Silicon-based megahertz ultrasonic nozzles for production of monodisperse micrometer-sized droplets

Shirley C. Tsai, Chih H. Cheng, Ning Wang, Yu L. Song, Ching T. Lee, Chen S. Tsai

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)

Abstract

Monodisperse ethanol droplets 2.4 m and water droplets 4.5 μm in diameter have been produced in ultrasonic atomization using 1.5- and 1.0-MHz microelectromechanical system (MEMS)-based silicon nozzles, respectively. The 1.5- and 1.0-MHz nozzles, each consisting of 3 Fourier horns in resonance, measured 1.20 cm × - 0.15 cm × - .11 cm and 1.79 cm × - 0.21 cm × - 0.11 cm, respectively, required electrical drive power as low as 0.25 W and could accommodate flow rates as high as 350 μl/min. As the liquid issues from the nozzle tip that vibrates longitudinally at the nozzle resonance frequency, a liquid film is maintained on the end face of the nozzle tip and standing capillary waves are formed on the free surface of the liquid film when the tip vibration amplitude exceeds a critical value due to Faraday instability. Temporal instability of the standing capillary waves, treated in terms of the unstable solutions (namely, time-dependant function with a positive Floquet exponent) to the corresponding Mathieu differential equation, is shown to be the underlying mechanism for atomization and production of such monodisperse droplets. The experimental results of nozzle resonance and atomization frequencies, droplet diameter, and critical vibration amplitude are all in excellent agreement with the predictions of the 3-D finite element simulation and the theory of Faraday instability responsible for atomization.

Original languageEnglish
Article number5278447
Pages (from-to)1968-1979
Number of pages12
JournalIEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
Volume56
Issue number9
DOIs
Publication statusPublished - 2009 Sept

All Science Journal Classification (ASJC) codes

  • Instrumentation
  • Acoustics and Ultrasonics
  • Electrical and Electronic Engineering

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