Analysis and Design of A New Class of Miniaturized Circular Waveguides Containing Anisotropic Metamaterial Liners

  • Author / Creator
    Pollock, Justin G
  • This work presents the analysis and design of a new class of miniaturized circular waveguides containing anisotropic metamaterial liners, and reveals in detail intriguing and potentially useful propagation and radiation phenomena. An analytical construction of the liner as a homogeneous, anisotropic medium is used to develop a theoretical formulation that predicts the general dispersion features, cutoff frequencies, and field configurations of a metamaterial-lined circular waveguide. It is shown that a circular waveguide whose interior surface is coated with a thin uniaxial metamaterial liner possessing an epsilon-negative and near-zero (ENNZ) permittivity can permit propagation well below the unlined waveguide’s fundamental-mode cutoff frequency, which is tantamount to extreme miniaturization. These liners are realized using a simple, printed-circuit implementation based on inductively loaded wires, which yields dispersion and miniaturization properties that are consistent with those observed for homogeneous, anisotropic metamaterial liners. A homogenization scheme is developed to characterize the liner’s anisotropic effective-medium parameters, which is shown to accurately describe a set of frequency-reduced cutoffs. This work numerically and experimentally demonstrates that the inclusion of the thin liner substantially improves the transmission between two embedded shielded-loop sources while maintaining access to the waveguide’s interior, thereby offering the potential for miniaturized waveguide components suitable for applications in which the waveguide volume must remain largely empty. Below-cutoff transmission through metamaterial-lined circular waveguides is shown to provide analogous benefits in equivalent metamaterial-lined open-ended waveguide (OEWG) probe antennas. Accordingly, this work presents the radiation performance of OEWG probe antennas that have been miniaturized by the introduction of thin ENNZ liners, which is shown to provide substantial gain improvements over a similarly sized (below-cutoff) waveguide probe. The far-field characteristics of a prototype metamaterial-lined waveguide excited by a shielded loop is investigated using full-wave simulations and near-field antenna measurements. Several emerging applications that may be enabled by these metamaterial lined circular waveguides and OEWG probe antennas are explored, including travelling-wave imaging in MRI scanner bores at low static magnetic-field strengths, characterization of the properties of small quantities of fluids, and sampling electromagnetic field profiles over sub wavelength spatial intervals. This work also investigates the application of the theoretical formulation, which describes a general class of anisotropic circular waveguides, towards the design of a metamaterial-coated PEC rod and metamaterial shell. It is shown that the introduction of anisotropic metamaterials provide new insights into controlling the dispersion of modes, cutoff frequencies, and field patterns. Relying on this theory, a transmission-line type metamaterial formed into a circular shell is shown to significantly enhance the radiation efficiency of a nearby antenna.

  • Subjects / Keywords
  • Graduation date
    Fall 2016
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.