DOI: https://doi.org/10.15368/theses.2008.22
Available at: https://digitalcommons.calpoly.edu/theses/7
Date of Award
6-2008
Degree Name
MS in Electrical Engineering
Department/Program
Electrical Engineering
Advisor
Dean Arakaki
Abstract
Natural structures exhibiting simultaneous negative bulk permittivity and permeability have not yet been discovered. However, research interest over the past five years has grown with the proposition that artificial structures exhibiting these properties are realizable using specially-designed metallic inclusions embedded in host dielectric bodies. A periodic structure of metallic inclusions much smaller than the guided wavelength and embedded in a host dielectric medium is known in the physics and microwave communities as a "metamaterial". Such frequency-dependent effectively homogeneous materials may be designed to exhibit negative permeability and permittivity at certain frequencies. As predicted by electromagnetic theory, such negative index or "left-handed" metamaterials are shown to have unique filtering properties and exhibit negative refraction and "backward wave" propagation. The "backward wave" phenomenon describes the anti-parallel nature of phase velocity and group velocity in a negative index metamaterial and can be additionally characterized in vector theory using the left hand rule. Additionally, "epsilon-near zero" (ENZ) metamaterials are characterized by a bulk permittivity equal to zero. Applications include focusing radiation emitted by small apertures. This thesis provides the theory for metamaterial structures supported by simulations conducted with the commercial finite element method solver: Ansoft HFSS. Metallic inclusions such as the split ring resonator structure (SRR), S-shaped split ring resonator (SSRR), wire rod and capacitively loaded strip (CLS) are presented analytically and simulated in HFSS. Metamaterial structures designed to exhibit left-handed behavior in the X-band frequency region are simulated for frequency-dependent transmission, reflection and refractive properties. A test configuration for measuring a metamaterial slab's match to free space is proposed and constructed. Additionally a prism design and test plan geared for anechoic chamber testing and refraction measurement is proposed and built. Simulated inclusions are fabricated on FR-4 epoxy laminate boards, combined to form metamaterial structures, and tested in the Cal Poly Anechoic chamber. Results show that transmission properties match closely with HFSS simulations. Prism metamaterial testing shows that negative refraction is visible in the 8 to 9 GHz region. A modified form of the Nicolson Ross-Weir method for parameter extraction using S-parameter data is shown to provide an initial approximation for the permeability and permittivity of the structure under test. Finally, both negative and zero-index metamaterials are analyzed in HFSS simulations to improve the directivity of EM radiation from sub-wavelength apertures. Epsilon-near zero metamaterials placed on sub-wavelength apertures are shown to improve directivity by two fold in the far-field at design frequencies.