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NASHVILLE, TENN. — Reseachers say bridges, chemical tanks and buildings could warn in advance of a failure, if they were salted with ``smart'' particles that respond to magnetic or electronic fields.

Several technical papers at International Composites Exposition described the research. Much more work is needed, and scientists and engineers need to develop a common database, said Justin Berman, materials engineer at the U.S. Army Construction Engineering Research Laboratories in Champaign, Ill.

``A lot of this is basic research at that this point,'' Berman said.

Berman, in a paper presented in Nashville, said ferromagnetically tagged particles, measuring 5 microns or smaller, would respond to an alternating magnetic field beamed onto the structure. This system of tiny sensors would detect the internal vibration or deformation of the material.

``These signals can be used to detect damage,'' Berman said.

Although it has been around since the early 1970s, ferromagnetic tagging has not been studied as an infrastructure safety check until recently. U.S. Army officials are interested in ways to monitor the health of its aging structures.

Members of the New York-based Composites Institute, sponsor of ICE, have helped researchers develop the tagged components.

``When this testing was first proposed several years ago, it was truly in the category of `Star Wars,' '' said Douglas Barno, director of market development for the Composites Institute, a unit of the Society of the Plastics Industry Inc.

Much of the research was conducted, under contract for the Army CERL, at the Center for Intelligent Material Systems and Structures at Virginia Polytechnic Institute and State University in Blacksburg, Va.

Another way to ``tag'' structures is to embed small patches that respond to electric stimulation at strategic points. This technique works well for tracking bond lines in concrete, Berman said.

A number of other papers presented in Nashville discussed ``smart composites'' techniques such as embedding fiber-optic sensors in filament-wound pressure vessels.