RFID Glossary of Terms

Acknowledge (AKA) 
Notation often used to denote the acknowledgement of a communication command within a wireless communication system.

Active Tag
Colloquial term for a radio frequency transponder powered partly or completely by a battery. Batteries may be replaceable or sealed within the device (when the term unitised active tag is sometimes used). Compare Passive Tag . Alternative term for Active Transponder.

Active Transponder
A battery-powered data-carrying device that reacts to a specific, reader produced, inductively coupled or radiated electromagnetic field , by delivering a data modulated radio frequency response.

Addressability
The ability to address bits, fields, pages, files or other defined areas of memory within a radio frequency tag.

AIDC
Automatic identification and data capture.

Air Interface
The conductor-free medium, usually air, between a transponder and the reader/interrogator through which data communication is achieved by means of a modulated inductive or propagated electromagnetic field.

AIM
Generic abbreviation for the non-commercial Automatic Identification Manufacturer Trade Association which covers all the AIDCtechnologies and features national chapters around the world.

Alignment
A term to express the orientation of a transponder, relative to the reader/interrogator antenna. Alignment can influence the degree of coupling between transponder and reader, separation being a further influence.

ALOHA
A multiple access technique used to facilitate the management of coincident signals or collisions within a communication system. Two variants offering different levels of through-put performance can be distinguished in addition to the basic ALOHA approach, namely slotted- ALOHA and slotted ALOHA with capture.

Alphanumeric
Strictly data comprising both alphabetical and numeric characters. For example, A1234C9 as an alphanumeric string. The term is often used to include other printable characters such as punctuation marks.

Amplitude Modulation (AM)
Representation of data or signal states by the amplitude of a fixed frequency sinusoidal carrier wave. Where data is in binary form the modulation involves two levels of amplitude and is referred to as Amplitude Shift Keying (ASK).

Amplitude Shift Keying (ASK)
Representation of binary data states, 0 and 1, by the amplitude of a fixed frequency sinusoidal carrier wave. Where the amplitudes are determined by the carrier being switched on and off, the process is known as On-Off Keying (OOK).

Antenna
A conductive structure specifically designed to couple or radiate electromagnetic energy . In a driven mode the structure is a transmitter antenna. In receiver mode the structure is a receiver antenna. Antenna structures, often encountered in radio frequency identification systems, may be used to both transmit and receive electromagnetic energy, particularly data modulated electromagnetic energy. See also dipole .

Anti-collision (Anti-contention)
A term describing a facility for avoiding contention at the reader/interrogator receiver for responses arising from transponders simultaneously present within the read or interrogation zone of a radio frequency identification system and competing for attention at the same time.

Application Identifier (AI)
A meta-data element used to define the meaning of the data that follows.

ASCII (American Standard Code for Information Interchange)
A binary code comprising 128 alphanumeric and control characters, each encoded with 7 bits.

ASN.1 (Abstract Syntax Notation1)
A syntax language for communicating processes, including transfer syntax or rules for converting variables, commands and requests into forms that are hardware independent.

Asynchronous Transmission (Start/stop transmission)
A method of data transmission that does not require timing or clocking information in addition to data. Transmission is achieved by receiver reference to start and stop bits positioned at the beginning and end of each character or blocks of characters. A variable time interval can exist between characters or blocks of characters. Compare Synchronous transmission .

Awake
The condition of a transponder when it is able to respond to interrogation .

Backscatter Modulation
A process whereby a transponder responds to a reader/interrogation signal or field by modulating and re-radiating or transmitting the response signal at the same carrier frequency.

Batch Reading
The process or capability of a radio frequency identification reader/interrogator to read a number of transponders present within the system’s interrogation zone at the same time. Alternative term for Multiple Reading.

Bandwidth
The range or band of frequencies, defined within the electromagnetic spectrum, that a system is capable of receiving or delivering.

Baud
A unit of signalling or transmission speed representing the number of signalling events per unit time. When the signal event is a single bit, binary state representation, the baud is equivalent to the bit rate, expressed in bits per second (bps). Compare Data Transfer Rate.

BCC (Block Check Character)
A parity error checking character added to data for the purposes of detecting transmission errors.

BER (Bit Error Rate)
The ratio of the number of bits received in error to the total of bits transmitted.

Bi-directional
A term used to describe the capability of two way communication.

Binary (Binary Number System)
A column-placing numbering system in which numbers are expressed as powers of 2 (.....23 22 21 20) using the digits, 0 and 1 to distinguish the weighting of powers to represent the number concerned. Eg 2510 = 0x25 1x24 1x23 0x22 0x21 1x20 = 011001

Binary Coded Decimal (BCD)
Representation of decimal numbers in binary form using a group of four bits to represent an individual digit (0-9). Eg. 0011 1000 = 3810

Bit
Abbreviation for binary digit. A single element (0,1) in a binary number.

