Resistor emulation approach to low-power RF energy harvesting

This paper presents an approach and associated circuitry for harvesting near maximum output power from electromagnetic waves in the RF/microwave region of the spectrum with variable incident power densities in the range of tens of mu W/cm(2). It is shown that open loop resistor emulation at the input port of a power converter is a suitable solution for tracking the peak power point of a low-power rectifying antenna source over a wide range of incident RF power densities. A boost converter with a simple low-power control approach for resistor emulation is presented. A hardware design example with detailed efficiency analysis is given using commercially available discrete circuitry. Experimental results are presented for a system harvesting 420 mu W to 8 mu W from a 6 cm x 6 cm rectifying antenna with incident RF power ranging from 70 mu W/cm(2) to 30 mu W/cm(2), respectively. The results demonstrate that resistor emulation is a simple and practical approach to energy harvesting with variable low-power radiative RF sources.