Remote powering link for a passive UHF RFID tag for capacitive sensor applications

This work discusses the remote powering link of a passive UHF RFID tag for sensor applications. The design, implementation, and measurements of the base-station antenna, tag antenna, and the rectifier are presented. The base-station antenna is a 50 Ω rectangular patch antenna with a measured far-field gain of 3.6 dBi. The tag antenna is an inductively coupled meandered dipole antenna impedance matched to the tag chip. The measured far-field gain of the tag antenna is 1.2 dBi. The three-stage, differential-input rectifier is measured to deliver 1 mW to a 5 kΩ load with a power conversion efficiency of 65% at a distance of 1.5 meters from the base station. The rectifier is implemented in 0.18 μm UMC CMOS process.