Research On Broadband RF Energy Harvesting Antenna Based On Artificial Magnetic Conductor

As the power consumption of devices such as sensors and microprocessors continues to decrease and the implementation of ultra-low power integrated circuits,it is a reality to collect environmental electromagnetic energy to achieve"self-powered"wireless network nodes.The antenna at the front end of the ambient RF energy harvesting system converts the ambient RF energy into an electrical signal.The performance of the operating bandwidth and gain pattern directly determines the power level that can be collected.This power level further affects the conversion of the back-end rectifier circuit.effectiveness.Therefore,the antenna plays an important role in the ambient RF energy harvesting system.The planar spiral antenna is a common ultra-wideband antenna with the advantages of frequency bandwidth,good circular polarization,small size,and easy conformality.It is the primary choice for ambient RF energy harvesting antennas.In this paper,an artificial magnetic conductor(AMC)is introduced as a reflector of a spiral antenna to achieve unidirectional radiation of the antenna.At the same time,the operating bandwidth of the helical antenna is increased by utilizing the zero reflection phase characteristic of the AMC.The main research results of this paper can be summarized as follows:(1)A new type of double-layer AMC structure is designed,and the design method of the double-layer AMC is analyzed.Introducing more extra inductance by etching the floor of the lower layer of the AMC,the reflection phase bandwidth of the AMC is increased.Under the same conditions,the single-layer AMC has a reflection phase bandwidth of 4.5 GHz to 5.6 GHz,and the double-layer AMC has a reflection phase bandwidth of 4.3 GHz to 6 GHz.(2)A composite spiral antenna is designed.The antenna combines the characteristics of a planar isometric spiral antenna and an Archimedes spiral antenna.It consists of an isometric spiral at the beginning and a terminal Archimedes spiral.The composite spiral antenna structure significantly improves the low frequency performance of the antenna,increases the operating bandwidth of the antenna,and reduces the transmission loss to a certain extent.(3)The new double-layer AMC structure is applied to the composite spiral antenna to realize the unidirectional radiation of the spiral antenna,and the influence of the AMC structure on the antenna performance is analyzed in detail.Finally,a composite reflector is designed to make the spiral antenna with good axial ratio characteristics and high gain between 2.5-10GHz.(4)Based on the design idea of slot antenna,the antenna structure is improved,and the standing wave effect caused by port truncation is reduced.The resistor is further introduced to achieve the absorption of the low-frequency reflected current of the antenna to achieve better broadband circularly polarized radiation characteristics.Finally,a balun with a bent structure was designed to significantly reduce the overall profile of the antenna system.The results show that the antenna has an axial ratio of less than 3 dB between 1.5 to 14.5 GHz and a stable gain of 7 dB over the entire operating band(maximum gain of 9.7 dB).Laid the foundation for improved conversion efficiency of the entire RF energy harvesting system.