Is there a passive (not battery-operated) RFID transponder out there that can be pinged at medium to long distances?
It depends on what you mean by "medium to long distances." Because the electromagnetic power output of passive ultrahigh-frequency (UHF) readers is limited by regulations, the distance at which a passive UHF tag can be interrogated is largely a function of the tag antenna's size and design. A very small antenna, such as that for tags used on pharmaceuticals, will have a short read range, while a tag with a larger antenna will have a longer read range.
The passive tag with the longest range that I have ever personally seen—as opposed to merely manufacturer claims—is Omni-ID's Ultra tag (see Omni-ID Launches New High-Performance UHF Gen 2 Tags), which I witnessed being read at a distance of about 80 feet. The Ultra is a large tag encased in plastic, designed for use on vehicles and other large assets. In terms of passive tags, it can be pinged at what would be considered long distances.
—Mark Roberti, Founder and Editor, RFID Journal
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