International Telemetering Conference Proceedings / October 27-30, 1997 / Riviera Hotel and Convention Center, Las Vegas, Nevada / This student paper was produced as part of the team design competition in the University of Arizona course ECE 485, Radiowaves, and Telemetry. It describes the design of a telemetry support package for interplanetary exploration. Control and processing of telemetric signals between an earth based control station, an exploratory orbiter and probe pods are the focus of this design. Using this design data retrieval is achieved at a highly reliable rate of 1 error in 10^-10 bits. The exploratory orbiter, carrying a payload of probes, is launched and proceeds along its predetermined trajectory. Commands from the earth-based control station is used to send the orbiter to planetary destinations. The craft then establishes a stable non-geosynchronous orbit. Several probe pods are launched towards the planet at predetermined locations. These probe pods collect and send data, as well as system monitoring information to the orbiting craft. The orbiting craft then retrieves the signals generated by all pods and relays that information to an earth-based control station.

En raison de l'expansion des données, les algorithmes de compression sont désormais cruciaux. Nous abordons ici le problème de trouver des algorithmes de compression optimaux par rapport à une source de Markov donnée. A cet effet, nous étendons l'algorithme de Huffman classique. Pour se faire premièrement on applique Huffman localement à chaque état de la source Markovienne, en donnant le résultat de l'efficacité obtenue pour cet algorithme. Mais pour bien approfondir et optimiser quasiment l'efficacité de l'algorithme, on donne un autre algorithme qui est toujours appliqué localement à chaque états de la source Markovienne, mais cette fois ci en codant les facteurs partant de ces états de la source Markovienne de sorte à ce que la probabilité du facteur soit une puissance de 1/2 (sachant que l'algorithme de Huffman est optimal si et seulement si tous les symboles à coder ont une probabilité puissance de 1/2). En perspective de ce chapitre on donne un autre algorithme (restreint à la compression de l'étoile) pour coder une expression à multiplicité, en attendant dans l'avenir à coder une expression complète / Due to the expansion of datas, compression algorithms are now crucial algorithms. We address here the problem of finding an optimal compression algorithm with respect to a given Markovian source. To this purpose, we extend the classical Huffman algorithm. The kernels are popular methods to measure the similarity between words for classication and learning. We generalize the definition of rational kernels in order to apply kernels to the comparison of languages. We study this generalization for factor and subsequence kerneland prove that these kernels are defined for parameters chosen in an appropriate interval. We give different methods to build weighted transducers which compute these kernels

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Approved for public release, distribution unlimited / Steam leakage from an aircraft carrier catapult is sometimes ingested into the aircraft engines upon launch which may induce compressor stall. Investigation of this phenomenon is of particular interest to the Navy with its new F35C, the aircraft carrier variant of the joint strike fighter. The single engine configuration of the F-35C makes this aircraft particularly vunerable to steam-induced stall. The present study examined both throttle-induced stall and steam-induced stall in a compressor at 90% and 95% speed through the use of 9 Kulite and 2 hot-film pressure transducers. The use of Fast Fourier Transform waterfall plots of the transient data before and during stall proved invaluable in determining stall precursors as well as the mode of rotor stall. In addition, a new computational fluid dynamic model was designed using CFX-5 software to represent a single blade passage of the compressor rotor, in order to predict compressor performance. The computed results were compared to experimental results gathered at various throttle settings. An accurate model will enable researchers to predict compressor performance for various and multiple gases. / Outstanding Thesis

A method is proposed which uses a lower-frequency transmit to create a known harmonic acoustical source in tissue suitable for wavefront correction without a priori assumptions of the target or requiring a transponder. The measurement and imaging steps of this method were implemented on the Duke phased array system with a two-dimensional (2-D) array. The method was tested with multiple electronic aberrators [0.39π to 1.16π radians root-mean-square (rms) at 4.17 MHz] and with a physical aberrator 0.17π radians rms at 4.17 MHz) in a variety of imaging situations. Corrections were quantified in terms of peak beam amplitude compared to the unaberrated case, with restoration between 0.6 and 36.6 dB of peak amplitude with a single correction. Standard phantom images before and after correction were obtained and showed both visible improvement and 14 dB contrast improvement after correction. This method, when combined with previous phase correction methods, may be an important step that leads to improved clinical images. / Dissertation

