Ultra-broadband polarization-independent metamaterial absorber from UV-C to LWIR: design and optimization

Abstract

This study presents the design and optimization of a polarization-independent ultra-broadband metamaterial absorber operating over an exceptionally wide spectral span from 150 nm (UV-C) to 10,000 nm (long-wave infrared). The proposed unit cell integrates elliptical titanium (Ti) and aluminum oxide (Al₂O₃) resonators with a multilayer stack composed of chromium (Cr), silicon monoxide (SiO), and iron (Fe), enabling strong plasmonic resonances, enhanced impedance matching, and efficient electromagnetic energy confinement across ultraviolet, visible, near-infrared, and infrared bands. A particle swarm optimization framework was employed to refine the geometric parameters via systematic parameter sweeps and an iterative global search, aiming to maximize the average absorptance over the full wavelength range. Numerical simulations based on the finite-difference time-domain method show that the optimized structure achieves an average absorption of 96.82% via stepwise optimization and 97.12% via simultaneous multi-parameter optimization, representing a substantial enhancement relative to the initial pre-optimized baseline of 86.09%. Electric- and magnetic-field distribution analyses reveal pronounced plasmonic hot-spot formation at metal–dielectric interfaces and confirm stable polarization-insensitive performance under both TE and TM excitations, consistent with the nearly overlapping absorption spectra for the two polarization states. Owing to its ultra-wide spectral coverage and robust polarization independence, the proposed absorber is a promising platform for broadband solar energy harvesting, multispectral sensing, thermal imaging, and infrared energy management.