Bit rate
Rate at which bits are electronically communicated, measured in bits.s-1

Bit Error Rate (BER)
The ratio of the number of bits received that are found to be in error to the total number of bits transmitted.

Bi-phase coding
A generic term for line or channel encoding schemes of the Manchester coding type in which each bit in the source code is replaced by two bits in the derived format.

Block Code
Error detection codes having a fixed length code format, wherein k message bits are accompanied by c parity bits to form an n-bit block code (n = k + c)

Byte
A group of bits, usually eight, used to represent characters in a binary processing system.

Capacity – Data
A measure of the data , expressed in bits or bytes, that can be stored in a transponder. The measure may relate simply to the bits that are accessible to the user or to the total assembly of bits, including data identifier and error control bits. Compare Capacity – Channel.

Capacity – Channel
A measure of the transmission capability of a communication channel expressed in bits.s-1 and related to channel bandwidth and signal to noise ratio by the Shannon equation; Capacity, C = B log 2 (1 + S/N), where B is the bandwidth and S/N the signal to noise ratio. Compare Capacity – Data

Capture Field / Area / Zone (also Interrogation Zone / Area / Volume)
The region of the electromagnetic field, determined by the reader/interrogator antenna, in which the transponders are signalled to deliver a response.

Carrier
Abbreviated term for Carrier Frequency .

Carrier Frequency
The frequency used to carry data by appropriate modulation of the carrier waveform, typically in a radio frequency identification system, by amplitude shift keying (ASK), frequency shift keying (FSK), phase shift keying (PSK) or associated variants. See also Tolerance .

CEPT (Conférence Européenne des Administrations des Postes et Télécommunications)
The body responsible for European standardisation and harmonisation of radio communications.

Channel
A medium or medium associated allocation, such as carrier frequency, for electronic communication.

Channel encoding
The application of coding schemes to facilitate effective channel transmission of the source encoded data. Compare Source encoding. See also Channel decoding.

Channel decoding
The process of operating upon a received transmission to separate the source-encoded data from the channel encoded form. Compare Source decoding. See also Channel encoding.

Character set
A set of characters assembled to satisfy a general or application requirement.

Checksum
A summation of check digits used to determine if an error has occurred in the transmission of data.

Chip
In data communication terms, the smallest duration of a pseudo-random code sequence used in spread spectrum communication systems.

Chip-based RFID
RFID systems using data carriers (transponders) containing silicon integrated circuits for achieving data storage and functionality.

Chipless RFID
RFID systems using data carriers (transponders) in which the data storage and functionality are achieved without using silicon integrated circuits.

Chipping
The process of moving from one chip to another in a spread spectrum transmission process, each chip being representative of a different spectral component or tone in the spread spectrum band. See also Frequency Hopping Spread Spectrum.

Clocking information
Timing signals or pulses used to synchronise the transfer of data from a source to a host destination.

Closed Systems
Within the context of radio frequency identification, they are systems in which data handling, including capture, storage, and communication are under the control of the organisation to which the system belongs. Compare with Open Systems.

Code Plate
An alternative colloquial term for transponder or tag .

Collision
A term to denote an event in which two or more data communication sources compete for attention at the same time and cause a clash of data, inseparable without some means of anti-collision or contention management.

Collision avoidance
A means of avoiding collisions or clashes of data from different sources competing for attention at the same time. See also Anti-clash (Anti-contention)

Compatibility
The condition that exists between devices or systems that exhibit equivalent functionality, interface features and performance to allow one to be exchanged for another, without alteration, and achieve the same operational service. An alternative term for Interchangeability. Compare Interoperability .

Concatenation
The facility to link together specific items of data, held in data carriers, to form a single file or field of data.

Continuous reporting
A mode of reader/interrogator operation wherein the identification of a transponder is reported or communicated continuously while the transponder remains within the interrogation field. See also In-field Reporting.

Continuous Wave Modulation (CW)
A data modulation scheme in which the data is represented by the carrier signal being switched on and off. The scheme is identical to amplitude shift keying (ASK) with 100% depth of modulation – known as on-off keying (OOK).

Control Characters
Characters within a character set which are used to denote a particular control function, such as new line, shift and print control.

Concentrator
A means of connecting a number of data communication devices and concentrating packets of data at a local point before onward transmission on a single link to a central data processor or information management system. In contrast to multiplexors concentrators usually have a buffering capability to ‘queue’ inputs that would otherwise exceed transmission capacity. See also Multiplexor .

