How can the antenna's range be improved?
I am not an electrical engineer, but my understanding is that an antenna can be tuned to function when wet. As I understand it, water on a substrate detunes an antenna, making it more difficult for the antenna to harvest energy from a reader antenna. Less energy means the tag cannot respond with anything but a very weak signal that might not be picked up by the reader antenna. Altering the antenna's impedance so that it operates closer to the chip's impedance when wet allows the tag to perform better. (I encourage readers who are engineers to correct me if I am wrong about this, or to explain more clearly if they can.)
RFMicron makes a chip that dynamically changes its impedance to match that of the antenna (by the same principal as above, except that impedance matching is carried out on the chip side). This not only improves performance, but also allows you to determine how wet the substrate is.
—Mark Roberti, Founder and Editor, RFID Journal