No description available.

[pt] Ondas acústicas, sônicas ou ultrassônicas, podem ser empregadas para a telemetria sem fio como alternativa a sistemas eletromagnéticos, transferindo dados e energia ao longo de um canal formado por uma ou mais camadas de sólidos elásticos ou fluidos acústicos. Um exemplo é a interrogação de sensores passivos através de uma parede metálica. Nesta configuração, pelo menos um transdutor acústico é fixado em um lado da parede (face externa), onde uma fonte de alimentação elétrica é disponível. No lado oposto (face interna), onde os sensores estão instalados, são fixados um ou mais transdutores. Na maioria das aplicações estes transdutores são cerâmicas piezelétricas que geram e recebem sinais ultrassônicos. Ondas acústicas ultrassônicas se propagam ao longo do sólido elástico, transferindo energia e dados entre as duas faces, possibilitando a alimentação e interrogação dos sensores. Este tipo de configuração pode ser empregado em aplicações onde o uso de penetradores elétricos ou ópticos não é recomendado. Entretanto, a resposta das piezocerâmicas pode sofrer influências de variações de temperatura e da própria deformação mecânica da parede metálica na qual são fixados. O presente trabalho procurou quantificar a influência da deformação mecânica e da variação de temperatura na comunicação entre dois transdutores piezocerâmicos ultrassônicos, aderidos à uma placa metálica por meio de adesivo epóxi. No estudo, tomou-se como parâmetro quantitativo o sinal S21, que é o logaritmo da razão entre a potência recebida pela saída do sistema (face interna da parede) pela potência transmitida pela entrada (face externa da parede). O trabalho apresenta comparações entre resultados experimentais e simulados através de um modelo numérico de elementos finitos desenvolvido no COMSOL Multiphysics. Os ensaios experimentais foram realizados com pastilhas piezocerâmicas circulares, do tipo PZT4, com diâmetro e espessura de 25 e 2 mm, respectivamente. Os transdutores foram fixados, de forma concentricamente alinhada e por meio de um adesivo epóxi, nas duas superfícies de uma placa de aço inoxidável AISI 316 L com 6 mm de espessura. O trabalho apresenta tabelas e funções para a amplitude do sinal S21 na frequência onde a transferência de potência é maximizada. Para os casos estudados, observou-se que a frequência ideal muda muito pouco com a temperatura ou a deformação da placa sobre a qual os transdutores são fixados, permanecendo com valores entre 0,988 e 0,995 MHz em todas as condições avaliadas. Em função da deformação da placa metálica, a amplitude do sinal S21 também variou muito pouco, de -3,70 para -3,14 dB, desde a condição indeformada da placa até a máxima deformação aplicada, que foi de 1250 (Micro)m/m. Quanto à variação com a temperatura, na faixa de 30 a 100 Graus C, mais uma vez observou-se apenas um pequeno aumento de 0,8 dB na amplitude do sinal S21. Entretanto, para temperaturas acima de 100 Graus C, o sinal passa a cair rapidamente. Em nenhuma das condições estudadas neste trabalho foi observado prejuízo na transferência de potência entre os transdutores, indicando que este tipo de comunicação pode ser uma alternativa robusta ao uso de penetradores elétricos. / [en] Acoustic, sonic or ultrasonic waves can be used for wireless telemetry as an alternative to electromagnetic systems, transferring data and energy along a channel formed by one or more layers of elastic solids or acoustic fluids. An example of this is the interrogation of passive sensors through a metallic wall. In this configuration, at least one acoustic transducer is attached to one face of the wall (external face) where electrical power supply is available. One or more transducers are also attached to its other side (internal face) where the sensors are installed. In most applications, these transducers are piezoelectric ceramics that generate and receive ultrasonic signals. Ultrasonic acoustic waves propagate along the elastic solid, transferring energy and data between both sides, which enables the power supply and interrogation of the sensors. This type of configuration can be used in applications where the use of an electrical or optical penetrator is not suitable. However, the response of piezoceramics may be affected by temperature variations and mechanical deformations of the metallic wall on which they are attached. The present work sought to quantify the influence of mechanical deformation and temperature changes on the communication between two ultrasonic piezo ceramic transducers, adhered to a metal plate by using an epoxy adhesive. The parameter used to quantify this influence was the S21 signal, which is the logarithm of the ratio between the power received from the output of the system (internal face of the wall) to the power transmitted by the input (external face of the wall). The work presents comparisons between experimental and simulated results obtained by using a finite element model developed through the commercial software COMSOL Multiphysics. In the configuration experimentally tested, two PZT-4 disks with diameter and thickness of, respectively, 25 and 2 mm were concentrically attached to both sides of a 6 mm thick, AISI 316 L stainless steel plate. Amplitudes of the S21 signal measured at the frequency where power transfer is maximized were obtained for different temperature and strain levels. Results for all of the evaluated conditions showed that the impedance matching frequency suffers little influence from temperature variations or strain in the plate on which the transducers are attached, having remained within a range from 0.988 to 0.995 MHz in all tests. As mechanical strains were applied to the metal plate, the amplitude of the S21 signal varied from -3.70 dB to -3.14 dB, from the undeformed condition to the maximum applied deformation (1250 (Micro)m/m). Regarding temperature changes, a small increase of 0.8 dB in the amplitude of the S21 signal was observed when increasing temperature from 30 C Degrees to 100 C Degrees. However, for temperatures above 100 C Degrees, the signal was found to quickly decay. None of the conditions studied in this work brought any impairment to the power transfer between the transducers, indicating that this type of communication can be a robust alternative to electrical penetrators.

