The computer circuitry of the so-called smart tags enables them to store and transmit information unique to each item, but their cost has limited their use.

Researchers at the University of Pittsburgh, however, have developed an antenna - a necessary component of the tags - that might be part of the cost solution. Though this antenna is 3.2 inches long, it is etched atop a silicon chip in a spiral so tight that the antenna fills a square measuring just 2.2 millimeters on each side.

Marlin Mickle, the Pitt electrical engineer who led the antenna-on-a-chip's development, said both the antenna and a small computer circuit could be etched onto the same chip, producing a radio frequency identification (RFID) tag. In mass production, these "smart tags" might cost pennies apiece.

"It's exciting work," said Charles Brandt, chief technical officer of the Pittsburgh Digital Greenhouse, the non-profit, state-funded agency that has sponsored some of Mickle's experiments. "Its full potential is hard to pin down."

Technologists have been predicting that smart tags will eventually replace optically scanned bar codes. While bar codes only identify a product, RFID tags could contain information particular to each item, such as place and date of manufacture, or expiration dates. Because this information is transmitted by radio, each item need not be optically scanned and so the tags might be used routinely to track inventory, as well as speed checkouts.

"The Holy Grail of such technology would be to have it be smart enough and cheap enough that it could go on every cereal box at a penny a part," Brandt said. Mickle's device isn't at that point of development yet, but "it's definitely leading edge."

Mickle's antenna operates at 915 megahertz, an unlicensed frequency reserved for scientific and industrial uses, such as microwave ovens.

Existing RFID tags, which consist of small computer chips with separate antennas, now can cost 50 cents or more each. Some of these tags also have small power sources attached, but most obtain their power inductively - a device called a reader emits radio frequency waves that energize the tag's antenna and power its computer chip, which then transmits information back to the reader.

The Pitt antenna was an outgrowth of work by Mickle and his students to develop low-power sensors that could be powered by electricity harvested from the ambient radio waves, or static, generated by the multitude of electronic devices now in use. Antennas are used to gather this radio frequency energy.

Pitt subsequently patented the energy-harvesting technology.

One application of the harvesting technology is being pursued in Dr. Robert Sclabassi's Neurophysiology Laboratory at the Pitt Medical School. Implantable computer chips for monitoring brain activity or connecting the brain to external electronics have been under study for some time both here and at other labs, he noted, but powering these implants has always been a problem.