8  RFID Tag Types and Components

Key Concepts

• Class 0 Tag: A factory-programmed read-only tag; the EPC is written at manufacture and cannot be changed
• Class 1 Gen1 Tag: A write-once read-many tag; the EPC can be programmed once after manufacture
• Class 1 Gen2 Tag (ISO 18000-6C): The dominant UHF tag class; supports multiple reads and writes, password protection, and kill command
• Class 3 Tag: A semi-passive tag with an integrated battery for powering sensors but using backscatter for communication
• Class 4 Tag: An active tag with battery-powered radio transmission; enables device-to-device communication without a reader in the field
• Memory Bank Structure: Gen2 tags have four memory banks: Reserved (passwords), EPC, TID (unique factory ID), and User (application data)
• TID (Tag Identifier): A factory-written read-only identifier unique to each tag IC; used for clone detection and track-and-trace even when the EPC is changed

8.1 In 60 Seconds

RFID tags come in three types: passive (no battery, powered by the reader’s RF field, cheapest at cents each, unlimited life), semi-passive (battery powers onboard sensors and memory while communication still uses backscatter), and active (full battery-powered transmitter, longest range up to 100+ metres, highest cost). Choose passive for high-volume tracking, semi-passive for cold-chain sensor logging, and active for real-time location of high-value assets. Sleep current often dominates battery life in duty-cycled active tags.

8.2 Learning Objectives

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

• Classify tag types: Distinguish passive, active, and semi-passive RFID tags by power source, communication method, and cost profile
• Analyse tag components: Explain the function of antennas, integrated circuits, and memory in each tag category
• Select appropriate tags: Choose the optimal tag type for specific IoT applications based on range, environment, and budget constraints
• Calculate battery life: Derive active tag power consumption and expected lifetime from duty-cycle parameters
• Justify design trade-offs: Defend tag selection decisions by balancing cost, range, sensor needs, and maintenance requirements

For Beginners: RFID Tag Types

RFID tags come in three varieties: passive (no battery, powered by the reader’s signal), semi-passive (battery for the chip but no transmitter), and active (has its own battery and transmitter). Each type has different range, cost, and lifespan trade-offs. Choosing the right tag type is one of the most important decisions in an RFID project.

8.3 Prerequisites

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

• RFID Introduction: Basic understanding of RFID concepts and terminology
• Basic electronics: Familiarity with concepts like antennas, circuits, and power consumption

8.4 Types of RFID Tags

There are three main types of RFID tags:

Figure 8.1: Comparison of passive, semi-passive, and active RFID tag types

Alternative View: RFID Tag Selection Decision Tree

This variant helps you choose the right RFID tag type for your application:

Most IoT applications use passive tags due to their low cost and maintenance-free operation.

Tag Types Overview

RFID Tag Types

Reader Hardware

RFID Reader

Reader Antenna

RFID Reader Antenna

Figure 8.2: RFID tag types and reader hardware configurations

8.5 RFID Tags (Transponders)

Tags store and transmit data to readers. They come in various forms:

Figure 8.3: RFID tag types hierarchy with power source, range, cost, and use cases

8.5.1 Tag Comparison Table

Type	Power Source	Typical Range	Relative Cost	Battery/Lifetime	Use Cases
Passive	Reader’s RF field	cm-meters (band dependent)	Low	No battery (packaging dependent)	Retail, inventory, access cards
Semi-Passive	Battery (sensor), RF (comm)	Similar to passive (design dependent)	Medium	Battery-limited	Cold chain, shipping
Active	Internal battery	Longer (deployment dependent)	High	Battery-limited	Vehicle tracking, asset management

8.5.2 Passive Tags

Passive tags are the most common RFID tags due to their low cost and maintenance-free operation.

