Electronics Guide

System Architecture

RFID systems consist of three core components: tags (also called transponders), readers (also called interrogators), and backend systems for data processing. Tags contain an integrated circuit and antenna, storing identification data and optionally additional information. Readers generate electromagnetic fields that power passive tags and communicate bidirectionally with tags to read and write data.

The communication link between reader and tag uses electromagnetic coupling, with the specific mechanism depending on operating frequency. Near-field systems use inductive coupling through magnetic fields, while far-field systems use propagating electromagnetic waves. This distinction fundamentally affects range, data rate, and application suitability.

Frequency Bands

RFID operates across multiple frequency bands, each with distinct characteristics. Low Frequency (LF) systems operate at 125 kHz or 134.2 kHz. These frequencies penetrate water and tissue well, making LF suitable for animal identification and applications requiring reading through challenging materials. Range is typically limited to a few centimeters, with data rates around 1 kbps.

High Frequency (HF) RFID operates at 13.56 MHz, the same frequency used by NFC. HF provides balanced performance with ranges up to about one meter for larger antennas and data rates of tens of kilobits per second. HF is widely used for access control, library books, and smart cards.

Ultra High Frequency (UHF) RFID operates in the 860-960 MHz range (varying by region). UHF systems achieve ranges of several meters or more with data rates exceeding 100 kbps. This makes UHF ideal for supply chain and inventory applications where reading multiple items at distance is required. However, UHF signals are absorbed by water and reflected by metal, complicating some applications.

Microwave RFID at 2.45 GHz and higher frequencies offers high data rates but shorter range due to greater path loss. These systems see specialized use in toll collection and some industrial applications.

Tag Types

Passive tags contain no battery, deriving operating power from the reader's electromagnetic field. This enables indefinite tag lifetime and very low cost, making passive tags dominant in supply chain and identification applications. The power limitation constrains range and processing capability.

Active tags include batteries powering the tag's electronics and transmitter. Battery power enables longer range (potentially 100 meters or more), larger memory, and more sophisticated processing. Active tags suit asset tracking, real-time location systems, and applications requiring sensor integration. Battery life limits deployment duration, typically years for well-designed systems.

Semi-passive (or battery-assisted passive) tags use batteries to power the integrated circuit but rely on the reader's field for communication. This hybrid approach extends range beyond purely passive tags while preserving some cost and lifetime advantages.

Tag Memory and Standards

RFID tags store varying amounts of data depending on type and standard. Simple tags may contain only a unique identifier, while sophisticated tags include kilobytes of user memory plus security features. Memory organization typically includes reserved (passwords), Electronic Product Code (EPC) or identifier, tag identification (TID), and user memory sections.

ISO 14443 defines proximity card standards for HF RFID, specifying physical characteristics, radio interface, and initialization protocols. Types A and B represent different modulation and coding schemes. ISO 15693 defines vicinity card standards with longer range but lower security, used for library books and access control.

EPC Gen2 (ISO 18000-63) standardizes UHF RFID for supply chain applications. This standard defines air interface protocols, tag memory structure, and dense reader mode for environments with multiple readers. GS1 administers EPC standards, ensuring global interoperability for supply chain applications.

NFC Overview

Near Field Communication operates at 13.56 MHz, building upon HF RFID standards while adding peer-to-peer communication capabilities. NFC's design intentionally limits range to approximately 10 centimeters, creating a natural security boundary and intuitive tap interaction model. This proximity requirement means users must deliberately bring devices together, reducing accidental transactions and eavesdropping risks.

The NFC Forum, an industry consortium, develops and promotes NFC specifications. Founded in 2004 by Nokia, Philips, and Sony, the forum has grown to include hundreds of members from various industries. NFC Forum specifications define technical standards and ensure interoperability across the ecosystem.

Operating Modes

NFC devices operate in three modes, enabling different use cases. Reader/Writer mode allows NFC devices to read and write NFC tags, similar to traditional RFID readers. Smartphones use this mode to read smart posters, configuration tags, and product information tags.

Peer-to-Peer mode enables bidirectional communication between two NFC-enabled devices. Both devices generate fields alternately, exchanging data in both directions. Android Beam (now deprecated) used this mode for sharing contacts, URLs, and small files between phones. Peer-to-peer suits connection handover, where devices exchange WiFi or Bluetooth pairing information to establish higher-bandwidth connections.

