UC San Diego

Surface acoustic wave devices (SAW) offer extraordinary power density to efficient manipulate the fluid surrounded around it. The SAW generated from the piezoelec- tric lithium niobate substrate is transmitted into the liquid as an intense sound beam that is progressively attenuated by the fluid’s viscosity as it propagates. This atten- uation is not lost, rather, it gives rise to a flux in the fluid’s momentum in a narrow ( 100μm) sound beam along the direction of the sound propagation. The sound prop- agates at an angle from the substrates, called Rayleigh angle, that is dependent on the characteristics of the fluid and the piezoelectric substrate. The fluid momentum grows as the sound attenuates, causing fluid transport, called acoustic streaming. Uniquely, they generate locally extreme accelerations of 108 to 1010 m/s2, driving acoustic streaming-driven fluid flow up to 1 m/s, and imparting acoustic forces upon objects present in the fluid down to the micro or nano sized scales. On the other hand, the major drawback of lithium batteries is its diffusion lim- itation, which limited its power density and energy density. However, both of the parameters are critical for the success of battery applications, especially with the ever growing demands for the electronic devices and electric vechiles: the current high en- ergy batteries with graphite anodes and metal oxides cathodes are unable to achieve the fast charge goals without adversely impact the performance and safety of a bat- tery. A novel mechanical approach oppose to the traditional chemical approaches is therefore required to fundamentally enhance the properties inside a battery. In my PhD thesis, the major focus is to integrate a SAW into a Li battery based on the assumption of the acoustic streaming fluid can enhance the Li+ ions diffusion rates and further improve the battery performances, especially its energy density at high charge rates, cycle life, and safety. The thesis starts with the design with consideration of the theories from both acoustofludics and electrochemistry, to the analysis of cell performances and electrodes degradation analysis. Moreover, a closed form mathematical model were proposed to describe the phenomenon. Furthermore, I also explored the applications of SAW into different areas. The self-assembled magnetic particles was achieved by the balanced force between magnetic forces and acoustic force was introduced. Moreover, the vibration behaviour of sub-micron sized gas vesicles under the acoustic vibration was investigated, giving insights to harmonic responses and the vibration behaviour. Finally, we proposed a first truly portable circuit for the acoustofludics applications, where the performance of the circuit board is demonstrated with the known acoustofludics phenomenon and is compared with the traditional benchtop equipment.