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Micromachines (Basel). 2017;8(2). pii: 56. doi: 10.3390/mi8020056. Epub 2017 Feb 14.

Faraday Waves-Based Integrated Ultrasonic Micro-Droplet Generator and Applications.

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Department of Electrical Engineering and Computer Science, University of California, Irvine, CA 92697, USA.
Department of Chemical Engineering and Materials Science, University of California, Irvine, CA 92697, USA.
Institute of Applied Mechanics, National Taiwan University, Taipei 106, Taiwan.
School of Medicine, University of Calfironia, San Diego, La Jolla, CA 92093, USA.
Division of Pulmonary and Critical Care Medicine, Beckman Laser Institute & Medical Clinics, School of Medicine, University of California, Irvine, CA 92697, USA.
Pulmonary, Critical Care and Sleep Medicine Division, State University of New York at Stony Brook, New York, NY 11790, USA.


An in-depth review on a new ultrasonic micro-droplet generator which utilizes megahertz (MHz) Faraday waves excited by silicon-based multiple Fourier horn ultrasonic nozzles (MFHUNs) and its potential applications is presented. The new droplet generator has demonstrated capability for producing micro droplets of controllable size and size distribution and desirable throughput at very low electrical drive power. For comparison, the serious deficiencies of current commercial droplet generators (nebulizers) and the other ultrasonic droplet generators explored in recent years are first discussed. The architecture, working principle, simulation, and design of the multiple Fourier horns (MFH) in resonance aimed at the amplified longitudinal vibration amplitude on the end face of nozzle tip, and the fabrication and characterization of the nozzles are then described in detail. Subsequently, a linear theory on the temporal instability of Faraday waves on a liquid layer resting on the planar end face of the MFHUN and the detailed experimental verifications are presented. The linear theory serves to elucidate the dynamics of droplet ejection from the free liquid surface and predict the vibration amplitude onset threshold for droplet ejection and the droplet diameters. A battery-run pocket-size clogging-free integrated micro droplet generator realized using the MFHUN is then described. The subsequent report on the successful nebulization of a variety of commercial pulmonary medicines against common diseases and on the experimental antidote solutions to cyanide poisoning using the new droplet generator serves to support its imminent application to inhalation drug delivery.


Faraday instability; Faraday waves; MFH ultrasonic nozzle; clogging free; integrated ultrasonic nebulizer; monodisperse; multiple Fourier horns (MFH); onset threshold for droplet ejection; polydisperse; pulmonary (inhalation) drug delivery; ultrasonic micro droplet generator; ultrasonic nebulizer

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