Fig. 3.
a THz wave absorption of periodic dual-ring structures with different outer radii of the inner split-ring (ri). The dual-ring structures have an opening width of 2 μm and a thickness of 10 nm. The outer radius of the outer split-ring is 17 μm and the width of both split-rings is 2 μm. b THz wave absorption of periodic structures of a combination of a split-ring and an Al disk with different radii of the disk (rd). The periodic structures have a thickness of 10 nm. The split-ring has an outer radius of 17 μm, a ring width of 2 μm and an opening width of 2 μm. c THz wave absorption of periodic structures of a combination of two split-rings and an Al disk with different radii of the disk (rd). The periodic structures have a thickness of 10 nm. The two split-rings have a ring width of 2 μm, an opening width of 2 μm and an outer radius of 17 μm and 14 μm, respectively