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How Does RFID Work?

Posted By RFID Journal, 01.13.2011
Can you please explain how radio frequency identification systems operate?

—Name withheld

That's not a simple question to answer, since different RFID systems work in different ways.

So let me start with what radio frequency identification is: RFID is any technology for which the primary purpose is to identify objects or individuals, and that employs radio waves to do so. That encompasses a lot of different systems, including inks that contain RF-resonant chemicals. For example, by mixing a variety of chemicals that resonate at differing frequencies, one can identify an object by "listening" to the different RF signals reflected back by one ink versus another.

Typically, most systems work by having a unique identifier stored on a microchip. A reader sends out a signal, and a tag responds. Passive tags use energy from the reader to reflect back a signal. Active tags respond by broadcasting, like a cell phone. Different systems utilize different means of communicating data from the tag. Passive systems change the amplitude or frequency of the interrogator's signal. If a wave is higher, then it is a one, and if it is normal, then it is a zero. This binary data is turned into a serial number by a computer, and then passed to back-end systems that can make use of the information.

Active tags used in real-time location systems (RTLS) broadcast their identifier at regular intervals, rather than when asked to do so by a reader. Several interrogators then receive those signals, and software triangulates on the tag to determine its location.

Again, this is very much a simplification, as there are a wide variety of systems and many protocols that govern how tags and readers communicate. We will soon publish a report explaining the different types of systems, though its focus is not on the technological differences, but rather on the different ways these systems behave, and thus the different applications for which they are most suitable (see How to Choose the Right RFID Technology for Your Application).

—Mark Roberti, Founder and Editor,
RFID Journal

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