Characteristics:

• No internal battery - powered entirely by reader’s electromagnetic field
• Simple construction: antenna + integrated circuit (chip)
• Lowest cost (cents per tag at volume)
• Unlimited operational life (until physically damaged)
• Range depends on frequency band and reader power

How They Work:

1. Reader transmits RF energy
2. Tag antenna captures energy via inductive coupling (LF/HF) or backscatter (UHF)
3. Captured energy powers the tag’s chip
4. Chip modulates the antenna impedance to transmit data back

Applications:

• Retail inventory tracking
• Library book management
• Access control cards
• Supply chain logistics
• Animal identification (pet microchips)

8.5.3 Semi-Passive Tags (Battery-Assisted Passive)

Semi-passive tags (also called Battery-Assisted Passive or BAP) combine features of passive and active tags.

Characteristics:

• Battery powers onboard electronics (sensors, memory, processing)
• Communication still uses passive backscatter (battery not used for transmission)
• Better read reliability than pure passive tags
• Can include sensors for temperature, humidity, shock detection
• Battery life typically 3-7 years depending on sensor activity

How They Work:

1. Battery continuously powers sensors and data logging
2. When interrogated by reader, communication uses passive backscatter
3. Battery does NOT power the RF transmission
4. Sensor data stored in memory is transmitted during reader interrogation

Applications:

• Cold chain monitoring (temperature logging)
• Pharmaceutical tracking
• High-value asset monitoring
• Perishable goods tracking
• Shock/vibration detection for fragile items

8.5.4 Active Tags

Active tags include their own power source and transmitter for longest range and most features.

Characteristics:

• Internal battery powers all tag functions including RF transmission
• Longest read range (30-100+ meters depending on configuration)
• Can include GPS, sensors, and advanced processing
• Highest cost per tag ($15-100+)
• Battery replacement required (typically 2-7 year life)
• Can operate independently of readers (beacon mode)

How They Work:

1. Battery powers continuous or periodic operation
2. Tag actively transmits signals (not backscatter)
3. Can beacon at regular intervals even without reader interrogation
4. More complex communication protocols possible

Applications:

• Shipping container tracking
• Vehicle fleet management
• Real-Time Location Systems (RTLS)
• Mining equipment tracking
• Airport ground equipment
• High-value asset protection

Alternative View: RFID Tag Types Comparison

This variant compares passive, semi-passive, and active RFID tags across key dimensions:

Passive tags are cheapest and last forever but have limited range. Semi-passive add sensors with moderate battery life. Active tags provide longest range but highest cost and limited lifetime.

8.6 RFID System Architecture

Alternative View: RFID System Architecture

This variant shows the complete RFID system from tag to enterprise software:

RFID systems consist of four layers: Tags (data carriers), Readers (RF interfaces), Middleware (processing and filtering), and Enterprise systems (business logic). Middleware is critical for reducing data volume and generating meaningful events.

8.7 RFID Readers (Interrogators)

Readers emit RF signals and decode tag responses:

Types:

• Fixed readers: Mounted at entry points (warehouses, toll booths)
• Handheld readers: Portable devices for inventory
• USB readers: Desktop accessories for PC access control
• Embedded modules: Integrated into IoT devices (ESP32, Arduino)

Components:

• Antenna(s)
• RF transceiver
• Control unit / microprocessor
• Communication interface (USB, Ethernet, Wi-Fi, Bluetooth)

8.8 Knowledge Check: Tag Selection

8.9 Battery Life Calculations for Active Tags

Understanding battery life is critical for active tag deployment planning.

8.9.1 Power Analysis Example

Scenario: A shipping company tracks containers with active RFID tags transmitting GPS location every 30 seconds using a 2,000 mAh battery that consumes 10 mA during 0.1s transmission and 0.05 mA while sleeping.

Power Analysis:

• Transmission: 10 mA for 0.1s every 30s = 0.0333 mA average
• Sleep: 0.05 mA for 29.9s every 30s = 0.0498 mA average
• Total average: 0.0831 mA

Battery Life Calculation:

• Battery capacity: 2,000 mAh
• Average current: 0.0831 mA
• Expected life: 2,000 / 0.0831 = 24,067 hours = 2.75 years

Critical insight: Sleep current (0.05 mA) actually dominates total power consumption despite being 200x lower than transmission current (10 mA), because the device sleeps 99.67% of the time.

