Smart threads act sensitively when hit.

Researchers at the Fraunhofer Institute in Germany have created gossamer threads of a compound that converts mechanical energy to electricity and vice versa. These threads form the heart of a miniature device that can be integrated into a material to act as a sensor or to dampen vibrations.

Dieter Sporn of Fraunhofer in Wurzburg and his colleagues formed 30-micrometer-thick fibers of PZT, a so-called smart compound of lead, zirconium, titanium, and oxygen. "Anyone who has tried to do this knows how difficult it is to make thin [PZT] fibers," says Eric Cross of Pennsylvania State University in State College. "It really is a major step forward."

Sporn arranged the PZT fibers across an array of thin metal electrodes and then embedded the structure in a composite material. When the composite was struck with a rubber mallet, the PZT produced a measurable electrical signal. Conversely, running an electric current through the structure caused the material to vibrate.

A device like this one offers some advantages over the sensors and actuators used now, Sporn says. The large strips or plates of smart materials employed today risk compromising the mechanical strength of any composite in which they're embedded. The goal is to have fibers "as thin as possible while maintaining the active properties," he explains. Such a multifiber arrangement should also make it easier to pinpoint an impact's location, he adds.