Experimental Techniques for Retrieving Flow Information from within Inkjet Nozzles

In drop-on-demand (DOD) inkjet printing microdroplets are ejected from the nozzle as a result of the internal acoustics set in motion by a pressure pulse from an expanding bubble or a piezoelement. The acoustic response, both in the frequency domain and in the time domain, and the resulting droplet formation processes are well-modeled and characterized by various experimental techniques. However, the behavior of the liquid meniscus in the nozzle is a critical mediator between these regimes and poorly accessible in experiment. The meniscus shape and motion vary between different print head designs, electrical pulse shapes and wetting conditions. In the last decade several novel approaches have been proposed and implemented to study experimentally the meniscus motion within inkjet nozzles. These experimental methods are reviewed here and compared in terms of accuracy and applicability.