Near field enhancement and absorption properties of the double cylindrical microcavities based on triple-band metamaterial absorber

We numerically study the near field enhancement and absorption properties inside the double cylindrical microcavities based on triple-band metamaterial absorber. The compact single unit cell consists of concentric gold rings each with a gold disk in the center, and a metallic ground plane separated by a dielectric layer. At the normal incidence of electromagnetic radiation, the obtained reflection spectra show that the resonance frequencies of the double microcavities are 16.65 THz,20.65 THz, and 25.65THz, respectively. We also calculate the values of contrast C(C = 1- Rmin), which can reach 95%,97%, and 95% at the corresponding frequencies by optimizing the geometry parameters of structure. Moreover, we demonstrate that the multilayer structure with subwavelength electromagnetic confinement allows 104～105-fold enhancement of the electromagnetic energy density inside the double cavities, which contains the most energy of the incoming electromagnetic radiation. Moreover, the proposed structure will be insensitive to the polarization of the incident wave due to the symmetry of the double cylindrical microcavities. The proposed optical metamaterial is a promising candidate as an absorbing element in scientific and technical applications because of its extreme confinement, multiband absorptions, and polarization insensitivity.