858  RFID Frequency Bands

858.1 Learning Objectives

By the end of this chapter, you will be able to:

• Explain frequency bands: Understand LF, HF, UHF, and microwave RFID characteristics
• Compare band trade-offs: Evaluate range, data rate, and environmental tolerance
• Select appropriate frequencies: Choose the right frequency band for specific applications
• Understand NFC relationship: Explain how NFC relates to HF RFID
• Apply frequency knowledge: Make informed decisions for RFID system design

858.2 Prerequisites

Before diving into this chapter, you should be familiar with:

• RFID Introduction: Basic RFID concepts and terminology
• RFID Tag Types: Understanding passive, active, and semi-passive tags

858.3 Frequency Bands Overview

RFID operates across different frequency bands, each with unique characteristics:

Frequency	Range	Speed	Best For
LF (125 kHz)	~10 cm	Slow	Access cards, animal tracking
HF (13.56 MHz)	~1 m	Medium	Library books, payments (NFC!)
UHF (860-960 MHz)	~12 m	Fast	Inventory, supply chain
Microwave (2.45/5.8 GHz)	~1-20 m (often active)	Very fast	Some toll systems, RTLS

858.4 Low Frequency (LF): 125-134 kHz

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graph LR
    subgraph LF["LF RFID: 125-134 kHz"]
        LF1["Frequency:<br/>125-134 kHz"]
        LF2["Range:<br/><10 cm"]
        LF3["Data Rate:<br/>1-2 Kbps"]
        LF4["Penetration:<br/>EXCELLENT<br/>(metal/water)"]
        LF5["Cost:<br/>Moderate"]
        LF6["Use Cases:<br/>Pet Microchips,<br/>Access Cards,<br/>Vehicle Keys"]
    end

    style LF fill:#E8F4F8,stroke:#16A085,stroke-width:3px

Figure 858.1: Low Frequency RFID characteristics: 125-134 kHz band specifications

Characteristics:

• Range: <10 cm (very short)
• Data Rate: Slow (~1-2 Kbps)
• Penetration: Good (works near metal/water)
• Power: Low
• Cost: Moderate

Applications:

• Animal identification (pet microchips)
• Access control (door cards)
• Vehicle immobilizers
• Library books

Why LF works near metal and water: LF uses near-field magnetic coupling with a wavelength of about 2,400 meters. At these wavelengths, the electromagnetic field behaves primarily as a magnetic field, which penetrates conductive materials better than electric fields at higher frequencies.

858.5 High Frequency (HF): 13.56 MHz

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graph LR
    subgraph HF["HF RFID: 13.56 MHz"]
        HF1["Frequency:<br/>13.56 MHz"]
        HF2["Range:<br/>10 cm - 1 m"]
        HF3["Data Rate:<br/>25 Kbps"]
        HF4["Penetration:<br/>MODERATE"]
        HF5["Cost:<br/>Low-Moderate"]
        HF6["Use Cases:<br/>NFC Payments,<br/>Library Books,<br/>Passports"]
        HF7["NFC Standard:<br/>ISO 14443,<br/>ISO 15693"]
    end

    style HF fill:#FFF5E6,stroke:#E67E22,stroke-width:3px

Figure 858.2: High Frequency RFID characteristics: 13.56 MHz band with NFC standards

Characteristics:

• Range: 10 cm - 1 m
• Data Rate: Medium (~25 Kbps)
• Penetration: Moderate
• Standards: ISO 14443 (NFC), ISO 15693
• Cost: Low to moderate

Applications:

• NFC payments (contactless credit cards)
• Public transport tickets
• Passports and ID cards
• Library management
• Smart shelf inventory

NoteNFC is HF RFID

NFC (Near Field Communication) is a subset of HF RFID operating at 13.56 MHz. All NFC devices are HF RFID, but not all HF RFID is NFC. NFC adds standardized protocols for peer-to-peer communication and smartphone integration.

