Self-focused acoustic ejectors using the Fresnel zone plate ͑FZP͒ 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 s͒, 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 evaluation of fractal dimension values from schlieren flow images has been investigated. It was found for passive mixing heated jet flows that a value of 2.31, close to that obtained by tomographic imaging, was obtained. For turbulent diffusion flames a value of 2.40 was obtained, and this increased slightly with axial movement and with acoustic excitation of the flame. Broadly counteracting effects due to the transverse differentiation and integration along the imaging beam inherent in the schlieren method was found to arise.