Simultaneous realization of the single-band and broadband terahertz perfect absorber using one piece of metamaterial resonator

A kind of terahertz metamaterial absorber, made of only an Au closed-ring resonator and a dielectric layer deposited on a continuous Au film, is presented to achieve bifunctional absorption characteristic. Unlike traditional absorbers having the single-functional absorption features of single-band or broadband, the designed device exhibits not only the single-band absorption response at frequency of 1.45 THz, but also a broadband absorption performance, which is caused by the superposition of three adjacent frequencies that are all localized at right side of the single-band absorption. Importantly, the relative absorption bandwidth of the broadband performance of the device over absorption rates of 50% and 80% can, respectively, reach 47.22% and 35.97%, which is very close to (and even exceed) the performance of previous single function of broadband absorbers that require several different lengths of metallic elements. The designed bifunctional absorber has the comprehensive advantages of the single functions of the single-band and broadband absorbers, and therefore, this work can offer an inspiring method to obtain a bifunctional absorber through using only one piece of metamaterial.