Tuning of on‐metal UHF RFID inlay tags loaded with a thin magneto‐dielectric slab

The input impedance of UHF radio frequency identification (RFID) inlay tags is analyzed when a thin material slab is placed between the antenna and a metal surface.The two‐layer slab is made of a thin magneto‐dielectric Emerson&Cuming Eccosorb MCS‐U layer with high permeability/permittivity and a thin Rohacell™ layer. Two common commercial UHF tag antennas are considered: the Alien ALN‐9640 Squiggle® and the ALN‐9654 G inlays. The antenna impedance is evaluated both numerically and experimentally, and the power transmission coefficient is calculated in the whole UHF RFID frequency band. It is shown that a tag nonintrinsically suitable for on‐metal applications (e.g. inlay tags) can be used on a conductive surface in a low‐profile configuration. Indeed, when the above magnetic substrate is used, the antenna input impedance rises up from the very low values induced by the presence of a near conducting surface. Then, with a simple trimming applied to the antenna layout, it is possible to tune the antenna to achieve a conjugate impedance matching with the chip impedance. It is demonstrated how an effective tuning is possible through some simple straight cuts of some antenna parts, without requiring a redesign of a new optimized tag antenna. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1630–1633, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26903