I would like to attach a passive UHF RFID tag to each student's ID, and also affix high-powered readers to the walls of our school. An app would tell the readers to interrogate the tags, and to send that data back to the app. Would the readers be able to interrogate the students' IDs as they remained sitting 20 meters away?
No, you would not be able to read all of the tags on students from 20 meters away, nor would it be a good idea to put "high-powered" readers on the walls to read the students' IDs. High amounts of RF energy—beyond the amount readers are legally allowed to emit—could be harmful to humans.
There are two sensible options for you to consider. One would be to read the students' tags as they enter a room. You could place a reader above the door and have antennas either facing down from the ceiling or on each side of the doorway. You might not be able to read every tag because the body of one student might prevent the tag on another child behind him or her from being read. You would need to test several configurations in order to make sure all tags could be interrogated.
Another option would be to use battery-assisted passive (BAP) tags. Convergence Systems Ltd. makes a BAP tag designed for use as an ID badge. The battery in this tag allows for a longer read range and more consistent reads near a human body. The cost would be more than that of standard passive tags, and the tags would need to be replaced as their batteries died, but it would be a good option for your application.
—Mark Roberti, Founder and Editor, RFID Journal
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