Abstract
Acoustofluidics has a strong pedigree in microscale manipulation, with particle and cell separation and patterning arising from acoustic pressure gradients. Acoustic waveguides are a promising candidate for localizing force fields in microfluidic devices, for which computational modelling is an important design tool. Meshed finite element analysis is a popular approach for this, yet its computation time increases rapidly when complex geometries are used, limiting its usefulness. Here, we present an analytical model of the acoustic pressure field in a microchannel arising from a surface acoustic wave (SAW) boundary condition that computes in milliseconds and provide the simulation code in the supplementary material. Unlike finite element analysis, the computation time of our model is independent of microchannel or waveguide shape, making it ideal for designing and optimising microscale waveguide structures. We provide experimental validation of our model with cases including near-field acoustic patterning of microparticles from a travelling SAW and two-dimensional patterning from a standing SAW and explore the design of waveguides for localised particle or cell capture.