Research On High Performance RF Energy Acquisition System For Wireless Energy Transmission

In recent years,energy has become a key factor restricting the development of the world economy.The development of clean,renewable energy sources has become imperative.Microwave Energy Transfer technology(MPT)can break through the transmission line limitations,in the form of microwave power transmission,compared to traditional physical connection more flexible and sustainable.With the development of artificial intelligence(AI)and 5G positioning the Internet of Everything as the future trend,Internet of Things(IoT)applications face the problem of constant power supply from a large number of ultra-low power portable electronic devices and wireless sensor networks(WSNS).In contrast to battery power,which has a limited lifespan,wireless energy acquisition technology(WEH)can capture energy from RF sources or the environment to provide a sustainable power solution for electrical devices.At the heart of both technologies is a high-performance RF energy harvesting system.Based on the characteristics of metasurface flexibly regulating the amplitude,phase and polarization of electromagnetic wave,it provides a new way to realize the high integration,high efficiency and multi-function RF energy acquisition system.This paper mainly carries out theoretical and experimental research on the new methods and technologies of microwave wireless energy transmission and wireless energy acquisition.The specific achievements and innovations are as follows:(1)Research and design of electromagnetic energy absorber insensitive to polarization and incident Angle.Abstract:The theory of metasurface equivalent medium and impedance matching principle were studied,and a new type of metasurface was proposed.The topological structure was designed to control the electromagnetic parameters,so that the surface impedance of the metasurface matched the natural space impedance,and the absorption rate of 99.8%was achieved.By designing the collection through hole location and optimal load impedance,the energy absorber achieves 98%efficiency.The multi-reflection interference theory of metasurface is studied.The consistency of the multi-reflection interference theory and the full-wave simulation results is proved by analyzing the efficiency of the metasurface energy absorber under vertical incidence and oblique incidence.The test results show that the working frequency of the proposed metasurface energy absorber is 5.8GHz.In the TE polarization mode,the acquisition efficiency is greater than 90%when the incident Angle is within±40°.In the TM polarization mode,the acquisition efficiency is greater than 95%when the incidence Angle is within±60 °.The peak efficiency of the absorber pair with arbitrary polarization perpendicular incident electromagnetic wave is 97%.(2)Research and design of harmonic suppression metasurface energy acquisition system insensitive to input power and load.A hook shaped U-slot metasurface with harmonic suppression function is proposed.The absorption rate and acquisition efficiency are 99%and 98%respectively at the operating frequency of 5.8GHz,and the broadband harmonic suppression is realized at 9GHz-12.5GHz and 15.5GHz-18GHz.A multi-functional and highly integrated electromagnetic energy acquisition system is proposed.A power synthesis network is designed at the bottom of the hook U-groove metasurface array to channel the collected AC energy to a single rectifier circuit,maximizing the available diode power and turn-on time.The space obtained by eliminating the independent harmonic suppression structure makes it possible to add the complex impedance compression network.The proposed impedance compression rectifier circuit realizes the insensitivity of input power and load impedance.The test results show that the RF to DC conversion efficiency of the metasurface energy acquisition system reaches 74.5%at the operating frequency of 5.8GHz.When the input power range is 6dBm-25dBm and the load range is 0.5kΩ-2kΩ,the RF to DC conversion efficiency is greater than 50%and 65%,respectively.(3)Research and design of a harmonic suppression rectification metasurface insensitive to polarization and incident Angle.A circular T-slot metasurface structure is proposed,which can effectively capture electromagnetic waves with arbitrary polarization and incident Angle range of±60°.The integrated harmonic suppression structure makes the reflection coefficient at higher harmonics better than-2dB.An expandable high integration metasurface design scheme is proposed.Due to the high impedance characteristics and harmonic suppression function of the designed metasurface structure,the matching network and harmonic suppression network between metasurface and diode are eliminated directly,and the system structure is simplified.Multiple metasurface units are connected to a common terminal load through a parallel DC synthesis network,and power adaptability is achieved by using different array sizes and diode types.The absorption and acquisition efficiency of annular T-metasurface are 99%and 96.8%,respectively.The test results show that the system efficiency of the 2×2 and 4×4 metasurface arrays is 71.2%and 75.6%at the operating frequency of 5.8GHz and the input power level of 11dBm,and the system efficiency varies less than 5%at any polarization Angle.The integrated harmonic structure improves the conversion efficiency of systems in the band of 5.6GHz to 6GHz by 2%to 4%.(4)Design of multi-band flexible miniaturized energy acquisition system.A new feed structure of coplanar waveguide-matched transition section-microstrip line and a circular patch antenna loaded with symmetrical sickle-shaped slots are proposed.The tested operating bandwidths are 0.7GHz-3.5GHz and 5.5GHz-6.6GHz,respectively,with relative bandwidths of 134%and 18%,and the radiation efficiency is greater than 95%.A miniaturized rectifier circuit based on dual-frequency matching network is proposed.The working bandwidths of the circuit are 0.7GHz-2.6GHz and 5.4GHz-5.9GHz respectively,which realizes the multi-band matching with the antenna.A power management circuit with the function of boosting voltage and regulating voltage is designed to smooth the DC output voltage,and the energy storage element is used to store micro electric energy.By integrating flexible design of multi-band antenna and miniaturized rectifier circuit,a design scheme of multi-band flexible miniaturized energy acquisition system is proposed.The experimental test proves that 30%-to-50%conversion efficiencyRF-DC is achieved in energy acquisition system in 0.9GHz,1.8GHz,2.45GHz and 5.8GHz bands.In different bending states,the system efficiency does not change obviously,and has good flexibility characteristics.