{
  const container = document.getElementById('kc-rfid-freq-1');
  if (container && typeof InlineKnowledgeCheck !== 'undefined') {
    container.innerHTML = '';
    container.appendChild(InlineKnowledgeCheck.create({
      question: "A public library is upgrading from barcode to RFID for its 200,000 books. Requirements: tags must fit inside book spines (thin profile), support self-checkout kiosks where patrons place stacks of books, work with security gates at exits, and allow future smartphone app integration for book information lookup. Which RFID technology best meets these needs?",
      options: [
        {text: "LF (125 kHz) passive tags - most reliable for book materials", correct: false, feedback: "LF tags have very limited read range (<10 cm) and slow data rates, making them impractical for reading stacks of books quickly. They also cannot work with smartphone NFC apps since phones use HF 13.56 MHz."},
        {text: "HF (13.56 MHz) ISO 15693 tags - supports NFC, fast enough for stacks, industry standard for libraries", correct: true, feedback: "Correct! HF RFID at 13.56 MHz is the library industry standard. ISO 15693 tags are thin, support reading multiple books at once with anti-collision, provide ~1m range for security gates, and operate at the same frequency as NFC for future smartphone integration."},
        {text: "UHF (915 MHz) passive tags - longest range for security gates", correct: false, feedback: "While UHF offers longer range, it's not ideal for libraries. UHF tags are typically larger (antenna length ~16 cm), don't fit well in book spines, and don't support smartphone NFC."},
        {text: "Active RFID tags with batteries - ensures reliable reads through book covers", correct: false, feedback: "Active tags are far too expensive ($10-50 each) for 200,000 books, too large to fit in book spines, and require battery replacement."}
      ],
      difficulty: "medium",
      topic: "rfid-frequency-bands"
    }));
  }
}

858.6 Ultra High Frequency (UHF): 860-960 MHz

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graph LR
    subgraph UHF["UHF RFID: 860-960 MHz"]
        UHF1["Frequency:<br/>860-960 MHz"]
        UHF2["Range:<br/>1-12 meters"]
        UHF3["Data Rate:<br/>640 Kbps<br/>(FAST)"]
        UHF4["Penetration:<br/>POOR<br/>(metal/water)"]
        UHF5["Cost:<br/>Low"]
        UHF6["Use Cases:<br/>Supply Chain,<br/>Inventory,<br/>Toll Collection"]
        UHF7["Multi-Read:<br/>100s tags/sec"]
        UHF8["Standard:<br/>EPC Gen2"]
    end

    style UHF fill:#F8E8E8,stroke:#2C3E50,stroke-width:3px

Figure 858.3: Ultra High Frequency RFID characteristics: 860-960 MHz with EPC Gen2 standard

Characteristics:

• Range: 1-12 m (long range for passive)
• Data Rate: Fast (~640 Kbps)
• Penetration: Poor (affected by metal/water)
• Multi-read: Excellent (100s of tags/second)
• Cost: Low

Applications:

• Supply chain & logistics (pallet tracking)
• Retail inventory (Walmart, Decathlon)
• Toll collection (E-ZPass, FAStrack)
• Race timing (marathon bibs)
• Parking access

{
  const container = document.getElementById('kc-rfid-freq-2');
  if (container && typeof InlineKnowledgeCheck !== 'undefined') {
    container.innerHTML = '';
    container.appendChild(InlineKnowledgeCheck.create({
      question: "A major retailer is deploying RFID to track 10 million clothing items across 500 stores. Requirements: read tags from 3-5 meters away, inventory an entire store (20,000 items) in under 2 hours using handheld readers, keep tag costs below $0.15 each, and read 200+ items per minute during cycle counts. Which RFID solution is most appropriate?",
      options: [
        {text: "HF (13.56 MHz) passive tags - proven technology used in many applications", correct: false, feedback: "HF tags have a maximum range of about 1 meter, making the 3-5 meter read distance impossible. Reading 20,000 items would require walking within 1 meter of every single item."},
        {text: "UHF (860-960 MHz) EPC Gen2 passive tags - long range, high throughput, low cost at volume", correct: true, feedback: "Correct! UHF EPC Gen2 is the retail industry standard. It provides 3-12m read range, supports reading 200+ tags/second with anti-collision, and passive tags cost $0.05-0.15 at volume."},
        {text: "LF (125 kHz) passive tags - most reliable with different fabric types", correct: false, feedback: "LF provides only ~10 cm range, making 3-5 meter reads impossible. Inventory counts would take days instead of hours."},
        {text: "Active UHF tags with batteries - guarantees reads even through stacks of clothing", correct: false, feedback: "At $15-50 per active tag, deploying them on 10 million items would cost $150-500 million in tags alone."}
      ],
      difficulty: "medium",
      topic: "rfid-uhf-applications"
    }));
  }
}

