Design Of Novel Metamaterials And Research On Their Electromagnetic Behaviors In Mid-Infared Spectrum

Metamterials has being researched intensively either in the development of materials or in the application of devices more than ten years, since its surprising electromagnetic response that cannot be found in natural materials. The electromagnetic behaviors of metameterials are mainly determined to the electric resonance and magnetic resonance of the patterns in unit cell. Therefore, studying the electromagnetic resonance of a pattern in detail is beneficial to improving the electromagnetic behaviors of traditional metamaterials or to instructing the design of novel metamaterials.To the best of my knowledge, there are no reports for the resonant property of square rings in metamaterials. In this work, the detailed resonant behavior of the square ring pattern in metamaterials has been investigated firstly to uncover the relation between the resonance wavelength and the geometrical parameters. And then, with the help of the resonant behaviors of square ring patterns, we devised a broadband perfect absorber which present perfect selective emission in the whole mid-infrared spectrum. Furthermore, we explored a new left-handed materials (LHM) that exhibits simultaneously hyper-transmission, polarization independence and small period based on the resonant property of the square ring. This condition is hardly achieved in traditional fishnet structure. At the end of this work, we numerically engineered a novel LHM with dual passbands using concentric square rings nested each other. This dual-passbands LHM overcame the drawback of narrow bandwidth of the traditional LHM to some extent. The four specific researches of the metamaterials mentioned above and their innovations as follows:(1) The first thing of this work is to study the electromagnetic behaviors of square ring pattern in metamaterial perfect absorber, which include frequency response of and polarization dependence of the fundamental mode and higher mode. Firstly, the variation of operating wavelength with the geometrical parameters of the square ring and the polarization-independent response of square ring on the electromagnetic wave were researched by virtue of full-wave simulation. Secondly, the absorptive mechanism of metamaterial perfect absorber was interpreted using the retrieval method for the scattering parameters and the results show that the absorption mechanism is magnetic resonance, namely, the operating wavelength is the magnetic resonance wavelength. Thirdly, an equivalent circuit model of square ring absorber has also been constructed newly according to monitored field distribution and from which we deduced magnetic resonance frequency formula. The formula describes quantitatively the relationship between the magnetic resonance frequency and the geometrical parameters and uncovers definitely the fact that the square ring shows higher reactance than those solid patches, which leads to smaller characteristic dimension at the same frequency and larger wavelength ratio of fundamental mode to higher mode. Finally, we verified the resonant behaviors of the square ring by the aid of experimental methods.There are three values of the foregoing research results. First, the smaller characteristic dimension of the square ring pattern than ordinary solid patches for the same operating wavelength is beneficial to the design of the continuous medium metamaterials; second, the exhibited larger wavelength ratio of fundamental mode to higher mode in square ring pattern than solid patches is useful in the contriving of broadband selective emitter; third, the square ring is insensitive to the polarization of electromagnetic wave either on the incident angle or the azimuth angle which is utilizable in the development of polarization-independent metamaterials.(2) Depending on the resonant property of the square ring and slow wave theory, we devised a broadband perfect absorber from5μm to8μm in virtue of multiple layer design of square rings with gradual change in size. The selective absorber only absorb the electromagnetic energy perfectly among the region of5μm-8μm for the whole middle infrared regime of3μm-14μm, and it have high reflectivity for the two atmospheric windows denoted as3μm-5μm and8μm-14μm. The forgoing situation is hardly satisfied for solid patches because their wavelength ratio of fundamental mode to higher mode is small so that the higher mode usually emerges at the higher frequency. From the point of view of thermal radition, the perfect absorber is an efficient selective thermal emitter. Comparing to the blackbody radition, this emitter modified significantly the emission spectrum of blackbody.(3) The traditional fishnet structure do not possess generally polarization independence, hyper-transmission and small period simultaneously. Small period is especially required since the designed structure will be photonic crystal without left-handed behaviors if the period is too large. Based on the resonant behavior of the square ring, we proposed a new polarization-independent LHM made up of a wire-net pairs (WNP) and a square ring pairs (SRP) array, where the hyper-transmission of90%and small period were achieved synchronously. The retrieval procedure and the effective medium theory of LHM were employed to analyze the mechanism of implementing the new LHM. In addition, we built a numerical model of the analytical permeability of the LHM. The numerical model is not only good agreement with that obtained from retrieval method, but also explained satisfactorily why the WNP has few influence on the magnetic properties of the LHM.(4) Seeing that the dispersion and narrow band of traditional LHM, a polarization-independent dualband LHM based on a concentric double square ring pairs (DSRP) array and a WNP has been designed. The dualband negative index was certified by applying retrieval procedure and the physical mechanism of implementing it was interpreted by combining the procedure with monitored field distribution. Finally, the abnormal phenomena of effective permittivity compared to the picture without substrate were discussed. It was believed that the abnormal features originate from the absence of translational symmetry of the sample in propagation direction.