Resumen
Ambient RF energy harvesting (RF-EH) is a particular case of wireless power transfer (WPT), which is characterized by ultra-low power operation. This work points out theoretical and practical aspects that should be considered in the design of RF rectifiers for ambient RF energy harvesting systems. The most common RF rectifier circuits are compared and discussed using simulations and experimental data. The efficiency is analyzed in terms of the input power and load resistance. It is demonstrated that the most efficient RF rectifier in ultra-low power conditions is the simple diode capacitor structure. As an illustrative example, an RF rectifier has been fabricated by designing an impedance-matching network to operate into the WIFI band. The fabricated prototype shows a measured 12% efficiency working at 2.47 GHz with around -30 dBm ambient input power, which is higher than the reported efficiencies in the literature. The fabricated energy harvesting system delivers power between 25.6 nW and 129.6 nW to a resistive 10 kO
10
k
O
load. The obtained results are applicable to ambient RF up to 6 GHz.