Army scientists improve calibration standards
February 19, 2014
- ECBC is part of the U.S. Army Research, Development and Engineering Command, which has the mission to develop technology and engineering solutions for America's Soldiers.
Army Technology Magazine: Partnerships
- March 2014
ABERDEEN PROVING GROUND, Md. (Feb. 19, 2014) -- Materials deposited on manmade or natural surfaces are more frequently being utilized as calibration standards for chemical and biological (chem-bio) detecting systems. To determine threshold sensitivity of systems which detect chemical, biological, and explosives materials, precise accurate quantities must be deposited without any additional interference.
Researchers at the U.S. Army Edgewood Chemical Biological Center have developed a new methodology for quantitatively depositing chemical materials (including explosives) on surfaces.
This new technique allows scientists and industry for the first time to accurately assess detection limits of potential chem-bio detection systems at proximal and standoff ranges. Previous testing methods required using a "drop and dry" methodology where the sample would be deposited from a pipette onto the desired surface and allowed to dry in the ambient atmosphere. This method made it difficult for scientists to control the mass, distribution of particles, shape, area, etc. of the sample, which in turn lead to potentially inaccurate quantitative and qualitative results for systems being assessed in the field.
To ensure accurate material deposition, ECBC has led an interagency working group to develop an on-demand inkjet printing and aerosol sprayer method that allows precise control of droplet volume, droplet size and dots-per-inch. Raphael Moon and Jason Guicheteau of ECBC along with Ashish Tripathi (Leidos), worked with Hung Technology Solutions LLC and Green Technologies Solutions LLC to develop inkjet printing and aerosol sprayer methodology to transfer samples to surfaces. Their research was funded under Army Technical Objective R.FP.2010.01 "Detection of Unknown Bulk Explosives."
"We knew testing in the field had an issue of accurately presenting standoff targets to systems", said Moon. "So we wanted to come up with a better method to benefit all types of potential sensors that would be quantitatively accurate with minimal statistical error. In doing so, we can now evaluate standoff surface detectors more precisely to determine low limits of detection, which is something that we could not do before."
A modified Direct Jet 1309 flat bed inkjet printer is used to deposit various chemicals on surfaces such as bare aluminum, Teflon, painted aluminum car panels, microscope slides, and others. Concentrations from 1 μg/cm² to150 μg/cm² are deposited in a single pass with increased amounts using multiple coatings. The maximum substrate size of the printer is 13" -- 9" -- 2," with maximum substrate weight 10 pound, resolution range from 720 dpi to 5760 dpi, droplet size from 1.5 to 21 picoliters, and the print head hole diameter is approximately 23 microns.
For larger concentration samples between the 150 μg/cm² to 2000 μg/cm² range, the team developed an aerosol spray deposition method. This method incorporates accelerated droplet evaporation to uniformly deposit the sample. A stationary airbrush spray in conjunction with a two-axis stage is used to generate an aerosol plume. The aerosol plume is deposited on the sample surface and is rapidly dried to prevent a coffee-ring effect. The process results in evenly distributed solid sample residue on the surface. The aerosol sprayer prints directly on concrete, metal, glass, plastic, and other surfaces. Its maximum substrate size, 13" -- 13" -- 5," with maximum substrate weight 50 pounds, and contains two-axes movement with 10" of travel per axis.
"A controlled amount of sample can give you controlled results, and that is what the government wants when evaluating new technologies," Moon said. "Accurate testing is the most important to determine how well these instruments can actually perform and can ensure that they are effective."
Moon said that the ECBC Laser Spectrometry Branch has been using the inkjet and aerosol sprayer method for all of their testing. "For quality control, we send test samples from each run of printed substrates to John Tokarz and Joy Ginter at the ECBC Forensic Analytical Center to perform quantitative analyses. To date results consistently showed that the printer produced uniform distributions as well as quantitatively accurate samples within seven percent of the predicted amount. Through these precise depositions, we are able to find sensitivities, identify low limits of detection levels and ultimately improve technology evaluation process on standoff surface detectors."
ECBC is part of the U.S. Army Research, Development and Engineering Command, which has the mission to develop technology and engineering solutions for America's Soldiers.
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