Figure 5. Methodology to increase seeding efficiency.

(a) A solution of 6.1-μm particles suspended in water is (b) exposed to a λ=21-μm, 0.52-W-applied power, 171-MHz two-dimensional acoustic field biased in one direction. This biased field translates particles across the array through the force of the partial travelling wave thus created, effectively ‘bumping' particles along so that only one particle occupies a given nodal position (see inset), pushing most excess particles to the chamber wall in the direction of bias. (c) The excess particles can then be removed from the chamber by pumping fluid into the chamber, manipulated either by hand or a syringe pump. The majority of patterned single particles, however, remain trapped. Scale bar, 100 μm.