Card Emulation mode allows NFC devices to behave like contactless smart cards. The device's NFC controller responds to external readers as if it were a physical card. This mode enables mobile payments, transit cards, and access credentials on smartphones. Secure element or host-based card emulation provides the security infrastructure.

Communication Technologies

NFC supports multiple underlying communication technologies. NFC-A (based on ISO 14443 Type A) uses Miller encoding for reader-to-tag communication and Manchester encoding for tag responses, with 106 kbps data rate. This technology underlies many contactless payment systems.

NFC-B (based on ISO 14443 Type B) uses NRZ encoding and BPSK modulation, also at 106 kbps. Type B is common in identity documents and some payment systems, particularly in certain regions.

NFC-F (based on Sony FeliCa) uses Manchester encoding at 212 or 424 kbps. FeliCa dominates transit systems in Japan and sees use in other Asian markets. Its higher data rate enables faster transactions.

NFC-V (based on ISO 15693) provides longer range at lower data rates, primarily for tag reading applications rather than payment or secure interactions.

NFC Data Exchange Format

NDEF (NFC Data Exchange Format) standardizes data structure for NFC communications. NDEF messages contain one or more NDEF records, each specifying a type name format and payload. This encapsulation enables interoperable data exchange regardless of the underlying NFC technology.

Common NDEF record types include URI records (launching web pages), Text records (displaying messages), Smart Poster records (combining URIs with additional metadata), and MIME type records (carrying arbitrary data). Android Application Records specify which app should handle the NFC data.

NDEF enables simple tag programming: a tag containing a URI record automatically opens the web browser when tapped to an NFC phone. This simplicity drives applications from marketing (smart posters) to configuration (WiFi setup tags) to pairing (Bluetooth handover).

Payment Card Standards

Contactless payments use NFC (or ISO 14443 RFID) to communicate between payment cards or devices and point-of-sale terminals. EMV Contactless specifications from EMVCo define the payment protocols, with variations for different card brands (Visa payWave, Mastercard PayPass, American Express ExpressPay, etc.).

The payment transaction follows a standardized flow: the terminal generates an RF field, the card or device is detected, application selection identifies the payment application, card authentication verifies the card's legitimacy, and cryptographic transaction authorization generates unique transaction data preventing replay attacks.

Transaction limits vary by card type, region, and merchant. Low-value transactions may proceed without PIN verification, while larger amounts require PIN or other authentication. Card-present verification methods provide security appropriate to transaction risk.

Mobile Payments

Smartphones enable mobile payments through NFC card emulation. Apple Pay, Google Pay, and Samsung Pay represent the dominant platforms. These systems store tokenized card credentials in secure elements or secure enclaves, generating unique cryptograms for each transaction.

Tokenization replaces actual card numbers with substitute values. Even if intercepted, tokens cannot be used for other transactions. Combined with per-transaction cryptographic codes, this approach provides security exceeding physical card transactions.

Host Card Emulation (HCE) enables card emulation without dedicated secure element hardware, using software security instead. Android supports HCE, enabling payment applications without carrier-controlled secure elements. Cloud-based security and limited-use credentials compensate for reduced hardware protection.

Transit Applications

Transit systems widely deploy contactless payment, with dedicated transit cards or integration with general payment systems. Fare collection requires fast transaction times (under 300 ms) to maintain passenger flow at gates and buses.

Closed-loop transit cards store value on the card itself, enabling offline transactions. Open-loop integration with bank payment cards simplifies user experience but requires terminal connectivity for authorization. Many transit systems support both approaches.

Mobile transit requires tight integration between transit agencies and mobile payment platforms. Stored value cards, period passes, and pay-per-ride options all have mobile equivalents in supported systems.

Physical Access Systems

Contactless access control uses RFID or NFC credentials instead of mechanical keys or magnetic stripe cards. Proximity cards (typically 125 kHz) and smart cards (13.56 MHz) form the basis of most systems. Readers installed at access points communicate with cards to verify authorization.

Legacy proximity cards like HID Prox transmit fixed identification numbers without encryption, enabling card cloning with readily available equipment. Modern systems use cryptographic authentication to prevent such attacks.

