Glossary of RFID Terms

a b c d e f g h i l m n o p r s t u w x


Active tag:
An RFID tag that comes with a battery that is used to power the microchip's circuitry and transmit a signal to a reader. Active tags can be read from 100 feet or more away, but they're expensive - more than $20 each. They're used for tracking expensive items over long ranges. For instance, the US military uses active tags to track containers of supplies arriving in ports.

Amplitude The maximum absolute value of a periodic curve measured along its vertical axis (the height of a wave, in layman's terms).

Antenna: The antenna is the conductive element that enables the tag to send and receive data. Passive tags usually have a coiled antenna that couples with the coiled antenna of the reader to form a magnetic field. The tag draws power from this field.

Anti-collision: A general term used to cover methods of preventing radio waves from one device from interfering with radio waves from another. Anti-collision algorithms are also used to read more than one tag in the same reader's field.

Auto-ID Center : A non-profit collaboration between private companies and academia that is pioneering the development of an Internet-like infrastructure for tracking goods globally through the use of RFID tags.

Automatic Identification: Sometimes called automatic data capture. These are methods of collecting data and entering it directly into computer systems without human involvement. Technologies normally considered part of auto-id include bar codes, biometrics, RFID and voice recognition.


Back scatter: A method of communication between tags and readers. RFID tags using back-scatter technology reflect back to the reader a portion of the radio waves that reach them. The reflected signal is modulated to transmit data. Tags using back scatter technology can be either passive or active, but either way, they are more expensive than tags that use inductive coupling.

Bar code: A standard method of identifying the manufacturer and product category of a particular item. The barcode was adopted in the 1970s because the bars were easier for machines to read than optical characters. Barcodes' main drawbacks are they don't identify unique items and scanners have to have line of sight to read them.


Contactless smart card: An awkward name for a credit card or loyalty card that contains an RFID chip to transmit information to a reader without having to be swiped through a reader. Such cards can speed checkout, providing consumers with more convenience.

Chipless RFID tag: An RFID tag that doesn't depend on an integrate microchip. Instead, the tag uses materials that reflect back a portion of the radio waves beamed at them. A computer takes a snapshot of the waves beamed back and uses it like a fingerprint to identify the object with the tag. Companies are experimenting with embedding RF reflecting fibers in paper to prevent unauthorized photocopying of certain documents. But chip less tags are not useful in the supply chain, because even though they are inexpensive, they can't communicate a unique serial number that can be stored in a database.

Closed-loop systems: RFID tracking systems set up within a company. Since the tracked item never leaves the company's control, it does not need to worry about using technology based on open standards.

Coupling: See inductive coupling


Die: The silicon block onto which circuits have been etched.


EEPROM (Electrically Erasable Programmable Read-Only Memory): A non-volatile storage device on microchips. Usually bytes can be erased and reprogrammed individually. RFID tags that use EEPROM are more expensive than factory programmed tags, but they offer more flexibility because the end user can write an ID number to the tag at the time the tag is going to be used.

Electromagnetic compatibility (EMC): The ability of a system or product to function properly in environment where other electromagnetic devices are used and not be a source itself of electromagnetic interference.

Electromagnetic interference (EMI): Interference caused when the radio waves of one device distort the waves of another. Cells phones, wireless computers and even robots in factories can produce radio waves that interfere with RFID tags.

Electronic article surveillance (EAS): Simple electronic tags that can be turned on or off. When an item is purchased (or borrowed from a library), the tag is turned off. When someone passes a gate area holding an item with a tag that hasn't been turned off, an alarm sounds. EAS tags are embedded in the packaging of most pharmaceuticals.

Electronic Product Code: (EPC): A 96-bit code, created by the Auto-ID Center, that will one day replace barcodes. The EPC has digits to identify the manufacturer, product category and the individual item. It is backed by the United Code Council and EAN International, the two main bodies that oversee barcode standards.

Error correcting code: A code stored on an RFID tag to enable the reader to figure out the value of missing or garbled bits of data. It's needed because a reader might misinterpret some data from the tag and think a Rolex watch is actually a pair of socks.

Error correcting mode: A mode of data transmission between the tag and reader in which errors or missing data is automatically corrected.

