UHF RFID Transponder Antenna Solutions for Enhanced Performance and Producibility: Dissertation

As a means of automatic identification, passive UHF RFID technology provides clear benefits over its competitor technologies, such as optical codes or RFID technologies operating at lower frequencies. Perhaps the greatest of these benefits is the long read range that can be achieved with a tag that is relatively simple and small. However, the exploitation of the radiating far field as the coupling method between the reader and the transponder, which enables the long read range, also makes the tags sensitive to their near environment. Consequently, the combination of a metallic use environment, long read range and a small, low-cost tag is difficult to achieve in practice.
In this thesis, new concepts of implementing UHF RFID transponders are studied and presented. Additionally to performance and versatility, the production cost is always an important parameter for a means of automatic identification. Therefore, in this thesis, a special emphasis has been put on the producibility of the presented tags. In practice, this means that the tags developed are suitable for mass production and their performance is not too sensitive to the parametric variation that always occurs in the industrial fabrication processes.
The tag solutions presented in this thesis are divided into two main categories: small all-platform tags and tags implemented with alternative conductor materials. The small all-platform tags are fabricated with printed circuit board and inlay technologies.
The alternative conductor materials studied are graphene and aluminium-doped zinc oxide (AZO). Graphene is an interesting new material that is eco-friendly and printable. Additionally to the raw material itself being non-toxic, fabricating the transponder by printing can replace the currently used etching process that produces toxic waste. Thin-film AZO is a transparent conductor material that enables transparent antennas and thus invisible transponders to be used on e.g. windows or windshields. Even though these new materials provide new features and benefits, they both set special challenges that mainly relate to the conductivity that is remarkably lower than that of bulk metal. The attachment of the microchip is another challenge that, in order to keep the tags commercially viable, should not form a bottleneck in the fabrication process.
Even though the radiating far-field is the main coupling method for a UHF RFID system, for some applications that do not require a long read range, inductive near-field coupling is an attractive option. Two near field tag solutions are presented in this thesis; the first one is a solution for tagging metal items that form a challenge to conventional near-field tags. The second one combines graphene as the conductor material and the chip attachment by glue-bonding, providing a small, eco-friendly and mass-producible tag.