“Smart materials” are already a big hit in sports. In baseball, for instance, new aluminum bats can now quiet the “bees” a player feels when hitting a ball off the handle. Likewise, smart skis can damp vibrations as needed. The “active” part of these sporting goods is a credit-card-sized wafer that uses quirky but well-studied materials called piezoelectrics. These compounds convert mechanical stresses, such as vibrations, into an electric signal (which can be harmlessly shunted), or, conversely, change shape or size in response to electricity.
But what if researchers could find ways to make the entire product active, rather than just a discrete embedded device? That could mean smart helicopter rotors or airplane wings that twist on command, changing shapes to reduce vibrations and noise. Key to that is finding active materials that are highly responsive and yet tough enough to form structural parts.
Researchers may have come a step closer to achieving that, as several groups of materials scientists, including ones at Pennsylvania State University and MIT, have identified “single-crystal” piezoelectric ceramics that are far more active than conventional materials. The MIT group, headed by Yet-Ming Chiang, a professor of materials science, and Nesbitt Hagood, director of the Institute’s Active Materials and Structures Lab, has now made novel single-crystal piezoceramics that can be easily made into fibers-a critical step to fabricating active composites that could be used to make entire structures smart.
Each type of the single-crystal materials has advantages. The MIT piezoceramics do not contain lead, which means they are less toxic and could be used in biological applications. The Penn State materials are more responsive but are lead-based and have not been made into fibers.
Nesbitt and his co-workers first developed active fiber composites several years ago using conventional piezo materials. The single-crystal piezos, however, could make the composites far cheaper and more practical, says Aaron Bent, founder of Continuum Control, a Cambridge, Mass.-based startup trying to commercialize the composites.
The MIT scientists hope to make an active fiber composite using the single-crystal piezoceramics within 18 months.
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