Circuit modeling and hybrid optimization of a lithography-free visible metamaterial absorber

Abstract This paper presents a lithography-free broadband metamaterial absorber designed to cover the visible wavelength spectrum. Two equivalent circuit models based on Transmission Line theory (TL) and Transfer Matrix Method (TMM) are introduced to accurately characterize the absorber's performance. The proposed models are validated by numerical simulations and compared with existing experimental data, showing a strong agreement with the results. To maximize absorption capability, the structure is further optimized using a hybrid Gravitational Search Particle Swarm Optimization (GSPSO) algorithm. The optimized tungsten structure, with a thin thickness of approximately 160 nm, can achieve absorption over 90% across the visible range from 400 to 785 nm and an average absorption of 96%. Moreover, the absorber exhibits a peak absorbance of over 95% within the range from 435 to 665 nm. In addition, the proposed absorber demonstrates high absorption characteristics, maintaining over 80% absorptivity for incident angles up to 60°, for both TE and TM modes. Therefore, the superior performance characteristics of this absorber, as well as the absence of the need for lithography in the fabrication process, make it a highly promising choice for large-scale manufacturing of devices that operate in the visible light region.