Resonant oscillation phenomena of a sessile droplet on electrohydrodynamic jetting nozzle

The resonant oscillation of a sessile droplet on the electrohydrodynamic (EHD) jetting nozzle was studied using a series of sinusoidal and square pulse voltage signal. At small amplitude oscillations, the lowest mode resonant frequency depended on a contact angle and the explicit relationship was developed assuming one-dimensional standing capillary wave. When the meniscus was oscillated with a higher voltage amplitude for jetting, its height became maximum at the phase delay of about Π/2 from the maximum applied voltage signal, which can be predicted in a harmonic oscillator model. In addition, there existed an effective resonant frequency where the meniscus oscillation was amplified quickly to initiate a jetting earlier, and the jetting continued every cycle afterwards. Therefore, the resonant oscillation would be effectively used for high speed printing of a simple regular pattern where the jetting should occur at a constant frequency.