Finding Needles in Haystacks

Sept. 1, 2001
People have long searched for easy ways to locate items. The search may be over.

Finding Needles in Haystacks

People have long searched for easy ways to locate items.The search may be over.

by Geva Barash

In warehouses, lift truck operators must match up pick listswith actual items on shelves, pallets and floor space. A worker may need tolocate a specific case on a pallet several boxes high. The list is endless.

A bar code system for doing this is not foolproof because itrequires human involvement, thus increasing the possibility of error. Also, barcoding does not allow for real-time inventory. If someone forgets to scan amoved item, scans it twice, or the bar code is damaged, its location and theinventory record are inaccurate.

Radio frequency identification (RFID) technology changes allthat. Unlike bar code systems, RFID works all the time, without humanintervention. The computer system always knows where a tagged item is located.

Now, the use of surface acoustic wave (SAW) technology isbeing recognized as a viable alternative to traditional RFID technology. SAWtechnology has been used for more than 20 years for items like TV remotecontrol devices. This recent integration into RFID, in conjunction withdatabase programs and highly sophisticated algorithms, is clearly abreakthrough.

In the past, passive RF tags could be read at an averagedistance of two feet. However, the use of SAW technology now allows for tags tobe read at 130 feet from the antenna. Active tags, possessing their own powersource, previously had an average read range of one mile. In the near future,readers will be able to pick up the signal of an active SAW tag fromapproximately six miles.

SAW systems can also locate a tag’s position within amuch smaller area than previously. Whereas other systems can only determine atag’s location within a 10-foot radius, SAW technology enables the tag tobe identified within two feet. These expanded read distances and more conciselocation identification features are now enabling small to medium-sized usersto consider new applications using RFID.

In combination with the other techniques, SAW technologyovercomes previous cost/distance obstacles that limited its implementation. Byimplementing SAW into a passive tag (which derives its energy from the RFbeam), the power needed to reflect the tag’s identification beam back tothe reader is minimal, and more efficient. This allows for greater readdistances. Passive SAW tags are currently priced at less than $5, far below theaverage market price for passive tags.

What is SAW?

SAW technology uses acoustic waves on the surface ofspecially designed tags of solid-state material to obtain unique signalprocessing capabilities. The solid-state material consists of a thin metal filmstructure deposited on top of a piezoelectric crystal substrate on the tag.

A base station sends out an electrical signal via atransmitting antenna. The input transducer on the tag converts this electricalsignal to tiny acoustic waves, which then travel through the solid-statematerial to the output transducer, located on the tag. Here, the waves arereconverted to electrical signals and sent back to the antenna.

Previous RFID systems use either close proximityelectromagnetic waves (otherwise known as inductive coupling) or propagatingelectromagnetic waves to transmit signals. Noise, interference and distortioncan cause data corruption. For example, a metal container will reflect an RFwave back to the antenna at the same rate as the tag attached to it. With a SAWdevice, the transmissions of the reply beams back to the reader are delayed.The wave will reflect from the metal and then, after a two-millisecond delay,it will reflect from the tag. By using special computer algorithms, the speedof the return signals can be calculated to separate the true tag signal fromthe false ones. This technique, coupled with the fact that the entire reflectedwave, not just its peaks, is read, allows for a more accurate read of each tagidentified. As a result, the factors that hindered RF in the past are no longerrelevant.

The database approach

Using SAW tags in conjunction with a database enables thetag’s identification to be read just like a fingerprint. Each tagcontains a distinct code linked in the database to a plethora of relevantinformation, such as tag or product history. This linking also increases thesecurity of the system. Valuable data is not transmitted from a tag to atransceiver. While existing RFID transmissions are often encrypted,there’s still the chance that information could be decoded. However, inRFID systems integrated with SAW technology, only a meaningless number istransmitted. All the important information remains in the safety of theuser’s database.

Another advantage to the SAW system is lower installationcosts. Since fewer base stations and transceivers are needed due to the longerread ranges, installation costs are greatly reduced.

When used in conjunction with SAW technology, an integrateddatabase and sophisticated algorithms, RFID has the ability to deliver alower-cost solution than has previously been available. This combination opensthe market to many mid-tier companies that need to locate items in acost-efficient manner. Now, virtually any company can realize thecost-effective benefits of implementing RFID combined with SAW technology.

About the author

Geva Barash is executive vice president, sales andmarketing, at I-Ray Technologies Inc., a provider of radio frequencyidentification (RFID) solutions for real-time tracking and management ofassets, with headquarters in Natick, Massachusetts.

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