The Effects of Driving Waveform and Frequency on the Droplet Formation Process

Abstract

For a piezoelectric stack (PZT) driven droplet generator, the driving waveform and driving frequency effects on liquid filament shape and droplet characteristics have been studied. A lumped element model (LEM) is developed to study the acoustic-mechanical behavior and the volumetric rejection of the droplet generator. Based on the LEM, the PZT displacement magnitude dominates the internal pressure variation within the chamber. However due to the natural response of droplet generator, the acoustic pressure in the droplet generator decays exponentially. Experimental data show that the droplet formation process can be waveform and frequency dependent. When the droplet formation process is driven in the “low frequency” regime, the droplet formation process is weakly affected by frequency. Meniscus interaction effects, which are the interaction of a liquid filament from different droplet generation cycles, on the droplet formation process will be present when the droplet formation process is driven in the “high frequency” regime. Due to meniscus interactions, the droplet formation process at “high frequency” is waveform and frequency dependent. Results show that the droplet volume reduces with driving frequency, and droplet velocity increases with driving frequency. However the droplet break-off time is only weakly affected by the driving frequency.