RF Energy Harvesting System And Measurement Platform

As development of wireless sensor network constantly expanding, the powering methods of sensor nodes have attracted great attention. Various kinds of new powering methods come out by harvesting ambient energy such as wind, solar, kinetic, therma l etc. Among these methods, radio frequency(RF) energy harvesting which collects electromagnetic wave signals emitted from communication base station or radio or television tower, shows bright prospect in power supply for low power wireless sensor node and implantable medical devices. However, there are many problems which still worth exploring in RF energy harvesting antenna, RF-DC convert circuit etc. This article embarks from electromagnetic wave direction detection system for finding the maximum radiation direction of signal source. Then, for ambient television signal harvesting, electrically small antenna array and conver t circuit are designed. And for evaluation method for estimate the efficiency of proposed system, indoor test platform is set up. Also, to improve the performance of harvesting antenna, three different antennas are proposed and tested. In the end, based on the theoretical and experimental research, methods to enhance the conversion efficiency are summarized, especially for harvesting antenna and convert circuit, which laid the foundation for engineering application.This paper consists of five parts. Firstly, the developments of RF energy harvesting technology are introduced. According to the research status, efficiency enhancing methods are summarized.Secondly, direction detection system for finding the maximum radiatio n direction of signal source is designed. Software and hardware designs including dual-axis rotating platform, MSP430 microcontroller and C# controlled interface are introduced. By using this detection system, the maximum wave direction can be found.Thirdly, for harvesting ambient television signal, harvesting system including electrically small antenna(ESA) array and RF-DC convert circuit are designed. CST, HFSS, ADS simulation results and measured data are also given.Fourthly, according to the framework of RF energy harvesting system, methods to enhance the conversion efficiency are explored. Three evaluation values such as harvesting efficiency, conversion efficiency and circuit efficiency are proposed. To compare the performance of harvesting antenna, indoor test platform imitating the TV signal is set up. And three contrast antennas and two connected methods are proposed and tested under the different conditions of input power on the test platform. After the test, the whole evaluation results are given.Finally, test results of the whole system by harvesting the TV signals are given. The test place is on the building roof, which is 1.5 km away from Suzhou TV Tower. Before harvesting test, electromagnetic wave direction detection system is used to find the maximum wave direction. And then, the experimental comparisons of four harvesting antenna are given, which determine symmetrical dipole antenna with the highest efficiency as the chosen antenna for the final system. Also, connected methods of convert circuit which consists of DC combination and RF combination are tested, which verifies the improvements of both two methods. At last, high-performance RF energy harvesting system consists of high gain dipole antenna and six order rectification circuit with voltage boosted. The largest harvested voltage is 3.25 V, and it supplies sustained and stable DC power for low power equipment. Experimental results show that proposed RF energy harvesting system has the characteristics such as high conversion efficiency, stable output, which is suitable for power supply of wireless sensor node and implantable medical devices.