A 2D chamber-free micro droplet generator array controlled by dynamic virtual walls

A chamber-free two-dimensional-array micro droplet generator has been realized by precise time-delayed control of micro bubble arrays as virtual chamber walls. Droplets can be ejected out by the bubbles around the ejection site in specific configuration of excitation, thus replacing physical chamber walls for pressure preservation. The volume, initial speed, and frequency response of the generated droplets was 3.6~3.8 pL, 15 m/s, and 20 kHz, respectively, meeting the standard of commercial printheads. The micro droplet generator is free of satellite droplets due to the precise control of meniscus that undergoes a "push-pull-push" progress which effectively cuts the liquid column short.