| The electrical permittivity e and the magnetic permeability μ are the fundamental characteristic quantities that determine the propagation of electromagnetic waves in matter. Almost all of the natural materials have positive permittivity, e and permeability, μ. In 1968, Veselago introduced the concept of left-handedmetamaterial-a medium in which both the permittivity and permeability aresimultaneously negative. Although metals have a negative s and ferromagnetic or anti ferromagnetic materials have a negative μ, no known materials exist in nature with simultaneously negative ε and μ. Veselago's analysis with e and μ both negative have remained a curious exercise in electromagnetic theory. However, in the mid-1990s, Pendry et al. suggested a model of periodic array on thin metallic wires to simulate plasma and obtained a negative εeff below the plasma frequency. An array of split ring resonators (SRRs) was adopted to realize a negative μeff at the region close to the resonance frequency. By combining SRRs and wires, Smith and his collaborators first demonstrated the negative index of refraction of LHMs. Many fabulous properties such as reversed Doppler shift, reversed Cherenkov radiation and flat lens effect in LHMs are reported recently.Generally, perfect LHMs and NPMs consisting of periodic array of uniform unit cells have some unchangeable behaviors of electromagnetic response, which may limit their application. The defects in LHMs and NPMs can be used to adjust the left-handed properties. In addition, the LHMs obtained are mainly in the microwave band, and LHMs in the infrared and visible region are still a challenging work. It is suggested that chemical method would be the key to the preparation of LHMs at visible or even higher frequency. Unfortunately, the size and the array of unit cells in micron and nanometer scale have some inevitable imperfections during the preparation. Therefore, the investigation of defect effects in LHMs is interesting not only in theory but also in applications.We used a rectangular waveguide method to systematically investigate the transmission of LHMs and NPMs with different kinds of defects, and the flollowing results have been completed.1. The experimental study of split ring resonator in waveguide. We used a rectangular waveguide method to systematically investigate the transmission, absorption, and transmission phase of the hexagon SRRs. The results show that the resonance frequency of an individual SRRs decreases with the increase of the radial gap, and the transmission phase has a shift at the resonance frequency. The distance affectsthe interaction between two identical SRRs, and the resonance frequency increases with the distance. The absorption peak occurs near the resonance frequency in the SRRs system. The azimuthal gap can adjust the electromagnetic resonance behavior of the multi-SRRs system, and the resonance frequency increases with the azimuthal gap. The investigation of SRRs is instructive for the preparation of the left-handed metamaterials.2. The defect effect in the one-dimensional and two-dimensional negative permeability material. It was shown theoretically and experimentally that a metamaterial composed of periodically positioned split ring resonators (SRR) can lead to a negative effective permeability μeff close to its resonance frequency. In our experiment, the nearest neighbor interactions between hexagon SRRs were investigated.(1). The experimental results show that there is only one resonance frequency for a one-dimensional negative permeability μeff material. The main and defect resonance frequency have a shift when the defect SRR are introduced into the materials, and the shifts of which increase with the resonance frequency difference between defect and based SRRs.(2). We measure the X-band transmission in 2-D negative permeability materials with different dot and line defects. The measured data shows that there is only one resonance frequency and high quality factor Q for a 2-D negative permeability materi... |
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