Directional droplet ejection by nozzleless acoustic ejectors built on ZnO and PZT

Abstract

This paper describes a technique to eject liquid droplets in almost any direction with a nozzleless self-focusing acoustic transducer (SFAT) built on a ZnO thin film as well as on a thick PZT substrate. Sectoring of the SFAT annular rings of half-wave-band sources to create a piezoelectrically inactive area causes the droplet ejections to be directed non-perpendicular (i.e., oblique) to the liquid surface. The direction of the droplet ejections depends on the size of the piezoelectrically inactive area within the 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 up to 90° of pie shape have been made and tested to show that the ejection direction becomes less vertical as the piezoelectrically inactive area in the transducer increases. Additionally, a multi-directional ejector built on ZnO film has been demonstrated to eject micron-sized liquid droplets (several microns in diameter) in any of eight predetermined directions on demand. Larger size liquid droplets (about a hundred microns in diameter) have also been directionally ejected from a sectored SFAT built on a PZT substrate.

Pumpless dispensing of a droplet by breaking up a liquid bridge formed by electric induction

“…Non‐contact printing methods use other driving forces such as electric field, pressure pulse, 6, or inertial force 11 instead of physical contact to generate droplets from a nozzle. Ink‐jet printing 12 and acoustic droplet ejection 13 use the electric signals indirectly via piezo‐electric transducers or resistors. In the ink‐jet type dispenser, the picoliter droplets (∼20 μm in diameter) are generated at 1–10 kHz per single nozzle 7.…”

A PZT-driven atomizer based on a vibrating flexible membrane and a micro-machined trumpet-shaped nozzle array

“…On the other hand, comparing to some atomizers, such as the spray-can device, femtoliter droplet generator, and array micro-jet, etc. (Yuan et al 2003;Kwon et al 2006;Kurosawa et al 1995), the size distributions of droplets ejected from these devices show a rather sharp peak at certain specified value. Below this value, the ejected liquid amount decreases dramatically.…”

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

“…Furthermore, although the mesh helps to select droplets of smaller diameters, it not only wastes expensive drugs but also causes clogging of the device by the viscous medicines. In addition to the Faraday waves-based multiple Fourier horn ultrasonic nozzles to be reviewed in detail in this paper, nozzleless droplet ejectors utilizing acoustic lens [ 3 ], liquid horn structure [ 4 ], PZT/tapered glass capillary [ 5 ], micro-machined transducers with annular piezoelectric disk [ 6 , 7 , 8 ], droplet generators using focused surface acoustic waves (SAW) [ 9 ], and planar SAW [ 10 ] were explored in recent years. Note that, since the basic ejector element of the first three droplet generators [ 3 , 4 , 5 ] produces only one droplet at a time, two-dimensional (2-D) array elements and electrical drivers are required to obtain desirable droplet throughput.…”

“…Note that, since the basic ejector element of the first three droplet generators [ 3 , 4 , 5 ] produces only one droplet at a time, two-dimensional (2-D) array elements and electrical drivers are required to obtain desirable droplet throughput. The fourth droplet generator [ 6 , 7 , 8 ] suffers from the same deficiencies as the current commercial droplet generators. While the focused SAW-based droplet generator [ 9 ] suffers from low droplet throughput, the planar SAW-based droplet generator [ 10 ] has yet to demonstrate a capability for producing narrow and controllable droplet size distribution.…”