Theory, Design and Development of Artificial Magnetic Materials

Artificial Magnetic Materials (AMMs) are a subgroup of metamaterials which are engineered to provide desirable magnetic properties not seen in natural materials. These artificial structures are designed to provide either negative or enhanced positive (higher than one) relative permeability. AMMs with negative permeability are used to develop Single Negative (SNG), or Double Negative (DNG) metamaterials. AMMs with enhanced positive permeability are used to provide magneto-dielectric materials at microwave frequencies where the natural magnetic materials fail to work efficiently. AMMs are realized by embedding metallic resonators in a host dielectric. These inclusions provide desirable magnetic properties near their resonance frequency. Artificial magnetic materials used as SNG, or DNG have many applications such as: sub-wavelength cavity resonators, sub-wavelength parallel-plate wave guides, sub-wavelength cylindrical and spherical core–shell systems, efficient electrically small dipole antennas, super lenses, THz active devices, sensitivity enhancement near-field probes using double and single negative media, and mutual coupling reduction between antennas. On the other hand, artificial magnetic materials used as magneto-dielectrics have other applications in developing enhanced bandwidth efficient miniaturized antennas, low profile enhanced gain antennas using artificial magnetic superstrates, wide band woodpile Electromagnetic Band Gap (EBG) structures, EBGs with enhanced in-phase reflection bandwidth used as artificial magnetic ground planes. In this thesis, several advances are added to the existing knowledge of developing artificial magnetic materials, in terms of analytical modeling, applications, realization, and experimental characterization. To realize AMMs with miniaturized unit cells, new inclusions based on fractal Hilbert curves are introduced, and analyzed. Analytical models, numerical full wave simulation, and experimental characterization are used to analyze, and study the new structures. A comprehensive comparison is made between the new inclusions, and perviously developed inclusions in terms of electromagnetic properties. The new inclusions have advantages of miniaturization, and less dispersion when compared to the existing structures in the literature. To realize multi-band AMMs, unit cells with multiple inclusions are proposed, designed, and analyzed. The new unit cells can be designed to give the desired magnetic properties either over distinguished multiple frequency bands, or over a single wide frequency band. Numerical full wave simulation is used to verify the proposed concept, and analytical models are provided for design, and optimization of the new unit cells. Unit cells with different configurations are optimized to get a wideband responce for the effective permeability. Space mapping technique is used to provide a link between analytically optimized structures, and full wave numerical simulation results. Two new methods are proposed for experimental characterization of artificial structures using microstrip, and strip line topologies. Using numerical results, the effect of anisotropy on the accuracy of the extracted parameters are investigated, and a fitting solution is proposed, and verified to address this challenge. New structures based on 2nd , and 3rd order fractal Hilbert curves are fabricated, and characterized using microstrip line, and strip line fixtures. Experimental results are presented, and compared with numerical results. The new experimental methods have advantages of lower cost, easier to fabricate and measure, and smaller sample size when compared to the existing methods in the literature. A new application is proposed for use of magnetic materials to develop wide band artificial magnetic conductors (AMC). Analytical models, and numerical analysis is used to validate the concept. A new ultra wideband AMC is designd, and analysed. The designed AMC is used as the ground plane to develop a low profile high gain ultra wide band antenna. The designed antenna is simulated, and its return loss, and gain is presented over a wide range of frequencies. A comprehensive study is presented on the performance of AMMs for the application of miniaturized antennas. A miniaturized antenna, using fractal Hilbert metamaterials as substrate, is fabricated, and measured. Measurement results are presented, and compared with numerical results. A parametric study is presented on the effect of the constitutive parameters of the artificial substrate on the performance of the miniaturized antenna. In this study, the effect of magnetic loss of AMM on the gain, and efficiency of the antenna, as well as the effect of dispersion of AMM on the bandwidth of the antenna is investigated

Metamaterials for Decoupling Antennas and Electromagnetic Systems

This research focuses on the development of engineered materials, also known as meta- materials, with desirable effective constitutive parameters: electric permittivity (epsilon) and magnetic permeability (mu) to decouple antennas and noise mitigation from electromagnetic systems. An interesting phenomenon of strong relevance to a wide range of problems, where electromagnetic interference is of concern, is the elimination of propagation when one of the constitutive parameters is negative. In such a scenario, transmission of electromagnetic energy would cease, and hence the coupling between radiating systems is reduced. In the first part of this dissertation, novel electromagnetic artificial media have been developed to alleviate the problem of mutual coupling between high-profile and ow-profile antenna systems. The developed design configurations are numerically simulated, and experimentally validated. In the mutual coupling problem between high-profile antennas, a decoupling layer based on artificial magnetic materials (AMM) has been developed and placed between highly-coupled monopole antenna elements spaced by less than Lambda/6, where Lambda is the operating wavelength of the radiating elements. The decoupling layer not only provides high mutual coupling suppression (more than 20-dB) but also maintains good impedance matching and low correlation between the antenna elements suitable for use in Multiple-Input Multiple-Output (MIMO) communication systems. In the mutual coupling problem between low-profile antennas, novel sub-wavelength complementary split-ring resonators (CSRRs) are developed to decouple microstrip patch antenna elements. The proposed design con figuration has the advantage of low-cost production and maintaining the pro file of the antenna system unchanged without the need for extra layers. Using the designed structure, a 10-dB reduction in the mutual coupling between two patch antennas has been achieved. The second part of this dissertation utilizes electromagnetic artificial media for noise mitigation and reduction of undesirable electromagnetic radiation from high-speed printed-circuit boards (PCBs) and modern electronic enclosures with openings (apertures). Numerical results based on the developed design configurations are presented, discussed, and compared with measurements. To alleviate the problem of simultaneous switching noise (SSN) in high-speed microprocessors and personal computers, a novel technique based on cascaded CSRRs has been proposed. The proposed design has achieved a wideband suppression of SSN and maintained a robust signal integrity performance. A novel use of electromagnetic bandgap (EBG) structures has been proposed to mitigate undesirable electromagnetic radiation from enclosures with openings. By using ribbon of EBG surfaces, a significant suppression of electromagnetic radiation from openings has been achieved

Metamaterial

In-depth analysis of the theory, properties and description of the most potential technological applications of metamaterials for the realization of novel devices such as subwavelength lenses, invisibility cloaks, dipole and reflector antennas, high frequency telecommunications, new designs of bandpass filters, absorbers and concentrators of EM waves etc. In order to create a new devices it is necessary to know the main electrodynamical characteristics of metamaterial structures on the basis of which the device is supposed to be created. The electromagnetic wave scattering surfaces built with metamaterials are primarily based on the ability of metamaterials to control the surrounded electromagnetic fields by varying their permeability and permittivity characteristics. The book covers some solutions for microwave wavelength scales as well as exploitation of nanoscale EM wavelength such as visible specter using recent advances of nanotechnology, for instance in the field of nanowires, nanopolymers, carbon nanotubes and graphene. Metamaterial is suitable for scholars from extremely large scientific domain and therefore given to engineers, scientists, graduates and other interested professionals from photonics to nanoscience and from material science to antenna engineering as a comprehensive reference on this artificial materials of tomorrow