Contention (Clash)
Term denoting simultaneous transponder responses capable of causing potential confusion, and misreading, within a reader/interrogator system unequipped with anti-contention facilities.

Corruption – data
In data terms, the manifestations of errors within a transmitted data stream due to noise, interference or distortion.

Cyclic Redundancy Check (CRC)
An error detection algorithm which exploits the attributes of modulo-2 arithmetic to generate, through the use of a generator polynomial, a transmission polynomial, comprising the message polynomial and a parity polynomial.

Data
Representations, in the form of numbers and characters for example, to which meaning may be ascribed. Compare with Information .

Data Capacity
See Capacity – Data

Data Carrier
A machine-readable device, symbol or structure designed and used to carry data on or with an item for the purposes of identification and/or item management. See also Item.

Data error rate
See Bit Error Rate

Data Rate (Data Transfer Rate)
In a radio frequency identification system, the rate at which data is communicated between transponder and the reader/interrogator , expressed in baud, bits.s-1 or bytes.s-1

Data Field
A defined area of memory assigned to a particular item or items of data.

Data Field Protection
The facility to control access to and operations upon items or fields of data stored within the transponder .

Data Identifier
A specific character, or string of characters, that denotes the nature or intended use of the data that follows.

Data transfer
The process of transferring data a data holding source to a destination.

Data Transfer Rate
See DataRate.

Decibel (dB)
A dimensionless measure of the relative power of two sources (P1 and P2) or a single source at different points, expressed on a logarithmic scale such that number of dB = 10 log 10 [P1/P2]. If voltage or current (or corresponding field-strength) values are used the number of dB = 20 log 10 [A1/B2], where A1/B2 denotes the corresponding voltage or current ratio.

Demodulation
Process of recovering channel encoded data from a modulated carrier waveform. Compare Modulation.

De-tuning
The reduction in performance of transponders and readers/interrogators caused by the close proximity of metal influencing the resonance of an electronic tuned circuit.

Dipole (antenna)
A fundamental form of antenna, comprising a single conductor of length approximately equal to half the wavelength of the carrier wave. Provides the basis for a range of other more complex forms of antenna.

Directivity – antenna
The ability of an antenna to concentrate radiated energy in a preferred direction, when considered in a transmitter mode. Alternatively, the ability to reject signals that are off-axis to the normal of the antenna, when considered in the receiver mode. May be expressed as a ratio of power radiated per unit solid angle in a defined direction to the total power radiated by the antenna. See also Efficiency – antenna.

Direct Sequence Spread Spectrum (DSSS)
A category of spread spectrum modulation in which the source base-band bit stream is multiplied by a fast pseudorandom binary sequence to produce a signal that exhibits broad-band characteristics. Alternatively, the pseudorandom sequence and its inverse are used to represent logic 1 and 0. See also Frequency Hopping Spread Spectrum

Dispersion – pulse
The spread in duration and form experienced by a pulse in transmission through a communication channel. See also Intersymbol Interference.

Distortion
Any disturbance that causes an unwarranted change in the form or intelligibility of a signal. The distortion exhibits a noise-like effect that can be quantified as the ratio of the magnitude of the distortion component to the magnitude of the undistorted signal, usually expressed as a percentage. See also Signal to Noise Ratio and Signal to Noise and Distortion Ratio.

Downlink
Term which defines the direction of communications as being from reader/interrogator to transponder . Alternative term for Forward Link. Compare Uplink .

Effective Aperture
A term denoting the reception capability of a practical antenna expressed as the product of actual aperture and antenna efficiency. See ‘Propagation’ summary box.

Effective Radiated Power (ERP)
A measure of the power of a radiating signal delivered from a defined antenna, expressed as the product of the power delivered to the antenna and the antenna gain relative to a half-wavelength dipole. ERP = EIRP + 2.15dB.

Effective Isotropic Radiated Power (EIRP)
The product of the input power to an antenna and the gain relative to an isotropic source.

Efficiency – antenna
Two components distinguishable, radiation efficiency and aperture efficiency. Radiation efficiency is expressed as the ratio of total power radiated by the antenna to total power accepted by the antenna from source – for the transmission mode. Aperture efficiency is expressed as the ratio of effective antenna area to the real area of the antenna.

Electromagnetic Coupling
A process of transferring modulated data or energy from one system component to another, reader to transponder for example, by means of an electromagnetic field.

Electromagnetic energy
The energy conveyed in an electromagnetic field or wave, wherein the power (energy per unit time) is expressed as the vector product of the magnetic and electric field strengths.

Electromagnetic Field
The spatial and temporal manifestation of an electromagnetic source in which magnetic and electric components of intensity can be distinguished and plotted as contours, like contour lines on a map, the planes of the electric and magnetic contours being at right angles to one another. Where the source is varying in time so too the field components vary with time. Where the source launches an electromagnetic wave the field may be considered to be propagating. See also ‘Electromagnetic Wave’ summary box.

