RFID Glossary (A-Z)

This glossary collects the terms you will meet in RFID data sheets, tenders, standards and project meetings. Entries are grouped alphabetically. Where a term is covered in depth elsewhere in the Academy, it links to that chapter. For the bigger picture, start with What is RFID?.

A

Absorption - Loss of RF energy as it passes through a material. Water and water-rich materials (liquids, food, the human body) absorb UHF energy strongly, which reduces read range for tags on or behind them.

Access password - A 32-bit password stored in the Reserved memory bank of a Gen2 tag. A reader must supply it before it can perform protected operations such as writing to locked memory.

Active tag - A tag with its own battery that powers both the chip and a built-in transmitter, so it can broadcast its own signal over tens to hundreds of metres. Used for vehicle tracking, yard management and RTLS. Compare passive tag and BAP. See Types of RFID Tags.

AFI (Application Family Identifier) - A byte in ISO 15693 and ISO 14443 Type B tags that indicates the application area, letting a reader address only tags belonging to a particular family.

Air interface - The rules for how a reader and tag talk over the radio link: frequency, modulation, encoding, timing and command set. EPC Gen2 and ISO 14443 are air interface protocols.

ALE (Application Level Events) - A GS1/EPCglobal standard interface that sits between readers and business applications. It lets software ask for filtered, grouped reports ("which unique EPCs passed dock door 3 in the last 10 seconds") instead of raw read streams.

Anti-collision - The method a reader uses to read many tags in the same field without their replies interfering. Gen2 uses a slotted random algorithm controlled by the Q parameter; HF protocols use binary tree or time-slot methods.

Anti-metal tag - See on-metal tag.

Antenna - The conductor that radiates or receives RF energy. Readers use external or built-in antennas; every tag has its own antenna (a coil at LF/HF, usually a dipole-like pattern at UHF).

Antenna gain - How strongly an antenna concentrates energy in one direction compared with a reference antenna, expressed in dBi (isotropic), dBic (isotropic, circular polarisation) or dBd (dipole). Higher gain means a narrower, longer beam, not more total power.

ASK (Amplitude Shift Keying) - A modulation method in which data is sent by varying the amplitude of the carrier. Gen2 readers use forms of ASK (DSB-ASK, SSB-ASK) or PR-ASK on the forward link.

B

Backscatter - The way passive UHF tags reply: the chip switches the impedance of its antenna, changing how much of the reader's carrier it reflects. The reader detects these tiny changes as data. See How RFID Works.

BAP (Battery-Assisted Passive) - A tag with a battery that powers the chip (and often a sensor) but still replies by backscatter rather than by its own transmitter. BAP tags are more sensitive than passive tags, giving longer and more reliable range. Also called semi-passive.

Bistatic antenna - An antenna arrangement that uses separate antennas for transmitting and receiving. Most modern UHF readers are monostatic instead.

BLF (Backscatter Link Frequency) - The rate at which a Gen2 tag modulates its reply, set by the reader. Gen2 allows roughly 40 to 640 kHz.

Bulk reading - Reading many tags at once, for example a whole carton or trolley, without line of sight. One of the main advantages of RFID over barcodes.

C

Cable loss - Power lost in the coaxial cable between reader and antenna, usually expressed in dB per metre. It must be included when calculating radiated power against regulatory limits.

Chip (IC) - The integrated circuit in a tag that stores data, runs the protocol and controls modulation. Common UHF chip families include Impinj Monza/M-series, NXP UCODE, Alien Higgs and EM Microelectronic EM4xxx.

Chipless RFID - Tags that encode an identity in their physical structure (for example resonant patterns or surface acoustic waves) instead of a silicon chip. Still mostly niche or experimental.

Circular polarisation - An antenna radiation pattern whose electric field rotates as it travels. Circularly polarised reader antennas read tags in any rotation around the beam axis, at the cost of about 3 dB compared with a perfectly aligned linear antenna. Usual choice when tag orientation is unpredictable.

