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The Basics of RFID Technology

There are many different types of radio frequency identification technology. This article explains the difference between active and passive tags and between low-, high- and ultra-high frequency systems.
By Bob Violino
Water, carbon and other materials absorb UHF energy, so products with high water content, such as fruit and soft drinks, or products made of carbon, such as batteries, can attenuate the signal reaching the tags on these products.

Electromagnetic interference: EMI is essentially noise that makes it harder to get a clear signal back from the UHF tag. It can be caused by a wide variety of machines. Motors emit EMI and may need to be shielded to prevent interference with RFID systems. Conveyors with nylon belts cause interference, as do most robots on manufacturing lines.

Interference can also be caused by other RF-based systems operating in a warehouse or other areas where RFID is used. For instance, many older wireless local area networks use the UHF frequency band. These interfere with UHF RFID systems and need to be upgraded to the 802.11 standard. Cordless phones, wireless computer terminals and other devices can also interfere with RFID systems.


The Department of Defense is combing passive and active systems
Combining Passive and Active RFID
The goal of using RFID in open supply chains is to gain "visibility"—that is to be able to "see" where your products are in real time. Visibility, however, is often lost once products are shipped. It's possible to combine active and passive systems to record which container goods are in and when a container has left a distribution yard on a truck. And with Global Positioning System technology, it's possible to track goods even while in transit. (This kind of system is expensive to implement today and is usually used only when a company is looking to reduce theft in the supply chain.)

The U.S. Department of Defense plans to combine passive RFID tagging of pallets, cases and some high-value items with the active tagging system it already uses to track many containers being shipped to bases and units overseas. The DOD will scan the passive tags on cases of meals ready to eat and other items and associate the EPCs on those cases with a pallet tag. As pallets are loaded onto a container, the case and pallet tag information will be written to an active tag on the container.

A test done last year validated the concept (subscribers, see Vendor to Foxhole Tracking). When a truck left a DOD depot, the active tag on the container was read and the fact that it left was uploaded to the military's Total Asset Visibility system, a global database for tracking goods. When the truck arrived at a train station, airport or port, the tag was read again and its location updated. Readers at ports, airports and depots have been installed overseas to give the DOD better visibility.

GPS transmitters on trucks can provide real-time location of trucks on the road. The benefits of such a system is the company can insure that high-value goods are not diverted in transit. In the future, a supply chain manager might be able to dynamically manage deliveries. For example, a potential out-of-stock situation could be averted by rerouting a truck to a store dangerously low on a given item.

It's clear that RFID has the potential to dramatically improve supply chain efficiencies, but the same technology can be used for many other applications, from securing buildings and ensuring the safety of workers to improving asset utilization and reducing manufacturing errors. The most common applications for RFID will be explained in RFID Business Applications. First, we'll explain the RFID System Components and Costs.

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