The Design Of Metamaterial Absorber Based On Microwave Absorption Performance Of Methylimidazolium Ionic Liquids

To obtain good performance of the absorbing materials,i.e."thin,light,wide,and strong",researchers have not only been developing further research into conventional materials,but also actively seeking and investigating novel materials for microwave absorption.As a new kind of soft functional material,ionic liquids?ILs?possess many excellent physicochemical properties and have been widely used in organic synthesis,catalysis,and electrochemistry.However,research on the electromagnetic properties of ILs,especially the microwave absorbing properties is rare until now.In this paper,the dielectric property and microwave absorption performance of methylimidazolium ILs with different anions and cations were studied at first.The results measured by conductivity meter and vector network analyzer show that methylimidazolium ILs have high ionic conductivities and dielectric loss factors which can cause large current loss and dielectric loss,indicating a great potential application in microwave absorption.Meanwhile,the relationship between the dielectric property of ILs and their chemical structures was investigated,that is the real part of permittivity decrease as the radii of anion and cation increase;the loss tangent decrease with increase of the cation radius;the loss tangent is positively related to the conductivity.The calculated results based on transmission line theory show that ILs layer with a thickness of 1mm can cause a strong absorption of microwave above 90%with a bandwidth of 14.3GHz in Ka-band.And the experimental results obtained by free space method verified the correctness of the calculation.On basis of the above research,a novel wideband metamaterial absorber based on methylimidazolium ILs was proposed.The ILs were properly arranged into periodic cylinder arrays supported by a 3D-printed dielectric bracket and the structural parameters?h,r,p?were optimized by using simulation software.The simulated results reveal that for IL[EMIm][N?CN?₂],the optimal structural sizes of the metamaterial absorber are h=3.0mm,r=5.5mm,and p=15mm.Such absorber has the capability of working in an ultra-wideband of 8.4-29GHz with more than 90%absorptivity,and is insensitive to temperature and polarization.As the incident angle is 45°,such absorber still displays a wideband absorption in frequency range of 12.57–29.21GHz.In addition,vector distributions of the electromagnetic field,current density and energy loss density were investigated at absorption peak frequencies,and the physical mechanism of the electromagnetic energy loss was analyzed by resonance theory.Mechanism investigations show that the energy loss in such absorber is mainly originated from the loss of dielectric polarization and induced ionic currents in ILs.Meanwhile,effective impedance of the metamaterial absorber was calculated for further interpretation of the wideband absorption.At last,the absorption characteristics of the absorber were measured by free space method and the experimental results agreed well with the simulation results.It is the first time that ILs are used in constructing metamaterial absorbers.Such ILs-based metamaterial absorber can not only broaden the bandwidth of microwave absorption greatly,but also can be potentially applied in a wider temperature range due to the excellent thermal stabilities of ILs.