Collision - When two or more tags reply at the same moment so the reader cannot decode either. Anti-collision algorithms detect and resolve collisions.

Commissioning - Writing the correct identity (for example an SGTIN) into a tag and associating it with an item in the business system, usually at the time of printing or tagging.

Coupling - The physical mechanism linking reader and tag. LF and HF systems use inductive (magnetic) coupling in the near field; UHF systems use radiative (electromagnetic) coupling with backscatter in the far field; some short-range systems use capacitive coupling.

CRC (Cyclic Redundancy Check) - An error-detecting checksum sent with data. Gen2 tags store a 16-bit CRC (StoredCRC) at the start of the EPC bank and use CRCs on the air to detect corrupted messages.

CW (Continuous Wave) - The unmodulated carrier a UHF reader transmits while a passive tag replies. The tag both harvests power from it and reflects it back as backscatter.

D

dB (decibel) - A logarithmic ratio. +3 dB is roughly double the power and +10 dB is ten times; -3 dB is roughly half.

dBd - Antenna gain relative to a half-wave dipole. 0 dBd = 2.15 dBi.

dBi - Antenna gain relative to an imaginary isotropic antenna that radiates equally in all directions. Typical UHF reader panel antennas are around 6 to 9 dBi.

dBic - Gain of a circularly polarised antenna relative to an isotropic circularly polarised reference. Often quoted on circular panel antennas.

dBm - Absolute power referenced to 1 milliwatt. 0 dBm = 1 mW, 20 dBm = 100 mW, 30 dBm = 1 W, 33 dBm = 2 W, 36 dBm = 4 W. Reader output and tag sensitivity are quoted in dBm.

Dense reader mode (DRM) - A Gen2 operating mode that lets many readers work close together. Readers keep their transmissions within tight spectral masks and tags reply on a subcarrier (Miller encoding), so reader signals do not drown out tag replies.

Detuning - A shift in a tag antenna's resonant frequency caused by nearby materials such as metal, liquid or even dense cardboard, reducing performance. Tags designed for specific materials are tuned to compensate.

Dipole - A simple two-arm antenna. Most UHF label inlays use folded or meandered dipole designs.

Duty cycle - The fraction of time a reader is actually transmitting. Lower duty cycles reduce interference and power use; some regulations limit it.

E

EAS (Electronic Article Surveillance) - Anti-theft systems used in retail. Traditional EAS uses acousto-magnetic (around 58 kHz) or RF (around 8.2 MHz) tags that only signal presence; RFID-based EAS uses the UHF tag itself, so the same label serves inventory and loss prevention.

Edge device - A computer or smart reader close to the readers that filters, aggregates and applies rules to read data before sending it to central systems.

EEPROM - Electrically erasable programmable read-only memory, the non-volatile memory used in most RFID chips. Data stays without power and can be rewritten many thousands of times.

EIRP (Effective Isotropic Radiated Power) - The power an ideal isotropic antenna would need to radiate to produce the same peak signal as the actual system. EIRP = transmitter power - cable loss + antenna gain (dBi). The USA (FCC) limits UHF RFID to 4 W EIRP (36 dBm). EIRP = ERP + 2.15 dB.

Encoding - Writing data into a tag's memory, for example programming an EPC. Also used for the way bits are represented on the air (FM0, Miller, PIE).

EPC (Electronic Product Code) - A GS1 identification scheme that gives every physical object a globally unique identity, defined in the GS1 EPC Tag Data Standard. Schemes include SGTIN (items), SSCC (logistic units), GRAI and GIAI (assets). See EPC Encoding & Tag Memory.

EPC memory bank - Bank 01 of a Gen2 tag. It holds the StoredCRC, the PC bits and the EPC (or other identifier) itself. Common EPC lengths are 96 and 128 bits.