858.7 Microwave: 2.45 GHz, 5.8 GHz

Characteristics:

• Range: Up to 30m (active tags)
• Data Rate: Very fast
• Penetration: Very poor
• Cost: Higher

Applications:

• Vehicle tracking
• Long-range access control
• Railway car identification

858.8 Frequency Comparison Table

Feature	LF (125 kHz)	HF (13.56 MHz)	UHF (900 MHz)	Microwave (2.4 GHz)
Range	<10 cm	10 cm - 1 m	1-12 m	Up to 30 m
Data Rate	Slow	Medium	Fast	Very Fast
Metal/Water	Good	Moderate	Poor	Very Poor
Multi-tag	No	Limited	Excellent	Excellent
Cost	Moderate	Low	Low	High
Power	Low	Low	Medium	High
Standards	ISO 14223	ISO 14443/15693	EPC Gen2	Proprietary

858.9 Frequency Selection Decision Tree

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flowchart TD
    START["RFID Application"] --> Q1{"Required<br/>range?"}

    Q1 -->|"< 10 cm"| Q2{"Smartphone<br/>interaction?"}
    Q1 -->|"10 cm - 1 m"| HF["HF 13.56 MHz<br/>Library, access cards"]
    Q1 -->|"> 1 meter"| Q3{"Environment?"}

    Q2 -->|"Yes"| NFC["NFC (HF)<br/>13.56 MHz<br/>Payments, pairing"]
    Q2 -->|"No"| LF["LF 125 kHz<br/>Animal tags, access"]

    Q3 -->|"Metal/Liquid"| Q4{"Budget for<br/>special tags?"}
    Q3 -->|"Open/Cardboard"| UHF["UHF 860-960 MHz<br/>Inventory, supply chain"]

    Q4 -->|"Yes"| UHF_METAL["UHF + Metal-mount tags<br/>Industrial tracking"]
    Q4 -->|"No"| HF2["HF 13.56 MHz<br/>More tolerant"]

    style START fill:#2C3E50,stroke:#16A085,color:#fff
    style NFC fill:#16A085,stroke:#2C3E50,color:#fff
    style LF fill:#E67E22,stroke:#2C3E50,color:#fff
    style HF fill:#16A085,stroke:#2C3E50,color:#fff
    style HF2 fill:#16A085,stroke:#2C3E50,color:#fff
    style UHF fill:#2C3E50,stroke:#E67E22,color:#fff
    style UHF_METAL fill:#2C3E50,stroke:#E67E22,color:#fff

Figure 858.4: RFID frequency selection decision tree for choosing the right band

858.10 Environmental Interference

WarningWhen RFID Fails: Material Interference

RFID isn’t magic - it’s physics. Here are scenarios where materials block or interfere with RFID signals.

858.10.1 Metal Objects Block UHF RFID

What Happens: UHF RFID tags (915 MHz) stop working when placed directly on metal surfaces.

Why It Happens:

• Radio waves at UHF frequencies reflect off metal like light off a mirror
• The reflected wave cancels out the incoming wave (destructive interference)
• Tag can’t harvest energy from the reader’s signal

The Fix:

• Use metal-mount RFID tags with foam spacer (separates antenna from metal by 3-5mm)
• Alternative: Switch to LF 125 kHz tags (but shorter range)

858.10.2 Liquids Absorb UHF Radio Waves

What Happens: UHF tags work great on empty bottles but fail ~80% of the time when bottles are full of water.

