RFID Glossary

Active RFID tags contain an onboard battery and radio transmitter, enabling them to broadcast their identifier continuously or at programmed intervals without needing to be powered by a reader's field. This allows read ranges of 30–100+ metres and the ability to include sensors (temperature, humidity, shock, motion) that log conditions over time. Active tags are significantly more expensive than passive tags (€15–€80 each) and have a finite battery life (typically 2–7 years). They are used where long range, real-time location awareness, or environmental sensing is required — tracking high-value assets, monitoring cold-chain conditions, or RTLS applications. The infrastructure cost is also higher, as active RFID requires a network of fixed receivers throughout the facility.

The air interface protocol defines every aspect of how an RFID reader and tag communicate: the radio modulation scheme, bit encoding, command and response structure, anti-collision algorithm, and session management. Different RFID frequencies use different air interface protocols. For UHF RFID, EPC Gen2 (ISO 18000-63) is the universal standard. For HF RFID, ISO 14443 covers proximity cards and NFC devices, while ISO 15693 covers vicinity cards used in libraries and industrial applications. For LF RFID, EM4100 and ISO 11784/11785 are common. The anti-collision component is particularly important: it defines how a reader queries many tags simultaneously without their responses colliding and becoming unreadable. UHF Gen2 uses a slotted Aloha anti-collision algorithm that allows a single reader to read hundreds of tags per second even in dense tag environments.

Backscatter is the communication mechanism used by passive and semi-passive RFID tags. Instead of generating their own radio signal (which would require a power source), the tag's chip modulates its antenna impedance to absorb or reflect the reader's incoming radio field in a controlled pattern. This modulated reflection carries the tag's data back to the reader. The reader detects the subtle variations in the reflected signal and decodes the tag's identifier. Backscatter allows passive tags to communicate without a battery — all the energy comes from the reader's transmitted field. The technique was originally developed from radar technology and is sometimes called 'radar cross-section modulation'. UHF EPC Gen2 tags use backscatter as their sole communication method.

Chipless RFID tags identify themselves using radio-frequency reflection without containing a traditional silicon microchip. Some use conductive polymers instead of silicon; others use metallic fibres or specially structured surfaces that reflect radio waves in a unique fingerprint pattern. A reader analyses the reflected signal to determine the tag's identity. Because they contain no chip, chipless tags are potentially cheaper to manufacture and can be printed or embedded directly into paper and packaging. However, current chipless technology has significant limitations compared to chipped RFID: much lower data capacity, shorter read range, reduced read reliability, and no ability to be written or updated in the field. Applications include document security (RF-reflective fibres in banknotes or certificates) and some specialised identification tasks.

Dense Reader Mode (DRM) is a feature of the EPC Gen2 UHF RFID standard that enables multiple readers to operate simultaneously in the same physical space without causing reader collision. Without DRM, readers transmitting on the same or adjacent frequency channels can interfere with each other's tag reads. DRM addresses this by specifying frequency channel plans that separate reader transmit frequencies from tag response frequencies, and by coordinating reader duty cycles so that reader transmissions do not overlap in time and frequency in ways that degrade tag reads. DRM is essential in high-density deployments such as warehouse dock doors, conveyor lines with multiple read stations, and retail back-of-house portals where several readers cover adjacent zones.

The Electronic Product Code (EPC) is a globally unique identification number stored on an RFID tag, analogous to a GTIN (Global Trade Item Number) barcode but with the addition of a unique serial number. While a barcode identifies a product type (e.g., 'this is a 330ml Coca-Cola can'), an EPC identifies a specific individual item (e.g., 'this is the 47,832nd 330ml Coca-Cola can produced at this facility on this date'). EPCs are structured according to GS1 standards and can encode GTINs, GLNs, SSCCs, and other GS1 identifiers. The EPC is stored in the tag's EPC memory bank and broadcast during standard Gen2 read operations. EPC is the foundation of GS1's vision of a fully serialised global supply chain.

