A reduced order admittance model for longitudinally loaded plasmonic nanorod antennas

It is demonstrated that the well-known network theory originally developed for microwave circuits can be successfully applied in the case of longitudinally loaded plasmonic nanorod antennas. By choosing different material constitution for the two loading volumes the antenna´s input admittance can be custom engineered and thus its optical response can be tuned as desired. The realization of the proposed technique requires that the appropriate terminal ports be defined across the nanorod where the necessary voltage and current quantities can be probed. Then a reduced order admittance matrix of the loaded nanoantenna can be trivially extracted. Furthermore, analytical expressions are derived that very accurately characterize the loading volumes in terms of their admittance. The combination of the admittance matrix information along with admittance characterization of the loading volumes provides a compact computational tool that allows the antenna´s optical response to be predicted without having to run lengthy full wave scattering simulations.