Novel wave phenomena in two- and three-dimensional (2D and 3D) phononic crystals were investigated experimentally using ultrasonic techniques. Resonant tunneling of ultrasonic waves was successfully observed for the first time by measuring the transmission of ultrasound pulses through a double barrier consisting of two 3D phononic crystals separated by a cavity. This effect is the classical analogue of resonant tunneling of a quantum mechanical particle through a double potential barrier, in which transmission reaches unity at resonant frequencies. For phononic crystals, the tunneling peak was found to be less than unity, an effect that was explained by absorption. The dynamics of resonant tunneling was explored by measuring the group velocities of the ultrasonic pulses. Very slow and very fast velocities were found at frequencies close to and at the resonance, respectively. These extreme values are less than the speed of sound in air and greater than the speed of sound in any of the crystal’s constituent materials. Negative refraction and focusing effects in 2D phononic crystals were also observed. Negative refraction of ultrasound was demonstrated unambiguously in a prism-shaped 2D crystal at frequencies in the 2nd pass band where the wave vector and group velocity are opposite. The Multiple Scattering Theory and Snell’s law allowed theoretical predictions of the refraction angles. Excellent agreement was found between theory and experiment. The negative refraction experiments revealed a mechanism that can be used to focus ultrasound using a flat phononic crystal, and experiments to demonstrate the focusing of ultrasound emitted by several point sources were successfully carried out. The importance of using phononic crystals with circular equifrequency contours, as well as matching the size of the contours inside and outside the crystal, was established. Both conditions were satisfied by a flat phononic crystal of steel rods, in which the liquid inside the crystal (methanol) was different from the outside medium (water). The possibility of achieving subwavelength resolution using this phononic crystal was investigated with a subwavelength line source (a miniature strip-shaped transducer, approximately lambda/5 wide, where lambda is sound wavelength in water). A resolution of 0.55lambda was found, which is just above the diffraction limit lambda/2.

Wind turbines have grown both in size and number in the past decades. The taller turbines has made it possible to place them in forest areas which is fortunate for a country like Sweden with lots of forest. An issue with wind turbines is the sound they produce. The sound mainly comes from the rotor blades when they pass through the air. The sound heard some distance away from the turbine is sometimes masked by ambient background noise such as wind induced sound in the vegetation, but this is not always the case. Noise concerns among some people living in the vicinity of wind turbines are sometimes raised. Sound propagation models are used to predict the wind turbine sound level at certain distance. It is important that these models are accurate. Sound propagation is greatly influenced by the meteorological conditions. These conditions change over the day and year and vary a lot depending on the terrain conditions. In the past, large meteorological propagation effects have been found for sound sources close to the ground. Higher elevated sources like wind turbines have not been studied as much. One reason for this is that wind turbines are a relatively new sound source. In this thesis the meteorological influence on the wind turbine sound propagation is studied. Continuous simultaneous acoustic and meteorological measurements are performed at two different wind turbine sites during two years to capture all variations in the weather. The two sites are covered by forest, one is flat and the other has shifting terrain. The sites are representative for many locations in Sweden and around the world. The differences between the measured and expected wind turbine sound levels are established for different meteorological categories. The median of all deviations within each meteorological category is then compared. During no snow cover conditions the variation of the median under different meteorological conditions is 6 dBA and during snow cover the variation of the median is 14 dBA. The variations are due to the combined effect of refraction, ground conditions and terrain shape. The deviations from an expected value are seen for all octave bands from 63 Hz to 1000 Hz but are found to most distinct at low frequencies of around 125Hz. Meteorological effects starts to be important somewhere between 400 m and 1000 m from wind turbines.The characteristic "swish" sound from wind turbines are also studied in this thesis. The swish sound or as it is also called, the amplitude modulated sound, is found to be more common under some meteorological conditions such as temperature inversions and downwind conditions. A metric for detection of amplitude modulation duration and strength is proposed. Amplitude modulation, is according to some, the reason why wind turbine sound is perceived as more annoying than other typical environmental sounds at the same sound level. The swishes probably increase the probability to hear the wind turbine sound in presence of other background noise.

Purpose: To study ???on??? and ???off-axis??? wavefront aberration of eyes of children and to determine the relationship with refractive error development. Methods: On and off-axis ocular aberrations of cyclopleged eyes of children (mostly 12 year olds) were measured and compared to data obtained from a group of mostly 6 year old children. Only data from the right eyes were analysed (pupil diameter=5 mm) and categorised into refractive error groups based on ???M???. Differences in ???on??? and ???off-axis??? aberrations between refractive and ethnic groups were analysed using univariate and multivariate analyses of variance with adjustment for multiple comparisons. Off-axis refraction was analysed using skiagrams and mean relative spherical equivalent. Results: Data from 1,636 12 year old children (mean age 12.6 ?? 0.4 years) was analysed. Lower order aberrations were the largest and higher order aberrations contributed to only 25% of the wavefront. There were no differences in the amount of total higher orders between refractive groups. Of the individual higher orders, spherical aberration was greater in hyperopic eyes (0.07 ?? 0.06 ??m) in comparison to emmetropic and myopic eyes (0.05 ?? 0.04 ??m and 0.05 ?? 0.04 ??m) (p<0.001). Myopic eyes had more positive values of Z(3,-1) (p<0.05). Similar results were obtained for the 1,364 6 year old children (mean age 6.7 ??? 0.4 years). Despite East Asian children being more myopic than other ethnic groups (p<0.01), there were no differences in higher orders except for low hyperopic East Asian eyes presenting with higher levels of positive spherical aberrations (p<0.001). When compared to the fovea, off-axis myopic eyes had hyperopia (0.55 to 1.66 D) and emmetropes and hyperopes had myopia (0.10 to -2.00 D). Astigmatism and defocus were the dominant off-axis aberrations. The magnitude of higher order aberrations (mostly 3rd orders) increased with eccentricity but was similar across refractive error groups. Conclusions: Myopic eyes do not have abnormal or excessive levels of on and off-axis higher order aberrations but had patterns of off-axis refraction that may be associated with progression. Considerable inter-subject variability in higher order aberrations was seen for all refractive groups. However, their magnitude was small and suggests that any impact on the optical quality of the eye is negligible.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2007. / Title from first page of PDF file (viewed Oct. 31, 2007). Includes bibliographical references (p. 152-161).

