Novel Electromagnetic Scattering Models for Nano-Composites and Nano-Sensor Applications
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Abstract
Nanoparticles composed of plasmonic materials have the unique capability of coupling to electromagnetic radiation of wavelengths far larger than their size and confining the coupled energy to the structure’s sub-wavelength vicinity. This unique ability has paved the way for a diverse range of energy harvesting, biological, and chemical sensing applications. Two of the main challenges in nanoparticle design are how to optimize the nanoparticle characteristics and how to account for their complex environment. Optimization of the electromagnetic response of a nanoparticle requires the accurate design of the nanoparticle’s shape, size, material, and environment. Traditional optimization processes use brute force search algorithms coupled with three-dimensional (3D) fullwave commercial electromagnetic solvers. These approaches are time-consuming, lack proper physical insights, and require huge computational resources and time. The second challenge is to accurately quantify the effect of the environment on nanoparticle’s electromagnetic response. In practical applications, nanoparticles rarely float in homogeneous media, and they are commonly embedded in or supported by finite thickness substrates that affect the electromagnetic response of the nanoparticle. This dissertation addresses the above two challenges by developing multiple novel frequency-domain electromagnetic scattering models for fast, efficient, and accurate analysis of plasmonic systems in homogeneous and multilayer media. First, a systematic optimization process is demonstrated for a complex three-dimensional (3D) plasmonic nanoantenna in free space. Characteristic mode analysis (CMA) is used to provide physical insights to systematically optimize the nanoantenna’s shape, size, and material leading to ∼ 700 % near-field enhancement. Next, the high aspect ratio carbon nanotube (CNT) dimers are studied in free space using the method of moments (MoM) for arbitrary thin wires (ATW). The emergence of plasmonic bonding resonance (BR) and anti-bonding resonance (ABR) are presented, for the first time, originated from different configurational asymmetries in CNT dimer. The unique near-field distributions of asymmetric CNTs are also studied in detail. Novel CNT dimer sensing capabilities are presented, such as the nanometric ruler application and the detection of foreign nanoparticles in the dimer’s vicinity. Next, the dissertation develops a full-wave electromagnetic solver for CNT reinforced composites. The basis of the model is the multilayer dyadic Green’s function (DGF) approach that accounts for the embedding layer effects without explicitly discretizing its inter-face/volume. We use an efficient semi-analytical method to solve the Sommerfeld-type integrals associated with the multilayer DGF. The in-house solver is found to be 50-570 times faster than the commercial solvers, with the same level of accuracy, over a GHz to THz frequency range, nm to mm substrate thickness, nm to cm lateral range, and a wide variety of dielectric properties to cover most CNT composite applications. Several embedded CNT networks are studied using the in-house solver, and the interactions between the CNTs and the embedding substrate are accurately quantified. It is observed that by controlling the proximity of embedded CNTs towards the slab interfaces and adjusting their lengths and distributions, it is possible to optimize the expression of BR and ABR according to the application of interest. The computational models and the design approaches developed in this dissertation can be used to realize new sensing modalities and can also be used to guide the non-destructive evaluations of nanocomposites.
Table of Contents
Plasmonic nano-antenna optimization using characteristic mode analysis -- Electromagnetic resonance analysis of asymmetric carbon nanotube dimers for sensing applications -- Method of moment analysis of carbon nanotubes embedded in a lossy dielectric slab using a multilayer dyadic Green's function -- Asymmetric CNT dimers embedded in a dielectric slab: new plasmonic resonance behavior -- Conclusion and future directions