Droplet spraying is utilized in diverse industrial processes and biomedical applications, including nanomaterial synthesis, biomaterial handling, and inhalation drug delivery. Ultrasonic droplet generators transfer energy into bulk liquids using acoustic waves to disrupt the free liquid surface into fine microdroplets. We previously established a method combining ultrasonic actuation, resonant operation, and acoustic wave focusing for efficient spraying of various liquids (e.g., low surface tension fuels, high viscosity inks, and suspensions of biological cells). The microfabricated device comprises a piezoelectric transducer, sample reservoir, and an array of acoustic horn structures terminated by microscale orifices. Orifice size roughly dictates droplet diameter, and a fixed reservoir height prescribes specific device resonant frequencies of operation. Here, we incorporate a continuously variable liquid reservoir height for dynamic adjustment of operating parameters to improve spray efficiency in real-time and potentially tune the droplet size. Computational modeling predicts the system harmonic response for a range of reservoir heights from 0.5 to 3 mm (corresponding to operating frequencies from ∼500 kHz to 2.5 MHz). Nozzle arrays with 10, 20, and 40 μm orifices are evaluated for spray uniformity and stability of the active nozzles, using model predictions to explain the experimental observations.

1.
J.-W.
Kim
,
Y.
Yamagata
,
M.
Takasaki
,
B.-H.
Lee
,
H.
Ohmori
, and
T.
Higuchi
, “
A device for fabricating protein chips by using a surface acoustic wave atomizer and electrostatic deposition
,”
Sens. Actuators B: Chem.
107
,
535
545
(
2005
).
2.
V. G.
Zarnitsyn
,
J. M.
Meacham
,
M. J.
Varady
,
C.
Hao
,
F. L.
Degertekin
, and
A. G.
Fedorov
, “
Electrosonic ejector microarray for drug and gene delivery
,”
Biomed. Microdev.
10
,
299
308
(
2008
).
3.
J.
Ho
,
Y.
Huang
,
M. K.
Danquah
,
H.
Wang
, and
G. M.
Forde
, “
Synthesis of biodegradable polymer–mesoporous silica composite microspheres for DNA prime-protein boost vaccination
,”
Eur. J. Pharm. Sci.
39
,
412
420
(
2010
).
4.
J. M.
Meacham
,
K.
Durvasula
,
F. L.
Degertekin
, and
A. G.
Fedorov
, “
Enhanced intracellular delivery via coordinated acoustically driven shear mechanoporation and electrophoretic insertion
,”
Sci. Rep.
8
,
3727
(
2018
).
5.
Y.
Lu
,
C.
Kacica
,
S.
Bansal
,
L. M.
Santino
,
S.
Acharya
,
J.
Hu
,
C.
Izima
,
K.
Chrulski
,
Y.
Diao
,
H.
Wang
,
P.
Biswas
,
J.
Schaefer
, and
J. M.
D'Arcy
, “
Synthesis of submicron PEDOT particles of high electrical conductivity via continuous aerosol vapor polymerization
,”
ACS Appl. Mater. Interfaces
11
,
47320
47329
(
2019
).
6.
B.
Joshi
,
J.
Kaur
,
E.
Khan
,
A.
Kumar
, and
A.
Joshi
, “
Ultrasonic atomizer driven development of doxorubicin-chitosan nanoparticles as anticancer therapeutics: Evaluation of anionic cross-linkers
,”
J. Drug Delivery Sci. Technol.
57
,
101618
(
2020
).
7.
J.
Meacham
,
M.
Varady
,
D.
Esposito
,
F. L.
Degertekin
, and
A. G.
Fedorov
, “
Micromachined ultrasonic atomizer for liquid fuels
,”
Atomization Sprays
18
,
163
190
(
2008
).
8.
I.
Ibrahim
,
T.
Farag
,
M.
Abdel-baky
,
A.
Abd El-samed
, and
H.
Gad
, “
Experimental study of spray combustion characteristics of air-blast atomizer
,”
Energy Rep.
6
,
209
215
(
2020
).
9.
A. G.
Fedorov
and
J. M.
Meacham
, “
Evaporation-enhanced, dynamically adaptive air (gas)-cooled heat sink for thermal management of high heat dissipation devices
,”
IEEE Trans. Compon. Packaging Technol.
