We use UHF RFID tags in a retail environment, and sometimes the tags fall asleep and cannot be read. This happens during inventory loads, and the tag that falls asleep usually does not wake up. Any idea why this would happen?
Is the tag readable again after a period of time, or once it goes to sleep, does it remain unreadable thereafter? If the tag is permanently unreadable, then it is a bad tag. The problem is probably a production issue. The leading inlay providers check that their tags work before delivering them to a label converter, but the contacts between an antenna and a chip can be damaged during the converting process. The converter should check each label before delivering it to a customer, but not every company does this.
If the tag wakes back up, there could be a problem with the settings in your reader. There is a feature in passive UHF systems called "sessions," which allows a tag to be read by one reader and then by another. It's possible the tag is being read, then is expecting another reader to start communicating with it so it stops communicating with the first reader.
If neither of these are the issue, then I would contact the tag provider and/or the reader company you are using.
—Mark Roberti, Founder and Editor, RFID Journal