Impact of Input Impedance Mismatch on the Receiver Efficiency of RF Wireless Power Transfer

The receiver efficiency of a radio-frequency (RF) wireless power transfer (WPT) system is determined by the RF-to-direct current (DC) conversion efficiency of the rectifier and the effectiveness of the preceding impedance matching network. The impedance mismatch at the rectifier's input, especially, hampers the power efficiency of RFWPT. In this paper, we experimentally examine the dependency of the rectifier input impedance of an off-the-shelf RF energy harvester on the average input RF power and the frequency of the incident RF signal as well as the load resistance. We develop a data-driven model of the RF energy harvester to study the receiver efficiency in terms of the matching efficiency and the rectifier efficiency. The results reveal that the matching efficiency varies significantly with the average input RF power and the load resistance. Moreover, the input impedance mismatch reduces the peak receiver efficiency of our RF WPT test-bed by around 1S%.