Miniaturized And Tunable Design Of Metamaterial For Low-Frequency Microwave Absorber

Microwave absorbing materials play an important role in realizing electromagnetic protection and compatibility,improving radar stealth ability of modern military equipment.With the development of microwave electronic devices and system toward miniaturization and lightweight,radar detection technology advances towards low frequency and multi frequency.Absorbing materials with the characteristics of low occupancy of space,low working frequency,wide bandwidth and excellent absorption performance will become the research focus in this field.At present,traditional absorbing materials are facing a series of performance bottlenecks that are difficult to break through.So,metamaterials have become the main development direction in the future because of their ultra-thin thickness,flexible designability and strong absorbing ability.However,there are still some shortcomings such as the oversize unit cell at low operating frequency and narrow absorption band.In this work,we have made efforts to solve these problems:At first,we present a metamaterial absorber with miniaturized unit cells for achieving strong microwave absorption at low-frequency.This design is based on a typical multi-layer configuration:by staggering stripe-like meta-surface with equal spacing and line width attach to layered dielectric substrate,we have successfully obtained an absorption peak with a strength higher than 95%at 1.2 GHz.At the same time,the unit period p of the metamaterial is controlled within?₀/20,and the thickness t is controlled within?₀/160??₀ is the working wavelength in vacuum?.This scheme significantly improves the dependence of the working wavelength of metamaterials on the period of unit cells.More importantly,with the further increase of the number of superimposed layers n,the period-wavelength ratio is approximately 1/4n,which means that the design still possesses great potential for expansion.In addition,we put forward some optimization schemes,including polarization-insensitive microwave absorbing metamaterials based on square patch arrays,multilayer transparent low frequency microwave metamaterial absorber and lightweight net-like metamaterial absorber.These achievements are expected to meet the design requirements of today's civil microwave electronic equipment and national defense military weapons.Furthermore,based on the miniaturized periodic,for the sake of expanding the multi-frequency absorption capacity of metamaterial absorber,we have introduced a mechanically tunable-configuration.Firstly,with the modular-separable structure,we construct a metamaterial absorber which is able to generate geometric reconfiguration in one-dimensional.The displacement of the flexible modular of the absorber will change the equivalent circuit parameters of the whole structure,and then make an effect on the frequency response characteristics of the absorber.Therefore,we can adjust the absorption frequency of the absorber by tune the key geometric parameters of the absorber.Besides that,according to the same principle,a metamaterial absorber with vertical unit cells consisting of compact multiple concentric split resonant rings also has been proposed for low frequency tunable microwave absorption,this design equipped routable embedded split ring.The sliding and rotation adjustments both are realized in-plane,and do not bring any change to the profile and space occupation.Both of the two designs can achieve a working-frequency range of more than 600 MHz at L band?1-2 GHz?and meanwhile,an absorption intensity of more than 90%can be maintained,with the volume occupation be constrained within an ideal level.