A main challenge in the field of special effects is to create special effects in real time in a way that the user can preview the effect before taking the actual picture or movie sequence. There are many techniques currently used to create computer-simulated special effects, however current techniques in computer graphics do not provide the option for the creation of real-time texture synthesis. Thus, while computer graphics is a powerful tool in the field of special effects, it is neither portable nor does it provide work in real-time capabilities. Real-time special effects may, however, be created optically. Such approach will provide not only real-time image processing at the speed of light but also a preview option allowing the user or the artist to preview the effect on various parts of the object in order to optimize the outcome. The work presented in this dissertation was inspired by the idea of optically created special effects, such as painterly effects, encoded in images captured by photographic or motion picture cameras. As part of the presented work, compact relay optics was assessed, developed, and a working prototype was built. It was concluded that even though compact relay optics can be achieved, further push for compactness and cost-effectiveness was impossible in the paradigm of bulk macro-optics systems. Thus, a paradigm for imaging with multi-aperture micro-optics was proposed and demonstrated for the first time, which constitutes one of the key contributions of this work. This new paradigm was further extended to the most general case of magnifying multi-aperture micro-optical systems. Such paradigm allows an extreme reduction in size of the imaging optics by a factor of about 10 and a reduction in weight by a factor of about 500. Furthermore, an experimental quantification of the feasibility of optically created special effects was completed, and consequently raytracing software was developed, which was later commercialized by SmARTLens(TM). While the art forms created via raytracing were powerful, they did not predict all effects acquired experimentally. Thus, finally, as key contribution of this work, the principles of scalar diffraction theory were applied to optical imaging of extended objects under quasi-monochromatic incoherent illumination in order to provide a path to more accurately model the proposed optical imaging process for special effects obtained in the hardware. The existing theoretical framework was generalized to non-paraxial in- and out-of-focus imaging and results were obtained to verify the generalized framework. In the generalized non-paraxial framework, even the most complex linear systems, without any assumptions for shift invariance, can be modeled and analyzed.