32
,
746
753
(
2009
).
10.
H.
Chen
,
W-l
Cheng
,
Y-h
Peng
,
W-w
Zhang
, and
L-j
Jiang
, “
Experimental study on optimal spray parameters of piezoelectric atomizer based spray cooling
,”
Int. J. Heat Mass Transfer
103
,
57
65
(
2016
).
11.
W.
He
,
Z.
Luo
,
X.
Deng
, and
Z.
Xia
, “
A novel spray cooling device based on a dual synthetic jet actuator integrated with a piezoelectric atomizer
,”
Heat Mass Transfer
56
,
1551
1563
(
2020
).
12.
L. E.
Murr
and
W. L.
Johnson
, “
3D metal droplet printing development and advanced materials additive manufacturing
,”
J. Mater. Res. Technol.
6
,
77
89
(
2017
).
13.
J.
Plog
,
Y.
Jiang
,
Y.
Pan
, and
A.
Yarin
, “
Electrostatic charging and deflection of droplets for drop-on-demand 3D printing within confinements
,”
Addit. Manuf.
36
,
101400
(
2020
).
14.
J.
Eggers
, “
Nonlinear dynamics and breakup of free-surface flows
,”
Rev. Mod. Phys.
69
,
865
930
(
1997
).
15.
P.
Wu
,
C.
Noland
,
M.
Ultsch
,
B.
Edwards
,
D.
Harris
,
R.
Mayer
, and
S. F.
Harris
, “
Developments in the implementation of acoustic droplet ejection for protein crystallography
,”
J. Lab. Autom.
21
,
97
106
(
2016
).
16.
E. K.
Sackmann
,
L.
Majlof
,
A.
Hahn-Windgassen
,
B.
Eaton
,
T.
Bandzava
,
J.
Daulton
,
A.
Vandenbroucke
,
M.
Mock
,
R. G.
Stearns
, and
S.
Hinkson
, “
Technologies that enable accurate and precise nano- to milliliter-scale liquid dispensing of aqueous reagents using acoustic droplet ejection
,”
J. Lab. Autom.
21
,
166
177
(
2016
).
17.
B.
Edwards
,
J.
Lesnick
,
J.
Wang
,
N.
Tang
, and
C.
Peters
, “
Miniaturization of high-throughput epigenetic methyltransferase assays with acoustic liquid handling
,”
J. Lab. Autom.
21
,
208
216
(
2016
).
18.
B.
de Heij
,
B.
van der Schoot
,
H.
Bo
,
J.
Hess
, and
N. F.
de Rooij
, “
Characterisation of a fL droplet generator for inhalation drug therapy
,”
Sens. Actuators A: Phys.
85
,
430
434
(
2000
).
19.
L.
Alhasan
,
A.
Qi
,
A. R.
Rezk
,
L. Y.
Yeo
, and
P. P.
Chan
, “
Assessment of the potential of a high frequency acoustomicrofluidic nebulisation platform for inhaled stem cell therapy
,”
Integr. Biol.
8
,
12
20
(
2016
).
20.
S.
Marqus
,
L.
Lee
,
T.
Istivan
,
R. Y. K.
Chang
,
C.
Dekiwadia
,
H.-K.
Chan
, and
L. Y.
Yeo
, “
High frequency acoustic nebulization for pulmonary delivery of antibiotic alternatives against Staphylococcus aureus
,”
Eur. J. Pharmaceutics Biopharmaceutics
151
,
181
188
(
2020
).
21.
T. S.
Last
,
N.
Roxhed
, and
G.
Stemme
, “
A self-sealing spray nozzle for aerosol drug delivery
,”
J. Microelectromech. Syst.
29
,
182
189
(
2020
).
22.
F.
Zabihi
and
M.
Eslamian
, “
Substrate vibration-assisted spray coating (SVASC): Significant improvement in nano-structure, uniformity, and conductivity of PEDOT:PSS thin films for organic solar cells
,”
J. Coat. Technol. Res.
12
,
711
719
(
2015
).
23.
U.
Scheithauer
,
J.
Pötschke
,
S.
Weingarten
,
E.
Schwarzer
,
A.
Vornberger
,
T.
Moritz
, and
A.
