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GLOSSARY OF RFID TERMS
  If there is a term that should be in this glossary but isn't, please let us know by sending e-mail to editor@rfidjournal.com.
 
A - E F - L M - S T - Z
Glossary Results   A - E
 A
Accelerometer: A device that measures acceleration (the rate of change of velocity). An accelerometer inherently measures its own motion (locomotion), as opposed to a device based on remote sensing.
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.
Addressability: The ability to write data to different fields, or blocks of memory, in the microchip in an RFID transponder.
Agile reader: A generic term that usually 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.
Alignment: See Orientation.
American National Standards Institute: An American technical standards body and the representative of the United States to the International Organization for Standardization.
Amplitude: The maximum absolute value of a periodic curve measured along its vertical axis (the height of a wave, in layman's terms).
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.
Amplitude shift keying: Changing the amplitude of the wave to communicate data stored on a tag.

ANSI: See American National Standards Institute
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.
API: A source-code interface provided by a computer system or program library to support a computer program's requests for services. Unlike an application binary interface, an API is specified in terms of a programming language that can be compiled when an application is built, rather than an explicit low-level description of how data is laid out in memory.
Applet: A software component designed to run in the context of another program, such as a Web browser.
Application Programming Interface: A source-code interface provided by a computer system or program library to support a computer program's requests for services. Unlike an application binary interface, an API is specified in terms of a programming language that can be compiled when an application is built, rather than an explicit low-level description of how data is laid out in memory.
Application-Specific Integrated Circuit (ASIC): An integrated circuit (IC) customized for a particular use (such as a chip designed solely to run a cell phone) rather than general use.
Applicator: A label-printing device that automatically prints and applies pressure-sensitive labels to various products. Such labels can be used for shipping, content, graphic images or complying with specific standards, such as UPC or GS1. A pressure-sensitive label consists of a label substrate and an adhesive.
ASIC: An integrated circuit (IC) customized for a particular use (such as a chip designed solely to run a cell phone) rather than general use.
Asset Tracking: One of the most common applications for RFID. Placing RFID transponders on or in high-value assets and returnable transport containers enables companies to gather data on their location quickly and with little or no manual intervention. Tagging assets allows companies to increase asset utilization, identify the last known user of assets, automate maintenance routines and reduce lost items.
Association for Automatic Identification and Mobility: A global trade association for companies that provide products and services related to automatic identification, data collection, networking and information management systems.
Attenuation: The reduction of energy. See signal attenuation.
Attenuator: A device that attaches to a transmission line (a coaxial cable) that reduces the power of the RF signal as the signal travels through the cable from the reader to the antenna. Attenuators usually work by dissipating the RF energy into heat.

Authentication: The verification of the identity of a person, object or process. In RFID, the term is used in two ways. For contactless smart cards and other payments systems, the reader must make sure the transponder is a valid device within the system. That is, someone is not using an unauthorized device to commit fraud. There is also some talk of using EPC technology to authenticate products as a way of reducing counterfeiting.
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 carrying Electronic Product Codes. The center closed its doors in September 2003. EPCglobal was set up to continue the work of commercializing EPC technology, and the center's research work is carried on by Auto-ID Labs at universities around the world.
Auto-ID Labs: Nonprofit research labs, headquartered at the Massachusetts Institute of Technology, which continue to do primary research into the development of EPC and related technologies.
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.
Automatic identification and data capture: A broad term that covers methods of identifying objects, capturing information about them 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.
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 B
Back channel: See reverse channel.
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.
Bar code: A standard method of identifying the manufacturer and product category of a particular item. The bar code was adopted in the 1970s because the bars were easier for machines to read than optical characters. The main drawbacks of bar codes main are they don’t, in most cases, identify unique items and scanners have to have line of sight to read them.
Barrier: See Shielding
Base station: An RFID reader that is connected to a host system.