Electromagnetic spectrum
The range or continuum of electromagnetic radiation, characterised in terms of frequency or wavelength.

Electromagnetic wave
A sinusoidal wave in which electric E and magnetic H components or vectors can be distinguished at right angles to one another, and propagating in a direction that is at right angles to both the E and H vectors. The energy contained within the wave also propagates in the direction at right angles to the E and H vectors. The power delivered in the wave is the vector product of E and H (Poynting Vector).

Electronic Data Interchange (EDI)
Communication of a data message, or messages, automatically between computers or information management systems, usually for the purposes of business transactions.

Electronic Data Transfer (EDT)
The transfer of data by electronic communication means from one data handling system to another.

Electronic Label
An alternative colloquial term for a transponder.

Electronic Product Code (EPC)
An item numbering and networking concept arising from research undertaken at the Massachusetts Institute of Technology (MIT) Auto- ID Center, and associated centres, for the unique identification of individual items. The concept has been extended to also allow identification of type of items.

Encryption of data
A means of securing data, often applied to a plain or clear text, by converting it to a form that is unintelligible in the absence of an appropriate decryption key. See also Scrambling .

Environmental Parameters
Parameters, such as temperature, pressure, humidity, noise that can have a bearing or impact upon system performance.

Error
In digital data terms, a result of capture, storage, processing or communication of data in which a bit or bits assume the wrong values, or bits are missing from a data stream.

Error burst
A group of bits in which two successive erroneous bits are always separated by less than a given number of correct bits.

Error control
Collective term to accommodate error detection and correction schemes applied to handle errors arising within a data capture or handling system. See also Redundancy .

Error detection
A term to denote a scheme or action to determine the presence of errors in a data stream.

Error correction
A term to denote a scheme or action for correcting an error detected in a data stream.

Error correcting code (ECC)
Supplemental bits introduced or source encoded into a data stream to allow automatic correction of erroneous bits and/or derivation of missing bits, in accordance with a specific computational algorithm.

Error correcting mode
Mode defined for a data communication or handling process in which missing or erroneous bits are automatically corrected.

Error correcting protocol
The rules by which an error correcting mode operates.

Error management
Techniques used to identify and / or correct errors within a data capture and handling system with the objective of assuring the accuracy of data presented to the system user.

Error rate
See Bit Error Rate.

ETSI (European Telecommunications Standards Institute)
The European standards organisation responsible for standardisation in telecommunications.

Exciter
The electronic circuits used to drive an antenna. The combination of exciter and antenna is often referred to as the transmitter or scanner.

Extended Binary Coded Data Interchange Code (EBCDIC)
An eight-bit binary code set, sometimes referred to as extended ASCII, wherein the 128 character set of ASCII are accommodated, together with other characters and control functions, making up a total set of 256 characters.

Factory Programming 
The entering of data into a transponder as part of the manufacturing process, resulting in a read-only tag. Compare Field Programming.

False Activation
The result of a ‘foreign’ or non-assigned transponder entering the interrogation zone of a radio frequency identification system and effecting a response, erroneous or otherwise.

Far Field
The region of an electromagnetic radiation field at a distance from the antenna in which the field distribution is unaffected by the antenna structure and the wave propagates as a plane wave. Compare Near Field.

Field of View
The zone surrounding a reader/interrogator in which the reader/interrogator is capable of communicating with a transponder.

Field Programming
Entry of data by an original equipment manufacturer (OEM) or user into a transponder by means of a proprietary programming system, usually undertaken before the device is attached to the item to be identified or accompanied. This facility is usually associated with ‘Write Once Read Many’ (WORM) and read/write (RW) devices.
The data entered into a transponder may be by a combination of factory and field programming. Compare In-use Programming.

Field Protection
See Data Field Protection.

Field strength
The intensity of a field measured in units appropriate to the field concerned. Electric field strengths are measured in volts per metre (V.m-1) and magnetic field strengths in amperes per metre (A.m-1).

File
A set of data stored within a computer, portable data terminal or information management system.

Filler Character
A redundant character inserted into a data field simply to achieve a desired field length. Also known as a pad character.

Forward Link
Communications from reader/interrogator to transponder . Alternatively known as Downlink. Compare Uplink.

Frequency
The number of cycles a periodic signal executes in unit time. Usually expressed in Hertz (cycles per second) or appropriate weighted units such as kilohertz (kHz), Megahertz (MHz) and Gigahertz (GHz).

