Optimization design of broadband absorber for high optical transparency

A broadband absorber with high optical transparency is proposed and realized using an optimization-designed method. The absorber's reflection, lossy, and dielectric layers are considered for obtaining high optical transparency. First, to maintain microwave absorption, the artificial structures of the reflection layer are designed on the micron scale. Low square resistance and high optical transparency are achieved simultaneously. Then, considering the artificial structure fabrication process [fabricated on polyethylene terephthalate (PET)], high light transmittance polymethyl methacrylate (PMMA) was selected as the material of the dielectric layer. The permittivity of PMMA is similar to that of PET. The light reflection of layer-to-layer is reduced, and the light transmittance is improved. Finally, under the same microwave absorption band and absorption efficiency, the topology structures of the lossy layer are optimized to increase the duty ratio and the light transmittance. Through the above-mentioned design, high optical transparency and broadband microwave absorption are achieved simultaneously. The simulated and measured results prove that more than 90% of the absorption rate is obtained from 4.4 to 11.5 GHz (89.3%) and the average light transmittance reached 80%. The results verify the optimization-designed method's effectiveness and provide technical support for transparent absorbers to be better applied to optical windows.