Design and Characterization of Compact On-Metal UHF RFID Tag Antenna for Smart Cities

In today's smart cities, the use of passive Radio-frequency Identification (RFID) tags gained popularity in access control, file tracking for healthcare, supply chain management in logistics, smart labels, vehicle tracking identification and others. The main advantages of using passive RFID tags are low cost and not requiring an internal power source to activate the tag. However, the metal surface has always been a challenge to passive RFID tags due to metal interference. The interference was caused by reflected energy from metal surfaces that were emitted from the RFID readers. As a result, the tag was unable to both transmit and receive information. This is also inconvenient to users as metal must not be present in the surroundings where the RFID tag is installed. As such, this paper proposed a compact passive Ultra High Frequency (UHF) RFID tag that can be installed on metal surfaces. To meet compactness requirements and flexibility over impedance matching, the antenna is designed in S-shaped by using computer simulation technology CST software. Two methods are used to model the antenna tag which firstly is to increase the gap between the antenna and the metal surface, secondly to place absorbing material between the antenna and metal surface. PP-4 flexible foam is used as the gap and three polyimide films are inserted which act as absorbing materials to ensure that the tag functions well in harsh environments for smart city sustainability. Thus, as a result, based on the Friis transmission equation, the antenna tag can achieve a read distance of up to 4.815 m.