The read range you're seeing also seems compatible with a low frequency device. I'm quite perplexed. I don't think the foil could be attenuating the signal di

The read range you're seeing also seems compatible with a low frequency device. I'm quite perplexed. I don't think the foil could be attenuating the signal directly. It might be reflecting it/altering the field pattern so as to reduce the effective gain between the transmitter and receiver antennas.