Michaelis
, “
Droplet-based additive manufacturing of hard metal components by thermoplastic 3D printing (T3DP)
,”
J. Ceram. Sci. Technol.
8
,
155
160
(
2017
).
24.
A. D.
Graham
,
S. N.
Olof
,
M. J.
Burke
,
J. P.
Armstrong
,
E. A.
Mikhailova
,
J. G.
Nicholson
,
S. J.
Box
,
F. G.
Szele
,
A. W.
Perriman
, and
H.
Bayley
, “
High-resolution patterned cellular constructs by droplet-based 3D printing
,”
Sci. Rep.
7
,
7004
(
2017
).
25.
X.
Li
,
J. M.
Zhang
,
X.
Yi
,
Z.
Huang
,
P.
Lv
, and
H.
Duan
, “
Multimaterial 3D printing: Multimaterial microfluidic 3D printing of textured composites with liquid inclusions
,”
Adv. Sci.
6
,
1800730
(
2019
).
26.
J. M.
Meacham
,
A.
O'Rourke
,
Y.
Yang
,
A. G.
Fedorov
,
F. L.
Degertekin
, and
D. W.
Rosen
, “
Micromachined ultrasonic print-head for deposition of high-viscosity materials
,”
J. Manuf. Sci. Eng.
132
,
030905
(
2010
).
27.
J.
Friend
and
L. Y.
Yeo
, “
Microscale acoustofluidics: Microfluidics driven via acoustics and ultrasonics
,”
Rev. Mod. Phys.
83
,
647
(
2011
).
28.
M.
Kumaraswamy
,
S.
Collignon
,
C.
Do
,
J.
Kim
,
V.
Nizet
, and
J.
Friend
, “
Decontaminating surfaces with atomized disinfectants generated by a novel thickness-mode lithium niobate device
,”
Appl. Microbiology Biotechnol.
102
,
6459
6467
(
2018
).
29.
J.
Meacham
,
M.
Varady
,
F.
Degertekin
, and
A.
Fedorov
, “
Droplet formation and ejection from a micromachined ultrasonic droplet generator: Visualization and scaling
,”
Phys. Fluids
17
,
100605
(
2005
).
30.
W.
Connacher
,
J.
Orosco
, and
J.
Friend
, “
Droplet ejection at controlled angles via acoustofluidic jetting
,”
Phys. Rev. Lett.
125
,
184504
(
2020
).
31.
D.
Kirpalani
and
K.
Suzuki
, “
Ethanol enrichment from ethanol–water mixtures using high frequency ultrasonic atomization
,”
Ultrasonics Sonochemistry
18
,
1012
1017
(
2011
).
32.
C. S.
Tsai
,
R. W.
Mao
,
S. K.
Lin
,
N.
Wang
, and
S. C.
Tsai
, “
Miniaturized multiple Fourier-horn ultrasonic droplet generators for biomedical applications
,”
Lab on a Chip
10
,
2733
2740
(
2010
).
33.
S. C.
Tsai
,
S. K.
Lin
,
R. W.
Mao
, and
C. S.
Tsai
, “
Ejection of uniform micrometer-sized droplets from faraday waves on a millimeter-sized water drop
,”
Phys. Rev. Lett.
108
,
154501
(
2012
).
34.
A.
Qi
,
J. R.
Friend
,
L. Y.
Yeo
,
D. A.
Morton
,
M. P.
McIntosh
, and
L.
Spiccia
, “
Miniature inhalation therapy platform using surface acoustic wave microfluidic atomization
,”
Lab on a Chip
9
,
2184
2193
(
2009
).
35.
S.
Collignon
,
O.
Manor
, and
J.
Friend
, “
Improving and predicting fluid atomization via hysteresis-free thickness vibration of lithium niobate
,”
Adv. Funct. Mater.
28
,
1704359
(
2018
).
36.
W.
Connacher
,
N.
Zhang
,
A.
Huang
,
J.
Mei
,
S.
Zhang
,
T.
Gopesh
, and
J.
Friend
, “
Micro/nano acoustofluidics: Materials, phenomena, design, devices, and applications
,”
Lab on a Chip
18
,
1952
1996
(
2018
).
37.
G.
Perçin
and
B. T.
Khuri-Yakub
, “
Micromachined droplet ejector arrays for controlled ink-jet printing and deposition
,”
Rev. Sci. Instrum.
