Wireless Monitoring of a Charge Storage in an RF Energy Harvesting Device

Abstract

Today’s advancements in modern technologies have grown the demand of low power wireless application devices usage. Using the batteries in any portable electronic devices results in a limitation in occupying the space and declining the lifetime of the application devices. Hence, one of the significant challenges in low power wireless technologies is providing the energy sources that are able to supply the required power for operating wireless devices continuously without degrading their performance. Energy harvesting is a growing interest technique to harvest ambient energy from renewable sources such as vibration, solar light, wind, thermal, and electromagnetic wave (EM) and convert these energies into useable electrical energy. Harvesting ambient energy from electromagnetic wave known as the RF energy harvesting is becoming increasingly important for powering the battery-less electronics devices and passive RFID tags. Indeed, this kind of power is readily available especially in HF and UHF frequencies due to the presence of propagating radio waves of wireless technologies such as cellular, TV, radio, satellites, and Wi-Fi signals in environment. Thus, it can be considered as a promising solution to meet the required of the battery replacement and providing a power supply over very long periods. In this project, a radio frequency (RF) energy harvesting unit integrating a passive UHF RFID tag as a charge storage indicator is presented. In this system, an energy harvesting unit converts the RF signal to DC and charges a storage capacitor. In addition, to transfer the maximum power through the system, an impedance matching network is designed between the RF power source and the RF rectifier. The RF switch, consists of a pin diode and UHF RFID tag, monitors the capacitor voltage. When the voltage across the capacitor terminals approaches 0.633 V, signal is transmitted to the RFID reader. The proposed RF energy harvesting system operates at European UHF RFID spectrum from 865.7 MHz to 867.7 MHz, which the frequency of 866 MHz is considered as our target frequency in this study. All the procedure of designing, simulation and fabrication are explained in details and the experimental results indicate that 0.633 V at the terminals of the storage capacitor can be achieved with −5.5 dBm of the RF input power applied into the energy harvesting unit.