Advances in Antennas, Design Methods and Analysis Tools for Passive UHF RFID Tags

Abstract

Radio-frequency identification (RFID) makes use radio waves to track objects equipped with electronic transponders, commonly known as tags. In passive RFID systems, the tags are remotely powered and they are composed of only two components: an antenna and an application specific integrated circuit (tag IC). At ultra high frequencies (UHF) this technology enables the rapid identification of a large quantity of tags at the distanc-es of several meters, also in the absence of line-of-sight connection with the tag. While the passive UHF RFID is currently used e.g. in supply chain management and access control, in the future the passive tags capable of ultra-low-power data transmission are envisioned to provide platforms for wireless sensor nodes.

The maintenance-free and fully integrated on-tag electronics holds the promise to small, cheap, and inconspicuous tags, but achieving this in practice requires completely new design methods and analysis tools for antennas. Unlike conventional antennas, tag antennas need to be directly interfaced with an active load (tag IC) and seamlessly integrated with objects of various sizes and material contents. Here, especially the materials having adverse effect on the operation of conventional antennas present a major challenge, while at the same time the fundamental limitations on the performance of small antennas need to be considered.

This work addresses the above-mentioned challenges in the design of antennas for passive tags. Based on the new analysis tools and modern computational electromagnetics, a framework specifically tailored for the development of tag antennas is established. Combined with novel electronics materials and new fabrication methods this is shown to provide compelling means for tag antenna development. In particular, it is shown that tags with antennas produced using printable electronics, which has great potential to enable fabrication antennas directly on various unconventional platforms, can achieve competitive performance against the copper-based references. Furthermore, novel high-permittivity materials can be exploited to develop miniature antennas for metal mountable tags. Finally, three case studies, where antennas for tags in challenging applications are developed using the proposed design framework, are presented. The prototype tags achieve performance exceeding state of the art and exhibit excellent structural properties for the seamless integration with the considered objects.