EPCglobal - The GS1 organisation that originally developed the EPC Gen2 air interface, LLRP, ALE and EPCIS. Its work now continues under GS1 standards.

EPCIS (Electronic Product Code Information Services) - A GS1 standard for capturing and sharing visibility events: what object, when, where, why (business step) and, since EPCIS 2.0, how (sensor data). It lets trading partners exchange RFID and barcode event data in a common format.

ERP (Effective Radiated Power) - Radiated power referenced to a half-wave dipole antenna. Europe usually states UHF RFID limits in ERP, while the US and India state them in EIRP. ERP = EIRP - 2.15 dB; for example 2 W ERP is about 3.3 W EIRP.

ERP (Enterprise Resource Planning) - Business software (SAP, Oracle, Tally-based systems and others) that manages inventory, purchasing, finance and production. RFID middleware normally feeds processed events into the ERP or WMS. Not to be confused with effective radiated power above.

ETSI (European Telecommunications Standards Institute) - The European standards body. ETSI EN 302 208 covers UHF RFID in Europe, centred on 865-868 MHz with up to 2 W ERP on four high-power channels.

F

Far field - The region more than roughly one wavelength from an antenna (formally beyond about λ/2π in simple models), where energy travels as a propagating electromagnetic wave. Passive UHF tags normally work in the far field; at 866 MHz the wavelength is about 35 cm.

FASTag - India's electronic toll collection tag, a passive UHF RFID sticker fixed on the vehicle windscreen and linked to a prepaid or bank account under the NETC programme. It is one of the largest deployments of UHF RFID in India.

FCC (Federal Communications Commission) - The US regulator. Under FCC Part 15, UHF RFID readers operate in 902-928 MHz using frequency hopping, with up to 1 W conducted power and 4 W EIRP.

FDX / HDX - Full duplex and half duplex, the two LF animal-identification technologies in ISO 11785. FDX-B tags reply while the reader field is on; HDX tags reply in the gap after the field switches off.

Ferrite - A magnetic ceramic material used in LF and HF tags and antennas to concentrate magnetic flux, and as a spacer to make HF tags work on metal.

FHSS (Frequency Hopping Spread Spectrum) - Rapidly switching the reader's transmission between channels to reduce interference. Used in the US band and, over fewer channels, in India and Europe.

Filter value - A small field in GS1 EPC schemes (3 bits in SGTIN-96) that indicates the packaging level, such as item, inner pack or case, so readers can select only the tags they need.

Fixed reader - A reader permanently mounted at a dock door, portal, conveyor or shelf, usually with several external antennas.

FM0 - A simple Gen2 tag-to-reader encoding (bi-phase space). Fastest data rate but most vulnerable to interference; Miller encoding is preferred in busy RF environments.

Forward link - The reader-to-tag direction of communication. In passive UHF systems the forward link (powering the tag) usually limits range, not the reverse link.

G

Gen2 (EPC Class 1 Generation 2) - The dominant passive UHF air interface protocol, published by GS1 and harmonised internationally as ISO/IEC 18000-63. Defines commands such as Select, Query, Read, Write, Lock and Kill, four memory banks, sessions and the Q algorithm.

Gen2v2 - Version 2 of the Gen2 protocol (2013) that added optional security features: cryptographic authentication, untraceable mode to hide memory, and finer-grained file and access control.

GIAI (Global Individual Asset Identifier) - A GS1 key for identifying an individual fixed asset, such as a laptop, machine or piece of furniture. Encoded on tags as GIAI-96 or GIAI-202.

GLN (Global Location Number) - A GS1 key identifying a location or party (a warehouse, a dock door, a company). Its EPC form is SGLN.

GPIO (General Purpose Input/Output) - Digital input and output ports on readers used to connect photo-eyes, motion sensors, stack lights, buzzers and gate barriers.

GRAI (Global Returnable Asset Identifier) - A GS1 key for reusable transport items such as pallets, crates, kegs, gas cylinders and roll cages. It combines an asset type with an optional serial number.

