What is passive RFID?

RFID, which stands for “Radio Frequency Identification”, is a contactless identification technology that has been developed for storing and remotely retrieving data using a transmitter/receiver system (reader) and markers (tags).

The technology uses electromagnetic fields received by an antenna relayed to a microchip to automatically identify people, vehicles or any miscellaneous object.

Picture of a woman using a passive RFID reader

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RFID transponders

RIFD transponders are small objects (cards/badges, keychains, bracelets/wristbands, hard or soft tags, adhesive labels, disc tags, etc.) containing a chip relayed to an antenna to receive and answer radio signals emitted by the transmitter/receiver (reader).

There are two major families of RFID transponders: Active and Passive

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RFID readers

Readers are equipment that transmit radiofrequency signals that detect all tags that enter into their field. They provide the energy for tags to be read.

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RFID frequencies

There are 3 categories of passive RFID frequencies:

  • Low frequency: 125 KHz
  • High frequency: 13.56 MHz
  • Ultra-high frequency: 863-915 MHz

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RFID active

These transponders are connected to an on-board battery and have a better range but a shorter lifespan and are more expensive.

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RFID passive

These tags use the energy transmitted by the reader’s radio signal. They are cheaper and smaller and have an almost unlimited lifespan.

STid specializes in passive RFID technologies.

How does it work?

When tags are detected by the reader, a predefined communication protocol is used for the exchange of data between the components. Unlike a bar code, RFID does not need the reader to be near the product for the identification process. Tags can be read at a distance, from a few centimeters to over ten meters away. Depending on the model used, tags can have the sole function of having their information read or can store/write additional information in their memories. Some tags also have a High Memory system, enabling data to be stored.

To communicate, the tag and reader need to be on the same frequency, but like a radio set, the frequencies can be on a wide band from low to ultra-high frequencies.


Sheme of how passive RFID works