A high-efficiency matching technique for low power levels in RF harvesting

Abstract

Radiofrequency (RF) energy can be harvested in order to power autonomous sen- sors either from the surrounding environment or from dedicated sources. A conventional RF harvester is mainly composed by an antenna, a matching network and a rectifler. At low power levels, e.g., i10dBm and below, the corresponding voltage amplitude at the antenna is low and comparable to the voltage drop of the diodes used in the rectifler. In order to boost the voltage at the rectifler input and thus the rectifler e-ciency, an L-network optimized for an input power of i10dBm at 868MHz is proposed in this work. As for the rectifler, a half-wave rectifler with a single zero-bias Schottky diode (HSMS2850) was selected. First, a theoretical analysis was performed followed by simulations with ADS (Harmonic Balance). Simulations show e-ciencies of 75% for an input power of i10dBm with ideal components but using the actual model of the diode rectifler. The incorporation of the PCB layout efiects and the actual components decreases the e-ciency to below 50%. Finally, a PCB implementation was performed using a 0.5pF capac- itor and a 27nH inductor for the L network. The input power was generated by an RF generator. The RF-to-DC e-ciency was of 45% at 868MHz with an optimum load of 2.5k›. E-ciencies of 34.5% and 22.5% were achieved at i15dBm and i20dBm, respectively.