FIGS. 3B-3D illustrate possible embodiments of an acoustic nozzle structure 320, 320???, 320???, respectively, for (for instance) use with a system such as depicted in FIG. 3A. Note that as used herein, a hydrodynamic nozzle refers to a conventional fluid nozzle governed by hydrodynamic forces, as compared to acoustic-induced forces in an acoustic nozzle.