Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xi, 100 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 83-86).

Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Durgin, Gregory; Committee Member: Ingram, Mary Ann; Committee Member: Nikitin, Pavel; Committee Member: Peterson, Andrew; Committee Member: Steffes, Paul.

Thesis (M.S.)--Brigham Young University. Dept. of Electrical and Computer Engineering, 2007. / Includes bibliographical references (p. 53-55).

The objective of the current work has been to develop a system which will allow continuous monitoring of areal mass density, lateral stress, and temperature during a process with real time presentation of results making possible either manual or automated control of the process. The system uses three quartz resonators of different crystallographic cuts (AT cut, BT cut and SC cut) in the same environment. The development of an algorithm to solve a system of equations representing a complete representation of the temperature characteristics of the three resonators is presented. This is followed by an analysis of the potential accuracy of the system and the limitations imposed by the assumptions made in the mathematical models of the system. Sputtering yields were verified using Rutherford backscattering analysis. Experimental apparatus including the physical mounting of the resonators in an experimental environment, details of the oscillator circuitry and frequency counter, and use of a personal computer for data acquisition and control are described. The results presented show, in addition to the mass change and lateral stress build-up which occur when sputtering a gold film with an argon ion beam, the radiation induced temperature rise and the radiation induced stress caused by temperature gradients. An experiment using beams of Sb+ at 50keV and Sb2+ at 100keV has been used to demonstrate the enhancement of sputtering yield that occurs when Au films are bombarded with monomers and dimers of Sb at the same energy per atom. Results are compared with simulations using both the TRIM program and molecular dynamics code.

La recherche de défauts dans les matériaux est un sujet complexe et important, en particulier lorsque la sécurité est en jeu comme dans le domaine aéronautique. Cette thèse s’inscrit dans cette problématique et s’organise en deux parties. La première partie est dédié à la détection des défaut dans les composites carbones par trois nouvelles méthodes radiofréquences permettant de détecter, en particulier, les impacts sur les peaux des composites carbones. La deuxième partie est consacrée à la détection des infiltrations d’eau dans les composites alvéolaires par une méthode multiphysique couplant une onde hydraulique non linéaire et une détection par un RADAR CW.

This thesis includes studies of developing distributed optical fiber vibration sensor based on Rayleigh backscattering with broad frequency response range and high spatial resolution. Distributed vibration sensor based on all-polarization-maintaining configurations of the phase-sensitive optical time domain reflectometry (OTDR) is developed to achieve high frequency response and spatial resolution. Signal fading and noise induced by polarization change can be mitigated via polarization-maintaining components. Pencil-break event is tested as a vibration source and the layout of the sensing fiber part is designed for real applications. The spatial resolution is 1m and the maximum distance between sensing fiber and vibration event is 18cm. Wavelet denoising method is introduced to improve the performance of the distributed vibration sensor based on phase-sensitive OTDR in standard single-mode fiber. Noise can be reduced more effectively by thresholding the wavelet coefficient. Sub-meter spatial resolution is obtained with a detectable frequency up to 8 kHz. A new distributed vibration sensor based on time-division multiplexing (TDM) scheme is also studied. A special probe waveform including a narrow pules and a quasi-continuous wave can combine the conventional phase-sensitive OTDR system and polarization diversity scheme together in one single-mode fiber without crosstalk. Position and frequency of the vibration can be determined by these two detection systems consecutively in different time slots. Vibration event up to 0.6 MHz is detected with 1m spatial resolution along a 680m single-mode sensing fiber. Continuous wavelet transform (CWT) is investigated to study the non-stationary vibration events measured by our phase OTDR system. The CWT approach can access both frequency and time information of the vibration event simultaneously. Distributed vibration measurements of 500Hz and 500Hz to 1 kHz sweep events over 20 cm fiber length are demonstrated using a single-mode fiber. Optical frequency-domain reflectometry (OFDR) for vibration sensing is proposed for the first time. The local Rayleigh backscatter spectrum shift in time sequence could be used to determine dynamic strain information at a specific position of the vibrated state with respect to that of the non-vibrated state. Measurable frequency range of 0-32 Hz with the spatial resolution of 10 cm is demonstrated along a 17 m fiber.