EPC Gen2 (formally GS1 EPC UHF Gen2 Air Interface Protocol, standardised as ISO/IEC 18000-63) is the specification that governs how UHF RFID readers and tags communicate. Published in 2004 and significantly updated in 2015 (Gen2v2), it defines the radio protocol, anti-collision algorithm (enabling bulk reading of hundreds of tags simultaneously), memory bank structure, and command set. Gen2v2 added cryptographic authentication, extended memory, and improved dense-reader performance. All major RFID hardware manufacturers — Zebra, Impinj, NXP, Alien Technology, Feig, Invengo — are fully Gen2v2 compliant, guaranteeing interoperability. EPC Gen2 is mandated by Walmart, Metro, Target, and the US Department of Defense for supply chain RFID deployments.

HF RFID operates at 13.56 MHz and encompasses several standards including ISO 14443 (used for access control cards and contactless payment), ISO 15693 (used for library books and industrial tracking), and FeliCa (used in Asian transit systems). Read range is typically 1–15 cm, making it suitable for applications requiring deliberate, close-range transactions. HF RFID is largely immune to interference from metal and liquid compared to UHF, making it more reliable in some environments. The technology behind most building access cards, hotel key cards, and bank contactless payment cards is HF RFID at 13.56 MHz.

An RFID inlay is the fundamental RFID component: a microchip bonded to a printed antenna, mounted on a PET or paper substrate. Inlays are the building blocks from which finished RFID products are made. A wet inlay has a pressure-sensitive adhesive backing and can be directly applied or laminated into a label. A dry inlay has no adhesive and is used in card manufacturing or embedded into hard tags during moulding. Label converters take wet inlays, overly them with face stock, print barcodes or text, and die-cut them into finished RFID labels. Card manufacturers embed dry inlays into PVC or PET-G card bodies under heat and pressure. Inlay antenna design is one of the most significant factors determining read range and performance on different substrates — specialist inlay designs exist for on-metal, near-liquid, and small-form-factor applications.

ISO 14443 is the international standard that defines the communication protocol for contactless smart cards (also called proximity cards) operating at 13.56 MHz. It specifies the physical characteristics of the card, the RF power and signal interface, the initialisation and anti-collision procedure, and the transmission protocol. ISO 14443 covers two card types: Type A (used by MIFARE, the most widely deployed contactless card technology) and Type B (used by some banking and government identity systems). NFC is built on ISO 14443 Type A and B. This is the standard behind the contactless functionality in building access cards, hotel keys, public transport cards, and bank payment cards worldwide.

ISO 15693 is an international standard for HF RFID tags (sometimes called 'vicinity cards') operating at 13.56 MHz. Unlike ISO 14443 (proximity cards with a maximum range of ~10 cm), ISO 15693 is optimised for longer read distances — up to 1.5 metres under ideal conditions. This makes it suitable for applications where the reader and tag are not in very close contact. ISO 15693 is the dominant standard for library book tracking (the RFID chip in a library book label is typically ISO 15693) and is used in some industrial asset tracking and ticketing applications. It supports anti-collision to allow multiple tags to be read simultaneously, though with lower throughput than UHF systems.

LF RFID operates between 125–134 kHz. It is the oldest RFID technology and has largely been superseded by HF and UHF for most applications, but remains in widespread use for animal identification (ISO 11784/11785 covers implantable pet and livestock chips), legacy access control systems (EM4100 and HID Prox cards), and certain industrial environments where other frequencies are impractical. LF signals penetrate water and tissue exceptionally well, which is why it is used for subcutaneous animal implants. Read range is limited to 10–30 cm. Data transfer rates are very slow compared to HF and UHF.

Microwave RFID operates at 2.45 GHz (and sometimes 5.8 GHz). It offers very high data transfer rates and relatively long read ranges, but radio waves at this frequency are strongly absorbed by water and human tissue, limiting penetration through materials. Microwave RFID is used in specific applications where these characteristics are acceptable or even advantageous: electronic toll collection (ETC) systems on motorways, some vehicle identification systems, and certain RTLS implementations. It is significantly less common than LF, HF, or UHF RFID for general supply chain and inventory applications. The 2.45 GHz band is also used by Wi-Fi and Bluetooth, which can cause interference in dense wireless environments.

