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Development and Demonstration of a TDOA-Based GNSS Interference Signal Localization System
Background theory, a reference design, and demonstration
results are given for a Global Navigation Satellite
System (GNSS) interference localization system comprising a
distributed radio-frequency sensor network that simultaneously
locates multiple interference sources by measuring their signalsâ
time difference of arrival (TDOA) between pairs of nodes in
the network. The end-to-end solution offered here draws from
previous work in single-emitter group delay estimation, very long
baseline interferometry, subspace-based estimation, radar, and
passive geolocation. Synchronization and automatic localization
of sensor nodes is achieved through a tightly-coupled receiver
architecture that enables phase-coherent and synchronous sampling
of the interference signals and so-called reference signals
which carry timing and positioning information. Signal and crosscorrelation
models are developed and implemented in a simulator.
Multiple-emitter subspace-based TDOA estimation techniques
are developed as well as emitter identification and localization
algorithms. Simulator performance is compared to the CramérRao
lower bound for single-emitter TDOA precision. Results are
given for a test exercise in which the system accurately locates
emitters broadcasting in the amateur radio band in Austin, TX.Aerospace Engineering and Engineering Mechanic
Co-Localization of Audio Sources in Images Using Binaural Features and Locally-Linear Regression
This paper addresses the problem of localizing audio sources using binaural
measurements. We propose a supervised formulation that simultaneously localizes
multiple sources at different locations. The approach is intrinsically
efficient because, contrary to prior work, it relies neither on source
separation, nor on monaural segregation. The method starts with a training
stage that establishes a locally-linear Gaussian regression model between the
directional coordinates of all the sources and the auditory features extracted
from binaural measurements. While fixed-length wide-spectrum sounds (white
noise) are used for training to reliably estimate the model parameters, we show
that the testing (localization) can be extended to variable-length
sparse-spectrum sounds (such as speech), thus enabling a wide range of
realistic applications. Indeed, we demonstrate that the method can be used for
audio-visual fusion, namely to map speech signals onto images and hence to
spatially align the audio and visual modalities, thus enabling to discriminate
between speaking and non-speaking faces. We release a novel corpus of real-room
recordings that allow quantitative evaluation of the co-localization method in
the presence of one or two sound sources. Experiments demonstrate increased
accuracy and speed relative to several state-of-the-art methods.Comment: 15 pages, 8 figure
Plasmonic Antennas Hybridized with Dielectric Waveguides
For the purpose of using plasmonics in an integrated scheme where single
emitters can be probed efficiently, we experimentally and theoretically study
the scattering properties of single nano-rod gold antennas as well as antenna
arrays placed on one-dimensional dielectric silicon nitride waveguides. Using
real space and Fourier microscopy correlated with waveguide transmission
measurements, we quantify the spectral properties, absolute strength and
directivity of scattering. The scattering processes can be well understood in
the framework of the physics of dipolar objects placed on a planar layered
environment with a waveguiding layer. We use the single plasmonic structures on
top of the waveguide as dipolar building blocks for new types of antennas where
the waveguide enhances the coupling between antenna elements. We report on
waveguide hybridized Yagi-Uda antennas which show directionality in
out-coupling of guided modes as well as directionality for in-coupling into the
waveguide of localized excitations positioned at the feed element. These
measurements together with simulations demonstrate that this system is ideal as
a platform for plasmon quantum optics schemes as well as for fluorescence
lab-on-chip applications
Modifying Single-Molecule Fluorescence with a Plasmonic Optical Antenna: Theory, Methodology, and Measurement
Nanophotonics is the study and technological application of light on the nanometer scale. This dissertation brings together two disparate branches of nanophotonics: plasmonics and single-molecule super-resolution microscopy. Plasmonics studies the collective oscillations of free electrons in a conductor, which enable light to be manipulated on subwavelength length scales. Plasmonics, and in particular plasmonic optical antennas, have generated a huge amount of interest due to their rich new physics and countless applications, ranging from surface-enhanced spectroscopies, to novel cancer therapies, and to quantum information platforms. With single-molecule fluorescence super-resolution microscopy, the optical properties of individual molecules can be studied with nanometer-scale resolution, far better than the micron scale of traditional microscopy. Super-resolution microscopy has revolutionized cellular biomedicine, ushering in a new generation of fundamental discoveries and associated medical therapies. Super-resolution microscopy is also increasingly enabling discoveries and advances across disciplines, allowing direct visualizations of phenomena ranging from chemical imaging of surface reactions to nanoscale fluid dynamics. By bringing together these two fields, this dissertation supports two synergistic directions for applications of this science: enhancing the resolution of single-molecule fluorescence super-resolution imaging and using a novel technique to directly study how a single emitter interacts with an optical antenna.
