Multiple scattering effects from bubble clouds are investigated in this study. A high performance, general purpose numerical tool for multiple scattering calculations is developed. This numerical tool is applied in three computational scenarios in this study. The total scattering cross section of a bubble cloud is investigated. Numerical results indicate that the resonant frequency of the bubble cloud is much lower than that of a single bubble. The variation of resonant frequency of multiple scattering is also studied. It is found that the resonant frequency decreases as the number of bubbles increases, or as the void fraction of the bubble cloud decreases. Phase distributions of bubble oscillations in various multiple scattering scenarios are presented. It is found that, at resonance, the bubbles synchronize to the same phase, which is indicative of the lowest mode of collective oscillation. At wave localization, half of the bubbles oscillate at phase 0 while the other half oscillate at phase Pi. An intuitive interpretation of this behavior is given.

The research presented in this manuscript introduces an independent structural health monitoring (SHM) system capable of performing impedance-based testing and detecting shifts in resonant frequencies. This independent structural health monitoring system incorporates a low power wireless transmitter that sends a warning signal when damage is detected in a structure. Two damage detection techniques were implemented on the SHM system and successfully used for evaluating structural damage. The first impedance-based technique is used to detect a gouge introduced to a composite plate. The second technique is a modal parameter technique that analyzes shifts in natural frequency; this technique was used to detect structural changes in an aluminum cantilever beam. In additional to the above test structures, an aircraft rib provided by the United States Air Force was also tested. This test was performed using the HP 4192A impedance analyzer so that the advantage of high frequency impedance-based tested could be demonstrated. Insight is given into the power characteristics of SHM systems and the need to incorporate power harvesting into these SHM devices is addressed. Also, a comparison between digital signal processors and microprocessors is included in this document. / Master of Science