Active tag: An RFID tag that has a transmitter to send back information, rather than reflecting back a signal from the reader, as a passive tag does. Most active tags use a battery to transmit a signal to a reader. However, some tags can gather energy from other sources. Active tags can be read from 300 feet (100 meters) or more, but they're expensive (typically more than US$20 each). They're used for tracking expensive items over long ranges. For instance, the U.S. military uses active tags to track containers of supplies arriving in ports.

Agile reader: A generic term that usual refers to an RFID reader that can read tags operating at different frequencies or using different methods of communication between the tags and readers.

Air interface protocol: The rules that govern how tags and readers communicate.

Amplitude modulation: . Changing the amplitude of a radio wave. A higher wave is interpreted as a 1 and a normal wave is interpreted as a zero. By changing the wave, the RFID tag can communicate a string of binary digits to the reader. Computers can interpret these digits as digital information. The method of changing the amplitude is known as amplitude shift keying, or ASK.

Antenna: The tag antenna is the conductive element that enables the tag to send and receive data. Passive, low- (135 kHz) and high-frequency (13.56 MHz) tags usually have a coiled antenna that couples with the coiled antenna of the reader to form a magnetic field. UHF tag antennas can be a variety of shapes. Readers also have antennas which are used to emit radio waves. The RF energy from the reader antenna is "harvested" by the antenna and used to power up the microchip, which then changes the electrical load on the antenna to reflect back its own signals.

Antenna gain: In technical terms, the gain is the ratio of the power required at the input of a loss-free reference antenna to the power supplied to the input of the given antenna to produce, in a given direction, the same field strength at the same distance. Antenna gain is usually expressed in decibels and the higher the gain the more powerful the energy output. Antennas with higher gain will be able to read tags from farther away.

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 pioneered the development of an Internet-like infrastructure for tracking goods globally through the use of RFID tags.

Automatic Identification: A broad term that covers 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.

Application Family Identifier (AFI): A feature of some RFID tags which enables separation of RFID tags by application, so that, for instance, a tag on a library item does not interfere with a system for handling baggage. Also used for security in some library RFID implementations.


Backscatter: A method of communication between passive tags (ones that do not use batteries to broadcast a signal) and readers. RFID tags using backscatter technology reflect back to the reader radio waves from a reader, usually at the same carrier frequency. The reflected signal is modulated to transmit data.


Carrier frequency: The main frequency of a transmitter, or RFID reader, such as 915 MHz. The frequency is then changed, or modulated, to transmit information.

Chipless RFID tag: An RFID tag that doesn't depend on a silicon microchip. Some chipless tags use plastic or conductive polymers instead of silicon-based microchips. Other chipless tags use 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. Chipless tags that use embedded fibers have one drawback for supply chain uses—only one tag can be read at a time.

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.

Cyclic redundancy check (CRC): A method of checking data stored on an RFID tag to be sure that it hasn't been corrupted or some of it lost. (See Checksum.)


Data transfer rate: The number of characters that can be transferred from an RFID tag to a reader within a given time. Baud rates are also used to quantify how fast readers can read the information on the RFID tag. This differs from read rate, which refers to how many tags can be read within a given period of time.

Data field: An area of memory on an RFID microchips that is assigned to a particular type of information. Data fields may be protected (see below) or they may be written over, so a data field might contain information about where an item should be sent to. When the destination changes, the new information is written to the data field.

De-tune: UHF antennas are tuned to receive RFID waves of a certain length from a reader, just as the tuner on the radio in a car changes the antenna to receive signals of different frequencies. When UHF antenna is close to metal or metallic material, the antenna can be detuned, resulting in poor performance.

Die: The silicon block onto which circuits have been etched to create a microchip.

Duty cycle: The length of time the reader can be emitting energy. Regulations in the European Union say readers can be on only 10 percent of the time.


Electrically Erasable Programmable Read-Only Memory (EEPROM) : A method of storing data on microchips. Usually bytes can be erased and reprogrammed individually. RFID tags that use EEPROM are more expensive than factory programmed tags, where the number is written into the silicon when the chip is made, 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 interferance (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 Product Code (EPC): A serial, created by the Auto-ID Center, that will complement barcodes. The EPC has digits to identify the manufacturer, product category and the individual item.

EPCglobal: A non-profit organization set up the Uniform Code Council and EAN International, the two organizations that maintain barcode standards, to commercialize EPC technology. EPCglobal is made up of chapters in different countries and regions. It is commercializing the technology origianally developed by the Auto-ID Center.

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.

