Optimal rate for continuous phase modulation in standing surface acoustic waves

Acoustofluidics, which combines microfluidics and acoustics, has been actively studied in order to manipulate micro-sized particles, cells and bacteria. In particular, there have been attempts to use standing surface acoustic waves (SSAWs) to locate move and stop target particles to specific locations with changing pattern of interdigital transducers (IDTs) or modulating acoustic waves. We developed a novel method called continuously phase modulated-standing surface acoustic waves (CPM-SSAWs) in our previous report and the maximum marginal value of frequency shift for the linear motion of target particles is defined as an optimal rate at a given condition. In this paper, we experimentally showed how the optimal rate changes with physical parameters or conditions such as particle size, frequency, and applied voltage. Our study will be helpful in developing a technique of multi-particle manipulation for bio equipment such as tweezing multiple particles simultaneously or sorting target cells using their own properties.