Approved for public release; distribution in unlimited. / Optical turbulence plays an important role in the propagation of electromagnetic waves through the atmosphere because it broadens and distorts the optical beam. A variety of optical, thermal, and acoustic instruments are used to detect the atmospheric turbulence and an acoustic echosounder has proven to be a valuable tool to probe the fine dynamic structure of atmospheric turbulence within first hundred meters above the surface. The first planar acoustic echosounder constructed at the Naval Postgraduate School was by Weingartner and Wroblewski, under Walters' supervision. Moxcey later modified this design by reducing the number of drivers from 25 to 19 and placing the drivers closer together into a hexagonal, close-packed array. This thesis explored the potential sources of the transducer ringing and implemented solutions to the problem. Additionally, we also improved the receiving sensitivity of the echosounder and lowered the electronics noise when receiving. Finally, we applied these techniques to another array assembled with new drivers to improve its performance compared to the previous echosounder array, while measuring and quantifying the level of improvement achieved. / Lieutenant Commander, Republic of China Navy

This thesis concerns the formation, sintering and humidity dependent electrical behaviour of the spinel ceramic material nickel germanate, Ni(_2)Ge0(_4).Ni(_2)Ge0(_4) has been prepared via the solid state reaction between NiO and GeO(_2) over a range of temperatures, and characterised using a number of techniques. The sintering behaviour of pressed pellets of Ni(_2)Ge0(_4) has also been investigated, together with a characterisation of the microstructure of the sintered bodies. Substitutional doping of Ni(_2)GeO(_4) with Li as a replacement for Ni is found to promote a high degree of shrinkage in the sintering process, probably due to the formation of a liquid phase. XRD revealed that even when 10 % of the Ni atoms were replaced with Li, no change in the crystal structure could be detected. A C. impedance spectroscopy of Ni(_2)Ge0(_4) samples was used to investigate the humidity sensitivity of this material. Equivalent circuit analysis, based on a network of resistors and constant phase elements, shows that the humidity sensitivity is due to conduction in a surface layer of water, in agreement with the models currently popular in the Uterature. Measurement of the water adsorption isotherm of Ni(_2)Ge0(_4) in pellet form indicates that a single monolayer of water is formed at around 20 %R(_H), with an approximately linear increase in water layer thickness up to around 80 %R(_H), after which capillary condensation causes a large increase in the volume of adsorbed water. The information gained on the thickness of this layer of water has been correlated with the resistance of the layer measured by impedance spectroscopy, and subsequently used to provide evidence for a model of the humidity sensitive conduction. The conduction in the surface layer is thought to be due to dissociation of the water, where the amount of dissociation is exponentially dependent on the humidity.

