Radio-frequency identification (RFID) is an automatic identification method, relying on storing and remotely retrieving data using devices called RFID tags or transponders. An RFID tag is an object that can be applied to or incorporated into a product, animal, or person for the purpose of identification and tracking using radio waves. Some tags can be read from several meters away and beyond the line of sight of the reader.

Most RFID tags contain at least two parts. One is an integrated circuit for storing and processing information, modulating and demodulating a radio-frequency (RF) signal, and other specialized functions. The second is an antenna for receiving and transmitting the signal. Chipless RFID allows for discrete identification of tags without an integrated circuit, thereby allowing tags to be printed directly onto assets at a lower cost than traditional tags.

Today, RFID is used in enterprise supply chain management to improve the efficiency of inventory tracking and management. However, growth and adoption in the enterprise supply chain market is limited because current commercial technology does not link the indoor tracking to the overall end-to-end supply chain visibility. Coupled with fair cost-sharing mechanisms, rational motives and justified returns from RFID technology investments are the key ingredients to achieve long-term and sustainable RFID technology adoption.

History

In 1946 Léon Theremin invented an espionage tool for the Soviet Union which retransmitted incident radio waves with audio information. Sound waves vibrated a diaphragm which slightly altered the shape of the resonator, which modulated the reflected radio frequency. Even though this device was a passive covert listening device, not an identification tag, it has been attributed as a predecessor to RFID technology. The technology used in RFID has been around since the early 1920s according to one source (although the same source states that RFID systems have been around just since the late 1960s).

Similar technology, such as the IFF transponder invented by the United Kingdom in 1939, was routinely used by the allies in World War II to identify aircraft as friend or foe. Transponders are still used by most powered aircraft to this day.

Another early work exploring RFID is the landmark 1948 paper by Harry Stockman, titled "Communication by Means of Reflected Power" (Proceedings of the IRE, pp 1196–1204, October 1948). Stockman predicted that "…considerable research and development work has to be done before the remaining basic problems in reflected-power communication are solved, and before the field of useful applications is explored."


RFID tags

RFID tags come in three general varieties:- passive, active, or semi-passive (also known as battery-assisted). Passive tags require no internal power source, thus being pure passive devices (they are only active when a reader is nearby to power them), whereas semi-passive and active tags require a power source, usually a small battery.

To communicate, tags respond to queries generating signals that must not create interference with the readers, as arriving signals can be very weak and must be differentiated. Besides backscattering, load modulation techniques can be used to manipulate the reader's field. Typically, backscatter is used in the far field, whereas load modulation applies in the near field, within a few wavelengths from the reader.

Passive

Passive RFID tags have no internal power supply. The minute electrical current induced in the antenna by the incoming radio frequency signal provides just enough power for the CMOS integrated circuit in the tag to power up and transmit a response. Most passive tags signal by backscattering the carrier wave from the reader. This means that the antenna has to be designed both to collect power from the incoming signal and also to transmit the outbound backscatter signal. The response of a passive RFID tag is not necessarily just an ID number; the tag chip can contain non-volatile data, possibly writable EEPROM for storing data.

Passive tags have practical read distances ranging from about 11 cm (4 in) with near-field (ISO 14443), up to approximately 10 meters (33 feet) with far-field (ISO 18000-6) and can reach up to 600 feet (183 meters)[6] when combined with a phased array. Basically, the reading and writing depend on the chosen radio frequency and the antenna design/size. Due to their simplicity in design they are also suitable for manufacture with a printing process for the antennas. The lack of an onboard power supply means that the device can be quite small: commercially available products exist that can be embedded in a sticker, or under the skin in the case of low frequency (LowFID) RFID tags.

Active

Unlike passive RFID tags, active RFID tags have their own internal power source, which is used to power the integrated circuits and to broadcast the response signal to the reader. Communications from active tags to readers is typically much more reliable (i.e. fewer errors) than those from passive tags due to the ability for active tags to conduct a "session" with a reader.

Active tags, due to their onboard power supply, also may transmit at higher power levels than passive tags, allowing them to be more robust in "RF challenged" environments with humidity and spray or with RF-dampening targets (including humans and cattle, which contain mostly water), reflective targets from metal (shipping containers, vehicles), or at longer distances: Generating strong responses from weak reception is a sound approach to success. In turn, active tags are generally bigger (due to battery size) and more expensive to manufacture (due to price of the battery). However, their potential shelf life is comparable, as self-discharge of batteries competes with corrosion of aluminates printed circuits.

Many active tags today have operational ranges of hundreds of meters, and a battery life of up to 10 years. Active tags may include larger memories than passive tags, and may include the ability to store additional information received from the reader.

Special active RFID tags may include specialized sensors. For example, a temperature sensor can be used to record the temperature profile during the transportation and storage of perishable goods. Other sensor types used include humidity, shock/vibration, light, nuclear radiation, pressure and concentrations of gases such as ethylene.

Semi-passive

Semi-passive tags are similar to active tags in that they have their own power source, but the battery only powers the microchip and does not power the broadcasting of a signal. The response is usually powered by means of backscattering the RF energy from the reader, where energy is reflected back to the reader as with passive tags. An additional application for the battery is to power data storage.

If energy from the reader is collected and stored to emit a response in the future, the tag is operating active.

