Do I need to use UHF near-field antennas, since the antennas would be close to the boxes on the conveyor?
You would need to use a passive ultrahigh-frequency (UHF) reader equipped with far-field antennas. Antennas can be circular- or linear-polarized; for this application, you would want to use circular-polarized antennas that emit energy in a spiral pattern. This would ensure that tags in random orientation could be read.
Generally speaking, it is not a good idea to try to write to tags on a conveyor. It takes twice as much time to write to a tag as it does to read one, and if the tag is moving, it might be difficult to complete the writing process, especially if you have dozens of tags to write to. It would be best to create a station at which the tags would be bulk-encoded. Then they would be put on the conveyor and the tags could be read as they moved down the conveyor, in order to confirm that all tags had been written to. You would probably need to have some mechanism in place to push a box off the conveyor if the expected number of tags was not read. Then you could open that box to ascertain if any items were not tagged, or if there were an issue with one of the tags.
The way to read tags on the conveyor would be to put antennas on two, three or even four sides of the conveyor. If you are interrogating a large number of tags, you should angle the reader antennas to elongate the read zone, thereby giving the system more time to singulate each tag. Shielding could be used both to prevent nearby tags from being read, and to keep the energy from the antennas in the read area, thus ensuring that more energy gets to the tags.
—Mark Roberti, Founder and Editor, RFID Journal
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