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Inkjet Droplet Metrology

 

Inkjet Droplet Metrology
Figure A. A sequence of images showing a reproducible burst of droplets emerging from a piezoelectric dispensing device. Ejection is normally tuned to be a single, simple droplet, but this illustrates our ability to reliably generate complex droplet patterns.

Gravimetric and Optical Sizing

We continue to develop and improve methods for determination of droplet mass and volume dispensed from a drop-on-demand dispenser that are applicable to a wide range of fluids. Total relative uncertainties in average droplet mass are near 1% while imprecisions are less than 0.5%. Sources of uncertainty (i.e., the corrections for buoyancy, droplet momentum transfer, and evaporative losses during droplet flight) were determined to be insignificant under the operating conditions described. These gravimetric methods permit the use of DOD dispense devices for high-mass-precision additive manufacturing applications, including the reliable manufacture of reference materials for testing performance of trace explosive and drug detectors. While superior in uncertainty to traditional optical methods for droplet mass characterization, this capability is now enabling evolutionary development of optical methods with comparable uncertainties… stay tuned!

Photo of drop-on-demand dispenser
Figure B. A drop-on-demand dispenser is fed by a reservoir of standard solution. Droplet generation is monitored by magnified optical microscopy with strobed illumination. The driving waveform that generates the droplets is tuned to give the droplet characteristics desired.

 

Photo droplet dispenser
Figure C. The dispenser ejects a known number of droplets in a pattern on a substrate used to test trace detectors. The mass of the droplets is determined by ejection into a sub-microgram balance (right).
Droplet image, plot parameters
Figure D. (Top) Magnified image of a droplet-in-flight and location of the horizontal grayscale profile. (Bottom) Plot of grayscale profile and optical droplet diameters at various grayscale thresholds. Comparison of gravimetric and optical measurements for the same droplets allows improved calibration of optical artefacts used for determination of length scales.

 

Publications

R. M. Verkouteren and J. R. Verkouteren, “Inkjet Metrology: High-Accuracy Mass Measurements of Microdroplets Produced by a Drop-on-Demand Dispenser,” Analytical Chemistry 81, no. 20 (2009): 8577–8584.

R. M. Verkouteren and J. R. Verkouteren, “Inkjet Metrology II: Resolved Effects of Ejection Frequency, Fluidic Pressure, and Droplet Number on Reproducible Drop-on-Demand Dispensing,” Langmuir 27, no. 15 (2011): 9644–9653.

M. Verkouteren, J. Verkouteren and C. Zeissler, “Gravimetric Traceability for Optical Measurements of Droplets-in-Flight,” In Technical Proceedings of the 2013 NSTI Nanotechnology Conference & Expo, Vol.2, Chapter 4. Inkjet Design, Materials & Fabrication, pages 224 -227. CRC Press.

Created August 10, 2017, Updated September 3, 2020