Putting Numbers to It

Let’s calculate duty cycle and verify sleep current dominance. Transmission duty cycle = \(0.1\) s every \(30\) s = \(0.1/30 = 0.0033\) (0.33%). Sleep duty cycle = \(1 - 0.0033 = 0.9967\) (99.67%).

\[I_{\text{avg}} = I_{\text{tx}} \times d_{\text{tx}} + I_{\text{sleep}} \times d_{\text{sleep}}\]

Substituting: \(I_{\text{avg}} = 10 \times 0.0033 + 0.05 \times 0.9967 = 0.033 + 0.0498 = 0.0831\) mA. The sleep current contributes 0.0498/0.0831 = 60% of total power despite being 200× smaller than TX current. This is why reducing sleep current from 0.05 mA to 0.01 mA (achievable with better voltage regulators) extends battery life from 2.75 years to 5.5 years.

Cold Weather Impact

At -20 degrees C, battery capacity can reduce by 50%. The same tag configuration would last only 1.4 years in cold conditions, potentially failing before a 6-month shipping voyage is complete.

Solution: Reduce transmission frequency from 30 seconds to 5 minutes, extending battery life to 4.3 years at 25 degrees C or 2.1 years at -20 degrees C.

8.10 Understanding Check: Marathon Race Timing

Understanding Check: Marathon Race Timing System Requirements

Scenario: You’re designing an RFID timing system for a marathon tracking 5,000 runners. The system must read timing chips attached to shoes as runners pass checkpoints at 3m distance while running at speed. Up to 50 runners may pass simultaneously per second. Timing chips must be reusable for 100+ races to justify the investment.

Think about:

1. What read speed (tags/second) is required to handle 50 simultaneous runners?
2. Why does passive vs active tag selection affect multi-race reusability?
3. How do different frequency bands affect the ability to read runners in motion at 3m distance?

Key Insight: This high-throughput, high-reliability scenario demands UHF passive RFID with anti-collision:

UHF Passive with Anti-Collision (recommended):

• Designed for high multi-tag throughput at checkpoints (anti-collision + engineered read zone)
• Mat/portal antennas can create a controlled read zone as runners pass through
• No battery (lower maintenance); durability and reusability depend on packaging and how tags are attached

Why alternatives fail:

LF 125 kHz: Very short range makes it hard to read reliably at speed unless tags pass extremely close to the antenna

HF 13.56 MHz: Short range often makes checkpoint reads challenging at a distance unless the read zone is tightly constrained

Active tags + GPS: Adds battery logistics and cost without clear benefit if you only need checkpoint timestamps (not continuous tracking)

Verify Your Understanding:

• Why is anti-collision algorithm critical when 50 runners pass simultaneously?
• How does mat antenna placement enable 3m read range for shoe-mounted tags?
• What are the lifecycle trade-offs (reusability, maintenance, infrastructure) between passive and active approaches?

Sensor Squad: Meet the Three Tag Siblings

Sammy the Sensor introduced the three RFID tag siblings to the class.

First was Pip the Passive Tag: “I don’t need any batteries! When the reader sends radio waves, I soak up the energy like a solar panel soaking up sunshine. I’m the cheapest in the family – only a few pennies each – and I never run out of power. You’ll find me in library books, pet microchips, and shop price tags. My only weakness? I can’t shout very far – the reader has to be within a few metres.”

Next was Sam the Semi-Passive Tag: “I carry a tiny battery, but I only use it to power my thermometer and notebook. When the reader asks me a question, I still answer the same way Pip does – using backscatter. My battery lets me keep a diary of temperatures every 15 minutes, which is perfect for making sure medicine stays cold during delivery!”

Finally, Alex the Active Tag bounded in: “I’ve got a big battery and my own radio transmitter! I can shout across a football field – over 100 metres! Ships use me to track cargo containers across the ocean. The downside? I’m the most expensive sibling, and my battery eventually runs out, usually after a few years.”

“So which one is best?” asked Lila the LED.

Bella the Battery smiled. “None of them is ‘best’ – each is perfect for different jobs. That’s why engineers need to understand all three!”