Whereas in passive tags the power level to power up the circuitry must be 100 times stronger than with active or semi-active tags, also the time consumption for collecting the energy is omitted and the response comes with shorter latency time. The battery-assisted reception circuitry of semi-passive tags leads to greater sensitivity than passive tags, typically 100 times more. The enhanced sensitivity can be leveraged as increased range (by one magnitude) and/or as enhanced read reliability (by reducing bit error rate at least one magnitude).

The enhanced sensitivity of semi-passive tags places higher demands on the reader concerning separation in denser population of tags. Because an already weak signal is backscattered to the reader from a larger number of tags and from longer distances, the separation requires more sophisticated anti-collision concepts, better signal processing and some more intelligent assessment of which tag might be where. For passive tags, the reader-to-tag link usually fails first. For semi-passive tags, the reverse (tag-to-reader) link usually collides first.

Semi-passive tags have three main advantages: greater sensitivity than passive tags; longer battery powered life cycle than active tags; they can perform active functions (such as temperature logging) under their own power, even when no reader is present for powering the circuitry.


Common applications of extended capability RFID include Yard Management, Parts Maintenance and Repair Operations, Cold-Chain Management, Reusable Transport Items tracking, High Value/High Security Asset tracking, and other applications where extended capabilities are needed.

Tagging positions

RFID tagging positions can influence the performance of air interface UHFID passive tags.
In many cases, optimum power from RFID reader is not required to operate passive tags. However, in cases where the effective radiated power (ERP) level and distance between reader and tags are fixed, such as in a manufacturing setting, it is important to know the location in a tagged object where a passive tag can operate optimally.

Tag environments

The proposed ubiquity of RFID tags means that readers may need to select which tags to read among many potential candidates, or may wish to probe surrounding devices to perform inventory checks or, in case the tags are associated to sensors and capable of keeping their values, question them for environmental conditions. If a reader intends to work with a collection of tags, it needs to either discover all devices within an area to iterate over them afterwards, or use collision avoidance protocols.

To read tag data, readers use a tree-walking simulation algorithm, resolving possible collisions and processing responses one by one. Blocker tags may be used to prevent readers from accessing tags within an area without killing surrounding tags by means of suicide commands. These tags masquerade as valid tags but have some special properties: in particular, they may possess any identification code, and may deterministically respond to all reader queries, thus rendering them useless and securing the environment.

Besides this, tags may be promiscuous, attending all requests alike, or secure, which requires authentication and control of typical password management and secure key distribution issues. A tag may also be prepared to be activated or deactivated in response to specific reader commands.

Readers that are in charge of the tags of an area may operate in autonomous mode (as opposed to interactive mode). When in this mode, a reader periodically locates all tags in its operating range, and keeps a presence list with a persist time and some control information. When an entry expires, it is removed from the list.

Frequently, a distributed application requires both types of tags: passive tags are incapable of continuous monitoring and perform tasks on demand when accessed by readers. They are useful when activities are regular and well defined, and requirements for data storage and security are limited; when accesses are frequent, continuous or unpredictable, there are time constraints to meet or data processing (internal searches, for instance) to perform, active tags may be preferred.

Current uses

Race Timing

• Registering race start and end timings for individuals in a marathon-type race where it is impossible to get accurate stopwatch readings for every entrant.

Passports

• RFID tags are being used in passports issued by many countries, including Malaysia (early 2000), New Zealand (November 4, 2005), Belgium, The Netherlands (2005), Norway (November 2005)[14], Ireland (2006), Japan (March 1, 2006), Pakistan, Germany, Portugal, Poland (2006), The United Kingdom, Australia and the United States (2007).

Transportation payments

• An Electronic Road Pricing gantry in Singapore. Gantries such as these collect tolls in high-traffic areas from active RFID units in vehicles.
• Throughout Europe, and in particular in Paris
• In Toronto, Ontario, Canada and surrounding areas
• In Seoul, South Korea and surrounding cities
• In Turkey, RFID has been used in the motorways and bridges as a payment system
• In Hong Kong, mass transit is paid for almost exclusively through the use of an RFID technology, called the Octopus Card
• The Washington, D.C. Metrorail became the first U.S. urban mass-transit system to use RFID technology when it introduced the SmarTrip card in 1999.

Product tracking

• The Canadian Cattle Identification Agency began using RFID tags as a replacement for barcode tags.
• High-frequency RFID or HFID/HighFID tags are used in library book or bookstore tracking, jewelry tracking, pallet tracking, building access control, airline baggage tracking, and apparel and pharmaceutical items tracking
• BGN has launched two fully automated Smartstores that combine item-level RFID tagging and SOA to deliver an integrated supply chain, from warehouse to consumer.

Animal identification

• Microchip implant (animal)

Inventory systems

• Wal-Mart, RFID reduced Out-of-Stocks by 30 percent for products selling between 0.1 and 15 units a day.

Libraries

• RFID tags used in libraries: square book tag, round CD/DVD tag and rectangular VHS tag.

Schools and universities

• School authorities in the Japanese city of Osaka are now chipping children's clothing, back packs, and student IDs in a primary school.

Replacing barcodes

RFID tags are often a replacement for UPC or EAN barcodes, having a number of important advantages over the older barcode technology. They may not ever completely replace barcodes, due in part to their higher cost and the advantage of multiple data sources on the same object. The new EPC, along with several other schemes, is widely available at reasonable cost.