The overall objective of this thesis was to predict, model and measure low frequency acoustic backscatter from the sea surface zone (SSZ). In particular, the objectives were fourfold: to relate the acoustic backscatter Doppler spectrum to the directional waveheight spectrum (DWS) through a perturbation analysis; to develop instrumentation suitable for measuring the properties of acoustic backscatter from the SSZ; to design and implement signal processing hardware and software to process raw data from the instrument; and to deploy the instrument and make measurements to test the validity of the predictions of the theoretical development. A theoretical framework was developed to enable a test of the acoustic analogue of the Coastal Ocean Dynamics Applications Radar (CODAR) technique, using beamforming techniques to simulate the CODAR antennas. Expressions relating the CODAR antenna outputs to the output of an array of omnidirectional acoustic point sensors were developed, and mathematical algorithms and techniques were derived to extract information about the DWS of surface gravity waves from acoustic Doppler backscatter measurements with the array. Models were developed and implemented, showing the expected form of the power spectral density of the acoustic Doppler backscatter seen by single omnidirectional receivers, and the expected form of data products of the beamformed array. An acoustic instrument — the Upward-Looking Sonar Array System (ULSAS) — was developed for stand-alone, remotely controlled operation in both bottom-situated and deep-water, surface-tethered configurations. This device can collect and store large quantities of acoustic data from a multi-element array, under the control of a distant operator over a radio link. The bottom-situated version was deployed in the coastal waters of British Columbia, and the deep water version was deployed in the recent Surface Wave Processes (SWAPP) experiment. A preliminary test of the acoustic CODAR technique was made, yielding information consistent with the known wind and wave field. The form of the non-directional part of the extracted DWS followed approximately the expected k⁻⁴ shape for k values above saturation. Beamforming results using frequency-domain data show that the Doppler-shifted acoustic backscatter is directional in nature. These are the first results of this kind to be reported. The deep-water version of ULSAS was tested for the first time during the SWAPP cruise. In spite of a problem limiting the power output of the projector, estimates of the surface scattering strength parameter over angles of incidence less than 45° were made, showing some surprising departures from the Chapman-Harris empirical formula for S₅ , and interesting angular structure. Measurements of the ambient noise field were also made under calm conditions and during 14 kt winds. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Spaceborne radar sounders are an important class of remote sensing instruments which operate by recording backscattered electromagnetic waves in the vicinity of a solid planetary body. The incoming waves are generally transmitted by the radar itself (active sounding), although external signals of opportunity can also be used (passive sounding). There are currently two major planetary radar sounders under development, both headed to the Jovian icy moons (Europa, Ganymede and Callisto). Designing a radar sounder is a very challenging process involving careful leveraging of heritage and predictive tools, and in which backscattering simulators play a central role. This is especially true for coherent simulators, due to their higher accuracy and the possibility they offer to apply advanced processing techniques on the resulting simulated data, such as synthetic aperture radar focusing, or any other operation which requires field amplitude, phase and polarisation. For this reason, designing computationally-efficient coherent simulators is an important and active research area. The first contribution of this thesis is a novel multilayer coherent simulator based on the Stratton-Chu equation and the linear phase approximation, which can generate realistic simulated radar data on a wide range of surface and subsurface digital elevation models (DEM), using only a fraction of the computational resources that a finite-difference time-domain method would need. Thorough validation was conducted against both theoretical formulations and real data, which confirmed the accuracy of the method. The method was then generalised to noisy active and passive sounding, which is an important capability in the context of the proposed use of passive sounding on the Jovian icy moons. Provided that representative information about the surface and this external field exists, the simulator could compare the relative scientific value of active and passive sounding of a given target under given conditions. However, quality DEMs of the Jovian icy moons are scarce. For this reason we also present a comparative study of the fractal roughness of Europa and Mars (a much better studied body), where we derive fractal analogue maps of twelve types of Europan terrains on Mars. These maps could be used to guide the choice of Martian DEMs on which to perform representative backscattering simulations for future radar missions on Europa. Finally, we explore the possibility of entirely new radar architectures with the novel concept of the distributed radar. In a distributed sounder, very large across-track antennas can be synthesised from smallsats flying on selected orbits, providing a way to obtain a highly-directive antenna without the need to deploy large and complex structures in space. We develop an analytical formulation to treat the problem of beamforming with an array affected by perturbations on the positions of its array elements, and propose a set of Keplerian parameters that enable the concept.

La recherche de défauts dans les matériaux est un sujet complexe et important, en particulier lorsque la sécurité est en jeu comme dans le domaine aéronautique. Cette thèse s’inscrit dans cette problématique et s’organise en deux parties. La première partie est dédié à la détection des défaut dans les composites carbones par trois nouvelles méthodes radiofréquences permettant de détecter, en particulier, les impacts sur les peaux des composites carbones. La deuxième partie est consacrée à la détection des infiltrations d’eau dans les composites alvéolaires par une méthode multiphysique couplant une onde hydraulique non linéaire et une détection par un RADAR CW. / Detecting default inside material is a complex and important topic, particularly when the safety is at riske like for instance in the aeronautic field. This phd thesis is divided in two parts. In a first part, mainly we will present three new RF methods allowing to detect, for example, impact damages on carbon composite skins. In a second part we will present a new method aimed to detect water ingress in cellular composite. This new method is based on the interaction of a nonb-linear water wawe with a RADAR

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