Lesson learned: Passive tags are cheapest and last forever but have limited range. Semi-passive tags add sensor capabilities. Active tags offer the longest range but cost more and need battery replacement. Choose based on your specific needs.

Interactive: RFID Tag State Machine Animation

8.11 Worked Example: Cold-Chain Pharmaceutical Tracking — Tag Type Selection

Scenario: PharmaFlow AG distributes temperature-sensitive vaccines across 14 European countries. They need to track 800,000 vaccine shipments per year from manufacturing through last-mile delivery, with continuous temperature logging from factory to clinic refrigerator.

Requirements analysis:

Stage	Containers/Year	Read Distance	Temp Logging	Dwell Time	Budget/Tag
Factory pallets	12,000	3-5 m (dock doors)	Every 5 min	2-8 hours	< EUR 5.00
Distribution boxes	120,000	1-2 m (conveyor)	Every 15 min	1-3 days	< EUR 1.50
Individual vials	800,000	10-30 cm (handheld)	None (ambient assumed)	1-90 days	< EUR 0.08

Tag type decision for each stage:

Stage 1 — Factory pallets: Semi-passive (BAP) UHF tags

• Tag: Confidex Carrier Pro with integrated thermistor, EUR 3.80/unit
• Battery life: 5 years at 5-minute logging interval (CR2032, 230 mAh)
• Power budget: sensor wake 12 uA x 200 ms every 5 min + sleep 1.8 uA = average 2.6 uA
• Battery life: 230,000 uAh / 2.6 uA = 88,460 hours = 10.1 years (derated to 5 years for cold exposure)
• Memory: 8 KB EEPROM stores 2,048 readings (7 days at 5-min intervals)
• Why not active: pallets stay within dock-door read zones; 3-5 m passive backscatter range is sufficient; active tags at EUR 25+ are 6.5x more expensive with no benefit
• Annual cost: 12,000 x EUR 3.80 = EUR 45,600

Stage 2 — Distribution boxes: Semi-passive HF/UHF dual-frequency tags

• Tag: custom inlay with NTC thermistor, EUR 1.20/unit at 120K volume
• Battery life: 3 years at 15-minute interval (CR1220, 40 mAh)
• Power budget: average 1.5 uA = 40,000 uAh / 1.5 uA = 26,666 hours = 3.0 years
• 4 KB memory stores 384 readings (4 days at 15-min intervals)
• HF interface allows pharmacist to tap-read temperature log with NFC phone at delivery
• Annual cost: 120,000 x EUR 1.20 = EUR 144,000

Stage 3 — Individual vials: Passive UHF inlays

• Tag: Avery Dennison AD-229r6 wet inlay, EUR 0.038/unit at 800K volume
• No temperature logging (vial travels inside monitored box)
• Purpose: unique serial number for anti-counterfeiting and inventory
• Read range: 4-6 m with fixed reader, sufficient for case-level bulk reads
• No battery, unlimited shelf life (critical for vaccines stored 1-5 years)
• Why not semi-passive: temperature already logged at box level; adding a battery to 800K vials adds EUR 640K+ and creates disposal liability
• Annual cost: 800,000 x EUR 0.038 = EUR 30,400

Total annual tag cost: EUR 45,600 + EUR 144,000 + EUR 30,400 = EUR 220,000

Key lessons from this design:

1. Match tag type to the container level, not the product level. Temperature logging at vial level (800K semi-passive tags) would cost EUR 960K+ vs EUR 144K at box level — a 6.7x cost difference for the same data
2. Battery derating matters. The CR2032 calculates to 10 years at room temperature, but cold-chain exposure (2-8 C) reduces capacity by 40-50%, yielding a realistic 5-year life
3. Passive tags win on volume. At EUR 0.038 each, passive vial tags cost less than the adhesive label they replace. The anti-counterfeiting value alone justifies the investment

8.12 How It Works: Passive Tag Energy Harvesting

The “magic” of battery-free operation:

