Terahertz (THz) regime which is sandwiched between microwave and optical regions refers to the frequency band of 0.1-10 THz. Because of the lack of natural materials that respond to THz regime, this regime may be the least developed frequency band. But, the advent of metamaterials opens a new way for achieving the THz functional devices. Metamaterials have numerous practical applications such as absorbers, antennas, filters, switches due to their unique electromagnetic responses. Among those, THz metamaterial absorbers play an important role in THz imaging, sensing, detecting, and so on. Most...