NFC (Near Field Communication) is a standardised communication protocol built on the ISO 14443 HF RFID standard, operating at 13.56 MHz with a maximum range of approximately 4 cm. Unlike standard HF RFID, NFC supports three operating modes: reader/writer mode (a device reads or writes to a passive NFC tag), peer-to-peer mode (two NFC-enabled devices exchange data), and card emulation mode (a device acts as an NFC card). Every modern smartphone includes an NFC chip, making NFC the only RFID technology that end-consumers can interact with using their own device. Common applications include contactless payment (Apple Pay, Google Pay), product authentication, smart packaging, and NFC-enabled marketing campaigns.

Passive RFID tags contain no internal power source. They harvest the energy they need from the electromagnetic field emitted by the reader, use this harvested power to briefly activate their chip, and transmit their stored identifier back to the reader via backscatter modulation. When outside a reader's field, a passive tag is completely inert and consumes no power. This gives passive tags a theoretically indefinite lifespan — there is no battery to deplete or replace. Passive tags are typically small, thin, and inexpensive (€0.05–€2.00 at volume), making them suitable for tagging high volumes of items. The trade-off is limited read range (determined by the reader's transmit power and the tag's antenna efficiency) and no ability to proactively report their location.

RFID (Radio Frequency Identification) is a technology that uses electromagnetic fields to automatically identify and track tags attached to objects. An RFID system consists of a reader (which emits radio waves), an antenna (which focuses the radio field), and one or more tags (which contain a microchip storing a unique identifier). When a tag enters the reader's field, it receives energy from the radio waves, powers its chip, and transmits its stored data back to the reader. This process happens in milliseconds and requires no physical contact or line of sight. RFID is used across industries for inventory management, access control, asset tracking, supply chain visibility, and more.

A Real-Time Location System (RTLS) continuously tracks where tagged assets are located within a defined space, updating position data in near-real-time (typically every 1–30 seconds). Unlike standard RFID — which tells you an asset has been seen at a specific reader — RTLS calculates position using signals from multiple fixed reference points (anchors) and algorithms such as Time of Flight (ToF), Time Difference of Arrival (TDoA), Angle of Arrival (AoA), or Received Signal Strength (RSSI). Technologies used for RTLS include UWB (Ultra-Wideband, sub-30 cm accuracy), Bluetooth Low Energy (room-level accuracy), and specialised UHF RFID systems such as RF Controls. Common RTLS applications include hospital equipment tracking, manufacturing work-in-progress tracking, and logistics yard management.

An RFID reader (also called an interrogator) is the active component of an RFID system that generates the radio frequency field, detects and decodes signals from tags, and forwards the data to a host system. Readers come in fixed form (mounted at chokepoints like dock doors, conveyor lines, or room entrances) or handheld form (carried by staff for mobile inventory counting or asset auditing). A reader connects to one or more antennas, which focus and direct the radio field. Modern enterprise RFID readers can manage 4–8 antennas simultaneously, effectively creating configurable read zones. Readers connect to host systems via Ethernet, Wi-Fi, USB, or GPIO interfaces and expose data via LLRP (Low Level Reader Protocol) or proprietary APIs.

An RFID antenna is a passive hardware element that converts the electrical signals from a reader into a propagating electromagnetic field and vice versa. The antenna's design determines the shape, directionality, and polarisation of the read zone. Circular polarisation (RHCP/LHCP) makes the read zone orientation-independent — tags can be read regardless of how they are oriented, which is important for general inventory applications. Linear polarisation provides higher gain and longer range but is sensitive to tag orientation. Antenna gain (measured in dBi or dBiC) determines how focused and powerful the radiated field is. Selection depends on whether you need broad coverage (circular, lower gain) or long-range point-to-point reading (linear, higher gain). Antennas are rated for indoor or outdoor use and may carry IP67 or IP68 ratings for wet environments.

