Search

Plasmonic nanoantennas are typically designed with RF-inspired rigorous parametric optimization processes that lack proper physical insights. In this article, we demonstrate a systematic optimization approach for nanoantennas based on characteristic mode analysis (CMA). A complex geometry, designated as split-ring two-wire antenna (SRA), is selected and optimized using the CMA technique. CMA identifies the dominant modes of the structure at the frequency of interest as well as explains the dependence of the modes on the structure’s shape, size and material properties. These insights from CMA have been used in this study to efficiently optimize SRA shape, size, and material which yield more than 700% near-field intensity enhancement (NFIE) at the desired operating frequency. This proposed CMA-based optimization method can be adapted easily for many other nanoantenna applications, facilitating the development of improved nanostructures. [ABSTRACT FROM AUTHOR]

Graphene flakes (GFs) in real composites are rarely perfectly flat, and often exhibit complicated crumpled shapes. Therefore, the goal of this paper was to quantify the electromagnetic scattering characteristics of individual crumpled GFs with shapes resembling those found in real composites. The extinction cross sections of tens of GFs, with different sizes and various levels of crumpleness, were calculated using multiple independent solvers. The results show that resonances in the extinction cross section spectrum decrease in amplitude as the GFs become more crumpled. Moreover, some crumpled GFs exhibited a broader resonance than that of perfectly flat GFs. To explain these results, we used a characteristic mode analysis to decompose the graphene surface currents into a set of fundamental currents or modes. For perfectly flat square GFs, the vertical and horizontal modes were found to overlap and resonate at the same frequencies. However, as the GFs became more crumpled, the horizontal/vertical symmetry broke down causing the corresponding modes to separate and resonate at different frequencies leading to an overall broader bandwidth. These results attest to the importance of modeling the exact shape of GFs to accurately characterize their electromagnetic response. [ABSTRACT FROM AUTHOR]