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The development of an aerodynamic shoe sampling system

In collaboration with the Transportation Security Laboratory, the National Institute of Standards and Technology has been developing a prototype shoe sampling system that relies on aerodynamic sampling for liberating, transporting, and collecting explosive contamination. Here, we focus on the measurement science of aerodynamic sampling with the goal of uncovering the underlying physics of the flow fields within these sampling systems. This paper will cover the results of a series of experiments that were used to help with the design of our prototype shoe sampling system. Laser light-sheet flow visualization revealed the bulk fluid motion inside and around the sampling system. Polymer microsphere particle standards were used to quantify the particle release efficiency of the shoe sampling system. Patches containing a known mass of explosives were also used to determine the effectiveness of particle release in the shoe sampler. Results from these experiments indicate that particle removal efficiency at a specific location is strongly influenced by its distance from an air jet and the type of explosive or material on the surface. The successful application of these flow visualization techniques and other metrology tools has helped us construct the sampling portion of a shoe screening prototype. The hope is that these tools will be useful to others who are developing next-generation aerodynamic sampling technologies.