Frequency Hop Rate
The frequency at which a frequency hopping spread spectrum (FHSS) system moves between transmission frequencies. It is equal to the reciprocal of the dwell time at a FHSS centre frequency.

Frequency Hop Sequence
A pseudorandom binary sequence (PRBS) determining the hopping frequencies used in frequency hopping spread spectrum (FHSS) systems.

Frequency Hopping Spread Spectrum (FHSS)
A category of spread spectrum modulation in which each bit of data is divided into chips and each chip is represented by a different spectral component or tone in the spread spectrum band using a pseudorandom sequence to assign tones. Modulated in this way the transmissions hop from frequency to frequency within the band, requiring a receiver synchronised to the pseudorandom chipping sequence to recover the data. See also Direct Sequence Spread Spectrum.

Frequency Modulation (FM)
Representation of data or signal states by using different transmission frequencies. Where data is in binary form the modulation constitutes two transmission frequencies and is referred to as Frequency Shift Keying (FSK).

Frequency Shift Keying (FSK)
Representation of binary data by switching between two different transmission frequencies.

Full Duplex (FDX)
A channel communications protocol that allows a channel to transmit data in both directions at the same time. Compare Half Duplex.

Handshaking
A protocol or sequence of signals for controlling the flow of data between devices, which can be hardware implemented or software implemented.

Half Duplex (HDX)
A channel communications protocol that allows a channel to transmit data in both directions but not at the same time. Compare Full Duplex.

Harmonics
Multiples of a principal frequency, invariably exhibiting lower amplitudes. Harmonics can be generated as a result of circuit non-linearities associated with radio transmissions resulting in harmonic distortion. See also Spurious emissions.

Hexadecimal (Hex)
A column placing method of representing data to the base of 16, using digits 0-9 and letters A to F for decimal values 10 to 15. For example, 1010 = A16 and 2210 = 6F16 Used as a convenient shorthand notation for representing 16 and 32 bit memory addresses.

ID Filter
A software facility that compares a newly read identification (ID) with those within a database or set, with a view to establishing a match.

Impact
Any influence upon a system, environmental or otherwise, that can influence its operational performance.

Incorrect Read
The failure to read correctly all or part of the data set intended to be retrieved from a transponder during read or interrogation process. Alternative term for Misread.

In-Field Reporting
A mode of operation in which a reader/interrogator reports a transponder ID on entering the interrogation zone and then refrains from any further reports until a prescribed interval of time has elapsed. See also Out of Field Reporting.

In-Use Programming
The ability to read from and write to a transponder while it is attached to the object or item for which it is being used. Compare Factory Programming, Field Programming.

Inductive coupling
A process of transferring modulated data or energy from one system component to another, reader to transponder for example, by means of a varying magnetic field.

Information – general
Something which is meaningful. Data may be regarded as information once its meaning is revealed.

Information – theoretic
A measure of the scarcity or probability of occurrence of an event. The more scarce the event the more information conveyed.

Interface
A physical or electrical interconnection between communicating devices. See also RS232, RS422 and RS485.

Interference
Unwanted electromagnetic signals, where encountered within the environment of a radio frequency identification system, cause disturbance in its normal operation, possibly resulting in bit errors, and degrading system performance.

Interchangeability
The condition that exists between devices or systems that exhibit equivalent functionality, interface features and performance to allow one to be exchanged for another, without alteration, and achieve the same operational service. An alternative term for compatibility. Compare Interoperability.

Interoperability
The ability of systems, from different vendors, to execute bi-directional data exchange functions, in a manner that allows them to operate effectively together. Compare Compatability, Interchangeability.

Interrogation
The process of communicating with and reading a transponder.

Interrogator
A fixed or mobile data capture and identification device using a radio frequency electromagnetic field to stimulate and effect a modulated data response from a transponder or group of transponders present in the interrogation zone. Often used as an alternative term to Reader. See also Reader.

Interrogation zone
The region in which a transponder or group of transponders can be effectively read by an associated radio frequency identification reader/interrogator.

Inter-symbol Interference
Interference arising within a serial bit stream as a result of pulse dispersion and consequential overlapping pulse edges, leading possibly to decoding errors at the receiver.

Isotropic source
An ideal electromagnetic source or radiator exhibiting a perfect spherical energy radiation pattern.

Item
As used in the context of data carriers the term denotes any entity to which a data carrier is attached or associated, ranging from physical structures such as materials, components, products, containers, carriers and so forth, to locations, animals and people.

Lifetime
The period of time during which an item of equipment exists and functions according to specification. See also Mean time between failures and Mean Time to Repair.

Manchester coding  
A bi-phase code format in which each bit in the source encoded form is represented by two bits in the derived or channel encoded form. The transformation rule ascribes 01 to represent 0 and 10 to represent 1.