In this dissertation, I present a new theoretical approach to understand the interaction of a single fluorescent molecule with an optical antenna, a broadly applicable new image analysis algorithm, and experimental measurements of antenna-modified fluorescence. The theoretical framework expands an established theory of antenna-modified fluorescence to incorporate the variability of real experiments. This research has uncovered a mislocalization effect: differences between the actual position of an emitter and the apparent, super-resolved position of the emitter image. I therefore present computational methods to predict the emission mislocalization of single fluorescent molecules coupled to an optical antenna and compare these predictions to experiments. I describe the SMALL-LABS algorithm, a general data analysis approach to accurately locating and measuring the intensity of single molecules, regardless of the shape or brightness of an obscuring background. Finally, I present the results of experiments studying the polarization dependence of coupling a single fluorescent molecule to a gold nanorod plasmonic optical antenna, and I compare these measurements with theoretical predictions. This work advances the fundamental science of nanophotonics and will pave the way for next generation super-resolution imaging and optical antenna technologies.PHDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/145846/1/isaacoff_1.pd
Enhancement and tunability of near-field radiative heat transfer mediated by surface plasmon polaritons in thin plasmonic films
The properties of thermal radiation exchange between hot and cold objects can
be strongly modified if they interact in the near field where electromagnetic
coupling occurs across gaps narrower than the dominant wavelength of thermal
radiation. Using a rigorous fluctuational electrodynamics approach, we predict
that ultra-thin films of plasmonic materials can be used to dramatically
enhance near-field heat transfer. The total spectrally integrated film-to-film
heat transfer is over an order of magnitude larger than between the same
materials in bulk form and also exceeds the levels achievable with polar
dielectrics such as SiC. We attribute this enhancement to the significant
spectral broadening of radiative heat transfer due to coupling between surface
plasmon polaritons (SPPs) on both sides of each thin film. We show that the
radiative heat flux spectrum can be further shaped by the choice of the
substrate onto which the thin film is deposited. In particular, substrates
supporting surface phonon polaritons (SPhP) strongly modify the heat flux
spectrum owing to the interactions between SPPs on thin films and SPhPs of the
substrate. The use of thin film phase change materials on polar dielectric
substrates allows for dynamic switching of the heat flux spectrum between
SPP-mediated and SPhP-mediated peaks.Comment: 25 pages, 11 figure
Quantum dot clusters as single-molecules: deciphering collective fluorescence and energy transfer signatures
2016 Fall.Includes bibliographical references.Applications of quantum dot nanocrystals span from the individual single-molecule use to large, densely-packed bulk solids. Already, the fluorescence behavior of individual particles is complex and nuanced, particularly involving the blinking phenomenon. When particles are combined into higher-order structures where interaction may occur, a complete description becomes intractable. However, clusters---between two and ten particles---can be effective model systems to explore the local behaviors that occur in larger networks. A benefit of small clusters is the viability of using single-molecule spectroscopic techniques, which are often more informative than bulk measurements. In this work we combine fluorescence microscopy with structure-probing electron microscopy to elucidate the fluorescence dynamics clusters of semiconductor nanocrystals. The spectral characteristics of clusters are explored in the context of an energy transfer model showing low-intensity emission is blue-shifted, corresponding to the weaker emission from donor particles with a larger band gap. Because energy transfer depends intimately on the specific topographical structure of the cluster, the inter-particle spacing, and relative alignment, characterization of specific cluster behavior is better informed by correlated measurements. Next, we present the mapping results from super-resolution microscopy where the spatial distributions of fluorescence in the sub-10 nanometer realm is clearly correlated with scanning electron microscopy imaging of the same clusters. Stochastic blinking events enable such observations. The enhanced blinking associated with energy transfer has practical implications for donor and acceptor roles in clusters. Finally, the dynamic evolution of the emission dipole orientation for single nanocrystals and nanocrystal clusters is measured. The orientation signature suggests coupling strengths and constitutes a first-step towards determining corrections to Förster resonant energy transfer theory involving nanocrystals
Super-resolution Luminescence Micro-Spectroscopy : A nano-scale view of solar cell material photophysics
Optical microscopy is a fundamental tool in a range of disciplines encompassed by the physical and biological sciences. At the dawn of this millennium, a break-through was made in optical microscopy where super-resolution methods emerged and declared imaging beyond the optical diffraction limit a possibility. Most of these methods are based on fluorescence detection of single molecules. These methods found particular prominence in the life sciences where small structures could be observed inside living organisms, due to the non-invasiveness of light. Currently there is a growing notion that these methods can be applied in physics and chemistry to study photo-induced phenomena in materials with resolution at the nanoscale. The aim of this thesis is to explore and develop these possibilities to study energy and charge transport in functional materials interesting for light harvesting and solar-energy conversion. We present a novel wide-field super-resolution microscopy method adapted from localization microscopy. In combination with fluorescence spectroscopy it allows for an interrogation of a materialâs photophysical properties down to the nanometer scale. We call the method super-resolution luminescence micro-spectroscopy (SuperLuMS). One of the examples that we present here is a study of energy migration and trapping in individual molecular J-aggregates. We show that so-called âoutliersâ (seldomly occurring trapping states) completely determine the exciton transport and dominate the fluorescence response. We also show that hybrid organic-inorganic perovskites are ideal objects for luminescence microscopy. These âhotâ solar cell and light-emitting materials possess rich structures at scales just beyond optical diffraction limit making them an ideal âplaygroundâ for employing SuperLuMS and demonstrating its abilities.The dynamics of charge carrier recombination in these materials is controlled by trapping and, as we demonstrate here, possess a great spatial inhomogeniety. For the first time we showed that one single trap can control the fate of charge carries in micrometer sized perovskite crystals which has important consequences for optical design of solar cells and other optoelectronic devices. We were also able to observe details of light-induced degradation and crystal phase transition in individual hybrid organic-inorganic perovskite crystals. We believe SuperLuMS is an approach which will continue to evolve and find more diverse applications in material science
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