Would there be problems with items remaining unread?
If passive high-frequency (HF) or ultrahigh-frequency (UHF) tags were lined up one behind another, then it is unlikely that you would be able to read all of them. The tags in the front would block the energy being emitted by the reader antenna from reading those in the back.
Magellan Technology, based in Australia, developed something called phase-jitter modulation (PJM) for reading HF tags. This approach enables you to interrogate an entire group of tags, even if there are many stacked up one behind another. I have seen tags on a stack of 25 sheets of paper being read consistently, for example.
I hope that answers your question.
—Mark Roberti, Founder and Editor, RFID Journal