Enhanced RF Energy Harvester for Power Efficient Internet-of-Things Wireless Sensors

RF power harvesting enables controllable and simultaneous wireless power delivery to many RF devices. Devices built with this unique technology can be sealed, embedded within structures, or made mobile, thus eliminating additional service for a battery. A key component of this technology is the "rectenna," which is composed of antennas and rectifying circuitry to convert RF energy into DC power. Rectenna could obtain the maximum microwave to direct current (mw-dc) conversion efficiency on the three stable conditions: an operation frequency, an input microwave power and a load. In this paper, a 2×4 circular polarized receiving antenna array with circular patches at 5.8 GHz is suggested to get higher microwave capture efficiency with an enhanced directivity of about 13.4 dBi and an overall size of about 18×17cm2. This receiving antenna is associated with a microstrip rectifier formed by a modified doubler voltage topology using two Zero-Bias Schottky diode HSMS2862. Using schematic simulation in ADS software, the proposed rectenna design provides an output DC voltage of more than 2.53 V and a RF-to-DC conversion efficiency of 92.45 % with an optimum load resistance of 5 kΩ at 0 dBm microwave incident power level.