Design of multi-narrowband metamaterial perfect absorbers in near-infrared band based on resonators asymmetric method and modified resonators stacked method

In this paper, we propose an idea of using asymmetric dielectric resonators to increase the number of perfect absorption bands. We break the symmetry of the dielectric resonators by reducing the length of one of the two silicon split strips. A quad-band MPA is achieved in the near-infrared band based on the asymmetric-dielectric-dielectric-metal (ASDDM) structure, which can excite two extra electric quadrupole (EQ) modes comparing with the symmetry structure exciting only two dipole modes. Operated as a refractive index sensor, those four narrow absorption bands have the figure of merit (FOM) as high as 338.6, 98.5, 38, and 60.6, respectively. This preliminary analysis shows that the resonators asymmetric method is feasible for designing multiple-band MPAs. To obtain more absorption bands, we propose another idea of stacking the dielectric resonators on metal resonators other than only stacking metal resonators. A single-band MPA is first designed based on the metal-dielectric-metal (MDM) structure. Next, we stack the asymmetric dielectric resonators of the quad-band MPA on the metal resonators of the single-band MPA. The absorption spectrum shows that five perfect absorption bands are achieved in the near-infrared band, which preliminary proves the feasibility of the modified resonators stacked method for designing multiple-band MPAs.