Performance of Printed Polymer-Based RFID Antenna on Curvilinear Surface

The performance of flexible printed RFID tags affixed onto cylindrical containers is dependent on the inductive behavior of the bent antenna on the tag. Conductive polymeric coil antennas were screen printed onto flexible substrates, and the coil resistances, the inductances, and the S-parameters of the antenna coils were measured and analyzed. The RFID dies were mounted onto the antenna coils and the read ranges were characterized as a function of curvature. The results show that the coil inductance decreased slowly with increasing curvature, and the maximum read range of the tags was markedly reduced with the curvature. The decrease in the coil inductance and the maximum read range were hypothesized to vary with the projected bent coil area instead of the geometric coil area. Experimental results confirmed that the maximum read range of an RFID tag affixed on a curvilinear surface can be predicted by the classical inductive coupling model with the bent projected coil area. On the basis of the experimental and analytical results, a reading reliability factor of two is proposed as a design parameter for flexible RFID tags.