A novel liquid droplet generator, or atomizer, capable of generating e
ither monodisperse droplet streams or a polydisperse spray, has been c
haracterized using phase-Doppler anemometry and two visualization tech
niques. The atomizer consists of a piezoelectric driver in a circular
housing with an orifice plate across the end of the housing. Unlike co
nventional droplet generators or atomizers, this device directly induc
es a high-amplitude velocity perturbation of the liquid jet. Orifice p
lates with a circular hole (diameter: 34 or 98 mum) or a rectangular h
ole (527 x 31 mum2) were used. In the low-power mode, the atomizer wit
h a circular orifice generated a stream of monodisperse water droplets
with a diameter 1.5 to 3.4 times the jet diameter and a separation 2.
3 to 26 times the jet diameter at 10 to 68 kHz. Droplets smaller than
the minimum size predicted by Rayleigh's criterion can be generated wi
th an increased modulation power. The droplet velocity can be adjusted
in a wide range (4 to 26 m/s), and a high Reynolds number (approximat
ely 250) can be attained. In the high-power mode, the atomizer produce
d a polydisperse water spray with a Sauter mean diameter less than hal
f the jet (equivalent) diameter. The rectangular orifice required sign
ificantly less driving power to generate a spray. This atomizer is sui
table for both fundamental studies and practical applications.