Electronic Article Surveillance (EAS): The use of electronic systems to secure physical items. Several technologies are included, though the interesting technology used for EAS of relevance to this discussion is implemented using RFID tags.


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. This data can't be written over or chagned.

Far-field communication: RFID reader antennas emit electromagnetic radiation (radio waves). If an RFID tag is outside of one full wavelength of the reader, it is said to be in the "far field." If it is within one full wavelength away, it is said to be in the "near field." The far field signal decays as the square of the distance from the antenna, while the near field signal decays as the cube of distance from the antenna. So passive RFID systems that rely on far field communications (typically UHF and microwave systems) have a longer read range than those that use near field communications (typically low- and high-frequency systems).

Field programming: Tags that use EEPROM, or non-volatile memory, can be programmed after it is shipped from the factory. That is, users can write data to the tag when it is placed on a product.

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.

Frequency hopping: A technique used to prevent readers from interfering with one another. In the United States, UHF RFID readers actually operate between 902 and 928 MHz, even though it is said that they operate at 915 MHz. The readers may jump randomly or in a programmed sequence to any frequency between 902 MHz and 928 MHz. If the band is wide enough, the chances of two readers operating at exactly the same frequency is small. The UHF bands in Europe and Japan are much smaller so this technique is not effective for preventing reader interference.


High-frequency: From 3 MHz to 30 MHz. HF RFID tags typically operate at 13.56 MHz. They typically can be read from less than 3 feet away and transmit data faster than low-frequency tags. But they 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.

Inlay: An RFID microchip attached to an antenna and mounted on a substrate. Inlays are essentially unfinished RFID labels. They are usually sold to label converters who turn them into smart labels.

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

Integrated Library System (ILS): The system that a library uses to manage its collection, typically comprising a database and software to support functions such as circulation, collection management, acquisitions, patron account management, item searching, etc.


Linear-polarized antenna: A UHF antenna that focuses the radio energy from the reader in a narrow beam. This increases the read distance possible and provides greater penetration through dense materials. Tags designed to be used with a linear polarized reader antenna must be aligned with the reader antenna in order to be read.

Low-frequency: From 30 kHz to 300 kHz. Low-frequency tags typical operate at 125 kHz or 134 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 subject to interference than UHF tags.


Memory: The amount of data that can be stored on the microchip in an RFID tag.

Memory block: Memory on the microchip in an RFID tag is usually divided into sections, which can be read or written to individually. Some blocks might be locked, so data can't be overwritten, while others are not.

Modulation: Changing the radio waves traveling between the reader and the transponder in ways that enable the transmission of information. Waves be changed in a variety of ways that can be picked up by the reader and turned into the ones and zeroes of binary code. Waves can be made higher or lower (amplitude modulation) or shifted forward (phase modulation). The frequency can be varied (frequency modulation), or data can be contained in the duration of pulses (pulse-width modulation).

Multiplexer: An electronic device that allows a reader to have more than one antenna. Each antenna scans the field in a preset order. This reduces the number of readers needed to cover a given area, such as a dock door, and prevents the antennas from interfering with one another.


Near-field communication: RFID reader antennas emit electromagnetic radiation (radio waves). If an RFID tag is within full wavelength of the reader, it is said to be in the "near field." If it is more than the distance of one full wavelength away, it is said to be in the "far field." The near field signal decays as the cube of distance from the antenna, while the far field signal decays as the square of the distance from the antenna. So passive RFID systems that rely on near-field communication (typically low- and high-frequency systems) have a shorter read range than those that use far field communication (UHF and microwave systems).

Noise: Unwanted ambient electrical signals or electromagnetic energy found in the operating environment of RFID equipment. Noise can be caused by other RF devices, robots, electric motors and other machines.

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.

NISO Circulation Interchange Protocol ( NCIP ): ANSI/NISO Z39.83-2002. A communication protocol for interoperability among integrated library systems to support library operations: Interlibrary Loan, Direct Consortial Borrowing, and Self Service. The NCIP standard was approved by the National Information Standards Organization in 2002. The intent of this standard is to succeed SIP2.


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.

One-time programmable tag: Also called a field-programmable tag. An RFID tag that can be written to once and read many times (see WORM).

Orientation: The position of a tag antenna vis-a-vis a reader antenna. With UHF systems, readers can be either circular-polarized or linear-polarized. When using a linear polarized antenna, the tag reader and antenna reader must be in alignment in order to achieve the longest reading distance. If that tag antenna is aligned vertically and the reader is sending out signals horizontally, only a small portion of the energy emitted by the reader will will hit the tag antenna.

