UC San Diego

Surface acoustic wave (SAW) devices have become popular as a practical and effective tool for fluid manipulation, particle/cell sorting and separation in various acoustofluidics and biomedical applications. In this dissertation, we study basic concepts, materials, and designs of SAW for micro/nano-scale particles/fluid manipulation. We propose an optimized Y-rotated cut of lithium niobate for multi-directional SAW propagation, simultaneously minimizing the anisotropic effects while maximizing electromechanical properties.

In microscale acoustofluidics, first, we present a novel omnidirectional spiral SAW design to rapidly rotate a microliter sessile drop to ~10g, producing efficient multi-size particle separation. We further extract the separated particles for the first time, demonstrating the ability to target specific particles. Red blood cells and platelets within mouse blood are further demonstrated to be separated with a purity of 93% and 84%, respectively. Second, we describe a new method to measure the opposing force upon the object producing the acoustic radiation. Our example employs a 40 MHz SAW device as a pendulum bob while immersed in a fluid, measuring a 1.5 mN propulsion force from an input power of 5 W to the SAW device.

In nanoscale acoustofluidics, first, in nanochannels of a height commensurate with the viscous penetration depth of the fluid, we find nonlinear interactions between the surrounding channel deformation and the leading order acoustic pressure field, generating flow pressures three orders of magnitude greater than any known acoustically-mediated mechanism. It enables the propulsion of fluids against significant Laplace pressure, sufficient to produce 6 mm/s flow in a 130–150 nm tall nanoslit. We find quantitative agreement between theory and experiment across a variety of fluids and conditions. Second, we present new regimes of acoustic wave interaction with 200 fL droplets of deionized water. By forming traps as locally widened regions along a fully transparent, high-aspect ratio, 130 nm tall, 20–130 micron wide, 5 mm long nanoslit channel, individual fluid droplets may be propelled from one trap to the next, split between them, mixed, and merged via 40 MHz-order SAW. A simple theory is provided to describe the mechanisms of droplet transport and splitting.