Error correcting protocol: A set of rules used by readers to interpret data correctly from the tag.

European Article Numbering (EAN): The bar code standard used throughout Europe, Asia and South America. It is administered by EAN International.

Excite: The reader is said to "excite" a passive tag when the reader transmits RF energy to wake up the tag and enable it to transmit back.

eXtensible markup language (XML): A widely accepted way of sharing information over the Internet in a way that computers can use, regardless of their operating system


Factory programming: Some read-only have to have their identification number written into the silicon microchip at the time the chip is made. The process of writing the number into the chip is called factory programming.

Field programming: Tags that use EEPROM, or non-volatile memory, can be programmed after it is shipped from the factory.

Fluidic Self-Assembly: A manufacturing process, patented by Alien Technology. It involves flowing tiny microchips in a special fluid over a base with holes shaped to catch the chips.

Frequency: The number of repetitions of a complete wave within one second. 1 Hz equals one complete waveform in one second. 1KHz equals 1,000 waves in a second. RFID tags use low, high, ultra-high and microwave frequencies. Each frequency has advantages and disadvantages that make them more suitable for some applications than for others.


GTAG (Global Tag): A standardization initiative of the Uniform Code Council (UCC) and the European Article Numbering Association (EAN) for asset tracking and logistics based on radio frequency identification (RFID). The GTAG initiative is supported by Philips Semiconductors, Intermec, and Gemplus, three major RFID tag makers.


High-frequency tags: They typically operate at 13.56 MHz. They can be read from about 10 feet away and transmit data faster. But they are consume more power than low-frequency tags.


Inductive coupling: A method of transmitting data between tags and readers in which the antenna from the reader picks up changes in the tag's antenna.

Industrial, Scientific, and Medical (ISM) bands: A group of unlicensed frequencies of the electromagnetic spectrum.

Integrated circuit (IC): A microelectronic semiconductor device comprising many interconnected transistors and other components. Most RFID tags have ICs.

Interrogator: See RFID reader.


Low-frequency tags: They typically operate at 125 KHz. The main disadvantages of low-frequency tags are they have to be read from within three feet and the rate of data transfer is slow. But they are less expensive and less subject to interference than high- frequency tags.

Memory: The amount of data that can be stored on a tag.

Microwave tags: Radio frequency tags that operate at 5.8 GHz. They have very high transfer rates and can be read from as far as 30 feet away, but they use a lot of power and are expensive.

Modulation: Changing the frequency or amplitude of a wave to transmit data that is converted into digital form. For example, a wave with the normal amplitude (or height) may be a one in binary code and a wave with a lower amplitude might be a zero.

Multiple access schemes: Methods of increasing the amount of data that can be transmitted wirelessly within the same frequency spectrum. RFID readers use Time Division Multiple Access, or TDMA, meaning they read tags at different times to avoid interfering with one another.

Multiplexer: An electronic device that allows a reader to have more than one antenna. Each antenna scans the field in a preset order.


Nano-block: The term Alien Technology uses to describe its tiny microchips, which are about the width of three human hairs.

Nominal range: The read range at which the tag can be read reliably.

Null spot: Area in the reader field that doesn't receive radio waves. This is essentially the reader's blind spot. It is a phenomenon common to UHF systems.


Object Name Service (ONS): An Auto-ID Center-designed system for looking up unique Electronic Product Codes and pointing computers to information about the item associated with the code. ONS is similar to the Domain Name Service, which points computers to sites on the Internet.


Passive tag: An RFID tag without a battery. When radio waves from the reader reach the chip's antenna, it creates a magnetic field. The tag draws power from the field and is able to send back information stored on the chip. Today, simple passive tags cost around 50 cents to several dollars.

Patch antenna: A small square antenna made from a solid piece of metal or foil.

Physical Markup Language (PML): An Auto-ID Center-designed method of describing products in a way computers can understand. PML is based on the widely accepted eXtensible Markup Language used to share data over the Internet in a format all computers can use.

PML Server: A server that responds to requests for Physical Markup Language (PML) files related to individual Electronic Product Codes. The PML files and servers will be maintained by the manufacturer of the item.