Object Identifiers (OID): It is a string of numbers that identifies an object.


Passive tag: An RFID tag without a battery. When radio waves from the reader reach the chip’s antenna, the energy is converted by the antenna into electricity that can power up the microchip in the tag. The tag is able to send back information stored on the chip. Today, simple passive tags cost from U.S. 20 cents to several dollars, depending on the amount of memory on the tag and other features.

Patch antenna: A small square reader 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. The idea is to create a computer language that companies can use to describe products so that computer can search for, say, all "softdrinks" in inventory.

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.

Protocol: A set of rules that govern communications systems. (See Air-interface protocol.)

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. They can be used in RFID systems to turn on readers.


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.

Read: The process of retrieving data stored on an RFID tag by sending radio waves to the tag and converting the waves the tag sends back into data.

Reader: A device used to communicate with RFID tags. The reader has one or more antennas, which emit radio waves and receive signals back from the tag. The reader is also sometimes called an interrogator because it "interrogates" the tag.

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.

Reader talks first: A means by which a passive UHF reader communicates with tags in its read field. The reader sends energy to the tags but the tags sit idle until the reader requests them to respond. The reader is able to find tags with specific serial numbers by asking all tags with a serial number that starts with either 1 or 0 to respond. If more than one responds, the reader might ask for all tags with a serial number that starts with 01 to respond, and then 010. This is called "walking" a binary tree, or "tree walking." (See Singulation.)

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 rate: Often used to describe the number of tags that can be read within a given period. The read rate can also mean the maximum rate at which data can be read from a tag expressed in bits or bytes per second. (See Data transfer rate.)

Read-write tag: an RFID tag that can store new information on its microchip. These tags are often used on reusable containers and other assets. When the contents of the container are changed, new information is written to the tag. Read-write tags are more expensive than read-only tags.

RFID tag: A microchip attached to an antenna that is packaged in a way that it can be applied to an object. The tag 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 can have a barcode printed on it, or the tag can simply be mounted inside a carton or embedded in plastic. RFID tags can be active, passive or semi-passive.


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 broadcast a signal to 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 can cost a dollar or more. These tags are sometimes called battery-assisted tags.

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.

Signal attenuation: The weakening of RF energy from an RFID tag or reader. Water absorbs UHF energy, causing signal attenuation.

Smart label: A generic term that usually refers to a barcode label that contains an RFID transponder. It's considered "smart" because it can store information, such as a unique serial number, and communicate with a reader.

Smart cards: See Contactless smart cards.

SAW (Surface Acoustic Wave): A technology used for automatic identification in which low power microwave radio frequency signals are converted to ultrasonic acoustic signals by a piezoelectric crystalline material in the transponder. Variations in the reflected signal can be used to provide a unique identity.

Synchronization: Timing readers or reader antennas near one another so that they don't interfere with one another.

SIP2: 3M™ Standard Interchange Protocol. A communication protocol that provides a standard interface between a library's integrated library system (ILS) and library automation devices (e.g., check-out devices, check-in devices, etc.). The protocol can be used by any application that has a need to retrieve information from an ILS or process circulation transactions via the ILS. There are two versions of SIP, version 1.0 and 2.0. SIP2 is based on a proprietary protocol, but has been opened for use by all parties providing systems for library circulation.


Tag talks first: A means by which a reader in a passive UHF system identifies tags in the field. When tags enter the reader's field, they immediately communicate their presence by reflecting back a signal. This is useful when you want to know everything that is passing a reader, such as when items are moving quickly on a conveyor. In other cases, the reader wants to simply find specific tags in a field, in which case it wants to broadcast a signal and have only certain tags respond. (See Reader talks first.)

Transceiver: A device that both transmits and receives radio waves.

Transponder: A radio transmitter-receiver that is activated when it receives a predetermined signal. RFID transponders come in many forms, including smart labels, simple tags, smart cards and keychain fobs. RFID tags are sometimes referred to as transponders.


Ultra-high frequency (UHF): From 300 MHz to 3 Ghz. Typically, RFID tags that operate between 866 MHz to 960 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.

Unique Identifier (UID): A serial number that identifies the transponder. The U.S. Department of Defense has also developed an identification scheme called UID.


WORM: Write once, read many. A tag that can be written to only once by the user. Thereafter, the tag can only be read.

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 searching a database based on the extensible markup language (XML). Files created using the Auto-ID Center’s Physical Markup Language can be searched using XQL.


Z39.50: Supporting information retrieval among different information systems