Asymmetric Propagation Of Electromagnetic Waves Based On Zero-Index Magnetic Metamaterials

With the rapid development of science and technology, nowadays, the properties of most natural materials have been discovered and thoroughly explored. Meanwhile, the limitations and shortcomings of natural materials come into appearance. As a result, artificial materials are proposed to meet the needs of research and applications. Since the 1960’s the concept of artificial electromagnetic materials, namely, metamaterials have been raised, which exhibit quite many exotic phenomena and features. Unprecedented freedom is supplied in molding the propagation of electromagnetic waves, signifying a new era of electromagnetic materials. More importantly, metamaterials can realize nearly arbitrary electromagnetic parameters that natural materials cannot. Therefore, metamaterials enable a variety of promising applications and play a crucial role in electromagnetics and related fields. In chapter one, we give a brief background introduction of the development, the electromagnetic properties, and the applications metamaterials. Especially, the novel electromagnetic properties that are not found in conventional natural materials, which are potentially important for some areas such as military, communications, medical therapy, and energy. Therefore, both theoretical and experimental research of metamaterials is of great significance. This dissertation is devoted to the investigation of the electromagnetic properties of metamaterials composed of YIG ferrite rods.In chapter two, we present Mie scattering theory for ferrite rod and the multiple scattering theory for photonic band calculation and field pattern simulation as well as the effective-medium theory to retrieve the effective parameters. In our work, the working wavelength is nearly 10 times of the lattice separation, satisfying long-wavelength limit. Therefore, magnetic metamaterials can be considered as a homogeneous medium with effective parameters which can be obtained from the effective-medium theory.In chapter three, we use multiple scattering theory and effective-medium theory presented in chapter two obtain an effective zero refractive index by optimizing the configuration parameters of magnetic metamaterials. Then, we simulate the field pattern of electromagnetic wave in magnetic wave propagating in magnetic metamaterials, which further corroborates the zero index of the system.. In the following part, we tune the effective index of the magnetic metamaterials from positive to negative by adjusting either the external magnetic field or the radius of the ferrite rods, which we will use to realize asymmetric wave propagation in next chapter.In chapter four, we first give a schematic illustration of the mechanism to realize asymmetric wave propagation with zero index material based heterostructures. Then, by use of magnetic materials we construct this heterostructure and realize the asymmetric wave control. To improve the tenability, we construct another heterostructure with both the dielectric based metamaterial and magnetic metamerials, which can implement the function as well. In addition, the later design can control the direction of the outgoing electromagnetic waves by tuning the external magnetic field.Finally, in chapter five we summarize the results of the dissertation. The future work on zero-index magnetic metamaterials is mentioned and the outlook of its potential application is also presented.