Near-field thermophotovoltaic (NFTPV) devices have received great attention lately as attractive energy harvesting systems, whereby a heated thermal emitter exchanges super-Planckian near-field radiation with a photovoltaic (PV) cell to generate electricity. This work describes the advancement of NFTPV technology through both simulations of next-generation devices, and experimental research addressing the technical challenges faced by NFTVPs, including nanostructured material properties, and large-area near-field heat transfer. The first part of this work seeks to improve the performance of a possible NFTPV device by using a periodic tungsten grating as the thermal emission source. The effects on the electrical power generation and the conversion efficiency are investigated via simulations with different grating geometries. It is found that using the selected grating geometry the power output and efficiency could be increased by 40% and 6%, respectively, over a flat tungsten emitter. The reasoning behind the enhancement is attributed to a plasmonic resonance that shifts towards lower frequencies at large wavenumbers. Extensive experimental research is undertaken to investigate the technical challenges in NFTPVs. The optical properties of thin tungsten films, which may serve as an emitter material, are extracted through spectroscopic measurements, and are found to be significantly different from reported bulk values due to a wide range of crystal structures that are present in sputtered films. A heat transfer experiment is designed and built to measure near-field radiation between two doped-silicon slabs separated by a submicron vacuum gap. The details of this system and the sample fabrication show a robust and straightforward method of measuring large-area near-field radiative heat transfer at distances between 200 nm and 800 nm. The results of this experiment show the largest energy throughput of submicron near-field heat transfer to date, and serve to address technical challenges behind practical near-field thermophotovoltaic technology.

When any method of surface wave testing that involves Rayleigh waves is performed, one important assumption is that plane Rayleigh waves are being measured. In the forward modeling or inversion procedure that is used to analyze the field dispersion curve to determine the field V[subscript s] profile, the analysis is based on the wave field consisting of plane Rayleigh waves. Therefore, field dispersion curves that contain near-field data could adversely distort the field V[subscript s] profile. To minimize the influence of near-field effects, several criteria have been recommended in the past. However, most of the criteria were based on empirical equations that implicitly assumed zones of influence, or numerical simulations. There is a lack of experimental investigation, particularly full-scale field investigations. Even, the numerical solutions have been based on simple soil profiles without significant velocity contrasts between soil layers and/or varying thicknesses of soil layers which can significantly influence near-field effects. Data from full-scale field test using the Spectral-Analysis-of-Surface-Waves (SASW) method was used in this thesis research. SASW tests performed at two stages in the construction of a deep, 90-ft thick backfill were studied. The V[subscript s] profiles were normally dispersive, with a substantial increase in the velocity of the layer beneath the backfill. The study shows the adverse distortions that can occur in the field dispersion curve from near-field effects when the spacing of the receiver pair is: (1) above the zone of rapidly increasing V[subscript s] near the surface and (2) less than the depth to the stiffer layer in deeper measurements. Other factors that affect the results are discussed and recommendations are presented to minimize the introduction of near-field effects, at least in these relatively simple V[subscript s] profiles. / text

With the escalating demands for optical communication network system, the need for broadband gain medium in optical communication has increased. Among them, Cr4+:YAG crystal has shown an exceptionally successful broadband amplified spontaneous emission (ASE) light source that fully cover 1.2-1.6 £gm range (3-dB bandwidth up to 265 nm). More recently, we demonstrated the realization of a waveguiding, low-loss, and ultralow threshold Cr4+:YAG double-clad crystal fiber (DCF) based ultrabroadband ASE light source, optical amplifier, and laser grown by the codrawing laser-heated pedestal growth (LHPG) technique. These results demonstrate the potential of the Cr4+:YAG DCF for the replacement of the erbium doped fiber in future optical communications. In this thesis, we focus on the correlation between the nanospectroscopy and nanostructure of the Cr:YAG DCF in order to further improve its device performance. For nanospectroscopic and nanostructural characterizations, near-field scanning optical microscopy (NSOM) and high-resolution transmission electron microscopy (HRTEM) techniques have played key roles. In this thesis, we successfully prepared the HRTEM specimen of Cr:YAG DCF, which is heterostructure, ultrahard, but fragile. Here we show the first study on the nanospectroscopy and nanostructure of the nanocrystals in the inner cladding of Cr:YAG DCF by highly spatial resolved NSOM. The NSOM results were compared with those obtained by HRTEM. In addition, the difference in thermal expansion coefficients between a YAG core and an inner cladding creates a significant localized strain field beneath the core, which can result in optical confinement and provide the possibility to simultaneously control the Cr3+ and Cr4+ fluorescence with systematically varied growth parameters. This new class of strain-tunable Cr:YAG DCF opens up new opportunity to improve the performance of the Cr:YAG DCF based ultrabroadband light source, optical amplifier, and crystal fiber laser in all-optic fiber communications.

