Double square rings with different dimensions produce multiple absorption bands.

The quantity of absorption bands is traditionally less than the quantity of resonator subunits. Based on the absorption theory of electromagnetic resonance, three-millimeter-wave metamaterial absorbers (MWMAs) based on periodic resonators with double square rings (DSRs) are proposed, discussed, fabricated, and measured. Multiple absorption bands including two, three, and four bands can be effectively achieved by adjusting the dimensions of the DSRs. The electric field distributions at the corresponding resonance frequency can adequately explain the physical mechanism of adjustable absorption bands affected by the strong LC, dipole, and surface responses complexly. Detailed influence produced by sizes and materials is elaborated. The adjustable absorption can be easily scaled to the entire spectrum by geometrical regulation. The presented MWMAs show attractive prospects in electromagnetic devices, biological sensing, material detection, and function materials because of their size adaptation, flexible design, ultrathin thickness, strong flexibility, and convenient fabrication.