A Micromachined Ultrasonic Droplet Generator: Design, Fabrication, Visualization, and Modeling

 

J. Mark Meacham1

F. Levent Degertekin and Andrei G. Fedorov2

 

1 Biochemical Sciences Division, NIST

2 G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology

 

The evolution of inkjet printing technology has relied on improvements in direct drop-on-demand (DOD) droplet formation and indirect droplet formation from capillary stream breakup; however, the utility of these technologies in biomedicine and biotechnology, mass spectrometry, and fuel processing has only recently been discovered. The goal of this work is to gain an understanding of the fundamental physics governing the operation of a novel piezoelectrically driven micromachined atomizer in order to achieve optimal design and controlled operation of this droplet generator. The device comprises an array of liquid horn structures wet etched into (100) silicon. At resonance, the transducer generates a standing ultrasonic pressure wave that is focused at the tip of the nozzles by the horn structures. High-resoluation stroboscopic visualization of discrete-droplet and continuous-jet fluid atomization of water is demonstrated by ejection from 6 and 12 um orifices at resonant frequencies between 0.5 and 2.5 MHz. The interactions between the focused pressure wave and capillary waves formed at the liquid-air interface are found to govern the ejection dynamics, leading to different ejection modalities. The results of these experiments provide an understanding of the physics governing the ejection process and allow for the establishment of simple scaling laws that prescribe the mode of ejection. In parallel, a detailed computational fluid dynamics (CFD) analysis of the fluid interface evolution and droplet formation and transport during the ejection process provides in-depth insight into the physics of the ejection process and determines the limits of validity of the scaling laws.

 

Presenting Author: J. Mark Meacham

Title: NRC Postdoctoral Research Associate

Mentor: David Ross

Division: Biochemical Sciences Division

Laboratory: Chemical Science and Technology Laboratory

Room: A345

Building: 227

Mail Stop: 8311

Phone: (301) 975-8643

Fax: (301) 975-4845

E-mail: j.mark.meacham@nist.gov

Not a Sigma Xi member

Category: Engineering