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Printer Friendly Reprinted with permission from Popular Mechanics, October 2002.
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Sounding Out Hiding Places
Coke and Diet Coke may taste alike, but they sound different. Dissimilarities in their molecular structure alter the way they propagate high-frequency sound. Building on this idea, Aaron Diaz, of Pacific Northwest National Laboratory (PNNL) in Richland, Wash., has developed the Acoustic Inspection Device (AID), shown above. Press a button, and it can determine if the contents of a liquid-filled drum or solid-packed container disagree with the container's label. In a field test, AID-armed federal agents in Newark, N.J., discovered that blocks of roofing pitch had been hollowed out and refilled with cocaine.
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