RFID stands for radio frequency identification, a technology that identifies, locates and tracks items using radio waves. When an item is tagged with a tiny silicon chip and an antenna -- collectively known as an RFID tag -- it can be scanned by a mobile or stationary reader to identify the item. RFID chips last varying lengths of time, depending on the design of the RFID tag and nature of the tagged item.
Active RFID tags carry their own power supply in the form of a battery, and run continually until the battery runs out. This means that their life expectancy is limited, typically to between one and three years. Active RFID tags are attached to commercial products to track them through the retail supply chain. RFID tags only need to operate while products are in the supply chain, up to the point-of-sale, so limited life expectancy is perfectly adequate.
Passive RFID tags do not carry their own power supply; the energy they need to communicate is provided by radiation from the RFID reader. They have no battery to run out and, as such, have a virtually unlimited life expectancy of perhaps 20 years or more. Passive RFID tags are usually attached to library books, for example, which may spend long periods of time on a shelf and be issued many times during their lifetime. Library books require RFID tags that operate reliably over and over again for years or decades.
Semi-active RFID tags carry their own power supply, but only run when receiving data from the RFID reader and transmitting data back in the opposite direction. Radiation from the reader turns the tag on and the tag switches off its power automatically once it has sent data back to the reader. This improves the power consumption of semi-active RFID tags compared with fully active tags, such that they typically have a life expectancy of between three and five years.
Various applications -- including car key tags, highway toll tags, security access cards and many others -- use RFID technology, which makes it difficult for manufacturers to quote the life expectancy of RFID chips, particularly those used in passive RFID tags, in terms of elapsed time. Manufacturers therefore tend to quote life expectancy in terms of cycles, or the number of read or write operations, or both, that an RFID chip can complete successfully before failure.