73
,
2193
2196
(
2002
).
38.
G.
Perçin
,
G. G.
Yaralioglu
, and
B. T.
Khuri-Yakub
, “
Micromachined droplet ejector arrays
,”
Rev. Sci. Instrum.
73
,
4385
4389
(
2002
).
39.
G.
Percin
and
B. T.
Khuri-Yakub
, “
Piezoelectrically actuated flextensional micromachined ultrasound droplet ejectors
,”
IEEE Trans. Ultrasonics, Ferroelectrics, Frequency Control
49
,
756
766
(
2002
).
40.
U.
Demirci
,
G. G.
Yaralioglu
,
E.
Haeggstrom
, and
B.
Khuri-Yakub
, “
Femtoliter to picoliter droplet generation for organic polymer deposition using single reservoir ejector arrays
,”
IEEE Trans. Semicond. Manuf.
18
,
709
715
(
2005
).
41.
Y.-R.
Jeng
,
C.-C.
Su
,
G.-H.
Feng
,
Y.-Y.
Peng
, and
G.-P.
Chien
, “
A PZT-driven atomizer based on a vibrating flexible membrane and a micro-machined trumpet-shaped nozzle array
,”
Microsystem Technol.
15
,
865
873
(
2009
).
42.
C.
Pan
,
J.
Shiea
, and
S.-C.
Shen
, “
Fabrication of an integrated piezo-electric micro-nebulizer for biochemical sample analysis
,”
J. Micromech. Microeng.
17
,
659
669
(
2007
).
43.
T.
Diepold
,
E.
Obermeier
, and
A.
Berchtold
, “
A micromachined continuous ink jet print head for high-resolution printing
,”
J. Micromech. Microeng.
8
,
144
147
(
1998
).
44.
L.
Palm
,
L.
Wallman
,
T.
Laurell
, and
J.
Nilsson
, “
Development and characterization of silicon micromachined nozzle units for continuous ink jet printers
,”
J. Imaging Sci. Technol.
44
,
544
551
(
2000
).
45.
Q.
Yan
,
W.
Sun
, and
J.
Zhang
, “
Study on the influencing factors of the atomization rate in a piezoceramic vibrating mesh atomizer
,”
Appl. Sci.
10
,
2422
(
2020
).
46.
J.
Meacham
,
C.
Ejimofor
,
S.
Kumar
,
F.
Degertekin
, and
A.
Fedorov
, “
A micromachined ultrasonic droplet generator based on liquid horn structure
,”
Rev. Sci. Instrum.
75
,
1347
1352
(
2004
).
47.
A. D.
Ledbetter
,
H. N.
Shekhani
,
M. M.
Binkley
, and
J. M.
Meacham
, “
Tuning the coupled-domain response for efficient ultrasonic droplet generation
,”
IEEE Trans. Ultrasonics, Ferroelectrics, Frequency Control
65
,
1893
1904
(
2018
).
48.
M. J.
Varady
,
L.
McLeod
,
J. M.
Meacham
,
F. L.
Degertekin
, and
A. G.
Fedorov
, “
An integrated MEMS infrastructure for fuel processing: Hydrogen generation and separation for portable power generation
,”
J. Micromech. Microeng.
17
,
S257
S264
(
2007
).
49.
COMSOL Multiphysics 5.4
, (
COMSOL Inc.
,
2018
).
50.
A.
Haenlein
, “
Über den zerfall eines flüssigkeitsstrahles
,”
Forschung auf dem Gebiet des Ingenieurwesens A
2
,
139
149
(
1931
).
51.
W. V.
Ohnesorge
, “
Die Bildung von Tropfen an Düsen und die Auflösung flüssiger Strahlen
,”
J. Appl. Mathematics Mech./Z. Angew. Mathematik und Mechanik
16
,
355
358
(
1936
).
52.
See supplementary material at https://www.scitation.org/doi/suppl/10.1121/10.0005908 for a movie of droplet ejection from a nozzle microarray with orifice diameter do = 10 μm at a frequency fE = fM = 1.00 MHz and voltage Vpp,E = 300 mV and for a gradually decreasing reservoir height.

Supplementary Material

You do not currently have access to this content.