Manufacturers Tag ID (MfrTagID)
A reference number which uniquely identifies the tag.

Mean time between failures (MTBF)
The average or mean time interval between failures, often expressed as the reciprocal of the constant failure rate.

Mean time to repair
The length of time that a system is non-operational between failure and repair.

Memory
A means of storing data in electronic form. A variety of random access (RAM), read-only (ROM), write once-read many (WORM) and read/write (RW) memory devices can be distinguished.

Memory Modules
Colloquial term for a read/write or re-programmable transponder.

Misread
A condition that exists when the data retrieved by the reader/interrogator is different from the corresponding data within the transponder. Alternative term for Incorrect Read. See Incorrect Read.

Modulation
A term to denote the process of superimposing (modulating) channel encoded data or signals onto a radio frequency carrier to enable the data to be effectively coupled or propagated across an air interface. Also used as a associative term for methods used to modulate carrier waves. Methods generally rely on the variation of key parameter values of amplitude, frequency or phase. Digital modulation methods principally feature amplitude shift keying (ASK), frequency shift keying (FSK), phase shift keying (PSK) or variants.
See also Amplitude, Frequency and Phase Modulation, Amplitude Shift Keying, Frequency Shift Keying and Phase Shift Keying.

Modulation Index
The size of variation of the modulation parameter (amplitude, frequency or phase) exhibited in the modulation waveform.

Multiple Reading
The process or capability of a radio frequency identification reader/interrogator to read a number of transponders present within the system’s interrogation zone at the same time. Alternative term for Batch Reading.

Multiplexor (Multiplexer)
A device for connecting a number of data communication channels and combining the separate channel signals into one composite stream for onward transmission through a single link to a central data processor or information management system. At its destination the multiplexed stream is de-multiplexed to separate the constituent signals. Multiplexors are similar to concentrators in many respects, a distinction being that concentrators usually have a buffering capability to ‘queue’ inputs that would otherwise exceed transmission capacity.
See also Concentrator.

Near field
The region of an electromagnetic field comprising two components, the reactive Rayleigh region immediately surrounding the antenna and a radiating near field or Fresnel component which exists when the major dimension of the antenna, D, is large compared with the wavelength, l, of transmission.

Noise
Unwanted extraneous electromagnetic signals encountered within the environment, usually exhibiting random or wide band characteristics, and viewed as a possible source of errors through influence upon system performance.
Compare Interference.

Noise immunity
A measure of the extent or capability of a system to operate effectively in the presence of noise.

Omnidirectional
A description of a transponder’s ability to be read in any orientation.

On-off Keying (OOK)
A special case of amplitude shift keying (ASK) in which the carrier is switched between full carrier amplitude and zero or absence of carrier amplitude, according to data value (1 or 0).

Open Systems
Within the context of radio frequency identification, they are systems in which data handling, including capture, storage and communication, is determined by agreed standards, so allowing various and different users to operate without reference to a central control facility.
Compare with Closed System.

Orientation
The attitude of a transponder with respect to the antenna, expressed in three dimensional angular terms, with range of variation expressed in terms of skew, pitch and roll.

Orientation Sensitivity
The sensitivity of response for a transponder expressed as a function of angular variation or orientation.

Out of Field Reporting
A mode of operation in which the identification of a transponder is reported as or once the transponder leaves the reader interrogation zone.

Parity
A simple error detecting technique, used to detect data transmission errors, in which an extra bit (0 or 1) is added to each binary represented character to achieve an even number of 1bits (even parity) or an odd number of 1bits (odd parity). By checking the parity of the characters received single errors can be detected. The same principle can be applied to blocks of binary data.

Passive Transponder (Tag)
A battery-free data carrying device that reacts to a specific, reader produced, inductively coupled or radiated electromagnetic field, by delivering a data modulated radio frequency response. Having no internal power source, passive transponders derive the power they require to respond from the reader/interrogator’s electromagnetic field.
Compare Active Transponders (Tags).

Penetration
Term used to indicate the ability of electromagnetic waves to propagate into or through materials. Non-conducting materials are essentially transparent to electromagnetic waves, but absorption mechanisms, particularly at higher frequencies, reduce the amount of energy propagating through the material. Metals constitute good reflectors for freely propagating electromagnetic waves, with very little of an incident wave being able to propagate into the metal surface.

Phase Modulation (PM)
Representation of data or signal states by the phase of a fixed frequency sinusoidal carrier wave. Where data is in binary form the modulation involves a phase difference of 180o between the binary states and is referred to as Phase Shift Keying (PSK).

Phase Shift Keying (PSK)
Representation of binary data states, 0 and 1, by the phase of a fixed frequency s inusoidal carrier wave, a difference of 180O being used to represent the respective values.

