NANO-TOPOLOGY OPTIMIZATION OF PHOTONIC METAMATERIAL

Abstract

Infrared (IR) and optical stealth for the defence application have gained pace with the ad vancement in metamaterials owing to their unique electromagnetic properties. But these stealth mechanisms and corresponding nano-photonic metamaterials posses a significant challenge in achieving perfect stealth. In the case of thermal IR stealth, most of the conven tional stealth coating achieves reasonable stealth, but it makes the device thermally unstable. The study aims to optimize the performance of nano-photonic metamaterials with topol ogy optimization (TO) algorithm and design metamaterials that can achieve ideal stealth performance. In this study, theTOalgorithmisproposedandimplementedundertwodifferentphysics, which are heat transfer and nano-photonics. The study also covers the analysis of nano photonicmetamaterial-basedselectiveabsorberthatcanachieveperfectstealthwithoutcom promising the thermal stability of the object. Owing to the relatively simpler physics of heat transfer, the TO algorithm is first imple mented for heat conduction problem to optimise the thermal compliance of the structure under different boundary conditions. Two dimensional analysis is conducted on a rectan gular design domain considering the symmetry of the problem, uniform heat generation is considered within the domain. The topology optimised geometry has found to perform better when considered for the tube layout of a ground heat exchanger. Owing to their tailored electromagnetic properties, nanostructured based metamaterials selective absorber have been analyzed for the thermal IR stealth capability. The selective absorber havebeenfoundtoachieveupto95%stealthperformanceinthedetectablespectral range 3−5µm and 8−10µm. At the same time, the device maintained the thermal stability through radiative cooling in undetectable range 5−8µm, whichhasbeenupto1500%higher as compared to stealth coating. Theexisting TOalgorithmimplementedonthemetagratinghasbeenanalysedforthede flection efficiency at different angles. The generated nanostructured metagrating through in verse design approach has beentested for different wavelengths 700nm, 1200nm and 2400nm and different deflection angles 45◦ and 75◦. The topology optimised metagrating could de flect the light in the desired angles with efficiency up to 90%. The complexity of size-dependent behaviour of nanostructures imposes great computa tional challenge for TO at nano-scale, but the results of the TO certainly over-weighs the computational cost. Nanotechnology, when integrated with TO can generate superior light trapping structures and nanostructured metamaterials that can find direct application in the growing defence and solar energy industries.