ULTRA-BROADBAND ABSORPTION WITH GRADIENT PYRAMIDAL METAMATERIALS

We propose a novel absorber by integrating four different-sized pyramidal metamaterials into a unit cell, which leads to a super broadband absorption by properly selecting the geometrical parameters for each pyramid. It is found that in such a design strategy, the high-order modes may be excited and further enhanced by multi-layer overlapping between adjacent unit cells. The as-designed MA, which consists of 13 pairs of alternating metal-dielectric layers with a total thickness of 4.13 mm, shows an absorption of above 90% in the whole frequency range of 7–21.5 GHz. The full width at half maximum is 101.8%, and the ratio of operational bandwidth to thickness achieves 7. The proposed MA is 30% broader and 5.2% thinner than previously reported absorbers working in the same spectral region. Numerical result shows that the proposed absorber is independent of the polarization. The absorption decreases with fluctuations as the incident angle increases but remains quasi-constant up to relatively large angles. Such a design shows great promise for a broad range of applications at microwave frequencies, and the proposed scheme may be extended to the visible, infrared, terahertz spectral regions.