GS1 - The global not-for-profit standards organisation behind barcodes (GTIN, EAN/UPC) and EPC/RFID standards. GS1 India is the national member organisation in India and issues company prefixes to Indian businesses.

GTIN (Global Trade Item Number) - The GS1 number identifying a product type (the number inside an EAN-13 or UPC barcode). On RFID tags it is serialised as an SGTIN so each individual item is unique.

H

Handheld reader - A portable reader, often an Android mobile computer with an integrated UHF module and barcode scanner, used for cycle counts, search and ad-hoc reading.

Hard tag - A rugged tag in a plastic, ceramic or metal housing for harsh conditions - outdoor assets, metal surfaces, laundry, high temperatures or heavy handling.

Header - The first 8 bits of a GS1 EPC that identify the coding scheme and length, for example 0x30 for SGTIN-96.

HF (High Frequency) - RFID at 13.56 MHz. Uses inductive coupling with typical read ranges from a few centimetres to around a metre. Standards include ISO 14443, ISO 15693 and NFC. Common in access cards, payments, libraries and ticketing.

I

Impedance matching - Designing the tag antenna (or reader circuit) so its impedance is the complex conjugate of the chip's, transferring maximum power. Poor matching shortens read range.

Inlay - The functional core of an RFID tag: a chip bonded to an antenna on a thin substrate (usually PET film). A dry inlay has no adhesive; a wet inlay has an adhesive backing; inlays are converted into labels, tickets and tags. See RFID Antennas & Inlays.

Interrogator - The formal standards term for an RFID reader: the device that transmits commands and receives tag replies.

Inventory (Gen2) - The sequence of commands (Query, QueryRep, QueryAdjust, ACK) by which a reader discovers and singulates the tags in its field.

ISO 11784 / 11785 - ISO standards for LF (134.2 kHz) animal identification. ISO 11784 defines the code structure and ISO 11785 the air interface (FDX-B and HDX).

ISO/IEC 14443 - The 13.56 MHz standard for proximity cards with a range of typically up to about 10 cm, in Type A and Type B variants. Used by contactless payment cards, e-passports, MIFARE and most NFC tags.

ISO/IEC 15693 - The 13.56 MHz standard for vicinity cards, with longer range than ISO 14443 (up to around a metre with large fixed antennas). Used in libraries, laundry, healthcare and industrial tracking; also the basis of NFC Forum Type 5 tags.

ISO/IEC 18000-63 - The ISO/IEC version of the passive UHF air interface, aligned with EPC Gen2 (formerly known as ISO 18000-6C). See RFID Standards & Regulations.

K

Kill command - A Gen2 command that permanently disables a tag when the correct non-zero 32-bit kill password is supplied. A killed tag never responds again. Used for consumer privacy at point of sale.

Kill password - The 32-bit password in the Reserved bank of a Gen2 tag that authorises the Kill command. A tag with an all-zero kill password cannot be killed.

L

Label (smart label) - A printable paper or synthetic label with an RFID inlay inside, so it carries human-readable text, a barcode and an RFID chip. Printed and encoded on an RFID printer.

LF (Low Frequency) - RFID at 125-134.2 kHz. Short range (typically up to a few tens of centimetres), slow data rate, but works well near water and body tissue. Used for animal ID, immobilisers and older access control.

Linear polarisation - An antenna whose electric field oscillates in a single plane. Gives longer range than circular when tag orientation is fixed and aligned, but poor reads when the tag is rotated 90 degrees.

Link budget - An accounting of all gains and losses between reader and tag (transmit power, cable loss, antenna gains, path loss, material losses) used to predict whether a tag will be powered and heard.

LLRP (Low Level Reader Protocol) - A GS1/EPCglobal standard network protocol for controlling UHF readers and collecting tag reports. Supported by most enterprise fixed readers, it lets software work with readers from different manufacturers.

