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Radio frequency identification, or RFID, is a generic term for technologies that use radio waves to automatically identify objects. There are several methods of identification, but the most common is to store a serial number that identifies the object, and perhaps other information, on a microchip that is attached to an antenna (the chip and the antenna together are called an RFID transponder or an RFID tag). The antenna enables the chip to transmit the identification information to a reader. The reader converts the radio waves reflected back from the RFID tag into digital information that can then be passed on to computers that can make use of it.



The basic hardware for RFID includes RFID tags and RFID readers. There are two basic types of tags, passive and active.
  1. Passive RFID tags have no battery. They draw power from the RFID reader which emits electromagnetic waves that induce a current in the tag's antenna. Semi-passive tags use a battery to run the chip's circuitry but communicate by drawing power from the RFID reader.

  2. Active RFID tags have a battery which is used to run the microchip's circuitry and to broadcast a signal to a reader, similar to the way a cell phone transmits signals to a base station.

Active and semi-passive tags are useful for tracking high-value goods that need to be scanned over long ranges, such as railway cars on a track, but they cost a dollar or more-making them too expensive to put on low-cost items. Passive UHF tags cost less than 50 cents each today - in volumes of about a million tags. Their read range isn't as far - typically less than 20 feet versus 100 feet or more for active tags - but they are far less expensive than active tags


RFID Tags and Readers