Bubble entrainment from acoustically driven meniscus shape deformations in a piezo-acoustic drop-on-demand inkjet nozzle

In piezo acoustic Drop-On-Demand (DOD) inkjet printing a single droplet is produced for each piezo driving pulse. A phenomenon that disturbs the droplet formation process is the entrainment of bubbles in the ink channel. Here, we study bubble entrainment during DOD inkjet printing as a result of meniscus deformations. We show that the fundamental low-frequency acoustic resonance mode of the ink channel (7 kHz) drives the high-amplitude meniscus motion and the corresponding concave meniscus shape. The higher frequency traveling acoustic waves (110 kHz) focus the flow at the concave meniscus which drives the meniscus shape deformations resulting in bubble entrainment. Depending on the piezo driving pulse length, we observe alternating windows of bubble entrainment and no bubble entrainment resulting from the interference of the high frequency acoustic waves that are mainly generated at the rising and falling edges of the piezo driving pulse.