Orientador: Fabricio Guimarães Baptista / Banca: Luiz Gonçalves Junior / Banca: Mário Anderson de Oliveira / Resumo: A técnica da impedância eletromecânica (E/M) tem sido amplamente estudada nas últimas décadas como um método não destrutivo para detectar danos estruturais em aplicações de monitoramento de integridade estrutural (SHM - structural health monitoring) usando transdutores piezelétricos de baixo custo. Esses transdutores operam simultaneamente como sensor e atuador e são fixados à estrutura monitorada utilizando um adesivo a base de cianoacrilato. Embora muitos estudos tenham relatado a eficácia desse método de detecção, inúmeros problemas práticos têm sido reportados, como os efeitos de ruído e vibração, que precisam ser considerados para permitir o uso eficaz desse método em aplicações reais. Portanto, esta dissertação de mestrado apresenta uma análise experimental dos efeitos do ruído e das vibrações na detecção de danos estruturais em sistemas de SHM baseados na técnica da impedância eletromecânica. Os experimentos foram realizados em uma barra de alumínio usando dois diafragmas piezelétricos, sendo que um deles foi usado para obter as assinaturas de impedância elétrica e o outro foi usado como atuador para introduzir ruído e vibração controlada. Para a simulação de dano foi utilizada uma pequena massa metálica fixada na estrutura com uso de adesivo a base de cianoacrilato. Os efeitos do ruído e da vibração sobre as assinaturas de impedância foram avaliados por meio do cálculo da função de coerência e de índices básicos de dano. Os resultados indicam que a vibração e o ruído ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The electromechanical impedance (EMI) technique has been extensively studied in recent decades as a non-destructive method for detecting structural damage in structural health monitoring (SHM) applications using low-cost piezoelectric transducers. These transducers operate simultaneously as actuator and sensor and they are fixed to the structure using cyanoacrylate-based glue. Although many studies have reported the effectiveness of this detection method, a lot of practical problems shown up, such as the noise effects and vibration, that need to be addressed to enable this method's effective use in real applications. Therefore, this master's thesis presents an experimental analysis of noise and vibration effects on the structural damage detection in impedance-based SHM systems. The experiments were performed on an aluminum bar using two piezoelectric diaphragms, where one was used to measure the electrical impedance signatures and the other was used as an actuator to introduce noise and controlled vibration. To simulate damage, a small metal mass was fixed to the structure using cyanoacrylate glue. The effects of noise and vibration on the impedance signatures were evaluated by computing the coherence function and basic damage indices. The results indicate that vibration and noise significantly affect the threshold of the lowest detectable damage, which can be compensated by increasing the excitation signal of the piezoelectric transducer that measure the electrical impedance... (Complete abstract click electronic access below) / Mestre

Há vários métodos descritos na literatura sobre a forma como os piezoeletretos ou ferroeletretos podem ser fabricados, sendo que cada uma dessas técnicas apresenta suas vantagens e desvantagens. Por exemplo, espumas de polipropileno (PP) são fáceis de serem processadas em grande escala aliada a um baixo custo de produção, entretanto, seu efeito piezoelétrico é dependente da temperatura, assim como não há um controle dos vazios internos durante sua fabricação, ocasionando uma heterogeneidade da geometria desses vazios. Por outro lado, em outros métodos as dimensões das cavidades podem ser controlada e polímeros termicamente mais estáveis podem ser utilizados, no entanto, a um maior custo de produção. Em relação aos métodos que visam a produção dos piezoeletretos, neste trabalho é apresentada uma nova técnica baseada em termo selagem e template de água para criar piezoeletretos com canais tubulares abertos. Este tipo de estrutura vazada foi inicialmente produzida pela laminação de filmes de etileno propileno fluorado (FEP) com o template de politetrafluoretileno (PTFE) entre eles, sendo o template descartado após a laminação, gerando resíduos. Com a substituição do template de PTFE pela água na etapa de produção dos novos piezoeletretos, foi possível eliminar o descarte de resíduos sólidos ao mesmo tempo em que um tratamento químico foi efetuado na superfície do filme. Pelo método desenvolvido, a estabilidade térmica do piezoeletreto foi melhorada sem a necessidade de um tratamento prévio ou posterior dos filmes, diminuindo assim o custo de produção. Outro método inovador para produção dos piezoeletretos também foi exposto neste trabalho. Essa inovação consiste na fabricação de piezoeletretos com cavidades controladas por meio da impressão de filmes de ABS. Para a impressão dos filmes uma impressora 3D de baixo custo foi utilizada. / There are several methods described in the literature on how piezoelectrets or ferroelectrets can be manufactured, each of these techniques present their advantages and disadvantages. For example, foamed polypropylene (PP) are easy to be processed on a large scale combined with a low cost of production, however, its piezoelectric effect is temperature dependent, and there is no control of internal voids during its manufacture, causing a heterogeneity of the geometry of these empty. Furthermore, in other methods the cavities dimensions can be controlled and more thermally stable polymers can be used, however, with a higher production cost. Regarding the methods for producing piezoelectrets, in this work we present a new technique based on hot sealing and water template for creating multi-layered piezoelectrets with open-tubular channels. This type of voided structure have been initially produced by laminating fluoroethylene-propylene (FEP) films with a polytetrafluorethylene (PTFE) template in between although the template was discarded after lamination, creating residual waste. With the replacement of the PTFE template by water in the production step of the new piezoelectrets, it was possible to eliminate the disposal of solid waste at the same time a chemical treatment was performed on the film surface. By the developed method, the piezoelectrets thermal stability was improved without the need for a prior or subsequent treatment of the films, reducing the production cost. Another innovative method for production of piezoelectrets was also exposed in this work. This innovation consists in manufacturing piezoelectrets with cavities controlled by printing ABS films. In order to print the films, a 3D printer was used.

