Differential Transmission Line Loop for RFID Reactive Near-Field Coupling

Journal article, 2018

The differential transmission line loop (DTLL) as an efficient reactive near-field coupling element for programming of radio frequency identification (RFID) inlays is proposed. It is validated, with simulations and measurements, that the differential excitation and the presence of a ground plane are fundamental properties for high performance in coupling while providing high electromagnetic isolation. As a proof of concept, super elliptical loop geometries as coupling elements are investigated for a number of commercially available inlay geometries. From simulations of the DTLL and inlay antenna, coupling efficiencies higher than 80% are predicted. Measurements of the \Delta \Gamma -value indicate a nonlinear input impedance with power, and verify the high values of simulated coupling efficiency. The threshold power levels read from interrogator are below 5 dBm, which are considered as very low in inlay encoding, and hence show that the DTLL is a promising candidate for efficient RFID programming in the reactive near field.