Mechanical waves are induced in solids due to the system's coupling with an external excitation. Depending upon the nature of the resulting displacement and phase difference between the vibrating particles at a particular frequency, the mechanical waves can be classified as standing waves, traveling waves or a combination of the two. This study focuses on the identification of these different forms of mechanical waves and discusses methods that can be suitably used for their classification. The Hilbert and Fourier methods of classification were validated using experimental results and then compared against each other. The experimental and theoretical analysis of mechanical waves was conducted on a beam with free-free boundary conditions excited by piezoelectric elements.

Carbon nanotube (CNT) aerogel sheets produce smooth-spectra sound over a wide frequency range (1-10(5) Hz) by means of thermoacoustic (TA) sound generation. Protective encapsulation of CNT sheets in inert gases between rigid vibrating plates provides resonant features for the TA sound projector and attractive performance at needed low frequencies. Energy conversion efficiencies in air of 2% and 10% underwater, which can be enhanced by further increasing the modulation temperature. Using a developed method for accurate temperature measurements for the thin aerogel CNT sheets, heat dissipation processes, failure mechanisms, and associated power densities are investigated for encapsulated multilayered CNT TA heaters and related to the thermal diffusivity distance when sheet layers are separated. Resulting thermal management methods for high applied power are discussed and deployed to construct efficient and tunable underwater sound projector for operation at relatively low frequencies, 10 Hz-10 kHz. The optimal design of these TA projectors for high-power SONAR arrays is discussed.

Mechanical waves can be broadly categorized into traveling waves and standing waves. In this study, the nature of the waves in a finite solid medium is investigated to reveal the excitation parameters that influence their behavior. Theoretical and experimental analysis is conducted to find the conditions for generating traveling waves using piezoelectric ceramics as the actuation agent in piezo-structural-coupled systems. A continuous electromechanical model is developed in order to predict the structural dynamics and is validated through experiments. The results from this study provide the fundamental physics behind the generation of mechanical waves and their propagation through finite mediums.

The demand for efficient small-scale wind harvester is continually increasing in order to meet the local power needs for applications ranging from wireless sensor networks to charging of mobile devices. The efficiency of wind turbines is dependent upon several structural variables including frictional contacts. In order to overcome the problem of gearing and losses in mechanical contacts, we propose here a novel small-scale windmill design that utilizes magnetic attractive and repulsive force to create mechanical oscillation in piezoelectric bimorphs which is then converted into electric charge through direct piezoelectric effect. This contact-less wind turbine has several advantages including operation at much lower wind speeds and longer life span. The prototype was fabricated as a vertical-axis wind turbine featuring a modular Sarvonius rotor. Characterization was performed by utilizing several configurations for this modular rotor. Output power magnitude for steady-state operation in wind speeds of 2 -10 mph was used to compare the performance of various configurations.

This study reports the design, fabrication, and implementation of a horizontal-axis, small-scale modular wind turbine termed as "small-scale wind energy portable turbine (SWEPT)". Portability, efficient operation at low wind speeds, and cost-effectiveness were the primary goals of SWEPT. The fabrication and component design for SWEPT are provided along with the modifications that can provide improvement in performance. A comparative analysis is presented with the prototype reported in literature. The results show that current version of SWEPT leads to 150% increase in output power. It was found that SWEPT can generate 160 mW power at rated wind speed of 7 mph and 500mW power at wind speeds above 10 mph with a cut-in wind speed of 3.8 mph. Furthermore, the prototype was subjected to field testing in which the average output was measured to be 40 mW despite the average wind distribution being centered around 3 mph.