Three-dimensional pyramid metamaterial with tunable broad absorption bandwidth

Three designs of tunable broadband resonators using three-dimensional pyramid metamaterials (3DPMs) are presented. They are pyramid-shaped absorbers with nine taper steps from bottom to top. Each step of three 3DPMs is composed of a metal–insulator–metal (MIM) layer, a metal–insulator–metal–insulator–metal (MIMIM) layer, and a metal–insulator–metal–insulator–metal–insulator–metal (MIMIMIM) layer denoted as 3DPM-1, 3DPM-2, and 3DPM-3, respectively. 3DPMs exhibit ultra-broad bandwidths of 9.56 µm spanning the wavelength of 8.88 µm–18.44 µm. Within the whole absorption bandwidth, there are near-perfect absorptions of 96.57%, 97.61%, and 99.15% for 3DPM-1, 3DPM-2, and 3DPM-3, respectively, at the strongest resonant wavelength. The average absorption intensities are 84.86%, 83.92%, and 87.47%, respectively, calculated at the whole absorption bandwidths. To enhance the flexibility of the proposed 3DPMs, we choose 3DPM-1 as an example to design a slot gap between 3DPM-1. By changing this gap from 0 nm to 250 nm, the absorption spectra could be tuned from the bandwidth of 9.56 µm to 3.56 µm. The absorption intensity can be kept as high as 80%. These superior electromagnetic characteristics provide the proposed 3DPMs to be used for sensor, detector, energy harvesting, and imaging applications with polarization-dependence, tunable bandwidth, broad absorption bandwidth, and high interference resistance characterizations.