Waveform-aware ambient RF energy harvesting

Abstract

In this paper we suggest a new class of RF energy harvesters, which we call “waveform aware harvesters”. In contrast to traditional rectenna designs, which are usually designed for high efficiency with continuous wave (CW) signals, waveform aware harvesters are RF to DC converters which are optimized for their performance with non-CW signals. We suggest that waveform aware harvesters may have significant advantages in ambient energy harvesting, where the available RF energy is in the form of communication waveforms of a variety of types. We present an initial proof-of-concept demonstration of a waveform aware harvester optimized for harvesting energy from 2.4 GHz Wi-Fi (802.11b/g) signals with a realistic traffic model. Under realistic traffic conditions, 802.11b/g client transmissions are bursty, with a high peak-to-average ratio and a low duty cycle. We demonstrate optimized recovery of harvested energy from single 802.11b/g transmission bursts on the order of 1 ms in duration. We present an expression for maximizing usable energy stored in an energy reservoir given a signal model and parameters of the energy-harvester circuit. In contrast to other work where assumptions of CW sources lead to the desirability of a large storage capacitor, our approach considers the existing communication signal model and optimizes capacitor size to maximize the stored usable energy for a short transmission burst.