Research On Dual-band Left-handed Metamaterials And Switchable Dual-band Resonant Modes

The left-handed material?LHM?is a kind of artificial subwavelength structures with simultaneous negative permittivity and permeability over the same frequency band,so it is also termed as double negative material.When electromagnetic waves propagate in LHM,the electric field,magnetic field and wave vector obey a left-hand rule.Since the artificial left-handed materials were proposed,researchers have designed various novel LHMs by adopting different methods.At present,LHMs have advanced from single and microwave frequency to multiband and high frequencies,from rigid LHMs with fixed frequency band to the flexible and tunable LHMs that could be applied to complex surfaces.The unique properties of LHMs make them be useful in many fields such as perfect imaging,microwave antennas,absorbers,et al.Based on the realization methods of the LHMs,we propose a new dual-band LHM and a switchable dual-band resonance LHM respectively in this paper.Numerical investigations are performed for these two LHMs by high frequency electromagnetic simulation software HFSS.The electromagnetic parameters,distributions of currents and electric fields and influences of structural parameters on the resonant characteristics of the LHMs are studied respectively.The research results may provide a reference for designing or manufacturing dual-band and multi-band LHMs,and have potential significance for expanding the fields of LHMs in different frequency bands.This thesis is arranged as follows:In Chapter 1,we first introduce the concept,realization and novel features of LHMs as well as the research progress at home and abroad,and present the realization methods of dual-band,multi-band and tunable LHMs.In Chapter 2,we propose a dual-band LHM composed of a pair of double split ring resonators?SRRs?and a pair of crosses.As the electromagnetic wave is incident perpendicularly,the electromagnetic responses of double SRRs and crosses are investigated,respectively.And then the dual-band response of double SRR-crosses composite structure is studied.Furthermore,the reasons of the dual-band response are analyzed by the distributions of currents and electromagnetic fields at the resonant frequencies.Finally,the influences of some parameters such as split width g,the horizontal length of crosses l1,the vertical length of crosses l₂,copper width w and incident angles on electromagnetic characteristics are discussed,respectively.In Chapter 3,based on the design idea of switchable LHM,a switchable dual-band resonance LHM is realized theoretically by loading RF MEMS switches at the gaps of symmetrical split rings.It is found that by controlling different states of the switches,the LHM can be switched between low-high-and dual-frequency responses.Moreover,by analyzing the distributions of currents and electromagnetic fields at the corresponding resonant frequencies,the mechanism of the switchable resonance characteristics are studied.Finally,the influence of structural parameters on electromagnetic properties is also investigated.In Chapter 4,we summarize the research results of this thesis and look forward to the future development of LHMs.