Theory And Application Of Key Techniques For Reconfigurable Metamaterials

Novel artificial electromagnetic materials, also widely known as metamaterials, are hot research spots of electromagnetic theory and information science. Metamaterials generate a lot of new concepts and applications, which provide a broad space for people to design controllable permittivity and permeability materials and new methods to regulate electromagnetic wave propagation. In recent years, with the development of cognitive radio technology, microelectronics, computer technology, the real-time circuit reconfiguration technology has also been introduced in metamaterials to satisfy the requirements of artificial metamaterials adaptability to the changes of environment and application objects, which is gradually developing into another hot area of research in metamaterials.The theory and application of key technologies for reconfigurable metamaterials are studied in this dissertation. Some of the key issues of reconfigurable metamaterials are solved, the design idea of "universal" metamaterial element is proposed, and novel metamaterial antennas for the future development of wireless communication system are designed. The main contributions of the dissertation are summarized as follows:1. The effective medium theory and local resonance mechanism of artificial electromagnetic micro-structures are elaborated in the dissertation. Based on the equivalent circuit and retrieval algorithm from scattering network parameters, a bridge is constructed which can contact the topology of metamaterials, equivalent lumped circuits and effective medium parameters of ε and μ. It is the interaction and unity of circuits and fields, which lays the theoretical foundation for the study of reconfigurable metamaterials integrating with microwave control components.2. Based on the real-time circuit reconfiguration technology, frequency reconfigurable magnetic negative medium model of SSRR and electric negative medium model of DELC are proposed. The regulating mechanism of external control circuits and components on two basic elements is discussed. The new reconfigurable double negative medium model of RDNG is proposed. The proposed model structures are simple and easy controlled, which can be used as the building blocks of universal metamaterials.3. The new design of reconfigurable electromagnetic band-gap(EBG) structures is proposed. Integrating microwave varactors and PIN switches into the compact mushroom-like EBG structures, the regulation can be flexibly carried on the surface wave suppression bandgap and in-phase reflection band. The design can produce wide bandgap, mult-bandgap, and ultra-wide bandgap characteristics by using the fixed EBG physical dimension, as well as new artificial magnetic conductor with both frequency and polarization reconfiguration. In this dissertation, a set of reconfigurable EBG prototype system is designed and fabricated, including varactors array, mushroom-like EBG array, the DC bias circuit board controlled by microprocessors and an automatic control software. The system can control the capacitance of varactors array through software programming and regulate the bandgap effectively and dynamically. The measured results verify the correctness and effectiveness of the proposed reconfigurable EBG system.4. The new design of "universal" metamaterial element(UME) is proposed in this dissertation. Combining the single split-ring resonator(SSRR) with double electric-field-coupled resonator(DELC), a universal metamaterial element is built. By controlling the states of ON or OFF of PIN switches, the four quadrants material characteristics and interconversion can be realized respectively among double positive medium, electric or magnetic negative medium, and double negative medium. In theory, an arbitrary artificial effective medium parameter can be built using the UME as building block, also with dynamically adjustable feature.5. On the basis of reconfigurable EBG design, the dissertation proposes the tunable metamaterial absorbing structures. A new thin planar absorbing structure is proposed by using Jerusalem cross slot. Theoretical simulation and experiments have been implemented to analyze the effect of structural parameters on the absorbing frequency band. By parallelly loading varactors and resistors on the artificial magnetic conductor, the absorbing bands can be regulated and the almost perfect frequency hopping absorbing can be achieved. On this basis, an idea of broadband absorbing structure with reconfigurable nest design is proposed, which has important application prospect.6. According to the requirement of future wireless communication system for new materials, antennas and devices, the design of new broadband, miniaturization, and high-gain antennas is inspired by using metamaterials. An ultra-wideband printed inverse-F antenna(PIFA) is proposed using an artificial capacitive surface. Simulation and experiment results confirm its excellent operating characteristics of ultra-wideband. The working mechanism of metamaterial superstrates for high-gain antenna is revealed by using Fabry-Perot resonant cavity. A reconfigurable composite right- and left-handed(CRLH) antenna is proposed which has the advantage of flexibility in the regulation of the zero-order resonant frequency. The reconfigurable antenna can be realized for broadband or multi-band properties according to the need of the communication channels. The proposed antenna has a simple structure, miniaturization and high performance. This work lays the metamaterial foundation for the research and development of reconfigurable high-performance and miniaturization antennas for next generation wireless mobile communication terminals.