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New form, better function: Pitt researchers' work leads to a tiny, cheap antenna

Monday, January 28, 2002

By Byron Spice, Science Editor, Post-Gazette

A microwave antenna not much bigger than a large grain of sand might help make electronic identification tags so cheap that they could replace the ubiquitous bar codes now used on products.

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, or 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 nonprofit, 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 European Central Bank reportedly is working to develop an RFID tag that can be embedded in its euro bank notes to foil counterfeiters.

"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.

Daniel Stancil, who directs Carnegie Mellon University's Antenna and Radio Communications group, said other researchers have worked on chip-based antennas. Those antennas generally operate at higher frequencies than Mickle's; higher frequencies require more expensive electronics and the antennas often must be in sight of the transmitter.

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 radiowaves, 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.

Sclabassi said Mingui Sun, a research associate professor of neurological surgery, plans to use Mickle's technology to power implantable devices that would monitor epilepsy in experimental animals. Federal funding for that work is anticipated soon, he added.

Though the early energy-harvesting sensors were circuit boards the size of a deck of cards, Mickle's team has been working to miniaturize the sensors, including smaller antennas. At the suggestion of Digital Greenhouse officials, Mickle devised an antenna that could be etched on a silicon chip and, to his delight, discovered that the tiny antennas were amazingly efficient.

A single antenna, he said, could capture up to 16 milliwatts of power. His early sensors, by contrast, consumed just 5 milliwatts.

"The amount of power we can get is much more than it takes to run a tag," Mickle said. "We know there's plenty of power out there to make it work."

Pitt has obtained patents or has patents pending on several aspects of the technology, Mickle noted, and already is talking with some tag companies that are interested in licensing the antenna technology.

"I'm not a good judge of what makes a good product," Mickle added, noting he has no ambitions to dive into the business himself. "I leave that to somebody else."

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