The Study Of Polarization Transformer Based On Metamaterials

Linear polarized wave could not satisfy the demands of modern applied engineering as wireless communication system getting complicated. Circularly polarized wave has many advantages in some circumstances, but the traditional methods to create it have a lot of deficiencies. Metamaterial is getting more and more attention, because of its quite unique electromagnetic properties. Metamaterial is able to effectively control the polarization of electromagnetic wave, it provides a new approach to convert polarization with high performance.This paper presents a study of polarization conversion based on metamaterial. We designed three structure models through two ways: anisotropy and chiral structures. The simulation and experiment were taken to analyze their performances and working mechanism. The main works of the dissertation includes:(1) A N-shaped metasurface based on chiral structure was designed. It is composed of two twisted N-shaped metal structures and the substrate. The structure could convert y-direction linear polarized wave into left and right hand circular polarized wave at 3.67 GHz and 3.78 GHz, respectively. The optical activity of the material is demonstrated by ellipticity and rotation angle. The results of the surface current distribution indicate that the cross polarization make the emitted wave have different phase velocity, so that the chiral material can control the polarization of electromagnetic wave.(2) We designed a non-twist Q-shaped metasurface based on anisotropic structure. The unit cell is composed of a pair of Q-shaped resonators and the substrate. It is work as linear birefringence, which could create different refractive index at two orthogonal directions. The simulated and experiment results show that the transformation are generated at 4.08 GHz with right circularly polarized(RCP) wave emitting and at 5 GHz with left circularly polarized(LCP) wave emitting, respectively. Base on similar mechanisms, a defected ring pair structure was designed. The unit cell of the achiral metasurface consists of aligned bilayered ring resonator pair, Q-shaped structure and the substrate. The results show that the LCP wave dominates the transmitted wave at 4.5 GHz, and the RCP wave is the main component at 4.9 GHz. The parameter simulation illustrates that we can adjust the performance of the material through change the parameters of it.Through these researches, metamaterial as an emerging electromagnetic technology has broad research potential.