A Compact Implantable UHF-RFID Rectenna Tag for Implantable Bolus-Based Wireless Animal Tracking

This paper proposes a compact implantable ultra-high frequency (UHF) radio frequency identification (RFID) rectenna tag designed for integration into an implantable bolus for in-body wireless animal tracking. The integrated design achieves dual functionality: passive RFID tag (920–925MHz) and RF energy harvesting via a Schottky diode rectifier. The rectenna tag structure incorporates a meandered dipole antenna with T-matching, optimized for conjugate impedance matching with a passive RFID chip operating in the 920–925 MHz band. A loop structure is integrated with a Schottky diode to enable RF-to-DC power conversion. Full-wave simulations within high-dielectric media (εr = 40–80) modeling internal bolus conditions demonstrate an input impedance of 30 + j300 Ω, exhibiting an omnidirectional radiation pattern with a gain of −19.0 dBi (RFID port) and -18.0 dBi (rectenna port), and a specific absorption rate (SAR) in 1 g of 0.231 W/kg and 0.336 W/kg, respectively. The system demonstrates an RF power harvesting efficiency of up to 10-20%. A prototype was fabricated and tested in water, achieving maximum read ranges of 2.0 m (free space) and 1.4 m (aqueous environment). Measured gains were -15.0 dBi (RFID port) and -18.0 dBi (Rectenna port). The measured SAR also remained at 0.27 W/kg (RFID tag port) and 0.35 W/kg (Rectenna port), well within established safety limits. These results validate the proposed rectenna tag as a promising solution for efficient and safe in-body animal tracking via implantable bolus tags. The system integrates a passive RFID chip and RF-DC rectifier, enabling dual-functionality: battery-free real-time animal identification and self-powered physiological sensing (e.g., rumen temperature/pH) for livestock health monitoring.