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News Release

May 21, 1998
Device determines food not fit to eat

Refrozen food detector patented by Sandia

[freeze/thaw detector]
WE REALLY PREFER PORTERHOUSE, but when meat has had the chance to go bad, we prefer the Sandia sensor, which can tell us so. The color on the simple detector changes irreversibly from green to red when the temperature rises above freezing.
(Photo by Randy Montoya)
Download 150dpi JPEG image, 'food.jpg', 1.3Mb

ALBUQUERQUE, N.M. -- If frozen food thawed on the cross-country truck transporting it, was then refrozen and you bought it, how would you know the food wasn't fit to eat?

Perhaps by a color change in a very inexpensive thaw indicator placed in the package.

The indicator, originated and patented at Sandia National Laboratories, changes color when its temperature rises above 32 degrees F, the point above which harmful bacteria multiply. The color doesn't change back if the temperature then drops below freezing, says Sandia manager David Martinez. Sandia is a laboratory of the Department of Energy.

"Many inventions are simple," says University of New Mexico engineering professor Mo Shahinpoor. "It's just that nobody thought of this before." Shahinpoor is a co-developer with Martinez of the temperature-detecting conceptual designs.

The invention, byproduct of a solar research project, depends upon an inexpensive "smart" material -- a thin wire that "remembers" multiple shapes and acts as a sensor, says Martinez.

Using no power source except warming or cooling, the wire changes shape markedly and powerfully at appropriate temperatures. When warmed, movement of the wire tears a colored paper, green, to reveal a different color beneath, red. When cooled, the wire returns to its prior position but because the paper is torn, the warning color remains visible.

Martinez and Shahinpoor have developed eight preliminary designs, all patented, in which a smart-material sensor exposes a color-coded paper. The wire actuators utilize nitinol, a smart material consisting of nickel and titanium. Shahinpoor participates in the Sandia team working on projects in "smart" structures and materials.

Manufactured by the thousands or millions, the crucial element in the design -- a wire about the size of a piece of thread less than 3/8 inches long -- would cost "pennies for the raw materials," says Martinez. "When there's pressure from Washington on food processors, transporters and displayers to protect consumers against spoiled food, we have a technology patented to do just that."

Jim Bickel, associate director of the New Mexico-based WERC (Waste Education and Research Consortium), says, "WERC is interested in commercializing certain technologies that concern food safety. We're entering discussions with the US Department of Agriculture and the U.S. Food and Drug Administration about several likely projects, including this one." The consortium was established in 1990 by Senator Pete Domenici, R-N.M., to benefit technologies that deal with environmental problems and to educate a workforce to deal with these problems. Sandia is a multiprogram DOE laboratory, operated by a subsidiary of Lockheed Martin Corp. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major research and development responsibilities in national security, energy, and environmental technologies.

Media contact:
Neal Singer, nsinger@sandia.gov, (505) 845-7078

Technical contacts:
David Martinez, drmarti@sandia.gov, (505) 844-1457

Mo Shahinpoor, shah@unm.edu, (505) 277-3966

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