Thesis (M.Sc.) -- Department of Physics, University of Adelaide, 1979.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 4 uppsatser.

Thesis (Ph. D.)--University of Texas at El Paso, 2008. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (M. Sc.)--University of Hong Kong, 2002. / Also available in print.

Thesis (M. Sc.)--University of Hong Kong, 2002.

CNPq, CAPES / Este trabalho apresenta a produção de redes de Bragg para a aplicação em sensoriamento e em telecomunicações. As redes para aplicação em sensoriamento foram gravadas utilizando incidência direta na máscara de fase bem como um interferômetro com máscara de fase, na Universidade Tecnológica Federal do Paraná. As redes de Bragg foram gravadas em fibra ótica hidrogenada padrão de telecomunicações e fibra ótica fotossensível com o uso de um laser de Nd: YAG (New Wave, Tempest-20) operando em 266 nm e de um laser de excímero KrF (Xantos XS-Coherent) em 248 nm. Foram realizados experimentos visando à estabilização térmica dos dispositivos, nos quais as redes de Bragg foram submetidas a ciclos de aquecimento e resfriamento. Testes para determinar a máxima temperatura de operação das redes de Bragg produzidas também foram realizados. Sensores refratométricos foram produzidos por meio da corrosão controlada da casca da fibra na região da rede de Bragg. Duas redes de Bragg corroídas com comprimentos de onda de Bragg de operação próximos a 1300 nm e 1500 nm foram utilizadas na análise de misturas de etanol e água. Quatro configurações para o sensor refratométrico foram estudadas, operando tanto com dois comprimentos de onda quanto somente em um comprimento de onda, e em duas temperaturas distintas das amostras. As curvas de calibração foram determinadas para uma extensão entre 0,0 e 100,0 % v/v de etanol em água. O desempenho do sensor em cada configuração foi analisado pela comparação das sensibilidades, conformidades, repetitividades e incertezas combinadas. As redes para aplicação em telecomunicações foram gravadas em fibra ótica fotossensível com a técnica de incidência direta da luz do laser na máscara de fase, no Instituto de Telecomunicações da Universidade de Aveiro, em Portugal. Redes de Bragg com gorgeio foram gravadas com um laser de excímero pulsado operando em 248 nm (BraggStar S-Industrial LN) e com o uso de posicionadores motorizados com resolução máxima de 1 nm. O estudo da evolução espectral da rede de Bragg com a variação da energia de gravação permitiu o projeto de dispositivos com características pré-definidas. / This work presents the production of fiber Bragg gratings with different profiles for application in sensing and in telecommunications. The gratings for sensing application were recorded using direct illumination of a phase mask as well as a phase mask interferometer, at the Federal University of Technology - Parana. The gratings were recorded in hydrogen loaded standard telecommunication fibers and photosensitive fibers using a Nd: YAG laser (Tempest-20, New Wave) at 266 nm and a KrF excimer laser at 248 nm (Xanto XS-Coherent). Experiments were performed in order to reach the thermal stabilization of the devices using a laboratory oven, where the gratings were submitted to thermal cycles which included both annealing and quenching. Tests to determine the maximum operating temperature of the produced fiber Bragg gratings were also performed. Refractometric sensors were produced by wet-etching of the fiber optic cladding using hydrofluoric acid and employed in the analysis of water-ethanol mixture. Two etched fiber Bragg gratings operating close to 1300 nm and 1500 nm were used in the experiment. Four configurations for the refractometric sensor were studied, in dual-wavelength and single-wavelength operation modes, and at two sample temperatures. Calibration curves were determined for the range between 0.0 and 100.0 % v/v of ethanol in water, and the sensor performance for each configuration was analyzed by comparing its sensitivity, conformity, repeatability and combined uncertainty. The gratings for the application in telecommunications were recorded in photosensitive fibers with direct illumination of phase mask at the Institute of Telecommunications of the Aveiro University, in Portugal. Chirped fiber Bragg gratings were produced with the use of an excimer laser operating at 248 nm (S-industrial BraggStar LN) and with the use of translation stages with maximum resolution of 1 nm. The study of Bragg grating spectral evolution with the writing energy allowed the project of devices with predefined characteristics.