Machine Design

NIST Builds Standardized Electric Dummy

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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