In response to the question, "Can RFID Technology Pinpoint an Item's Location to Within Inches?" you wrote: "Generally speaking, it is impossible to read a tag from 1000 feet, or even 30 feet, away and pinpoint an object's location to within a few inches… On the other hand, there are systems that can identify individual vials in a holder, even when they are inches apart. So it really depends on your application." I would like to know which exact applications can pinpoint an object's location. Also, if RFID technology can't do this, then what could be used to pinpoint an object's exact location without altering the object's size of weight, within reason?
You can place a tiny high-frequency (HF) tag on each vial of drugs, and place a tiny reader antenna in each slot where a vial is held. An interrogator can determine which of its antennas reads a tag. So by cycling through each antenna, a reader can determine which tag is in which slot. This application requires multiple reader antennas, which can be expensive if you have a lot of area to cover.
What's more, this doesn't work as easily over larger distances. Placing an ultrahigh-frequency (UHF) reader antenna under every square floor tile in an office building would tell you within a square foot where an item is located—but it would be far too expensive to be practical.
Ultra-wideband (UWB) technology can provide fairly high levels of accuracy over longer distances. There are also passive phased-array antennas that can provide accuracy to within a few feet. But within inches is very, very difficult. The reason is that it's not easy to ensure that radio waves came directly from the tagged object. If a wave bounces off different objects, providing inch-level accuracy becomes impossible.
I am unaware of any technology that can provide accuracy to within inches over distances of, say, 20 feet or more. Ultrasound and infrared can provide room-level accuracy or indicate if an item is in a particular drawer or container, but they cannot tell you where an item is located in an open area to within a few inches.
—Mark Roberti, Editor, RFID Journal
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