RF And Wireless Energy Harvesting Technology Based On Electromagnetic Metamaterials

Metamaterials(MMs)are synthetic materials composed of an arrangement of periodic electromagnetic(EM)resonance unit cells,which have some physical properties not found in natural materials such as negative refractive index and inverse Doppler effect.The metamaterial absorber,as an important research direction,achieves perfect absorption of EM waves by dissipating the energy of the incident EM waves in the resonant structure.Nowadays,the metamaterial absorber is developing in the direction of flexibility,transparency,encodability and intelligence,and is widely used in national defense,civil,aerospace and communication fields.On the other hand,the development of 5G communication technologies and devices as well as the development and application of a large number of low-power devices(especially micro-watt devices)have provided the impetus for the development of RF and wireless energy harvesting technologies.As a result,RF and wireless energy harvesting technology based on EM metamaterials has emerged to play an increasingly important role in environmental energy harvesting,and has incubated a number of new innovations and technologies to boost the development of smart cities,smart agriculture,and smart factories.In this paper,based on EM metamaterials and RF wireless energy harvesting theory,a combination of numerical simulation and measurements is used to study the metamaterial RF and wireless energy harvesting technology,which is mainly as follows.(1)An energy transfer method based on EM metamaterial energy harvester is studied,and a metamaterial energy harvester operating in the X～Ku band is designed.The energy transmission channel is constructed by interconnecting metamaterial unit cells,which effectively transmits and aggregates the EM energy captured by the unit metamaterial cells and achieves a half-power bandwidth(HPBW)of 98% at 12.75 GHz.By coplanar integration of the multiplier rectifier circuit and the terminal of the metamaterial array,additional dielectric layers are eliminated to build a power combination network,the structure design of the metamaterial energy collector is simplified,the processing difficulty is reduced,and the harvesting efficiency of EM energy is improved.The fabricated sample is then tested by building a test setup,and the results show that a DC collection efficiency of 56.2% at 12.8 GHz is achieved when the incident power reaches 16 d Bm.Besides,the energy harvester is able to maintain high energy harvesting efficiency over a wide input power range.By simulation,testing and comparison with other works,the practicality and effectiveness of the metamaterial energy harvester is verified for energy harvesting in the satellite microwave communication band.(2)A dual-band,polarization-insensitive and wide-angle metamaterial energy harvester is designed.By adopting a double-ring nested centrosymmetric design and interconnection of structural unit cells,energy transfer channels are constructed in the rows and columns of the metamaterial array,thus achieving perfect absorption of incident EM waves at 2.1 GHz and 5.8GHz in any polarization direction.Moreover,it has consistent and stable absorption for largeangle incident EM waves at both TE and TM polarizations.The dual-band rectifier circuit is based on two single series diode rectifier circuits,which are connected in parallel to rectify the RF energy at 2.1 GHz and 5.8 GHz simultaneously.Measurements show that when the incident power is 5 d Bm,the prototype achieves energy harvesting efficiency of 64.8% and 41.1% in the two bands,respectively.It can also achieve high EM energy harvesting efficiency in two bands simultaneously over a wide input power range.Furthermore,such simple design,low cost and scalability make it suitable for harvesting EM energy in complex environments and spaces.(3)A multi-band metamaterial energy harvester with polarization-controlled characteristics is investigated,and the active modulation of energy harvesting in three WIFI bands and four other bands is achieved by manipulating the polarization direction of the incident EM waves.By non-uniform nesting of multiple split-ring resonator(SRR),the energy harvester achieves more than 98% absorption of EM waves at 2.4 GHz,5.2 GHz and 5.8 GHz under TE polarization and more than 90% absorption at 4.6 GHz,5.3 GHz,6.5 GHz and 6.8 GHz under TM polarization.For rectification,based on the single series diode rectifier,a tri-band rectifier circuit is designed in parallel,which can realize the effective rectification of tri-band EM energy simultaneously.As for the overall design of the energy harvester,it achieves efficient harvesting of multi-band EM energy by interconnecting structural unit cells to build transmission channels and integrating them with the rectifier circuit in a co-planar manner.When the incident power is 5 d Bm,the energy harvesting efficiency reaches 66.5%,40.6% and35.6% for TE polarized waves at WIFI bands,and 38.3% for TM polarized waves at 5.3 GHz,respectively,which verifies the rationality and feasibility of the energy harvester design.(4)An integrated rectifier and metamaterial energy harvester design is investigated.It has scalable,polarization-insensitive and wide-angle incidence characteristics and achieves efficient EM energy harvesting at 5.8 GHz.Based on a planar orthogonal dipole structure,an impedance matching network is eliminated by integrating a rectifier diode at the feed gaps of the unit cell,and efficient rectification of EM energy is achieved.By connecting inductors between resonant unit cells,a DC power combination network is constructed to achieve efficient collection of DC energy.Then,an RF energy harvesting system consisting of a metamaterial energy harvester,an energy management circuit and an energy storage load is constructed.Performance test of the metamaterial energy harvester is conducted.Experiments on the power supply of RF energy harvesting system to low-power light-emitting diode and the energy storage of supercapacitor are also conducted.The test results show that the metamaterial energy harvester has the RF energy harvesting efficiency of 77.9% at 5.8 GHz.While the RF energy harvesting system has the ability to drive the light-emitting diode to work continuously and to realize the stable energy storage of the supercapacitor,which verifies the effectiveness and practicality of the integrated design of the rectified metamaterial energy harvester.