, and the reasons of the absorption peak shifted when the angle of the incident wave increased are explained. Subsequently, the absorber is verified by experiment and analyzed with theoretical method. The surface current, electric field intensity and magnetic field intensity are analyzed to research the principle of this absorber. Finally, the loss analysis are researched and designed from the metal ohmic loss and dielectric loss of the dielectric plate, respectively. This absorber has the characteristics of very large absorption angle for TE and TM wave.3. An ultrathin and broadband metamaterial absorber using multi-layer structures is designed and researched. Firstly, the top matching layer is researched deeply, and the relationship between the thickness of the matching layer and absorption rate is got. Then, a detailed theoretical analysis was given that the relationship of the thickness is inversely related to the two absorption peaks in the high frequency. At the same time, the polarization stability of the absorber is studied and the absorption spectra as a function of frequency and incident angle are plotted for TE and TM wave, respectively. Then,we analyzed the chart. In the study of wave absorption principles, the reflection cancellation principle and the resonance absorption principle are adopted to study the absorption curve in this dissertation. Analyzed results show that, the formation of three absorption peaks is olated due to resonance absorption. The absorption spectrum of the intermediate band formation reason is the reflection cancellation of electromagnetic wave.4. Two miniaturized antenna with metamaterial loading are designed and researched. Starting from the research of the metamaterial unit, a single ring and double rings metamaterial structures are designed and researched. The relationship between equivalent permittivity, permeability, refractive index and the structure parameters of the single ring metamaterial is researched deeply. The single ring metamaterial is loaded at the end of the antenna to reduce the resonant frequency. The reason of the resonant frequency reduces and occurs a new resonant frequency point was explained. At the same time, the relationship between the antenna resonant frequency and equivalent refractive index of this single ring metamaterial is studied in detail. We analyzed the relationship between the resonant frequency of the antenna and the real part of refractive index of metamaterial. In order to further reduce the resonant frequency of the antenna, a double ring metamaterial loaded antenna is designed.5. A wideband end fire directional microstrip antenna with metamaterial is designed and research. This designed antenna has the characteristics of wide bandwidth and the maximum radiation direction in the endfire. First of all, starting from the study of new periodic structures of two-dimensional, we calculated the dispersion curve of this structure. Then this periodic structure was used to design a broadband antenna, which is compared with a reference. Finally, the designed antenna was fabricated and measured.