e transponder at a time. This means that transponders need to be separated and processed sequentially, which in practice may be laborious and time consuming. Anti-contention protocols also differ in their ability to process unique or duplicate identities, different volumes of transponders, and stable or changing populations of transponders.

Read-only memory transponders have a unique code programmed into them by the manufacturer that cannot be changed. The transponder identity has to be associ

ated with a specific item via a lookup table. This provides a high level of data security, but is relatively inflexible.

Write-Once, Read-Many (WORM) transponders can be programmed according to the specifications of the user in a process subsequent to manufacturing. Once encoded, the data cannot be changed. This provides a high level of security, and it is more flexible than read only memory.

Read-Write transponders contain memory that can be modified during normal operation. They're often used in dynamic database applications.

 

 

A vehicle body with an embedded RFID tag passes though Toyota South Africa’s assembly line.

 

Two-bucket cases of Blue Bunny ice cream get RFID tags written and affixed during the wrapping process at Wells’ Dairy before freezing and shipping to Wal-Mart’s distribution centers.

 

 

In a typical RFID scenario, the electromagnetic field of a reader/transceiver excites the circuitry of a tag, which produces enough power for data to be exchanged between them. The data can then be relayed though controllers, and onward to PLCs, PCs, and databases as needed.