Experimental characterization of high viscosity droplet ejection

Additive Manufacturing via Microarray Deposition (AMMD) expands the allowable range of physical properties of printed fluids to include important, high-viscosity production materials (e.g., polyurethane resins). This technique relies on a piezoelectrically-driven ultrasonic printhead that generates continuous streams of droplets from 45 mm orifices while operating in the 0.5 to 3.0 MHz frequency range. Unique to this new printing technique are the high frequency of operation, use of fluid cavity resonances to assist ejection and acoustic wave focusing to generate the pressure gradient required to form and eject droplets. Specifically, we found that peaks in the ejection quality corresponded to predicted device resonances. Our results indicate that the micromachined ultrasonic print-head is able to print fluids up to 3000 mN-s/m², far above the typical printable range.