The Research And Design Of RF Wireless Energy Harvesting And Transmission System

With the rapid development of low power electronic equipment,the sensor nodes of the Internet of Things have improving the requirements for safety,reliability and self-sustaining functions.The RF electromagnetic wave energy harvesting research has become a hotspot in the field of new energy,which has a broad application prospects and practical significance.In order to solve the huge waste of human resources and the environmental pollution caused by traditional batteries during the development of low-power electronic devices,this paper studies the RF-based battery-less self-sustaining device and designs a RF energy harvesting system for multi-frequency band and a RF energy transmission system for high power applications.The main research work includes the design of antenna module and rectifier circuit module:(1)The research and design of antenna module.In this paper,two novel broadband energy harvesting receiving antennas are designed based on fractal self-similarity structure and exponential gradient structure respectively.The measured bandwidth of the designed fractal antenna is from 0.88 to 8.45 GHz,and the Vivaldi antenna is from 1.2 to 1.89 GHz and 1.96 to 4.1GHz.In order to improve the antenna radiation performance and increase the harvested RF energy,a pair of Vivaldi antennas and a 3dB power divider are used to construct a binary parallel feeding antenna array.The gain of the antenna array at 1.85 GHz is 7dBi,and its maximum radiation direction is concentrated in the direction of antenna wave propagation,which has a good front-toback ratio.In the actual fabrication,the ground plane of power divider is used as the reflector to improve the directional radiation ability of the antenna array.The measured bandwidth of the antenna array can completely cover the common bands of energy harvesting such as GSM-1800,UMTS-2100,WiFi 2.4 GHz and 4G TD-LTE.Subsequently,a 433 MHz energy transmission antenna is designed according to the normal helix structure,and the miniaturization structure is also realized.The measured bandwidth of the antenna is from 424 to 441 MHz with the resonant frequency of 432.85 MHz,and the antenna gain is omnidirectional 2dBi.(2)The research and design of rectifier circuit module.For the RF energy harvesting and transmission applications,Schottky diodes are selected as RF rectifier diodes respectively.After optimizing the capacitance and load of the voltage doubler rectifier circuit,the matching network is constructed.For the RF harvesting,two type rectifier circuits are designed by using microstrip line branch matching,the maximum rectifying efficiency of the single branch rectifier circuit is 64%,and the maximum rectifying efficiency of the double branch dual-frequency rectifier circuit is 57% and 52%,respectively.Then,the energy transfer rectifier circuit based on T-shape LC matching is designed,and its maximum rectifying efficiency is approximately 70%.(3)The construction and measurement of the designed Systems.The energy transmission system is composed of a simple power signal source,a helical antenna and a rectifier circuit.When the maximum working distance between the transmitting antenna and the receiving antenna is fixed at 0.5 meter,the designed system can drive a ZigBee sensor node,a temperature and humidity instrument and a clock,simultaneously.The voltage of ZigBee sensor node,temperature and humidity instrument and a clock is 3.18 V,1.31 V and 1.54 V,respectively.At last,this experiment shows that the proposed energy transmission system can power the electronic device successfully.For the designed RF energy harvesting system,when the receiving antenna is 0.5 meters away from the transmitting antenna,the harvested WiFi power is stored by 300 mF super-capacitor,and its voltage can reach 1V.When connected to the energy management circuit,the stable output voltage of the system is 3V,which proves that the energy harvesting system is practically available under low-power conditions.