Could an RFID system alert an end user—a school, for example—if an individual were carrying two RFID cards instead of just one?
This would be a challenge, but it would depend on how the system was set up and what technology was used. Generally speaking, passive RFID systems will tell you only that a tag is in the read field. In an education setting, if you were to set up a portal and have each student stand in a specific spot, you could identify that there were two tags on that person. However, most systems don’t work this way. Students simply stream into a room, passing a reader antenna as they enter. There might be several tags in the read field at any given time, and there would be no way to determine whether the three tags were on three people or two.
It might be possible to use a passive ultrahigh-frequency (UHF) phased-array antenna system, such as the one offered by Mojix, which can identify a tag’s location in three-dimensional space. If desks were spaced a few feet apart, the system could ascertain if someone were wearing or holding two tags. An active ultra-wideband (UWB) system could also do the same thing. However, this approach would likely be too expensive, as you would need readers and antennas or exciters in each room.
Another option might be to use an electric eye or video analytics to count the number of people entering a room, and to then compare that to the number of tag reads. If there isn’t a match, the system could alert the teacher, who could then have each student walk past the reader antenna until he or she found the individual carrying two tags. The knowledge that the system could not be gamed would likely deter students from trying to get a friend to carry a tag in for them.
—Mark Roberti, Founder and Editor, RFID Journal
Is It Necessary to Use Four Antennas With a UHF Reader? »