Predicting droplet landing in angle-controlled surface acoustic wave jetting

Abstract

Nozzle-free droplet generation eliminates the need for a dispensing orifice, but useful printing also requires control over where droplets are deposited. Here we demonstrate predictable droplet deposition using a nozzle-free, angle-controlled surface acoustic wave jetting platform. Opposing focused interdigital transducers steer droplets from a pendant parent drop toward a collection substrate, with the ejection angle set by the time-integrated acoustic acceleration imbalance. The overall acceleration ratio identifies the operating window for single-droplet ejection and separates it from no-ejection, satellite-droplet, and multiple-droplet regimes. We then connect ejection angle to landing position through a geometric deposition model referenced to a balanced shot in each experiment. At a 5.2 mm parent-drop-to-substrate spacing, 80 steered shots across twenty experiments show strongly anisotropic relative placement scatter: 0.59 mm in the steering direction and 0.06 mm transverse to it. In tests conducted independently over several days, a model calibrated on six earlier collection dates predicted landing positions on two later dates with a root-mean-square error of 0.71 mm; bootstrap resampling placed the 95% confidence range for this error between 0.41 and 1.01 mm. The results establish a practical framework for predicting relative droplet landing in angle-controlled surface acoustic wave jetting and identify the limits imposed by steering angle, separation distance, and actuation regime from an orifice-free, clog-free droplet ejection method.