Load modulation - The way LF and HF tags reply: the chip switches a load across its coil, causing small changes in the reader's magnetic field that the reader detects.

Lock - A Gen2 command that sets the write and access permissions of memory banks and passwords. Memory can be unlocked, locked (writable only with the access password) or permanently locked (permalocked).

M

Mask designer ID (MDID) - A code in the TID memory identifying the chip manufacturer. Together with the model number it tells you exactly which chip a tag uses.

Memory bank - One of the four logical memory areas of a Gen2 tag: Reserved (bank 00), EPC (01), TID (10) and User (11).

Middleware - Software between readers and business applications that manages devices, filters duplicate reads, applies business rules and turns raw reads into meaningful events. See RFID Middleware & Software.

MIFARE - A family of 13.56 MHz ISO 14443 Type A chips from NXP, widely used in transit and access cards. Variants include MIFARE Classic (older proprietary security, now considered weak), Ultralight, Plus and DESFire (AES-based security).

Miller encoding - A Gen2 tag-to-reader encoding using a subcarrier (M = 2, 4 or 8 cycles per bit). Higher M values are slower but more robust against interference and are used in dense reader environments.

Monostatic antenna - A single antenna used for both transmitting and receiving. The standard arrangement for UHF readers.

Multipath - Radio waves arriving at a tag or reader by several paths (direct and reflected). The paths can add or cancel, creating hot spots and dead spots (nulls) in the read zone.

Multiplexer - A device that lets one reader port drive several antennas in turn, extending coverage at lower cost but reducing time per antenna.

N

NDEF (NFC Data Exchange Format) - The NFC Forum format for storing messages such as URLs, text, contact cards or Wi-Fi settings on NFC tags, so any phone can interpret them.

Near field - The region close to an antenna (within roughly λ/2π) dominated by reactive magnetic or electric fields. LF and HF systems work entirely in the near field; UHF near-field antennas are used for very short, controlled reads such as item-level reading on a counter.

NFC (Near Field Communication) - A 13.56 MHz technology built on ISO 14443, ISO 15693 and FeliCa, with a range of a few centimetres. Built into most smartphones for payments, pairing, product authentication and smart posters.

NFC Forum tag types - Interoperability classes (Type 1 to Type 5) defined by the NFC Forum. For example NTAG chips are Type 2, DESFire is Type 4 and ISO 15693 chips are Type 5.

NTAG - A popular NXP family of NFC Forum Type 2 chips. NTAG213, NTAG215 and NTAG216 offer 144, 504 and 888 bytes of user memory respectively.

Null - A location in the read zone where reflected signals cancel and a tag cannot be read, even though nearby positions read well. Moving the tag a few centimetres often fixes it.

O

On-metal tag - A tag designed to work when mounted directly on metal, usually with a spacer or a ground plane built into the design. Ordinary label inlays fail on metal.

Orientation sensitivity - How much a tag's read performance changes as it is rotated relative to the reader antenna. Dipole tags have weak spots along their axis.

P

Passive tag - A tag with no battery that is powered entirely by the reader's field. The cheapest and most common type, used in labels, cards and wristbands.

Path loss - The weakening of a radio signal with distance. In free space, received power falls with the square of distance, so doubling the distance costs about 6 dB.

PC bits (Protocol Control) - A 16-bit word in the EPC bank of a Gen2 tag that tells the reader the length of the EPC, whether user memory is present, whether extended PC bits exist and whether the identifier follows GS1 or ISO numbering.

Permalock - A permanent lock that can never be undone. Permalocking memory as read-only protects the EPC from being changed; permalocking a password prevents it from being read or changed.

Phase - The angle of the tag's reply signal relative to the reader's carrier. Many readers report it, and software uses phase changes to estimate tag movement and direction.

PIE (Pulse Interval Encoding) - The encoding readers use to send data to Gen2 tags; a logical 0 and 1 are distinguished by the length of the interval between pulses.

