Increasing awareness of the issues of climate change and sustainable energy use has led to growing levels of interest in small-scale, decentralised power generation. Small-scale wind power has seen significant growth in the last ten years, partly due to the political support for renewable energy and the introduction of Feed In Tariffs, which pay home owners for generating their own electricity. Due to their ability to respond quickly to changing wind conditions, small-scale vertical axis wind turbines (VAWTs) have been proposed as an efficient solution for deployment in built up areas, where the wind is more gusty in nature. If VAWTs are erected in built up areas they will be inherently close to people; consequently, public acceptance of the turbines is essential. One common obstacle to the installation of wind turbines is noise annoyance, so it is important to make the VAWT rotors as quiet as possible. To date, very little work has been undertaken to investigate the sources of noise on VAWTs. The primary aim of this study was therefore to gather experimental data of the noise from various VAWT rotor configurations, for a range of operating conditions. Experimental measurements were carried out using the phased acoustic array in the closed section Markham wind tunnel at Cambridge University Engineering Department. Beamforming was used in conjunction with analysis of the measured sound spectra in order to locate and identify the noise sources on the VAWT rotors. Initial comparisons of the spectra from the model rotor and a full-scale rotor showed good qualitative agreement, suggesting that the conclusions from the experiments would be transferable to real VAWT rotors. One clear feature observed in both sets of spectra was a broadband peak around 1-2kHz, which spectral scaling methods demonstrated was due to laminar boundary layer tonal noise. Application of boundary layer trips to the inner surfaces of the blades on the model rotor was found to eliminate this noise source, and reduced the amplitude of the spectra by up to 10dB in the region of the broadband peak. This method could easily be applied to a full-scale rotor and should result in measurable noise reductions. At low tip speed ratios (TSR) the blades on a VAWT experience dynamic stall and it was found that this led to significant noise radiation from the upstream half of the rotor. As the TSR was increased the dominant source was seen to move to the downstream half of the rotor; this noise was thought to be due to the interaction of the blades in the downstream half of the rotor with the wake from the blades in the upstream half. It was suggested that blade wake interaction is the dominant noise source in the typical range of peak performance for the full-scale QR5 rotor. Different solidity rotors were investigated by using 2-, 3- and 4-bladed rotors and it was found that increasing the solidity had a similar effect to increasing the TSR. This is due to the fact that the induction factor, which governs the deflection of the flow through the rotor, is a function of both the rotor solidity and the TSR. With a large body of experimental data for validation, it was possible to investigate computational noise prediction methods. A harmonic model was developed that aimed to predict the sound radiated by periodic fluctuations in the blade loads. This model was shown to agree with similar models derived by other authors, but to make accurate predictions very high resolution input data was required. Since such high resolution blade loading data is unlikely to be available, and due to the dominance of stochastic sources, the harmonic model was not an especially useful predictive tool. However, it was used to investigate the importance of the near-field components of the sound radiated by the wind tunnel model to the acoustic array. It was shown that the near-field terms were significant over a wide range of frequencies, and the total spectrum was always greater than that of the far-field component. This implied that the noise levels measured by the acoustic array represented an upper bound on the sound radiated to the far-field, and hence that the latter would also be dominated by stochastic components. An alternative application of the harmonic model, which attempted to determine the blade loading harmonics from the harmonics in the sound field was proposed. This inversion method utilised a novel convex optimisation technique that was found to generate good solutions in the simulated test cases, even in the presence of significant random noise. The method was found to be insensitive at low frequencies, which made it ineffective for inverting the real microphone data, although this was shown to be at least partly due to the limitations imposed by the array size. In addition to the harmonic models, an empirical noise prediction method using the spectral scaling laws derived by \citet*{Brooks_1989} was trialled, and was found to be capable of making predictions that were in agreement with the measured data. The model was shown to be sensitive to the exact choice of turbulence parameters used and was also found to require good quality aerodynamic data to make accurate noise predictions. If such data were available however, it is expected that this empirical model would be able to make useful predictions of the noise radiated by a VAWT rotor.

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The huge advancement in the textiles industry and the accurate control on the mechanization process coupled with cost-effective manufacturing offer an innovative environment for new electronic systems, namely electronic textiles. The abundance of fabrics in our regular life offers immense possibilities for electronic integration both in wearable and large-scale applications. Augmenting this technology with a set of precepts and a simulation environment creates a new software/hardware architecture with widely useful implementations in wearable and large-area computational systems. The software environment acts as a functional modeling and testing platform, providing estimates of design metrics such as power consumption. The construction of an electronic textile (e-textile) hardware prototype, a large-scale acoustic beamformer, provides a basis for the simulator and offers experience in building these systems. The contributions of this research focus on defining the electronic textile architecture, creating a simulation environment, defining a networking scheme, and implementing hardware prototypes. / Ph. D.

The present final thesis discusses the transmission of a narrowly directional parametric sound beam through an amplitude-modulated ultrasonic wave, utilizing the effect of auto-demodulation in a nonlinear medium and ensuring the subsequent processing of the input signal for the parametric sound transmitter. Emphasis is placed on the mathematical tools that relate to parametric sound transmission in a nonlinear medium. The basic part of the thesis describes a parametric speaker and the associated amplitude modulation techniques, which constitute a major prerequisite for the processing of the transmitted signal. In the following section, the author then analyzes the computational intensity of these techniques, considering applicable hardware approaches. Finally, the fabrication and practical use of the proposed solution are discussed, including the measurement of typical parameters such as the spatial radiation characteristics, total harmonic distortion, and transmission channel bandwidth.

The master´s thesis deals with theoretical research and practical application of the principle of spreading acoustic waves through nonlinear medium. The theoretical part describes five different types of amplitude modulation and their mathematic representation, which were verified by the program Matlab. Next, the impedance characteristic of ultrasound PZT transducer was measured and the design of PWM modulator and class D amplifier was described. The practical part of the master´s thesis contains the realization of the parametric loudspeaker assembled from the class D amplifier and the PWM modulator. In conclusion, the designed parametric loudspeaker was measured and the individual types of amplitude modulation were compared with respect to the total harmonic distortion of transmitted useful signal.