What obstacles would this present?
RF energy is absorbed by water, and the human body is mostly composed of water, so if a tag were shielded from a reader by a person's body, it would be very difficult to read that tag. One way to overcome this would be to use battery-assisted passive (BAP) tags. Such tags use battery power to run the chip's circuitry, so they can reflect back a stronger signal to the reader than a purely passive tag.
BAP tags are more expensive than purely passive tags, so this might be an option. It might be possible to read tags by creating a portal through which someone must walk. You would need to place readers on a variety of angles to completely surround each person as he or she passed through the portal—and, if possible, you should use foam spacers around each tag to keep it off the body. You would need to perform some testing to determine whether or not this could ensure tag detection.
—Mark Roberti, Founder and Editor, RFID Journal
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