This chapter provides a schematic illustration of a high-resolution electrohydrodynamic inkjet system. It discusses that the frequency of jet pulsation (f) is controlled simply by adjusting the magnitude of a fixed, DC voltage. In this case, the distances between neighboring printed droplets are determined by the substrate moving speed and f as the nozzle scans over the substrate. To solve this challenge, the driving voltage can be turned on and off using pulsed signals, instead of the constant DC voltages, so that ejection of each individual droplet is under direct computer control. This drop-on-demand printing mode can improve the droplet positioning. An interesting feature of the electrohydrodyanmic inkjet process is that the printed droplets contain an overall net charge. This property can be exploited to produce a charge printer able to form complex patterns of positive and/or negative ionic charge, with high resolution, on any dielectric surface.
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