I am looking at some UHF RFID readers for a project and I have a few questions about the overall concept of detecting passive RFID tags.
The system is concerned with keeping track of people passing through a specific point (doorway, staircase, etc.). This is not an access-control application; ideally the people walking through a certain checkpoint would have RFID tags on them but wouldn't take them out for scanning. Sort of like a car passing through an automated barrier after RFID tag detection, only in this case there is no barrier involved.
Think of it as a passive personnel locating system. The system would only keep track of "Person A was last seen walking through stairwell 4, half an hour ago", that's about it.
I have looked at readers like this one with circular polarization antenna and a range of 3-5 meters. I'll be using passive RFID cards. My questions are:
- My assumption is that the readers like this work only in a straight line-of-sight. If that is correct, on what factor does the "width" of the scannable area depend? If my assumption is incorrect, does the range of 5 meters mean it's actually the radius of the area that is covered by this reader?
- If a scanner like this were to be placed on the ceiling above a door, would it effectively be able to scan the tags passing below it through that door? How big a problem would "shadowing" be in this case (when a person has the tag in their pocket or two people walk next to each other so that the one in front is blocked by the one in back)?