A Characteristic Mode Analysis of Conductive Nanowires and Microwires Above a Lossy Dielectric Half-Space
Abstract
Nanowires possess extraordinary mechanical, thermoelectric and electromagnetic
properties which led to their incorporation in a wide variety of applications. The purpose of
this study is to investigate the effect of material on the electromagnetic response of these
nanowires. We used the Method of Moments (MOM) for Arbitrarily Thin Wire (ATW)
formulation as an efficient computational technique for calculating the electromagnetic
response of nanowires. To explain the calculated electromagnetic response, we evoked the
Characteristic Mode Analysis (CMA) which decomposes the current on the wire into a
superposition of fundamental current modes. These modes are weighted by two coefficients:
(i) the relative importance of each mode at a certain frequency, termed Modal Significance,
and (ii) the level of coupling between the incident field and the mode termed the Modal
Excitation Coefficient. In this, work we study how the wire’s material affect the Modal
Significance and the Modal Excitation Coefficient of nanowires. Our results show that the
material of the nanowire has a strong effect on the resonance frequency, the bandwidth, and
the overlap of the modes showing that the material of the nanowire can be used as a tuning
factor to develop sensors with desired radiation characteristics.
Nanowires are commonly grown vertically on a substrate and, therefore, we also study
the effect of the presence of a lossy dielectric half-space on their electromagnetic response. To
efficiently account for this interface, we utilize a modified Green’s function using the rigorous
Sommerfeld integrals. Our results show that the relative permittivity of the substrate decreases
the resonance frequencies of the nanowires and significantly alters their radiation patterns.
Most importantly, we find that, if the nanowire is near the interface, its evanescent field’s
couple to the dielectric half space leading to the majority of the scattered power radiated into
the substrate with high directivity. The results of this thesis has the potential to quantify the
electromagnetic response of vertical nanowires in their realistic environment as well as
facilitate the incorporation of nanowires in novel sensing applications.
Table of Contents
Introduction -- Theoretical model -- Dielectric and magnetic properties of nanowires and microwires -- Graphical user interface -- Results and discussion -- Conclusion and future work
Degree
M.S.