Analysis and design of microwave and optical plasmonic antennas

Open Access
Author:
Lu, Bingqian
Graduate Program:
Electrical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
March 30, 2016
Committee Members:
  • Douglas Henry Werner, Thesis Advisor/Co-Advisor
  • Pingjuan Li Werner, Thesis Advisor/Co-Advisor
  • John Roe, Thesis Advisor/Co-Advisor
Keywords:
  • spoof spp
  • surface plasmon
  • nanoloop antenna
  • nanoloop coupling
Abstract:
The plasmonic antenna has become a popular research topic, largely as a result of the development of nano-technology. This thesis covers the design and analysis of these devices in both the microwave and optical frequency regions. First, we will present a compact methodology for the design of periodic leaky wave antennas. These antennas enable spoof plasmon type surface waves to radiate at microwave frequencies. This approach is based on structurally modifying a corrugated reactance surface. In particular, a properly engineered periodic perturbation is introduced to enable the excitation of the n = -1 spatial Floquet mode. This mode is characterized by a complex wavenumber, the real part of which is less than that of free space. As a result, the guided spoof plasmons are efficiently coupled to the radiating modes. Numerical simulation software (HFSS) has been used to validate the proposed design methodology. Second, we will present closed form expressions for the radiated fields, directivity and gain for a single nanoloop antenna. In the terahertz, infrared and optical regimes nanoloops show great promise for a variety of applications, such as solar cells and optical sensors. However, due to the complex behavior of metals at these frequencies, prior studies had not yet completed a theoretical derivation for the radiation parameters of a nanoloop. We propose a solution based on the extension of the formulation for a thin-wire Perfect-Electric Conductor (PEC) loop to include the effects of loss and dispersion. These proposed expressions contain integrals of Bessel and Lommel-Weber functions as well as Q-type integrals. Various series representations for these integrals will be presented along with guidelines for solving them. We will validate these equations through the comparison of results from full-wave solvers. These simulations typically require hours of processing time, whereas our analytical expressions can be evaluated within seconds. Finally, we will present an extended study on the derivation of coupling between nanoloops. Due to their properties of highly directive transmission and reception, nanoloop arrays have many practical applications, such as energy harvesting. Specific equations involving numerical integrals are proposed in Chapter 4. More importantly, far-zone approximations are employed to generate simplified closed form analytical solutions. The induced current on a passive loop has been derived for the general case, where the passive loop can be located anywhere with respect to the active loop. The induced current equations have also been derived for two special cases, where the passive loop is coplanar to the active loop and where the passive loop is stacked above the active loop. Both the numerical and closed form analytical results were verified with FEKO (a full-wave Method of Moments solver). A significant reduction in computing time was observed.