Optimum Performance of UHF RFID Tags in Dielectric Environment

Abstract

Ultra High Frequency Radio Frequency Identification (UHF RFID) technology has gained prominence in recent years. It is being deployed extensively in supply chain and asset tracking by retailers to better control their inventory. The main drawback of UHF RFID tag antenna is that it is sensitive to the environment in which it operates. The performance of the tag degrades when placed on conductive or dielectric objects. While RFID tags near metal have been extensively evaluated in the literature, tags on and in dielectric media have received less scrutiny and rigorous evaluation. In this thesis, we develop a rigorous theoretical model for the behavior of RFID tags immersed in a dielectric medium using the Uda model and embedded T-match antenna. From this, we are able to investigate a number of criteria for optimality. We find that the simplest optimality condition is not physically realizable, and more realizable models yield several results that are of practical interest. Also, we propose a method to determine the input impedance of a center-fed dipole using a five element equivalent circuit. We relax the conditions for optimality and do an exhaustive search for the optimal design over the parametric space. Finally, we validate the model and present the trade-off to be made with the power transfer efficiency to obtain a tag working in wider range of dielectric materials. We make two specific recommendations for future work to increase the accuracy and usefulness of this work.