Acoustic actuation in micro-channels through Surface Acoustic Waves

Although ultrasound is widely used in biomedical imaging, acoustic manipulation of fluids and particles on the micro to nano scale is still at research level. Acoustic streaming represents one of the very few inertial phenomena that may play a significant role in microfluidic devices. The goal of this Master thesis is to analyze a phoenomenon called acoustic streaming, which is generated by a nonlinear acoustic field with a finite amplitude propagating in a viscid fluid. The acoustic field is radiated by an Interdigitated Transducer (IDT), which creates a Surface Acoustic Wave (SAW) propagating at the surface of a piezoelectric layer. In particular first it is presented a general overview of the phenomenon and its current applications. In chapter 2 the fundamental mathematical models are detailed, dedicating high focus on the analytical description of surface acoustic waves (SAW) and how the non-linearities of acoustic streaming are taken into account. The third chapter shows the results of numerical simulations aimed to study how the geometrical properties of the piezoelectric substrate, and the operating frequency, affect the characteristics of Surface Acoustic Waves. The outcomes of FEA (Finite Element Analysis) simulations of acoustic streaming are discussed in chapter 4. In particular, it has been decided to limit the study to 2D cases and briefly describe how a 3D analysis should be carried out. The final chapter presents the general conclusions based on the previous chapters, and make suggestions for interesting future work.