I understand how an RFID tag works, but I am not sure how the eraser mat works. When I purchased a package of batteries at a local store, the clerk rubbed the package on a mat. He said it was to disable the RFID tag. I am curious what the mat did. Does it overload the tag and disable it? I know the tag is passive, so that makes me wonder. Can you tell me what happened when he passed the tag over the mat?
It sounds like this is a conventional electronic article surveillance (EAS) tag, and not radio frequency identification. Very few low-cost items like batteries have RFID tags. EAS tags have a single bit that is switched either on or off by an RF-based reader. So if a worker ran such a tag over a pad on a counter, that would tell the bit to turn off. Then, when the customer walked out of the store, the readers at the gate would not be able to read that bit and the alarm would not sound. If it did receive a one-bit response from the tag, the alarm would sound.
RFID tags can work the same way, though very few retailers are using them in this manner at present. The difference is that RFID transponders have at least 96 bits, and if someone were to walk through a reader with a tagged item, the reader would pick up a serial number and the store would thus know what was stolen. Turning off the RFID transponder would require that the database be told when an item is sold. So if a person walked through the gate, the reader would pick up a unique serial number and there would be a quick look-up. If that item was sold, the alarm would not sound. If the database indicated it was not sold, however, the alarm would sound.
It is possible to "kill" an RFID tag, rendering it permanently inoperable. However, this requires the use of a unique serial number for that tag, which means looking up the serial number and sending it to the tag to kill it. This is a bit cumbersome when you are dealing with hundreds of millions of unique tags, so it is not yet being done.
I hope that answers your question.
—Mark Roberti, Founder and Editor, RFID Journal