Research On Stereometamaterial Broadband Absorber And Its Application In Transparent Absorption

Microwave absorbers(MAs)have been playing an important role in the fields of military stealth,electromagnetic compatibility and civil protection.With the progress of science and technology and continuously improve the level of informationization,the MAs are always expected to have high performance and versatility.However,tradition microwave absorbers are reaching the ceiling of microwave absorption performance.This makes them impossible to have the applications in some special occasions.Recently,there have been increasing interests in metamaterials.As a matter of fact,metamaterial absorbers(MMAs)have been demonstrated to show advantages such as near perfect absorption,thin thickness.Because resonance is utilized in the process of absorption,the absorption bandwidth is often narrow.The broadband absorption can be further improved by using multiple resonance units or multi-layered gradually varied structures at the expense of the thickness and weight of the material,which is contrary to the development trend of the absorbing material,also the absorption bandwidth is limited.Thus,this thesis designed non-planar unit cell to obtain broadband absorption performance.The standing-up MMA proposed here provides an effective way to achieve broadband microwave absorption and high compatibility with optical transparency.The details as follows:Firstly,we designed a standing-up metamaterial absorber yield absorption of more than 85% at the frequency of 7.1 to 23 GHz.The influence of the parameters such as the period of the structure unit,the length of the meta-structure,the line width and the square resistance of the material on the absorption performance is systematically studied.The results show that the non-planar structure is independent of resonance,which is in favor of expand the absorption bandwidth.At the same time,the as-designed standing-up MMA can maintain the excellent absorption performance at a large incident angle.Secondly,we use standing-up closed-ring resonators(CRRs)on indium tin oxide(ITO)backed Plexiglas board,we have in experiment and calculation demonstrated a MMA with both broadband microwave absorption and excellent optical transparency.The as-designed MMA shows a strong microwave absorption of 85% covering a wide frequency of 5.5-19.7 and 22.5-27.5 GHz.In contrast to planar optically transparent MMAs,which utilize multi-layer or various resonant units to achieve broadband absorption,the standing-up MMA enables both electric and magnetic resonances,as well as multiple reflections.Due to the small coverage of the ITO part and avoiding multi-layer configuration,the optical transparency of the designed MMA has been substantially improved,which is approved by theoretical model based on transfer matrix method.Compared to multi-layered planar MMAs,even the two-layer one,the standing-up MMA always prevails in optical transmittance.The experimental results show that the sample has the performance of more than 85% in the range of 5.5-19.7 and 22.5-27.5 GHz.An average optical transparency of around 82% is measured in the visible spectrum.In a word,in this thesis,we use non-planar structure unit to further expand the absorber bandwidth,and this sturcture is applied in the design of optical transparent microwave absorber.The as-proposed design method is inspiring for both multiple functional or ordinary materials.