Performance Evaluation of a Metasurface-enabled Wearable Quasi-Yagi Antenna with End-fire Radiation Pattern on Textile Substrate

We present the performance evaluation of a wearable quasi-Yagi RFID reader antenna fabricated using a 2mm thick flexible Ethylene Propylene Diene Monomer (EPDM) foam substrate, exhibiting end-fire radiation properties along the human body surface. The designed antenna operates for Wireless Body Area Networks (WBAN) and UHF RFID reader applications at 915MHz frequency. The quasi-Yagi antenna comprises the Yagi-type radiator, a periodic surface that launches a surface-wave to achieve the end-fire radiation properties, and a ground plane that provides isolation between the radiating element of the antenna and the human body. In a full-wave EM simulator, the wearable antenna achieved the end-fire directivity of 5.9dBi, when mounted on a homogenous cylindrical body model. The relative size of the quasi-Yagi antenna is $0.22 \lambda_{o} \times 0.33 \lambda_{o}$ with an overall thickness of 4mm. The cording to the theory of transformation acoustics and its performance of the wearable antenna is evaluated at various locations of the human body i.e., on the head, the shoulder, and the back, and also under different bending scenarios. The results show that the antenna is robust towards these variations and retains its impedance matching under the bending scenarios that can be expected in the application. We also measured the realized gain of the antenna using a dipole UHF RFID test tag with a gain of 0dBi at 915MHz frequency. The wearable antenna shows realized gain of -6.7 dBi for the head, - 6.9 dBi for the shoulder, and -7.6 dBi for the back of the human body. Overall, the antenna shows promising results for the wearable WBAN and UHF RFID reader applications.