Battery-assisted tag: These are RFID tags with batteries, but they communicate using the same backscatter technique as passive tags (tags with no battery). They use the battery to run the circuitry on the microchip and sometimes an onboard sensor. They have a longer read range than a regular passive tag because all of the energy gathered from the reader can be reflected back to the reader. They are sometimes called "semi-passive RFID tags."
Beacon: An active or semi-active RFID tag that is programmed to wake up and broadcast its signal at a set intervals.
Biometrics: The study of methods to uniquely recognize and authenticate the identity of humans based upon one or more intrinsic physical or behavioral traits (fingerprints, retinal patterns and so forth). Biometric technology offers several advantages over traditional systems. Unlike passwords, biometric traits cannot be lost or forgotten, and are very difficult to copy, share or distribute. Biometric systems can be used in tandem with passwords or tokens, improving existing security systems rather than replacing them.
Bistatic: A bistatic RFID interrogator, or reader, uses one antenna to transmit RF energy to the RFID tag and a different antenna to receive energy reflected back from the tag.
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 C
Capacitor: An electric circuit element used to store a charge temporarily. A capacitor usually consists of two metallic plates separated and insulated from each other by a dielectric substance.
Card operating system: The software program stored in the smart card IC, which manages the basic functions of the card, such as communication with the terminal, security management and data management in the smart card file system.
Carrier frequency: A frequency used to transmit data.
Central processing unit: The brains of a computer, which controls all the other parts of the computer.
Checksum: A code added to the contents of a block of data stored on an RFID microchip that can be checked before and after data is transmitted from the tag to the reader to determine whether the data has been corrupted or lost. The cyclic redundancy check is one form of checksum.
Chip: A programmable digital electronic component (also called a microprocessor) designed to incorporate the functions of a central processing unit (CPU) onto a single semiconducting integrated circuit (IC). Multiple chips can serve as the CPU in a computer system, embedded system or handheld device.
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.
Circular-polarized antenna: A UHF reader antenna that emits radio waves in a circular pattern. These antennas are used in situations where the orientation of the tag to the reader cannot be controlled. Since the waves are moving in a circular pattern, they have a better chance of hitting the antenna, but circular-polarized antennas have a shorter read range than linear-polarized antennas.
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.

Cold Chain: A temperature-controlled supply chain for perishable goods such as foods and pharmaceuticals, as well as for some chemical applications. In the cold chain, storage and distribution activities must maintain a given temperature range to prevent product spoilage. Specific temperature tolerances vary, depending on the actual items being shipped.
Collaborative planning, forecasting and replenishment: A general term used to describe cooperation between manufacturers and retailers to better match supply of goods with demand for them.
Commissioning a tag: This term is sometime used to refer to the process of writing a serial number to a tag (or programming a tag) and associating that number with the product it is put on in a database.
Compatibility: Two RFID systems are considered compatible if they use the same protocols, frequencies and voltage levels and are able to operate together within the same overall application (see interoperability).
Compliance Label: A label that conforms with data content and format standards, usually established by an industry.

Compliance Labeling: Many industries, including the auto, technology and aerospace industries, have established label standards for products and goods moving through the supply chain. These standards specify the use of mandatory data fields, acceptable bar code symbologies, print quality minimums and environmental considerations. Compliance labeling standards ensure that everyone practices a similar labeling approach that clearly defines the label format, usage, and the information to include on the label. There are no compliance labeling standards yet for RFID, but some consider bar-code labels with embedded UHF EPC tags as compliance labels.
Concentrator: A device connected to several RFID readers to gather data from the readers. The concentrator usually performs some filtering and then passes only useful information from the readers on to a host computer.

Conducted Power: Conducted power is the RF power that is supplied by an RFID system to the antenna. Typically, it is calculated or measured at the cable to antenna connection. In the United States, Federal Communication Commission regulations require a maximum conducted power of 1 Watt.
Conductive Ink: A type of ink able to conduct a signal, usually containing powdered silver and carbon. With conductive ink, companies can draw or print circuits on a variety of materials. Conductive ink provides a cheap method for printing circuit boards on paper, for instance.
Conductor: A material, such as aluminum and copper, which readily conducts electricity. Conductors have a significant impact on the performance of RFID tags. Conductors near tags can reflect RF energy in a way that reduces tag performance, and they can also detune the tag.
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.