1. Reader transmits RF energy (continuous wave at 915 MHz for UHF)
2. Tag antenna captures RF (acts like tiny solar panel for radio waves)
3. Rectifier converts AC to DC (diode bridge charges capacitor)
4. Capacitor powers chip (stores ~10-50 µJ, enough for microseconds of operation)
5. Chip modulates antenna (backscatter: changes impedance to reflect signal)
6. Reader detects modulation (demodulates reflected signal to recover data)

Power budget example (UHF passive tag):

• Reader transmit: 1W EIRP at 3m distance
• Tag receives: ~1 µW (path loss + antenna gain)
• Harvested power: ~0.3 µW (30% efficiency typical)
• Chip consumption: ~5 µW peak (during read), ~0 µW (when no reader present)
• Result: Tag operates only when reader is actively interrogating

Why unlimited life? No battery to deplete. Tag degrades only from physical damage (UV, moisture, bending).

8.13 Concept Relationships

Tag type selection flowchart:

Need sensors? → Yes → Semi-passive or Active
             → No  → Need range > 10m? → Yes → Active
                                       → No  → Passive (cheapest)

How types relate:

• Passive → foundation (simplest, no battery)
• Semi-passive → adds battery for sensors (communication still passive)
• Active → fully autonomous (battery powers everything)

Prerequisite knowledge:

• Frequency bands (determines passive tag read range)
• Power budgets (critical for active tag battery life)
• Backscatter modulation (how passive tags communicate)

Foundation for:

• Tag selection for specific applications
• Cost-benefit analysis (TCO over tag lifetime)
• Battery replacement planning (active/semi-passive)

8.14 See Also

Tag selection guides:

• RFID Frequency Bands - Band affects tag type viability
• RFID System Components - Readers and antennas
• RFID Real-World Apps - Type selection examples

Power management:

• Energy Harvesting - RF energy capture
• Battery Technologies - Active tag batteries
• Low-Power Design - Minimizing consumption

Alternative technologies:

• NFC Tags - HF passive tags with phone support
• BLE Beacons - Active battery-based alternative
• UWB Tags - Active tags for precise positioning

Common Pitfalls

1. Confusing the TID With the EPC

The TID is factory-programmed and unique to the IC; it cannot be changed. The EPC is user-programmable and represents the item identity in the application. Fix: use the TID for anti-cloning verification and the EPC for business item identification; never conflate the two.

2. Not Using the Access Password to Protect Critical Tag Data

Gen2 tags can be locked to prevent EPC modification using a 32-bit access password. Without it, anyone with a Gen2 writer can change the EPC. Fix: set a non-zero access password and lock the EPC bank before deploying tags in any application where data integrity matters.

3. Assuming All Gen2 Tags Have the Same User Memory Size

User memory size varies from 0 bytes (some inlay-only tags) to 512 bytes+ (premium sensor tags). Assuming 32 bytes of user memory when the selected tag has 0 bytes causes application failures. Fix: verify the user memory size in the tag IC datasheet and select a tag with at least 20% more memory than the maximum expected payload.

🏷️ Label the Diagram

💻 Code Challenge

8.15 Summary

This chapter covered RFID tag types and components:

• Passive tags: Battery-free, powered by reader, lowest cost, unlimited life
• Semi-passive tags: Battery powers sensors/memory, RF for communication, ideal for data logging
• Active tags: Full battery power, longest range, highest capability and cost
• Power analysis: Sleep current often dominates battery life in duty-cycled systems
• Selection criteria: Match tag type to range, cost, sensor, and maintenance requirements

Interactive: Match Tag Types to Their Characteristics

Interactive: Order the Tag Selection Process

8.16 What’s Next

Now that you understand RFID tag types, explore these related topics:

Next Chapter	Description
RFID Frequency Bands	LF, HF, UHF, and microwave band characteristics and how to choose
RFID System Components	Readers, antennas, middleware, and system architecture
RFID Standards and Protocols	EPC Gen2, ISO standards, and air interface protocols
RFID Real-World Applications	Industry case studies and tag selection examples
RFID Design and Deployment	Complete decision framework for RFID system planning