Transmission Properties In Gradient Phase Metamaterials

Metamaterials (MMs), as a new type of artificially composite structured materials with extraordinary material properties, have attracted substantial attention of researchers in recent years. There is no doubt that metamaterials have become an extremely exciting research area due to its unique electromagnetic properties such as negative refraction, giant optical activity and asymmetric transmission. Capasso proposed a single-layered ultrathin metamaterial called"metasurfaces" in 2011,which is generally made of arrays of subwavelengh,anisotropic resonators. Gradient phase metasurfaces introduce varying phase abrupt changes to realize flexible control of the directions of reflection and refraction beams. Capasso has verified the generalized Snell's law for reflection and refraction by using transverse gradient design and gradually realized bipolar lens, beam manipulation, anomalous reflection and refraction by gradient metasurfaces. In this paper,we theoretically and experimentally investigate the phase gradient metasurfaces and realize cross-polarization transmission and background free beam direction manipulation, which shows significant importance of achieving ultra-thin,broadband photoelectronic devices. The main research topics and innovative achievements gained are as follows:Firstly, we mainly investigate the principles of electromagnetic response of phase gradient metasurfaces, generalized Snell's law, and regulation of phase gradient. We also summarized the condition of anomalous refraction and explored the methods of flexible control of polarization states and transmission directions of electromagnetic waves.Secondly, we propose a single-layered metasurface using V-shaped structure, which is able to realize anomalous refraction and reflection of electromagnetic waves in microwave frequencies. Refraction and reflection beams of cross-polarized are well deflected at an anomalous refraction and reflection angle under normally incident x-polarized wave due to the existence of transverse phase gradient.Thirdly, we propose a bilayered metasurface using I-shaped structure, which can realize the independent controls of orthogonally-polarized in microwave range. It would general two phase gradients for x-polarized and y-polarized which are identical but with opposite directions by designing the geometrical parameters of structures. Therefore,orthogonally-polarized transmitted waves would be deflected at opposite directions with an equal angle under normal incidence of x-polarized and y-polarized waves.Fourthly, we propose a bilayered gradient metasurface by using asymmetrical split ring apertures structures. The results of theoretical and experimental study indicate that it can effectively suppress co-polarization transmission and realize beam direction manipulation for cross-polarization transmission. Output waves only contain the cross-polarized wave with x-component without y-polarized wave under normally incident y-polarized wave in the range of 6GHz-8GHz. Transmitted wave exists a deflection angle of 24° with an intensity of 0.71 after passing through the proposed metamaterial. We have completed a lot of simulations and experiments point at structural parameters,materials properties,and the results indicate that the transmission intensity of cross-polarized wave is 0.68 with a deflection angle of 25° under normally incident x-polarized wave. Experiment results are in good agreement with the simulated ones.