Radio frequency identification (RFID) tags come in two flavors -- active and
passive. Active tags are little radio sender-receivers. Because they need a
battery, they are relatively large and expensive. Active tags are the heart
of those electronic toll-paying gadgets you see on some dashboards.
Much more interesting are the smaller, cheaper passive tags, which are powered by a radio signal.
Radio waves are a form of electromagnetic radiation. Conductors can pick up current from an electromagnetic field.
Remember Michael Faraday, the British genius who found that moving a wire inside a magnetic field would cause it to pick up an electric current?
Passive RFID devices don't need a power source; they are energized by radio
waves. That glowing unit is the antenna where the current is induced.
Faraday's little discovery opened the door to electrical research and electrical gadgetry: Induction is used in motors, generators and transformers, to name three everyday devices.
Induction is also used in passive RFID tags, the ones that are already tracking cats, dogs, and humans, and will soon be tracking packages and all manner of what-not.
For induction, either the conductor (antenna) or the magnetic field must be moving. In an RFID, the wave-like electromagnetic field is, in effect, moving, so a stationary conductor can pick up a current, explains John Booske, a professor of electrical and computer engineering at the University of Wisconsin-Madison. "Currents are set up in the antenna. Currents are moving electrons, and their movement energy is utilized to activate the integrated circuit and radiate back to the reader," says Booske, who studies microwave devices.
The integrated circuit, or "chip," is the brain of an RFID tag. Some brain: Usually, all it does is beam an identification number back to the reader.
The range of passive tags is limited by the "inverse square law." The power of sound, light, or other electromagnetic energy falls off with distance squared: A signal with a strength of 1 watt per square meter at a distance of 1 centimeter (1/12 ) will drop to 1/4 watt per square meter at 2 centimeters (1/22).
Move to 4 centimeters, and the signal loses 15/16th of its strength (1/42).
a handheld RFID reader, you can make sense of a mountain of shipping containers.
Northwest National Laboratory
As you can see, power plummets as distance increases. (Why can an FM radio tune to a station 25 miles away? Because after the antenna picks up a signal, the radio amplifies it.)
But distance is not the only problem. If the antenna is not oriented correctly to the reader, efficiency can drop substantially, says Booske. This is why cell-phone users sometimes "dance in place" to improve reception.
Cell-phoniacs also know how their surroundings can affect radio reception. Steel
in buildings, for example, is famous for dampening signals, and this could
be a problem when steel products are tagged. Likewise, water (found in soup
or paint cans, for example) can also absorb signals.
You can count on inefficiency with the ultra-cheap antenna and electronics in
an RFID tag, says Booske. "Only a fraction gets picked up, because the antenna is so small" and yet that current is what activates the integrated circuit.
While many of the tags are supposed to be read from only a few inches away, a South African firm has announced a system that reads from 11 meters. That's a great advance, unless you are a privacy advocate. We'll return to privacy. Promise.
RFID systems also face, literally, interference, from other electronic signals. When IBM Global Services ran a test at seven Wal-Mart stores, bug zappers emitted surges of radio waves as they electrocuted insects in the storeroom. Cell-phone towers, walkie-talkies and forklifts can also cut the vital "read rate."
This RFID capsule was just approved for human implantation.
Despite the outbreak of RFID fever at Wal-Mart and the U.S. Defense Department, some shippers seem skeptical. "I don't think RFID is a mature application at this point and time," one anonymous employee of a Wal-Mart supplier told CIO Magazine. "I think it's probably two years premature" (see "Tag, You're Late..." in the bibliography). A worker at a different Wal-Mart supplier added, "Our experiences in our pilot have shown that this is not ready for prime time. The tag and reader performance problems are a long way from being solved."
Nonetheless, Wal-Mart is moving ahead. According to RFID Journal, by the end of 2005, the retail giant "expects to be tracking all pallets and cases of all products from its top 100 U.S. suppliers. By the end of the following year, it hopes to be tracking all pallets and cases from all of its U.S. suppliers. Wal-Mart will then begin rolling the technology out internationally."
And if Wal-Mart shipments must carry the tag, you can bet tags will be on a lot of other shipments. That, in a sentence, explains the growing sense that RFID is unstoppable.
But even if the technical problems are overcome, will the new technology make money? We read in Industry Week that tags cost at least 55 cents, readers cost about $2,000, and a local server and an "encoding printer" about $5,000 apiece (see "RFID's ROI..." in the bibliography). And that doesn't count the labor to do the tagging.
Where, exactly, does the profit come in? For one thing, these costs will come down as tags proliferate. And Wal-Mart, at least, is counting on RFID to enhance its time-tested strategy of using information to cut costs.
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