Formation Process of Acoustophoretic Patterns

Abstract

The acoustic radiation force is a nonlinear wave effect that exerts a non-zero time- averaged force on objects in the wave. In recent years, the acoustic radiation force has been widely explored for manipulating objects and small particles. These applications range from moving a few objects at a time, to acting on a continuous flow of particles, to arranging many particles into patterns. In particular, using the acoustic radiation force to move embedded materials into patterns provides many opportunities for advanced manufacturing and 3D printing of composite materials.

There are three key considerations in acoustophoretic patterning: 1) the overall pattern geometry, 2) the quality of the final pattern, and 3) the time required to make the pattern. While much work in the literature has been devoted to increasing the pattern geometries that can be made using acoustophoresis, the effort is largely still in the proof of concept stage and the final pattern quality is often only evaluated qualitatively. There is also a need to measure the pattern formation process so that the inherent design tradeoffs can be quantified. This thesis quantifies the tradeoff between pattern quality and patterning time by using the local microsphere concen- tration to describe the pattern formation process. Existing method of measuring the absolute magnitude of the ARF by particle tracking is extended to 2D, which facilitates mapping the patterning device. Finally, this thesis utilizes the design trade-off between time and hardware complexity to create acoustophoretic patterns with non-uniform spacing without increasing hardware complexity by sequencing multiple frequencies.