860  RFID Fundamentals and Operation

860.1 What is RFID?

RFID (Radio Frequency Identification) is a wireless technology that uses radio waves to automatically identify and track objects, animals, or people. An RFID system consists of two main components: tags (attached to objects) and readers (that interrogate tags).

Key Characteristics:

  • Contactless: No physical contact or line-of-sight required
  • Automatic: Identification happens without human intervention
  • Simultaneous: Can read multiple tags at once (anti-collision)
  • Durable: Tags can withstand harsh environments
  • Range: From centimeters to tens of meters depending on frequency
  • No Power Needed: Passive tags powered by reader’s electromagnetic field
Diagram illustrating RFID system operation: RFID reader antenna on left emits electromagnetic radio waves (shown as curved lines) that propagate through space to multiple RFID tags on right. Tags harvest energy from these radio waves to power their internal circuits, then respond by backscattering modulated signals containing stored identification data back to the reader antenna for decoding and processing. Demonstrates contactless wireless identification using radio frequency communication between reader interrogator and passive transponder tags.
Figure 860.1: RFID working principle with reader and tags

860.2 Historical Context

Year Milestone
1945 Léon Theremin invents “The Thing” - first espionage RFID device
1973 Charles Walton patents first modern RFID device
1990s Walmart pioneers RFID for supply chain management
2000s RFID becomes mainstream in logistics, retail, access control
2010s Explosion in IoT integrates RFID with cloud and mobile
2020s Chipless RFID, blockchain integration, ubiquitous deployment

860.3 How RFID Works

860.3.1 Basic Operating Principle

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flowchart LR
    subgraph Reader["📡 RFID READER"]
        R1["RF Transmitter"]
        R2["Receiver"]
        R3["Decoder"]
        R4["Processor"]
    end

    subgraph Field["🌊 ELECTROMAGNETIC FIELD"]
        F1["13.56 MHz<br/>(HF example)"]
        F2["Energy Transfer"]
    end

    subgraph Tag["🏷️ RFID TAG"]
        T1["Antenna<br/>(coil)"]
        T2["Chip<br/>(IC)"]
        T3["Memory<br/>(ID data)"]
    end

    R1 -->|Emits RF| F1
    F1 -->|Powers| T1
    T1 --> T2
    T2 --> T3
    T3 -->|Modulates| T1
    T1 -->|Backscatter| F2
    F2 -->|Signal| R2
    R2 --> R3
    R3 --> R4
    R4 -->|Tag ID| Output["💻 System<br/>(Database)"]

    style Reader fill:#E8F4F8,stroke:#16A085,stroke-width:3px
    style Field fill:#FFF5E6,stroke:#E67E22,stroke-width:3px
    style Tag fill:#F8E8E8,stroke:#2C3E50,stroke-width:3px

Figure 860.2: RFID system operation flowchart showing reader, electromagnetic field, and tag interaction

Step-by-Step:

  1. Reader emits RF signal: Creates electromagnetic field
  2. Tag harvests energy: Passive tag powered by field (or uses battery for active)
  3. Tag responds: Modulates reader’s signal with its unique ID
  4. Reader decodes: Extracts tag ID and any stored data
  5. Action taken: System logs, triggers, or processes the identification

RFID system architecture diagram from IIT Kharagpur NPTEL course showing the complete HF 13.56 MHz contactless RFID system. Components include: (1) Tagged Item with barcode at top, (2) RFID Tag with internal coil antenna displaying ID 'ABC123', (3) Tag Cover protecting the tag, (4) Contactless RFID Reader operating at 13.56 MHz at bottom, (5) Magnetic Lines of Force shown as concentric elliptical field lines representing electromagnetic coupling between reader antenna coil and tag antenna coil, (6) RFID Software backend system for data processing, and (7) Power connection to the reader. The diagram illustrates inductive coupling principle where the reader's antenna generates an alternating magnetic field that induces current in the tag's coil antenna, powering the tag circuit and enabling bidirectional data communication.

HF RFID contactless system showing tag-reader electromagnetic coupling

Source: IIT Kharagpur - NPTEL Introduction to Internet of Things

This academic diagram illustrates the inductive coupling principle used in HF RFID systems:

  • Magnetic field lines (shown as elliptical curves) emanate from the reader’s antenna coil
  • The tag’s coil antenna intercepts these field lines, inducing a current that powers the tag
  • At 13.56 MHz, this near-field magnetic coupling provides reliable communication up to ~1 meter
  • The tag modulates the field by changing its antenna impedance (load modulation), allowing data transmission back to the reader

Question: A library manages 500,000 books. Books must be checked out/in quickly (5 books/second), detected if carried through security gates, and tags must be thin enough to fit in book spines. Which RFID frequency works best?

💡 Explanation: B. HF RFID (13.56 MHz) is commonly used for library tags (often ISO 15693): thin tags fit in spines, the data rate supports rapid check-in/out, and gate readers can detect tags as patrons exit. LF is typically too short-range/low-rate for fast multi-book workflows, and UHF is more sensitive to detuning/multipath near dense shelving unless the environment is carefully engineered.