Why It Happens:

• Water molecules absorb radio frequency energy (same reason microwave ovens work!)
• UHF 915 MHz particularly affected (near microwave oven frequency of 2.45 GHz)

The Fix:

• Use HF 13.56 MHz tags (longer wavelength, less absorption)
• Place tag on bottle cap (away from liquid) instead of bottle body

{
  const container = document.getElementById('kc-rfid-freq-3');
  if (container && typeof InlineKnowledgeCheck !== 'undefined') {
    container.innerHTML = '';
    container.appendChild(InlineKnowledgeCheck.create({
      question: "A beverage company wants to track inventory of canned drinks in a warehouse. Initial UHF RFID tests show 95% read rates on empty aluminum cans but only 40% read rates on filled cans containing carbonated beverages. The aluminum can material is the same in both cases. What explains this dramatic difference and what is the best solution?",
      options: [
        {text: "The carbonation creates electrical interference with RF signals - use shielded tags", correct: false, feedback: "CO2 carbonation does not create electrical interference. The issue is the water content of the beverage, not dissolved gases."},
        {text: "Water in the beverages absorbs UHF radio waves - place tags on can tops away from liquid or switch to HF frequency", correct: true, feedback: "Correct! Water strongly absorbs UHF (915 MHz) energy because its molecular resonance is near microwave frequencies. The liquid essentially steals the energy meant for the tag. Solutions: (1) Place tags on can tops/lids above the liquid level, (2) Switch to HF which is less affected by water."},
        {text: "The weight of the liquid deforms the tag antenna - use rigid tag substrates", correct: false, feedback: "Tag antennas are not affected by the weight of adjacent liquid. The problem is RF absorption by water, not physical deformation."},
        {text: "Full cans have different metal thickness - use thicker tag antennas", correct: false, feedback: "The aluminum can material is identical whether full or empty. The variable is the water content, which absorbs UHF energy."}
      ],
      difficulty: "medium",
      topic: "rfid-environmental-interference"
    }));
  }
}

{
  const container = document.getElementById('kc-rfid-freq-4');
  if (container && typeof InlineKnowledgeCheck !== 'undefined') {
    container.innerHTML = '';
    container.appendChild(InlineKnowledgeCheck.create({
      question: "An automotive assembly plant needs to track metal engine blocks through the manufacturing process. Tags will be mounted directly on metal surfaces, must survive 200 degree Celsius paint curing ovens, read reliably at 2-meter distance for automated scanning at workstations, and identify the correct part as it enters each assembly station. Which RFID approach addresses these challenging requirements?",
      options: [
        {text: "Standard UHF passive tags - longest range meets the 2-meter requirement", correct: false, feedback: "Standard UHF tags fail completely when mounted on metal surfaces. The metal acts as a reflector that detunes the antenna and creates destructive interference."},
        {text: "UHF on-metal tags with ceramic substrates - designed for metal mounting, high-temperature rated, sufficient range", correct: true, feedback: "Correct! On-metal UHF tags use a foam/ceramic spacer and specially designed antenna that actually uses the metal surface as a ground plane. High-temperature ceramic versions can survive 200+ degrees C."},
        {text: "LF (125 kHz) tags - best frequency for metal environments", correct: false, feedback: "While LF is more tolerant of metal, its <10cm range cannot meet the 2-meter automated scanning requirement."},
        {text: "Active RFID tags - battery ensures reliable reads near metal", correct: false, feedback: "Active tags face the same metal interference problems plus cannot survive 200 degree C ovens (batteries and electronics fail)."}
      ],
      difficulty: "hard",
      topic: "rfid-metal-interference"
    }));
  }
}

858.11 Summary

This chapter covered RFID frequency bands:

• LF (125 kHz): Short range, excellent metal/water tolerance, used for pet microchips and access control
• HF (13.56 MHz): Medium range, NFC compatible, used for payments, library books, and passports
• UHF (860-960 MHz): Long range, fast multi-tag reads, poor metal/water tolerance, used for supply chain and retail
• Microwave (2.45 GHz): Very long range, very poor material tolerance, used for vehicle tracking
• Selection criteria: Range, environment (metal/water), data rate, cost, and smartphone compatibility

858.12 What’s Next

Continue to RFID Standards and Protocols to learn about ISO standards, EPC Gen2, and anti-collision protocols.

NoteRelated Chapters

RFID Series:

• RFID Introduction - Basic concepts and terminology
• RFID Tag Types - Passive, active, semi-passive tags
• RFID Standards and Protocols - ISO, EPC Gen2, NFC
• RFID Design and Deployment - Decision framework

Related Technologies:

• NFC Fundamentals - NFC is HF RFID for smartphones
• Wireless Channel Characteristics - Radio propagation