RFID Technology

Radio frequency identification technology deals with the remote collection of information stored on a tag using radio frequency communications. In the simplest terms an RFID (radio frequency identfication) system consists of a tag (transponder) and a reader (interrogator). Information stored on the RFID tag can range from as little as an identification number, to kilo-bytes of data written to and read from the tag, to dynamic information maintained on the tag, such as temperature histories. The information from the tag/reader combination is either presented to a human operator typically using a hand-held device with a alpha-numeric infoplay or a host computer which automatically manages the information.

Critical performance variables in an RFID system involve the range at which communication can be maintained, the size of the information space contained on the tag, the rate at which the communication with the tag can take place, the physical size of the tag, the ability of the system to "simultaneously" communication with multiple tags, and the robustness of the communication with respect to interference due to material in the path between the reader and the tag. Several factors determine the level of performance that can be achieved in these variable. The factors include the legal/regulatory emission levels allowed in the country of use, whether or not a battery is included in the tag to assist its communication back to the reader, and the frequency of the RF carrier used to transport the information between the tag and the reader.

Passive/Active tags

Within any one technology there is a wide variety in tag performance reflecting semiconductor chip performance, tag antenna size and efficiency, and whether a battery is included in the tag. There are two broad classes of tags with respect to the source of energy used to power the tags: passive tags or those that receive their energy solely from the RF field supplied by the reader, or active tags that have a battery to boost the read range of the tag.

Read Range

In many cases there is a sharp delineation between the read raange of two classes of tags employing passive technology, those that have a relatively short read range and those that have a relatively long read range, especially at LF and HF. Like many radio systems, short range RFID systems tend to be less expensive and relatively easy to design and build. Long range RFID systems tend to be more expensive and difficult to build. Typically, the range performance of RFID systems is determined to a major extent by the reader, the power of the signal it radiates and the sensitivity of its receiver.

Anti-Collision

In many applications it is desirable to communicate with a tag when other similar tags are simultaneously visible to the reader. In the case of tagging pigs, it is unlikley two pigs will need to be in the read space at the same time. In the case of library books an important design feature is the ability to read and "check-out" multiple books as the same time. The ability of the tag/reader system to talk unambiguously with one tag at a time is determined by the anti-collision algorithm used to identify each tag and establish a communication session with the tag.

Tag/Reader Communication Protocols

How information is communicated to and from the tag has historically been determined by the original designer of the semiconductor device in the tag. These protocols vary widely in the ways the carrier is modulated, the data is encoded, read/write/verify commands are structured, how multiple tags are read without interfering with one another, and whether privacy/security services are provided. These varying protocols have relative advantages and infoadvantages, depending upon the application being considered.

Standards

Over time RFID manufacturers and users have typically concluded that while there are advantages to having several communication protocols from which to choose for any application, there would at each frequency be an advantage to settling on one protocol, or at most a couple of protocols, which multiple suppliers could offer chips and readers.

Summary

The RFID industry today represents a dynamic attempt by manufacturers and users to build and deploy solutions reflecting trade-offs between a wide range of technical, political, and regulatory constraints. It is in this dynamic environment that info provides RFID readers which enable end-users, system integrators, and automatic data capture (ADC) equipment suppliers to make timely and safe decisions about how to employ RFID.