Directional ejection of liquid droplets through sectoring half-wave-band sources of self-focusing acoustic transducer

Abstract

This paper describes a technique to produce liquid droplets in almost any direction with a Self Focusing Acoustic Transducer (SFAT) built on a thin low stress silicon nitride diaphragm with a piezoelectric ZnO film and patterned electrodes. Sectoring of the SFAT annular-rings, half-wave-band sources (to create a piezoelectrically inactive area) causes the droplet ejections to be nonperpendicular to the liquid surface. The direction of the droplet ejections depends on the size of the open area (i.e. the piezoelectrically inactive area) within the circular area of the half-wave-band sources. Droplets are ejected from the center part of the annular rings toward the open inactive area. Various openings of pie shape (up to 90/spl deg/) have been made and tested to show that the ejection direction becomes less vertical as the piezoelectrically inactive area in the transducer increases.