Abstract
In this paper, a new type of broadband tunable metamaterial absorber is proposed. The structure consists of a single-layer ring graphene and a metal ground plane separated by a dielectric spacer. The graphene rings are connected each other to be easily tuned by the voltage. In addition, this absorber is polarization-independent at normal incidence due to the symmetric pattern of the unit cell. Results reveal the bandwidth of 90% absorption reaches to 2.25 THz for a single-ring structure. The bandwidth of 90% absorption increases to 3.2 THz by combining two similar rings with different sizes in one unit cell. The physical mechanism of the single-ring and dual-ring absorbers are given based on the impedance matching theory.
Highlights
Terahertz metamaterial absorbers have potential applications in many scopes, such as biosensing, imaging, communications, and so on.[1]
Since the first thin and near-perfect metamaterial absorber was proposed in 2008,2 various metamaterial absorbers have been demonstrated from microwave to optical frequencies.[3,4,5,6]
Tunable terahertz graphene-based metamaterial absorbers have been attracted much attention as conductivity of the graphene can be changed by external voltages.[7,8,9]
Summary
Terahertz metamaterial absorbers have potential applications in many scopes, such as biosensing, imaging, communications, and so on.[1]. One method is to stack multiple resonant structures with different geometric dimensions separated by dielectric layers.[15,16] A wide terahertz graphene absorber with the bandwidth of 6.9 THz was obtained by using 3 layers of asymmetrically patterned graphene.[15]. It was reported that broadband absorbers were designed by using periodic arrays of graphene ribbons,[17] periodic graphene analog of electromagnetically induced transparency structure,[18] and periodic sinusoidally-patterned graphene on the surface of dielectric-metal structure.[19] A wider and near polarization-independent absorber was obtained by putting the periodic metal unit on the surface of graphene-dielectric-metal.[20] These structures mentioned above are polarization-dependent and usually have wide absorption in one polarization at normal incidence.[17,18,19,20]. The absorber can achieve polarization-independence at normal incidence due to the symmetric pattern of the unit cell
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