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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.
The Review of scientific instruments 06/2010; 81(6):065102. · 1.52 Impact Factor
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ABSTRACT: Self-focused acoustic transducers using using Fresnel zone plates have been fabricated and used to eject droplets of high-viscosity liquid, without nozzle, in the drop-on-demand mode. The Fresnel zone plate consists of a series of annular electrodes of half-wave-band source, and the acoustic waves are focused by constructive wave interference. Droplets of glycerin with a high-viscosity of 1400 cP can be ejected under a field of 200 kV/m and at a repetitive frequency of 120 Hz. The acoustic pressure distribution in the glycerin has been been simulated using an open-source computational fluid dynamic code OpenFOAM and measured using a needle-type hydrophone. Both the simulation and measurement give the location of two focal points which agree with the observations in the droplet ejection experiment.
Frequency Control Symposium, 2009 Joint with the 22nd European Frequency and Time forum. IEEE International; 05/2009
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ABSTRACT: Congenital brain tumours are rare. They account for 0.5% to 1.9% of intracranial tumours in childhood and have an incidence of 0.34 per million live births. Most congenital brain tumours are neuro-ectodermal tumours and medulloblastomas; giant cell astrocytoma and other tuberous sclerosis-related tumours are rare. We report on a neonate who developed seizures that were refractory to medical treatment. Imaging studies revealed a right frontal calcified tumour. Surgical resection was performed successfully and pathology revealed the tumour to be a giant cell astrocytoma. The child was seizure-free afterwards.
Hong Kong medical journal = Xianggang yi xue za zhi / Hong Kong Academy of Medicine 07/2006; 12(3):222-4.
