Optimization of pulsed voltage waveform for electrohydrodynamic jetting on-demand

For electrohydrodynamic jetting-on-demand, the conventional positive voltage pulse superposed by a dc bias voltage have been widely used. Once this voltage pulse was induced, the meniscus at the nozzle tip oscillated and its volume changed owing to the fluid supplied through the nozzle as well. To increase the maximum frequency for consistent jetting, it is desirable to minimize these phenomena. When the oscillation amplitude was sufficiently small to assume the occurrence of linear behavior and no jetting, the above phenomena could be well explained by using a harmonic oscillator model and a one-dimensional flow model. Based on this physical understanding, the root-polar voltage waveform was proposed and could significantly decrease the change in meniscus height; thus it was possible to increase the maximum frequency for consistent jetting. In addition, the residual oscillation could be also suppressed using an extra voltage pulse waveform. Furthermore, the root-polar voltage waveforms with a minus voltage pulse as well as a positive one could be demonstrated; thus it was shown that the root-polar voltage waveform could be implemented into ac-pulse modulated EHD jetting as well.