Study of piezoelectric transducer for liquid ejection

Self-focused acoustic transducers using using Fresnel zone plates have been fabricated and used to eject droplets of high-viscosity liquid, without nozzle, in the drop-on-demand mode. The Fresnel zone plate consists of a series of annular electrodes of half-wave-band source, and the acoustic waves are focused by constructive wave interference. Droplets of glycerin with a high-viscosity of 1400 cP can be ejected under a field of 200 kV/m and at a repetitive frequency of 120 Hz. The acoustic pressure distribution in the glycerin has been been simulated using an open-source computational fluid dynamic code OpenFOAM and measured using a needle-type hydrophone. Both the simulation and measurement give the location of two focal points which agree with the observations in the droplet ejection experiment.