[pt] A modelagem da propagação de ondas cilíndricas em materiais elásticos,tradicionalmente tem sido feita a partir de abordagens analíticas, baseadasna teoria de propagação de ondas, ou a partir de métodos numéricos, comoo método dos elementos finitos. Contudo, dependendo da frequência, resultados numéricos transientes podem ser difíceis de serem obtidos, seja pelo custocomputacional, seja pelo tempo despendido para os cálculos. Dentro desse contexto, alguns trabalhos envolvendo transferência de energia por ondas acústicas, utilizando-se de transdutores piezoelétricos, utilizam métodos alternativospara modelagem. Dentre os métodos disponíveis na literatura para a modelagem deste tipo de problema, a abordagem de rede de duas portas, provenienteda análise de circuitos elétricos, mostrou ser consideravelmente proeminente.Nesta tese, utilizando analogias de impedância, o método é trazido para o contexto de propagação de ondas acústicas, resultando em matrizes de transferência compostas por parâmetros de transmissão, ou parâmetros ABCD, comocomumente conhecidos. De fato, resultados iguais com menos esforços computacionais são obtidos a partir desta abordagem. Até o presente momento, essemétodo foi apenas desenvolvido para propagação de ondas planas em sólidoselásticos e materiais piezoelétricos. No entanto, como grande parte das aplicações envolve superfícies curvas, o método neste trabalho é estendido para ocaso de ondas cilíndricas. Os novos parâmetros ABCD encontrados são entãoimplementados em um código computacional, modelando testes pulso-eco epitch-catch dentro de meios cilíndricos. A validação é feita a partir de umaanálise de convergência a partir das respostas adquiridas para diferentes valores de raio interno do canal, uma vez que algumas expressões encontradas paraos parâmetros ABCD se mostraram inversamente proporcionais ao raio. Alémdisso, o método desenvolvido foi capaz de modelar um teste experimental detransmissão de sinal, a partir de um transdutor cilíndrico submerso em umtanque com água, assim como modelar a transmissão do mesmo sinal atravésde uma barreira cilíndrica. / [en] Cylindrical wave propagation in elastic materials has usually been modeled with analytical approaches or with numerical methods, such as the finite element method. However, depending on the frequency, obtaining results can be a hard task, requiring high computational efforts. Within this context, some studies on acoustic energy transfer, using piezoelectric transducers, had adopted alternative methods for modeling wave propagation, by means of acoustic-electric channels. Among the available methods in the literature, the two-port network approach, derived from the electric circuit analysis, proved to be prominent. In this thesis, by using impedance analogies, this method is brought into the context of acoustic wave propagation, leading to transfer matrices based on transmission parameters, or the so-called ABCD parameters. It was verified that the same results with less computational effort were obtained. So far, this method was only developed for the plane wave propagation in elastic solids and piezoelectric materials. However, since many real applications are curved, the two-port network approach is extended for the cylindrical wave case in this work. The novel ABCD parameters are then implemented in a computational routine, modeling pulse-echo and pitch-catch tests inside cylindrical media. The validation was performed by means of a convergence analysis, varying the internal radius of the entire channel, since the new ABCD parameters showed an inverse proportionality with the radius of the layer. Furthermore, the developed method was capable of modeling a signal transmission experimental setup, coming from a cylindrical transducer submerged in a water tank, as well as modeling the transmission of the same signal through a cylindrical barrier.

No description available.

No description available.

No description available.

No description available.

Induced vibrations due to tire-pavement interaction are one of the main sources of vehicle exterior noise, especially near highways and main roads where traveling speeds are above 50 kph. Its dominant spectral content is approximately within 500-1500 Hz. However, accurate prediction tools within this frequency range are not available. Current methods rely on structural modeling of the complete tire using finite elements and modal expansion approaches that are accurate only at low frequencies. Therefore, alternative physically-based models need to be developed. This work proposes a new approach that incorporates wave behavior along the tire's circumferential direction, while modes are assumed along its transversal direction. The formulation for new infinite plate and cylindrical shell structural models of a tire is presented. These are capable of accounting for orthotropic material properties, different structural parameters between the belt and sidewalls, inflation pressure, and rotation of the tire. In addition, a new contact model between the pavement and the tire is developed presented. The excitation of the tire due to the impact of the tread-pattern blocks in the contact patch region is characterized and coupled to the structure of the tire. Finally, a Boundary Element Method is implemented in order to compute the vibration-induced noise produced by the tire. All the modeling components are combined in a single prediction tool named Wave Pro Tire. Lastly, simulated responses and validation cases are presented in terms of harmonic responses, Frequency Response Functions (FRF), and produced noise. / Doctor of Philosophy / Induced vibrations due to tire-pavement interaction are one of the main sources of vehicle exterior noise, especially near highways and main roads where traveling speeds are above 50 kph. Accurate prediction tools are not currently available. Therefore, new physically based models need to be developed. This work proposes a new approach to model the tire’s structure with a formulation that accounts for multiple physical phenomena. In addition, a model that simulates the contact between the pavement and the tire’s tread is presented. Finally, the vibrations are coupled to the produced noise in a single prediction tool named Wave Pro Tire. This work also includes simulated responses and validation cases.

No / New representations and efficient calculation methods are derived for the problem of propagation from an infinite regularly spaced array of coherent line sources above a homogeneous impedance plane, and for the Green's function for sound propagation in the canyon formed by two infinitely high, parallel rigid or sound soft walls and an impedance ground surface. The infinite sum of source contributions is replaced by a finite sum and the remainder is expressed as a Laplace-type integral. A pole subtraction technique is used to remove poles in the integrand which lie near the path of integration, obtaining a smooth integrand, more suitable for numerical integration, and a specific numerical integration method is proposed. Numerical experiments show highly accurate results across the frequency spectrum for a range of ground surface types. It is expected that the methods proposed will prove useful in boundary element modeling of noise propagation in canyon streets and in ducts, and for problems of scattering by periodic surfaces.