Printer Friendly

Scientists uncover basis of material oddball.

Some crystals change their size when exposed to an electric current and also generate electric signals when squeezed. These so-called piezoelectric materials, which are usually ceramic, appear widely in ink-jet printer heads, microphones, and some other electronic products (SN: 3/17/01, p. 167).

Specially treated polypropylene foam, a mainstay of the packaging industry, can mimic the defining behavior of traditional piezoelectric crystals. Now, researchers have shown that the resemblance extends to other desirable properties.

Finnish researchers 15 years ago discovered that the lightweight foam acquires piezoelectric properties after it's zapped with several thousand volts. Compared to ceramic piezoelectrics, the foam is soft, flexible, and relatively inexpensive. It has already been incorporated into a few products, including key pads and musical-instrument pickups. Because it can cover large areas and conform to irregular shapes, the foam opened new technological prospects, says Siegfried Bauer of Johannes Kepler University in Linz, Austria.

Investigating how the foam becomes a piezoelectric impersonator, Bauer and his colleagues showed a year ago that air in a pore breaks down into electrons and positively charged ions that cling to opposite walls. Like lightning, visible flashes of light accompany those "microstorms," Bauer says.

Additional research had shown that, like many piezoelectric materials, the foam is ferroelectric. Such a substance harbors an electric field that can be flipped by a voltage.

At a symposium on ultrasound research this October, Bauer and his coworkers plan to present evidence that the similarity between the foam and conventional piezoelectrics extends even further. Both materials can respond to an electric current by simultaneously expanding in some areas and contracting in others. To implement this differential response, scientists take advantage of materials' ferroelectric nature and flip internal fields in some regions but not others. This permits such capabilities as sophisticated ultrasound focusing and hidden piezoelectric bar codes, Bauer says.

The foam loses its piezoelectric quality above 55[degree] C, a temperature sometimes reached in a car's glove box, notes materials scientist Tom Rosenmayer of W.L. Gore in Munich.

If it can be made to retain piezoelectric properties at higher temperatures, the foam could be a "breakthrough" discovery in electrically active plastics, comments Michael R. Wertheimer of the Ecole Polytechnique in Montreal.
COPYRIGHT 2003 Science Service, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2003, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:piezoelectric materials; Electric Foam
Author:Weiss, P.
Publication:Science News
Geographic Code:4EUFI
Date:Aug 9, 2003
Previous Article:Marking original documents with a lick of gloss.
Next Article:Emergency gardening: labs step in to help conserve the rarest plants on earth.

Related Articles
Kynar and gentler streets.
Fantastic plastic: it talks, listens and knows if you're there.
Taking a walk on the lighter side.
Smart threads act sensitively when hit.
Tiny acoustic wave sensors will find food applications.
Cold sliver may sense electron quiver. (Physics: from Seattle, at the American Physical Society's annual March meeting).
Make foams and emulsions stable.
Polymeric blends for sensor and actuation dual functionality.
Electronics detox: leadfree material for ecofriendly gadgetry.
System and method for generating electric power from a rotating tire's mechanical energy.

Terms of use | Privacy policy | Copyright © 2020 Farlex, Inc. | Feedback | For webmasters