Figure 7

Stepwise reduction in the pitch of the periodic patterns with the increasing frequency. (a) Typical periodic patterns with n × n units, where n=4, 6, 8 and 10. (b) The mean pitch of the periodic units as a function of the frequency at which the pulse signals were applied. The mean pitch decreased in a stepwise manner, and each pattern persisted throughout a wide range of frequencies. At frequencies above 120 Hz, the pattern gradually disappeared, starting at the periphery, owing to the decay of the standing wave. (c) C6 micro-rods were gathered at the pressure maxima in the p₊ stage but not at the pressure maxima in the p₋ stage. Expanded images on the right side clearly show the aggregated microparticles.