Polar Field Diagram
A graphical representation of the electric or magnetic field intensity components of an electromagnetic field, expressed on a polar co-ordinate system (distance v angle, through 360O). Typically used to illustrate the field characteristics of an antenna.

Polarisation
The locus or path described by the electric field vector of an electromagnetic wave, with respect to time.
See Polarisation summary.

Port Concentrator
A device that accepts the outputs from a number of data communication interfaces for onward transmission into a communications network.
See also Concentrator, Multiplexor.

Power – levels and flux density
The vector product of electric and magnetic field strengths within an electromagnetic wave, expressed as levels in watts and as a power flux density, measured at a distance from the source, in watts per square metre (W.m-2). Low power radio frequency transmissions are generally expressed in milli- or microwatts.
It is usual to express the levels and flux densities in terms of decibels, whereby the power level is referenced to an appropriate level, such as a watt or a milliwatt. Using this approach levels are distinguished in dBW (reference to 1 watt) and dBm (referenced to 1mW) and power flux densities in terms of dBW.m-2.

Note: Power level (dB) = 10 log10 Pr / Pref
where Pr is the measured power and Pref the reference power level.

Programmability
The ability to enter data and to change data stored in a transponder.

Programmer
An electronic device for entering or changing (programming) data in a transponder, usually via a close proximity, inductively coupled data transfer link.

Programming
The act of entering or changing data stored in a transponder.

Projected lifetime
The estimated lifetime for a transponder often expressed in terms of read and / or write cycles or, for active transponders, years, based upon battery life expectancy and, as appropriate, read/ write activity.

Protocol
A set of rules governing a particular function, such as the flow of data/information in a communication system.

Proximity
Term often used to indicate closeness of one system component with respect to another, such as that of a transponder with respect to a reader.

Proximity sensor
An electronic device that detects and signals the presence of a selected object. When used in association with a radio frequency identification system the sensor is set up to sense the presence of a tagged or transponder -carrying object when it enters the vicinity of the reader/interrogator so that the reader can then be activated to effect a read.

Pulse dispersion
The spread in width or duration of a pulse during transmission through a practical transmission system, due to the influence of distributed reactive components.

Radio Frequency Identification (RFID) system
An automatic identification and data capture system comprising one or more reader/interrogators and one or more transponders in which data transfer is achieved by means of suitably modulated inductive or radiating electromagnetic carriers.

Radio Frequency Tag
Alternative term for a transponder.
See also RF Tag.

Range – Read
The maximum distance between the antenna of a reader/interrogator and a transponder over which the read function can be effectively performed. The distance will be influenced by orientation and angle with respect to the antenna, and possibly by environmental conditions.

Range – Programming
The maximum distance between the antenna of a reader/interrogator and a transponder over which a programming function can be effectively performed. Usually shorter than the read range, but may be influenced by orientation and angle with respect to the antenna, and possibly by environmental conditions.

Read
The process of retrieving data from a transponder and, as appropriate, the contention and error control management, and channel and source decoding required to recover and communicate the data entered at source.

Readability
The ability to retrieve data under specified conditions.

Reader / Interrogator
An electronic device for performing the process of retrieving data from a transponder and, as appropriate, the contention and error control management, and channel and source decoding required to recover and communicate the data entered at source.
The device may also interface with an integral display and/or provide a parallel or serial communications interface to a host computer or industrial controller.

Read/Write
A term to denote the capability to perform both read and programming functions, usually on a transponder attached to an object to be identified.

Read Only
Term applied to a transponder in which the data is stored in an unchangeable manner and can therefore only be read.
See also Factory Programming.

Read Rate
The maximum rate at which data can be communicated between transponder and reader/interrogator, usually expressed in bits per second (bps or bits.s-1).

Read / Write
Applied to a radio frequency identification system, it is the ability both to read data from a transponder and to change data (write process) using a suitable programming device.

Redundancy
In information terms it is a term to describe the additional bits, such as those for error control or repeated data, over and above those required for transmitting the information message.

RFID
Radio Frequency Identification

RFID Inlet
A fully functional passive RFID transponder suitable for incorporation into a structural holding or device form, typically a flexible label-like structure in which the inlet is sandwiched between two label-forming layers to form what is often termed a smart label.

Reprogrammability
The ability to change the data content of a transponder using a suitable programming device.
See also I n-use Programming.

RF Tag
Alternative, shorthand term for a transponder.

RS232
A common physical interface standard specified by the EIA for the interconnection of devices. The standard allows for a single device to be connected (point-to-point) at baud values up to 9600 bps, at distances up to 15 metres. More recent implementations of the standard may allow higher baud values and greater distances.

