Dimitrios C. Tzarouchis

Characteristic Mode Analysis of Plasmonic Nanoantennas

The theory of characteristic modes (TCMs) based on the surface integral equation (SIE) formalism is presented for the analysis of plasmonic nanostructures. With TCM, excitation-independent characteristic solutions of the underlying electromagnetic field problem are obtained. Both single and multiple particle nanostructures are analyzed using the conventional SIE approach and the TCM formalism. By comparing these results, the modes that are responsible of the observed scattering and absorption characteristics can be identified. These solutions can be further utilized in the design and tuning nanoantenna configurations for specific application purposes.

Resonant Scattering Characteristics of Homogeneous Dielectric Sphere

In this paper, the classical problem of electromagnetic scattering by a single homogeneous sphere is revisited. Main focus is the study of the scattering behavior as a function of the material contrast and the size parameters for all electric and magnetic resonances of a dielectric sphere. Specifically, the Padé approximants are introduced and utilized as an alternative system expansion of the Mie coefficients. Low order Padé approximants can give compact and physically insightful expressions for the scattering system and the enabled dynamic mechanisms. Higher order approximants are used for predicting accurately the resonant pole spectrum. These results are summarized into general pole formulae, covering up to fifth order magnetic and forth order electric resonances of a small dielectric sphere. Additionally, the connection between the radiative damping process and the resonant linewidth is investigated. The results obtained reveal the fundamental connection of the radiative damping mechanism with the maximum width occurring for each resonance. Finally, the suggested system ansatz is used for studying the resonant absorption maximum through a circuit-inspired perspective.

Plasmonic properties and energy flow in rounded hexahedral and octahedral nanoparticles

The resonant plasmonic properties of small dual rounded nanoscatterers are numerically investigated. A set of silver (Drude-like) hexahedral and octahedral structures are studied and compared with a reference spherical particle through a numerical surface integral equation technique. Surface, near-field, Poynting field, and streamline distributions are presented illustrating novel plasmonic features arising from the complex shapes of the nanoparticles, while several designing rules are described. These qualitative observations can be used appropriately toward sensing, sorting, harvesting, and radiation control applications.

Plasmonic modes on rounded hexahedral and octahedral nano-antennas

In this paper, the resonant spectrum of plasmonic, Drude-like, silver nano-antennas is presented. The central focus is the study of the radiation pattern of shapes, such as rounded cornered hexahedra and octahedra, under a full electrodynamic surface integral equation numerical scheme. Several aspects regarding their dipole, quadrupole, and higher order far-field distribution are revealed, giving special emphasis in their qualitative characteristics. Aspects of their resonant behavior, such as quadrupole mode “Huygens” nano-antennas or peculiarities related with their far field planes are further discussed, expanding our understanding on single plasmonic nano-antennas and their emerging functionalities.

General Scattering Characteristics of Resonant Core–Shell Spheres

We present the general features and aspects regarding the electromagnetic scattering by a small core-shell sphere. First, the thickness effects on the plasmonic resonances are described in the Rayleigh limit, utilizing the MacLaurin expansion of the Mie coefficients of hollow scatterers. The results are connected with the plasmon hybridization model. A brief study regarding the core effects is given, illustrating resonant scattering peculiarities. Finally, new electrodynamic aspects of the scattering process are revealed through a the newly introduced Padé expansion of the Mie coefficients. The proposed methods can be readily applied for the studies of the dynamical dependencies for other canonical shapes, carving ways for engineering the overall properties of a single composite scatterer.

Resonances of Characteristic Modes for Perfectly Conducting Objects

Resonances, i.e., extrema of the eigenvalues of characteristic modes for closed perfectly conducting objects are investigated. The characteristic modal solutions based on the electric, magnetic, and combined field integral operators (EFIO, MFIO, and CFIO) are studied and compared with analytical solutions for a sphere. All these formulations are found to capture both external (radiating) and internal (cavity) resonances predicted by the analytical expressions. At the internal resonances, the eigenvalues obtained with the EFIO- and MFIO-based approaches are not correct, and the corresponding modes are nonunique. These solutions also exhibit a strong duality between the electric (TM) and magnetic (TE) type modes. A connection is found between the external and internal resonances and the condition numbers of the matrices. The modal expansion of the CFIO-based solution is correct, even though it also experiences the nonuniqueness of the EFIO- and MFIO-based solutions.

Characteristic mode-surface integral equation analysis of plasmonic nanoparticles

The theory of characteristic modes (TCM) is applied to analyze optical properties of plasmonic nanoparticles. TCM gives excitation independent characteristic solutions of the electromagnetic problem formulated with surface integral equations and can provide additional information of the plasmonic resonances that can be difficult to obtain with conventional electromagnetic field analysis methods.

Wideband monopole antenna for RF power scavenger

In this paper, a simulated and measured results of a broadband monopole antenna is presented. The proposed design will be used in the RF power scavenger application of the 2016 IEEE AP-S Student Design Contest. The antenna has a -6-dB impedance bandwidth from 930 MHz up to 2420 MHz and omnidirectional radiation pattern in the horizontal plane. The simulated and measured results indicate that the antenna is applicable to an RF scavenger.

General scattering characteristics of resonant core-shell spheres

This paper presents and discusses the general features and aspects regarding the electromagnetic scattering by a small Core–Shell plasmonic sphere. First, the thickness effects on the plasmonic resonances are presented in the electrostatic (Rayleigh) limit, utilizing the MacLaurin expansion of the Mie coefficients of hollow scatterers. Several aspects regarding the core effects are given, illustrating the enabling mechanisms and peculiarities of its resonant scattering response on the electrostatic limit. The electrodynamic aspects of the scattering process are revealed through the newly introduced Padé expansion of the Mie coefficients. Additionally, we expose how the core material affects the dynamic mechanisms, such as the dynamic depolarization and radiative damping. The described method can be expanded for other types of resonances and canonical shapes, while the general characteristics presented here are expected to stimulate further studies regarding the functionalities of the core–shell scatterers.

Study of Plasmonic Resonances on Platonic Solids

In this study we discuss the plasmonic subwavelength scattering resonances of five regular polyhedra, i.e., the Platonic solids tetrahedron, hexahedron, octahedron, dodecahedron, and icosahedron. A brief discussion regarding their geometrical characteristics and the numerical method used in the study is given. All results are compared with the benchmark case of a sphere, in order to observe how the geometry of the solid affects the spectral characteristics. The principal finding is that the shift of the main dipole resonance exhibits a solid-vertex hierarchical order, in other words, the position of the resonance correlates with the solid angle of the vertex of the given solid. This is in contrast with the blackhedra-hierarchical order found for the electrostatic dielectric response of these solids. These results can create new avenues for applications and devices that require plasmonic particles with on-demand functionalities.