Research On Metamaterial Absorber Based On Lumped Elements

Lumped elements loaded electromagnetic metamaterial absorbers constructed by sub-wavelength structures,have attracted more and more people's interests because of their unique advantages such as thin thickness,strong absorption,resonant frequency(or bandwidth)tunability and easy integration.According to the equivalent circuit theory,the structure of metamaterial absorbers can be equivalently regarded as a circuit model consisting of equivalent resistors,capacitors and inductors in series and parallel,lumped element on the top metal structure of the absorbers can convert the electromagnetic resonance into a circuit resonance,which changes the input impedance and loss characteristics by adjusting the value of lumped elements.This kind of absorbers provide a new idea for the research and development of absorbers by combining the design idea of "field" + "circuit" with lumped elements.It also provides an effective means for the application of broadband absorption,adjustable central frequency,and miniaturized structure.This kind of reconfigurable metamaterial absorbers have a wide application value in energy harvesting,signal source detection,(5G communication)electromagnetic compatibility,MIMO antenna,ship stealth and so on.In this paper,absorption characteristics of dual-band metamaterial absorber and based on lumped elements metamaterial absorber are studied,the related theoretical analysis,numerical simulation and experimental measurements are carried out.The main work is as follows:Firstly,A kind of nearly perfect metamaterial absorber with super-close dual bands is designed and fabricated at microwave frequency.This super-compact and space saving structure integrate cross-shaped resonator(CSR)and complementary cross-shaped resonator(CCSR)in one unit cell,corresponding to lower and higher resonances respectively.It has a characteristic of better impedance matching to the free space with absorption rates of 99.9% at 6.78 and 7.42 GHz.The physical mechanism of absorption is analyzed by observing the intensity distribution of the surface current,electric field and magnetic field at the resonance frequency.Effective electromagnetic parameters including relative permittivity,permeability,refractive index and impedance are calculated by S-parameter retrieval method to verify the two nearly perfect absorption peaks.Secondly,The effects of different polarization angles,oblique incidence and different dimensions of the model on absorption characteristics of dual-band metamaterial absorber are studied,and the changes of absorption intensity and frequency offset are explained in detail.In addition,lumped resistance elements of dual-band metamaterial absorber can effectively change the input impedance and reduce the quality factor(Q)of the equivalent circuit,so as to achieve a good impedance matching characteristic of absorber,thus broadening the absorption bandwidth at the resonance frequency of dual-band metamaterial absorber.Thirdly,a cross-ring metamaterial absorber based on lumped resistance in the microwave is proposed.The simulation results show that absorption is over 90% in the frequency range of 4.31-10.25 GHz,and the relative absorption bandwidth is about 81.6%.The loss mechanism of the absorber with and without lumped resistance is analyzed by comparing the power loss density distribution at 5.16 and 8.72 GHz.The effects of different loss tangent,polarization angle and oblique incidence on absorption performance are discussed,respectively.Finally,the broadband absorption of the model in terahertz frequency band is realized by adjusting the size of the structure.