COS: See card operating system
Coupling: See inductive coupling.
CPFR: See collaborative planning, forecasting and replenishment
CPU: See central processing unit

CRC: See cyclic redundancy check

Cryptographic coprocessor: Special circuitry that perform cryptographic calculations, such as modular arithmetic and large integer calculations. These circuits are added to a standard processor core and therefore are called coprocessors.
Cyclic redundancy check: 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.)
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 D
Data carrier: A medium that holds machine-readable data. Bar codes and RFID tags are types of data carriers. The term is also applied to a carrier frequency used to transmit data.
Data field: An area of memory in 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. When the destination changes, the new information is written to the data field.
Data field protection: The ability to prevent data stored in a specific area of memory of an RFID microchip from being overwritten. Companies might want to protect the data field that stores an Electronic Product Code, which doesn't change during the life of the product it's associated with.
Data retention: The ability of a microchip to maintain the information stored in EEPROM. RFID tags and other microchips can typically retain data for 10 years or more, but data retention depends on temperature, humidity and other factors.
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.
dB: See decibel.
dBi: The gain of an antenna compared to an isotropic antenna—that is, an antenna that radiates energy equally in every direction. A typical dipole antenna has a dBi of 2.2 when compared to an isotropic antenna.
dBm: See decibel
dBw: Decibels (dB) referenced to 1.0 watt. Using the decibel formula: dB=10 log(P1/P2), P2 equals 1.0 watt and P1 is in units of watts.
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.
Dead tag: An RFID tag that cannot be read by an interrogator.
Decibel: A unit used to express the ratio between two values, including antenna gain, cable losses and reader power output. The formula for decibel is: dB=10 log (P1/P2). In layman’s terms, dB represents the difference in the intensity of an emitted signal or power where 0 dB is the reference, 3 dB is twice the intensity of 0 dB, 10 dB is 10 times the intensity, and 20 dB is 100 times the intensity and so on. (See also dBi, dBm and dBw.)
Die: The silicon block onto which circuits have been etched to create a microchip.
Dielectric: Unable to conduct direct electric current. Dielectric substances are used as insulators.
Dielectric constant: The measure of a material’s ability to store a charge when an electric field is applied, or its “capacitance.” If a material has a high dielectric constant, it reflects more RF energy and detunes the antenna more, which makes it harder to tag. Examples of materials with a low dielectric constant are dry paper (2), plastics (most are between 2 and 4), and glass (between 5 and 10). Water’s dielectric constant changes: At room temperature it is 80; near boiling it is 55; and when frozen it is 3.2.

Digital certificate: A digital message that contains the identity of an company or organization, its public key combined and a signature of this data from a certificate authority (Trust Center) proving the correctness of this data.
Digital signal processor: As special kind of microprocessor that converts changes in analog waves into digital information. DSPs are used in RFID readers.
Digital signature: A cryptographic protocol that ensures the authenticity as well as the integrity of digital data. A digital signature typically is realized by encrypting the hash value of the data to be protected with the private key.
Digital signature algorithm: A cryptographic algorithm approved by the United States government for use in creating digital signatures.
Dipole: An antenna made of two straight electrical conductors (poles). In an RFID transponder, these are connected to a microchip. The antenna is typically 1/2 wavelength from end to end.
DSP: See digital signal processor
Dual dipole: An antenna that has two dipoles. In an RFID transponder, these are attached to a chip. The dual dipole design greatly reduces the tag’s orientation sensitivity.
Dual interface smart card: A card that contains a microchip that can be read either when in content with a reader or remotely using radio waves.

Dumb reader: A generic term for a