How RFID Works

RFID Tags Past and Present

RFID technology has been around since 1970, but until recently, it has been too expensive to use on a large scale. Originally, RFID tags were used to track large items, like cows, railroad cars and airline luggage, that were shipped over long distances, These original tags, called inductively coupled RFID tags, were complex systems of metal coils, antennae and glass.

Inductively coupled RFID tags were powered by a magnetic field generated by the RFID reader. Electrical current has an electrical component and a magnetic component -- it is electromagnetic. Because of this, you can create a magnetic field with electricity, and you can create electrical current with a magnetic field. The name "inductively coupled" comes from this process -- the magnetic field inducts a current in the wire. You can learn more in How Electromagnets Work.

Capacitively coupled tags

were created next in an attempt to lower the technology's cost. These were meant to be disposable tags that could be applied to less expensive merchandise and made as universal as bar codes. Capacitively coupled tags used conductive carbon ink instead of metal coils to transmit data. The ink was printed on paper labels and scanned by readers. Motorola's BiStatix RFID tags were the frontrunners in this technology. They used a silicon chip that was only 3mm wide and stored 96 bits of information. This technology didn't catch on with retailers, and BiStatix was shut down in 2001 [source: RFID Journal].

Newer innovations in the RFID industry include active, semi-active, and passive RFID tags. These tags can store up to 2 kilobytes of data and are composed of a microchip, antenna, and, in the case of active and semi-passive tags, a battery. The tag's components are enclosed within plastic, silicon or sometimes glass.

At a basic level, each tag works in the same way:

• Data­ stored within an RFID tag's microchip waits to be read.
  
  
• The tag's antenna receives electromagnetic energy from an RFID reader's antenna.
  
  
• Using power from its internal battery or power harvested from the reader's electromagnetic field, the tag sends radio waves back to the reader.
  
  
• ­The reader picks up the tag's radio waves and interprets the frequencies as meaningful data.
  

Inductively coupled and capacitively coupled RFID tags aren't used as commonly today because they are expensive and bulky. In the next section, we'll learn more about active, semi-passive and passive RFID tags.