Performance evaluation of 13.56 MHz RFID antenna operating in metallic environments

The present paper analyses and measures the effects that the presence of a metallic surface can induce on the integrated antennae of HF RFID systems operating on a 13.56 MHz frequency. The results of the conducted measurements have been compared with those arrived at by means of the Ansoft HFSS application. Thus, the conducted tests and simulations reveal the fact that the resonant frequency increases in direct ratio to the distance between the loop antenna and a parallel metallic surface. When the antenna is positioned within less than 3 cm from a metal surface, its performance is drastically reduced and the resonant frequency increases from 13.56 MHz to 14.75 MHz, which eventually compromises the entire communication process, since the interrogation zone is considerably reduced. Further analyses are conducted on the influences exerted on the performance of the antenna, which is made from various materials, such as copper or aluminium. Apart from the detailed account of these issues, we also suggest a series of solutions that will eventually enable the expansion of the interrogation zone.