(a) Schematic of the proposed metamaterial absorber, which can efficiently absorb the incident wave in a broad frequency band. (b) Details of the unit cell configuration. Four metallic via holes are embedded into the dielectric substrate and connected to the metallic circular patches that are isolated from the ground with a gap width of 0.1 mm. The via hole has a radius of 0.15 mm, while the patch has a radius of 0.4 mm. Four semicircular corners are cut from the metallic ring structure on the top layer.