Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/2486
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Title: Self-focused acoustic ejectors for viscous liquids
Authors: Hon, SF
Kwok, KW 
Li, HL
Ng, HY
Issue Date: Jun-2010
Source: Review of scientific instruments, June 2010, v.81, no. 6, 065102, p. 1-6
Abstract: Self-focused acoustic ejectors using the Fresnel zone plate (FZP) have been developed for ejecting viscous liquids, without nozzle, in the drop-on-demand mode. The FZP is composed of a lead zirconate titanate piezoelectric plate patterned with a series of annular electrodes, with the unelectroded region of the plate removed. Our results show that the acoustic waves are effectively self-focused by constructive interference in glycerin (with a viscosity of 1400 mPa s), giving small focal points with a high pressure. Due to the high attenuation, the wave pressure decreases significantly with the distance from the FZP. Nevertheless, the pressure at the focal points 2.5 and 6.5 mm from the FZP is high enough to eject glycerin droplets in the drop-on-demand mode. Driven by a simple wave train comprising a series of sinusoidal voltages with an amplitude of 35 V, a frequency of 4.28 MHz, and a duration of 2 ms, the ejector can eject fine glycerin droplets with a diameter of 0.4 mm at a repetition frequency of 120 Hz in a downward direction. Droplets of other viscous liquids, such as the prepolymer of an epoxy with a viscosity of 2000 mPa s, can also be ejected in the drop-on-demand mode under similar conditions.
Keywords: Acoustic waves
Drops
Fresnel diffraction
Nozzles
Piezoelectric devices
Plastic flow
Publisher: American Institute of Physics
Journal: Review of scientific instruments 
ISSN: 0034-6748
EISSN: 1089-7623
DOI: 10.1063/1.3442526
Rights: © 2010 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in S.F. Hon et al., Rev. Sci. Instrum. 81, 065102 (2010) and may be found at http://link.aip.org/link/?rsi/81/065102
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