I have an application which uses animal tags and a RFID reader operating at 134.2KHz. The tags are embedded in wooden objects that are passed through the coil. The coil at the moment is about 110 mm in diameter. I have wound it to the specified inductance and have also tuned it with an oscilloscope. All is fine except that about 5 per cent of tags fail to be read. This is probably because I can't control the orientation of the tag as they pass through the coil. I made another coil slightly smaller at 100mm, same inductance, and the performance is slightly worse. I'm not sure whether size matters - my instinct was that a bigger coil is likely to have a dead spot in the middle, and that using a smaller one would give a greater chance that the tag will be near the side of the coil as it passes through. But maybe I'm wrong - my experiment suggests that I might get a better result with a bigger coil.
Any thoughts, please?
Any thoughts, please?