A UHF RFID Tag With Improved Performance on Liquid Bottles

The effect of liquid on the performance of a UHF RFID tag is investigated in this letter. It is found that the presence of the liquid increases the loss resistance in the equivalent circuit of the antenna. This leads to impedance mismatching with a narrower bandwidth and degraded return loss. The proposed solution for compensating this effect is to add a resonant RLC circuit with smaller resistance in parallel to the antenna body. This resistance corrects the increased loss resistance when the resonant frequency of the added part is close to the working frequency of the tag. The simulation and measurement results confirm an improvement in impedance matching that leads to the increase of the reading range.