Advancements in Artificial Magnetic Conductor Design for Improved Performance and Antenna Applications
Open Access
- Author:
- Kern, Douglas John
- Graduate Program:
- Electrical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 15, 2009
- Committee Members:
- Douglas Henry Werner, Dissertation Advisor/Co-Advisor
Douglas Henry Werner, Committee Chair/Co-Chair
Pingjuan Li Werner, Committee Member
Kultegin Aydin, Committee Member
Milton Walter Cole, Committee Member - Keywords:
- frequency selective surfaces
metamaterials
artificial magnetic conductors
antennas
negative impedance converters
electromagnetics - Abstract:
- Artificial Magnetic Conductors (AMCs) are a class of metamaterials that exhibit a reflection coefficient of unity with phase of zero degrees over a narrow frequency range. In this research the AMC consists of a frequency selective surface placed above a PEC ground plane, with a dielectric material in between. Such a structure can be modeled as a parallel L-C circuit, which gives rise to a resonant frequency at which the surface impedance of the AMC becomes quite large. One method for increasing the bandwidth is the use of an active load, in this case a negative impedance converter, to change the inductance and capacitance of the structure. Additionally, the use of magnetic materials within the substrate also allows for a small increase in operating bandwidth for all resonances of multi-band AMCs. Tunable AMC surfaces are also realized by means of an electrically tunable, high dielectric substrate material, as well as incorporating mechanical switches as part of the FSS geometry to provide tunable performance for different screen geometries. A unique application of AMC surfaces is the equivalence between a high impedance AMC structure and a magnetic substrate backed by a PEC ground plane. The resulting structure is called a metaferrite and can be optimized, much like a conventional AMC, to achieve a desired magnetic permittivity for one or more frequencies for use as lightweight, thin absorbers for electromagnetic radiation. Further research into metasurfaces resulted in the ability to design a matched impedance metamaterial to act as a magneto-dielectric substrate without using magnetic materials. The metamaterial is GA optimized to obtain an equivalent low-loss dielectric and magnetic constant. The primary application of this magneto-dielectric metastructure is to reduce the aperture size without negatively impacting antenna operating bandwidth. Since no magnetic materials are used in this metastructure, a thin, lightweight, low-profile antenna system can be developed. Finally, the combination of electromagnetic bandgap AMC surfaces and low-profile antennas will be examined to obtain improved antenna performance over the desired frequency band. The optimized result is an antenna system that achieves improved realized gain compared to the conventional antenna alone.