Mixing presents a notoriously difficult problem in small amounts of fluids. Herein, surface acoustic waves provide a convenient technique to generate time-dependent flow patterns. These flow patterns can be optimized in such a way that advected particles are mixed most efficiently in the fluid within a short time compared to the time pure diffusion would take. Investigations are presented for the mixing efficiency of a flat cylinder that is driven by two surface acoustic waves. The experimental results favorably agree with model calculations of the flow patterns and the advective transport.