PoE (Power over Ethernet) - Supplying power and data over a single Ethernet cable (IEEE 802.3af, or 802.3at PoE+ for higher power). Many fixed readers run on PoE, simplifying installation.

Polarisation - The orientation of the electric field of a radio wave. See linear polarisation and circular polarisation.

Portal - A read point formed by antennas on both sides (and sometimes above) a doorway, dock door or gate so that tagged goods passing through are read.

Printer-encoder - A thermal label printer with a built-in RFID module that prints the label and encodes and verifies the tag in one pass.

Proximity card - A contactless card (ISO 14443 at 13.56 MHz, or older 125 kHz formats) read at a few centimetres, typically for access control and payments.

Q

Q algorithm - The Gen2 anti-collision method. The reader sets a value Q (0 to 15); each tag picks a random slot between 0 and 2^Q - 1 and replies only when its slot counter reaches zero. The reader adjusts Q up or down depending on whether it sees collisions or empty slots.

Query - The Gen2 command that starts an inventory round, setting parameters such as session, target flag, Q and link settings.

R

RAIN RFID - The industry brand name for passive UHF RFID based on EPC Gen2 / ISO/IEC 18000-63, promoted by the RAIN Alliance. "RAIN" stands for RAdio frequency IdentificatioN and suggests the link to cloud computing.

Read range - The maximum distance at which a reader can reliably read a tag. It depends on reader power, antenna gain, tag sensitivity, tag size, orientation, materials and environment. See RFID Read Range & Performance.

Read rate - Either the number of tag reads per second a reader can perform, or the percentage of tags successfully read in a test (read accuracy). Always check which meaning a data sheet uses.

Read zone - The three-dimensional space in which tags are reliably read. Good projects deliberately shape the read zone to avoid stray reads.

Reader - The device that powers, commands and receives data from tags. It can be fixed, handheld, desktop, integrated into a printer or embedded as a module.

Reader sensitivity - The weakest tag reply a reader can decode, in dBm. Better (more negative) sensitivity matters most for BAP tags and in noisy environments.

Reader-talks-first (RTF) - A protocol style in which tags stay silent until commanded by a reader. Gen2 is reader-talks-first.

Reserved memory - Bank 00 of a Gen2 tag, holding the 32-bit kill password and 32-bit access password.

Reverse link - The tag-to-reader direction of communication (the backscatter reply).

RF (Radio Frequency) - Electromagnetic energy in the radio part of the spectrum, roughly from a few kHz to hundreds of GHz.

RFID (Radio Frequency Identification) - Automatic identification of objects using radio waves between a reader and a tag, without line of sight.

RSSI (Received Signal Strength Indicator) - The strength of a tag's reply as measured by the reader, usually in dBm. Useful for estimating relative proximity, filtering far-away tags and tuning installations, but not a precise distance measure.

RTLS (Real-Time Locating System) - A system that continuously tracks the position of tagged people or assets in a building or site. Uses active RFID, UWB, BLE or Wi-Fi rather than passive tags in most cases.

S

Select command - A Gen2 command that chooses a subset of tags (for example by EPC prefix or filter value) to take part in the next inventory, so the reader ignores irrelevant tags.

Semi-passive tag - See BAP.

Session (S0-S3) - Four independent inventory contexts in Gen2. Each tag holds an inventoried flag (A or B) per session with different persistence: S0 resets almost immediately when the tag loses power, S1 lasts briefly (about 0.5 to 5 seconds), while S2 and S3 persist for at least 2 seconds after power loss. Choosing the right session controls whether tags reply repeatedly or once.

SGTIN (Serialised GTIN) - The EPC scheme for individual trade items: a GTIN plus a unique serial number. SGTIN-96 has an 8-bit header, 3-bit filter, 3-bit partition, company prefix and item reference (44 bits together) and a 38-bit serial number.

