Surface ripple wave suppression by anti-reflection in apertured free ink surface level controllers for acoustic ink printers

In response to the foregoing need, the cap structures that are provided by this invention for controlling the free ink surface levels of acoustic ink printers are characterized by having aperture configurations that are more or less equally subdivided into "reflectively balanced" sectors that radially differ from each other by 1/4 of the dominant wavelength of the surface ripple waves that are generated by the droplet ejection process. The 1/4 wavelength difference in the radii of the two generally equal reflectively balanced fractional parts of these apertures causes the dominant frequency components of the retroreflected ripple waves to destructively interfere with each other in the critical central regions of the apertures.