RS422
A balanced interface standard similar to RS232, but using differential voltages across twisted pair cables. Exhibits greater noise immunity than RS232 and can be used to connect single or multiple devices to a master unit, at distances up to 3000 metres.

RS485
An enhanced version of RS422, which permits multiple devices (typically 32) to be attached to a two wire bus at distances of over one kilometre.

SAW (Surface Acoustic Wave) devices
Devices using a transponder technology in which low power microwave signals are converted to ultrasonic waves by and on the surface of a piezoelectric crystal material forming the tag. Surface applied ‘finger’ transducers determine the form and data content of the reflected return signal.

Scrambling
The rearrangement or transposition of data to enhance security of stored data or the effectiveness of error control schemes.

Scanner
The combination of antenna, transmitter (or exciter), and receiver into a single unit is often referred to as a scanner. With the addition of electronics to perform the necessary decoding and management functions to deliver the source data, the unit becomes a reader.

Screening
The process of avoiding or minimising electromagnetic interference by use of electromagnetic reflective and absorptive materials, suitably structured or positioned to reduce interaction between the source of potential interference and the circuit being protected.

Sensor
An electronic device that senses a physical entity and delivers an electronic signal that can be used for control purposes.

Separation
A term used to denote the operational distance between two transponders.

Signal to Noise (S/N)
The ratio of signal level to the level of noise present in a system, usually expressed in decibels.

Signal to Noise & Distortion (SINAD)
The ratio of combined signal, noise and distortion levels to the combined level of noise and distortion present in a system.

Sinusoidal carrier
A fundamental waveform, characterised by a single frequency and wavelength, used to carry data or information by modulating some feature of the waveform.
See also Modulation.

Smart Label
A passive RFID data carrier structured into a flexible label-like form that allows over-printing with text, graphics or data carrier symbols such as linear bar codes, multi-row bar codes or matrix code symbols. Alternatively, it is used to describe a passive chip or chipless RFID devices that are used to emulate and extend a printed label function.

Source Decoding
The process of recovering the original or source data from a received source encoded bit stream.
Compare Source Encoding.
See also Data Flow Model.

Source Encoding
The process of operating upon original or source data to produce an encoded message for transmission.
Compare Source Decoding.
See also Data Flow Model.

Spectrum – electromagnetic
The continuum of electromagnetic waves, distinguished by frequency components and bands that exhibit particular features or have been used for particular applications, including radio, microwave, ultraviolet, visual, infrared, X-rays and gamma rays.

Spectrum-signal
Expression used to denote the make-up of a signal or waveform in terms of sinusoidal components of different frequency and phase relationship (spectral components).

Spectrum Mask
The maximum power density of a transmission expressed as a function of frequency.

Spurious Emissions
Usually denotes unwanted electromagnetic harmonics. Type Approval testing includes measurement of harmonic emissions arising from the reader, to ensure they are within specified limits.

Spread Spectrum
Techniques for uniformly distributing or spreading the information content of a data carrying signal over a frequency range considerably larger than required for narrow band communication, allowing data to be recoverable under conditions of strong interference and noise.

Synchronisation
The process of controlling the transmission of data using a separate or derived clocking signal.

Synchronous transmission
A method of data transmission that requires timing or clocking information in addition to data.

Tag  
Colloquial term for a transponder. Commonly used and the term preferred by AIM for general usage.

Tolerance
The maximum permissible deviation of a system parameter value, caused by any system or environmental influence or impact. Usually expressed in parts per million (ppm).
Tolerances are specified for a number of radio frequency parameters, including carrier frequencies, sub-carriers, bit clocks and symbol clocks.

Transmitter (Exciter)
An electronic device for launching an electromagnetic wave or delivering an electromagnetic field for the purpose of transmitting or communicating energy or modulated data/information. Often considered separately from the antenna, as the means whereby the antenna is energised. In this respect it is also referred to as an exciter.

Transponder
An electronic TRANSmitter / resPONDER, commonly referred to as a Tag.

Unitised active tag
An active tag or transponder in which the batteries are replaceable or sealed within the device.

Uplink
Term which defines the direction of communications as being from transponder to reader/interrogator.
Compare Downlink.

Vector
A quantitative component that exhibits magnitude, direction and sense.

Verification
The process of assuring that an intended operation has been performed.

Write
The process of transferring data to a transponder, the internal actions of storing the data, which may also encompass the reading of data to verify the data content.

Write Rate
The rate at which data is transferred to a transponder and stored within the memory of the device and verified. The rate is usually expressed as the average number of bits or bytes per second over which the complete transfer is performed.

Write Once Read Many (WORM)
Distinguishing a transponder that can be part or totally programmed once by the user, and thereafter only read.