Singulation - Isolating a single tag from a population so the reader can communicate with it individually. Achieved through anti-collision.

SSCC (Serial Shipping Container Code) - The 18-digit GS1 key that identifies a logistic unit such as a pallet or shipping carton. Encoded on tags as SSCC-96.

Stray reads - Unwanted reads of tags outside the intended read zone, such as goods on a neighbouring dock door. Controlled by power settings, antenna placement, shielding, RSSI filtering and software logic.

Substrate - The base material that carries the tag antenna, usually PET film; paper and other materials are also used.

T

Tag - The device attached to an object that carries its identity: a chip plus antenna, packaged as a label, card, wristband, key fob or hard tag. Also called transponder.

Tag Data Standard (TDS) - The GS1 standard that defines how EPC schemes such as SGTIN, SSCC, GRAI and GIAI are structured and binary-encoded on tags.

Tag sensitivity - The minimum RF power a chip needs to wake up and respond (read sensitivity) or to write (write sensitivity), in dBm. Modern UHF chips are typically around -20 to -25 dBm for reading.

Tamper-evident tag - A tag designed to break or change state when removed, for example a windscreen tag that destroys its antenna if peeled off, as used for vehicle tags.

Tari - The reference time interval for a data-0 symbol in Gen2 reader-to-tag signalling, between 6.25 and 25 microseconds. Shorter Tari gives faster commands.

TID (Tag Identifier) - Bank 10 of a Gen2 tag, written and locked by the chip manufacturer. It identifies the chip maker and model and, in most modern chips, contains a unique serial number that cannot be changed.

Transponder - From transmitter + responder. The traditional engineering term for an RFID tag.

Tunnel reader - An enclosed, shielded reading station, often over a conveyor, that reads all tagged items in a box or tote as they pass through while blocking reads from outside.

U

UHF (Ultra High Frequency) - RFID in the 860-960 MHz range. In India the permitted band is 865-867 MHz; Europe uses 865-868 MHz and the USA 902-928 MHz. Passive UHF offers read ranges of several metres and fast bulk reading.

UID (Unique Identifier) - The factory-programmed serial number of an HF chip, such as the 4- or 7-byte UID of ISO 14443 Type A chips or the 8-byte UID of ISO 15693 chips.

Untraceable - A Gen2v2 feature that lets an authorised reader hide part of the EPC, TID or user memory, or reduce read range, so the tag reveals less information to unauthorised readers.

User memory - Bank 11 of a Gen2 tag, an optional area for extra data such as batch numbers, maintenance history or dates. Size varies from zero to several kilobits depending on the chip.

UWB (Ultra-Wideband) - A radio technology using very short pulses over a wide bandwidth, enabling precise (often tens of centimetres) location. Used in RTLS rather than classic RFID identification.

V

VSWR (Voltage Standing Wave Ratio) - A measure of how well an antenna and cable are matched to the reader. A VSWR close to 1:1 means little reflected power; high VSWR indicates a damaged cable, loose connector or mistuned antenna.

W

Wet inlay - An inlay supplied with an adhesive backing on a liner so it can be applied directly as a sticker. See inlay.

WMS (Warehouse Management System) - Software that manages warehouse locations, receiving, put-away, picking and shipping. A frequent destination for RFID events.

WORM (Write Once, Read Many) - Memory that can be written one time and then only read. Some tags or memory blocks are WORM to make data tamper-resistant.

WPC (Wireless Planning & Coordination Wing) - The wing of India's Department of Telecommunications that manages radio spectrum. WPC has delicensed 865-867 MHz for RFID, with up to 4 W EIRP (1 W transmitter power), and administers Equipment Type Approval (ETA) for wireless equipment sold in India.

Wristband - A tag in the form of a band worn on the wrist, used in hospitals, events, water parks and access control, available in LF, HF, NFC and UHF.

Write range - The distance at which a tag can be written. Writing needs more power than reading, so write range is typically shorter than read range.