"An Introduction to RFID Technology"

Lorcan sent me this very interesting paper. It explains in detail how the RFID technology actually works, and a number of potential applications for it. RFID can be divided into the two types active and passive. The system I am using is passive where by the RFID tags do not need their own power source but are activated by the reader. There are again two types, magnetic induction and and electromagnetic wave capture. The main difference is the range of the reader. I am using near field RFID based on magnetic induction.



Basically the reader contains a coil and passes an alternating electrical current through which creates a localised alternating magnetic field. The tag contains a smaller coil. The readers magnetic field creates an alternating voltage across the tags coil when it enters this field. A capacitor causes a charge to build up, thus powering the tag. The tag can then generate its own magnetic field which opposes that of the reader. The reader can interpret this as an increasing current. The tag can vary its load over its coil which results in variations in its magnetic field corresponding to its binary ID. The reader interprets these signals through the change in current through its own coil.



The paper describes other interesting techniques but they are not applicable to my project.