Os circuitos ou modelos elétricos equivalentes destinam-se à modelagem de transdutores piezoelétricos, incluindo todo seu comportamento eletromecânico. Os modelos elétricos convencionais e clássicos foram elaborados inicialmente para materiais cerâmicos e cristalinos e só posteriormente adaptados para a simulação de polímeros piezoelétricos. Seguindo estes estudos, este trabalho apresenta um circuito elétrico equivalente para transdutores construídos com a tecnologia dos piezoeletretos termo-formados, desenvolvida no Grupo de Alta Tensão e Materiais da Escola de Engenharia de São Carlos (EESC-USP). Este circuito, baseado em um modelo proposto por Fiorillo (2000) para simular um transdutor curvo de fluoreto de polivinilideno (PVDF), foi aprimorado para melhor representar o comportamento em baixas frequências. Nele existem dois ramos: um mecânico e um elétrico. Os parâmetros do ramo mecânico foram calculados nas proximidades da frequência de ressonância das amostras, enquanto que os componentes do ramo elétrico foram determinados pelos ajustes das curvas de condutância e de susceptância para frequências distantes da ressonância. Esta etapa compreendeu o desenvolvimento de um algoritmo baseado na taxa de variação da condutância pela frequência, o qual permitiu determinar um método para separação do espectro de frequência em uma região próxima e outra distante da frequência de ressonância. Após a determinação de todos os parâmetros do modelo elétrico, circuitos para simulação no software Pspice foram elaborados para cada transdutor. Os resultados das simulações da condutância, da susceptância, do módulo da impedância e do ângulo de fase dos circuitos mostraram relevante concordância com as medições quando comparados grafica e numericamente. Esta última análise foi feita através da expressão de erro relativo percentual médio. Neste trabalho, empregou-se a metodologia fundamentada nas medidas da condutância e da susceptância de diferentes amostras, incluindo filmes de polipropileno (PP), de PVDF e de piezoeletretos de canais tubulares abertos de Teflon®FEP. / Equivalent electric circuits or models are regularly employed in piezoelectric transducers modeling, including its electromechanical behavior. Conventional and classic electric models were initially developed for ceramic and crystalline materials and later adapted for simulating piezoelectric polymers. Following these studies, this work presents an equivalent electric circuit for transducers built with the piezoelectret thermo-formed technology, developed by the High Voltage and Materials Group of São Carlos Engineering School (EESC-USP). This circuit, based on a model proposed by Fiorillo (2000) for simulating a curved polyvinylidene fluoride (PVDF) transducer, was improved to represent the behavior at low frequencies. There are two branches in this circuit: a mechanical and an electrical branches. The mechanical branch parameters were calculated in the vicinity of the resonance frequency, whereas the components of the electrical branch were determined by conductance and susceptance curves fittings for frequencies far from resonance. This stage included the development of an algorithm based on the rate of change of conductance, which allowed determining a method to separate the frequency spectrum in near resonance and far from resonance. After determining all parameters, electrical circuits were designed to perform simulations using Pspice software. The results for conductance, susceptance, impedance magnitude and phase angle simulations presented relevant agreement with measurements when compared graphically and numerically. This latter analysis was done by error relative expression. In this work, the methodology was based on conductance and susceptance measurements for different samples, including porous polypropylene (PP), PVDF and Teflon®FEP piezoelectrets with open-tubular channels films.