NIST Builds Standardized Electric Dummy

Feb. 17, 2009
The process of testing metal detectors used at airports and other public spaces can be tricky

The process of testing metal detectors used at airports and other public spaces can be tricky. There are currently two methods. In one, a person walks through the detector adorned with various metal objects, such as eyeglasses, belt buckles, jewelry, and coins. The other method puts the same kind of metal objects on a piece of plywood that gets pushed through the detector. But human subjects have so many physical differences — including sizes, body-fat makeup, and walking gaits — that standardization is impossible. The plywood method is reproducible, but can’t tell researchers how a human body might affect the detector’s ability to tell the difference between innocuous objects and weapons.

To solve the problem, NIST engineers mixed a polymer with carbon black, a fine powder almost entirely made of elemental carbon, to create a compound that mimics the average electrical conductivity of the human body. This mix is molded into bricks then arranged on a nonconductive fiberglass frame so that they mimic the mass and height of an average adult American human man. For the test, the dummy is stood on a low-friction, nonmetallic cart and passes through a detector at 0.5 m/sec, a common walking pace for men..

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