Ultra-Broadband Perfect Absorbers Based on Biomimetic Metamaterials with Dual Coupling Gradient Resonators.

Ultra-broadband metamaterial absorbers can achieve near-perfect absorption of omnidirectional electromagnetic waves, crucial for light utilization and manipulation. Traditional ultra-broadband metamaterials rely on the superposition of different resonator units either in the plane or in perpendicular directions to broaden absorption peaks. However, this approach is subject to quantity restrictions and complicates the fabrication process. This study introduces a novel concept for broadband absorption metamaterial design-Metal-Insulator-Metal metamaterials with gradient resonators (GR-MIMs) to surpass limitations in quantity and fabrication. The GR-MIMs absorber features gradient resonant cavities in both nanoscale and microscale dimensions, each with continuous resonance points. By converting "resonance points" into "resonance bands" and perfectly coupling the two gradient resonators, the GR-MIMs absorber with a thickness of only 200 nm demonstrates 93% ultra-broadband high absorption across the UV, visible, near-infrared, and mid-infrared spectra (0.2-5 µm). Moreover, the solar spectrum absorption rate of the GR-MIMs absorber can reach 94.5%, offering broad prospects for applications in solar energy utilization. The design of gradient resonators provides a new approach for the development of ultra-broadband metamaterials and photothermal conversion metamaterials.