The Woodruff School

SUMMARY

A common method of fluid ejection utilized when fine control of droplet generation and placement are required is inkjet printing. All of these devices exhibit excellent controllability and repeatability in the atomization of low viscosity fluids. However, at viscosities greater than approximately 10 mPas, atomization with inkjets can produce undesirable behavior, such as the creation of satellite droplets, or cease fluid ejection completely. Horn-based ultrasonic atomization is a new method for fluid ejection that employs a resonant acoustic field that is focused by a horn structure connected to the fluid cavity and terminating at the ejection nozzle. Horn-based ultrasonic atomization devices incorporate a piezoelectric transducer, a fluid reservoir, and a micromachined array of horns such that, when a device is driven at the combined resonant frequency of the horn and fluid cavity, a locally increased pressure gradient results at the horn aperture (ejection nozzle) leading to fluid ejection. The acoustics and fluid mechanics of horn-based ultrasonic atomizers have been previously characterized for low viscosity Newtonian fluids. Achieving controlled ejection of highly viscous fluids and minimizing the unwanted effects of atomization requires an in-depth understanding of inkjet acoustics, including prediction of the pressure distribution in the ejector fluid cavity and fluid-transducer interactions. This dissertation develops a fundamental understanding of the behavior underlying the operation of inkjets and horn-based ultrasonic atomizers focusing on ejection of highly viscous fluids. The understanding gained by this work is applied to explore new concepts of piezoelectric transducer-driven fluid atomizers aiming to achieve ejection of high viscosity fluids. In particular, the main outcomes of this work are: a fundamental understanding of piezoelectric droplet ejectors via first-principle analytical modeling of electromechanical behavior for atomization of high viscosity liquids; exploration of new designs and operating modes of piezoelectric fluid ejectors, as well as the effect of fluid cavity geometries; development of design principles for piezoelectric fluid ejectors in general.

SUBJECT:	Ph.D. Dissertation Defense

BY:	Drew Loney

TIME:	Tuesday, June 24, 2014, 10:00 a.m.

PLACE:	Love Building, 210

TITLE:	Coupled Electrical and Acoustic Modeling of Viscous Fluid Ejectors

COMMITTEE:	Dr. Andrei Fedorov, Co-Chair (ME) Dr. Levent Degertekin, Co-Chair (ME) Dr. David Rosen (ME) Dr. Massimo Ruzzene (AE) Dr. William Hunt (ECE)

SUMMARY A common method of fluid ejection utilized when fine control of droplet generation and placement are required is inkjet printing. All of these devices exhibit excellent controllability and repeatability in the atomization of low viscosity fluids. However, at viscosities greater than approximately 10 mPas, atomization with inkjets can produce undesirable behavior, such as the creation of satellite droplets, or cease fluid ejection completely. Horn-based ultrasonic atomization is a new method for fluid ejection that employs a resonant acoustic field that is focused by a horn structure connected to the fluid cavity and terminating at the ejection nozzle. Horn-based ultrasonic atomization devices incorporate a piezoelectric transducer, a fluid reservoir, and a micromachined array of horns such that, when a device is driven at the combined resonant frequency of the horn and fluid cavity, a locally increased pressure gradient results at the horn aperture (ejection nozzle) leading to fluid ejection. The acoustics and fluid mechanics of horn-based ultrasonic atomizers have been previously characterized for low viscosity Newtonian fluids. Achieving controlled ejection of highly viscous fluids and minimizing the unwanted effects of atomization requires an in-depth understanding of inkjet acoustics, including prediction of the pressure distribution in the ejector fluid cavity and fluid-transducer interactions. This dissertation develops a fundamental understanding of the behavior underlying the operation of inkjets and horn-based ultrasonic atomizers focusing on ejection of highly viscous fluids. The understanding gained by this work is applied to explore new concepts of piezoelectric transducer-driven fluid atomizers aiming to achieve ejection of high viscosity fluids. In particular, the main outcomes of this work are: a fundamental understanding of piezoelectric droplet ejectors via first-principle analytical modeling of electromechanical behavior for atomization of high viscosity liquids; exploration of new designs and operating modes of piezoelectric fluid ejectors, as well as the effect of fluid cavity geometries; development of design principles for piezoelectric fluid ejectors in general.