Smart card systems like HID iCLASS, MIFARE DESFire, and SEOS provide cryptographic authentication and mutual verification. These systems generate session keys, preventing capture and replay of credentials. Diversified keys ensure that compromising one card does not compromise the system.

Mobile Credentials

Smartphones can replace physical access cards through NFC or Bluetooth Low Energy. NFC mobile credentials work similarly to mobile payments, using secure element or HCE approaches. BLE-based systems enable hands-free access at longer range.

Mobile credential provisioning occurs over the air, simplifying administration. Credentials can be remotely revoked or updated. Temporary access for visitors can be granted and automatically expire. These capabilities improve security and convenience over physical cards.

Integration challenges include smartphone battery dependency, reader infrastructure upgrades, and support for diverse device platforms. Many deployments maintain physical card fallback alongside mobile options.

Item-Level Tagging

UHF RFID enables item-level identification in retail and logistics. Tags attached to individual products carry unique EPCs (Electronic Product Codes) enabling precise inventory tracking. Unlike barcodes requiring line-of-sight scanning, RFID readers can inventory items in boxes, on shelves, or moving on conveyors.

Retail applications include inventory accuracy improvement, out-of-stock reduction, and theft prevention. Apparel retailers widely deploy item-level RFID, with tags integrated into labels or hang tags. Studies show inventory accuracy improvements from typical 65% to above 95% with RFID.

Supply chain visibility improves through tracking items at each handling point: manufacturing, warehouse operations, shipping, and retail receipt. The EPC Information Services (EPCIS) standard enables sharing tracking events across organizations.

Asset Tracking

Reusable containers, tools, equipment, and other assets benefit from RFID tracking. Unlike disposable item tags, asset tags must withstand repeated use and harsh environments. Rugged tag designs protect electronics from impacts, chemicals, and temperature extremes.

Read zones at doorways, workstations, or defined areas automatically record asset movements. Real-time location systems (RTLS) using active RFID or hybrid technologies provide continuous position tracking for high-value assets.

Return on investment comes from reduced search time, loss prevention, utilization improvement, and maintenance tracking. Healthcare, manufacturing, and logistics see significant benefits from asset tracking deployments.

Anti-Counterfeiting

RFID provides authentication capabilities for anti-counterfeiting applications. Cryptographic tags can prove authenticity through challenge-response protocols that cannot be duplicated without access to secret keys. This enables verification that tagged items are genuine.

Pharmaceutical serialization regulations in various jurisdictions require unique identification of drug packages. RFID provides one option for serialization, though barcodes dominate current implementations due to cost.

Luxury goods, electronics, and documents use RFID authentication to combat counterfeiting. The tag presence and cryptographic verification provide confidence in product authenticity throughout the distribution chain.

Reader Architecture

RFID readers consist of RF frontend, digital signal processing, protocol handling, and host interface components. The RF frontend generates the interrogating field and receives tag responses. Modulation and demodulation circuits implement the air interface protocol. Microcontrollers or ASICs handle protocol processing and tag management.

Antenna design significantly affects read range and coverage pattern. Antenna gain, polarization, and pattern must match application requirements. Circular polarization handles tag orientation variation common in supply chain applications. Linear polarization provides better range when tag orientation is controlled.

Multi-antenna configurations extend coverage and enable spatial filtering. Phased arrays can steer beams to focus on specific areas. Multiple antennas time-multiplexed to a single reader reduce cost while expanding coverage.

Tag Antenna Design

Tag antennas must operate with minimal power from the reader's field. For passive UHF tags, the antenna must efficiently harvest energy while maintaining acceptable bandwidth. Dipole and variants thereof dominate UHF tag designs, with meander patterns shrinking physical size.

HF tag antennas are typically planar coils tuned to 13.56 MHz. Coil inductance, combined with on-chip capacitance, creates a resonant circuit maximizing energy transfer. Larger coils improve range but increase tag size. Multi-turn coils balance size and performance.

Attachment surface affects antenna performance dramatically. Metal surfaces detune and shield antennas, requiring special designs with spacers or modified antenna geometry. Water and human tissue absorb RF energy, affecting UHF more than HF systems.

