Insights / Hardware & Electronics
RFID in IoT: How Tags and Readers Work Inside a Connected System
How RFID tags and readers work, which frequency band suits which job, and how RFID becomes the identity layer of a connected system.
The short answer
RFID (radio-frequency identification) lets a reader identify a tagged object by radio, without line of sight. The reader's field powers or wakes the tag, a small chip with an antenna, which answers with its ID and sometimes a little stored or sensed data. In IoT, RFID is the identity and presence layer: tags are cheap enough to put on individual items, and the reader is the connected device that turns "tag seen here" into data the platform can act on. The frequency band sets range, speed and how the tag copes with water and metal.
What RFID is, and why it was the first idea behind the Internet of Things
When Kevin Ashton used the phrase "Internet of Things" in 1999, he meant radio tags that would let Procter & Gamble track products through its supply chain. The term has grown far beyond that, but RFID is everywhere: anti-theft tags in shops, office and hotel keycards, toll tags on cars, transit cards, pet microchips, passports and contactless bank cards, which use NFC, a short-range form of RFID.
- RFID system
- Readers that transmit a radio signal and listen for replies, plus tags attached to objects. Each tag combines an integrated circuit that stores and processes data with an antenna tuned to the reader's operating frequency.
How RFID technology works
Place a tuned circuit in an alternating electromagnetic field and a current is induced in it. That current creates the circuit's own field, its response. If the circuit's natural frequency matches the field, resonance makes the response strong enough to detect against everything else. The effect was studied in the 1930s, used in mass-market devices from the 1970s, and became mass RFID in the 1990s.
- Passive tags have no battery. They take their energy from the reader's field, so they are cheap and last indefinitely, but only work close to the reader.
- Active tags carry a battery and transmit their own signal, reaching much further at higher cost and with a finite life.
- Battery-assisted passive tags sit between the two: a battery runs the chip or a sensor, while the reply still uses the reader's energy.
- Memory can be read-only, write-once or rewritable, depending on the chip.
- On-chip cryptography in some tags encrypts or authenticates the reply, which is what makes RFID usable for access control and payment.
The tag's reply is much weaker than the reader's signal, so the further the tag, the harder it is to detect. The international ISO/IEC 18000 series defines the air interfaces for the main bands, which span roughly 120 kHz to 5.8 GHz.
RFID frequency bands compared
| Band | Typical read range | Typical uses | Behaviour near water and metal |
|---|---|---|---|
| Low frequency (about 125–134 kHz) | A few centimetres | Animal microchips, older access cards, immobilisers | Most tolerant of water and the body |
| High frequency (13.56 MHz, including NFC) | Up to around 10 cm for cards; further for vicinity tags | Payment and transit cards, passports, keycards, phone-readable NFC tags | Moderate; affected by nearby metal |
| Ultra-high frequency (about 860–960 MHz) | Several metres for passive tags | Retail and logistics item tagging, toll collection, inventory | Absorbed by water; needs metal-mount tags on metal |
| Microwave (2.45 GHz and 5.8 GHz) | Metres | Vehicle identification, some toll systems | Strongly affected by water |
| Active (battery-powered) | Tens to hundreds of metres | Locating vehicles, containers and high-value assets | Depends on band and antenna |
UHF passive tags are what made item-level tracking practical: a reader at a gate or dock door can read many tags at once without anyone scanning them. That is the main advantage over barcodes and QR codes, which are cheaper to print but need line of sight, are read one at a time and are easier to copy. UHF frequencies are allocated differently by region, so readers and tags must match the band of each market.
Where RFID struggles: water, metal and damage
- Water, especially salt water, absorbs high- and ultra-high-frequency signals. A long-range UHF tag will not read through a few tens of centimetres of water, even in a sealed waterproof housing.
- Metal shields and detunes antennas. A tag inside a closed metal box will not respond, and a standard tag stuck directly on metal reads poorly.
- Antenna damage lowers the antenna's Q-factor and so the read range. A broken antenna disables the tag even if the chip is intact.
- Eavesdropping and cloning: simple tags answer anyone who asks. Passports use shielding and access cards use cryptographic tags for this reason.
Where RFID fits in an IoT architecture
In most systems the tag is not the IoT device; the reader is. The tag supplies identity, and sometimes a reading from a simple sensor. The reader supplies power, connectivity and context: which gate, which shelf, what time.
- TagReceives the reader's signal and returns its ID, plus stored or sensed data if it has any.
- Reader and antennaEnergises the field, decodes replies and timestamps each read with its location.
- Edge filteringRemoves the duplicate reads a tag generates while it sits in the field, and turns raw reads into enter and leave events.
- ConnectivityThe reader or a gateway sends events to the platform over Ethernet, Wi-Fi or cellular.
- Platform and business systemMatches the ID to a product, asset or person, and updates stock, access or tracking records.
Passive tags can also carry simple, energy-efficient sensors powered by the reader's field. Spread across a field, tags measuring soil temperature or moisture can feed a system that adds water or fertiliser where it is needed, with no batteries to replace.
Before you design RFID into a product
Questions to settle first
- What read range do you need, and how many tags must be read at once?
- Will tags sit on or near metal, liquids or people? Choose the band and tag type for that, and test on the real objects.
- Does the use case need identity only, or stored data, sensing or cryptographic authentication?
- Which regional UHF bands and certifications apply to the reader in each market?
- Where will duplicate reads be filtered, on the reader, at the edge or in the cloud?
- How will the reader be powered, connected and updated in the field?
Questions engineers ask
Is RFID IoT?
RFID is one of the technologies IoT is built on, and the phrase "Internet of Things" was first used about RFID. A passive tag on its own is not a connected device, but an RFID reader that sends reads to a platform is part of an IoT system.
How is RFID used in IoT?
As the identity and presence layer. Tags on items, assets or people tell readers what is where; the reader adds time and location and sends events to a platform, which updates inventory, access, tracking or maintenance records.
How does RFID tracking work?
Readers are placed at known points such as gates, dock doors or shelves. Each time a tag passes through a reader's field, the reader records the tag ID, time and location, so the system can follow the item from point to point. Active tags with batteries can be located over longer distances.
Is an RFID tag an embedded computer?
Not in the usual sense. A passive tag has a small integrated circuit that stores an ID, modulates its reply and sometimes runs simple logic or cryptography, but it has no processor running application software and is powered only while the reader's field reaches it.
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Where this shows up in our work
ExpertiseHardware and electronics engineering for connected productsChoosing the band, tuning the antenna, designing the reader's power and RF path, and passing regional certification is hardware and electronics work we own with the firmware team.Tracking parts, tools and work in progress through a plant is one of RFID's most common industrial jobs. See Engineering connected products for machines that keep running.
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