Adaptive Programming of RFID Inlays in the Reactive Near Field

Doktorsavhandling, 2018

Radio frequency identification (RFID) offers a vast variety of options to improve the functionality and efficiency in the automated data collection (ADC) industry and Internet of Things (IoT). In the inventory process of RFID with passive data carriers, a population of battery less tags is located in the working range of an interrogator system. These tags contain transponders receiving operating energy from radio waves which can demodulate and modulate a digital signal from an RF carrier. The fundamental prerequisite in RFID is unique user identities (IDs) stored in the tag memories. Commonly, programming of these IDs occurs in the reactive near field, where the cavity of an RFID enabled bar code printer represents a typical example of such an environment. The two major challenges of user ID programming are the change of the electrical environment presented towards the transponder, as compared to the nominal far field or propagating near field conditions, and electromagnetic spatial selection, to prevent non-target tag programming. This thesis presents the results from an industrial Ph.D. project, in collaboration between industry and university. In a first part, novel measurement and characterization techniques of RFID transponders are presented, with the main goal of understanding the impact of non-linearity on communication quality under altered reactive near field conditions. The remaining part of the thesis addresses fundamental components needed in the concept of self adaptive reactive near field coupler technology, for geometry independent and spatially selective programming of RFID tags. The core of the technology is the differential transmission line loop (DTLL), exhibiting highly efficient and spatially selective coupling for varying inlay geometry; as such an array based spatial distribution of the reactive near field coupling is enabled. As exemplary simulations show, the versatility of the DTLL offers flexibility in array design, of creating a phase controlled reactive near field over the entire structure, which hence acts as a sensitive array. The elements act independently, where the amount of phase alteration in each element is a compensation for the geometrical size of the element itself. A fundamental property of the sensitive array is the independency of a software system, controlling the coupling elements. In other words, the reactive near field coupling of the array is self contained.