Anisotropic artificial substrates for microwave applications

Résumé

Anisotropic materials exhibit different electromagnetic properties in different directions and therefore they provide some degrees of freedom in the design of electromagnetic devices and enable many applications. Some kinds of anisotropic materials are available in the nature such as ferrimagnetic materials, while many others can be artificially designed for specific applications. The artificial materials are composite structures made of sub-wavelength metallic implants in a host medium, which constitute novel effective materials. These materials may exhibit properties not readily available in the nature, such as negative refractive index, chirality or bi-anisotropy, and therefore are called metamaterials. Due to the diversity of their possible implants, they have a great potential in unique and novel components, such as specific antennas, miniaturized antennas, non-reciprocal devices, analog signal processors, and biomedical engineering devices. Since in most of the artificial materials, the effect of the implants in the host medium is not the same in all the directions, these materials exhibit anisotropic characteristics which can be controlled by the properties of the implant. This characteristic provides some additional degrees of freedom in the design of novel devices. The anisotropy effect in the artificial structures is more evident in most of the anisotropic artificial substrates due to their 2D planar structure. Rigorous electromagnetic analysis of the anisotropic artificial substrates is required for gaining a better understanding of their properties which is essential for proposing novel applications. Insufficient available analysis in the literature has motivated this thesis whose objective is to perform rigorous electromagnetic analysis of the anisotropic artificial substrates towards exploring their applications. To acquire more insight into the anisotropic properties of artificial substrates, their analysis method, and their applications, it is useful to first better understand anisotropy of existing natural substrates such as ferrimagnetic materials. This approach may also lead to novel applications of the natural anisotropic materials. In addition, to investigating some of properties and applications of the anisotropic substrates, foremost we may need to clarify some unclear aspects regarding the isotropic materials. Based on the objectives and methodology of the thesis which were explained above, this thesis contributes to the following achievements and advances in microwave engineering. The perfect electromagnetic conductor (PEMC) boundary is a novel fundamental electromagnetic concept. It is a generalized description of the electromagnetic boundary conditions including the perfect electric conductor (PEC) and the perfect magnetic conductor (PMC) and due to its fundamental properties, it has the potential of enabling several electromagnetic applications. However, the PEMC boundaries concept had remained at the theoretical level and has not been practically realized. Therefore, motivated by the importance of this electromagnetic fundamental concept and its potential applications, the first contribution of this thesis is focused on the practical implementation of the PEMC boundaries by exploiting Faraday rotation principle and ground reflection in the ferrite materials which are intrinsically anisotropic. As a result, this thesis reports the first practical approach for the realization of PEMC boundaries.