Development of electromagnetic metamaterials for microwave applications

Abstract

Metamaterials are artificial materials engineered to have properties that may not be found in nature and they usually gain their properties from structure than composition. Study on electromagnetic metamaterials has been very active over the past decades due to the peculiar electromagnetic responses of these materials and potential applications in communication systems, optics, microelectronics and etc. In the microwave range, electromagnetic metamaterials have stimulated a variety of novel designs of components and antennas, and yet the applications are rather limited. Research work for this thesis focused on metamaterials with an emphasis on the formation and tuning of their band structures as well as applications in microwave engineering, especially those featured with ultra-wideband, low radiation and/or high directionality. The research was mainly conducted by using software simulation as well as experimental studies. Tools for solving electromagnetic problems include Finite Element Methods (FEM) using commercial software FHSS. Prototype samples were fabricated by printed circuit board (PCB) method and characterized using standard microwave technologies. Interesting results have been obtained in the research. First, the correlation between structure and electromagnetic bandgap (EBG) of metamaterial has been established and general techniques for tuning the EBG structure have been developed. Several prototype EBG plates applicable at different operating frequencies have been fabricated and characterized, and the measurement results matched well with simulations. A number of antennas exhibiting advantages over conventional ones have been designed and fabricated. Second, the theory of composite left-right handed metamaterials (CRLH MTM) has been applied for manipulating bandwidth and near-field electromagnetic behavior of the materials. Based on the research, a supercompact ultra-wideband antenna and a low SAR mobile phone antenna, exhibiting excellent electromagnetic properties and ready for commercial applications, have been develop. Thirdly, some fundamental analysis on the control of electromagnetic radiation directionality has been made based on the electromagnetic theories and using simulation tools. Novel designs based on unconventional material selections have been proposed to achieve compactness and unidirectionality.