Integration Options

Discrete reader modules provide RF and protocol functionality for integration into larger systems. These modules connect via serial, USB, or Ethernet interfaces, enabling rapid development of RFID-enabled products.

Smartphone NFC controllers are dedicated ICs handling NFC communications, typically connected to application processors via I2C or SPI. Secure element connections enable payment and access applications. Reference designs and development kits from NFC controller vendors accelerate product development.

Embedded reader ICs integrate reader functionality for cost-sensitive high-volume applications. These devices may include microcontrollers, reducing external component count. Applications include smart locks, toys, and appliances with NFC features.

Attack Vectors

Eavesdropping captures communication between reader and tag. While NFC's short range limits eavesdropping opportunity, sensitive applications require encryption. RFID at longer ranges presents greater eavesdropping risk.

Relay attacks extend the apparent range of NFC devices. Attackers use readers and emulators connected by a communication link to relay transactions between a victim's card and a distant terminal. Protocols requiring timing bounds help detect relay attacks.

Tag cloning copies tag data to create duplicates. Simple tags without cryptographic protection are easily cloned. Cryptographic authentication prevents cloning by requiring proof of secret key possession that cannot be extracted from captured communications.

Denial of service attacks jam or disrupt RFID communications. Continuous interference prevents legitimate transactions. Physical security and monitoring help detect such attacks in critical applications.

Cryptographic Protection

Modern RFID and NFC systems employ various cryptographic mechanisms. Symmetric key authentication uses shared secrets for mutual verification. Diversified keys, derived from master keys and tag identifiers, ensure key uniqueness. AES encryption protects data confidentiality.

Asymmetric cryptography enables public key verification without sharing secrets. Elliptic curve cryptography provides strong security with key sizes practical for constrained tags. Digital signatures verify data authenticity and integrity.

Secure elements provide tamper-resistant storage and processing for cryptographic operations. Payment cards, SIM cards, and dedicated secure element ICs protect sensitive credentials from extraction. Host card emulation trades hardware security for flexibility, using software protections and limited-use credentials.

Privacy Protection

Unique tag identifiers enable tracking of tagged items and associated individuals. Privacy-sensitive applications must consider whether identifiers should be readable by any reader or protected from unauthorized access.

Kill commands permanently disable tags, preventing post-purchase tracking. Kill passwords protect against unauthorized deactivation. Many retail tags are killed at point of sale.

Pseudonymous identifiers change periodically, preventing long-term tracking while maintaining functionality. NFC privacy modes and changing identifiers protect user privacy in payment and access applications.

Technology Selection

Selecting the appropriate RFID or NFC technology requires matching capabilities to requirements. Range requirements drive frequency selection: centimeters suggest LF or NFC, meters suggest UHF. Data volume affects memory requirements and protocol selection.

Environmental factors influence technology choice. Water or tissue presence favors LF or HF over UHF. Metal surfaces require specialized tag designs. Temperature extremes affect battery-powered active tags.

Standards compliance ensures interoperability. Payment applications require EMV Contactless certification. Supply chain applications typically follow EPC Gen2 and GS1 standards. Access control may use proprietary or standards-based approaches depending on requirements.

Deployment Considerations

Site surveys characterize RF environments before deployment. Existing RF interference, metal structures, and multipath effects influence reader placement and performance. Testing with actual tagged items in actual positions validates coverage.

Dense reader environments require coordination to prevent interference. EPC Gen2 dense reader mode and careful frequency planning enable multiple simultaneous readers. Portal and conveyor applications particularly challenge reader coordination.

Tag placement affects readability. Orientation relative to reader antenna polarization matters for UHF. Proximity to metal or liquid requires special tag selection or placement. Tag attachment method must survive product handling and use.

Testing and Validation

Read rate testing determines the percentage of tags successfully read under operational conditions. Testing should include worst-case scenarios: maximum product loading, minimum dwell time, and challenging orientations.

Interoperability testing verifies operation across different readers, tags, and firmware versions. Regression testing ensures updates do not break existing functionality. Field pilots validate performance before full deployment.

Performance monitoring tracks read rates, response times, and error rates in production systems. Degradation may indicate antenna problems, tag quality issues, or environmental changes requiring attention.