November 21, 2005
RFID primer
An RFID system basically consists of readers, tags, and information processing software. The software is used for filtering and analyzing the gathered information that can be acted upon.
The tag is made up of a chip, an antenna, and a casing. The EPC resides in the chip, the chip is attached to a coiled antenna and this assembly is housed in a packaging best suited to be affixed to the object that has to be monitored.
Tags are classified as active, passive, and semi-passive. EAS tags used widely in the retail industry are the best examples of passive tags. They are also classified in terms of their memory as read only, read/write, and combination tags. Passive tags do not have their own source of energy and use the method known as “energy harvesting” to absorb energy from a reader and use it to transmit the data back to the reader at a different frequency. Smart labels are passive RFID tags that can be printed on demand. These can be read by a bar code scanner. Smart tags may well be the only type of tags used in the future.
Active tags have their own power source but can be read only when they come in the read range of the reader. An internal power source means that active tags have a greater range than passive tags. They can be read from a distance of around 30 yards. However, the inclusion of a battery has increased the weight and cost of active tags and has reduced its life to equal the span of the battery, which currently is around five years.
Semi-passive tags are equipped with a sensor that enables the monitoring of temperature, movement, etc. They are used in situations like cold chains where it is important to track the movement as well as the condition of an item.
The Electronic Product Code is used for identifying the object to which the tag is attached. The EPC has a 96-bit capacity and is made up of a header that gives information on the length of the EPC number, the type and version of code, the header requires 8 bits of memory; the EPC manager requires 28 bits and identifies the manufacturing company; the object class takes 24 bits and classifies the item; the serial number requires 36 bits and identifies an item within a class.
The reader has three main components; an antenna, a receiver, and a decoder. The complexity of the readers is a function of the type of tags they are meant to support. The read range is a function of the size and efficiency of the antenna and the transmitter power. The area covered and range of operation increases with the number of antennas. Upon receiving information from a tag in its read range, the reader processes the information in its decoding software and then transmits it to the information management system that it is connected to.
RFID readers will soon be a part of electronic devices as diverse as cell phones and PDAs. The rate at which data is transferred is directly proportional to the frequency of the radio waves. The variations in the regulations that govern the frequency ranges used in different countries are an impediment to the growth of RFID. The read range of the tag is influenced by the frequency of the radio waves, the power in the tag, the power in the reader, working environment, and antenna size.
Factors that affect the read rates include the type of tags and their placement on the pallet, case, or item; the orientation of the antenna; reader settings, etc. Pilots conducted in controlled conditions are very often inaccurate indicators of tag-reader performance. Sources of interference in actual work conditions include cell phones, walkie-talkies, metals, liquids, etc.
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