This thesis is in support of the Precision Personnel Locator (PPL) project being conducted by Worcester Polytechnic Institute (WPI). The overall goal of the PPL project is to locate firemen and other emergency personnel in buildings using Radio Frequency (RF) techniques. The aspiration is to prevent a tragedy similar to the Worcester Cold Storage fire of 1999. The Mantenna homing wand is a spinoff of the PPL system which uses the Near Field properties of Very Low Frequency (VLF band) waves. The Mantenna has been used to successfully demonstrate the ability to locate targets inside harsh RF environments and other radio opaque environments where normal radiation field based systems have degraded performance, such as commercial, industrial, and apartment buildings. This thesis builds upon the Mantenna rescue device by construction of a transmitter subsystem which is physically smaller than the previous version by redesign of the compact VLF antenna. Additionally, exploitation of the approach used by the Mantenna for homing purposes is explored for full location estimation. This work provides the theoretical background and proof of concept test of a Near Field based location system. Simulation and test results are compared for a minimal configuration involving a single receiver.

Tese de mestrado integrado. Engenharia Electrotécnica e de Computadores. Universidade do Porto. Faculdade de Engenharia. 2011

Not available / text

Thesis (PhD) - Swinburne University of Technology, Faculty of Engineering and Industrial Sciences, Centre for Micro-Photonics, 2005. / A thesis submitted for the degree of Doctor of Philosophy, Centre for Micro-Photonics, Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, 2005. Typescript. Bibliography: p. 129-142.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2008. / Title from title screen (site viewed Mar. 10, 2009). PDF text: xv, 182 p. : ill. (some col.) ; 6 Mb. UMI publication number: AAT 3331444. Includes bibliographical references. Also available in microfilm and microfiche formats.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

It has been shown that the energy exchange between two objects can be greatly enhanced when the separation between the objects is on the order of the wavelength of thermal emission. The earliest theoretical and computational work focused on simple planar and spherical geometries, or they resorted to approximations that separated the object to outside of the thermal wavelength \(\lambda_T = hc/(k_BT)\). Since those original works, the study of near-field energy exchange has expanded to object shapes that can be described by a separable coordinate system using a spectral expansion of the dyadic Green function of the system. The boundary element method has also been used to study arbitrary shapes in thermal equilibrium. Application of these new expansion methods to general shapes out of thermal equilibrium will facilitate in the optimization of nanoscale structures. A three step process is used to investigate the effects of object shape on the total and directionality of the energy exchange between objects. First, a general expression for the energy flux between the objects will be formulated. Second, a computational method to evaluate the expression will be implemented. Finally, the effects of varying the surface geometry will be explored. The computational results demonstrate that the total energy exchange between two bodies is influenced by the surface shape of the objects even when the surface areas are held constant. While the primary increase over the classical blackbody energy exchange \(\sigma T^4 A\) is primarily governed by separation of the surfaces, we show that the view factors from classical far-field radiative transfer can be used to predict the change in the total energy exchange from a reference configuration at the same separation when the surface area of the two objects is comparable. Additionally, we demonstrate that the spatial distribution of the energy exchange can be localized into small spatial region with a peak value increased over \SI{30}{\percent} by using two objects with dramatically different projected areas.