A read with an RFID tag begins when the RFID reader transmits a signal to the tag. This is followed by the reception of the signal by the tag, which will transmit back an ID number or any other data. Decoding of the returned signal takes place, after which software associates the tag ID with the product, pallet, tool, or other assets within the system.
An RFID system involves the tag, the reader, the reader’s antenna, and the software. Different factors like the type of tag, frequency, antenna configuration, and environmental materials affect the read process. Below is an overview of the processes that take place in a passive RFID read process.
How Do RFID Tags Work? Step by Step
Step 1 – The Reader Creates the Read Zone
RF energy is transmitted by the reader antennas to form the zone of interaction of RFID devices. LF and HF systems operate on the basis of near-field magnetic coupling, whereas passive UHF operates with radiated RF energy. The strength of the field and the reader antennas determine the size and shape of the read zone.
Step 2 – The Tag Picks Up the Signal
The RFID tag antenna or coil receives the RF signal from the reader antenna. For passive tags, it also captures the energy needed for the activation of the chip. RFID tag properties, orientation, location, and environment influence the level of signal reception.
Step 3 – The Passive Tag Powers Up
RF energy from the reader field is received by the tag chip to perform the operation. The reader’s command is processed, and the data in the memory of the chip is accessed. The tag becomes inactive when leaving the field.
Step 4 – The Reader Requests the Data
The reader sends a command to the tag to access its data. During an inventory read in UHF technology, many tags are in the read zone, and so anti-collision rules are used to control the response time.
RAIN UHF technology usually utilizes the air interface GS1 EPC Gen2/ISO/IEC 18000-63.
Step 5 – The Tag Sends Its Reply
Passive UHF tags respond using backscatter by varying their reflection of the reader’s transmission. LF and HF tags use magnetic coupling for communication.
The response can consist of the tag ID and any other data the tag can hold that are compatible with the RFID standard.
Step 6 – The Reader Decodes the Response
The reader interprets the data from the response into digital format. Middleware filters any duplicate responses and passes the valid response to the business application.
Step 7 – The System Records What Happened
The software uses the tag ID to correlate the item record. Often, the tag holds the unique ID, while the name of the product, its status, location, or history information is held in the backend system.
It’s like a dock read will indicate receipt of the pallet, confirmation of shipment, or delivery of the part to the workstation. This can be recorded in a WMS, ERP, MES, POS, or asset tracking system.
How Do Passive RFID Tags Work Without Batteries?
Passive RFID tags don’t have their own source of power. The antenna/coil captures energy from the field of the reader and uses it to activate the chip just enough to read the command and send the information back. As soon as the RFID tag is outside the reader’s field, it’s deactivated.
How Passive RFID Tags Work
Passive RFID systems avoid using batteries in each tag, which makes the system effective for item-level and asset tagging. It’s used by retailers in apparel and consumer packaged goods, warehouses for boxes, pallets, and bins, and manufacturers for tool, fixture, and component tagging, where stronger tags are required.
Reading performance becomes a function of how the tag is mounted on the actual object. The reader’s power level, antenna location, tag orientation, and antenna design all become important factors. The presence of metal, liquid, closely packed items, and poor tag orientation affect UHF performance, so open testing might reflect real performance.
How Active RFID Tags Work
In active RFID tags, there’s a battery attached to the chip of the tag that powers the device itself, which provides a greater communication range compared to passive RFID tags. There can be two types of active RFID tags: one works at periodic intervals, and the other responds when contacted by the reader.
Their greater communication range means that they have larger tag sizes and are quite expensive as well.
How Battery-Assisted Passive Tags Work
The battery-assisted passive tag consists of a battery, but the RFID reader initiates communication with the tag. The battery keeps the microchip, sensors, or electronic components energized between communications. In UHF systems, it’s possible for the tag to communicate back using backscatter.
This system is used when the tag requires data collection between communications. For instance, a temperature tag collects information on temperatures between communication periods while being stored or transported.
How Do LF, HF, NFC, and UHF RFID Work Differently?
Frequency determines the communication between the reader and the tag, the size of the read zone, and the application areas of each technology.
| Type | Frequency | Communication | Common Usage |
| LF | 125-134.2 kHz
| Close contact or magnetic coupling | Animal ID, access control |
| HF | 13.56 MHz
| Close contact or magnetic coupling | Libraries, identification cards |
| NFC | 13.56 MHz | Contactless tap or very close contact | Phones, payments, smart packaging |
| UHF RFID | 860-960 MHz, depending on the region | Extended read zone and backscattering technology | Retail, warehouse, and manufacturing |
NFC is a branch of HF RFID that operates at 13.56 MHz and is designed for close-contact reading. RAIN UHF RFID works at a higher frequency with an increased reading range defined by regional regulatory standards. The reader and tag should be tuned to the same frequency and have a common air-interface protocol.
How On-Metal RFID Tags Work
A typical UHF RFID tag will suffer from a reduced read range when used directly on metal because the metal interferes with the antenna’s interaction with RF signals.
The tags are usually modified through antenna spacing, RF material, or other means to be compatible with metal surfaces. They can therefore be found on tools, machinery, pipes, metal containers, and IT infrastructure.
The geometry of the surface and location of attachment are still important factors since the performance of the same tag varies greatly from one metal surface to another.
Frequently Asked Questions
How do RFID tags work without batteries?
The energy that powers the chip in a passive tag comes from the reader field; once out of it, the tag becomes inactive and can’t be used again until a reader provides energy to it.
How does an RFID tag send information back?
Backscatter transmits data from passive UHF tags; LF and HF use magnetic coupling, whereas active tags rely on the battery for transmitting data.
Can RFID tags work through walls?
RFID signals might be capable of going through non-metallic objects, but the signal strength will become less reliable; metal reflects RF energy, and some materials rich in water lessen UHF performance.
Do RFID tags track your exact location?
An ordinary RFID tag is unaware of its position; the system only detects the reader and antenna that find it. To get more precise information about location, you need multiple antennas, active RFID, BLE, or GPS.
How long do RFID tags last?
Without any battery that can consume, the life of a passive tag depends upon the type of tag, its adhesive, temperature, humidity, chemistry, bends, and shock resistance. Battery-operated tags have a limited battery lifespan.
Conclusion
The performance of an RFID tag can vary based on the nature of the product material, positioning, reader configuration, other products, and environmental factors in the read environment. Testing the product and the proposed read environment provides more insight than simply citing a read range in the literature.
When you feel you are prepared to progress from knowing about RFID to evaluating tags, JLTRFID may be your next step in that evaluation process.