An RFID tag (also called a transponder) is the component attached to the object being tracked. It consists of an integrated circuit (chip) that stores the tag's unique identifier and may store additional data, and an antenna that receives the reader's signal and transmits the tag's data back. Tags come in many physical forms: adhesive labels (inlays), rigid plastic enclosures for harsh environments, glass capsules for animal implants, fabric-encapsulated versions for laundry, and ceramic-substrate versions for metal surfaces. The chip's memory is organised into banks: the EPC bank (stores the identifier), the TID bank (manufacturer-programmed, unique and tamper-proof), the User bank (optional, for custom data), and the Reserved bank (passwords). Tag selection depends on the application environment, required read range, attachment method, and cost constraints.

Read range is the maximum distance at which an RFID reader can reliably detect and communicate with a tag. It is one of the most misunderstood RFID specifications because it depends on many interacting variables. Frequency has the largest impact: LF tags read at under 30 cm, HF at 1–15 cm, and UHF at 0.5–12 metres under ideal conditions. Reader transmit power (regulated by country — 2W EIRP in Europe, 4W EIRP in the USA) sets the upper limit. Antenna gain and polarisation shape the field. Tag antenna size and design determine how efficiently the tag harvests energy. Environmental factors — nearby metal, liquids, RF interference, other tags — all reduce effective read range. Published read range figures from manufacturers represent best-case free-space conditions. Actual deployed read range in a real environment is typically 50–80% of published figures and must be validated through site testing.

Reader collision occurs when two RFID readers transmit signals simultaneously in overlapping coverage areas, causing interference that prevents tags in the overlap zone from responding to either reader. It is most common in large-scale UHF RFID deployments such as warehouses with multiple fixed readers or retail stores with dense reader infrastructure. Solutions include time-division multiple access (TDMA), where readers take turns transmitting; frequency hopping across available channels; physical shielding between adjacent read zones; and software coordination of reader timing. The EPC Gen2 standard includes a 'dense reader mode' (DRM) that uses frequency channel planning and duty-cycle management to minimise reader collision in high-density deployments.

Semi-passive RFID tags (also called battery-assisted passive, or BAP, tags) occupy the middle ground between passive and active RFID. They contain a small battery that powers the tag's microchip and any onboard sensors continuously, eliminating the need to harvest power from the reader's field. However, they still communicate by backscattering the reader's signal rather than actively transmitting — so a reader must still be present to read the tag. The battery-assisted approach extends effective read range compared to standard passive tags and enables continuous sensor logging (e.g. temperature recording throughout a cold-chain journey) even when outside a reader's field. Costs are higher than passive tags but lower than fully active tags.

Tag collision occurs when more than one RFID tag in a reader's field reflects back a signal at the same time, creating overlapping transmissions that the reader cannot decode. It is one of the fundamental challenges of dense-tag RFID environments. Anti-collision algorithms built into air interface protocols — particularly the slotted Aloha algorithm used in EPC Gen2 — resolve this by assigning tags to separate time slots so they respond individually. The process is fast enough (milliseconds per tag) that a reader can process hundreds of tags per second without perceptible delay. In practice, tag collision is managed through proper system design: appropriate reader power, antenna placement that limits unnecessary read-zone overlap, and selecting protocols with robust anti-collision capabilities.

UHF RFID operates in the 860–960 MHz frequency band (the exact range varies by region: 865–868 MHz in Europe, 902–928 MHz in North America). It is the dominant technology for supply chain, retail, and logistics applications. UHF tags can be read at distances of 1–12 metres depending on reader power and tag design. A single reader can read hundreds of tags per second, enabling bulk reading of entire pallets without manual scanning. The EPC Gen2 (ISO 18000-63) standard governs UHF RFID interoperability globally. UHF performance can degrade near metal and liquids, though specialised on-metal and near-liquid tags mitigate this.

WORM (Write Once, Read Many) RFID tags allow a user or system to write a unique identifier to the tag once — at the point of application — after which the memory is permanently locked and cannot be overwritten. This provides a middle ground between read-only tags (pre-programmed at the factory with a fixed ID) and fully read-write tags (which allow ongoing data updates). WORM tags are well-suited to serialisation applications where a unique identifier needs to be assigned at a specific point in the supply chain (e.g. at a printing or encoding station) and must then remain immutable for the tag's lifetime. Most UHF EPC Gen2 tags implement the EPC memory bank as effectively WORM — once encoded and locked, the EPC cannot be changed.