| As the world’s military powers cast their sights from the past sea,land and air domains to beyond the earth-space,as one of the most important links in space competition,the electromagnetic stealth of artificial satellites has been put on the agenda of all countries.An artificial satellite is usually composed of a body and several huge solar panels.These solar panels are a kind of energy supply device that can absorb solar energy.Their area is usually a few hundred square meters,and some even thousands of square meters,which will introduce significant backscattering of microwaves,thereby exposing artificial satellites to danger.In addition,the optically opaque stealth material will reduce the energy conversion efficiency of the solar cell,thereby affecting the daily energy conversion of the solar cell.It can be seen that the key to realize the stealth of artificial satellites with huge solar panels is to minimize the backscattered waves of the solar panels,while maximizing the solar energy conversion efficiency of the solar cells.For the absorber,if you want to meet these two conditions for the stealth of an artificial satellite at the same time,it must have a high optical transmittance while being able to absorb broadband waves.Traditional periodic structure optically transparent microwave absorber based on electromagnetic metamaterials,due to the use of transparent conductive materials,such as indium tin oxide(ITO)or graphene,are limited by the inherent uniform carrier concentration.Once these materials are attached to the substrate with a certain thickness,their sheet resistance on a single surface is usually only a single resistance value.Because the structure of single resistance value is difficult to meet the demand of broadband absorption,in order to increase the absorption bandwidth,some researchers stack multiple conductive structures in the vertical direction of the structure or insert lossy cavities.Although these designs increase the absorption bandwidth of the absorber,at the same time they sacrifice the optical transmittance and thickness of the absorber.In view of the above situation,this paper designs resistive film pattern structures with different resistance values in the same plane of a single-layer substrate with high light transmittance to increase the degree of structural freedom in the plane.As a proof of concept,this article takes the local electrical-global optics characteristic relationship of the non-uniform micro-nano metal grid as a starting point,and organically combines the electromagnetic wave absorption method with the visible light design.On this basis,this article uses advanced nanoimprint technology to introduce non-uniform micro-nano metal grids as optically transparent conductive materials,and integrate conductive pattern structures with different resistance values in the same plane of the substrate,so as not to increase the depth of the device.In the case of the degree of freedom of the directional structure,the degree of freedom of the structure in the plane is increased to realize a microwave absorber with broadband absorption and high light transmittance.After experimental testing,the absorber designed in this paper can achieve an absorptivity of more than 90% in the range of 7.2-18.5GHz,and the average light transmittance in the range of 300-1200 nm is as high as 88%,which is in line with theoretical calculations.The light transmittance of 88.5% is very matched,and the overall thickness of the absorber is only 2.7mm.In addition,in order to explore the influence of the absorber proposed in this article on the solar-energy power conversion efficiency of solar cells,we used flexible perovskite solar cells and silicon solar cells as experimental objects to test solar-energy power conversion efficiency.Experimental results show that our absorber can retain 95% of the solar-energy power conversion efficiency of flexible perovskite solar cells and 92% of the solar-energy power conversion efficiency of silicon solar cells. |
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