Micro-perforated sound absorbers with sub-millimeter size holes can provide high absorption coefficients. Various types of micro-perforated absorbers are now available in literature for different applications. This thesis presents results of work on the development of an effective single layer micro-perforated sound absorber from the commercial composite material Parabeam with micro diameter holes drilled on one side. Parabeam is used as a structural material made from a fabric woven out of a E-glass yarn and consists of two decklayers bonded together by vertical piles in a sandwich structure with piles (thick fibers) woven into the decklayers. The thesis includes, the analytical model developed for prediction of absorption coefficients, finite element solution using commercial software MSC.ACTRAN and experimental results obtained from impedance tube measurements. Different absorption characteristics can be achieved by variations in hole diameter and hole spacing. Based on the developed models, an optimization is performed to obtain an efficient absorber configuration. It has been anticipated that several different and interesting applications can be deduced by combining structural and sound absorption properties of this new micro-perforated absorber along with conventional fibrous absorbers.

The use of a patterned resistive sheet as an infrared-selective absorber, including the effects of a mechanical support dielectric layer is discussed. Also, modified dielectric coated Salisbury Screen can improve both the wavelength selectivity and the speed of thermal response for microbolometers. These patterned resistive sheets and Modified dielectric coated Salisbury Screen are a modified form of classical Salisbury Screens that utilize a resistive absorber layer placed a quarter-wavelength in front of a mirror. These structures can show a narrower detection bandwidth when compared to conventional microbolometers. For a Modified dielectric coated Salisbury Screen for multi-spectral system, wavelength selectivity can be varied by changing the distance to the mirror, and for patterned resistive sheet, wavelength selectivity can be varied by changing the lithographically drawn parameters of the array. Hence, different pixels in a focal plane array can be designed to produce a “multi-color” infrared imaging system. Also, the thermal mass of microbolometer is reduced using patterned resistive structure. / text

The overall efficiency of photovoltaics is dictated by processes occurring within it. These processes include exciton formation, diffusion, dissociation and charge collection. This dissertation will focus around the fundamental issue of charge collection. In organic photovoltaics (OPVs) the rate of charge injection is dominated by the interaction between dissimilar materials, usually organic compound interacting with inorganic ones. In order to improve this rate of injection and, by direct consequence the efficiency of this process, fundamental knowledge of this organic-inorganic interface must be gained. In this work the focus will reside solely on creating molecules capable of probing the interface between the indium tin oxide (ITO) and the donor layer. At this interface, the usual charge transfer being transferred is the hole. Chapters 2 and 3 detail the synthesis and photophysical characterization of porphyrin-perylene diimide (Por-PDI) and porphyrin-fullerene (Por-C₆₀) molecular dyads. The idea behind these moieties is that covalent attachment of these species to ITO should lead to a robust ohmic contact. Since these molecular dyads are capable of producing charge-separated states after photoexcitation, they should have the capacity to produce a radical-cation in close proximity to the ITO. This will translate to a capacity for probing the dynamics of the hole injection at this interface. Studies performed demonstrate that in fact these dyads are capable of producing a charge-separated state upon photo-excitation. The lifetimes of these states were determine to be 35 ps and 3 ns for the Por-PDI and Por-C₆₀ respectively. Chapter 4 takes a different turn. It is focused on the application and extension of a solvent-free synthesis of metallated phthalocyanines (Pcs). Shown in chapter 4 is the synthesis of a series of metallated Pcs using various transition metals and group 3 elements. Photophysical and electrochemical investigation of these materials shows that they have near-infrared absorption and relative high HOMO levels making them potential candidates for OPV applications. In addition, they displayed non-linear optical behavior due to their highly polarizable pi-systems and the presence of axial susbtituents. Finally Chapter 5 describes the synthesis and characterization of porphyrin possessing rigid linkers. This chapter also shows the further directions in which the various ideas presented in this work could be driven.

No description available.

No description available.

No description available.

Zugl.: Stuttgart, Universiẗat, Diss., 2008.

Zugl.: Stuttgart, Univ., Diss., 2009

Universiẗat, Diss., 2002--Jena.

Neste trabalho utilizamos a técnica de mistura de duas ondas quase degeneradas na investigação das propriedades ópticas não lineares, associadas à mudança de índice de refração com a intensidade da luz, em materiais dopados com cromo: Al2O3:Cr3+ (rubi), BeAl2O4:Cr3+ (alexandrita) e GdAlO3:Cr3+ (aluminato de gadolínio dopado com cromo). A não linearidade Kerr para o GdAlO3: Cr3+ é bastante significativa, de modo que neste material o parâmetro de ganho do feixe de prova apresenta um comportamento muito peculiar e que não encontra explicação nos tratamentos teóricos usuais do processo de mistura de duas ondas. Em particular, o ganho do feixe de prova neste material atinge percentuais superiores a 200%. Desta forma, desenvolvemos um tratamento teórico que descreve a mistura de duas ondas quase degeneradas em meios onde o índice de refração depende da intensidade (n= n0+n2I). Esta abordagem teórica leva em consideração os efeitos de saturação da grade de população produzida pela intersecção dos feixes de luz no meio Kerr (não harmonicidades da grade) e o processo de mistura de duas ondas é considerado como um caso particular do fenômeno da auto-difração difração de ordem zero. Os resultados teóricos foram comparados com os resultados experimentais e várias previsões teóricas como, a dependência do parâmetro de ganho do feixe de prova com a intensidade de saturação do meio, a dependência da diferença de freqüência entre os dois feixes incidentes onde o ganho é máximo com a intensidade do feixe de bombeamento, foram confirmadas experimentalmente / In this work nearly degenerate two-wave mixing technique is used in order to investigate nonlinear optical properties, associated to the refractive índex change by incident light, in a few doped crystals: Al2O3:Cr3+ (ruby), BeAl2O4:Cr3+ (alexandrite) e GdAlO3:Cr3+ (gadolinium aluminate chromium doped). The Kerr nonlinearity in GdAlO3:Cr3+ is very high, so that the probe gain parameter has peculiar behavior in this material and this cannot be explained by using the current approach found in the literature. In particular, the probe gain parameter in this material reaches percentuals above 200%. In this way, we develop a theoretical approach which describes nearly degenerate two-wave mixing in media where the refractive índex is intensity dependent. This theoretical approach takes into account the saturation of the travelling population grating produced by two interesting beams (anharmonicities of the population grating) and the two-wave mixing process is regarded as the zero-order self-diffraction of the incident waves in this grating. The theoretical results are compared with the experimental ones and several theoretical predictions such as, the dependence of the probe gain parameter on the médium saturation intensity were experimentally verified