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Radio-frequency identification (RFID) is the use of a wireless non-contact system that uses radio-frequency electromagnetic fields to transfer data from a tag attached to an object, for the purposes of automatic identification and tracking. Some tags require no battery and are powered and read at short ranges via magnetic fields (electromagnetic induction). Others use a local power source and emit radio waves (electromagnetic radiation at radio frequencies). The tag contains electronically stored information which may be read from up to several meters away. Unlike a bar code, the tag does not need to be within line of sight of the reader and may be embedded in the tracked object.

RFID tags are used in many industries. An RFID tag attached to an automobile during production can be used to track its progress through the assembly line. Pharmaceuticals can be tracked through warehouses. Livestock and pets may have tags injected, allowing positive identification of the animal.

Since RFID tags can be attached to clothing, possessions, or even implanted within people, the possibility of reading personally-linked information without consent has raised privacy concerns.

Design

A radio-frequency identification system uses tags, or labels attached to the objects to be identified. Two-way radio transmitter-receivers called interrogators or readers send a signal to the tag and read its response. The readers generally transmit their observations to a computer system running RFID software or RFID middleware.

RFID systems typically come in three configurations. One is a Passive Reader Active Tag (PRAT) system that has a passive reader which only receives radio signals from active tags (battery operated, transmit only). The reception range of a PRAT system reader can be adjusted from 1-2,000 feet. Thereby allowing for great flexibility in applications such as asset protection and supervision. Another configuration is an Active Reader Passive Tag (ARPT) system that has an active reader, which transmits interrogator signals and also receives authentication replies from passive tags. Finally, there is the Active Reader Active Tag (ARAT) system in which active tags are awoken with an interrogator signal from the active reader. A variation of this system could also use a Battery Assisted Passive (BAP) tag which acts like a passive tag but has a small battery to power the tag's return reporting signal.

RFID tags can be either passive, active or battery assisted passive. An active tag has an on-board battery and periodically transmits its ID signal. A battery assisted passive (BAP) has a small battery on board and is activated when in the presence of a RFID reader. A passive tag is cheaper and smaller because it has no battery. Instead, the tag uses the radio energy transmitted by the reader as its energy source. The interrogator must be close for RF field to be strong enough to transfer sufficient power to the tag. Since tags have individual serial numbers, the RFID system design can discriminate several tags that might be within the range of the RFID reader and read them simultaneously.

Tags may either be read-only, having a factory-assigned serial number that is used as a key into a database, or may be read/write, where object-specific data can be written into the tag by the system user. Field programmable tags may be write-once, read-multiple; "blank" tags may be written with an electronic product code by the user.

The tag's information is stored electronically in a non-volatile memory. The RFID tag includes a small RF transmitter and receiver. An RFID reader transmits an encoded radio signal to interrogate the tag. The tag receives the message and responds with its identification information. This may be only a unique tag serial number, or may be product-related information such as a stock number, lot or batch number, production date, or other specific information.RFID tags contain at least two parts: an integrated circuit for storing and processing information, modulating and demodulating a radio-frequency (RF) signal, collecting DC power from the incident reader signal, and other specialized functions; and an antenna for receiving and transmitting the signal.

Fixed readers are set up to create a specific interrogation zone which can be tightly controlled. This allows a highly defined reading area for when tags go in and out of the interrogation zone. Mobile readers may be hand-held or mounted on carts or vehicles.

RFID frequency bands [1][2]
Band Regulations Range Data speed Remarks Approximate tag cost
in volume (2006) US $
120–150 kHz (LF) Unregulated 10 cm Low Animal identification, factory data collection $1
13.56 MHz (HF) ISM band worldwide 1 m Low to moderate Smart cards (MIFARE, ISO/IEC 14443) $0.50
433 MHz (UHF) Short Range Devices 1–100 m Moderate Defence applications, with active tags $5
865-868 MHz (Europe)
902-928 MHz (North America) UHF
ISM band 1–2 m Moderate to high EAN, various standards $0.15 (passive tags)
2450-5800 MHz (microwave) ISM band 1–2 m High 802.11 WLAN, Bluetooth standards $25 (active tags)
3.1–10 GHz (microwave) Ultra wide band to 200 M High requires semi-active or active tags $5 projected

Signaling between the reader and the tag is done in several different incompatible ways, depending on the frequency band used by the tag. Tags operating on LF and HF frequencies are, in terms of radio wavelength, very close to the reader antenna, only a small percentage of a wavelength away. In this near field region, the tag is closely coupled electrically with the transmitter in the reader. The tag can modulate the field produced by the reader by changing the electrical loading the tag represents. By switching between lower and higher relative loads, the tag produces a change that the reader can detect. At UHF and higher frequencies, the tag is more than one radio wavelength away from the reader, requiring a different approach. The tag can backscatter a signal. Active tags may contain functionally separated transmitters and receivers, and the tag need not respond on a frequency related to the reader's interrogation signal.[3]

An Electronic Product Code (EPC) is one common type of data stored in a tag. When written into the tag by an RFID printer, the tag contains a 96-bit string of data. The first eight bits are a header which identifies the version of the protocol. The next 28 bits identify the organization that manages the data for this tag; the organization number is assigned by the EPCGlobal consortium. The next 24 bits are an object class, identifying the kind of product; the last 36 bits are a unique serial number for a particular tag. These last two fields are set by the organization that issued the tag. Rather like a URL, the total electronic product code number can be used as a key into a global database to uniquely identify a particular product.[4]

Often more than one tag will respond to a tag reader, for example, many individual products with tags may be shipped in a common box or on a common pallet. Collision detection is important to allow reading of data. Two different types of protocols are used to "singulate" a particular tag, allowing its data to be read in the midst of many similar tags. In a slotted Aloha system, the reader broadcasts an initialization command and a parameter that the tags individually use to pseudo-randomly delay their responses. When using an "adaptive binary tree" protocol, the reader sends an initialization symbol and then transmits one bit of ID data at a time; only tags with matching bits respond, and eventually only one tag matches the complete ID string.[5]

File:RFID search environment.png

Both methods have drawbacks when used with many tags or with multiple overlapping readers.

Miniaturization

RFIDs are easy to conceal or incorporate in other items. For example, in 2009 researchers at Bristol University successfully glued RFID micro-transponders to live ants in order to study their behavior.[6] This trend towards increasingly miniaturized RFIDs is likely to continue as technology advances.Template:Citation needed

Hitachi holds the record for the smallest RFID chip, at 0.05mm × 0.05mm. This is 1/64th the size of the previous record holder, the mu-chip.[7] Manufacture is enabled by using the silicon-on-insulator (SOI) process. These dust-sized chips can store 38-digit numbers using 128-bit Read Only Memory (ROM).[8] A major challenge is the attachment of antennas, thus limiting read range to only millimeters.

References

  1. Template:Citation, pp. 1-48
  2. Template:Citation
  3. Daniel M. Dobkin, The RF in RFID: Passive UHF RFID In Practice, Newnes 2008 ISBN 978-0-7506-8209-1, chapter 8
  4. John R. Vacca Computer and information security handbook, Morgan Kaufmann, 2009 ISBN 0-12-374354-0, page 208
  5. Bill Glover, Himanshu Bhatt ,RFID essentials, O'Reilly Media, Inc., 2006 ISBN 0-596-00944-5, pages 88-89
  6. Ants' home search habit uncovered
  7. Template:Cite web
  8. Template:Cite web


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