  We focus on cone-shaped nano- and microparticles, which have recently been
found to show particularly strong propulsion when they are exposed to a
traveling ultrasound wave, and study based on direct acoustofluidic computer
simulations how their propulsion depends on the cones' aspect ratio. The
simulations reveal that the propulsion velocity and even its sign are very
sensitive to the aspect ratio, where short particles move forward whereas
elongated particles move backward. Furthermore, we identify a cone shape that
allows for a particularly large propulsion speed. Our results contribute to the
understanding of the propulsion of ultrasound-propelled colloidal particles,
suggest a method for separation and sorting of nano- and microcones concerning
their aspect ratio, and provide useful guidance for future experiments and
applications.
