I have an RFID antenna that has been delivered with a flat metallic plate glued to its back. I don't know much about this antenna it arrived without any documentation, it is square and can read tags in every orientation (not polarised). I am wondering whether I could remove it or if this might have been glued for a reason (insulation? amplification?). I guess in a more general sense my question is: does a metallic object behind an RFID antenna change the readings?
Electronic – Will put a metallic plate behind an RFID antenna change the readings
rfid
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RFID tags can be made Damn Small™. Among the smaller ones are subdermal tags used for instance in animal identification:
IIRC in Belgium every horse must have such a subdermal RFID tag.
Other small tags (smaller than a credit card, anyway) are key fob sized tags
and, about the same size, RFID tags that look like a wrist watch, I often see those in, again Belgian, cafés and restaurants to identify the waiter at the cash register computer.
RFID most often uses 125kHz or 13.5MHz carriers. If you go to 2.4GHz you can further miniaturize the tag. The following, 0.4mm x 0.4mm in size, is the smallest I could find:
So RFID tags can be made very small indeed. I guess there are much less miniaturization possibilities for the transmitter if it wants to extend the near field to a workable distance. The tag has to be in the near field to be detectable.
You'll find that it won't work, the metal will block the signal from your standard cheap RFID reader completely. Drilling holes will make absolutely no difference.
You would need to cut out an aperture the size of the RFID antenna plus a decent margin (20 mm or more all round?) and mount the reader within that aperture or on the RFID tag-side, not the 'other side' to where your tags are.
One option to consider is putting your reader in a tough plastic box and mounting that on the tag-side of the metal wall, with a hole drilled though to take the cable. Make sure the plastic box keeps the reader inside away from the metal by at least 20 mm, preferable 40 mm or more. You'll find out best by buying one and mocking this up by your wall.
A couple of years ago, I spent a good amount of time investigating RFID technology for use in a machine in a large metal enclosure. One part was me experimenting with a commercial (£30) USB reader and how it would read through different materials when near or surrounded by metal. Was interesting stuff.
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I assume that OP means "change antenna parameters", not digital content of ID. Note that RFID "Near Field Communication" antenna in smartphones is frequently glued to phone's battery, Samsung phones (S3, S4, J3, etc.) have it. The battery case is essentially metal, and the antenna works just fine. So the metallic plate might limit the distance of sensing (my speculations), so two persons with tags approaching the RFID base won't accidentally interfere.
There were quite a few studies on this subject, "because metallic surface changes its radiation pattern, input impedance, radiation efficiency and resonant frequency", see this article, and sophisticated modeling methods were used to evaluate the plate effects.
To reduce the influence of metaillc mounting surfaces on performance of RFID installations, special flexible ferrite tiles are offered,
I would hazard to guess that the plate is inseparable part of the antenna design, and I wouldn't remove it.