  Geometry of the fluid container plays a key role in the shape of acoustic
streaming patterns. Inadvertent vortices can be troublesome in some cases, but
if treated properly, the problem turns into a very useful parameter in acoustic
tweezing or micromixing applications. In this paper, the effects of sinusoidal
boundaries of a microchannel on acoustic streaming patterns are studied.
Results show that while top and bottom sinusoidal walls are vertically actuated
at the resonance frequency of basic hypothetical rectangular microchannel, some
repetitive acoustic streaming patterns are recognized in classifiable cases.
Such patterns can never be produced in rectangular geometry with flat
boundaries. Relations between geometrical parameters and emerging acoustic
streaming patterns lead us to propose formulas in order to predict more cases.
Such results and formulations were not trivial at a glance.