Power level: The amount of RF energy radiated from a reader or an active tag. The higher the power output, the longer the read range, but most governments regulate power levels to avoid interference with other devices.

Programming: Writing data to an RFID tag.

Proximity sensor: A device that detects the presence of an object and signals another device. Proximity sensors are often used on manufacturing lines to alert robots or routing devices on a conveyor to the presence of an object.


Radio Frequency Identification (RFID): A method of identifying unique items using radio waves. Typically, a reader communicates with a tag, which holds digital information in a microchip. But there are chipless forms of RFID tags that use material to reflect back a portion of the radio waves beamed at them.

Range: See read range.

Read: The process of turning radio waves from a tag into bits of information that can be used by computer systems.

Read rate: The maximum rate at which data can be read from a tag expressed in bits or bytes per second.

Reader (also called an interrogator): The reader communicates with the RFID tag via radio waves and passes the information in digital form to a computer system.

Reader field: The area of coverage. Tags outside the reader field do not receive radio waves and can't be read.

Read-only tags: Tags that contain data that cannot be changed unless the microchip is reprogrammed electronically.

Read range: The distance from which a reader can communicate with a tag. Active tags have a longer read range than passive tags because they use a battery to transmit signals to the reader. With passive tags, the read range is influenced by frequency, reader output power, antenna design, and method of powering up the tag. Low frequency tags use inductive coupling (see above), which requires the tag to be within a few feet of the reader.

Read-write tags: RFID tags that can store new information on its microchip. San Francisco International Airport uses a read-write tag for security. When a bag is scanned for explosives, the information on the tag is changed to indicate it has been checked. The tag is scanned again before it is loaded on a plane. Read-write tags are more expensive than read only tags, and therefore are of limited use for supply chain tracking.

RFID tag: A microchip attached to an antenna that picks up signals from and sends signals to a reader. The tag contains a unique serial number, but may have other information, such as a customers' account number. Tags come in many forms, such smart labels that are stuck on boxes; smart cards and key-chain wands for paying for things; and a box that you stick on your windshield to enable you to pay tolls without stopping. RFID tags can be active tags, passive tags and semi-passive tags.


Scanner: An electronic device that can send and receive radio waves. When combined with a digital signal processor that turns the waves into bits of information, the scanner is called a reader or interrogator.

Semi-passive tag: Similar to active tags, but the battery is used to run the microchip's circuitry but not to communicate with the reader. Some semi-passive tags sleep until they are woken up by a signal from the reader, which conserves battery life. Semi-passive tags cost a dollar or more.

Sensor: A device that responds to a physical stimulus and produces an electronic signal. Sensors are increasingly being combined with RFID tags to detect the presence of a stimulus at an identifiable location.

Silent Commerce: This term covers all business solutions enabled by tagging, tracking, sensing and other technologies, including RFID, which make everyday objects intelligent and interactive. When combined with continuous and pervasive Internet connectivity, they form a new infrastructure that enables companies to collect data and deliver services without human interaction.

Smart label: A label that contains an RFID tag. It's considered "smart" because it can store information, such as a unique serial number, and communicate with a reader.

Smart cards: See contact less smart cards.


Tag: See RFID Tag

Time Division Multiple Access (TDMA): A method of solving the problem of the signals of two readers colliding. Algorithms are used to make sure the readers attempt to read tags at different times.

Transponder: A radio transmitter-receiver that is activated when it receives a predetermined signal. RFID tags are sometimes referred to as transponders.


Ultra-high frequency (UHF): Typically, tags that operate between 866 MHz to 930 MHz. They can send information faster and farther than high- and low-frequency tags. But radio waves don't pass through items with high water content, such as fruit, at these frequencies. UHF tags are also more expensive than low-frequency tags, and they use more power.

Uniform Code Council (UCC): The nonprofit organization that overseas the Uniform Product Code, the barcode standard used in North America.

Uniform Product Code (UPC): The barcode standard used in North America. It is administered by the Uniform Code Council.


Write rate: The rate at which information is transferred to a tag, written into the tag's memory and verified as being correct.


XML: See eXtensible Markup Language.

XML Query Language (XQL): A method of querying a database based on XML. Files created using the Auto-ID Center's Physical Markup Language can be searched using XQL.