Knitted Antenna Design for UHF RFID and Wearable IoT Applications

This paper presented a knitted antenna design for ultra-high frequency (UHF) radiofrequency identification (RFID) and wearable internet of things (IoT) applications. The proposed antenna consists of a dual slot-match structure that provides a good impedance match with RFID microchip on high permittivity surfaces such as the human body. The slot-match structure is designed and optimized using characteristic mode analysis (CMA). The slot-match structure poses a very high inductive impedance and very low real impedance in free space. However, this impedance behavior helps in countering high capacitive effects caused by the human body and other high permittivity materials. The proposed antenna is fabricated by knitting using conductive thread. This antenna design features a read range of 2.4 m measured using an RFID reader setup after placing the tag on the human body abdomen. Moreover, the proposed antennas can be used as a sensor for vital signs or breath monitoring as its stretched state provide less read range as compared to the unstretched state. Therefore, the proposed antenna design can be used for UHF RFID, sensing, and wearable IoT applications.