Can you suggest an RFID reader that can read three passive tags in close proximity to each other? The device should have a range of no more than 1 foot.
Australian RFID company Magellan Technology developed something called phase jitter modulation (PJM), which enabled a reader to interrogate passive high-frequency (HF) RFID tags, even when one was placed right above another. In 2013, SATO, a Japan-based provider of automatic identification and data collection solutions, acquired Magellan (see SATO Acquires Magellan Technology). I do not know if SATO is still producing and selling tags and readers that use PJM technology, but I suggest that you contact them and ask. Other HF readers might also work, depending on how close the tags are to each other.
—Mark Roberti, Founder and Editor, RFID Journal