<span>Radio Frequency (RF) harvesting seems to be catching up as an alternate energy source whereby RF energy is scavenged from ambient sources and converted into renewable energy in terms of DC power. This converted DC power is then utilized to power up devices that require a low start up power in which eliminates the need for battery replacement. In this paper, a novel RF energy harvesting prototype is presented which consists of two microstrip patch antennas operating on GSM (900MHz) and WIFI (2.4GHz) &amp; WiMAX (2.3GHz) frequency bands with a bandwidth of 220MHz and 10.11MHz respectively to harvest RF signals from ambience. Two matching networks are presented as well to ensure efficient power transfer to load. Rectifiers are designed to transform the RF signals to DC power. The converted DC signals are then combined and fed to a power management circuit which charges a 4.2V NiMh battery and drives a load at a regulated output of 3V.</span>

A complete energy harvesting system via Radio Frequency (RF) is designed in a broadcast station where multiple frequency sources are readily available. These frequency sources are the Intermediate Frequency (IF), 70 MHz, Wi-Fi frequency band, 2.4 GHz, and the Ku-band frequency, 13 GHz. The RF source via the Wi-Fi band (2.4 GHz) is harvested via a microstrip patch antenna designed with its matching network. The harvested RF energy is transformed into usable DC power via an 8-stage Villard voltage doubler circuit. The DC power is managed by a power management system handled by the BQ25570 circuit which gives a regulated output of 3 V, powers up a low power motion sensor, and charges a battery at the same time. This system comes with a backup source which is the battery and able to take over the system in case the incoming RF signal fails. The RF energy harvested from the IF 70 MHz and Ku-band at 13 GHz is derived from coupler outputs which are available in broadcast stations, transmission lines, etc. Both these RF signals are converted to DC signals via a 5-stage Villard voltage doubler circuit with different matching networks. The DC power is managed by a power mux via the TPS2122 which selects the highest available power. Over the years, no works on RF harvesting have focused on smart phone charging as its application, due to the limitation in power availability. This work strives to provide enough power to charge phones and effectively gives a 5 V output to charge smart phones with a charging current of 0.5 A which is similar to a USB charging port.

Radio Frequency harvesting has recently become one of the alternate approaches to power up low power wireless networks. This evolving technology opens the gate for positive energy renewal for wireless components. This paper presents a comprehensive review which includes all the important components in a RF energy harvesting system which are microstrip patch antennas, rectifier modules and power management modules. Different types of microstrip patch antennas and its designs and outputs are discussed. Rectifier modules with Schottky diodes operating under two different frequency bands are also compared and discussed. In addition, different methods of available power management circuits with different methods are also deliberated in this paper. This review also explores various key design issues and envisions some open research directions.